Abstract
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.Keywords: Staphylococcus aureus, Antimicrobial susceptibility, Antibiotic resistance, Tetracycline, Pakistan
Highlights
Tetracyclines are broad spectrum antibiotics used against a wide variety of bacterial infections, including both Gram-positive and Gram-negative
There were 60 (46.15%) isolates that were resistant to cefoxitin, i.e., were methicillin-resistant S. aureus (MRSA)
These MRSA strains were confirmed by polymerase chain reaction (PCR)
Summary
Tetracyclines are broad spectrum antibiotics used against a wide variety of bacterial infections, including both Gram-positive and Gram-negative. After their discovery in the 1940’s, tetracyclines have continuously been used in both humans and animals with no major adverse effects. There are 38 acquired tetracycline resistance genes that are known and all use one of three strategies to render the bacteria resistant [2]. These include (1) efflux proteins, (2) ribosomal protection proteins and (3) enzymatic inactivation of tetracycline
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