Prevalence of qnr Genes among Multidrug Resistance Staphylococcus aureus from Clinical Isolates

Objectives: Staphylococcus aureus (S. aureus) is regarded as an important aetiological agent of various human infections. Fluoroquinolones are routinely used in the chemotherapeutic management of these infections; nonetheless, in recent years, a growing rate of resistance to these drugs has been reported worldwide. The aims of this study were to isolate and discover the prevalence of plasmid-mediated (qnrA, qnrB, and qnrS) genes among the quinolone-resistant clinical S. aureus isolates in Bayelsa State, Nigeria.

Methods: A total of 25 (31.25%) clinical isolates of S. aureus were collected from hospitalized patients. The bacterial isolates were identified through standard laboratory protocols and further confirmed using the API Staph system (bioMérieux, France) test strips. The antimicrobial susceptibility and minimum inhibitory concentration (MIC) were determined by the standard disk diffusion and serial dilutions methods respectively. Polymerase chain reaction (PCR) was used for detecting qnrA, qnrB, and qnrS genes.

Results: Of the 25 S. aureus isolates, 19(76.00%) were resistant to ampicillin-cloxacillin, while 14 (56.00%) each were resistant to norfloxacin and Amoxicillin, 13 (52.00%) each to gentamicin and erythromycin, 11 (44.00%) were resistant to streptomycin, rifampicin and ciprofloxacin, respectively. The resistance pattern among the isolates to chloramphenicol and levofloxacin were 10 (40.00%) and 7 (28.00%) respectively. All the eleven ciprofloxacin resistant were high-level (1000 µg/mL) resistance isolates and only one (9.00%) of these isolates was positive for the qnrB gene.

Conclusion: The study results were indicative of the presence of low frequency of qnr genes among the clinical isolates of S. aureus in Yenagoa, indicating that other mechanisms are employed in resisting to these fluoroquinolones. This, however, emphasizes the need for establishing discreet policies associated with infection-control measures in hospital settings.