Evaluation of Phenotypic and Molecular Methods for Detection of Oxacillin Resistance in Members of the Staphylococcus sciuri Group

Abstract

In this paper we report on an experimental evaluation of phenotypic and molecular methods as means for the detection of oxacillin resistance in members of the Staphylococcus sciuri group. A total of 109 S. sciuri group member isolates (92 S. sciuri isolates, 9 S. lentus isolates, and 8 S. vitulinus isolates) were tested by the disk diffusion method, the agar dilution method, the oxacillin salt-agar screening method, slide latex agglutination for PBP 2a, and PCR assay for mecA as the reference method. The mecA gene was detected in 29 S. sciuri isolates, and the true-positive and true-negative results of the other tests were defined on the basis of the presence or the absence of the mecA gene. For the different methods evaluated, the sensitivities and specificities were as follows: for the disk diffusion test with a 1-g oxacillin disk, 100% and 55.9%, respectively; for the disk diffusion test with a 30-g cefoxitin disk, 93.5% and 100%, respectively; for the agar dilution method, 100% and 50%, respectively; for the oxacillin salt-agar screen test (with 6 g of oxacillin per ml and 4% NaCl) 100% and 100%, respectively; and for the slide latex agglutination test for PBP 2a, 100% and 100%, respectively. The disk diffusion test with various ␤-lactam antibiotics was performed to evaluate their use for the prediction of oxacillin resistance. The results indicate that meropenem, cefazolin, cefamandole, cefuroxime, cefotetan, cefoperazone, cefotaxime, ceftriaxone, moxalactam, cefaclor, and cefprozil may be used as surrogate markers of oxacillin resistance, although further studies of their use for the detection of oxacillin resistance are required.Staphylococcus sciuri, Staphylococcus lentus, and Staphylococcus vitulinus are novobiocin-resistant, oxidase-positive, coagulase-negative staphylococci (CoNS) which compose the Staphylococcus sciuri group. The rate of isolation of these bacteria from humans ranges from 0.042% from the urinary tract (31) to 0.087% from the female genital tract (32). They constitute between 0.79% and 4.3% of the total number of CoNS isolated from human clinical samples (12, 31). Although they are rarely isolated from humans, 21.4% of the S. sciuri group isolates were found to be clinically significant (29). These bacteria have been associated with serious human infections, such as endocarditis (14), peritonitis (37), septic shock (15), urinary tract infections (31), endophthalmitis (1), pelvic inflammatory disease (32), and, most frequently, wound infections (28, 30). The sources of S. sciuri group bacteria for humans are animals (13, 16, 33); food of animal origin (10, 24); and the environment, such as soil, sand, and water (16, 23), as well as the hospital environment (7).Oxacillin-resistant staphylococci are recognized as important nosocomial and, recently, community pathogens. The major mechanism of oxacillin resistance in staphylococci is mediated by the production of PBP 2a, which is encoded by the mecA gene (3). S. sciuri attracted special attention after it was suggested that the mecA gene o...

Detection of PBP2a (penicillin-binding protein 2a) and mecA gene in methicillin resistant staphylococci originated from animals

“…This finding was in agreement with other authors(Zhang et al, 2011).For S. haemolyticus oxacillin MIC value was 2 mg/mL and for S. vitulinus 0.5 mg/mL, so both strains were resistant to oxacillin by broth microdilution. Other authors(Stepanovi} et al, 2006) had similar results for S. vitulinus. Only one of 11 S. haemolyticus strains was mecA negative, which was similar to findings of other authors(Hussain et al, 2000) who classified staphylococci based on the presence of the mecA gene to four categories.…”

“…One of S. haemolyticus and S. vitulinus isolates were mecA negative (Table 1). There are many problems in the detection of methicillin resistance in CoNS (Stepanovi} et al, 2006). One of the problems is heterogeneous resistance (Chambers, 1988;Hussain et al, 2000;Ferreira et al, 2003) that is more present in CoNS strains than in MRSA strains (Yamazumi et al, 2001).…”

Comparison of Tests To Detect Oxacillin Resistance in Staphylococcus intermedius , Staphylococcus schleiferi , and Staphylococcus aureus Isolates from Canine Hosts

“…The mecA gene has been detected by PCR in isolates of S. intermedius, S. schleiferi, and S. aureus from canine hosts (11,15). Also, an S. sciuri-specific homolog of mecA, as well as a mecA sequence identical to that found in oxacillin-resistant S. aureus strains from human hosts, has been reported for S. sciuri isolates from humans and dogs (25). Recently, cefoxitin disk susceptibility testing was recommended as an equivalent or improved replacement for oxacillin susceptibility testing of S. aureus and most CNS from humans (26).…”

“…It was noted previously that several mecApositive strains of S. simulans were not detected by the cefoxitin disk diffusion test (26), nor were five mecA-positive S. epidermidis strains from a collection of 241 CNS isolates (6). In a study of 109 S. sciuri isolates, 27% of which were from animals, the cefoxitin disk diffusion test had 93.5% sensitivity and 100% specificity for detecting mecA-positive strains (25).…”

Origin and Molecular Evolution of the Determinant of Methicillin Resistance in Staphylococci

“…The group is composed of the following four species, which are resistant to novobiocin and catalase production and coagulase nonproduction: S. sciuri, S. vitulinus, Staphylococcus lentus, and Staphylococcus fleurettii (20,25,29,30). They are usually isolated from a variety of animals and food products of animal origin and not frequently isolated from humans (20,23,25,29,30).…”