Molecular study of methicillin-resistant Staphylococcus aureus isolates at a neonatal high-risk unit in Merida, Venezuela.

BACKGROUND: Methicillin-resistant Staphylococcus aureus (MRSA) is a multiresistant microorganisms which holds first place in the world as a nosocomial pathogen. Special attention has therefore been directed to specific nosocomial surveillance systems and strict infection control measures for this microorganism in which the microbiological laboratory plays an important role by applying phenotypic and genotypic methods that permit establishing their epidemiological relationship especially in hospital outbreaks. In the present study the general objective was to study MRSA strains isolated from neonates with nosocomial infections and from healthcare personnel working in the Neonatal High Risk Unit (NHRU) of the Andes University Hospital Autonomous Institute (AUHAI) in Mérida, Venezuela. MATERIAL/METHODS: Forty-three S. aureus isolates were analyzed by phenotypic and genotypic methods. RESULTS: In these strains, antibiotypes resistant to oxacillin, gentamicin, erythromycin, and tobramycin predominated (50%). The greater percentage of MRSA strains isolated from health personnel as well as two neonates were described as pulse types Ia and Ib, belonging to phage group II, containing type IV SCCmecA and resistant to macrolides and aminoglycosides and sensitive to clindamycin and trimethoprim-sulfamethoxazole. CONCLUSIONS: This is the first reported case of SCCmecA type IV MRSA found in the NHRU of the AUHAI.

Caracterización fenotípica de cepas de Staphylococcus coagulasa negativa aisladas de una unidad de alto riesgo neonatal / Phenotypic characterization of coagulase-negative Staphylococcus strains isolated from a high risk neonatal unit

Las infecciones nosocomiales constituyen un problema de salud pública, debido a las altas tasas de morbimortalidad que ocasiona y por los altos costos económicos que generan. Las unidades de cuidados intensivos son una de las principales áreas donde se registra una alta incidencia de infección nosocomial, siendo la sepsis la principal infección en la cual se involucran una gran variedad de microorganismos. El grupo de Staphylococcus coagulasa negativa (SCN), es uno de los agentes etiológicos más frecuentemente aislados. De ahí nuestro interés en realizar la caracterización de 32 cepas de SCN aisladas de neonatos con infección nosocomial en la Unidad de Alto Riesgo Neonatal (UARN) del Instituto Autónomo Hospital Universitario de Los Andes (IAHULA), Mérida, Venezuela; durante el período diciembre 1997-Abril 1999. Los resultados muestran que el aislamiento de SCN fue de 47,37 por ciento. El 78,1 por ciento de las cepas estudiadas se aislaron de neonatos con bacteremia. Las especies más frecuentes fueron S. epidermidis (46,9 por ciento) y S. warneri (34,4 por ciento). Todas las cepas evaluadas mostraron resistencia a la penicilina y en un 18,8 por ciento de ellas mediada por la producción de B-lactamasa. El 68,8 por ciento de las cepas fueron resistentes a oxacilina y el 78,1 por ciento a gentamicina. La mayoría de las cepas resistentes a oxacilina mostraron valores de CIM g/mL, y se detectó la presencia de la PBP2a. Ninguna de las cepas fueron hiperproductoras de B-lactamasa. Se observó una excelente actividad de la vancomicina y quinupristin-dalfopristin sobre todas las cepas SCN evaluadas. Debido al papel que tienen los SCN en la UARN del IAHULA, es necesario extremar las medidas de asepsia durante los procedimientos de diagnóstico y terapéuticos invasivos, con el propósito de evitar las infecciones causadas por este grupo de microorganismos.

Nosocomial infections constitute a public health problem due to a high level of morbidity and mortality, generating high health-care costs in hospitals. Intensive care units are the principal areas where a high incidence of nosocomial infections is reported. Bacterimia is the principal infection involving a large variety of microorganisms; coagulase-negative Staphylococcus (CNS) is one of the most frequently isolated pathogens. Therefore, the purpose of this study was to characterize the 32 strains of CNS isolated from neonates with nosocomial infections in the High Risk Neonatal Unit (HRNU) at the University of the Andes Hospital Autonomous Institute (UAHAI), Mérida, Venezuela, from December 1997 to April 1999. Results showed that the isolation of CNS was 47.37 percent; 78.1 percent of the species were isolated from neonates with bacteremia. S. epidermidis (46.9 percent), and S. warneri (34.4 percent) were the species most frequently found. All pathogens showed resistance to penicillin and 18.8 percent of them produced ß-lactamase; 68.8 percent were resistant to oxacillin and 78.1 percent to gentamicin. Most of the oxacillin-resistant strains showed MIC values above 0.5 mg/mL and the presence of PBP2a was detected. None of the strains were hyper-producers of ß-lactamase. Vancomicin and quinuprintin/dalfopristin showed excellent activity against these CNS. Due to the role of CNS as a pathogen in the HRNU of UAHAI, strong asepsis measures during diagnosis and therapeutic invasive procedures must be taken to prevent infections caused by this group of microorganisms.