Virulence profiling of shiga toxin-producing Escherichia coli O111 : NM isolates from cattle

Shiga toxin-producing Escherichia coli (STEC) O111:NM is an important serotype that has been incriminated in disease outbreaks in the United States. This study characterized cattle STEC O111:NM for virulence factors and markers by PCR. Major conclusions are that STEC O111:NM characterized in this study lacks stx2 and the full spectrum of nle gene markers, and it has an incomplete OI-122.http://aem.asm.org/am2013mn201

FimH Adhesin of Type 1 Fimbriae Is a Potent Inducer of Innate Antimicrobial Responses Which Requires TLR4 and Type 1 Interferon Signalling

Components of bacteria have been shown to induce innate antiviral immunity via Toll-like receptors (TLRs). We have recently shown that FimH, the adhesin portion of type 1 fimbria, can induce the innate immune system via TLR4. Here we report that FimH induces potent in vitro and in vivo innate antimicrobial responses. FimH induced an innate antiviral state in murine macrophage and primary MEFs which was correlated with IFN-β production. Moreover, FimH induced the innate antiviral responses in cells from wild type, but not from MyD88−/−, Trif−/−, IFN−α/βR−/− or IRF3−/− mice. Vaginal delivery of FimH, but not LPS, completely protected wild type, but not MyD88−/−, IFN-α/βR−/−, IRF3−/− or TLR4−/− mice from subsequent genital HSV-2 challenge. The FimH-induced innate antiviral immunity correlated with the production of IFN-β, but not IFN-α or IFN-γ. To examine whether FimH plays a role in innate immune induction in the context of a natural infection, the innate immune responses to wild type uropathogenic E. coli (UPEC) and a FimH null mutant were examined in the urinary tract of C57Bl/6 (B6) mice and TLR4-deficient mice. While UPEC expressing FimH induced a robust polymorphonuclear response in B6, but not TLR4−/− mice, mutant bacteria lacking FimH did not. In addition, the presence of TLR4 was essential for innate control of and protection against UPEC. Our results demonstrate that FimH is a potent inducer of innate antimicrobial responses and signals differently, from that of LPS, via TLR4 at mucosal surfaces. Our studies suggest that FimH can potentially be used as an innate microbicide against mucosal pathogens

Differential Gene Expression and Adherence of Escherichia coli O157:H7 In Vitro and in Ligated Pig Intestines

BACKGROUND: Escherichia coli O157:H7 strain 86-24 grown in MacConkey broth (MB) shows almost no adherence to cultured epithelial cells but adheres well in pig ligated intestines. This study investigated the mechanisms associated with the difference between in-vitro and in-vivo adherence of the MB culture. METHODOLOGY/PRINCIPAL FINDINGS: It was found that decreased adherence in vitro by bacteria grown in MB was mainly due to lactose, possibly implicating the involvement of carbon catabolite repression (CCR). Expression of selected virulence-related genes associated with adherence and CCR was then examined by quantitative PCR. When bacteria were grown in MB and Brain Heart Infusion with NaHCO(3) (BHIN) plus lactose, pH was reduced to 5.5-5.9 and there was a significant decrease in expression of the locus of enterocyte effacement (LEE) genes eae, tir, espD, grlA/R and ler, and an increase in cya (cAMP), and two negative regulators of the LEE, gadE and hfq. Putative virulence genes stcE, hlyA, ent and nleA were also decreased in vitro. Reversal of these changes was noted for bacteria recovered from the intestine, where transcripts for qseF and fis and putative virulence factors AidA(15), TerC and Ent/EspL2 were significantly increased, and transcripts for AIDA(48), Iha, UreC, Efa1A, Efa1B, ToxB, EhxA, StcE, NleA and NleB were expressed at high levels. CONCLUSIONS/SIGNIFICANCE: Presence of lactose resulted in decreased expression of LEE genes and the failure of EHEC O157:H7 to adhere to epithelial cells in vitro but this repression was overcome in vivo. CCR and/or acidic pH may have played a role in repression of the LEE genes. Bacterial pathogens need to integrate their nutritional metabolism with expression of virulence genes but little is known of how this is done in E. coli O157:H7. This study indicates one aspect of the subject that should be investigated further

Characterization of Verotoxin-Encoding Phages from Escherichia coli O103:H2 Strains of Bovine and Human Origins▿

The objectives of this study were to induce and characterize verotoxin-encoding phages from a collection of 91 verotoxin-producing Escherichia coli (VTEC) O103:H2 strains of human and bovine origins. All the strains carried the vt1 gene, and two carried the vt2 gene as well. The phages were induced by UV irradiation and characterized by DNA restriction fragment length polymorphism (RFLP), genome size, morphology, and Q and P genes, characteristic of lambdoid phages. A total of 32 vt-positive phages were induced and isolated from 31 VTEC O103:H2 strains. Thirty phages were vt1 positive, and two were vt2 positive. Ten of the 30 vt1-positive phages (33.3%) were from cattle strains, and 20 (66.6%) were from human strains. The two vt2-positive phages were from human strains. Phages belonged to 21 RFLP profiles, of which 17 were single-phage profiles and 4 were multiple-phage profiles. The estimated genome size of the phages ranged from 34 to 84 kb. Two phages that were examined by electron microscopy possessed hexagonal heads with long tails, and one had an elongated head with a long tail. The Q and P genes were amplified in all 32 phages, and the Q-stxA1 gene region yielded an amplicon in 19 phages (59.3%). It is concluded that the VTEC O103:H2 strains of human origin were more readily inducible than those of bovine origin and that the genotypic profiles of verotoxin-encoding phages were highly diverse, as revealed by their RFLP profiles