Studies on Escherichia coli in pigs. IV. Reactions of Escherichia coli strains in the ligated intestine test

Virulence determinants of Escherichia coli isolated from milk of sows with coliform mastitis

Escherichia coli isolates recovered from the milk of sows with coliform mastitis were examined to determine their biochemical and serologic characteristics, serum resistance and ability to adhere to fibronectin and bovine fetal fibroblasts. No common biotype was identified, and a variety of serovars were detected. Ninety-five per cent of the investigated strains were serum resistant in swine serum. Binding to fibronectin was demonstrated in most of the strains. At a binding level above 13% of the added fibronectin the strains also adhered to fibroblasts. The results of the study indicate a galactogenous route of infection. The importance of the identified virulence factors need to further elucidated.

Occurrence of fimbriae and enterotoxins in Escherichia coli strains isolated from piglets in Poland

1125 and 1146 E. coli strains isolated from suckling and weaned piglets with diarrhea, respectively, and 724 strains from healthy piglets were tested for the presence of fimbriae and production of enterotoxins. The fimbriae were determined by hemagglutination and slide agglutination tests, enterotoxins--by the use of ileal loop test in piglets (LT and STb enterotoxins) and suckling mouse assay (STa enterotoxin). It was found that 72.8 and 53.0% strains, isolated from diseased suckling and weaned piglets, respectively, possessed specific fimbrial hemagglutinins, in most cases with K88 antigen. Additionally, 987P fimbriae were detected in 14.0 and 0.7% strains isolated from piglets with diarrhea. Only 5 strains (0.7%) recovered from healthy piglets had specific fimbriae, usually with undetermined antigenic structure. F1 fimbriae (called common or unspecific) were found in strains isolated both from diseased (15.2 and 16.3% strains, respectively) and healthy piglets (27.1% strains). It was noted that the strains isolated from suckling and weaned piglets with diarrhea in most cases were enterotoxigenic (90.5 and 69.1% strains, respectively) and most frequently produced heat-labile toxin LT alone or with STb. 18.5% of enterotoxigenic strains isolated from healthy piglets produced STa toxin.

Evaluation of three different STb assays and comparison of enterotoxin pattern over a five-year period in Swedish porcine Escherichia coli

The pig intestinal loop (PIL) assay, inhibition enzyme-linked immunosorbent assay (ELISA), and DNA hybridization assay were compared for analysis of Escherichia coli heat-stable enterotoxin b (STb) on 201 porcine E. coli strains. The DNA hybridization had a 95% correlation with the STb ELISA and was therefore chosen as the method for subsequent screening of enterotoxin genes: heat labile (LT), heat-stable a (STa), and/or STb. In contrast to the PIL assay, both the STb ELISA and DNA hybridization assays were more sensitive, reliable, reproducible, and showed good correlation with each other. Consequently, the STb ELISA is preferable for analysis of toxin preparations and screening of E. coli, whereas the DNA hybridization is better for large-scale epidemiologic screening. Escherichia coli strains (n = 437) associated with porcine diarrhea isolated in Sweden during 1989 were investigated. Of the strains, 135 (31%) were positive for at least one of these toxins and, therefore, designated enterotoxigenic E. coli (ETEC). Our results were compared with the enterotoxin pattern found in earlier studies of Swedish porcine strains. The only change in occurrence of toxins was found in strains isolated from piglets less than 1 week of age. LT- and STb-producing ETEC had decreased, and STa-producing ETEC had increased in prevalence. The occurrence of STb among ETEC of weaned pigs was 93%. This toxin was also found to be more common than STa when strains from all age groups were considered.

Enzyme-linked immunosorbent assay for Escherichia coli heat-stable enterotoxin type II

The gene for Escherichia coli heat-stable enterotoxin type II (STII) was fused to the genes for protein A from Staphylococcus aureus and beta-galactosidase in two different expression systems. Antibodies raised in rabbits against the protein A-STII fusion protein recognized the beta-galactosidase-STII fusion protein. The latter fusion protein was used as the immobilized antigen in an enzyme-linked immunosorbent assay (ELISA) for detection of STII. The correlation between the results of the ELISA and the intestinal loop test in piglets was 95%, suggesting that the ELISA can be used to reliably detect STII.

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.

Evaluation of different cell cultures for the detection of heat-labile enterotoxins of Escherichia coli strains isolated from pigs

The sensitivity of various cell cultures to heat-labile enterotoxins (LT) and Verocytotoxin (VT) of fifteen E. coli strains isolated from cases of pig colibacillosis in Poland was estimated and compared with the effect of enterotoxins of four standard E. coli strains. Of ten tested cell cultures, only the following were susceptible: CHO, Vero, GMK, and HeLa. Eight strains showed CTE in He La and CHO cells and five of these reacted in Vero cells. The results appear to suggest that some of the tested E. coli strains isolated from pigs produced VT enterotoxin. Morphological changes caused by the above mentioned E. coli toxins in Vero and GMK cells took the form of cell rounding, followed by cell dissolution.

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.