Exposure to third generation cephalosporin induces L-form transition in Shigella sonnei, potentially acting as a bacterial reservoir for persistent infection

Shigellosis is a major global health threat with a significant Disability Adjusted Life years (DALY) burden, particularly in India, where rising multidrug-resistance (MDR) compromises therapies. Bacteria may survive antibiotics by transitioning into cell wall-deficient L-forms, which are intrinsically resistant to {beta}-lactams and can revert to a virulent state, potentially causing relapsing infections. Here we characterized a clinical MDR isolate Shigella sonnei HK8, a.k.a. PD552A, whose genome contains key resistance (gyrA, PBP3) and virulence (icsA) genes. Exposure to ceftriaxone induced a transition into a viable L-form state that was hyper-adhesive to macrophages in vitro. However, this survival adaptation was linked to a profound loss of pathogenicity. Using murine and guinea pig models, the L-form variant was shown to be completely attenuated, failing to cause the keratoconjunctivitis, diarrheal disease, or significant histopathology characteristic of the wild-type strain. These findings reveal a critical virulence-survival trade-off, positioning the L-form as a "stealth" phenotype that enables bacterial persistence at the expense of acute virulence. This offers a potential mechanism for asymptomatic carriage and recurrent infections, highlighting a significant challenge in the management of shigellosis. ImportanceOur research provides critical insight into the challenge of antibiotic treatment failure in shigellosis. By demonstrating that a clinical MDR Shigella sonnei isolate survives ceftriaxone pressure by transitioning into a non-virulent L-form, we uncover a crucial virulence-survival trade-off. The significance of this finding has profound implications for clinical practice: standard antibiotic regimens may inadvertently resolve acute symptoms while simultaneously selecting for a cryptic, persistent bacterial population poised for relapse. This work challenges the conventional view of therapeutic success and highlights an urgent need to develop novel diagnostic and therapeutic strategies capable of identifying and eliminating these resilient, "stealth" L-form persisters to achieve true bacterial clearance and prevent chronic infections.