ABSTRACT
Three types of serotypically atypical Shigella flexneri strains were isolated from 2007 to 2008 in patients at the Korea National Institute of Health (NIH). These strains were characterized and compared with serologically typical S.flexneri. One type of strain either displayed nonreacting typing or grouping sera, reacting strongly only with polyB antisera, which indicates this strain is S. flexneri (polyB:un). The second type displayed reactions with one of the typing sera (IV) and did not bind any grouping sera (IV:un). The remaining type of strain displayed a plural agglutination pattern, reacted with one typing sera (II), and bound with two grouping sera (II:(3)4,7(8)). Among these atypical strains IV:un and II:(3)4,7(8) strains showed higher multi-antibiotic resistance in ampicillin, streptomycin, and trimethoprim-sulfamethoxazole than typical strains. Furthermore, all II:(3)4,7(8) strains harbored integrons. This study suggests that these multiple antibiotic-resistant atypical S. flexneri are new subserotypes of S.flexneri that await further serological classification.
Subject(s)
Dysentery, Bacillary/microbiology , Shigella flexneri/genetics , Shigella flexneri/isolation & purification , Anti-Bacterial Agents/pharmacology , Bacterial Proteins/genetics , Bacterial Proteins/metabolism , Drug Resistance, Bacterial , Humans , Integrons , Microbial Sensitivity Tests , Republic of Korea , Serotyping , Shigella flexneri/classification , Shigella flexneri/drug effectsABSTRACT
Cytolethal distending toxins (CDTs) represent an emerging family of newly described bacterial products that are produced by a number of pathogens. The genes encoding these toxins have been identified as a cluster of three adjacent genes, cdtA, cdtB, and cdtC, plus 5 cdt genetic variants, designated as cdt-I, cdt-II, cdt-III, cdt-IV, and cdt- V, have been identified to date. In this study, a general multiplex PCR system designed to detect Escherichia coli cdts was applied to investigate the presence of cdt genes among isolates. As a result, among 366 E. coli strains, 2.7% were found to carry the cdtB gene. In addition, the use of type-specific primers revealed the presence of cdt-I, cdtIV, and cdt-V types of the cdt gene, yet no cdt-II or cdt- III strains. The presence of other virulence genes (stx1, stx2, eae, bfp, espA, espB, and espD) was also investigated using a PCR assay. Among the 10 cdtB gene-positive strains, 8 were identified as CDT-producing typical enteropathogenic E. coli (EPEC) strains (eae(+), bfp(+)), whereas 2 were identified as CDT-producing atypical EPEC strains (eae(+), bfp(-)). When comparing the cytotoxic activity of the CDT-producing typical and atypical EPEC strains, the CDT-producing atypical EPEC strains appeared to be less toxic than the CDT-producing typical EPEC strains.
