Species identification, slime production and oxacillin susceptibility in coagulase-negative staphylococci isolated from nosocomial specimens

Abstract

Ninety-two coagulase negative staphylococci (CNS) (forty-five of clinical origin and forty-seven of environmental origin), collected in a hospital in San Luis, Argentina, from March to June, 1999, were identified to species level by the ID 32 Staph and API Staph System (bioMérieux). Slime production was investigated by the quantitative and qualitative methods. Oxacillin susceptibility was determined by the disk diffusion test (1 µg), the agar dilution method (0.125 to 4 mg/ml) and agar screen (6 µg/ml). The presence of mecA gene was investigated by PCR. The clinical CNS species most commonly isolated were S. epidermidis, S. haemolyticus, S. hominis and S. saprophyticus. The frequency of slime production by clinical and environmental isolates was similar (25/45 and 27/47, respectively) and the results obtained by the quantitative and the qualitative methods correlated well. The mecA gene was detected in all S. epidermidis, S. haemolyticus and S. hominis isolates, which were resistant to oxacillin by the phenotypic methods. However, this gene was not present in S. klossii, S. equorum, S. xylosus and S. capitis strains. The gene was neither found in two out of the six S. saprophyticus isolates, in two out of three S. cohnii subsp. urealyticum isolates and in two out of five S. cohnii subsp. cohnii isolates, all of which resulted oxacillin resistant according to MIC. The gene was not found in oxacillin-susceptible strains either. Most of the CNS isolates (enviromental and clinical) that were slime producers were found to be oxacillin resistant, which makes the early detection of these microorganisms necessary to prevent their dissemination in hospitals, particularly among immunocompromised patients.

Comparison of methods for the detection of biofilm production in coagulase-negative staphylococci

“…Other CNS species were also identified, including S. cohnii, S. saprophyticus, S. warneri, S. haemolyticus, S. xylosus, S. capitis, and S. lugdunensis. Similar results have been reported in other studies [35,36]. The finding of S. epidermidis as the most frequently isolated species in most studies might be due to the fact that this microorganism possesses certain mechanisms that favor its adaptation to some sites, with this species being the most prevalent bacterium in human skin and mucosa [37].…”

Comparison of methods for the detection of biofilm production in coagulase-negative staphylococci

“…Similar biofilm production by CNS strains isolated from different sources, including clinical specimens, environment and microbiota of healthy individuals, has also been reported by other investigators [35,38]. …”

Detection of methicillin resistance and slime factor production of Staphylococcus aureus in bovine mastitis

“…It is reported that slime factor production in S. aureus isolates from mastitis cause antibiotic resistance which is due to the decreased diffusion of antibiotics through the biofilm matrix and decreased metabolic activity of bacteria (4,36). Several phenotypic methods such as standard tube method, Christensen’s method, Congo Red Agar and microdilution methods are used to detect slime production (2). In the present study, slime producing S. aureus isolates were detected on Congo Red Agar (CRA) plates in vitro.…”