First human isolates of methicillin-resistant Staphylococcus aureus sequence type 398 in Spain

Abstract

To the Editor, An emerging sequence type (ST) 398 methicillin-resistant Staphylococcus aureus (MRSA) clone producing infections in humans has been detected across Europe [1]. Recent studies indicate that it is widely distributed in farm animals, particularly in pigs, suggesting transmission between animals and humans [2]. The frequency of MRSA ST398 in the Spanish population is unknown. In this study, we present the first three human cases of MRSA ST398 infections admitted to two hospitals in the north-west of Spain. Forty-four MRSA strains were isolated in 2006 in both hospitals. They were studied by the analysis of restriction fragment length polymorphism (RFLP) of the coagulase gene patterns and pulsed-field gel electrophoresis (PFGE) [3, 4]. Three non-Sma I typeable MRSA strains were identified; the three strains were EagI PFGE typeable. Next, they were analyzed by multilocus sequence typing (MLST) and spa typing [5, 6]. The staphylococcal chromosome cassette (SCC) mec, the accessory gene regulator (agr) types, and the Panton–Valentine leukocidin (PVL)-encoding genes were polymerase chain reaction (PCR)-identified [7–9]. The three strains were resistant to tetracycline. Besides, one isolate was resistant to levofloxacin, tobramycin, and erythromycin, and another isolate was resistant to levofloxacin and clindamycin, and susceptible to erythromycin; this rare phenotype has already been described [2]. The three MRSA isolates were identical by RFLP. By EagI PFGE, they were closely related following Tenover’s criteria (Fig. 1) [10]. All isolates were ST398, SCCmec-V, agr-1, and PVL genes-negative. They belonged to three spa types; t108, t011, and t1255. The age of the three patients was 59, 82, and 83 years, respectively. Two patients owned pigs and the other a calf. Two patients were diabetic and were hospitalized because they developed skin and soft-tissue infections by MRSA ST398. The third patient had bronchitis and the strain was isolated from a respiratory secretion submitted to the laboratory from an outpatient clinic. The three patients had had multiple hospital admissions in the last 12 months. As it has been described previously, the ST398 isolates were resistant to tetracycline [2]. Only another strain from the 44 MRSA strains studied was also resistant to tetracycline. This one belonged to the ST239 clone that was epidemic in north-west Spain until 2002, and since then, it has scarcely been isolated [3]. The ST239 clone is easily identified because of the homogeneity in the resistance profile (it is also resistant to levofloxacin, gentamicin, tobramycin, erythromycin, clindamycin, trimethoprim-sulfamethoxazole, and chloramphenicol) [3]. Therefore, it can be stated that the resistance to tetracycline could be a local marker for a presumptive identification of the ST398 clone. C. Potel (*) : S. Perez Microbiology Laboratory, Complejo Hospitalario Universitario de Vigo, Pontevedra, Spain e-mail: carmen.potel.alvarellos@sergas.es