Serotypes of CNF1-producing Escherichia coli strains that cause extraintestinal infections in humans

Screening of a Drug Library Identifies Inhibitors of Cell Intoxication by CNF1

Cytotoxic necrotizing factor 1 (CNF1) is a toxin produced by pathogenic strains of Escherichia coli responsible for extra-intestinal infections. CNF1 deamidates Rac1, thereby triggering its permanent activation and worsening inflammatory reactions. Activated Rac1 is prone to proteasomal degradation. There is no targeted therapy against CNF1, despite its clinical relevance. In this work we developed a fluorescent cell-based immunoassay to screen for inhibitors of CNF1-induced Rac1 degradation among 1120 mostly approved drugs. Eleven compounds were found to prevent CNF1-induced Rac1 degradation, and five also showed a protective effect against CNF1-induced multinucleation. Finally, lasalocid, monensin, bepridil, and amodiaquine protected cells from both diphtheria toxin and CNF1 challenges. These data highlight the potential for drug repurposing to fight several bacterial infections and Rac1-based diseases.

Isolation and characterization of potentially pathogenic antimicrobial-resistant Escherichia coli strains from chicken and pig farms in Spain

To ascertain whether on animal farms there reside extended-spectrum beta-lactamase (ESBL) and plasmidic class C beta-lactamase-producing Escherichia coli isolates potentially pathogenic for humans, phylogenetic analyses, pulsed-field gel electrophoresis (PFGE) typing, serotyping, and virulence genotyping were performed for 86 isolates from poultry (57 isolates) and pig (29 isolates) farms. E. coli isolates from poultry farms carried genes encoding enzymes of the CTX-M-9 group as well as CMY-2, whereas those from pig farms mainly carried genes encoding CTX-M-1 enzymes. Poultry and pig isolates differed significantly in their phylogenetic group assignments, with phylogroup A predominating in pig isolates and phylogroup D predominating in avian isolates. Among the 86 farm isolates, 23 (26.7%) carried two or more virulence genes typical of extraintestinal pathogenic E. coli (ExPEC). Of these, 20 were isolated from poultry farms and only 3 from pig farms. Ten of the 23 isolates belonged to the classic human ExPEC serotypes O2:H6, O2:HNM, O2:H7, O15:H1, and O25:H4. Despite the high diversity of serotypes and pulsotypes detected among the 86 farm isolates, 13 PFGE clusters were identified. Four of these clusters contained isolates with two or more virulence genes, and two clusters exhibited the classic human ExPEC serotypes O2:HNM (ST10) and O2:H6 (ST115). Although O2:HNM and O2:H6 isolates of human and animal origins differed with respect to their virulence genes and PFGE pulsotypes, the O2:HNM isolates from pigs showed the same sequence type (ST10) as those from humans. The single avian O15:H1 isolate was compared with human clinical isolates of this serotype. Although all were found to belong to phylogroup D and shared the same virulence gene profile, they differed in their sequence types (ST362-avian and ST393-human) and PFGE pulsotypes. Noteworthy was the detection, for the first time, in poultry farms of the clonal groups O25b:H4-ST131-B2, producing CTX-M-9, and O25a-ST648-D, producing CTX-M-32. The virulence genes and PFGE profiles of these two groups were very similar to those of clinical human isolates. While further studies are required to determine the true zoonotic potential of these clonal groups, our results emphasize the zoonotic risk posed especially by poultry farms, but also by pig farms, as reservoirs of ESBL- and CMY-2-encoding E. coli.

Chapter 8 Adhesins and receptors for colonization by different pathotypes of Escherichia coli in calves and young pigs

This chapter provides an overview of the virulence factors and their genetic regulators in Escherichia coli. The most important adhesins and their receptors playing a role in the pathogenesis of different pathotypes of enteric E. coli are also described. The main pathotypes involved in enteric colibacillosis of pigs and calves are the enterotoxigenic E. coli (ETEC), verotoxigenic E. coli (VTEC), enteropathogenic E. coli (EPEC), and necrotoxigenic E. coli (NTEC). Adhesion and colonization are the first (but not the only) functional prerequisites for a mucosal bacterium to be pathogenic. The adhesins represent surface proteins, governed by specific operons and constructed in ways according to the particular adhesin. Besides their structure, the adhesins can also be grouped according to their receptors present on the intestinal mucosal epithelium and on the urinary epithelium. Apart from direct practical applications, there are further significant scientific developments and applications expected in the area of neonatal biology and comparative human pathobacteriology.

Murine monoclonal antibodies against Escherichia coli O4 lipopolysaccharide and H5 flagellin

Two murine monoclonal antibodies (MAb), 2C5-F10 and 8D1-H10, reactive with Escherichia coli O4 and H5 antigens, respectively, were generated and characterized. Enzyme immunoassays and immunoblots demonstrated that MAb 2C5-F10 reacted specifically with lipopolysaccharide O antigen of E. coli O4 isolates, while MAb 8D1-H10 reacted with E. coli strains expressing H5 flagella.

Distribution and characterization of faecal necrotoxigenic Escherichia coli CNF1+ and CNF2+ isolated from healthy cows and calves

Faecal swabs obtained from a random sample of 268 cows and 90 calves on 19 Lugo (northwestern Spain) farms were examined for necrotoxigenic Escherichia coli (NTEC) producing the cytotoxic necrotizing factors type 1 (CNF1) and type 2 (CNF2). We found NTEC CNF1+ and CNF2+ on 11% and 95% of the farms, respectively, NTEC producing CNF2 were significantly more frequently isolated from calves (58%) than from cows (17%) (P < 0.001). The proportion of animals colonized with CNF2+ strains on each farm ranged from 0% to 60%. NTEC strains producing CNF2 isolated from healthy cattle belonged to 27 O serogroups; however, 64% were of one of 12 serogroups (O2, O8, O8-O75, O14, O15, O55, O86, O88, O115, O121, O147, and O168). Furthermore, the serogroups determined in CNF2+ strains isolated from cows (O2, O8, and O14) were different from those found in NTEC producing CNF2 isolated from calves (O8-O75, O15, O55, O86, O88, O115 and O147).

Prevalence and characteristics of necrotoxigenic Escherichia coli CNF1+ and CNF2+ in healthy cattle

From February to July of 1994, 328 faecal samples from 32 herds were collected and examined for necrotoxigenic Escherichia coli (NTEC). Strains producing the cytotoxic necrotizing factors type 1 (CNF1) and type 2 (CNF2) were found on 4 and 63% of the farms, respectively. The proportion of animals infected within each herd varied from 0 to 38%. NTEC producing CNF2 were significantly more frequently isolated from calves (24%; 17 of 71) than from cows (4%; 11 of 257) (chi 2corr. 25.088; P < 0.001). Although the bovine CNF2+ strains belonged to 16 different serogroups, 5 (O15, O77, O88, O142 and O153) accounted for 44% of strains. This study confirmed that healthy cattle are a reservoir of NTEC producing CNF2, and revealed that CNF2+ strains are more frequently carried by calves than by adult cows.

Detection of pap, sfa and afa adhesin-encoding operons in uropathogenic Escherichia coli strains: relationship with expression of adhesins and production of toxins

A total of 243 Escherichia coli strains isolated from patients with urinary tract infections (UTI) were investigated for the presence of pap, sfa and afa adhesin-encoding operons by using the polymerase chain reaction. It was found that 54%, 53% and 2% of the strains exhibited the pap, sfa and afa genotypes, respectively. Pap+ and/or sfa+ strains were more frequent in cases of acute pyelonephritis (94%) than in cases of cystitis (67%) (P < 0.001) and asymptomatic bacteriuria (57%) (P < 0.001). The pap and/or sfa operons were found in 90% of strains expressing mannose-resistant haemagglutination (MRHA) versus 37% of MRHA-negative strains (P < 0.001). The presence of pap and sfa operons was especially significant in strains belonging to MRHA types III (100%) (without P adhesins) and IVa (97%) (expressing the specific Gal-Gal binding typical of P adhesins). Both pap and sfa operons were closely associated with toxigenic E. coli producing alpha-haemolysin (Hly+) and/or the cytotoxic necrotizing factor type 1. There was an apparent correlation between the pap and sfa operons and the O serogroups of the strains. Thus, 93% of strains belonging to O1, O2, O4, O6, O7, O14, O15, O18, O22, O75 and O83 possessed pap and/or sfa operons, versus only 32% of strains belonging to other serogroups (P < 0.001). The results obtained in this study confirm the usefulness of our MRHA typing system for presumptive identification of pathogenic E. coli exhibiting different virulence factors. Thus, 85% of strains that possessed both pap and sfa adhesin-encoding operons showed MRHA types III or IVa previously associated with virulence of E. coli strains that cause UTI and bacteraemia.

The Hha protein as a modulator of expression of virulence factors in Escherichia coli

We constructed hha derivatives from both a clinical uropathogenic Escherichia coli isolate (strain FVL4) and a wild E. coli strain causing bovine diarrhea (strain CCB21) and analyzed the effect of the hha allele on the expression of the different virulence factors exhibited by these strains. Expression of hemolysin and of the Vir antigen was altered in hha mutants. Whereas production of hemolysin by strain FVL4 was repressed both at a low temperature and at high osmolarity, the hha allele accounted for a significant increase of hemolysin production under these conditions. Also, the low temperature-sensitive expression of the Vir adhesin was modified in hha mutants, which were able to express this adhesin at a low temperature. Expression of other virulence factors, such as cytotoxic necrotizing factor type 1 and 2 toxins, remained unmodified in hha derivatives of strains FVL4 and CCB21.

Virulence factors and O groups of Escherichia coli isolates from patients with acute pyelonephritis, cystitis and asymptomatic bacteriuria

The relationship between the presence of bacterial virulence factors and the severity of urinary tract infection (UTI) was analized in this study. The production of alpha-hemolysin (Hly), the expression of P-fimbriae and the mannose-resistant hemagglutination (MRHA) type IVa (associated with the presence of P-fimbriae), were all detected more frequently in Escherichia coli strains from acute pyelonephritis than in strains isolated from cystitis and asymptomatic bacteriuria. In contrast, the production of cytotoxic necrotizing factor type 1 (CNF1) and the expression of MRHA types III and IVb were distributed uniformly between strains causing different clinical categories of UTI. Thus 88% of the E. coli strains from acute pyelonephritis showed some of the virulence factors investigated in this study, whereas only 60% (p < 0.01) and 56% (p < 0.01) repectively of the strains isolated from cystitis and asymptomatic bacteriuria possessed virulence factors. There were no significant differences in the prevalence of virulence properties between strains isolated from patients with or without complicating factors. Only 16% (p < 0.001) of the fecal isolates from healthy individuals showed virulence factors. The virulence factors were concentrated in strains belonging to 10 (O1, O2, O4, O6, O7, O14, O18, O22, O75 and O83) of the 12 serogroups most frequently detected in uropathogenic E. coli strains. The majority of uropathogenic O4, O6, O14, O22, O75 and O83 E.coli strains were Hly+CNF1+ and expressed P-fimbriae or MRHA type III, whereas the strains of serogroup O18 were Hly+CNF1- and P-fimbriated. Among O1 and O7 strains we found Hly-CNF1-strains that expressed P-fimbriae. Among O2 strains we found Hly+CNF1+ strains that expressed P-fimbriae or MRHA type III and other Hly-CNF1-strains that possessed P-fimbriae. We conclude that E.coli strains isolated from pyelonephritis show virulence factors more frequently than those from cystitis and asymptomatic bacteriuria, and that strains that cause urinary tract infections in Spain belong to the same serogroups as uropathogenic E.coli isolated in other areas of the world. Our results support the special pathogenicity theory and suggest that many cases of serious urogenital disease may be caused by a limited number of P-fimbriated E.coli strains that usually produce alpha-hemolysin.