Antimicrobial activity of antibiotic-induced resistant lactobacilli against carbapenemase-producing Enterobacterales

Abstract

Carbapenemase-producing Enterobacterales (CPE) are a critical global health threat with limited treatment options. Lactobacilli have been reported to exhibit antimicrobial activity against CPE, but whether this activity, together with key probiotic characteristics, is preserved after antibiotic-resistance induction—a clinically relevant condition given the concurrent antibiotic exposure that colonized or infected patients often receive—has not been characterized. Wild-type Lactiplantibacillus plantarum (LYC1322), Lacticaseibacillus paracasei (LYC1154), and Lacticaseibacillus rhamnosus (LYC1511), along with antibiotic-induced resistant variants generated by serial sublethal exposure to ampicillin, minocycline, and erythromycin (designated “ame”), were tested against 17 clinical CPE isolates spanning six species and five carbapenemase types (KPC, NDM, OXA-181, IMP-8, VIM-1) using an in vitro co-culture assay. Gastrointestinal tolerance (pepsin and oxgall assays) and Caco-2 epithelial adhesion were also evaluated for all six strains. Both wild-type and ame-induced lactobacilli variants substantially reduced CPE viability, reducing recoverable CPE to below the limit of detection (<10 CFU/mL) for the majority of isolates by 24 h and for all 17 isolates by 48 h, compared with CPE-only controls sustaining 10 6 –10 9 CFU/mL. This activity was consistent across all six species and all five carbapenemase types tested. Under simulated gastric (pepsin, pH 3.0) and intestinal bile salt (0.3% oxgall) conditions, ame-induced variants showed no obvious reduction in viability relative to their wild-type parental strains, although bile tolerance varied appreciably between strains; adhesion to Caco-2 monolayers appeared similar between wild-type and ame-induced variants at both inoculum densities tested. Under the in vitro conditions tested, antibiotic-resistance induction was not associated with an obvious reduction in anti-CPE activity, gastrointestinal stress tolerance, or epithelial adhesion, and the induced variants remained active against all CPE isolates examined, although bile tolerance differed between strains. Because reversibility testing and whole-genome sequencing were not performed, the induced phenotype may represent stable acquired rather than adaptive resistance, and the safety assessment of these variants remains incomplete. These findings are therefore preliminary and hypothesis-generating; mechanistic, genomic, animal, and clinical studies, including evaluation under concurrent antibiotic therapy—are required before any adjunctive probiotic application can be considered.