The distribution of carbapenem- and colistin-resistance in Gram-negative bacteria from the Tamil Nadu region in India

Purpose. The occurrence of carbapenem-and colistin-resistance among Gram-negative bacteria is increasing worldwide. The aim of this study was to understand the distribution of carbapenem-and colistin-resistance in two areas in Tamil Nadu, India. Methodology. The clinical isolates (n=89) used in this study were collected from two diagnostic centres in Tamil Nadu, India. The bacterial isolates were screened for meropenem-and colistin-resistance. Further, resistance genes bla(NDM-1), bla(OXA-48-like), bla(IMP), bla(VIM), bla(KPC), mcr-1 and mcr-2 and integrons were studied. The synergistic effect of meropenem in combination with colistin was assessed. Results. A total of 89 bacterial isolates were studied which included Escherichia coli (n=43), Klebsiella pneumoniae (n=18), Pseudomonas aeruginosa (n=10), Enterobacter cloacae (n=6), Acinetobacter baumannii (n=5), Klebsiella oxytoca (n=4), Proteus mirabilis (n=2) and Salmonella paratyphi (n=1). MIC testing showed that 58/89 (65 %) and 29/89 (32 %) isolates were resistant to meropenem and colistin, respectively, whereas 27/89 (30 %) isolates were resistant to both antibiotics. Escherichia coli, K. pneumoniae, K. oxytoca, Pseudomonas aeruginosa, and Enterobacter cloacae isolates were bla(NDM-1)-positive (n=20). Some strains of Escherichia coli, K. pneumoniae and K. oxytoca were bla(OXA-181)-positive (n=4). Class 1, 2 and 3 integrons were found in 24, 20 and 3 isolates, respectively. Nine NDM-1-positive Escherichia coli strains could transfer carbapenem resistance via plasmids to susceptible Escherichia coli AB1157. Meropenem and colistin showed synergy in 10/20 (50 %) isolates by 24 h time-kill studies. Conclusion. Our results highlight the distribution of carbapenem-and colistin-resistance in Gram-negative bacteria isolated from the Tamil Nadu region in South India.