ABSTRACT
Aims: Novel methicillin-resistant Staphylococcus aureus have been causing infections in the community and are now invading hospitals. In this study we aimed to determine, using epidemiological and microbiological parameters, the characteristics of circulating S. aureus clinical isolates. Methods: From July 2009 to April 2012, S. aureus isolates from children hospitalized in Santa Casa de São Paulo, a tertiary care-center in São Paulo, Brazil, were included. All isolates grew in cultures from sterile sites and we included only one isolate per patient. Results: Fifty-five isolates were included during the study period, 47 from blood, six from abscesses, one from pleural fluid and one from spinal fluid. Among these isolates, 34 were methicillin susceptible S. aureus (MSSA) and 21 were methicillin-resistant S. aureus (MRSA). Eleven patients were excluded (5 MSSA and 6 MRSA) because clinical charts were not available for review, reducing the total to 29 MSSA and 15 MRSA isolates. After searching for risk factor for healthcare-associated infections, 11 of the 15 MRSA isolates were epidemiologically considered health care-associated MRSA (HCA-MRSA) and 4 community-associated MRSA (CA-MRSA). Using the microbiological classification (multiresistance), five were considered as HCA-MRSA and 10 were CA-MRSA. Interestingly, of the 11 isolates considered as epidemiological HCA-MRSA (presence of any risk factor), six had a microbiological profile (non-multiresistant) consistent with CAMRSA circulating clones. Conclusion: Our results clearly show that the boundaries between CA-MRSA and HCAare increasingly difficult to determine.
ABSTRACT
Methicillin-resistant Staphylococcus aureus (MRSA) are now a worldwide problem. Cystic fibrosis (CF) patients are commonly colonized and infected by MRSA. Accurate oxacillin susceptibility testing is mandatory for the adequate management of these patients. We performed a comparison of the accuracy of different tests in CF isolates, including methicillin-susceptible S. aureus and MRSA with different SCCmec types, and using the mecA gene as the gold-standard. The sensitivity and specificity of oxacillin disc, Etest, and oxacillin agar screening plate were 100%. Sensitivity of the cefoxitin disc was 85% and specificity was 100%. For clinically relevant isolates, laboratories may consider the use of a combination of two phenotypic methods.
Staphylococcus aureus resistentes à oxacilina (MRSA) são, atualmente, um problema global. Pacientes com fibrose cística (FC) são frequentemente colonizados e infectados por MRSA. A realização de testes de susceptibilidade acurados é extremamente importante para o manejo da terapia antimicrobiana nesses indivíduos. Nesse estudo, realizamos comparação entre as acurácias de diversos testes de susceptibilidade à oxacilina, em cepas de S. aureus isoladas de pacientes com fibrose cística, tanto sensíveis como resistentes à oxacilina, com diferentes tipos de SCCmec, e utilizando a detecção do gene mecA como método padrão. A sensibilidade e a especificidade do disco de oxacilina, do Etest, e da placa de agar screening com oxacilina foram de 100%. A sensibilidade do disco de cefoxitina foi 85%, com especificidade de 100%. Em cepas clinicamente relevantes, a utilização combinada de mais de um método deveria ser considerada.
Subject(s)
Humans , Anti-Bacterial Agents/pharmacology , Bacterial Proteins/genetics , Cystic Fibrosis/microbiology , Oxacillin/pharmacology , Staphylococcal Infections/microbiology , Staphylococcus aureus/drug effects , Culture Media/chemistry , Methicillin-Resistant Staphylococcus aureus/drug effects , Methicillin-Resistant Staphylococcus aureus/genetics , Microbial Sensitivity Tests/methods , Phenotype , Reproducibility of Results , Sensitivity and Specificity , Staphylococcus aureus/classificationABSTRACT
Apesar das diversas recomendações disponíveis na literatura sobre o diagnóstico laboratorial da resistência à oxacilina em Staphylococcus aureus, a verdade é que ainda não existe consenso absoluto sobre qual ou quais métodos utilizar e quando utilizar cada um deles. Segundo a literatura, a maioria dos métodos disponíveis apresenta um índice não desprezível de erros diagnósticos. Em casos de isolados de processos infecciosos invasivos, ou de infecções persistentes e/ou refratárias aos antimicrobianos, o uso de um método adicional ou confirmatório pode ser importante. Além disso, a contínua reavaliação desses testes é necessária.
Despite guidelines published in the literature, the optimal routine phenotypic method for detecting methicillin resistance in Staphylococcus aureus remains controversial. Most available methods have a considerable rate of errors, according to the literature. When testing invasive isolates or isolates from persistent/refractory infections, using an additional or confirmatory method could be important. In addition, the continual evaluation of these tests is necessary.