Investigation of the Genetic Basis of Tetracycline Resistance in Staphylococcus aureus from Pakistan

Purpose: To determine the prevalence and genetic basis of tetracycline resistance in Staphylococcus aureus. Methods: One hundred and thirty (130) clinical isolates of S. aureus were collected from Khyber Teaching Hospital, Peshawar, Pakistan. Susceptibility to antibiotics (doxycycline, tetracycline and minocycline) was determined by Kirby-Bauer disc diffusion method with minimum inhibitory concentration (MIC) evaluated on Muller-Hinton agar as described by the Clinical and Laboratory Standards Institute (CLSI). The tetracyclineresistant strains (TET-R) were screened by polymerase chain reaction (PCR) for the presence of four common tetracycline resistance determinants, viz, tet(K), tet(L), tet(M) and tet(O). Results: Sixty (46.0 %) of these isolates were methicillin-resistant S. aureus (MRSA) while 70 (54.0 %) were methicillin-susceptible S. aureus (MSSA). Seventy four (56.9 %) strains were resistant to tetracycline (TET-R), 30 (23.1 %) to minocycline and 23 (17.7 %) to doxycycline. A majority of the MRSA were resistant to tetracyclines and all the MSSA were sensitive to doxycycline and minocycline. The tet(K) gene was found in 58 isolates and tet(L) in one isolate. No tet(M) and tet(O) were detected. Conclusion: This study indicates that resistance to tetracyclines is mainly by efflux pumps mediated by tet(K) in S. aureus in northwestern Pakistan.