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.

DNA sequencing of a pathogenicity-related plasmid of an avian septicemic Escherichia coli strain

A 43-MDa conjugative plasmid isolated from an avian septicemic Escherichia coli (APEC) strain possessing genes related to the adhesion and invasion capacities of in vitro-cultured cells was sequenced. The results demonstrated that the 43-MDa plasmid harbors bacterial pathogenicity-related sequences which probably allow the wild-type pathogenic strain to adhere to and invade tissues and to cause septicemia in poultry. The existence of homology sequences to sequences belonging to other human pathogenic Enterobacteriaceae like Escherichia coli O157:H7, Shigella and Salmonella was also observed. The presence of these sequences in this plasmid could indicate that there is horizontal genetic transfer between bacterial strains isolated from different host species. In conclusion, the present study suggests that APEC strains harbor high-molecular weight plasmids that present pathogenicity-related sequences and that these are probably responsible for the pathogenicity exhibited by these strains. The presence of human pathogenicity-associated sequences in APEC conjugative plasmids suggests that these strains could represent a zoonotic risk.