<a name="top1"></a>Resistencia a antibióticos y epidemiología molecular de Shigella spp. en el nordeste argentino Antibiotic resistance and molecular epidemiology of Shigella spp. in northeastern Argentina

OBJETIVOS: Evaluar la resistencia a antibióticos de cepas de Shigella spp. aisladas de muestras de heces en el nordeste argentino y caracterizarlas desde el punto de vista de su epidemiología molecular. MÉTODOS: Se estudiaron 132 aislamientos de Shigella spp. obtenidos de las heces de igual número de pacientes con diarrea que asistieron a diferentes laboratorios privados y estatales de las provincias del Chaco y Corrientes, Argentina, durante el período de 1998 a 2002. Cada cepa se caracterizó según su serotipo, su resistencia a 13 antibióticos individuales o combinados y su sensibilidad a las piocinas. A 52 cepas seleccionadas en función de sus perfiles de susceptibilidad antimicrobiana se les determinaron la dotación plasmídica mediante lisis alcalina y las secuencias repetitivas palindrómicas extragénicas mediante la amplificación de segmentos repetitivos de ADN con la reacción en cadena de la polimerasa (REP-RCP). Se aplicó la prueba de ji al cuadrado para comparar proporciones. El nivel de significación estadística fue de 0,05. RESULTADOS: Shigella flexneri fue la especie más frecuente (78%), seguida de S. sonnei (22%). En general, la resistencia de S. flexneri a los antibióticos estudiados fue mayor que la de S. sonnei y esta diferencia fue estadísticamente significativa (P OBJECTIVES: To evaluate the antibiotic resistance of strains of Shigella spp. isolated from feces samples from northeastern Argentina and to characterize the strains in terms of their molecular epidemiology. METHODS: We studied 132 isolates of Shigella spp. obtained from feces samples from 132 patients with diarrhea who were seen at various private and public laboratories in the Argentine provinces of Chaco and Corrientes during the period of 1998 to 2002. Each strain was characterized according to its serotype, its resistance to 13 individual or combination antibiotics, and its sensitivity to pyocins. With 52 strains selected in relation to their antimicrobial susceptibility profiles we conducted plasmid profile analysis using alkaline lysis, and the repetitive extragenic palindromic sequences were determined by amplifying repetitive DNA segments using polymerase chain reaction. The chi-square test was used to compare proportions, with a level of statistical significance of 0.05. RESULTS: Shigella flexneri was the most common species (78%), followed by S. sonnei (22%). In general, the resistance of S. flexneri to the antibiotics studied was greater than that of S. sonnei, and this difference was statistically significant (P < 0.001) for ampicillin, tetracycline, chloramphenicol, and the combination of ampicillin and sulbactam. The S. flexneri strains also showed multiple resistance more often than S. sonnei strains (84.5% vs. 31.0%; P < 0.001). The strains isolated from S. flexneri were grouped into five pyocin types, three plasmid profiles, and five patterns of repetitive palindromic sequences. The strains of S. sonnei formed three pyocin types, two plasmid profiles, and three patterns of repetitive palindromic sequences. CONCLUSIONS: Given that the Shigella species that were studied showed a high level of resistance to the most frequently used antibiotics, surveillance activities should be implemented in order to detect and control the appearance of new resistant strains. Applying epidemiological typing techniques can provide more precise information about the distribution and evolution of resistant strains of circulating microorganisms