Genetic characterization of tigecycline and carbapenem resistant Acinetobacter baumannii in a tertiary care hospital of Northern India.

BACKGROUND

Acinetobacter baumannii has emerged as a predominant cause of hospital-acquired infections worldwide, posing a significant challenge due to its extraordinary ability to acquire resistance to multiple antibiotics. According to recent data, infections caused by multidrug-resistant A. baumannii lead to increased morbidity, longer hospital stays, and higher healthcare costs. Carbapenems and tigecycline have historically provided reliable treatment for A. baumannii infections; however, recent global trends indicate a significant increase in carbapenem and tigecycline resistance among circulating isolates.

OBJECTIVES

The study aimed to determine the prevalence and genetic characterization of tigecycline resistance in A. baumannii (TRAB) among carbapenem-resistant isolates and to assess the transferability of carbapenem and tetracycline resistance genes between isolates.

METHODS

All 160 clinical isolates were obtained from admitted patients in SGPGIMS, Lucknow (India). Identification of the isolates was performed using MALDI-TOF MS, followed by antimicrobial susceptibility testing (AST), determination of minimum inhibitory concentrations (MICs), and PCR-based detection of carbapenem and tetracycline resistance genes. The transferability of resistance genes was further assessed through conjugation assays, and the AST of transconjugant isolates was evaluated accordingly.

RESULTS

A total of 32 out of 160 isolates (20%) were resistant to both carbapenem and tigecycline. All these isolates were multidrug-resistant (MDR), exhibiting resistance to more than three classes of antibiotics. Genetic screening showed the blaNDM and blaOXA-48 carbapenemase genes in 25% and 18.75% of the respective isolates; blaKPC was not detected. Among tetracycline resistance genes, only tet(B) was present in 15.63% (5/32) of the isolates; other genes such as tet(A), tet(K), tet(M), and tet(S) were absent. Both carbapenemase and tetracycline resistance genes were plasmid-mediated, and often co-existed in the same isolates. However, only the carbapenemase genes were transferable by conjugation; the tetracycline resistance genes were not transferable.

CONCLUSIONS

The increasing prevalence of carbapenem and tigecycline-resistant A. baumannii is primarily linked to plasmid-mediated carbapenemase genes, which facilitate their spread. In contrast, tigecycline resistance, although present, appears to be non-transferable under the conditions studied.