Abstract
Following a surge in the prevalence of chloramphenicol-resistant methicillin-resistant Staphylococcus aureus (MRSA) in Kuwait hospitals, this study investigated the genotypes and antibiotic resistance of the chloramphenicol-resistant isolates to ascertain whether they represented new or a resurgence of sporadic endemic clones. Fifty-four chloramphenicol-resistant MRSA isolates obtained in 2014–2015 were investigated. Antibiotic resistance was tested by disk diffusion and MIC determination. Molecular typing was performed using spa typing, multilocus sequence typing, and DNA microarray. Curing and transfer experiments were used to determine the genetic location of resistance determinants. All 54 isolates were resistant to chloramphenicol (MIC: 32–56 mg/L) but susceptible to florfenicol. Two chloramphenicol-resistance determinants, florfenicol exporter (fexA) and chloramphenicol acetyl transferase (cat), were detected. The fexA-positive isolates belonged to CC5-ST627-VI-t688/t450/t954 (n = 45), CC5-ST5-V-t688 (n = 6), whereas the cat-positives isolates were CC8-ST239-III-t037/t860 (n = 3). While cat was carried on 3.5–4.4 kb plasmids, the location of fexA could not be established. DNA sequencing of fexA revealed 100% sequence similarity to a previously reported fexA variant that confers chloramphenicol but not florfenicol resistance. The resurgence of chloramphenicol resistance was due to the introduction and spread of closely related fexA-positive CC5-ST5-V and CC5-ST627-VI clones.
Highlights
Chloramphenicol is a broad-spectrum antibiotic that was derived from Streptomyces venezuelae initially [1,2,3] but has been produced synthetically [3,4]
The epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) in Kuwait hospitals has changed substantially since the 1990s with the ST239-MRSA-III clone that was dominant in the 1990s gradually replaced by diverse CA-MRSA clones starting in the early 2000s [13,21,22]
Molecular typing revealed that most of the chloramphenicol-resistant isolates belonged to CC5-ST627-VI-t688/t450/t954 (45/54) or CC5-ST5-V-t688 (6/54), while a small number (3/54) belonged to ST239-III/t037/t860
Summary
Chloramphenicol is a broad-spectrum antibiotic that was derived from Streptomyces venezuelae initially [1,2,3] but has been produced synthetically [3,4]. Chloramphenicol was introduced into clinical practice in 1940s for the treatment of infections caused by Gram-positive and Gram-negative organisms such as Staphylococcus aureus, Streptococcus pneumoniae, Salmonella Typhi, Haemophilus influenzae, Escherichia coli, and Neisseria meningitides [1,5]. Chloramphenicol diffuses through the bacterial cell wall and binds to the bacterial 50S ribosomal subunit. Whereas chloramphenicol and some derivatives such as thiamphenicol have been used in human medicine over the years for treating bacterial infections due to its effectiveness, low cost, and broad spectrum of activity, florfenicol, a fluorinated derivative of chloramphenicol, is licensed for veterinary use and is used exclusively in veterinary medicine [4,5,8]
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