Molecular Characterization of Class A-ESBLs, Class B-MBLs, Class C-AmpC, and Class D-OXA Carbapenemases in MDR Acinetobacter baumannii Clinical Isolates in a Tertiary Care Hospital, West Bengal, India

Background Acinetobacter calcoaceticus baumannii (ACB) complex has become a major concern nowadays because of its increasing involvement in several severe infections associated with catheter-related bloodstream and urinary tract infections, ventilator-associated pneumonia, cerebrospinal shunt-related meningitis, and wound infections. Multiple drug-resistant (MDR) ACB cases have been described with an increasing trend where at least it is resistant to a minimum of three antimicrobial groups. The mortality rate associated with A. baumannii is significantly higher than all Acinetobacter spp. isolates with the most prevalence seen in India and Thailand. The rapid spread of high resistance to most potent antimicrobial drugs is due to its ability to incorporate resistance determinants despite multifactorial reasons such as alteration in permeability of cell membrane by either losing expression of outer membrane porins or excess production of efflux pumps. This study aims to characterize resistance determinants responsible for MDR at the genetic level and emphasizes the use of genotyping in routine diagnosis as genotype analysis is reliable and valid. Methodology A total of 289 ACB complex clinical isolates were included in this study. The study for species-level identification of A. baumannii was conducted at the Department of Microbiology, IQ City Medical College Hospital, Durgapur, West Bengal. In addition, the detection of encoded genes associated with class A-extended spectrum beta-lactamases (i.e., CTX-M, KPC, SHV, and TEM genes), class B-metallo-beta-lactamases (i.e., IMP, NDM, and VIM genes), Class C-AmpC cephalosporinase, and classD-OXA carbapenemases (i.e., bla(OXA-10/11), bla(OXA-24), bla(OXA-48), bla(OXA-58), bla(OXA-143), and bla(OXA-235) was done using real-time polymerase chain reaction. Results All 289 non-repetitive ACB complex clinical isolates were confirmed as A. baumannii, of which 277 (96%) isolates were MDR. There were no findings of bla(CTX-M), bla(KPC), bla(SHV), bla(TEM), bla(IMP), bla(VIM), bla(AmpC), bla(OXA-10/11), bla(OXA-24), bla(OXA-48), bla(OXA-58), bla(OXA-143), and bla(OXA-235) genes in our study. However, there were four (1.44%) positive findings of the blaNDM gene. All MDR isolates (n = 277) were positive for the bla(OXA-51) gene. In addition, bla(OXA-23) was positive in 269 (97.12%) isolates. Conclusions The oxacillinase production corresponding to bla(OXA-23) and bla(OXA-51) were the most prevalent antibiotic resistance determinants among MDR A. baumannii in our study. Four (1.44%) isolates had the multiple genes bla(OXA-51), bla(OXA-23), and bla(NDM) that shows the coexistence of diverse genetic elements involved in MDR A. baumannii, resulting in total resistance except for a few potent drugs such as colistin and tigecycline. Genotyping is helpful in determining the contribution of the isolates in understanding their association with encoded genes, which, in turn, helps in designing effective surveillance and control strategies in the management of such MDR isolates.

Automated summary

This study characterizes resistance determinants responsible for multidrug-resistant (MDR) A. baumannii and emphasizes the use of genotyping in routine diagnosis. The most prevalent antibiotic resistance determinants among MDR A. baumannii were oxacillinase production corresponding to bla(OXA-23) and bla(OXA-51). Genotyping helps in understanding the association of isolates with encoded genes and designing effective surveillance and control strategies for MDR isolates.