An inexpensive and reliable method for routine identification of staphylococcal species

Abstract

The aim of this study was to develop a simple, reliable, and inexpensive in-house system for routine species identification of staphylococci in clinical practice. The system combines 15 key tests (including carbohydrate fermentation) performed in micro-well strips and antimicrobial disk diffusion susceptibility tests performed on standardised paper disk method antibiotic sensitivity medium agar. Twenty-eight staphylococcal reference strains belonging to 18 different species were correctly identified using this in-house system. A total of 291 clinical staphylococci isolates were evaluated with the in-house system and a conventional identification scheme. The in-house system identified 281 (96.6%) of these 291 isolates. Eleven different species were recognised. The five species most frequently identified were Staphylococcus epidermidis (48.6%), Staphylococcus aureus (27.8%), Staphylococcus haemolyticus (8.2%), Staphylococcus hominis (5.7%), and Staphylococcus warneri (5.3%). There was an agreement of 86.3% between the species identification obtained with the in-house system and the conventional identification scheme. All coagulase-negative isolates initially identified as species other than Staphylococcus epidermidis as well as indistinctly identified isolates were also evaluated with a commercial identification system. The agreement between species identification obtained with the in-house system and the commercial system for 101 identified isolates was 73%. Several isolates that were difficult to distinguish with the conventional scheme and/or the commercial system were identified with the aid of the antimicrobial susceptibility test included in the in-house system. The described test scheme should be of value for identification of clinically significant staphylococci species.

Coagulase-Negative Staphylococci: Comparison of Phenotypic and Genotypic Oxacillin Susceptibility Tests and Evaluation of the Agar Screening Test by Using Different Concentrations of Oxacillin

“…Only one strain from each patient was analyzed. Identification of the staphylococcal strains to the species level was carried out by Gram staining; the oxidation-fermentation test; detection of enzyme production (coagulase, catalase, phosphatase, ornithine, and urease); L-pyrrolidonyl-␤-naphthylamide hydrolysis; hemolytic properties on sheep blood agar; acid production from mannitol, mannose, and trehalose; and resistance to novobiocin, polymyxin B, and desferrioxamine (16,19). Isolates were kept frozen at Ϫ20°C in tryptic soy broth containing 20% glycerol (vol/vol).…”

Cefoxitin disc diffusion test for detection of meticillin-resistant staphylococci

“…These isolates were recovered from blood (11 S. aureus and 14 CoNS), peripheral intravenous devices (26 S. aureus and eight CoNS), skin swabs collected from the site of peripheral intravenous device insertion (20 S. aureus and nine CoNS) and anterior nasal fossa (40 S. aureus and 16 CoNS) referred to the Department of Microbiology from the Department of Pediatrics, Chhatrapati Sahuji Maharaj Medical University, India. Isolates were collected over a period of 1 year from January to December 2005 and identified to species level using standard methods (Kloos & Bannerman, 1999;Monsen et al, 1998).…”

Molecular Epidemiology of Staphylococcus saprophyticus Isolated from Women with Uncomplicated Community-Acquired Urinary Tract Infection

“…Significant or nonsignificant uropathogens were quantified (CFU/ml) as previously described (6,7). For the present study, all coagulase-negative staphylococcal isolates were reanalyzed according to a previously described species identification system (15). This reevaluation identified 76 isolates of S. saprophyticus and 10 isolates of other coagulase-negative staphylococcus species.…”

“…All S. saprophyticus isolates demonstrated a zone diameter breakpoint of Ͻ13 mm using a 5-g disk of novobiocin (ISA medium; Oxoid Ltd.) (15).…”