Evaluation of the accuracy of various phenotypic tests to detect oxacillin resistance in coagulase-negative staphylococci

Abstract

In this study, we determined the accuracy of phenotypic tests (cefoxitin agar dilution, 30µ µ µ µ µg-cefoxitin and 1µ µ µ µ µg-oxacillin disks) to detect the oxacillin resistance/mecA gene among coagulase-negative staphylococci (CoNS) isolates. The presence of the mecA gene was detected by PCR technique (gold standard). A total of 176 CoNS isolates from blood of hospitalized patients were evaluated. Of these, 138 (78.4%) harbored the mecA gene. Using 30µ µ µ µ µg-cefoxitin and 1µ µ µ µ µg-oxacillin disks we obtained 100 and 98.3% accuracy, respectively. In addition, when cefoxitin was used as marker in an agar dilution method, the higher accuracy (99.4%) was established with 8µ µ µ µ µg cefoxitin per mL breakpoint. Thus, despite of the agar dilution method using cefoxitin as a marker not being standard for this detection, our results suggested that it is an excellent alternative to detect the oxacillin resistance/mecA gene among CoNS isolates.

Methods for Detection of Oxacillin Resistance among Coagulase-Negative Staphylococci Recovered from Patients with Bloodstream Infections at the University Hospital in Brazil

“…In the present study, oxacillin resistance was detected by PCR in 85 (82.5%) of the CoNS isolates studied. Similar results have been reported by Perez and d'Azevedo (2008), who reported a rate of 78.4% of oxacillin-resistant CoNS strains using amplification of the mecA gene as the gold standard.…”

Antimicrobial resistance profile of Staphylococcus aureus isolates obtained from skin and soft tissue infections of outpatients from a university hospital in Recife -PE, Brazil

“…8 As quality control, standard strains for MRSA and MSSA were used: S. aureus ATCC 29213 and S. aureus ATCC 33591, respectively. 12 …”

Bacteremias por Staphylococcus coagulase negativos oxacilina resistentes em um hospital escola na cidade de Santa Maria, Estado do Rio Grande do Sul

“…De acordo com dados americanos, os SCN são responsáveis por 20,2% das ICS 8 . Já no Brasil, este percentual varia entre 10% e 20%, sendo que 70% a 90% dos isolados apresentam resistência à oxacilina 9,10 . Esta resistência está relacionada à presença do gene cromossômico mecA, o qual codifica a produção de proteínas ligadoras de penicilina (PBP) alteradas, denominadas PBP2a ou PBP2', com baixa afinidade por antibióticos β-lactâmicos 4,11 .…”

“…Contudo, a emergência de cepas com resistência heterogênea MÉTODOS RESULTADOS dificulta a interpretação dos testes de difusão do disco na rotina laboratorial 9,13,14 De acordo com a sensibilidade a agentes antimicrobianos, efetuada pelo método de difusão do disco (Tabela 1), as cepas de SCN apresentaram resistência significativa a várias classes de antimicrobianos. As maiores sensibilidades obtidas foram frente aos antimicrobianos rifampicina (43 de 60/72%) e tigeciclina (60 de 60/100%).…”

“…1,9,[20][21][22][23] . Do ponto de vista epidemiológico, o S. epidermidis tem desenvolvido estratégias interessantes para conquistar o ambiente hospitalar e se transformar em um patógeno notório.…”