Journal of Antimicrobial Chemotherapy

Long-acting cabotegravir and rilpivirine combination (LA-CAB/RPV) is approved for HIV treatment whilst long-acting cabotegravir alone (LA-CAB) is approved for HIV prevention, both in adults. However, individuals who become pregnant might prefer to discontinue it due to lack of definitive data on safety. The aim of this study was to characterise the tail-phase maternal and fetal pharmacokinetics of LA-CAB/RPV following discontinuation at steady-state early in pregnancy. A virtual population of non-pregnant women (n = 100 per scenario) initiated intramuscular injections of LA-CAB/RPV at the approved dosage and continued maintenance dose (400/600 mg once monthly or 600/900 mg once every two months) until steady state. We simulated discontinuation at steady state after only one injection during pregnancy. Tail-phase pharmacokinetics of CAB and RPV from LA injections were characterised during gestation and until 6 months postpartum. Pharmacokinetic tails of LA-CAB/RPV were driven by the residual drug in the muscle depot which stabilised at steady state and reduced steadily upon dosing discontinuation. Upon discontinuation of the monthly dosing, predicted median (IQR) maternal plasma concentrations for LA-CAB were 415 (386-448) ng/mL at delivery and 125 (115-139) ng/mL 6 months postpartum. For LA RPV, these were 11.6 (11.0-12.6) ng/mL and 7.84 (7.30-8.49) ng/mL at delivery and 6 months postpartum, respectively. Pharmacokinetic tails of LA-CAB/RPV extend to several months postpartum, with levels falling below established minimum effective concentration in most women after gestation week 33. Potential strategies to minimise potential risks associated with LA-CAB/RPV discontinuation in this population are needed.

Cefiderocol exhibits excellent in vitro activity against Pseudomonas aeruginosa; however, resistance can emerge. We investigated the molecular mechanisms underlying cefiderocol resistance (MIC >2 mg/L) in 103 clinical strains collected from 61 hospitals (2021-2024). MICs ranged from 4 to >128 mg/L, with 39.8% of strains showing MICs >8 mg/L. Although 37.8% were classified as difficult-to-treat resistant (DTR), acquired {beta}-lactamases were detected in 72.8% of strains, including carbapenemases (39.8%), mainly NDM-1 (29.1%), and Extended Spectrum {beta}-Lactamases (ESBLs) (38.8%). Cloning of 11 {beta}-lactamases into pUCP24, including the acquired cephalosporinase PAC-1 and ESBLs (VEB-1, and VEB-9), resulted in marked increases in cefiderocol MICs (up to 128-fold). Introduction of 6 mutations in the PDC enzyme into a PAO1{Delta}blaPDC-1 background increased MICs up to 4 mg/L and conferred cross-resistance to ceftolozane/tazobactam, notably F121L, G157D, T70I, and E219K. Alterations in siderophore transporters or regulators were identified in 38.8% of strains, most frequently a PirR frameshift (R132fs), consistent with PirR inactivation, which was confirmed in the PAO1 strain to contribute to cefiderocol resistance. Overall, cefiderocol resistance in clinical strains is multifactorial, mainly involving acquired {beta}-lactamases (ESBLs, carbapenemases) and impaired siderophore uptake (PiuA/PiuD, PirA, PiuC), leading to high-level resistance (>8 mg/L). The polyclonal distribution and diversity of mechanisms highlight the need for routine susceptibility testing and surveillance. Detection of NDM producers is critical, as cefiderocol should be used with caution in this context.

Urinary tract infections (UTIs) are among the most common infectious diseases worldwide, with Escherichia coli being the predominant uropathogen. The increasing prevalence of extended-spectrum beta-lactamase (ESBL)-producing strains and their association with fluoroquinolone resistance pose a significant challenge to empirical therapy, particularly in community settings. The aim of this study was to determine the epidemiology and predictive factors associated with ESBL-producing E. coli and its concomitant fluoroquinolone resistance in community-acquired clinical isolates. A retrospective cross-sectional study was conducted analyzing 244 clinical E. coli isolates. Demographic and microbiological data were collected, including age, sex, sample type, and antibiotic susceptibility. Associations between variables and ESBL production were assessed using Pearsons chi-squared test, and odds ratios (ORs) with 95% confidence intervals (CIs) were calculated. Of the isolates, 165 (68%) were ESBL-producing. A significant association was observed between age group and ESBL production (p < 0.001), with the highest frequency in the 20-39 age group. Most ESBL-positive isolates were obtained from women (73%), although odds ratio (OR) analysis suggested a non-significant trend toward a higher probability in men (OR = 1.29; 95% CI: 0.72-2.31). High rates of fluoroquinolone resistance were identified among the ESBL-producing isolates, with 30% resistance to levofloxacin and 35% to ciprofloxacin (p < 0.001). Urine samples showed the highest concentration of ESBL-positive isolates, with a significant association between sample type and resistance (p < 0.001). The high prevalence of ESBL-producing E. coli and its concomitant resistance to fluoroquinolones highlight a critical challenge for the empirical treatment of urinary tract infections in Mexico, underscoring the need to strengthen antimicrobial use management and local surveillance strategies.

Many studies have identified antibiotic resistant (ABR) Escherichia coli on meat. Appropriate hand hygiene and cooking practices should minimise the risk of gastrointestinal colonisation with ABR E. coli found on meat, and the subsequent chance of causing resistant opportunistic extraintestinal infection. There are large gaps in our understanding of the prevalence, origins and zoonotic potential of ABR E. coli found on meat, however, and particularly for meat reared in extensive farming systems. Wales is a devolved nation within the United Kingdom having large populations of extensively-reared sheep and beef cattle. To help address knowledge gaps around ABR E. coli on extensively reared meat, therefore, beef mince and lamb loin/leg steaks/chops were purchased from 50 (beef) and 46 (lamb) independent butchers across Wales. Following enrichment culture, 200 g meat samples were found to be positive for E. coli resistant to amoxicillin (31% positivity), streptomycin (28%), spectinomycin (29%), amoxicillin-clavulanate (11%), 3rd generation cephalosporins (2%) and fluoroquinolones (5%). Phylogenetic analysis confirmed that Welsh lamb meat ABR E. coli isolates (n=79) are more closely related to those found in faecal samples collected around sheep (n=352) than around beef cattle (n=361) on Welsh farms. This suggests that faecal contamination at or around slaughter is their primary origin. We found no closely related meat/infection clones (<20 SNPs distant and the same antibiotic resistance genes) when comparing ABR E. coli from Welsh meat (n=92) and those causing extraintestinal infections in people (n=2387) in an English region bordering Wales. We conclude, therefore, that the wider zoonotic implications of finding ABR E coli on beef and lamb meat sold at independent butchers in Wales are small.

Objectives: To identifiy risk factors for antimicrobial resistance (AMR) in seven pathogen-antimicrobial combinations in patients with cancer and cancer survivors. Methods: Using data from patients with recent or past cancer diagnostic codes in Oxfordshire, UK, we examined associations between 22 potential risk-factors and AMR in blood culture isolates, collected between 1-April-2015 and 31-March-2025. Results: Among 5,975 bacteraemias in 4,365 adults, we analysed 3,141 (52.6%) due to Enterobacterales and 620 (10.4%) due to Enterococcus faecalis/faecium in 2,752 patients. Fourteen risk-factors for antimicrobial-resistant bacteraemia were identified, varying across pathogen-antimicrobial combinations. Compared with no previous antimicrobial susceptibility test result, prior resistance to the same antibiotic in any culture in the last year was strongly associated with AMR across all pathogen-antimicrobial combinations (all p<=0.001). Prior antibiotic exposure and younger age were also positively associated with AMR in four and five combinations, respectively. Cancer type showed modest effects; lymphoid/haematopoietic malignancies were associated with higher odds (vs colorectal cancer) of trimethoprim-sulfamethoxazole-resistant Enterobacterales (aOR=2.07 95%CI 1.40-3.06) and vancomycin-resistant Enterococcus bacteraemia (aOR=6.68, 1.21-36.91). Conclusions: Previous resistance was the greatest risk factor for bacteraemia with AMR in cancer patients and survivors, with prior antibiotic exposure and age also contributing. Lymphoid/haematopoietic malignancies increased risk of resistance to specific antimicrobials. Keywords: antimicrobial resistance, bacteraemia, cancer, risk factors

Background: Metronidazole (MTZ) is a first-line antibiotic for several enteric infections. Its use is common in low-income countries, where most primary-care consultations are conducted by nurses. However, increasing resistance among some enteric pathogens is a growing concern. Using WHO guidelines, we conducted a register-based cross-sectional study to assess MTZ prescribing practices and their determinants in public and private primary healthcare facilities in South Benin. Methods: We performed a register-based cross-sectional study covering the year 2020 in 11 primary healthcare facilities (5 public and 6 private) in Abomey-Calavi, South Benin, following WHO recommendations. In total, 200 visits per facility were selected using systematic random sampling. The primary outcome was the prevalence of MTZ prescription. Determinants of MTZ prescription were identified using multivariable logistic regression analysis. Results: In total, 2,200 medical visits were analyzed. The median age of patients was 19 years, and 57% were female. Antimalarials were prescribed in 52% of visits. Antibacterial agents were prescribed in the majority of visits, with MTZ being the second most frequently prescribed antibiotic (18%), after aminopenicillins (27%). In multivariable analysis, digestive symptoms (adjusted odds ratio [aOR], 8.65; 95% confidence interval [CI], 6.49-11.6), genitourinary symptoms (aOR, 6.84; 95% CI, 3.18-15.0), and skin lesions (aOR, 2.39; 95% CI, 1.58-3.60) were independently associated with increased odds of MTZ prescription. In contrast, fever (aOR, 0.66; 95% CI, 0.49-0.87), respiratory symptoms (aOR, 0.44; 95% CI, 0.26-0.71), and malaria (aOR, 0.21; 95% CI, 0.15-0.28) were associated with decreased odds. Visits in the private sector were also associated with higher odds of MTZ prescription compared with the public sector (aOR, 2.31; 95% CI, 1.78-3.02). Conclusion: MTZ is the second most commonly prescribed antibiotic in primary care in the study area, with its use largely driven by digestive symptoms. Further studies are needed to assess the appropriateness of this prescription. Additionally, research is warranted to understand better the determinants of higher antimicrobial prescribing in the private healthcare sector.

Antimicrobial resistance (AMR) is classified by the World Health Organization (WHO) as one of humanity's ten global public health threats. This review aimed to estimate the prevalence, temporal trends and regional distribution of AMR in WHO priority bacteria across human, animal and environmental sources in Cameroon. This review was conducted following PRISMA 2020 guidelines, with the protocol registered in PROSPERO. A systematic literature search was conducted in Google Scholar, PubMed, African Journals Online, Hinari, and Africa indexus Medicus. Random effects models were used to estimate pooled prevalence and 95% confidence intervals (CIs), with subgroup analyses by bacterial source, region, and sampling period. Of 1566 articles screened, 115 met the inclusion criteria. The reported data encompassed 16 bacteria-antibiotic combinations in 16,948 isolates. Globally, third-generation cephalosporin (3GC) resistance in E. coli was the most prevalent (49.0%, 95% CI: 39.0-60.0%, I2=97.7%), reaching 77.0% (95% CI: 46.0-98.0%, I2=95.6%) in environmental isolates. The pooled prevalence of ESBL production in all included Enterobacterales was 37.0% (95% CI: 30.0-45.0%). Most of the highest resistance rates were observed in the Littoral region. The resistance rates between 2016 and 2025 were significantly higher than those from 2000 to 2015. These increases were more marked in fluoroquinolone-resistant Salmonella spp (1.0% to 48.0%, I2=97.3%, p<0.001), carbapenem-resistant E. coli (0% to 15%, I2=93.5%, p<0.001), and 3GC-resistant E. coli (34.0% to 64.0%, I2=97.6%, p=0.003). Antimicrobial resistance in WHO priority bacteria in Cameroon is high, unevenly distributed across regions and significantly increasing over time. These results underscore the crucial need for strengthened AMR surveillance to curb the growing threat of AMR in Cameroon.

Background Antibiotic use is prevalent in hospitals, driving the emergence of drug-resistant pathogens. We investigated the contextual influences on antibiotic prescribing behaviour across hospitals in high, middle, and low-income countries in Asia with an aim to provide actionable insights to improve prescribing behaviour. Methods We conducted a large qualitative study across ten institutions in Singapore, Nepal, and Thailand. Semi-structured interviews and ethnographic observations involving physicians, nurses, pharmacists, and management staff were conducted. Data were analysed thematically using QSR NVivo 14. Findings A total of 194 interviews were conducted amongst physicians (54{middle dot}1%), nurses (19{middle dot}6%), pharmacists (12{middle dot}4%), and management staff (13{middle dot}9%). Structural factors such as limited microbiology laboratory capabilities, concerns about antibiotic quality, weak infection prevention and control policies, and the lack of relevant, updated guidelines were prominent drivers for prolonged and broad-spectrum antibiotics prescriptions. Where these system supports were in place, prescribing decisions were less defensive and more targeted, although prescriber responsibility and concerns about immediate patient deterioration continued to influence practice. Across settings, clinicians tended to prioritise short-term perceived benefits of antibiotic treatment over the longer-term risks of antimicrobial resistance.

Background: Ribavirin is a guanosine analogue with clinical antiviral activity against a range of RNA viruses including hepatitis C virus (HCV), respiratory syncytial virus and Lassa virus. Several potential mechanisms of action have been proposed, but there is limited data supporting them clinically. Methods: We studied 196 HCV-infected participants from a trial of short-course directly antiviral therapy (STOPHCV-1) which included a factorial randomisation to ribavirin versus no ribavirin. Deep sequencing of the HCV genome was performed on samples with detectable viremia from three time-points: baseline (n = 191), day 3 of treatment (n = 25) and post-treatment failure (n = 47). Results: Ribavirin exposure significantly increased total mutational load at treatment failure (P = 0.0065) and enriched classical ribavirin-associated transitions, including G->A (P = 0.026) and C[-&gt;]U (P = 0.004), along with other key changes including A->G (P = 0.005), U->C (P = 0.023), C->G (P = 0.010), and U->A (P = 0.026). The resulting mutational signature was broad, not dominated by G-related changes. Region-specific analyses demonstrated this increase was broadly distributed across the viral genome, without strong evidence for protection of specific regions. Non-synonymous to synonymous mutation ratios (dN/dS) rose at day 3 (P = 5.5e-5) before declining at failure (P = 8.5e-7), with trends toward higher dN/dS in the ribavirin group at day 3 (P = 0.06). Conclusions: Ribavirin acts as a potent in vivo mutagen, driving viral populations toward genome-wide diversity rather than selecting a few highly fit drug-resistant clones. These findings support an error-catastrophe model.

Phage therapeutics are re-emerging as adjuncts or alternatives to antibiotics and their clinical translation will be enhanced with production methods that minimise downstream processing. We evaluated whether an endotoxin-reduced E. coli strain developed for production of recombinant proteins, ClearColi(R), can serve as a useful, safe phage production host without compromising yield and whether targeted receptor complementation can expand its utility. The parent strain BL21(DE3), and its lipid A modified derivative, ClearColi(R), were compared with respect to infection and generation of phage. Across a panel of 31 phage, a similar host range was observed between BL21(DE3) and ClearColi(R). To expand host range ompC was genetically engineered into the chromosome of ClearColi(R), thereby adding OmpC-dependent phage to its production capacity. Production metrics were broadly comparable between the hosts; efficiency of plating and final titres for representative phage were not significantly different; burst size varied by phage but without consistent host bias. Endotoxin activity in ClearColi(R)-propagated lysates was reduced by over 1000-fold relative to BL21(DE3), reaching the low hundreds of endotoxin units (EU) versus hundreds of thousands for BL21(DE3). Intravesical administration of ClearColi(R)-derived phage (LUC4) into pigs elicited no clinical abnormalities and no significant increases in circulating cytokines up to 48 hours after administration. ClearColi(R) allows efficient production of diverse phage with low endotoxin, reducing the requirement for downstream processing. Although its minimal LPS reduces its capacity for producing some LPS-dependent phage and its growth is slower than BL21(DE3), requiring optimisation for maximal phage titre, the safety and simplified manufacturing process support further development of endotoxin modified strains for phage production. Impact statementAntibiotic resistance is a current global problem and treatments based on phage and phage products already have a proven track record with particular bacterial infections, especially in the urinary tract. While progress is being made on in vitro phage synthesis, large scale bacteriophage preparations require a bacterial host for production, consequently toxic components in the initial lysate need to be removed or significantly diluted for safe clinical use. This is a study of the potential to utilise an endotoxin-reduced E. coli strain, ClearColi(R), to produce safer phage therapeutics. Such endotoxin modified strains should minimise the processing steps required and reduce overall production costs of a phage preparation. The research demonstrates that the endotoxin-reduced strain was able to produce a wide range of phage and for studied examples at phage titres equivalent to the more toxic parent strain. We also show that the strain can be modified to increase its host range and confirm the very low endotoxicity of basic phage lysates produced by the strain. Replicating this process to engineer additional low-toxicity bacterial production strains will accelerate the development of safer, more cost-effective phage therapeutics.

ObjectivesAntimicrobial resistance (AMR) in Gram-negative pathogens is driven by complex and coordinated molecular mechanisms that remain incompletely characterized. This study integrated phenotypic, genomic, and quantitative proteomic analyses to characterize multidrug-resistant (MDR) and extensively drug-resistant (XDR) Gram-negative bacteria circulating in an intensive care unit (ICU) in Northeastern Brazil. MethodsA total of 259 Gram-negative isolates collected between 2019 and 2021 underwent species identification, antimicrobial susceptibility testing, and targeted qPCR for resistance genes. Klebsiella pneumoniae, Acinetobacter baumannii, and Pseudomonas aeruginosa representing susceptible, MDR, and XDR phenotypes were selected for whole-genome sequencing and label-free quantitative proteomics. Differential protein abundance was assessed using Limma with |log2FC| > 1 and p < 0.05. ResultsK. pneumoniae (47%), A. baumannii (24%), and P. aeruginosa (21%) predominated. Carbapenem resistance reached 44%, 93%, and 61%, respectively, and MDR/XDR phenotypes occurred in >30% of isolates. Genomic analyses revealed dense resistomes with coexisting {beta}-lactamases (blaKPC, blaNDM, blaCTX-M, OXA) and widespread efflux systems. Proteomic profiling demonstrated phenotype-associated differences in outer membrane proteins, transport systems, regulatory proteins, and metabolic pathways. XDR isolates showed additional enrichment of envelope remodeling proteins, stress response mechanisms, and proteostasis-associated factors. ConclusionsMDR and XDR Gram-negative ICU pathogens exhibit coordinated resistance architecture characterized by accumulation of resistance genes and adaptive proteomic remodeling. Integrated multi-omics approaches provide mechanistic insight into antimicrobial resistance and support improved surveillance and therapeutic strategies. What is known?O_LIAntimicrobial resistance is a priority and a serious problem in global health, resulting in high rates of morbidity and mortality. C_LIO_LIKlebsiella pneumoniae, Acinetobacter baumannii, and Pseudomonas aeruginosa are on the World Health Organizations (WHO) priority list as major causes of morbidity and mortality worldwide. C_LIO_LIClassical characterization of susceptibility and resistance phenotypes does not capture the complexity of antimicrobial resistance and hampers effective control measures and actions to minimize the evolutionary dynamics of resistance in these bacteria. C_LI What is new?O_LIThe study characterizes the phenotypic pattern of antimicrobial susceptibility, the presence and sequencing of the resistome and virulome, and analyzes the label-free quantitative proteome of susceptible, MDR, and XDR phenotypes in strains of K. pneumoniae, A. baumannii, and P. aeruginosa circulating in hospital ICUs in Brazil. C_LIO_LIMDR and XDR gram-negative phenotypes are associated with a dense resistome, with widespread dissemination of beta-lactamase genes (bla_KPC, bla_NDM, bla_CTX-M, and OXA) and RND-type (MEXs) and acrAB-tolC efflux pumps, without changes in virulence genes. C_LIO_LIProteomic analysis demonstrated increased production of beta-lactamases, components of efflux pump systems, outer membrane protein synthesis, protection for oxidative stress mechanisms, proteins for iron acquisition, and systemic regulators. XDR strains additionally showed enhanced remodeling of the cell envelope, activation of proteostasis, and metabolic adaptation. C_LI

Objectives: To better define the clinical features of Acinetobacter spp. infection in Northern Thailand, including a comparison of hospital- and community-acquired infections (HAIs and CAIs). Methods: A prospective clinical study of Acinetobacter spp. infections at two Northern Thailand hospitals from 2019 to 2022, collecting data on sample sources, patient demographics, comorbidities, antimicrobial resistance profiles, and outcomes. Results: Of 129 enrolled patients, 81.4% had Acinetobacter spp. isolated from a respiratory sample. A significant minority (25.6%) of infections were CAIs, 33.3% of which were admitted to ITU within 24 hours of admission. Compared to HAIs, CAIs were significantly more likely to be caused by blood (15.2%, p=0.0258), wound (21.2%, p=0.0120), or urine infections (12.1%, p=0.0370). Acinetobacter spp. HAIs mainly occurred after admission to ITU (87.7%, p<0.0001) and were more likely to be multidrug-resistant than CAIs (76.3% vs. 34.4%, p<0.0001). Overall, the median length of hospital stay was 27 days and there was a 27.1% in-hospital mortality, which was increased in patients with CVA/brain (p=0.005), and multidrug-resistant (p=0.010) or carbapenem-resistant infections (p=0.003). Conclusions: These data define the clinical profile of Acinetobacter spp. infections in Northern Thailand, confirming their high mortality and demonstrating CAIs are a significant proportion of all cases.

Numerous factors may influence the optimal rollout of new gonococcal antibiotics. We compared eight rollout strategies using a gonorrhea transmission model and ranked strategies by the number of gonococcal infections and clinically useful antibiotic lifespan. Rankings were most sensitive to the starting ceftriaxone resistance prevalence and screening frequency.

BackgroundVirtual colony count is a kinetic, 96-well turbidimetric assay that has been used since 2003 to determine the antimicrobial activity of antimicrobial peptides including the defensin HNP1. Virtual colony count results differed from traditional colony counting results in studies of the antimicrobial activity of the human cathelicidin LL-37 and related peptides. The difference could possibly have been caused by an inoculum effect. MethodsThe virtual colony count assay was conducted using inocula that varied from 1250 to 1x108 virtual colony forming units (CFUv) per milliliter. ResultsThe virtual colony count assay demonstrated a pronounced inoculum effect of HNP1 against Staphylococcus aureus ATCC 29213, accompanied by biofilm formation observed in the wells of the 96 well plates at all inocula. The S. aureus inoculum effect was not as drastic as previously reported for Escherichia coli. ConclusionsThe inoculum effect is further evidence that biofilm formation is a resistance mechanism used by a variety of bacteria against antimicrobial peptides such as HNP1.

Shiga toxin-producing Escherichia coli (STEC) are an important public health concern due to their association with foodborne gastroenteritis and severe outcomes including haemolytic uraemic syndrome (HUS), particularly linked to the stx2a subtype of the Shiga toxin. We investigated the temporal dynamics and acquisition of stx2a among STEC isolates submitted to the United Kingdom Health Security Agency (UKHSA) between 2016 and 2024. 12,888 whole genome STEC sequences and associated metadata were analysed. 31.9% of STEC isolates harboured stx2a, spanning 78 O serogroups with a marked shift from STEC O157 to non-O157 serogroups over time. STEC O26:H11 and STEC O145:H28 were the primary drivers of observed increases, most commonly associated with stx2a alone or in combination with stx1a. The widespread and increasing presence of stx2a across the STEC population in England highlights an emerging public health risk and demonstrates the value of routine genomic surveillance in monitoring high-severity Shiga toxin subtypes.

Background Five-biomarker-defined hypervirulent Klebsiella pneumoniae (hvKp) causes invasive infections, but its burden in bloodstream infections versus classical K. pneumoniae (cKp) is unclear. Methods This retrospective cohort study at a tertiary hospital in Japan included K. pneumoniae bloodstream infection episodes from January 2022-December 2024. hvKp was defined by the presence of all 5 genotypic biomarkers (rmpA, rmpA2, iucA, iroB, and peg-344). The primary outcome was abscess complications, and secondary outcomes were length of stay and antibiotic duration. Whole-genome sequencing was performed for 164 isolates. Results Among the 207 episodes, 28 (14%) were of hvKp. Abscess complication occurred in 17 (61%) hvKp versus 23 (13%) cKp episodes (adjusted odds ratio 10.7; 95% CI, 4.36-26.2). Median length of stay in hvKp versus cKp was 28 versus 14 days (adjusted ratio 1.60; 95% CI, 1.18-2.16) and median antibiotic duration was 43 versus 14 days (adjusted ratio 2.13; 95% CI, 1.64-2.77). These associations were attenuated after adjusting for abscess-related complications. No significant difference in 30-day mortality was observed, although the study was underpowered. Multidrug resistance was less frequent in hvKp strains than in cKp strains (11% vs. 30%; P = .040). Among the sequenced hvKp episodes, abscess rates varied across lineages, from 9 of 10 in ST23 to 1 of 4 in ST412. Conclusions Five biomarker-defined hvKp strains delineated a bloodstream infection subgroup with frequent abscess complications and prolonged care. hvKp and cKp present distinct clinical challenges; diagnostic tools distinguishing these subgroups may aid abscess evaluation and source control.

Carbapenem-resistant Gram-negative bacteria pose a critical public health threat. The role of mobile genetic elements in driving their transmission and persistence remains poorly defined. In 2022, we investigated a suspected outbreak of carbapenem-resistant Acinetobacter baumannii (CRAB) in a Nigerian adult intensive care unit (ICU), using short-read whole genome sequencing (WGS) of carbapenem-resistant clinical and environmental isolates during the cluster period. Mobile element dynamics were then inferred from hybrid assemblies of Illumina and Oxford Nanopore reads. The suspected CRAB outbreak was ruled out by WGS but a carbapenem-resistant Enterobacter hormaechei ST114 bloodstream isolate was found to be indistinguishable from two environmental isolates, all recovered during the Acinetobacter surge. Hybrid assemblies revealed a strikingly conserved [~]19 Kb resistance island shared across all ST114 genomes. The island contained a blaNDM-5 cassette alongside many other antimicrobial resistance genes, within class 1 integronns and flanked by insertions sequences, located on a 46,176 bp plasmid. Using the ST114 plasmids hybrid assembly as scaffold, the same plasmid was identified in the genome of a Klebsiella pneumoniae ST15 isolate from the ICU environment during the same period. Additionally, re-interrogation of genomic surveillance data uncovered four clonal 2020 ST109 Enterobacter bloodstream isolates from the same facility that carried the resistance genes in the same context on a large 267,242 bp plasmid. Carbapenem resistance in hospital Enterobacterales is driven by both clonal expansion and horizontal spread of mobile resistance elements. These findings underscore the need to track mobile elements alongside bacterial lineages to inform evidence-based infection control, especially in low-resource settings. Impact StatementCarbapenem resistance among Enterobacterales remains a major public health threat, yet how mobile genetic elements contribute to their persistence and spread in hospital settings is still poorly understood. In this study, we investigated a suspected outbreak of carbapenem-resistant Acinetobacter baumannii in an adult intensive care unit in Nigeria. Although the outbreak was eventually ruled out, genomic analysis has shown the importance of careful interpretation of suspected outbreak cases in hospital settings. Our findings highlight the importance of close monitoring of ICU environments, the implementation of blood culture-based diagnostics, and the value of genomic support in outbreak investigations. These findings demonstrate that carbapenem resistance in hospital Enterobacterales is driven not only by clonal expansion but also by the horizontal dissemination of a highly stable blaNDM-5-associated MDR island capable of integrating into diverse plasmid backbones. This study emphasizes the need for genomic surveillance that tracks both mobile elements and bacterial lineages to strengthen outbreak investigations, especially in low-resource settings. It further underscores the links between clinical and environmental AMR reservoirs and reinforces the value of a One Health approach to controlling carbapenem resistance. Data summaryFASTQ sequences were deposited in the NCBI BioSample database under accession numbers SAMN55915584 - SAMN55915597.

The Klebsiella pneumoniae species complex (KpSC) is a clinically important group of closely related pathogens associated with invasive infections. The complex comprises seven closely related members, which are often reported as K. pneumoniae, particularly in resource-limited settings. Accurate differentiation of KpSC members remains challenging because routine laboratory methods lack sufficient resolution, and approaches like mass spectrometry and whole genome sequencing (WGS) are not widely available. Consequently, the epidemiology and clinical significance of non-K. pneumoniae members of the KpSC remain underrecognized. We developed a conventional multiplex mismatch amplification mutation assay (MAMA) PCR targeting species- and subspecies-specific single-nucleotide polymorphisms in the housekeeping gene rpoB, with six primer sets for differentiation of common KpSC members. The assay was validated against 49 genomically characterized clinical isolates, after which 179 wastewater-derived isolates provisionally identified as Klebsiella spp. by standard microbiological methods were tested. Of these, 174 were assigned to specific KpSC members by the assay, while 5 produced inconclusive amplification patterns. A subset of 16 environmental isolates was selected for WGS, including four of the five inconclusive isolates. All environmental isolates with interpretable MAMA PCR patterns were concordant with WGS. The four inconclusive environmental isolates were identified as Enterobacter spp. Overall, comparison of MAMA PCR with WGS showed 100% sensitivity and 100% specificity for all tested targets, and the total cost was approximately US$1. This rpoB-based multiplex MAMA PCR provides a simple, accurate, and low-cost approach for differentiation of KpSC members in routine laboratories and may support improved identification and surveillance in resource-limited settings. ImportanceThe Klebsiella pneumoniae species complex (KpSC) has seven members but is often reported as a single organism in routine laboratories, masking clinically and epidemiologically important diversity. As a result, the contribution of non-K. pneumoniae KpSC members to human and environmental microbiology remains poorly defined, especially in low-resource settings. We developed a conventional multiplex mismatch amplification mutation assay (MAMA) PCR based on discriminatory rpoB single nucleotide polymorphisms for differentiation of common KpSC members using standard PCR and agarose gel electrophoresis. The assay demonstrated 100% sensitivity and 100% specificity against whole-genome sequencing and excluded non-Klebsiella environmental isolates initially identified as Klebsiella pneumoniae using standard microbiological procedures. With an estimated per-test cost of about US$1, this method offers an affordable and scalable option for laboratories seeking more accurate KpSC identification and improved surveillance.

BackgroundThe Toto Bora trial tested whether a course of azithromycin reduced rates of re-hospitalization or death in the 6 months following hospitalization among Kenyan children. We hypothesized that azithromycin would reduce enteric bacteria and increase carriage of macrolide resistance in the subsequent 3 months. MethodsKenyan children (1-59 months) hospitalized and subsequently discharged for non-traumatic conditions provided fecal samples before and 3 months after randomization to a 5-day course of azithromycin or placebo. Quantitative PCR identified enteropathogens and AMR-conferring genes in fecal samples. Generalized estimating equations assessed the impact of the randomization arm on pathogen and resistance gene detection, accounting for baseline presence and site. ResultsAmong 1,393 baseline stools, 12.4% had at least one bacterial enteropathogen, 94.7% had at least one macrolide-resistance gene, and 92.6% had at least one beta-lactamase-resistance gene identified. At month 3, children randomized to azithromycin had a 6.1% higher likelihood of carrying a macrolide resistance gene compared to placebo (adjusted prevalence ratio [aPR], 1.06; 95% CI, 1.04-1.08; P<0.001). Specifically, azithromycin randomization was associated with a higher relative prevalence of erm(B) (aPR, 1.09 [95% CI, 1.04-1.15]; P=0.001), erm(C) (aPR, 1.23 [95% CI, 1.14-1.31]; P<0.001), msr(A) (aPR, 1.14 [95% CI, 1.04-1.25]; P=0.007), and msr(D) (aPR, 1.07 [95% CI, 1.03-1.11]; P=0.001). There was no difference in overall bacterial pathogen prevalence (18.9% vs 17.3%) between randomization arms, but a slightly lower proportion of children had Shigella after randomization in the azithromycin arm (3% vs. 5%, aPR, 0.79 [95% CI, 0.62, 1.01]; P=0.063). InterpretationAzithromycin at hospital discharge was associated with higher carriage of macrolide-resistance-conferring genes in the post-discharge period compared with placebo, without significant declines in enteric pathogen carriage other than modest changes to Shigella. The potential benefits and risks of empiric azithromycin need to be considered, as children are increasingly exposed to this broad-spectrum antibiotic.

Azithromycin plus ethambutol plus rifabutin (azithromycin-ethambutol-rifabutin) is the standard-of-care (SOC) for Mycobacterium avium-complex lung disease. The SOC achieves sustained sputum culture conversion in only 43-53% of patients, after an average of 18 months of therapy. Recent quantitative analyses ranked omadacycline, ceftriaxone, and minocycline highest for microbial kill. Azithromycin-minocycline-ethambutol, azithromycin-omadacycline-ethambutol, epetraborole-omadacycline-ethambutol, ceftriaxone-omadacycline-rifabutin, and the SOC were compared in the intracellular hollow fiber system model of M. avium lung disease (HFS-MAC). HFS-MAC units were treated once daily for 28 days to mimic the intrapulmonary pharmacokinetics of each drug. The ceftriaxone concentrations measured in the HFS-MAC were only 1% of those achieved in the lung by standard clinical doses. Changes in the bacterial burden were described using basis functions (BF). For liquid cultures, BF 1 (BF1) was described by a linear regression-based slope, with steepest kill slope (95% Confidence interval) of 7.87 (1.52 to14.23) by ceftriaxone-omadacycline-rifabutin versus 1.04 (-0.84 to 2.92) for SOC. For the CFU/mL readout, the BF1 steepest non-linear kill slope was for ceftriaxone-omadacycline-rifabutin of 0.55 (0.35 to 0.98) log10 CFU/mL/day versus 0.16 (0.07 to 0.25) log10 CFU/mL/day for the SOC. Thus, ceftriaxone-omadacycline-rifabutin is potentially better than the SOC, even though further ceftriaxone dose optimization is required. BF2 described rebound growth and drug-resistant subpopulation growth, and demonstrated that contrary to popular belief, SOC rebound was best explained by ethambutol-resistance (r2>0.99, p=0.01) and not by azithromycin-resistance (r2=0.27, p=0.32), questioning ethambutols role in the SOC. The BF framework is potentially easy to adapt for modeling other anti-infective agents across many infectious diseases.