Api staph strip

One colony was re-suspended in 5 mL 0.9% saline and 100 µL was dispensed in each well of an API® Staph strip (bioMérieux SA, Marcy l’Etoile, France), containing 20 miniature biochemical tests and lysostaphin resistance test, and incubated overnight at 37 °C. After addition of the reagents, the strips were read for their specific colour pattern, generating an identification numerical profile. The APIweb™ software (bioMérieux SA) was used to obtain the organism identification that corresponded to the biochemical or numerical profile of the strip.

The staphylococcal reference strains used were: Staphylococcus aureus ATCC 29213, Staphylococcus aureus ATCC 25923, Staphylococcus aureus ATCC 6538, and Staphylococcus epidermidis RP62A, known for its ability to form a biofilm (Schumacher-Perdreau et al. [1994 (link)]). Four staphylococcal isolates from the Istituto Zooprofilattico Sperimentale, Sicily (IZS) bacterial collection including strain 657 isolated from a milk sample from an individual sheep affected by mastitis, strain 688 and 700 and strain 702 isolated from bulk milk samples from different sheep flocks. The isolates were selected on blood agar plates and on Mannitol Salt Agar (Difco, Sparks, MD). The colonies were typed by API Staph strip (bio-Mérieux) and tube coagulase test was performed (Canicatti and Roch [1989 (link)]).
Pseudomonas aeruginosa ATCC 15442, the reference strain in official tests for antibacterial evaluation in vitro (UNI EN European Standard), was also used in this study.

All 126 S. aureus isolates used in this study were recovered from milk samples taken from cows presenting clinical mastitis between February 2010 and February 2011 from 26 farms in Ireland. Sample collection and bacterial isolation methods have been described previously [15 (link)]. Staphylococci were identified based on colony morphology, Gram stain, haemolysis, catalase test and growth on Baird Parker and Mannitol Salt agar plates. Putative S. aureus were distinguished from coagulase negative Staphylococci by the above tests as well as the coagulase test and the API Staph strip (BioMerieux). Isolates were routinely grown in Trypticase Soy broth (TSB) or on Trypticase Soy agar for further study.