F17 fimbriae in Escherichia coli from lambs and kids

Characterization of Intestinal Microbiota in Lambs with Different Susceptibility to Escherichia coli F17

Diarrhea is one of the most commonly reported diseases in young farm animals. Escherichia coli (E. coli) F17 is one of the major pathogenic bacteria responsible for diarrhea. However, the pathogenicity of diarrhea in lambs involving E. coli F17 strains and how E. coli F17 infection modifies lambs' intestinal microbiota are largely unknown. To evaluate diarrhea in newborn lambs with an infection of E. coli F17, 50 lambs were selected for challenge experiments and divided into four groups, namely, a high-dose challenge group, low-dose challenge group, positive control group, and negative control group. The E. coli F17 challenge experiments caused diarrhea and increased mortality in the experimental lamb population, with a higher prevalence (90%), mortality (35%), and rapid onset time (4-12 h) being observed in the high-dose challenge group than the results observed in the low-dose challenge group (75%, 10%, 6-24 h, respectively). After the challenge experiment, healthy lambs in the high-dose challenge group and severely diarrheic lamb in the low-dose challenge group were identified as lambs sensitive/resistant to E. coli F17 (E. coli F17 -resistant/-sensitive candidate, AN/SE) according to the histopathological detection. Results of intestinal contents bacteria plate counting revealed that the number of bacteria in the intestinal contents of SE lambs was 10^2~3-fold greater than that of the AN lambs, especially in the jejunum. Then, 16S rRNA sequencing was conducted to profile the intestinal microbiota using the jejunal contents, and the results showed that SE lambs had higher Lactococcus and a lower Bacteroidetes:Firmicutes ratio and intestinal microbiota diversity in the jejunum than AN lambs. Notably, high abundance of Megasphaera elsdenii was revealed in AN lambs, which indicated that Megasphaera elsdenii may serve as a potential probiotic for E. coli F17 infection. Our study provides an alternative challenge model for the identification of E. coli F17-sensitive/-resistant lambs and contributes to the basic understandings of intestinal microbiota in lambs with different susceptibilities to E. coli F17.

Characterization of nonenterotoxigenic Escherichia coli strains producing F17 fimbriae isolated from diarrheic lambs and goat kids

Forty-five ovine and caprine nonenterotoxigenic Escherichia coli strains producing F17-related fimbriae were characterized with respect to the fimbrial structural subunit and adhesin subtypes produced. In addition, several characteristics related to the virulence of strains producing F17 fimbriae were studied. Most of the strains (73%) possessed the f17cA structural subunit gene, whereas the f17aA and f17dA genes were detected only on three (6%) and two (4%) strains, respectively. The f17bA gene was not detected. All but one of these strains possessed the f17G genes of the adhesin subfamily II. The only strain having the f17G gene of subfamily I possessed the structural subunit gene f17dA. Sequencing of the f17A and f17G genes of four selected strains confirmed the association of f17cA and f17dA structural subunit genes with the f17G genes of the adhesin subfamily II. These results indicated that adhesins of the subfamily II are prominent among ovine and caprine isolates and that they are indistinctly associated with the F17 structural subunit subtypes on these field strains. CS31A- and CNF2-related genes were not detected. Most of the strains adhered in vitro to ovine intestinal brush borders (36 of 45) and agglutinated the erythrocytes of different species in the presence of D-mannose (39 of 45). F17-positive strains produced colicin V (57%) and were resistant to the bactericidal effect of serum (91%) in significantly higher percentages than F17-negative strains (34% produced colicin V, and 66% were serum resistant). Thus, most of the studied ovine and caprine strains showed phenotypic characteristics of septicemic strains.

Serogroups, toxins and antibiotic resistance of Escherichia coli strains isolated form diarrhoeic goat kids in Spain

Fifty-five Escherichia coli strains isolated from 55 diarrhoeic goat kids from 13 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-hemolysin (Hly) and enterohemolysin (EntHly), and for antibiotic resistance. Only 3 (5%) strains were toxigenic: 1 VT1+EntHly+ (serogroup O8) and 2 CNF2+ (both of serogroup O153). The strains serotyped belonged to 19 serogroups. However, 31 (56%) were of one nine serogroups (O3, O8, O9, O10, O11, O21, O44, O103 and O153) and only three of them (O8, O9 and O11) accounted for 29% of the strains. The highest percentages of antibiotic resistance in order of frequency were: streptomycin (93%), sulfadiazine (89%), tetracyline (84%), kanamycin (82%), neomycin (82%) and ampicillin (69%). We conclude that E. coli strains isolated from diarrhoeic goat kids are usually non-toxigenic and belong to a large number of serogroups.

In vitro susceptibility of Escherichia coli strains isolated from diarrhoeic lambs and goat kids to 14 antimicrobial agents

The in vitro activities of 14 anti-microbial agents were determined against 92 strains of E. coli isolated from lambs (60 strains) and kids (32 strains) affected by neonatal diarrhoea. The overall percentage of resistant strains to streptomycin, sulphadimethoxine and tetracycline was very high (above 70%). A high level of resistance (from 30% to 50%) to ampicillin, kanamycin, neomycin and chloramphenicol was also detected. The E. coli strains were highly susceptible to cephalosporins, polymyxin and quinolones. Most of the strains showed multiresistance: 77.2% of isolates were resistant to at least two antibiotics, 55.4% were resistant to at least four antibiotics and 33.7% were resistant to at least six antibiotics. A total of 34 antibiotypes could be distinguished.

Role of enteric pathogens in the aetiology of neonatal diarrhoea in lambs and goat kids in Spain

Faeces samples from diarrhoeic and non-diarrhoeic lambs and goat kids aged 1-45 days were examined for enteric pathogens. Cryptosporidium parvum was detected in both diarrhoeic lambs (45%) and goat kids (42%) but not in non-diarrhoeic animals. F5+ (K99+) and/or F41+ Escherichia coli strains were isolated from 26% and 22% of the diarrhoeic lambs and goat kids, respectively, although these strains, which did not produce enterotoxins ST I or LT I, were found with similar frequencies in non-diarrhoeic animals. A F5-F41-ST I+ E. coli strain was isolated from a diarrhoeic lamb (0.6%). Verotoxigenic E. coli was isolated from both diarrhoeic and non-diarrhoeic lambs (4.1% and 8.2%, respectively) and there was no association between infection and diarrhoea. The prevalence of group A rotavirus infection in diarrhoeic lambs was very low (2.1%). Groups A and B rotaviruses were detected in three (8.1%) and five (13.5%) diarrhoeic goat kids from two single outbreaks. Group C rotaviruses were detected in four non-diarrhoeic goat kids. An association of diarrhoea and infection was demonstrated only for group B rotavirus. Clostridium perfringens was isolated from 10.8% of the diarrhoeic goat kids but not from non-diarrhoeic goat kids or lambs. Salmonella arizonae was isolated from a diarrhoeic goat kid (2.7%) and the clinical characteristics of the outbreaks where these two latter enteropathogens were found different from the rest. Picobirnaviruses were detected in a diarrhoeic lamb. No coronaviruses were detected using a bovine coronavirus ELISA. No evidence was found of synergistic effect between the agents studied. Enteric pathogens were not found in four (8.7%) and three (20%) outbreaks of diarrhoea in lambs and goat kids, respectively.

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.

Characterization of glycoprotein glycan receptors for Escherichia coli F17 fimbrial lectin

The specificity of N-acetylglucosamine-binding F17 fimbrial lectin of coli (also called FY or Att25) for the oligosacharide structures was investigated by mannose-resistant hemagglutination inhibition tests and direct binding assays. The linkage position of N-acetyl-glucosamine influenced its affinity in the preferential order of beta 1-3 > beta 1-6 > beta 1-4 beta > beta 1-2. Minimal GlcNAc beta 1-3Gal beta 1-sequence strongly bound to F17 lectin, whether located in terminal nonreducing position or internally in carbohydrate moieties. F17 lectin specifically interacted with this unit in O-glycosidically linked oligosaccharides of the bovine glycophorins and intestinal mucins. On the contrary, GlcNAc beta 1-NAsn, GlcNAc beta 1-6Man beta- and GlcNAc beta 1-4GlcNAc- of N-glycosylated proteins failed to bind to the lectin. Our findings emphasized the presence of multiple F17 mucosal receptor complex in the newborn calf intestines. Furthermore, the density of receptors for F17 fimbrial lectin seemed to depend on the age of the calf and the intestinal segment.