Abstract
Background: Colistin is one of the oldest antibiotics in the polymyxin group, and is used mostly against gram-negative bacteria. Because of developing resistance among clinical isolates colistin has become an alternative drug for multidrug resistant bacteria.
Objectives: To determine colistin resistance among isolates from Tamil Nadu, India.
Methods: We included 94 gram-negative isolates from two centers in Tamil Nadu in the present study. Isolates were identified by 16S rRNA sequencing. Minimal inhibitory concentrations (MICs) were determined by agar dilution.
Results: The isolates identified at species level included 48 Escherichia coli, 9 Klebsiella pneumoniae, 10 Pseudomonas aeruginosa, 5 Proteus mirabilis, 4 Salmonella enterica, 3 Enterobacter hormaechei, 3 Enterobacter cloacae, 2 Achromobacter xylosoxidans, 2 Acinetobacter baumannii, 1 Providencia vermicola, 1 Acinetobacter towneri, 1 Enterobacter gergoviae, 2 Providencia rettgeri, 1 Enterobacter asburiae, 1 Pseudomonas stutzeri, and 1 Salmonella typhi. The MIC of colistin ranged from 0.12 mu g/ml to 128 mu g/ml. The MIC50 was 1 mu g/mL and MIC90 was >128 mu g/ml. The MIC >= 8 mu g/mL was resistant breakpoint for all the species. A total of 27 isolates were resistant to colistin. Colistin resistant isolates included E. coli (9/48), K. pneumoniae (6/9), P. aeruginosa (3/10), A. baumannii (1/2), P. mirabilis (4/5), E. cloacae (1/3), P. rettgeri (2/2), and S. enterica (1/4). Carbapenem susceptibility of colistin resistant isolates was tested and 14 were found to be resistant to meropenem.
Conclusions: Our study indicates the emergence of colistin resistant isolates from clinical samples among different groups of gram-negative organisms. Resistance to both carbapenem and colistin occurs. Developing new antibiotics and programs to reduce nosocomial infections is necessary especially for multidrug resistant isolates.