Increasing Burden of Antibiotic Resistance in India Due to Co-existence of Multiple Classes of Carbapenem and Different Aminoglycoside Resistance Genes in Clinical Isolates of Acinetobacter baumannii.

Acinetobacter baumannii is a significant pathogen responsible for resistant recalcitrant infections and outbreaks in hospitals worldwide, which is of much concern. The main goal of the present study is to determine the levels of antibiotic resistance in recent clinical isolates of Acinetobacter baumannii and to investigate the presence of diverse resistance determinants among these isolates and also to correlate these findings. A total of 133 A. baumannii clinical isolates from hospitalized patients were investigated for antibiotic resistance levels by determining their MIC by microbroth dilution method. The presence of β-lactamase-encoding genes (blaPER-1, blaNDM-1, blaIMP-1, blaADC, blaOXA51, blaOXA23, blaOXA58 and blaOXA24), aminoglycoside resistance-related genes (armA, aph3(III), aac3(I), aac6, ant3, and aph3(I) and genes associated with biofilm formation were checked by amplifying them by PCR using gene specific primers. The genotyping of isolates was carried out by REP-PCR. Coexistence of diverse intrinsic and acquired carbapenem-hydrolyzing β-lactamases (CHDLs) genes was observed in the isolates: Ambler class A: blaPER-1 (50.37%), Class B: blaNDM-1 (63.90%), blaIMP-1 (76%), Class C: blaADC (75.93) and class D: blaOXA-23 (91.7%), blaOXA-51 (97.74%). A significant difference (P < 0.05) was observed in the prevalence of blaOXA-23 among the isolates obtained from ICU (n = 52) patients and with that of non-ICU (n = 81) patients. MIC results revealed 105 (79%) isolates were extremely drug-resistant (XDR) while 28 (21%) isolates were multi-drug-resistant. All the isolates were susceptible only to colistin. Rampant emergence of XDR isolates and co-existence of multiple CHDLs and different aminoglycoside-modifying enzymes genes in A. baumannii isolates in this study points out the increasing burden of antibiotic resistance in our region.