Identification of Staphylococcus aureus: DNase and Mannitol salt agar improve the efficiency of the tube coagulase test

Abstract

BackgroundThe ideal identification of Staphylococcus aureus clinical isolates requires a battery of tests and this is costly in resource limited settings. In many developing countries, the tube coagulase test is usually confirmatory for S. aureus and is routinely done using either human or sheep plasma. This study evaluated Mannitol salt agar and the deoxyribonuclease (DNase) test for improving the efficiency of the tube coagulase test in resource limited settings. The efficiency of human and sheep plasma with tube coagulase tests was also evaluated.MethodsOne hundred and eighty Gram positive, Catalase positive cocci occurring in pairs, short chains or clusters were subjected to growth on Mannitol salt agar, deoxyribonuclease and tube coagulase tests. Of these, isolates that were positive for at least two of the three tests (n = 60) were used to evaluate the performance of the tube coagulase test for identification of S. aureus, using PCR-amplification of the nuc gene as a gold standard.ResultsHuman plasma was more sensitive than sheep plasma for the tube coagulase test (sensitivity of 91% vs. 81% respectively), but both plasmas had very low specificity (11% and 7% respectively). The sensitivity and specificity of the tube coagulase test (human plasma) was markedly improved when Mannitol salt agar and DNase were introduced as a tri-combination test for routine identification of Staphylococcus aureus (100% specificity and 75% sensitivity). The specificity and sensitivity of Mannitol salt agar/DNase/tube coagulase (sheep plasma) combination was 100% and 67%, respectively.ConclusionThe efficiency of the tube coagulase test can be markedly improved by sequel testing of the isolates with Mannitol salt agar, DNase and Tube coagulase. There is no single phenotypic test (including tube coagulase) that can guarantee reliable results in the identification of Staphylococcus aureus.

Antibiotic Resistance Pattern of Methicillin Resistant and Methicillin Sensitive Staphylococcus aureus Isolates in Tehran, Iran

“…All of the isolates were confirmed as Staphylococcus genus by different biochemical tests such as Gram staining, catalase and oxidase (17). Catalase, Gram positive and oxidase negative isolates were defined as Staphylococcus.…”

“…Catalase, Gram positive and oxidase negative isolates were defined as Staphylococcus. Isolates indicating Staphylococcus characteristics were further analyzed by fermentation in manitol salt agar medium, DNase and coagulase tests (17). All S. aureus were DNase and coagulase positive and fermented manitol.…”

Prophage Typing of Methicillin Resistant Staphylococcus aureus Isolated from a Tertiary Care Hospital in Tehran, Iran

“…Identification of the clinical isolates of S. aureus was performed by traditional biochemical tests, including catalase, DNase, coagulase and mannitol fermentation tests, and Gram staining (12,13). S. aureus ATCC 29213 and S. epidermidis ATCC 35984 were used as negative and positive controls.…”

Atualização sobre tratamento medicamentoso de infecções causadas por Staphylococcus aureuse resistência a drogas antiestafilocócicas

“…São capazes de produzir peróxido de hidrogênio na presença de oxigênio, sendo caracterizadas como catalase positivas (Santos, Santos et al 2007; Kateete, Kimani et al 2010). Este gênero possui 33 espécies, porém somente 17 podem ser isoladas de material biológico humano (Santos, Santos et al 2007).…”