Virulence factors of bacteraemic Escherichia coli with particular reference to production of cytotoxic necrotising factor (CNF) by P-fimbriate strains

An overview on mastitis-associated Escherichia coli: Pathogenicity, host immunity and the use of alternative therapies

Escherichia coli is one of the leading causes of bovine mastitis; it can cause sub-clinical, and clinical mastitis characterized by systemic changes, abnormal appearance of milk, and udder inflammation. E. coli pathogenicity in the bovine udder is due to the interaction between its virulence factors and the host factors; it was also linked to the presence of a new pathotype termed mammary pathogenic E. coli (MPEC). However, the presence of this pathotype is commonly debated. Its main virulence factor is the lipopolysaccharide (LPS) that is responsible for causing an endotoxic shock, and inducing a strong immune response by binding to the toll-like receptor 4 (TLR4), and stimulating the expression of chemokines (such as IL-8, and RANTES) and pro-inflammatory cytokines (such as IL-6, and IL-1β). This strong immune response could be used to develop alternative and safe approaches to control E. coli causing bovine mastitis by targeting pro-inflammatory cytokines that can damage the host tissue. The need for alternative treatments against E. coli is due to its ability to resist many conventional antibiotics, which is a huge challenge for curing ill animals. Therefore, the aim of this review was to highlight the pathogenicity of E. coli in the mammary gland, discuss the presence of the new putative pathotype, the mammary pathogenic E. coli (MPEC) pathotype, study the host's immune response, and the alternative treatments that are used against mastitis-associated E. coli.

Cloning, Expression, and Immunogenicity of Fimbrial-F17A Subunit Vaccine against Escherichia coli Isolated from Bovine Mastitis

There is a need to identify and select new promising immunodominant antigens that have the ability to provide protective immunity against E. coli causing bovine mastitis. Recently we showed that f17a was found to be the most prevalent and crucial virulent factor among the pathogenic E. coli isolated from bovine mastitis. Here, in this report, the recombinant F17A based subunit vaccine adjuvant with MF59 was tested for immunogenicity against E. coli in a murine model. The vaccinated mice did not show any abnormal behavioral changes and histopathological lesions after vaccination. The specific antibody level against F17A was significantly higher in MF59-adjuvant-group, and also lasted for longer duration with a significant (P < 0.01) production level of IgG1 and IgG2a. Moreover, we noted higher survival rate in mice injected with F17A-MF59-adjuvant group after challenging with the clinical E. coli strain. Our findings of bacterial clearance test revealed that elimination rate from liver, spleen, and kidney in MF59-adjuvant-group was significantly higher than the control group. Finally, the proportion of CD4+T cells was increased, while CD8+ was decreased in MF59-adjuvant group. In conclusion, the current study reveals the capability of F17A-MF59 as a potential vaccine candidate against pathogenic E. coli causing mastitis in dairy animals.

Evaluation of Virulence Factors and Antibiotic Sensitivity Pattern of Escherichia Coli Isolated from Extraintestinal Infections

Introduction 

Identification of virulence determinants among the clinically isolated microorganisms assumes greater significance in the patient management perspective. Among the hospitalized patients, extremes of age groups (neonatal and geriatric age patients), patients who are debilitated due to other associated medical conditions, patients taking immunosuppressive therapy, and patients undergoing major surgeries are prone to infections with previously nonpathogenic or opportunistic pathogens. Screening of the pathogenic potential of such bacteria and identifying their virulence factors and antimicrobial susceptibility patterns could be instrumental in better patient care and management.

Materials & methods 

In this study, we evaluated the virulence determinants and antimicrobial susceptibility patterns of 100 clinical isolates of E. coli collected from extraintestinal infections and 50 control strains of E. coli. Hemolysin production, serum resistance, cell surface hydrophobicity, and gelatinase production were tested using standard laboratory procedures.

Results 

Results showed that E. colistrains have a variable pattern of virulence markers that included hemolysin production (9%), cell surface hydrophobicity (9%), serum resistance (93%), and gelatinase production (2%). Antimicrobial susceptibility testing revealed a higher rate of resistance against cephalothin (84%) and ampicillin (98%). Susceptibility to amikacin (80%) and co-trimoxazole (47%) was variable and none of the test strains revealed resistance to imipenem. The control strains in contrast exhibited fewer virulence factors and the least resistance to antibiotics.

Conclusion 

In conclusion, the study results revealed that E. coli isolated from extraintestinal infections had demonstrated greater virulence and higher resistance to antibiotics as compared to the E. coli strains isolated from healthy individuals.

Bacterial factors exploit eukaryotic Rho GTPase signaling cascades to promote invasion and proliferation within their host

Actin cytoskeleton is a main target of many bacterial pathogens. Among the multiple regulation steps of the actin cytoskeleton, bacterial factors interact preferentially with RhoGTPases. Pathogens secrete either toxins which diffuse in the surrounding environment, or directly inject virulence factors into target cells. Bacterial toxins, which interfere with RhoGTPases, and to some extent with RasGTPases, catalyze a covalent modification (ADPribosylation, glucosylation, deamidation, adenylation, proteolysis) blocking these molecules in their active or inactive state, resulting in alteration of epithelial and/or endothelial barriers, which contributes to dissemination of bacteria in the host. Injected bacterial virulence factors preferentially manipulate the RhoGTPase signaling cascade by mimicry of eukaryotic regulatory proteins leading to local actin cytoskeleton rearrangement, which mediates bacterial entry into host cells or in contrast escape to phagocytosis and immune defense. Invasive bacteria can also manipulate RhoGTPase signaling through recognition and stimulation of cell surface receptor(s). Changes in RhoGTPase activation state is sensed by the innate immunity pathways and allows the host cell to adapt an appropriate defense response.

The E. coli CNF1 as a pioneering therapy for the central nervous system diseases

The Cytotoxic Necrotizing Factor 1 (CNF1), a protein toxin from pathogenic E. coli, modulates the Rho GTPases, thus, directing the organization of the actin cytoskeleton. In the nervous system, the Rho GTPases play a key role in several processes, controlling the morphogenesis of dendritic spines and synaptic plasticity in brain tissues. This review is focused on the peculiar property of CNF1 to enhance brain plasticity in in vivo animal models of central nervous system (CNS) diseases, and on its possible application in therapy.

Intravital models of infection lay the foundation for tissue microbiology

In complex environments, such as those found in the human host, pathogenic bacteria constantly battle the unfavorable conditions imposed by the host response to their presence. During Escherichia coli-induced pyelonephritis, a cascade of events are shown in an intravital animal model to occur in a timely and sequential manner, representing the dynamic interplay between host and pathogen. Today, intravital techniques allow for observing infection in the living host. At resolutions almost on the single-cell level, improved detection methods offer a movie-like description of infection dynamics. Tissue microbiology involves monitoring host-pathogen interaction within the dynamic microecology of infectious sites in the live host. This new field holds great promise for insightful research into microbial disease intervention strategies.

Bacteriocin synthesis in uropathogenic and commensal Escherichia coli: colicin E1 is a potential virulence factor

Background

Bacteriocin production is an important characteristic of E. coli strains of human origin. To date, 26 colicin and 9 microcin types have been analyzed on a molecular level allowing molecular detection of the corresponding genes. The production incidence of 29 bacteriocin types and E. coli phylogroups were tested in a set of 361 E. coli strains isolated from human urinary tract infections (UTI) and in 411 control strains isolated from feces of patients without bacterial gut infection.

Results

Production of 17 and 20 individual bacteriocin types was found in the UTI and control strains, respectively. Microcin H47 encoding determinants were found more often among UTI strains compared to controls (37.9% and 27.0% respectively, p = 0.02) and strains producing microcin H47 belonged predominantly to phylogroup B2 when compared to other bacteriocin producers (67.4% and 36.7%, respectively; p < 0.0001). Producers of 3 or more identified bacteriocin types were more common in the UTI group (20.0% compared to 12.4% in controls, p = 0.03). In the UTI strains, there was a markedly higher number of those producing colicin E1 compared to controls (22.1% to 10.2%, respectively, p = 0.0008). Moreover, colicin E1 production was more common in the UTI bacteriocinogenic strains with multi-producer capabilities. As shown by Southern blotting, pColE1 DNA was not recognized by the ColIa probe and vice versa suggesting that pColE1 was independently associated with pColIa in UTI strains.

Conclusion

E. coli strains isolated from human urinary tract infections showed increased incidence of microcin H47 and colicin E1 production, respectively. Moreover, colicin E1 itself appears to be a potentially important virulence factor of certain uropathogenic E. coli strains.

Recent emergence of clonal group O25b:K1:H4-B2-ST131 ibeA strains among Escherichia coli poultry isolates, including CTX-M-9-producing strains, and comparison with clinical human isolates

To discern the possible spread of the Escherichia coli O25b:H4-ST131 clonal group in poultry and the zoonotic potential of avian strains, we made a retrospective search of our strain collection and compared the findings for those strains with the findings for current strains. Thus, we have characterized a collection of 19 avian O25b:H4-ST131 E. coli strains isolated from 1995 to 2010 which, interestingly, harbored the ibeA gene. Using this virulence gene as a criterion for selection, we compared those 19 avian strains with 33 human O25b:H4-ST131 ibeA-positive E. coli strains obtained from patients with extraintestinal infections (1993 to 2009). All 52 O25b:H4-ST131 ibeA-positive E. coli strains shared the fimH, kpsMII, malX, and usp genes but showed statistically significant differences in nine virulence factors, namely, papGIII, cdtB, sat, and kpsMII K5, which were associated with human strains, and iroN, kpsMII K1, cvaC, iss, and tsh, which were associated with strains of avian origin. The XbaI macrorestriction profiles of the 52 E. coli O25b:H4-ST131 ibeA-positive strains revealed 11 clusters (clusters I to XI) of >85% similarity, with four clusters including strains of human and avian origin. Cluster VII (90.9% similarity) grouped 10 strains (7 avian and 3 human strains) that mostly produced CTX-M-9 and that also shared the same virulence profile. Finally, we compared the macrorestriction profiles of the 12 CTX-M-9-producing O25b:H4-ST131 ibeA strains (7 avian and 5 human strains) identified among the 52 strains with those of 15 human O25b:H4-ST131 CTX-M-14-, CTX-M-15-, and CTX-M-32-producing strains that proved to be negative for ibeA and showed that they clearly differed in the level of similarity from the CTX-M-9-producing strains. In conclusion, E. coli clonal group O25b:H4-ST131 ibeA has recently emerged among avian isolates with the new acquisition of the K1 capsule antigen and includes CTX-M-9-producing strains. This clonal group represents a real zoonotic risk that has crossed the barrier between human and avian hosts.

Escherichia coli cytotoxic necrotizing factor 1 (CNF1): toxin biology, in vivo applications and therapeutic potential

CNF1 is a protein toxin produced by certain pathogenic strains of Escherichia coli. It permanently activates the regulatory Rho, Rac, and Cdc42 GTPases in eukaryotic cells, by deamidation of a glutamine residue. This modification promotes new activities in cells, such as gene transcription, cell proliferation and survival. Since the Rho GTPases play a pivotal role also in several processes in vivo, the potentiality of CNF1 to act as a new pharmacological tool has been explored in experimental animals and in diverse pathological contexts. In this review, we give an update overview on the potential in vivo applications of CNF1.

Hemolysin of uropathogenic Escherichia coli evokes extensive shedding of the uroepithelium and hemorrhage in bladder tissue within the first 24 hours after intraurethral inoculation of mice

Many uropathogenic Escherichia coli (UPEC) strains produce both hemolysin (Hly) and cytotoxic necrotizing factor type 1 (CNF1), and the loci for these toxins are often linked. The conclusion that Hly and CNF1 contribute to urovirulence is supported by the results of epidemiological studies associating the severity of urinary tract infections (UTIs) with toxin production by UPEC isolates. Additionally, we previously reported that mouse bladders and rat prostates infected with UPEC strain CP9 exhibit a more profound inflammatory response than the organs from animals challenged with CP9cnf(1) and that CNF1 decreases the antimicrobial activities of polymorphonuclear leukocytes. More recently, we created an Hly mutant, CP9Delta hlyA(1)::cat, and showed that it was less hemolytic and destructive for cultured bladder cells than CP9 was. Here we evaluated the relative effects of mutations in hlyA(1) or cnf(1) alone or together on the pathogenicity of CP9 in a mouse model of ascending UTI. To do this, we constructed an hlyA(1)-complemented clone of CP9Delta hlyA(1)::cat and an hlyA(1) cnf(1) CP9 double mutant. We found that Hly had no influence on bacterial colonization of the bladder or kidneys in single or mixed infections with the wild type and CP9Delta hlyA(1)::cat but that it did provoke sloughing of the uroepithelium and bladder hemorrhage within the first 24 h after challenge. Finally, we confirmed that CNF1 expression induces bladder inflammation and, in particular, as shown in this study, submucosal edema. From these data, we speculate that Hly and CNF1 may be largely responsible for the signs and symptoms of cystitis in humans infected with toxigenic UPEC.

Occurrence and characteristics of cytotoxic necrotizing factors, cytolethal distending toxins and other virulence factors in Escherichia coli from human blood and faecal samples

Escherichia coli isolates from human blood (n=266) and faecal (n=237) samples were examined for cytotoxic necrotizing factors 1 and 2 (CNF 1 and 2), cytolethal distending toxin (CDT), and putative virulence factors that have been associated with disease conditions in humans and animals. PCR showed that the chromosomally encoded, Rho-activating, CNF1 (68/544, 12.5%) was more common than the transmissible plasmid-borne CNF2 (3/544, 0.6%). The relative risk of having either CNF or CDT toxin genes in blood compared to faecal isolates was 3.88 (95% CI 2.36-6.38). This was highly significant (P<0.0001) and demonstrates the importance of these factors in bloodstream infections. Fifty-one of 65 (78%) E. coli bearing CNF1 and 11 of 21 (52%) of E. coli bearing CDT also carried the pyelonephritis-associated pilus gene, papG. The S fimbrial adhesin gene, sfa, was found in 57 blood (21%) and eight faecal samples (3%). The F17 fimbrial adhesin gene and afimbrial adhesin gene afa did not occur frequently. Haemolysin (hly) was found in all of the isolates tested. Further studies must be designed to identify the clinical significance of these genes and their role in pathogenesis.

Prevalence of virulence factors in Escherichia coli strains isolated from the genital tract of healthy cows

The prevalence of virulence genes expressing fimbriae, production of hemolysin, colicin and aerobactin, was determined in Escherichia coli isolates from healthy cow’s genital tract not showing clinical signs of infection. The presence of fimbriae expression genes (pap, sfa, afa) was assayed using specific primers in a polymerase chain reaction; none were detected in any of the isolates. Yet, a prevalence of 90.4%, 69.8%, and 28.5% of virulence factors for colicin, hemolysin and aerobactin respectively, was detected in the isolates. Analysis of the bacterial pathogenicity of isolates from the bovine genital tract may contribute towards the understanding of E. coli behavior.

The virulence markers of Salmonella enterica serovar Typhimurium. Different phage-type strains isolated in Slovakia

Phage-typing determination of cell-surface hydrophobicity, motility, and serovar-specific virulence plasmid was performed in a collection of 154 clinical isolates of S. enterica serovar Typhimurium (SeT) isolated in Slovakia. All isolates were also examined in PCR for the presence of both stn (enterotoxin) and iroB (siderophore) genes. The DT104 was the definitive phage type most frequently identified (37.7 %), the second most frequently isolated phage type was DT41 (5.8 %); the occurrence of other phage types was not epidemiologically significant. On the basis of virulence-marker investigation, 46.1 % of isolates were hydrophobic in the assay of bacterial adherence to xylene, and 97.4 % were hydrophobic in salt-aggregation test. Motility of more than 50 mm was expressed by 20.8 % isolates. The serovar-specific 90-kb virulence plasmid was contained in 138 (89.6 %) of isolates. All SeT isolates were found (according to PCR) to carry the Salmonella-enterotoxin (stn) gene and the siderophore (iroB) gene. The increasing incidence of SeT DT104 human strains in Slovakia requires continuous attention; this can be markedly improved by surveillance efficiency and made possible by determining relationships between sporadic isolates.

Evaluation of adherence, hemagglutination, and presence of genes codifying for virulence factors of Acinetobacter baumannii causing urinary tract infection

Acinetobacter baumannii is a strictly aerobic bacterium which causes severe infections, however its pathogenic characteristics are not well defined. Thirteen A. baumannii strains isolated from urine of hospitalized and nonhospitalized patients with different ages were investigated for the presence of virulence factors. The isolates belonged to biotypes 2, 6, and 9 and were sensitive to imipenem. The majority of them showed resistance to amikacin, ceftazidime, ceftriaxone, ciprofloxacin, gentamicin, norfloxacin, and trimethoprim-sulfamethoxazole. None of A. baumannii strains presented genes codifying for 17 different virulence factors previously described in uropathogenic Escherichia coli, when tested by polymerase chain reaction (PCR). Nine isolates agglutinated human group AB erythrocytes, in presence of mannose, but none of them agglutinated group O erythrocytes. Adherence to polystyrene was observed in 7 isolates, and this result did not correlate with that obtained in hemagglutination assay. All the isolates were able to grow in iron-limiting conditions, showing that A. baumannii produces some type of siderophore. However, the genes iutA and fyuA, from iron uptake system of E. coli and Yersinia sp., respectively, were not present in the isolates, suggesting the presence of a different type of siderophore. The fimbriae of A. baumannii strains that mediates the adherence are possibly mannose-resistant, even though the mechanism of adherence to human epithelial cells still remains to be elucidated.

Production by Escherichia coli isolates of siderophore and other virulence factors and their pathogenic role in a cutaneous infection model

Escherichia coli isolates from urinary tract infections (UTIs) (n = 124), extra-urinary sites (n = 37) and normal faecal samples (n = 51) were examined for the presence of virulence factors, including siderophores (aerobactin and enterobactin). The proportion of aerobactin producers was significantly higher in UTI (69.4%; p 0.001) and extra-urinary samples (70.3%; p 0.007) than in controls (41.2%), while the proportion of enterobactin producers was significantly lower in the UTI samples than in the controls (p 0.027). In a cutaneous infection model, aerobactin-positive E. coli showed more growth than non-aerobactin and non-enterobactin isolates, even when other virulence factors were identical.

Cloning and sequencing of cnf1 from Escherichia coli incriminated in mink and bovine colibacillosis

Colibacillosis is responsible for significant losses to the mink and cattle industries. Previous work in our laboratory and by others has suggested that possession of cnf1, the gene encoding cytotoxic necrotizing factor (CNF1), may contribute to the virulence of isolates of E. coli from mink and cattle. The cnf1 gene from E. coli isolated from a mink with colisepticaemia and a bovid with scours was amplified and cloned as a 3.5 kb fragment, and the fragment was sequenced. The cnf1 sequences from the mink and bovine isolates of E. coli were compared to each other and to cnf1 sequences of E. coli from urinary tract and diarrhoea-associated infections of humans. The difference was only 7 nucleotides between the cnf1 sequences of the mink and bovine isolates of E. coli, which translated into 7 differences in amino acids. The cnf1 sequence of the mink isolate of E. coli had 15 nucleotide differences from the cnf1 sequences of the human isolate of E. coli (GenBank X70670), which translated into 11 differences in amino acids between these proteins. The cnf1 sequence of the bovine isolate of E. coli had 14 nucleotide differences from the cnf1 sequence of the human isolate of E. coli (GenBank X70670), which translated into 10 differences in amino acids between these proteins. The highly conserved sequences of the amino acids of CNF1 proteins make them a promising target for detection and control of the CNF1-producing E. coli involved in disease among various host species.

Microbial virulence determinants and the pathogenesis of urinary tract infection

The most frequent and best-studied agent of urinary tract infection (UTI) is Escherichia coli, which serves as a useful model pathogen for understanding microbial virulence in relation to UTI pathogenesis. The E. coli strains that cause most UTIs and other extraintestinal E. coli infections represent a highly specialized subset of the total E. coli population. The enhanced virulence potential of such strains, which collectively are known as uropathogenic E. coli or extraintestinal pathogenic E. coli (ExPEC), is thought to be caused mainly by their multiple virulence factors. These virulence factors include diverse adhesins, siderophores, toxins, polysaccharide coatings, and other properties that assist the bacteria in avoiding or subverting host defenses, injuring or invading host cells and tissues, and stimulating a noxious inflammatory response. Although the true evolutionary basis for ExPEC is unknown, the virulence factors of ExPEC serve as useful epidemiologic markers and in the future may provide effective targets for anti-UTI interventions.

Toxinogenicity and markers of pathogenicity of Pseudomonas aeruginosa strains isolated from patients with tumor diseases

Potential virulence factors (elastase, proteinase, lipase, phospholipase C, alginate) as well as surface properties (hydrophobicity, motility) were determined in 103 Pseudomonas aeruginosa strains isolated from patients with cancer. Nontypable strains were the dominant group (60%), followed by serotypes O11 (17%), O12 (7%) and O4 (5%). Seventy-one strains (69%) produced high level of elastase (10-60 mg/L), 87% of the strains possessed high activity of proteinase (bacterial) (10-250 mg/L) and 69% of the strains demonstrated higher level of lipase (20-150 U/mL); these elevated levels of enzymes were associated mainly with nontypable strains. On the other hand, 79% of the strains did not produce or produced only a low level of phospholipase C and 60% of isolates did not manifest any or very low production of alginate. Hydrophobicity demonstrated by adherence of the bacteria to xylene was shown by 69% of strains; 94% of strains aggregated with ammonium sulfate. Motility in the range of 31-80 mm was found in 76 strains (74%). The considerable virulence of tested P. aeruginosa strains was confirmed. The nontypable strains manifested the most frequent group with high level of elastase, proteinase, lipase, hydrophobicity and motility.

Influence on Enterobacter cloacae metabolism, cell-surface hydrophobicity and motility of suprainhibitory concentrations of carbapenems

The impact of postantibiotic effect (PAE) of carbapenems (imipenem, meropenem) on the metabolism (biosynthesis of macromolecules, respiration), cell-surface hydrophobicity and motility of a clinical isolate of Enterobacter cloacae was examined. The metabolism was evaluated after 16 h and after 1 d of cultivation using 2x and 4x minimum inhibitory concentrations (MIC) of both antibiotics for the induction of PAE. Imipenem at 4 x MIC did not induce PAE. After a 16-h cultivation (in the postantibiotic phase of both carbapenems), inhibition of nucleosynthesis and protein synthesis was found; after a 1-d cultivation, during regrowth stimulation of mainly 14C-leucine incorporation was found. The presence of the exogenous intermediates of citrate cycle, viz. 2-oxoglutarate, increased the respiratory activity of the cells. The cell-surface hydrophobicity (evaluated by three methods--bacterial adhesion to hydrocarbon, nitrocellulose-filter test and salt-aggregation test) decreased after PAE of both carbapenems; meropenem was more effective. Motility (an important virulence factor) was inhibited in the postantibiotic phase of both carbapenems; the 4 x MIC caused a higher inhibition.

Characterization of necrotoxigenic Escherichia coli (NTEC) strains isolated from healthy calves in Poland

Faecal samples from 132 healthy, 4-8-week-old calves from four different farms were examined for necrotoxigenic Escherichia coli (NTEC) producing the cytotoxic necrotizing factors type 1 (CNF1) and type 2 (CNF2). CNF2 genes were detected by polymerase chain reaction in 24 (6.1%) of the 396 E. coli strains tested; these strains were found in 18 (13.6%) calves used in the study. None of the 396 E. coli isolates examined possessed the gene encoding CNF1. Overall, 28.8% of E. coli examined expressed the F17 fimbrial antigen. A strong association between CNF2 toxin and F17 fimbriae was found (62.5% of CNF2-positive strains were F17-positive). Moreover, six out of 24 NTEC strains had the Stx1 or the Stx2 shiga toxin genes, and three additional isolates possessed the eae genetic marker of the intimin protein.

Biological and genetic characteristics of uropathogenic Escherichia coli strains

The aim of the present study was to determine biological characteristics such as expression of fimbriae, Congo red binding, production of hemolysin and aerobactin, adhesion to HeLa and uroepithelial cells and invasion of HeLa cells by Escherichia coli isolates obtained from patients showing clinical signs of urinary tract infection (UTI). Also, the presence of genes (apa, afa, spa) for fimbria expression and cytotoxic necrotizing factors (CNF1, CNF2) was assayed using specific primers in PCR. The data obtained were compared with the clonal relationships obtained by analysis of multilocus enzyme electrophoresis (MLEE), restriction fragment length polymorphism (RFLP) of the rDNA (ribotyping) and enterobacterial repetitive intergenic consensus-PCR (ERIC-PCR). All isolates but one presented a combination of at least two of the characteristics studied, a fact suggesting the presence of pathogenicity islands (PAIs). Diffuse adherence type to HeLa cells was observed to occur in most of the strains, but adhesion to uroepithelial cells seems to be a more reliable test to verify pathogenicity. Although four strains seemed to be able to invade HeLa cells when assayed by light microscopy, electron microscopy studies demonstrated that these strains were not invasive. MLEE, RFLP and ERIC-PCR were able to group the isolates differently into main clusters that were not correlated with the presence of pathogenic traits.

Characteristics of necrotoxigenic Escherichia coli isolated from septicemic and diarrheic calves between 1958 and 1970

A total of 434 Escherichia coli isolated from septicemic calves between 1958 and 1965 and 430 E. coli isolated from diarrheic calves between 1967 and 1970 were studied by colony hybridisation and PCR assays for the presence of the cnf1- and the cnf2-like genes. They were also studied for the presence of genes coding for putative virulence factors associated with the CNF toxins including F17-, Pap- and Sfa-fimbrial adhesins and the recently described CDT-III toxin and AfaVIII-afimbrial adhesin. Thirty (7%) of the 434 septicemic strains were positive for CNF by colony hybridisation. Twenty-six were confirmed as necrotoxigenic E. coli type 2 (NTEC2) and four as NTEC1 by PCR. Thirty-five (8%) of the 430 diarrheic strains were positive for CNF by colony hybridisation. Five of them were studied by PCR and confirmed as NTEC1. The 26 septicemic NTEC2 strains and 20 of the 35 diarrheic NTEC including three of the five NTEC1 were positive for CDT-III. All adhesins studied were present in NTEC as well as in non-NTEC. NTEC1 were mainly Pap-, Sfa- and/or Afa8-positive, whereas NTEC2 were mainly F17- and/or Afa8-positive. This study shows that necrotoxigenic E. coli with their associated adhesins and toxins were present in calves as early as 1958, but their prevalence seems to have increased since that time.

Cytotoxic necrotizing factor type 1 of uropathogenic Escherichia coli kills cultured human uroepithelial 5637 cells by an apoptotic mechanism

Pathogenic Escherichia coli associated with urinary tract infections (UTIs) in otherwise healthy individuals frequently produce cytotoxic necrotizing factor type 1 (CNF1), a member of the family of bacterial toxins that target the Rho family of small GTP-binding proteins. To gain insight into the function of CNF1 in the development of E. coli-mediated UTIs, we examined the effects of CNF1 intoxication on a panel of human cell lines derived from physiologically relevant sites (bladder, ureters, and kidneys). We identified one uroepithelial cell line that exhibited a distinctly different CNF1 intoxication phenotype from the prototypic one of multinucleation without cell death that is seen when HEp-2 or other epithelial cells are treated with CNF1. The 5637 bladder cell line detached from the growth surface within 72 h of CNF1 intoxication, a finding that suggested frank cytotoxicity. To determine the basis for the unexpected toxic effect of CNF1 on 5637 cells, we compared the degree of toxin binding, actin fiber formation, and Rho modification with those CNF1-induced events in HEp-2 cells. We found no apparent difference in the amount of CNF1 bound to 5637 cells and HEp-2 cells. Moreover, CNF1 modified Rho, in vivo and in vitro, in both cell types. In contrast, one of the classic responses to CNF1 in HEp-2 and other epithelial cell lines, the formation of actin stress fibers, was markedly absent in 5637 cells. Indeed, actin stress fiber induction by CNF1 did not occur in any of the other human bladder cell lines that we tested (J82, SV-HUC-1, or T24). Furthermore, the appearance of lamellipodia and filopodia in 5637 cells suggested that CNF1 activated the Cdc42 and Rac proteins. Finally, apoptosis was observed in CNF1-intoxicated 5637 cells. If our results with 5637 cells reflect the interaction of CNF1 with the transitional uroepithelium in the human bladder, then CNF1 may be involved in the exfoliative process that occurs in that organ after infection with uropathogenic E. coli.

The afa-related gene cluster in necrotoxigenic and other Escherichia coli from animals belongs to the afa-8 variant

Six hundred and nine necrotoxigenic Escherichia coli type 1 and 2 (NTEC1 and NTEC2) and non-NTEC isolated in Western and Southern Europe, North Africa and Canada from diseased calves, pigs, humans, poultry, and 55 isolated from asymptomatic calves were studied for the identification of afa-related sequences to the recently described afa-7 and afa-8 gene cluster variants from two bovine Escherichia coli (Lalioui et al., 1999). Colony hybridization and PCR assays for the afaD-7, afaE-7, afaD-8 and afaE-8 identified the afa-related sequences to the afa-8 gene cluster in most (67/79; 85%) of the E. coli positive with the Afa-f family probe and in 14 additional strains negative with the Afa-f probe. No E. coli was positive for the afa-7 gene cluster. The existence of afa-8 positive strains was thus confirmed among bovine E. coli and for the first time among porcine, poultry and human E. coli. Sequencing of the afaE-8 amplicon of nine strains from the different host species showed a high degree of conservation (>95% at the DNA level; >92% at the amino-acid level). The afa-8 gene cluster was more frequent in E. coli from diseased calves (18%) than from piglets (12%), humans (6%) and poultry (5%). Bovine NTEC2 (26%) were more frequently positive than NTEC 1 (20%) and non-NTEC (11%). E. coli isolated from asymptomatic calves were rarely positive: one NTEC2 (3%) and no non-NTEC. The afa-8 gene cluster was located on the Vir plasmid in 11/23 NTEC2, but no plasmid localization was detected in NTEC1 or non-NTEC.

Prevalence of virulence genes and clonality in Escherichia coli strains that cause bacteremia in cancer patients

Phenotypic analysis of Escherichia coli strains causing bacteremia in cancer patients suggests that they possess specific virulence properties. To investigate this hypothesis, we compared the frequency of the virulence-related genes cnf1, cnf2, papC, hlyC, and iut in 155 E. coli strains isolated from hospitalized cancer patients with epidemiologically unrelated cases of bacteremia to their frequency in 70 E. coli strains isolated from the feces of healthy unrelated volunteers. Of the blood isolates, 24, 37, and 26% were positive for cnf1, papC, and hlyC, respectively, versus only 6, 17, and 6% of the fecal isolates (P < 0.05 in all instances). By contrast, 47% of both isolates carried the iut gene. The patients' clinical characteristics did not significantly influence these frequencies. The presence on various pathogenicity islands (PAIs) of a combination of the cnf1, papC, and hlyC genes on the chromosome was strongly suggested by Southern blotting of pulsed-field gel electrophoresis (PFGE) patterns with specific DNA probes. The phylogenetic relatedness among 60 strains carrying three, two, one, or no virulence genes and 6 ECOR strains included as references was determined by neighbor joining, the unweighted pair-group method with arithmetic mean, and Wagner analysis of the randomly amplified polymorphic DNA (RAPD) patterns generated by 11 primers. Identification of a major cluster including 96.4% of the strains carrying the cnf1, papC, and hlyC genes and ECOR subgroup B2 strains suggested that the virulent E. coli strains causing bacteremia in cancer patients are closely related to ECOR B2 strains. The presence in the E. coli population surveyed of a strong linkage disequilibrium, and especially of a highly significant correlation between PFGE and RAPD genetic distances, confirms that clonal propagation has a major impact on the E. coli population structure. Nevertheless, low bootstrap values in the phylogenetic tree suggested that frequent genetic exchange inhibits the individualization of discrete genetic lineages, which are stable on an evolutionary scale.

Identification of the F17 fimbrial subunit- and adhesin-encoding (f17A and f17G) gene variants in necrotoxigenic Escherichia coli from cattle, pigs and humans

Putative colonization factors of the F17 family of fimbrial adhesins have been identified in necrotoxigenic Escherichia coli Type 1 and Type 2 (NTEC1 and NTEC2) from calves, pigs, and humans. The f17A and f17G gene variants, coding respectively for the major subunit and for the adhesin of the F17 fimbriae, were typed in 70 E. coli carrying f17-related sequences (15 NTEC1, 51 NTEC2, and four non-NTEC) by colony hybridisation with gene probes derived from the different f17A gene variants (a, b, c, and d) and by PCRs specific for each f17A and f17G (I and II) gene variants. Typing of f17A genes was not possible by colony hybridisation, as most 70 E. coli were positive with more than one gene probe. On the other hand, the PCRs allowed the typing of the f17A gene in 37 E. coli and of the f17G gene in all 70 E. coli. The f17Ab gene variant was detected in 13 NTEC2; the f17Ac, in all 15 NTEC1, six NTEC2 and two non-NTEC; and the f17Ad, in one non-NTEC. Seven additional NTEC2 were positive with the PCRs for two variants: f17Ab and f17Ac in three of them; f17Ac and f17Ad in four of them. Either these seven NTEC2 harbour two variants or the variant present can be detected by two PCRs. The remaining 25 NTEC2 and one non-NTEC tested negative with the PCRs for the four f17A gene variants, suggesting the existence of other variant(s). In contrast, all 70 E. coli were positive with the PCR for the f17GII gene variant and none with the PCR for the f17GI gene variant. The f17-related sequences were present on the CNF2/Vir plasmids in 27 out of the 46 NTEC2 from which plasmid DNA could be extracted: all but one of those positive for the f17Ab gene variant and various proportions of those positive for other variants. In contrast, no plasmid carried f17-related sequences in NTEC1 and non-NTEC.

The role of cytotoxic necrotizing factor-1 in colonization and tissue injury in a murine model of urinary tract infection

Cytotoxic necrotizing factor-1 (CNF1) is commonly found in Escherichia coli isolates from patients with urinary tract infection (UTI). To determine whether CNF1 is an important UTI virulence factor we compared the ability of a clinical E. coli UTI isolate and a CNF1-negative mutant of that isolate to colonize and induce histological changes in the urinary tract in a murine model of ascending UTI. We found no evidence that the mutant strain was attenuated.

Frequency of Escherichia coli strains producing the cytotoxic necrotizing factor (CNF1) in nosocomial urinary tract infections

The presence of cytotoxic necrotizing factor 1 (CNF1), together with various associated virulence factors (alpha-haemolysin, P-, S- and A-fimbriae), was screened in 175 uropathogenic Escherichia coli strains isolated from hospitalized adult patients. The cnf1 gene was detected in 30% of the selected strains independently of the severity of the clinical urinary infection. A significant association between CNF1, haemolytic activity and the products of the pap/sfa genes was found. However, CNF1 appeared not to play a major role in nosocomial E. coli urinary tract infections.

Lack of a role of cytotoxic necrotizing factor 1 toxin from Escherichia coli in bacterial pathogenicity and host cytokine response in infected germfree piglets

Some Escherichia coli strains isolated from intestinal or extraintestinal infections in pigs produce cytotoxic necrotizing factor 1 (CNF1). In order to analyze the role of CNF1 in the pathogenesis of porcine colibacillosis, newborn colostrum-deprived germfree piglets were orally inoculated with a wild-type CNF1-producing strain (M623) or with an isogenic cnf1 mutant (M623DeltaCNF1). The two isogenic strains induced a high mortality with similar lung and serosal inflammatory lesions, indicating that both strains were pathogenic in these piglets. Bacterial counts in various organs of inoculated piglets revealed an intestinal predisposition of M623 and M623DeltaCNF1 strains for the cecum and colon. Extraintestinal organs (lungs, liver, spleen, and kidney) were also colonized by both strains. Similar colonization of intestinal and extraintestinal tissues in animals inoculated with either strain was observed, except in the ileum, where M623 showed a higher colonization than M623DeltaCNF1. Intestinal (ileum and colon), extraintestinal (lung and kidney), and immune (mesenteric lymph nodes and spleen) tissues were sampled at 1 day postinoculation and analyzed for cytokine expression by a reverse transcriptase PCR technique. Inoculation with E. coli M623 induced an enhanced expression of inflammatory cytokines (interleukin-1alpha [IL-1alpha], tumor necrosis factor alpha, and IL-12p40) in the intestinal organs compared to uninoculated piglets or piglets inoculated with nonpathogenic intestinal E. coli 862B, which is also able to colonize the intestinal tract. There was little difference in cytokine transcript levels in the intestinal and extraintestinal organs in piglets inoculated with E. coli strains M623 or M623DeltaCNF1, except in the ileum, where IL-1alpha and IL-8 mRNA levels correlated with bacterial colonization. Expression of regulatory cytokines (gamma interferon and IL-4) was weak in immune tissues from piglets inoculated with M623 or M623DeltaCNF1. Taken together, our data indicate that the CNF1-producing strain, M623, is pathogenic and induces inflammatory cytokine expression in germfree, colostrum-deprived piglets. Nevertheless, in this model, the CNF1 toxin does not appear to be a major factor for pathogenicity or cytokine response, as demonstrated by the use of an isogenic cnf1 mutant.

Postantibiotic effects of gentamicin and netilmicin on Serratia marcescens: effects on hydrophobicity and motility

The impact of postantibiotic effect (PAE) of aminoglycosides (gentamicin, netilmicin) on cell-surface hydrophobicity and motility of a clinical isolate Serratia marcescens was evaluated. For the induction of PAE 2x and 4xMIC concentrations of both antibiotics were used. Gentamicin and netilmicin induced a PAE of similar duration after 2xMIC concentration (2.7 and 2.8 h, respectively). Both aminoglycosides demonstrated concentration-dependent PAE. At a concentration of 4xMIC they produced PAEs of 5.9 and 8.2 h, respectively. The evaluation of hydrophobic properties of S. marcescens after affecting PAE showed that both aminoglycosides inhibited adherence to xylene. This inhibition was also concentration-dependent. More expressive was netilmicin which inhibited the adhesion by 70.5% at 2xMIC and by 85.2% at 4xMIC. Netilmicin inhibited also the adhesion to nitrocellulose filter by 34.7% at 4xMIC. Exposure of the bacterial cells to suprainhibitory concentrations of both aminoglycosides resulted only in moderate inhibition of motility of strain tested compared to the unexposed cells.

Comparison of necrotoxigenic Escherichia coli isolates from farm animals and from humans

Necrotoxigenic Escherichia coli (NTEC) isolated from animals and humans can belong to the same serogroups/types and produce or carry the genes coding for fimbrial and afimbrial adhesins of the same family, P, S, F17, and/or AFA, raising the question of a potential zoonotic source of human infection. The main purpose of this study was to compare 239 NTEC1 strains (45 from cattle, 65 from humans and 129 from piglets) and 98 NTEC2 strains from cattle, using a uniform and standardized typing scheme. The O serogroups and the biotypes recognized amongst NTEC1 and NTEC2 strains were quite varied, although some were more frequently observed (serogroups O2, O4, O6, O8, O18, O78, and O83 and biotypes 1, 2, 5, 6, and 9). Hybridization, results with gene probes for the P family (PAP probe), S family (SFA probe), AFA family (AFA probe), F17 family (F17 probe) of fimbrial and afimbrial adhesins, could differentiate most NTEC1 strains, which are PAP-, SFA- and/or AFA-positive, from NTEC2 strains, which are mainly F17- and/or AFA-positive, but were of no help in differentiating between NTEC1 strains from cattle, humans, and piglets. All but seven (98%) NTEC1 and NTEC2 strains were serum resistant, 199 (59%) produced an aerobactin, and colicin (I, V, or unidentified) was produced by 22-34% of them. On the other hand, more than 90% of the NTEC1 strains were haemolytic on sheep blood agar compared with only 40% of the NTEC2 strains. Production of a classical haemolysin, active on sheep erythrocytes, and hybridization with the PAP probe were associated in a majority of NTEC1 strains (63-81%), but very rarely in NTEC2 strains (3%). Production of enterohaemolysin and hybridization with the PAP probe were much less frequently associated in NTEC strains (1-9%). It was thus possible neither to completely differentiate NTEC1 strains from cattle, humans, and pigs, nor to define a signature for the NTEC strains. Necrotoxigenic E. coli must still be identified on the basis of the production of the Cytotoxic Necrotizing Factors 1 or 2 (or of their encoding genes) and complete differentiation of NTEC1 strains from cattle, humans, and piglets, use additionnal methods.

Cytotoxicity of hemolytic, cytotoxic necrotizing factor 1-positive and -negative Escherichia coli to human T24 bladder cells

Approximately one-half of Escherichia coli isolates from patients with cystitis or pyelonephritis produce the pore-forming cytotoxin hemolysin, a molecule with the capacity to lyse erythrocytes and a range of nucleated cell types. A second toxin, cytotoxic necrotizing factor 1 (CNF1), is found in approximately 70% of hemolytic, but rarely in nonhemolytic, isolates. To evaluate the potential interplay of these two toxins, we used epidemiological and molecular biologic techniques to compare the cytotoxicity of hemolytic, CNF1(+), and CNF1(-) cystitis strains toward human T24 bladder epithelial cells in vitro. A total of 29 isolates from two collections of cystitis-associated E. coli were evaluated by using methylene blue staining of bladder monolayers at 1-h intervals after inoculation with each strain. Most (20 of 29) isolates damaged or destroyed the T24 monolayer (less than 50% remaining) within 4 h after inoculation. As a group, CNF1(+) isolates from one collection (11 strains) were less cytotoxic at 4 h than the CNF1(-) strains in that collection (P = 0.009), but this pattern was not observed among isolates from the second collection (18 strains). To directly evaluate the role of CNF1 in cytotoxicity of hemolytic E. coli without the variables present in multiple clinical isolates, we constructed mutants defective in production of CNF1. Compared to the CNF1(+) parental isolates, no change in cytotoxicity was detected in these cnf1 mutants. Our results indicate that CNF1 does not have a detectable effect on the ability of hemolytic E. coli to damage human bladder cell monolayers in vitro.

Postantibiotic effects of imipenem and enoxacin against S. typhimurium and S. enteritidis and the influence on their surface hydrophobicity

The influence of the postantibiotic effect (PAE) and the postantibiotic sub-MICs effect (PA SME) of imipenem and enoxacin on the surface hydrophobicity of S. typhimurium and S. enteritidis strains were studied by evaluating Congo red binding and the aggregation in molar solutions of ammonium sulfate (SAT). A PAE was induced by 2x and 4 x MIC of antibiotics tested for 0.5 h. Suprainhibitory concentrations of imipenem against S. typhimurium induced a short PAE (0.3-0.6 h) compared to S. enteritidis (6.0-9.7 h). Suprasubinhibitory concentrations of imipenem did not allow a regrowth of S. enteritidis. Similar results were also found for enoxacin. Evaluation of surface hydrophobic properties of the salmonellas after affecting both PAEs and PA SMEs has shown that imipenem at concentrations 4 x MIC and 4 x MIC + 0.3 x MIC partially influenced the hydrophobicity of S. typhimurium. S. enteritidis was more susceptible toward both antibiotics tested.

Interactions between bacterial toxins and intestinal cells

Bacterial toxins which act on intestinal cells display a great diversity of size, structure and mode of action. Some toxins interact with the cell by transducing a signal across the membrane leading to stimulation of intracellular second messenger (E. coli heat stable enterotoxin), others form pores (C. perfringens enterotoxin, ...) permitting the leakage of cellular components and cell lysis. The most sophisticated toxins comprise at least two functional domains or components, one being a binding domain permitting the internalization into the cell of an enzymatic domain which modifies an intracellular target. The enzymatic modification (ADP-ribosylation, UDP-glucosylation, glycohydrolysis, proteolysis, ...) of a specific target (heterotrimeric G-protein, small G-protein, monomeric actin, ribosomal RNA, ...) alters the cell physiology (increase of ions and water secretion, cytoskeleton rearrangement, protein synthesis inhibition, apoptosis, ...) and tissue organization (modification of barrier permeability, necrosis, ...). The study of bacterial toxins leads to the understanding of the interactions between pathogenic bacteria and their hosts and constitutes also a new approach in cell biology, by facilitating the exploration of certain regulatory pathways such as that controlling actin polymerization.

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.

Production of toxins (enterotoxins, verotoxins, and necrotoxins) and colicins by Escherichia coli strains isolated from septicemic and healthy chickens: relationship with in vivo pathogenicity

Since the mechanism of virulence of Escherichia coli strains pathogenic to birds is not fully understood, the prevalence of toxic factors produced by E. coli strains pathogenic to other animals was investigated. A total of 625 E. coli strains isolated from visceral organs of chickens with colisepticemia and from feces of healthy chickens in Spain were tested for production of enterotoxins (heat labile [LT] and heat stable [STa]), verotoxins (VT1, VT2, and VT2v), cytotoxic necrotizing factors (CNF1 and CNF2), alpha-hemolysin (Hly), enterohemolysin (EntHly), colicin V (Col V) and other types of colicins, and necrotic and lethal activities. Only 45 (7%) of avian E. coli strains were toxigenic: 20 strains produced a cytotoxic response in HeLa but not in Vero cells, indicating the production of a cytotoxin not related to the VTs; 16 were EntHly+; 5 produced a new cytotonic product that causes the appearance of whitish vacuola in Vero and HeLa cells; 3 synthesized soluble factors that cause lethal activity in mice; and 1 elaborated LT. None of 625 avian E. coli strains was positive for production of VTs or CNFs. In contrast, colicinogenicity occurred in 335 (73%) of the 458 septicemic strains and 97 (58%) of 167 fecal isolates (P < 0.01), and this property was correlated with in vivo pathogenicity of strains. Thus, 80% (P < 0.001) and 66% (P < 0.001) of strains producing Col V and other types of colicins were characterized as being of high pathogenicity, whereas only 15% of the noncolicinogenic strains were classified as highly pathogenic. Our results clearly support the special pathogenicity theory, because 60% of the E. coli strains belonging to 18 serogroups (O1, O2, O5, O8, O12, O14, O15, O18, O20, O53, O78, O81, O83, O102, O103, O115, O116, and O132) most frequently identified among clinical septicemic strains were classified as highly pathogenic in in vivo assays, whereas only 24% of the strains with O serogroups less prevalent among diseased chickens were considered highly pathogenic (P < 0.01).

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.

CNF producing Escherichia coli isolated from cattle in Northern Ireland

Tissue culture assays were used to investigate the incidence of cytotoxic necrotising factors (CNFs) 1 and 2 in Escherichia coli strains from cattle. E. coli cultures were obtained from faeces collected from 223 cases of diarrhoea and from 113 healthy animals. In addition, strains cultured from 62 cases of mastitis, 66 cases of septicaemia and 68 cases of abortion were also investigated. E. coli producing CNF 1 or 2 were identified in all sample groups except for the abortion cases. Comparable levels of CNF1 strains were present in E. coli from the faces of diarrhoeic (4%) and healthy faeces (4.4%) whereas lower levels of CNF2 were identified in the faeces from diarrhoeic animals (19.3%) in comparison with healthy animals (30.9%). One CNF1 producing strain was identified among the E. coli isolated from mastitis samples, while 3% and 10.6% of septicaemic strains were positive for CNF1 and 2, respectively. Serogrouping of CNF isolates did not reveal the association of any particular serogroups with the different conditions.

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.

Fimbriae extracts from enterotoxigenic Escherichia coli strains of bovine and porcine origin with K99 and/or F41 antigens

Fimbriae extracts obtained using the thermal shock method, from bovine and porcine enterotoxigenic Escherichia coli strains with K99 and/ or F41 antigens, were analyzed by SDS-PAGE, immunoblotting and haemagglutinating activity. Three major protein bands with molecular weights 17 kDa, 29.3 kDa and 30.9 kDa were detected depending on the strain assayed. A 17 kDa band was identified as the fimbrial subunit for K99 fimbriae and was detected in strains of bovine and porcine origin. The 30.9 kDa band was identified as the fimbriae subunit for F41 fimbriae and was detected in all porcine strains with F41 antigen and only in the bovine strains of serogroups O9 and 0101 that proved positive for F41 antigen. The 29.3 kDa band was shown to be antigenically related to F41 and K88, and was only detected in bovine strains of serogroups O8 (5 strains) and O20 (a single strain). We speculate that the 29.3 kDa band may be related to the CS31A antigen.

Escherichia coli cytotoxic necrotizing factor 1: evidence for induction of actin assembly by constitutive activation of the p21 Rho GTPase

Cytotoxic necrotizing factor type 1 (CNF1) induces in HEp-2 cells an increase in F-actin structures, which was detectable by fluorescence-activated cell sorter analysis 24 h after addition of this factor to the culture medium. Increase in F-actin was correlated with the augmentation of both the cell volume and the total cell actin content. Actin assembly-disassembly is controlled by small GTP-binding proteins of the Rho family, which have been reported recently to be modified by CNF1 treatment. Clostridium difficile toxin B and Clostridium botulinum exoenzyme C3, both known to act on the Rho GTPase, were used as biological tools to study the effect of CNF1 on this protein. CNF1 incubated before, during, or after exposure to the chimeric toxin C3B (which is the product of a genetic fusion between the DNA coding for C3 and the one coding for the B fragment of diphtheria toxin) protected HEp-2 cells from the disruption of F-actin structures caused by inactivation of the Rho GTPase through its ADP-ribosylation. On the other hand, C. difficile toxin B cytopathic effect was not observed upon preincubation of cells with CNF1. Toxins acting through a Rho-independent mechanism, such as cytochalasin D and Clostridium spiroforme iota-like toxin, could not be modified in their cellular activities by CNF1 treatment. All of our results suggest that CNF1 modifies the Rho molecule, thus probably protecting this GTPase from further bacterial toxin modification.

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

The O:K:H serotypes of 137 necrotoxigenic Escherichia coli (NTEC) producing the cytotoxic necrotizing factor type 1 (CNF1) isolated from human extraintestinal infection were determined. Although NTEC producing CNF1 belonged to 58 different serotypes, only 10 of them accounted for 54% of strains. The most common serotypes, in order of frequency, were: O4:K?:H5, O6:K13:H1, O83:K1:H31, O75:K95:H5, O2:K1:H6, O2:K7:H-, O75:K1:H7, O2:K?:H1, O4:K12:H1 and O22:K13:H1. CNF1 strains of serotypes O2:K7:H- and O4:K12:H1 express P-fimbriae, whereas CNF1 strains of serotypes O2:K?:H1, O2:K1:H6 and O75:K95:H5 possess the adhesin responsible for MRHA type III. Among CNF1 strains of serotype O4:K?:H5 there exist some that express P-fimbriae and others that possess MRHA type III. Lastly, the majority of CNF1 strains of serotypes O6:K13:H1, O22:K13:H1, O75:K1:H7 and O83:K1:H31 do not express P-fimbriae nor the adhesin responsible to MRHA type III. Our results show that extraintestinal infections are caused by a limited number of virulent clones, as suggested by the theory of special pathogenicity.

Fimbriation, surface hydrophobicity and serum resistance in uropathogenic strains of Escherichia coli

A total of 80 Escherichia coli strains were examined for expression of P-fimbriae, mannose-sensitive haemagglutination (MSHA) and mannose-resistant haemagglutination (MRHA) of human group A erythrocytes and guinea pig erythrocytes, cell surface hydrophobicity and resistance to serum bactericidal activity. Isolates were obtained from urine of children and adults, either with acute pyelonephritis (n = 15 and n 12) or lower urinary tract infection (UTI) (n = 30 and n = 23, respectively). Results obtained showed that, in E. coli strains isolated both from children and adults with lower UTI, significant differences were not found concerning the incidence of P-fimbriae, cell surface hydrophobicity and serum resistance. In pyelonephritogenic E. coli isolated from children and adults, the incidence of P-fimbriae and cell surface hydrophobicity was associated more frequently with the former (87% vs. 42% and 100% vs. 67%, P < 0.05), while serum resistance was associated with the latter (47% vs. 67%, P < 0.05).

Serotypes of bovine Escherichia coli producing cytotoxic necrotizing factor type 2 (CNF2)

The serotypes of 101 faecal bovine necrotoxigenic Escherichia coli (NTEC) producing the cytotoxic necrotizing factor type 2 (CNF2) were determined. Although, NTEC producing CNF2 belonged to 48 different O:K:H serotypes, only eleven of them accounted for 54% of strains. The most common serotypes in order of frequency were: O123:K-:H16, O3:K-:H21, O88:K-:H8, O15:K14:H21, O1:K-:H12, O1:K1:H46, O2:K1:H5, O55:H21, O88:K?:H25, O117:K?:H21 and O123:K-:H-. The serotypes of CNF2 NTEC were different from those found in NTEC producing CNF1 and in enterotoxigenic, verotoxigenic, enteropathogenic, enteroinvasive and enteroadherent E. coli strains that cause infections in humans and animals.