Plasmids coding for enterotoxins, K88 antigen and colicins in porcine Escherichia coli strains of O-group 149

Relationship between virulence factors and antimicrobial resistance genes of pathogenic Escherichia coli from diarrheic weaned piglets

A total of 690 pathogenic Escherichia (E.) coli isolates from weaned piglets were examined for antimicrobial resistance phenotypes, resistance genes, and virulence gene profiles. Also, 29 enterotoxigenic E. coli (ETEC) and 35 Shiga-toxin producing E. coli (STEC) isolates were analyzed using multi-locus sequence typing (MLST). Comparisons of the associations between antimicrobial resistance phenotypes, resistance genes, and virulence genes were performed separately by assessing odds ratio (OR). Although majorities of associations were not confirmed however, we found that associations between specific virulence factors-antimicrobial resistance. F18 encoding isolates showed association with resistance to cefazolin (OR = 3.08) and cefoxitin (OR = 3.65), and also with antimicrobial resistance gene mcr-3 (OR = 4.58). There was a high correlation between F4-STb (OR = 13.56), F4-LT (OR = 8.77), F4-EAST-I (OR = 4.97), and F18-Stx2e (OR = 3.83). Most of ETEC (21 of 29, 72.4%) isolates were assigned to ST100, and 20 of 35 STEC isolates (57.1%) were ST1. There were 5 clusters, and each cluster showed specific antimicrobial resistance patterns. Cluster I showed resistance to gentamicin, streptomycin, neomycin, nalidixic acid, ciprofloxacin, norfloxacin, trimethoprim / sulfamethoxazole, and tetracyclines whereas, cluster V showed resistance to ampicillin, amoxicillin / clavulanic acid, cephalothin, cefoxitin, cefazolin, norfloxacin, and colistin. Although there is need to do more experiments to clarify why certain virulence factors showed relationship with antimicrobial resistance, it is clear that there is a significant association between specific virulence genes and antimicrobial resistance in E. coli from weaned piglets with enteric colibacillosis in Korea.

An Integrated Perspective on Virulence-Associated Genes (VAGs), Antimicrobial Resistance (AMR), and Phylogenetic Clusters of Pathogenic and Non-pathogenic Avian Escherichia coli

Avian pathogenic Escherichia coli (APEC) is an important bacterial pathogen that causes avian colibacillosis and leads to huge economic losses in the poultry industry. Different virulence traits contribute to pathogenesis of APEC infections, and antimicrobial resistance (AMR) has also been an overwhelming issue in poultry worldwide. In the present study, we aimed to investigate and compare the presence of virulence-associated genes (VAGs), AMR, and phylogenetic group's distribution among APEC and avian fecal E. coli (AFEC) strains. E. coli from birds with colisepticemia and yolk sac infection (YSI) (APEC) plus E. coli strains from the feces of healthy birds (AFEC) were compared by the aforementioned traits. In addition, the clonal relatedness was compared using Enterobacterial repetitive intergenic consensus PCR (ERIC-PCR). Although all strains were susceptible to fosfomycin, ceftriaxone, and cefixime, almost all strains (98%) were multi-drug resistant (MDR). All strains (except two) harbored at least three or more VAGs, and the virulence scores tended to be higher in pathogenic strains especially in the colisepticemic group. All phylogenetic groups were found in isolates from YSI, colisepticemia, and the feces of healthy birds; however, the frequency of phylogroups varied according to the source of the isolate. B1 and C phylogroups were statistically more likely to be found among APEC from YSI and colisepticemic E. coli groups, respectively, while phylogroup A was the most frequently occurring phylogroup among AFEC strains. Our findings also revealed that AMR and VAGs are not essentially co-evolved traits as in some instances AMR strains were more prevalent among AFEC. This reflects the divergent evolutionary pathways of resistance acquisition in pathogenic or non-pathogenic avian E. coli strains. Importantly, strains related to phylogenetic group C showed higher virulence score and AMR that requires further attention. To some extent, ERIC-PCR was able to group strains by isolation source, phylogroup, or virulence genes. Further integrated studies along with assessment of more detailed genotypic and phenotypic features could potentially lead to better understanding of virulence, resistance, and evolution of ExPEC.

Animal Enterotoxigenic Escherichia coli

Enterotoxigenic Escherichia coli (ETEC) is the most common cause of E. coli diarrhea in farm animals. ETEC are characterized by the ability to produce two types of virulence factors: adhesins that promote binding to specific enterocyte receptors for intestinal colonization and enterotoxins responsible for fluid secretion. The best-characterized adhesins are expressed in the context of fimbriae, such as the F4 (also designated K88), F5 (K99), F6 (987P), F17, and F18 fimbriae. Once established in the animal small intestine, ETEC produce enterotoxin(s) that lead to diarrhea. The enterotoxins belong to two major classes: heat-labile toxins that consist of one active and five binding subunits (LT), and heat-stable toxins that are small polypeptides (STa, STb, and EAST1). This review describes the disease and pathogenesis of animal ETEC, the corresponding virulence genes and protein products of these bacteria, their regulation and targets in animal hosts, as well as mechanisms of action. Furthermore, vaccines, inhibitors, probiotics, and the identification of potential new targets by genomics are presented in the context of animal ETEC.

Adhesins of Enterotoxigenic Escherichia coli Strains That Infect Animals

The first described adhesive antigen of Escherichia coli strains isolated from animals was the K88 antigen, expressed by strains from diarrheic pigs. The K88 antigen was visible by electron microscopy as a surface-exposed filament that was thin and flexible and had hemagglutinating properties. Many different fimbriae have been identified in animal enterotoxigenic E. coli (ETEC) and have been discussed in this article. The role of these fimbriae in the pathogenesis of ETEC has been best studied with K88, K99, 987P, and F41. Each fimbrial type carries at least one adhesive moiety that is specific for a certain host receptor, determining host species, age, and tissue specificities. ETEC are the most frequently diagnosed pathogens among neonatal and post-weaning piglets that die of diarrhea. Immune electron microscopy of animal ETEC fimbriae usually shows that the minor subunits are located at the fimbrial tips and at discrete sites along the fimbrial threads. Since fimbriae most frequently act like lectins by binding to the carbohydrate moieties of glycoproteins or glycolipids, fimbrial receptors have frequently been studied with red blood cells of various animal species. Identification and characterization of the binding moieties of ETEC fimbrial adhesins should be useful for the design of new prophylactic or therapeutic strategies. Some studies describing potential receptor or adhesin analogues that interfere with fimbria-mediated colonization have been described in the article.

Antimicrobial resistance, virulence genes, and phylogenetic background in Escherichia coli isolates from diseased pigs

Escherichia coli isolates from diseased pigs were examined for antimicrobial susceptibility to 12 antimicrobials and possession of virulence genes (VGs), and then grouped according to the phylogenetic background and genetic relatedness. Associations between antimicrobial resistance (AMR) and VGs and between AMR and phylogenetic group were subsequently assessed. The results showed that most isolates (91%) were epidemiologically unrelated. Multiple antimicrobial-resistant phenotypes (>or=5 antimicrobials) were observed in 89% of E. coli strains and the most frequent types of resistance were to sulfamethoxazole (95%), tetracycline (94%), chloramphenicol (89%), and streptomycin (84%). The majority of isolates belonged to phylogenetic group A (84%). The most prevalent VG was EAST1 (64%), followed by Stx2e (63%) and eae (47%). Resistance to ceftiofur was associated with the presence of certain VGs, whereas resistance to doxycycline and kanamycin was associated with the absence of certain VGs. These findings suggest that multidrug resistance phenotypes, a variety of VGs, and the clear associations between resistance and VGs are commonly present in E. coli strains from diseased pigs. These results indicate that there is a great need for surveillance programs in China to monitor AMR in pathogenic E. coli strains.

Virulence genes of O149 enterotoxigenic Escherichia coli from outbreaks of postweaning diarrhea in pigs

The goal of this research was to determine whether isolates of O149 porcine enterotoxigenic Escherichia coli (ETEC) recovered from recent outbreaks of severe diarrhea in weaned pigs in Ontario, Canada, had virulence attributes different from those of isolates of the same serogroup from diarrhea of pigs in the 1970s and 1980s. Polymerase chain reaction amplification was used to determine the distribution of 11 virulence-associated genes in recent (100 isolates) and old (35 isolates) Ontario O149 porcine ETEC. These tests demonstrated that 92% of the recent isolates possessed the estA gene for STa enterotoxin, whereas none of the old isolates had this gene. H antigen determination showed that all the isolates which lacked the estA gene (all 35 old isolates plus 8 recent isolates) were H43, whereas isolates which had the estA gene were H10. The astA gene for enteroaggregative heat-stable enterotoxin (EAST1) and the K88ac antigen were present in all 135 isolates. Plasmid analyses identified a cryptic 5.1kb plasmid in 99% of recent and 60% of old isolates. Suppressive subtractive hybridization associated several types of DNA fragments with the recent O149 ETEC, namely, fragments with no homology to DNA in databases, fragments of LPS biosynthesis genes, and F plasmid DNA. We conclude that the recent outbreaks of PWD in Ontario pigs were associated primarily with a new serotype of O149 ETEC and that isolates of this serotype possessed the estA gene that was not present in old O149 ETEC isolated from pigs in Ontario.

Interactions among strategies associated with bacterial infection: pathogenicity, epidemicity, and antibiotic resistance

Infections have been the major cause of disease throughout the history of human populations. With the introduction of antibiotics, it was thought that this problem should disappear. However, bacteria have been able to evolve to become antibiotic resistant. Nowadays, a proficient pathogen must be virulent, epidemic, and resistant to antibiotics. Analysis of the interplay among these features of bacterial populations is needed to predict the future of infectious diseases. In this regard, we have reviewed the genetic linkage of antibiotic resistance and bacterial virulence in the same genetic determinants as well as the cross talk between antibiotic resistance and virulence regulatory circuits with the aim of understanding the effect of acquisition of resistance on bacterial virulence. We also discuss the possibility that antibiotic resistance and bacterial virulence might prevail as linked phenotypes in the future. The novel situation brought about by the worldwide use of antibiotics is undoubtedly changing bacterial populations. These changes might alter the properties of not only bacterial pathogens, but also the normal host microbiota. The evolutionary consequences of the release of antibiotics into the environment are largely unknown, but most probably restoration of the microbiota from the preantibiotic era is beyond our current abilities.

Colicin V virulence plasmids

ColV plasmids are a heterogeneous group of IncFI plasmids which encode virulence-related properties such as the aerobactin iron uptake system, increased serum survival, and resistance to phagocytosis. These plasmids have been found in invasive strains of Escherichia coli which infect vertebrate hosts including humans and livestock. Colicin V was the first colicin to be identified, in 1925, but not until the field experienced a renewed interest has the mechanism of colicin V activity been explored. As encoded by ColV plasmid pColV-K30, the aerobactin iron uptake system has been extensively investigated, but other ColV-encoded phenotypes remain largely uncharacterized. Restriction enzyme mapping of the 144-kb pColV-K30 and of the 80-kb pColV-B188 has facilitated systematic study, so that questions can be addressed by a molecular and comparative approach regarding the contributions of individual factors and plasmids to the virulence of host E. coli in model systems. The family of large ColV plasmids could be analogous to other families of large virulence plasmids, and insights gained from studying these plasmids should contribute to our understanding of cross-genetic interactions and the role of large plasmids in bacterial pathogenesis.

Specific DNA fragments coding for ST1 and LT1 toxins, and K88 (F4) adhesin in enterotoxigenic Escherichia coli

Ten porcine strains of enterotoxigenic Escherichia coli possessing the K88 (F4) adhesion fimbriae, were selected for study of enterotoxin- and fimbriae-encoding plasmids. Plasmid DNA, separated according to size by gel electrophoresis was transferred to nylon membranes by Southern blotting, and hybridized with enzyme-labelled oligonucleotide probes for ST1 and LT1 enterotoxins, and a 32P-labelled probe for the F4 fimbriae. Plasmids possessing the enterotoxin genes ranged from 50 MDa to 78 MDa in size. The ST1 genes were located on a common 8-MDa EcoR1 restriction endonuclease fragment, while the LT1 genes were located on a 4.5-MDa EcoR1 fragment from the different plasmids. Plasmids with the F4 genes ranged from 50 MDa to 118 MDa in size, but the F4 encoding genes were located on a common 3-MDa HindIII restriction endonuclease fragment. ST1 and LT1 genes were found on the same plasmid in only one strain, LT1 and F4 genes on the same plasmids in 5 strains, while no plasmid contained genes for both ST1 and F4.

Plasmid profile analysis and restriction enzyme fingerprinting of Salmonella DO-group strains

In Sweden Salmonella dublin is the most common serotype within the DO-group isolated from animals. In recent years also salmonella strains belonging to the DO-group but lacking H-antigen have been isolated from cattle in different areas. It was not possible to further differentiate the latter strains by serological methods. However, all Salmonella dublin strains and those strains lacking H-antigen carried a 50 Mdal plasmid exhibiting the same EcoRI and Hind III restriction enzyme digestion pattern. Two of the 26 strains contained an additional 5 Mdal plasmid. Other serotypes within the DO-group investigated, namely Salmonella enteritidis and Salmonella panama, carried plasmids smaller than 50 Mdal. The plasmid profiles and restriction enzyme digestion patterns indicated that the salmonella strains lacking H-antigen were variants of Salmonella dublin. Thus, analysis of plasmid profile and restriction enzyme fingerprinting are useful complements to serological methods in the differentiation of salmonella DO-group strains.

DNA probes for the detection of toxin genes in Escherichia coli isolated from diarrhoeal disease in cattle and pigs

DNA gene probes specific for genes coding for heat labile toxin (LT), heat stable toxins (STpa, STpb) and Vero-cell toxins (VT1, VT2) were used to examine 1031 diarrhoeal disease isolates of E. coli (345 from cattle and 686 from pigs). Of the bovine strains, 60 hybridized with the STpa probe and most possessed the K99 (F5) or F41 adhesin. Five bovine strains possessed STpb genes and five either VT1 or VT2 genes. Of the porcine strains, 245 hybridized with one or more gene probes. Of 160 K88 (F4) positive strains, 133 possessed both LT and STpb genes, whilst 17 possessed LT or STpb or STpa alone or in combination. Ten K88 strains did not possess toxin genes. Isolates bearing the K99 (F5) adhesion possessed either STpa, STpb and VT2 genes alone or in combination; in one isolate only the LT gene was detected. Isolates belonging to serogroup 0138:K81 were more heterogeneous as to their toxin genes; of the 60 strains, fourteen carried only VT2 genes, thirty-two carried VT2, STpa and STpb genes, one carried LT, VT2, STpa and STpb genes, two carried STpb gene, four carried STpa and STpb genes, one carried LT and VT2 genes, two carried LT and STpa genes, whilst four carried none. Twenty-four percent of all toxigenic strains apparently did not possess adhesins.

Virulence factors in Escherichia coli strains isolated from Swedish piglets with diarrhea

Parenteral vaccination of sows against Escherichia coli diarrhea in their newborn piglets has become more common during the last decade in Sweden, and the vaccination has generally had positive effects. For more than 20 years we have investigated E. coli strains isolated from piglets and weaned pigs with enteric disorders, noting the presence of O groups, enterotoxins, and adhesins. There has been a continuous change in the frequency of these virulence factors. The present study was performed during 1983 and 1984 to follow this change, since such information is essential for the proper choice of vaccines. A total of 856 E. coli strains were obtained from 683 herds divided into three age groups: 1 to 6 days old, 1 to 6 weeks old, and weaned pigs. O group 149 still dominated in the last two age groups, while O group 101 was, for the first time, the most frequent O group in neonatal piglets. All but four O149 strains carried the K88 antigen, which was found in only one other strain (O group 8). K99 antigen was most often found in O groups 101 and 64, and among all the K99 strains ST mouse was the most common (44 of 57), followed by ST mouse-ST pig strains (12 of 57). The 987P antigen was demonstrated in 26 strains belonging to O groups 141 and OX46 and nontypable strains. Two strains belonging to O group 101 were positive for F41 antigen; one of them also carried the K99 antigen. Among all non-O149 strains, ST mouse was the most common type of enterotoxigenic E. coli ( n = 88), followed in decreasing order by ST mouse-ST pig strains ( n = 69) and ST pig strains ( n = 33). In 114 strains producing enterotoxins no adhesive factor was found. Thus, vaccination of the Swedish sow population for more than 5 years with vaccines containing O149 and K88 antigens has apparently changed the pattern of enterotoxigenic E. coli in neonatal diarrhea. The frequency of O149:K88 strains has been reduced, and O101:K99:ST mouse strains now dominate. However, O149 strains remain the dominant O group in piglets older than 1 week. In spite of all our diagnostic efforts, no virulence factors were detected in about one third of the piglets and weaned pigs with enteric disorders.

Antimicrobial drug resistance in porcine enterotoxigenic Escherichia coli of 0-group 149 and non-enterotoxigenic Escherichia coli

Enterotoxigenic Escherichia coli (ETEC) strains (104) and 96 non-ETEC, all isolated from herds with piglet diarrhea in 1981 and 1982, were investigated with regard to antimicrobial drug resistance and colicinogeny. Eighty strains (77%) of the ETEC were drug resistant as compared to 66 strains (69%) of the non-ETEC. There were no significant differences between ETEC and non-ETEC in the frequencies of the drug resistance determinants investigated, except for tetracycline, to which 51 (49%) of the former and 30 (31%) of the latter strains were resistant (0.05 greater than P greater than 0.01). Of all strains 116 (58%) were resistant to streptomycin, 93 (47%) to sulphadimidin, 81 (41%) to tetracycline, 20 (10%) to trimethoprim, 14 (7%) to ampicillin, 11 (6%) to neomycin, 6 (3%) to chloramphenicol and none to nitrofurantoin. The frequencies of the different drug resistance determinants correlated well with the total amount of active substance of each drug used in farm animals in Sweden in 1981. Of the ETEC, 97 (93%) were colicinogenic whereas only 13 (14%) of the non-ETEC were colicinogenic.

Concurrent transfer and recombination between plasmids encoding for heat-stable enterotoxin and drug resistance in porcine enterotoxigenic Escherichia coli

The frequency of and genetic mechanisms for simultaneous transfer of genes encoding for tetracycline and sulpha-streptomycin resistance, heat-labile (LT) and heat-stable (ST-mouse) enterotoxin production in porcine enterotoxigenic Escherichia coli to Escherichia coli K12 were investigated. Seven E. coli strains of 0-group 149 were studied by conjugation and transformation experiments. All strains transferred tetracycline-resistance plasmids at a high frequency. No interaction was observed between these plasmids and those encoding for LT production. However, most tetracycline-resistant recipient cells were ST-mouse+ following recombination events between plasmids encoding for colicin B and ST-mouse production and plasmids encoding for tetracycline resistance. Alternatively, when selecting for sulpha or streptomycin resistance a majority of the transconjugants were also ST-mouse+, as plasmids coding for sulpha and streptomycin were mobilized by the colicin B and ST-mouse encoding plasmid. Since the simultaneous transfer of genes encoding for drug resistance, colicin B and ST-mouse production are common events in vitro, they might also occur frequently in vivo during antibiotic selective pressure.

Genetic transfer of antimicrobial resistance and enterotoxigenicity among Escherichia coli strains

To understand the role of enterotoxin (Ent) plasmids in epidemics of enterotoxigenic (ET) Escherichia coli diarrhea in the United States, we studied the genetics of Ent plasmids in relation to E. coli serotypes and R plasmids. Twenty-nine ET E. coli strains, including all epidemic isolates available at the Centers for Disease Control, Atlanta, Ga. (CDC), were assessed for the ability to transfer antimicrobial resistances (if present) by conjugation, to mobilize a nonconjugative R plasmid, and to cotransfer enterotoxigenicity with R determinants. Of the 12 ET E. coli strains isolated in the United States, 5 were able to transfer R plasmids; one strain cotransferred detectable enterotoxigenicity. Another four U.S. isolates were able to mobilize plasmid DNA, but no toxin production was detected in transconjugants. Of 17 resistant ET E. coli from South Asia, 13 were able to transfer R plasmids; 5 of those 13 cotransferred detectable Ent plasmids. In all, 22 ET E. coli strains (76%) were able to initiate conjugation and genetic transfers. Six of these strains (20%) were able to cotransfer enterotoxigenicity with a conjugative R plasmid at a detectable frequency. One of the six strains transferred R and Ent determinants on a single plasmid. These data are addressed in relation to the observed immobility of Ent and R during outbreaks of ET E. coli, the efficacy of prophylactic tetracycline, and the worldwide occurrence of a limited number of ET E. coli serotypes.

Effect of parenteral vaccination of dams on intestinal Escherichia coli in piglets with diarrhea

To evaluate the effect of widely used parenteral vaccination of dams against neonatal colibacillosis, the virulence factors of the intestinal Escherichia coli flora, namely, O serogroup, enterotoxin(s) produced (heat labile, porcine heat stable, and murine heat stable) and adhesins (K88, K99, and 987P antigens) of 149 piglets from different herds in Sweden were investigated. Three categories were investigated: healthy piglets, diarrheal piglets born to unvaccinated dams, and diarrheal piglets born to dams vaccinated with a polyvalent Formalin-killed whole-cell vaccine containing K88 antigen (Porcovac; Hoechst Pharmaceuticals, Hounslow, England). Piglets less than 1 week old and those 1 to 8 weeks old were evaluated separately. Diarrheal piglets less than 1 week old from vaccinated dams yielded a higher incidence of K99 antigen-positive E. coli of the murine heat-stable enterotoxigenicity type compared with piglets of the same age group from unvaccinated dams. The percentage of diarrheal cases from which E. coli lacking recognized virulence attributes were isolated was also higher in the former compared with the latter group. In the 1- to 8-week-old diarrheal piglets of vaccinated dams, the overall incidence, enterotoxigenicity type, and serotype of the E. coli isolates resembled those of diarrheal piglets less than 1 week of age from unvaccinated herds. Enterotoxigenic E. coli bearing 987P antigen detectable in vitro was rare. Most of the enterotoxigenic isolates lacking K88, K99, and 987P antigens produced only ST. The investigation pinpoints some of the inadequacies of vaccines of the type studied under field conditions.