Investigation of the genetic basis of erythromycin resistance in Staphylococcus aureus, including MRSA, from Pakistan

Abstract number: P1198

Ullah F., Malik S.A., Ahmed J., Snelling A.M.

Objectives: Erythromycin (ERY) is used extensively in clinical practice in Pakistan for skin and throat infections, but little surveillance work has been done to assess the extent of resistance amongst common pathogens. Similarly, there is a paucity of information about the MRSA clones circulating. The aim of this study was to determine the prevalence and mechanisms of ERY resistance amongst S. aureus from specimens being processed at a diagnostic laboratory in the North West of Pakistan. Also, to see if there were differences in the extent of ERY resistance between meticillin sensitive (MSSA) and resistant (MRSA) strains.

Methods: Sequential isolates of S. aureus were collected from wounds and burn/skin infections of in- and out-patients at a tertiary care hospital in Peshawar. Isolates were identified by standard methods, including PCR for mecA/nuc genes to confirm MRSA, which were also ribotyped. MIC profiles for commonly used antibiotics were determined using CLSI criteria. Presence of erm(A), erm(B), erm(C) and msr(A) genes was determined by PCR.

Results: Of 133 isolates of S. aureus collected, 59 (44.4%) were resistant to ERY, with MIC values ranging from 8 to >1024 mg/L. Just 3.3% (n = 3) of the 70 MSSA were resistant, while in contrast, of the 63 MRSA strains, 41.3% (n = 35) were ERY-R. The most common resistance gene detected amongst the ERY-R strains was erm(A) (44.1%), followed by erm(C) (42.3%), msr(A) (8.4%) and erm(B) (5%). No strain carried multiple genes. Eight ribotypes (A to H) of MRSA were present: erm(A) was found in ribotypes A, B and C, erm(C) was found in ribotypes D, E and F. The erm(B) +ve strains were restricted to ribotype G, and msrA to ribotype H. Overall, ERY-R strains of MRSA were generally co-resistant to ciprofloxacin (86.8%), gentamicin (86.8%) and tetracycline (83.6%). However, resistance amongst such strains to chloramphenicol and fusidic acid was much lower (20% and 16.3% respectively).

Conclusion: ERY-R was surprisingly rare amongst skin isolates of MSSA from this area, and thus this antibiotic may still be useful for treating infections if MSSA status is confirmed. Amongst the MRSA, ERY-R is common, mediated mostly by erm(A) and erm(C), and the resistance genes map to the clonal lineages. Where the skin infection is due to an MRSA, topical fusidic acid may still have utility in this area of Pakistan.

Session Details

Date: 19/04/2008
Time: 00:00-00:00
Session name: 18th European Congress of Clinical Microbiology and Infectious Diseases
Location: Barcelona, Spain
Presentation type:
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