Frecuencia de Aparición de Estafilococos Resistentes a Meticilina, Conclusiones

1. Nuestros resultados reflejan la prevalencia de 27% de cepas de Staphylococcus sp. resistentes a meticilina, para las cuales predomina en 77%, el fenotipo de resistencia heterogéneo con la presencia del gen mecA, mientras que 23% posee otros mecanismos de resistencia que necesitan ser detectados por la determinación de la concentración mínima inhibitoria (MIC).

2. Se demostró la existencia en estas cepas de resistencia cruzada a otras familias de antibióticos, así como la presencia en todas de penicinilasas.

3. Del total de cepas ensayadas, 93% es resistente a penicilinas y 17 % presenta un fenotipo inducible de resistencia a antibióticos macrólidos.

4. Los resultados de resistencia encontrados son el reflejo de las ventajas obtenidas de la aplicación de una política de uso racional de antibióticos, lo que implica un control directo sobre la resistencia, una protección a los antibióticos como recursos naturales y por consiguiente una mejora en la calidad de vida del paciente. Sin embargo, debemos mantener una vigilancia sistemática en nuestros hospitales para prevenir un aumento de resistencia y la aparición de brotes fatales.

5. Aunque la investigación de los mecanismos moleculares de la resistencia a la meticilina ha avanzado, aún no hemos llegado al nivel de conocimiento necesario para controlar este fenómeno. Se espera que la total comprensión de los mecanismos de resistencia del MRSA se logre tomando en consideración la diversidad genética de la especie S. aureus. Desde este punto de vista, los estudios futuros deben incluir la identificación epidemiológica de esas cepas que son analizadas.

6. La vigilancia a nivel mundial de la resistencia a los antibióticos ayudará a identificar los factores que llevan a la emergencia y a la diseminación de dichos aislados y por tanto, permitirá descubrir nuevos genes o factores que conducirán a la mejor comprensión de este fenómeno y su control.

Summary

In this study we evaluated 425 nosocomial strains of Staphylococcus sp. which were obtained from seven hospitals in Habana (Cuba), following the reference methods suggested in the guidelines of NCCLS. The mechanism of resistance in all resistant strains was determined and also the presence of the mecA gen, using the polymerase chain reaction (PCR). A correlation was established between the mechanism of resistance, disc diffusion methods and MIC’s. Of all 425 strains, 273 (68%) were S. aureus and133 (32%) Staphylococcus coagulase negative. In general, 27% of all strains were methicillin-resistant by the disc-diffusion method, 25% grew in the presence of oxacillin and only 21% were carriers of the mecA gen. 22% of the S. aureus isolates were resistant to oxacillin by the disc-diffusion method, whereas 20% grew in the Müller-Hinton-oxacillin plates and demonstrated the presence of the mecA gen, showing that 98% of methicillin resistance was due to production of PBP2A. In the case of coagulase-negative Staphylococcus, only 24% of the oxacillin-resistant isolates were conditioned by the presence of mecA; other mechanisms, mainly beta-lactamase production, was involved in the rest of the strains.

All methicillin-resistant strains were resistant to penicillins and also showed high degree of cross resistance with erithromycin (60-68%), trimethoprim-sulfa (72-84%), tetracycline (55-50%), cloramphenicol (53-51%) and gentamicin (48-50%) for S. aureus and coagulase negative Staphylococcus respectively.

These results establish for the first time information about the current state of resistance among Staphylococcus sp. in Habana. It also alerts the Minister of Public Health about the potential of rapid dissemination of these strains to other areas of the city and their ability for developing vancomycin intermediate or resistant strains.

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