UNSPECIFIED. (2000) Expression of resistance to tetracyclines in strains of methicillin-resistant Staphylococcus aureus. JOURNAL OF ANTIMICROBIAL CHEMOTHERAPY, 45 (6). pp. 763-770. ISSN 0305-7453

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Abstract

A diverse collection of methicillin-resistant Staphylococcus aureus (MRSA) isolates resistant to tetracycline was screened by PCR for the presence of the resistance determinants tetK, tetL, tetM or tetO. Twenty-four of 66 isolates had tetM alone, 21 had tetK alone and 21 had both tetK and tetM (tetKM). All isolates were tetL- and tetO-negative. MICs of tetracycline, doxycycline and minocycline were evaluated for all isolates with or without preincubation in the presence of subinhibitory concentrations of tetracycline or minocycline. All isolates with one or more tetracycline resistance determinants were resistant to tetracycline 8 mg/L without induction of resistance. Some MRSA isolates of each of these three genotypes showed an unexpected lack of resistance to tetracyclines when the disc diffusion or agar dilution method was applied to uninduced cells. Resistance to tetracycline and doxycycline was greater (two- to four-fold) in tetK cells preincubated with tetracycline (tetK MRSA isolates were susceptible to minocycline less than or equal to 0.25 mg/L under all conditions tested). For isolates with tetM alone, preincubation with tetracycline or minocycline gave up to a four-fold increase in the level of resistance to doxycycline and minocycline. Induction of doxycycline and minocycline resistance was clearly observed for tetKM Isolates when cells were preincubated with minocycline. This study suggests that, despite the results of susceptibility testing, all tetracycline-resistant S. aureus isolates should be treated as resistant to doxycycline, and all tetM-positive isolates should be treated as resistant to all tetracyclines. A double disc diffusion method has been developed to identify inducible resistance to minocycline and to distinguish between tetK, tetM and tetKM isolates.

Item Type:	Journal Article
Subjects:	Q Science > QR Microbiology > QR355 Virology Q Science > QR Microbiology R Medicine > RS Pharmacy and materia medica
Journal or Publication Title:	JOURNAL OF ANTIMICROBIAL CHEMOTHERAPY
Publisher:	OXFORD UNIV PRESS
ISSN:	0305-7453
Date:	June 2000
Volume:	45
Number:	6
Number of Pages:	8
Page Range:	pp. 763-770
Publication Status:	Published
URI:	http://wrap.warwick.ac.uk/id/eprint/13240

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