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.
