Epidemiological characterization of resistance and PCR typing of Shigella flexneri and Shigella sonnei strains isolated from bacillary dysentery cases in Southeast Brazil

Shigella spp are Gram-negative, anaerobic facultative, non-motile, and non-sporulated bacilli of the Enterobacteriaceae family responsible for "Shigellosis" or bacillary dysentery, an important cause of worldwide morbidity and mortality. However, despite this, there are very few epidemiological studies about this bacterium in Brazil. We studied the antibiotic resistance profiles and the clonal structure of 60 Shigella strains (30 S. flexneri and 30 S. sonnei) isolated from shigellosis cases in different cities within the metropolitan area of Campinas, State of São Paulo, Brazil. We used the following well-characterized molecular techniques: enterobacterial repetitive intergenic consensus, repetitive extragenic palindromic, and double-repetitive element-polymerase chain reaction to characterize the bacteria. Also, the antibiotic resistance of the strains was determined by the diffusion disk method. Many strains of S. flexneri and S. sonnei were found to be multi-resistant. S. flexneri strains were resistant to ampicillin in 83.3 percent of cases, chloramphenicol in 70.0 percent, streptomycin in 86.7 percent, sulfamethoxazole in 80.0 percent, and tetracycline in 80.0 percent, while a smaller number of strains were resistant to cephalothin (3.3 percent) and sulfazotrim (10.0 percent). S. sonnei strains were mainly resistant to sulfamethoxazole (100.0 percent) and tetracycline (96.7 percent) and, to a lesser extent, to ampicillin (6.7 percent) and streptomycin (26.7 percent). Polymerase chain reaction-based typing supported the existence of specific clones responsible for the shigellosis cases in the different cities and there was evidence of transmission between cities. This clonal structure would probably be the result of selection for virulence and resistance phenotypes. These data indicate that the human sanitary conditions of the cities investigated should be improved.

Integrones y cassettes genéticos de resistencia a antimicrobianos en cepas de Shigella flexneri / Integrons and antimicrobial resistance gene cassettes in Shigella flexneri strains

BACKGROUND: The resistance of Shigella flexneri to antimicrobial agents can be associated to the presence of integrons that may contain and express antimicrobial resistance gene cassettes. AIM: To study antimicrobial resistance and the presence of integrons and antimicrobial gene cassettes in Shigella flexneri strains. MATERIAL AND METHODS: In vitro susceptibility to 27 antimicrobials was studied in twenty four Shigella flexneri strains isolated from stools. The presence of integrons class 1, 2 and 3 and antimicrobial resistance gene cassettes was investigated by polymerase chain reaction (PCR) using specific primers for each gene. RESULTS: Most strains were resistant to one of the following antimicrobials: ampicillin, sulphonamide, trimethoprim, tetracycline, streptomycin, sulfamethoxazole-trimethoprim or chloramphenicol. Twenty nine percent were simultaneously resistant to all these antimicrobials. Integrons class 1 and 2 were found in 19 strains (79 per cent). Class 3 integrons were not found. Gene cassettes dfrA1 and ant(3")I were associated to integrons class 2 in most strains (15/20, 75 per cent). Genes cat, tetB and blarTEM were detected in 18/24 (75 per cent), 7/24 (29 per cent) and 4/24 (17 per cent) of the strains, respectively and were not associated to any of the studied integrons. Genes that codify enzymes AAC(6')Ib and APH(3')VI were not detected in any strain. CONCLUSIONS: The high frequency of integrons found in the studied strains, could partly explain the increasing antimicrobial resistance of Shigella flexneri strains, isolated in Chile.