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

Prevalence and characteristics of necrotoxigenic Escherichia coli (NTEC) strains isolated from diarrhoeic dairy calves

Fecal samples from 246, 1-90-days old diarrhoeic dairy calves in 72 herds were screened for the presence of cytotoxic necrotizing factors (CNF)-producing Escherichia coli (NTEC). NTEC were detected by tissue culture assays and PCR in 39 (15.8%) of the diarrheic calves, and the majority of these animals (34 of 39, ca. 87.2%) were infected by NTEC producing CNF2. Calves were grouped according to their age (1-7 days, 8-14 days, 15-21 days, 22-30 days and 31-90 days) and analyses of prevalence were done by the Mantel-Haenzsel chi2-test for trend. A significant age-associated increase in the prevalence of NTEC producing CNF2 (p<0.0001) was found. Eighty-one (8.4%) of the 958 E. coli isolates from the 246 diarrheic calves were positive for CNF in the tissue culture assays. These strains were analyzed by PCR and this technique showed that three (3.7%) strains were CNF1-positive and 75 (92.6%) were CNF2-positive. Moreover, three of the strains positive in the tissue culture assays were negative by PCR. These strains were subsequently assayed in several biological tests (rabbit skin test, mouse intraperitoneal test and mouse footpad test) which showed that they were really NTEC, probably producing CNF2, but with some different properties to classical strains producing CNF2. NTEC strains producing CNF2 belonged to different serogroups (O2, O7, O9, O14, O15, O41, O43, O45, O55, O76, O86, O88, O109, O115, O123, O128, O153 and O159) than strains producing CNF1 (O11 and O32) or PCR-negative strains (O111). Moreover, a strong association between CNF2 and F17 fimbriae was found (78.6% of CNF2-positive strains were F17-positive, whereas only 22.9% of CNF2-negative strains were F17-positive).

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.

Serogroups, toxins and antibiotic resistance of Escherichia coli strains isolated from diarrhoeic lambs in Spain

One hundred and forty-four Escherichia coli strains isolated from 144 diarrhoeic lambs (5 to 21 days old) from 38 flocks in Spain were serotyped and investigated for production of enterotoxins (LT and STa), verotoxins (VT1 and VT2), cytotoxic necrotizing factors (CNF1 and CNF2), alpha-haemolysin (Hly) and enterohaemolysin (EntHly), for necrotic and lethal activities and for antibiotic resistance. The strains belonged to 39 different serogroups; however, 58% were of one of 13 serogroups (O4, O6, O7, O8, O9, O11, O23, O26, O77, O80, O101, O103 and O161) and only four of them (O8, O9, O11 and O77) accounted for 34% of strains. In total 10 (7%) toxigenic strains were detected: two LT+, two VT1+ EntHly+, four VT1+ EntHly-, one CNF1+ Hly+ and one CNF2+. The highest percentages of antibiotic resistance were reached in the group of antibiotics (tetracycline, streptomycin, sulphadiazine, ampicillin, kanamycin, neomycin, chloramphenicol, trimethoprim and cotrimoxazole) that are most generally used by Spanish veterinary clinics. We conclude that E. coli strains isolated from diarrhoeic lambs are not generally toxigenic and belong to a large number of serogroups.

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.

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.