Prevalence of qnr and aac(6′)-Ib-cr Genes in Community-Acquired Enterobacteriaceae Isolated in Healthy Volunteers in Hochiminh City

Abstract

Background: Multi-drug resistance in Gram-negative microorganisms is emerging. Data on the prevalence of multi-drug resistant organisms in the community are sparse, particularly in developing countries. We studied the carriage of multi-drug resistant Enterobacteriaceae in healthy volunteers in Hochiminh city, Vietnam, and determined the prevalence of genes encoding transferable quinolone resistance. Methods: Strains were isolated from stool samples or rectal swabs of 27 healthy adults, 77 healthy children (aged 5–15) and 100 healthy neonates (aged 1–3 days). Samples were cultured on MacConkey agar supplemented with gentamicin (8 mg/ml), ceftazidime (2 mg/ml), or nalidixic acid (16 mg/ml). One colony representative of each morphology, was subcultured before identification by API 20E. Antibiotic resistance was determined by disc diffusion test and E-test. Quinolone resistance genes qnrA, qnrB, qnrS, and aac(6′)-Ib-cr were detected by PCR and sequencing. All qnr and aac(6’)-Ib-cr positive isolates were typed by RAPD. Results: Antibiotic resistant Enterobacteriaceae were cultured from 25/27 (93%) adults, 68/77 (88%) children and 42/100 (42%) neonates. A total of 60, 252 and 97 strains were isolated in each group respectively. ESBL-positive strains were present amongst 67/334 (20%) E. coli, 18/43 (42%) K. pneumoniae and 9/32 (28%) other Enterobacteriaceae. Out of 409 strains of Enterobacteriaceae, 309 (76%) strains were resistant to nalidixic acid, 263 (64%) to gentamicin, 19 (5%) to amikacin, 43 (11%) to piperacillin-tazobactam. qnrA, qnrB, qnrS and aac(6′)-Ib-cr genes were present in 3 (0.7%), 3 (0.7%), 47 (11.5%), and 12 (2.9%) isolates, respectively, which were shown to be unique by RAPD. The MIC50 to ciprofloxacin of qnr and aac(6′)-Ib-cr positive isolates was >0.75 mg/l, the MIC90 >32 mg/l. Conclusion: The carriage rate of drug-resistant Enterobacteriaceae in healthy people in Hochiminh City is extremely high. Moreover, genes encoding transferable quinolones, in particular qnrS, are highly prevalent in these strains.