Unusual susceptibility to vancomycin in Elizabethkingia meningoseptica: mechanisms and clinical implications

Elizabethkingia meningoseptica, an environmental, non-fermenting Gram-negative bacillus, poses a serious clinical challenge due to its intrinsic multidrug resistance. Paradoxically, the pathogen exhibits exceptional in vitro susceptibility to vancomycin, a glycopeptide antibiotic normally directed only against Gram-positive organisms. This review systematically synthesizes recent evidence-published since earlier key reviews-on this paradoxical susceptibility. The review clarifies taxonomic evolution and identification challenges within the genus Elizabethkingia, highlighting how frequent misidentification between E. meningoseptica and E. anophelis has confounded historical susceptibility data. It proceeds to critically evaluate methodological variations in antimicrobial susceptibility testing and their impact on vancomycin susceptibility reporting. It discusses emerging mechanistic insights, including hypothesized increased outer-membrane permeability and biofilm inhibition at sub-minimum inhibitory concentrations, as plausible but not yet conclusively proven explanations for vancomycin activity. Finally, it proposes evidence-based treatment strategies, emphasizing susceptibility-guided combination regimens over vancomycin monotherapy. This updated synthesis aims to provide both theoretical grounding and pragmatic clinical guidance for managing multidrug-resistant Elizabethkingia infections.