Environmental isolates of Citrobacter braakii that agglutinate with Escherichia coli O157 antiserum but do not possess the genes responsible for the biosynthesis of O157 somatic antigen

While searching for Escherichia coli O157 in the aquatic environment of Calcutta using an immunodetection procedure, we fortuitously detected five strains of Citrobacter braakii, which cross-reacted with the commercially available O157 polyvalent antiserum. The five C. braakii isolates gave positive results when a sensitive dot-ELISA was performed with E. coli O157 monoclonal antibody. Further, the O157 monoclonal antibody recognized the bands of proteinase K treated whole cells of lipopolysaccharide of all the C. braakii isolates. Apart from weak reactions with two or three of the DNA probes, all the C. braakii strains did not hybridize with the other probes spanning the minimum region required for O157 O-antigen biosynthesis. These strains did not possess any of the virulence genes that are commonly found in the Shiga toxin-producing E. coli (STEC) specially the serotype O157: H7. Therefore, it appears that the serological cross-reaction between C. braakii and E. coli O157 antiserum is based on structural mimicry between the O-polysaccharide of C. braakii and E. coli O157.     

大肠杆菌O157:H7的分离鉴定及应用复合PCR法同时检测其三个毒力因子

[目的]对驻滇部队感染性腹泻患者、猪和污水进行大肠杆菌O157：H7(E O157：H7)的分离鉴定。[方法]用O157免疫磁珠富集后，接种S-MAC琼脂平板培养，用MUG试验初筛，VlATEK32全自动微生物鉴定仪鉴定，应用复合PCR法同时检测其三个毒力因子。[结果]从腹泻患者和猪中检出E coli O157：H7，该菌具有三个毒办因子。[结论]云南战区部队存在E coli O157：H7感染。复合PCR法的建立，为腹泻研究领域的病原学监测和流行病学调查提供了新手段。     

Detection of Shiga toxin-producing Escherichia coli O26, O45, O103, O111, O113, O121, O145, and O157 serogroups by multiplex polymerase chain reaction of the wzx gene of the O-antigen gene cluster

O-antigens on the surface of Escherichia coli are important virulence factors that are targets of both the innate and adaptive immune system and play a major role in pathogenicity. O-antigens that are responsible for antigenic specificity of the strain determine the O-serogroup. E. coli O26, O45, O103, O111, O113, O121, O145, and O157 have been the most commonly identified O-serogroups associated with Shiga toxin-producing E. coli (STEC) implicated in outbreaks of human illness all over the world. A multiplex polymerase chain reaction assay was developed to simultaneously detect the eight STEC O-serogroups targeting the wzx (O-antigen-flippase) genes of all O-antigen gene clusters. The sensitivity of the multiplex polymerase chain reaction was found to be 10 colony forming units for each O-group when enriched in broth and 100 colony forming units when enriched in artificially inoculated apple juice diluted with tryptic soy broth for 16?h at 37°C. The method can be used for detecting STEC O-groups simultaneously and may be exploited for improving the safety of food products.     

Acquisition of genes from an O18:K1:H7 ColV+ strain of Escherichia coli renders intracranially-inoculated E. coli K12 highly virulent for chickens, ducks and guinea-pigs but not mice

The virulence of intracranially-inoculated mutant forms of an O18ac:K1:H7 ColV+ strain of Escherichia coli (designated MW) that lacked different combinations of its O and K antigens and ColV, and of an E. coli K12 strain to which these characters had been transmitted was studied in mice, chickens, ducks and guinea-pigs. The O18+K1+ColV+ form of MW was highly virulent for chickens and mice but the corresponding form of K12 was only highly virulent for chickens; the O18-K1-ColV- forms of both strains were of low virulence for chickens and mice. K1 was more important than O18 or ColV in determining virulence for both animal species. Ducks and guinea-pigs resembled chickens, not mice, in their response to infection with the O18+K1+ColV+form of K12. Pathogenesis studies revealed that the virulence of the forms of MW and K12 was associated with their ability to proliferate in the central nervous system; only low numbers of organisms were found in the blood and spleen of inoculated animals. The O18+K1+ColV+ form of K12 multiplied in mouse brain and in mouse blood in vitro; its multiplication in chicken blood was partially inhibited. Agglutinins to this and other forms of K12 were found in chicken serum but not in mouse serum. Large doses of mouse serum given to chickens and large doses of chicken serum given to mice did not alter the manner in which these animals responded to K12 O18+K1+ColV+ infection. Vaccination protected chickens and mice against lethal intracranial infection with the O18+K1+ColV+ forms of K12 or MW; it produced a much stronger immunity in mice against intraperitoneal challenge than against intracranial challenge.     

Acquisition of genes from an O18:K1:H7 ColV+ strain of Escherichia coli renders intracranially-inoculated E. coli K12 highly virulent for chickens, ducks and guinea-pigs but not mice.

The virulence of intracranially-inoculated mutant forms of an O18ac:K1:H7 ColV+ strain of Escherichia coli (designated MW) that lacked different combinations of its O and K antigens and ColV, and of an E. coli K12 strain to which these characters had been transmitted was studied in mice, chickens, ducks and guinea-pigs. The O18+K1+ColV+ form of MW was highly virulent for chickens and mice but the corresponding form of K12 was only highly virulent for chickens; the O18-K1-ColV- forms of both strains were of low virulence for chickens and mice. K1 was more important than O18 or ColV in determining virulence for both animal species. Ducks and guinea-pigs resembled chickens, not mice, in their response to infection with the O18+K1+ColV+form of K12. Pathogenesis studies revealed that the virulence of the forms of MW and K12 was associated with their ability to proliferate in the central nervous system; only low numbers of organisms were found in the blood and spleen of inoculated animals. The O18+K1+ColV+ form of K12 multiplied in mouse brain and in mouse blood in vitro; its multiplication in chicken blood was partially inhibited. Agglutinins to this and other forms of K12 were found in chicken serum but not in mouse serum. Large doses of mouse serum given to chickens and large doses of chicken serum given to mice did not alter the manner in which these animals responded to K12 O18+K1+ColV+ infection. Vaccination protected chickens and mice against lethal intracranial infection with the O18+K1+ColV+ forms of K12 or MW; it produced a much stronger immunity in mice against intraperitoneal challenge than against intracranial challenge.