Frequent carriage of enterococci and other Lactobacillales with OptrA and PoxtA ribosomal protection resistance mechanisms among children from rural areas of Bolivia

Objectives: Oxazolidinones are antibiotics of remarkable clinical importance, and resistance to these drugs is a matter of concern. This study investigated the presence of optrA, poxtA and cfr transferable oxazolidinone resistance determinants among enterococci and other non-obligate anaerobic fecal Gram-positives from healthy children living in a rural area of Bolivia. Methods: Fecal samples were collected in transport medium and screened for isolates growing on Colistin-Nalidixic Acid blood agar containing florfenicol 16 mg/L. Isolates were identified by MALDI-ToF mass spectrometry and subjected to Real-time PCR to detect the presence of optrA, poxtA and cfr genes. Antimicrobial susceptibility to florfenicol, vancomycin and linezolid was tested by reference broth microdilution. Results: Overall, 184/420 (43.8%) faecal samples yielded growth on the selective medium and 241 isolates of 13 different species of Lactobacillales (mostly Enterococcus spp. but also lactococci and Vagococcus teuberi) were obtained for further investigation. Most of them carried either optrA (182/241) or poxtA (43/241) or a combination thereof (7/241). cfr was detected in 5/241 isolates, always in combination with the other genes. Conclusions: Present findings report the highest prevalence of faecal carriage of optrA- and poxtA-positive commensals so far observed in healthy subjects, raising concerns about the potential clinical and epidemiological implications.