Effects of gyrA and parC Mutations in Quinolones Resistant Clinical Gram Negative Bacteria from Nigeria

The most important of fluoroquinolones resistance mechanisms is the accumulation of mutations in the bacterial enzymes targeted by fluoroquinolones; DNA gyrase and DNA topoisomerase IV. The effect of gyrase and Topoisomerase IV enzymes mutations on quinolones resistance in clinical Gram negative bacteria in Nigeria was extensively investigated. 115 Gram-negative bacteria of 4 species were analyzed for antimicrobial susceptibility, polymerase chain reaction amplifications of quinolone resistance determining regions, mutation detection using denaturing high-performance liquid chromatography or sequencing. These strains were Klebsiella pneumoniae , Escherichia coli , Proteus mirabilis , Pseudomonas aeruginosa . Minimum inhibitory concentrations showed that the level of resistance was high with MIC50 greater than clinical break point for all drugs. 85 of the 115 isolates carried a mutation in QRDRs. Mutations in gyrA were found at positions 83 and 87 of the quinolone resistance determining regions (QRDRs). 4 amino acid substitutions were seen in gyrA including double mutations at codons 83 + 87 while 2 substitutions were seen within parC at codons 80 and 87. All parC mutations were seen in strains which also carried a gyrA mutation. Mutation at codon position 83 with amino acid subtitution of leucine for serine resulted in a higher MIC than substitution to threonine at position 83 or double mutations of serine 83 and asparagine 87. In conclusion, quinolone resistance in clinical Gram negative bacteria in Nigeria is also mediated by accumulation of mutations at QRDR.