Molecular Epidemiology and Resistance Mechanisms of Tigecycline-Non-Susceptible A. baumannii Isolated from a Tertiary Care Hospital in Chongqing, China

Abstract

Abstract Objectives This study aimed to investigate the epidemiology and tigecycline resistance mechanisms of Tigecycline-Non-Susceptible A. baumannii (TNAB) isolates in a large tertiary care hospital in Chongqing, China. Methods From July 2019 to June 2022, 34 non-duplicate isolates of A. baumannii determined as tigecycline-non-susceptible by broth microdilution method were collected from a tertiary care hospital in Chongqing. The resistance-related genes were sequenced and the expression level of the resistance-nodulation-cell division (RND) efflux pumps was investigated. The activity of the RND efflux pumps was examined by adding efflux pump inhibitors (EPIs). The molecular epidemiology was analyzed by multi-locus sequence typing (MLST) and goeBURST software. Results In this study, the TNAB strains were primarily obtained from ICU and had high resistance rates to commonly used antibiotics. Tigecycline resistance-associated genes adeR, adeS, adeL, adeN, rrf, and rpsJ were detected in most strains. All TNAB strains exhibited 240 nucleotide deletion mutation in the trm gene. The expression level of the RND efflux pumps in TNAB strains was higher than the reference strain ATCC19606. 58.82% of strains had a decrease in the tigecycline minimum inhibitory concentration (MIC) after the addition of carbonyl cyanide 3-chlorophenylhydrazone (CCCP). A total of 8 ST types were identified, including ST195 (35.29%), ST208 (17.65%), and ST369 (14.71%). EBURST analysis found that 8 of the ST types belonged to the Clonal Complex 92. Conclusion The TNAB strains in our hospital have a high degree of affinity and antibiotic resistance. Regular surveillance should be conducted to prevent outbreaks of TNAB epidemics.