Phenotypic and genotypic characterization of virulence factors of Escherichia coli isolated from broiler chickens with simultaneous occurrence of cellulitis and other colibacillosis lesions.

The objective of this study was to characterize virulence factors of Escherichia coli isolates from broilers with simultaneous occurrence of cellulitis and other colibacillosis lesions. Thirty flocks were sampled and 237 birds with cellulitis were examined. Eighty-two (34.6%) of 237 birds condemned for cellulitis had gross lesions in the heart, air sacs, joints, or liver. In 58 chickens, E. coli was isolated from both the cellulitis and other lesions of colibacillosis, and 18.9% of the E. coli isolates from the 2 types of lesions belonged to the same O group. Escherichia coli of serogroups O78, O1, and O2 predominated. Isolates of the same serogroup that were derived from different lesions in the same birds had similar patterns of biotype, aerobactin production, serum sensitivity profile, antibiotic sensitivity, and K1 capsule production. Escherichia coli derived from cellulitis lesions produced virulence factors similar to those found in E. coli isolated from other colibacillosis lesions in poultry.     

Isolation of Escherichia coli from cellulitis and other lesions of the same bird in broilers at slaughter.

Cellulitis results in substantial losses to the broiler industry due to condemnations at slaughter. This study was conducted to clarify the association between Escherichia coli isolated from cellulitis and other lesions caused by E. coli in individual birds. Fourteen flocks were sampled and 118 birds with cellulitis were examined. Escherichia coli was isolated from all but 2 of the cellulitis lesions, and serogroups O78, O1, and O2 predominated. Thirty-six birds had at least 1 other lesion in addition to the cellulitis lesion. Isolation of E. coli from cellulitis and other lesions occurred in 7 of the 14 flocks. Escherichia coli of the same serogroup were isolated from cellulitis and other lesions in some birds, suggesting that a single E. coli may sometimes be responsible for both types of lesions.     

Persistence of cellulitis-associated Escherichia coli DNA fingerprints in successive broiler chicken flocks

Avian cellulitis in broiler chickens is primarily caused by Escherichia coli. Previous research found that the E. coli isolates of cellulitis origin were unique to each ranch, suggesting that these E. coli were endemic within the ranch environment. To test the hypothesis that the E. coli associated with cellulitis are endemic in the litter of the broiler house, we designed a study to determine whether E. coli DNA fingerprints associated with cellulitis persist over successive flocks that are grown in the same house. In addition, we assessed the impact of different cleaning and disinfection strategies on this persistence. Two broiler houses were followed on each of five farms over 3-4 flocks. A total of 353 E. coli isolates from cellulitis lesions were analyzed in this study, and 314 of these isolates (89%) were DNA fingerprinted by PFGE. In each ranch, there were several DNA fingerprint patterns that were present over successive flocks, regardless of the cleaning and disinfection strategy utilized. Isolates persisted as long as 191 days, implying that these E. coli are capable of persisting in the broiler house environment for long periods of time. In addition, these E. coli isolates were associated with cellulitis lesions in successive flocks. Thus, the isolates of E. coli that are associated with cellulitis in broiler chickens appear to be endemic in the litter environment of the broiler house.     

Prevalence of pathogenic Escherichia coli in the broiler house environment

Matched sampling of Escherichia coli from broiler house litter and bird lesions of either cellulitis or colibacillosis was conducted to investigate the relationship of pathogenic E. coli to those found in the environment. Isolates were collected from six broiler flocks representing six geographically disparate ranches. Isolates were compared by flock for similarity in serotype and genotyped by pulsed-field gel electrophoresis. Serotyping revealed a considerable dissociation between the two groups of isolates. The prevalence of pathogenic E. coli that matched the environmental isolates from the same house was 0 to 3%. Statistical analysis of the serotype data showed a strong dependence of serotype on isolate source, indicating a high probability that a particular serotype would be found among lesions or litter but not in both groups. Genotyping of isolates on two farms supported the results of serotyping and provided differentiation of isolates that could not by typed by serology. These results suggested that the prevalence of pathogenic E. coli in the broiler house was independent of the prevalence of other commensal or environmental E. coli. Understanding the composition of E. coli populations in commercial poultry production may have bearing on the epidemiology and control of E. coli related diseases.     

Virulence-associated traits in avian Escherichia coli: comparison between isolates from colibacillosis-affected and clinically healthy layer flocks

Colibacillosis appears to be of increasing importance in layer flocks. The aim of this study was to determine characteristics of avian pathogenic Escherichia coli associated with the occurrence of colibacillosis outbreaks at flock level. Forty E. coli strains originating from layers from healthy flocks ('control isolates'), consisting of 25 caecal and 15 extra-intestinal isolates, were compared with 40 strains isolated from layers originating from colibacillosis-affected flocks ('outbreak isolates'), consisting of 20 caecal and 20 extra-intestinal isolates. The examined characteristics were adhesins, invasivity in T84 cell culture, serum resistance, iron uptake, colicin production, and toxinogenicity. The following traits were significantly more often detected in the outbreak isolates than in the control isolates: tsh, iss, iucA, iutA, irp2, fyuA, iroC, cvaC, colicin and colicin V production. A comparison of the extra-intestinal outbreak isolates and the caecal control isolates yielded the same results as when the caecal isolates, extra-intestinal isolates and total number of isolates of the outbreak and the control group were compared. When comparing the caecal and extra-intestinal isolates within the control and within the outbreak group, no significant differences were detected. The O78 and O2 groups showed significant differences with other O-types and NT strains for prevalence of most of the same characteristics. The combination of type 1 fimbriae, tsh, serum resistance, iss, traT, iucA, fyuA, iroC and colicin or colicin V production was significantly more often present in extra-intestinal outbreak isolates than in extra-intestinal control isolates. Only the combination of serum resistance, fyuA and colicin production was present in all outbreak isolates, with a significantly lower prevalence in the control isolates. None of the characteristics or combinations examined were exclusive to the outbreak isolates.     

Histopathologic and bacteriologic evaluations of cellulitis detected in legs and caudal abdominal regions of turkeys

The objective of this study was to identify the causative agent of cellulitis in turkeys. Eighteen flocks from nine producers were sampled at the local processing plant, and 37 birds with cellulitis on legs or caudal thoracic area were obtained. None of the 37 birds with cellulitis had lesions in other organs. On gross examination, lesions were categorized into two groups: cellulitis with unopened skin lesions (type a) and cellulitis with opened skin lesions (type b). Histopathologically, cellulitis with unopened skin lesions had dermal necrosis with underlying fibrin and inflammatory exudate but cellulitis with open skin lesions had chronic granulomatous/granulation tissue-type reaction associated with foreign material. A complete bacteriologic study was conducted on 25 of 37 birds. Bacteria were isolated from 12 of the 25 birds with cellulitis lesions. No aerobic, microaerophilic, or anaerobic bacteria were isolated from the remaining 13 birds with cellulitis lesions. Escherichia coli was isolated in low numbers in mixed cultures with Proteus mirabilis, Lactobacillus spp., Klebsiella spp., and Staphylococcus spp. in 9 of 12 lesions. The remaining few cases yielded P. mirabilis in pure culture or in mixed culture with Pseudomonas aeruginosa. Types a and b cellulitis lesions in turkeys could be associated with primary contact dermatitis and skin abrasions, respectively. Their occurrence is likely associated with different management practices.     

Pathogenic and fecal Escherichia coil strains from turkeys in a commercial operation

The biochemical phenotypes and antimicrobial susceptibility patterns of 105 clinical Escherichia coli isolates from flocks with colibacillosis in a turkey operation were compared with 1104 fecal E. coli isolates from 20 flocks in that operation. Clinical isolates and 194 fecal isolates with biochemical phenotypes or minimum inhibitory concentrations for gentamicin and sulfamethoxazole similar to clinical isolates were tested for somatic antigens and the potential virulence genes hylE, iss, tsh, and K1. The predominant biochemical phenotype of clinical isolates contained 21 isolates including 14 isolates belonging to serogroup 078 with barely detectable beta-D-glucuronidase activity. Thirty-five fecal isolates had biochemical phenotypes matching common phenotypes of clinical isolates. Sixty-six (63%) clinical isolates exhibited intermediate susceptibility or resistance to gentamicin and sulfamethoxazole compared with 265 (24%) fecal isolates (P < 0.001). Seventy-seven clinical isolates reacted with O-antisera, of which 51 (66%) belonged to the following serogroups: O1, O2, O8, O25, O78, O114, and O119. In comparison, 8 of 35 (23%) fecal isolates subtyped on the basis of biochemical phenotype belonged to these serogroups and four of 167 (2%) fecal isolates subtyped on the basis of their antimicrobial resistance patterns belonged to these serogroups. Iss, K1, and tsh genes were detected more often among clinical isolates than these fecal isolates (P < 0.05). In summary, a small subgroup of E. coli strains caused most colibacillosis infections in this operation. These strains existed at low concentration in normal fecal flora of healthy turkeys in intensively raised flocks. The data suggest that colibacillosis in turkey operations may be due to endogenous infections caused by specialized pathogens.     

A prospective study of management and litter variables associated with cellulitis in California broiler flocks

Cellulitis has emerged as an economically important disease of broiler chickens. The impact of environmental risk factors on the incidence of cellulitis has not been evaluated in the United States. Escherichia coli (E. coli), the causative agent, is introduced through skin scratches during the grow out. Our previous work suggested that the litter was an important reservoir for cellulitis-associated E. coli. We hypothesized that factors contributing to a positive environment for E. coli growth would increase the opportunity for exposure of a broiler to an infectious dose of E. coli, capable of initiating a cellulitis lesion. This prospective study of 304 flocks on five farms from two integrated broiler companies was conducted to determine the effect of environmental factors on the prevalence of cellulitis in California broiler flocks. Environmental variables included temperature, wind velocity, and relative humidity (RH) at the litter surface. Litter variables measured included E. coli and total gram-negative bacteria load (colony forming units/g dry matter), water activity, and pH. Management variables such as clean out, the number of flocks reared on the same litter (litter run, LR), and downtime (DT) between flocks were also evaluated. Cellulitis ranged from 0.197% to 6.04%. Significant associations were identified using linear regression between farm, LR, DT, ambient temperature during the brooding period, gram-negative bacteria load in the litter during the brooding period, RH mid-grow out, and E. coli load late in the grow out. The significant variation in the rate of cellulitis between farms combined with the strong association of LR and DT with cellulitis demonstrated that management choices were highly influential in this disease syndrome. Based on these data and our previous findings, managers would be advised to increase DT between flocks and perform a total clean out of the house when a flock processes with a high incidence of cellulitis.     

Dermatitis in broilers caused by Escherichia coli: isolation of Escherichia coli from field cases, reproduction of the disease with Escherichia coli O78:K80 and conclusions under consideration of predisposing factors

A dermatitis in broiler chickens, especially on the caudal back, thighs and around the cloaca is observed more frequently in the last years. The skin is swollen at sites of inflammation and a fibrineous plaque extends between muscle and subcutis. No clinical signs are visible in the living flock but the disease causes economical losses because of degrading and rejection of carcasses. Studies of literature and own field observations suggest that Escherichia (E.) coli is involved in the development of the dermatitis. The following serotypes were isolated from field cases: O78:K80 (3X), O2:K56 (2X), O127:K63 (3X), O9:K57 (1X), O140 (2X); two isolates could not be identified. The reproduction of the dermatitis was successful by infection via feather follicles with E. coli O78:K80. The density of broilers kept on farms may contribute to the outbreak of dermatitis by violation of the skin followed by infection of the injuries. Massage of the infected sites by close contact of birds and insufficient hygiene may support the development of the disease.     

Virulence factors of Escherichia cofi from cellulitis or colisepticemia lesions in chickens

This study was designed to compare virulence factors of cellulitis-derived Escherichia coli to colisepticemic E. coli in order to clarify whether E. coli associated with cellulitis comprise a unique subset of pathogenic E. coli. Isolates were tested for serotype, capsule, aerobactin production, colicin production, the presence of the iss gene, and serum resistance. Untypable isolates made up the greatest percentage of each group. Serotypes O2 and O78 were the most commonly identified among both groups of isolates. No statistical differences in the distribution of aerobactin or colicin production, capsule, or iss gene were observed between groups. Cluster analysis showed that 90% of the E. coli isolates had greater than 42% livability in serum-resistance tests. No separation of colisepticemic vs. cellulitis E. coli isolates was observed on the basis of SR. Colicin production by E. coli was highly correlated with serum resistance (P = 0.0029). These data suggest that cellulitis E. coli have virulence traits similar to those of colisepticemic E. coli.     

An enzyme-linked immunosorbent assay for detection of antibodies against Escherichia coli: association between indirect hemagglutination test and survival

An enzyme-linked immunosorbent assay (ELISA) was modified for detection of antibodies against the two main pathogenic serotypes of Escherichia coli: serotypes O78:K80 and O2:K1. The ELISA was a more sensitive and repeatable test than the indirect hemagglutination test (IHT), which is a common method for detecting antibodies against E. coli. Cross-reactivity between the two strains was measured by reacting antisera of each serotype against homologous and heterologous antigens. The results suggest that aside from similar determinants expressed by the two serotypes, serotype O2:K1 expresses more strain-specific determinants than does O78:K80. Comparison of mean antibody titers of immunized chicks by IHT and ELISA along the primary response revealed that during the first 15 days after immunization with inactivated E. coli, the titers in both tests were parallel. After 15 days post-immunization, antibody titers measured by IHT decreased rapidly, whereas titers measured by ELISA decreased only slightly. In addition, a higher correlation was found between titers detected by ELISA and survival through challenge with E. coli than between titers detected with IHT and survival through challenge. The results suggest that the ELISA is a better test for detection of antibody in flocks suspected of being infected with E. coli.     

Duplex real-time PCR assays for rapid detection of virulence genes in E. coli isolated from post-weaning pigs and calves with diarrhoea

Duplex real-time PCR assays were used as modules to cover partially automated detection of 12 genes encoding adhesins, enterotoxins and Shiga toxins in faecal E. coli isolates. For this a total of 194 E. coli isolates from pigs suffering from post-weaning diarrhoea (PWD), including 65 isolates with haemolytic activity, and 83 isolates from calves with diarrhoea were examined. Data obtained by PCR were compared with O-typing and with haemolytic activity as indirect virulence markers. E. coli O-types O139:K82, O141:K85, and O149:K91 accounted for 43.8% (n = 85) of all porcine strains and for 55.4% (n = 36) of the porcine strains, which exhibited haemolytic activity. These strains carried virulence genes by 65.9% (n = 56) and 80.6% (haemolytic E. coli, n = 29), respectively. The E. coli O-types O139:K82 and O141:K85 were significantly associated with the adhesin gene F18, and O149:K81 with the F4 gene. In this context, detection of the gene encoding F18 was coupled predominantly with the genes responsible for the production of the toxins ST-I, ST-II and Stx2, and the F4 gene with those of the enterotoxins ST-I, ST-II and LT. Both virulence patterns were detected more pronounced in E. coli strains with haemolytic activity. Fifty-six of a total of 83 E. coli isolates originating from calves were O-typed as O101 (O101:K28, O101:K30, O101:K32; n = 29), O78:K80 (n = 23), and O9:K35 (n = 4). Most of the E. coli O78:K80 strains carried the F17 gene (69.6%, n = 16). Virulence genes encoding for F4, F5 or ST-I were detected only in single cases. Intimin and Shiga toxin genes that are present in enterohaemorrhagic E. coli (EHEC) were not detected.     

Assessing cellulitis pathogenicity of Escherichia coli isolates in broiler chickens assessed by an in vivo inoculation model.

The purpose of this study was to identify Escherichia coli isolates that could be characterized as cellulitis pathogens. Twelve E. coli isolates from diagnostic cases of cellulitis or mixed infections with various serotypes were compared for ability to produce cellulitis and internal lesions indicative of systemic infection. Ranking of isolates was based on the premise that E. coli isolates that were "cellulitis-type" would cause cellulitis lesions without causing systemic infection. A quantitative scoring system was also used so both the time required for a lesion to develop and lesion severity could be evaluated as determinants of virulence. Escherichia coli isolates were inoculated by subcutaneous injection of a standardized dose in 24 broiler chickens per isolate. Necropsy was performed on four birds per group at 6, 12, 24, 36, 48, and 60 hr postinoculation (PI). Cellulitis lesions were scored on a 0 to 5 scale based on size, migration from the inoculation site, and gross characteristics. Lesions of the pericardium, liver, joint, or body cavity were evaluated. Gross lesion scores of 1 or 2 were evident by 6 hr PI with all isolates. Mortality occurred in 4 of 12 experimental groups. Internal lesions were observed in 3 to 12 birds per group. Escherichia coli was reisolated from all lesions. The four isolates with the highest lesion score and highest lesion points as determined by the quantitative scoring system did not vary. However, the rankings of two other isolates were affected. Four isolates that were below average for mean internal lesion score and above average for mean cellulitis points were characterized as cellulitis-type. Three isolates that were above average for internal lesion score and below average for mean cellulitis points were characterized as systemic-type. The E. coli serotype was not a determining factor for cellulitis-type pathogenicity. Isolates discriminated as cellulitis-type or septicemic-type E. coli in this study are being used to further investigate virulence factors involved in the pathogenesis of cellulitis in broiler chickens.     

Prevalence of enteropathogenic Escherichia coli in naturally occurring cases of poult enteritis-mortality syndrome

Enteropathogenic Escherichia coli (EPEC) previously were identified in poult enteritis-mortality syndrome (PEMS)-affected turkeys and associated as a cause of this disease. In the present study, the prevalence of EPEC in PEMS-affected turkeys was examined retrospectively with archived tissues and intestinal contents collected from 12 PEMS-affected turkey flocks in 1998. Formalin-fixed intestinal tissues were examined by light and electron microscopy for attaching and effacing (AE) lesions characteristic of EPEC, and frozen (-75 C) intestinal contents were examined for presence of EPEC. Escherichia coli isolates were characterized on the basis of epithelial cell attachment, fluorescent actin staining (FAS) test, and presence of E. coli attaching/effacing (EAE), shigalike toxin (SLT) type I, SLT II, and bundle-forming pilus (BFP) genes by polymerase chain reaction procedures. EPEC isolates were examined for pathogenicity and ability to induce AE lesions in experimentally inoculated young turkeys. AE lesions were identified by light microscopy in Giemsa-stained intestines from 7 of 12 PEMS-affected turkey flocks. Lesions consisted of bacterial microcolonies attached to epithelial surfaces with epithelial degeneration at sites of attachment and inflammatory infiltration of the lamina propria. Electron microscopy confirmed the identity of AE lesions in six of seven flocks determined to have AE lesions by light microscopy. EPEC were identified in 4 of 12 flocks on the basis of the presence of EAE genes a nd absence of SLT I and SLT II genes; all isolates lacked BFP genes. EPEC isolates produced AE lesions and variable mortality in turkeys coinfected with turkey coronavirus. In total, EPEC were associated with 10 of 12 (83%) naturally occurring PEMS cases on the basis of identification of AE lesions and/or EPEC isolates. These findings provide additional evidence suggesting a possible role for EPEC in the pathogenesis of PEMS.     

Shiga-like toxin production and attaching effacing activity of Escherichia coli associated with calf diarrhea

Four hundred twenty-nine isolates of Escherichia coli from calves were tested for the production of HeLa cell cytotoxin(s). Isolates that produced enough cytotoxin to be detected in culture supernatants of iron-depleted broth were considered to produce increased amounts of cytotoxins. Isolates also were tested for homology with a DNA probe for a gene that encodes localized adherence of human enteropathogenic E coli. Four isolates produced increased amounts of cytotoxin that was neutralized by Shiga antitoxin (toxin designated as Shiga-like toxin-I [SLT-I]). A 5th isolate produced increased amounts of cytotoxin (SLT+) that was not neutralized by the Shiga antitoxin, but was neutralized by antitoxin against a variant of SLT (toxin designated as SLT-II). None of the isolates hybridized with the probe for the localized adherence gene. Three of the SLT+ isolates belonged to human enteropathogenic E coli serogroups O26 and O111. All 5 of the SLT+ isolates were from calves with diarrhea, but none of the 5 SLT+ isolates contained genes for classic heat-labile or heat-stable enterotoxins, for K99 fimbriae, or for invasiveness; neither did any of them adhere to HeLa cells in culture. Three of the 5 SLT+ isolates had attaching and effacing activities when inoculated into ligated intestinal loops of rabbits. One of the isolates with attaching and effacing activity in rabbits was originally isolated from a calf with lesions characteristic of those produced by attaching effacing E coli (AEEC). Calves inoculated with this SLT+ AEEC isolate developed focal colonic lesions characteristic of those produced by AEEC, but did not develop diarrhea.(ABSTRACT TRUNCATED AT 250 WORDS)     

Studies on Cellulitis and Other Disease Syndromes Caused by Escherichia coli in Broilers in Sri Lanka

Cellulitis caused by Escherichia coli in broilers results in substantial losses to the broiler industry in North America and Europe due to condemnations at slaughter. The objective of this study was to identify cellulitis in broilers in Sri Lanka and to characterize the E. coli from cellulitis and other colibacillosis lesions. Twenty-four farms from the low- and mid-country were selected and bacterial isolations were obtained from 241 birds. Two hundred and ninety-one gross lesions were observed in these 241 birds and 162 E. coli isolates were obtained. Cellulitis was observed in 21% of the birds. Twenty-one per cent of the birds had multiple lesions due to E. coli. The frequency of detection of other disease syndromes was 162 (67%) birds with pericarditis, 26 (11%) airsacculitis, 24 (10%) hepatitis, 12 (5%) perihepatitis, and 16 (7%) polyserositis (a combination of pericarditis, perihepatitis and airsacculitis). Serogroups O78, O2, O85 and O88 were distributed among the 32% of typable E. coli and 81% of isolates were assigned to three biotypes. Forty-four per cent of the E. coli isolates produced aerobactin and 88% demonstrated resistance to the bactericidal effect of normal chicken serum. The majority of the E. coli isolates were resistant to the antibiotics commonly used in poultry. All the E. coli isolates were non-haemolytic and 25% of the isolates produced K1 capsule. This study demonstrated the presence of cellulitis in Sri Lanka and this report describes some of the phenotypic characteristics of the E. coli isolates.     

Spatial heterogeneity of Escherichia coli DNA fingerprints isolated from cellulitis lesions in chickens

Avian cellulitis in broiler chickens is characterized by subcutaneous lesions that result in economic losses because of the partial or complete condemnation of the carcasses at processing. Escherichia coli is the primary causative agent of this condition. Previous research with a biotyping system found that the E. coli of cellulitis origin were unique to each ranch, suggesting that these E. coli were endemic within the ranch environment. The objective of our study was to analyze the genetic variability of E. coli isolates associated with cellulitis. We analyzed the genetic relatedness of the isolates in relation to the houses, ranches, and complexes in which the broilers were grown. This analysis enabled us to assess the spatial heterogeneity, or genetic diversity on a spatial scale, of the isolates. Forty-nine broilers with cellulitis lesions were necropsied. These broilers came from six houses on four ranches on three complexes that had been placed with chicks from the same hatchery within a 2-wk period. Isolates of E. coli from the lesions were DNA fingerprinted by pulsed-field gel electrophoresis. Relatedness among isolates was determined with the Dice coefficient and an unweighted pair group method with average linkages cluster analysis. The complexes possessed isolates with a variety of DNA fingerprints, yet each complex appeared to have isolates with a unique set of DNA fingerprints. Isolates from the same complex tended to form clusters with similarity coefficients greater than 90%. Isolates from different complexes were genetically distinct. This heterogeneity at the level of the complex suggests that isolates were not disseminated from a source common to the complexes. The spatial heterogeneity of the E. coli isolates in this study implies an endemic population of cellulitis-associated E. coli exists in the broiler house environment.     

Virulence characteristics of Escherichia coli isolates obtained from broiler breeders with salpingitis

Thirty isolates of Escherichia coli from broiler breeders with salpingitis were studied. Using the slide agglutination test, the isolates were found to belong to serogroups O1, O2, O5, O36, O45, O53 and O78. Pathogenicity for day-old chicks was determined by air sac inoculation and isolates were categorized as having high, intermediate or low virulence. Growth on iron starvation medium was observed together with aerobactin production. Based on the results of in vitro adherence tests, attachment to oviduct epithelium from old birds was found to be superior to that observed using corresponding material from young birds. DNA hybridization testing for type 1, P, and S fimbriae revealed predominant expression of type 1, correlating with mannose-sensitive hemagglutination using guinea-pig erythrocytes. In this study, P and S fimbriae were not considered to be important adherence factors. Study findings would suggest that, as far as salpingitis is concerned, type 1 fimbriae can play an important role in E. coli infection in breeders. An interesting result to emerge from the study was the observation that E. coli isolates were completely resistant to serum from young breeders, whereas they were completely sensitive using serum from older breeders. Based on serogroups involved, pathogenicity for day-old chicks and virulence indicators, the salpingitis isolates were similar to those from cases of chronic respiratory disease.     

In vitro and in vivo characterization of avian Escherichia coli. I. Serotypes, metabolic activity, and antibiotic sensitivity

Over a 2 1/2-year period (January 1981 to June 1983), 177 Escherichia coli isolates were obtained from 145 field-reared broiler flocks in the Delmarva peninsula, and 20 were obtained from clinically normal day-old hatchery chickens representing an additional 17 flocks in Delmarva. Ninety-one isolates obtained from the field-reared birds between 2 and 8 weeks of age were associated with complicated air-sac disease. Serotyping efforts demonstrated a predominance of O2, O35, and O78 serogroups and a large number of untypable isolates. More than 50% of the isolates in each of the three dominant serogroups were collected from broilers with colibacillosis, but they were never detected in the yolk-sac samples of clinically normal day-old hatchery chickens. In vitro biochemical characterization of the E. coli isolates revealed variable rates of carbohydrate fermentation and amino acid decarboxylation. No common characteristics appeared to be shared by the predominant serogroups isolated from clinically affected birds, although several serogroup-specific reactions were noted. The majority of the isolates were sensitive to chloramphenicol, gentamicin, nalidixic acid, ormethoprim-sulfadimethoxine, spectinomycin, neomycin, and ampicillin. About half of the isolates were sensitive to nitrofurantoin and the sulfa compounds. Less than 25% of the isolates were sensitive to streptomycin, erythromycin, tetracyclines, novobiocin, penicillin, bacitracin, and lincomycin.     

Interaction between attaching and effacing Escherichia coli serotypes O157:H7 and O26:K60 in cell culture

Ruminants harbour both O157:H7 and non-O157 Attaching Effacing Escherichia coli (AEEC) strains but to date only non-O157 AEEC have been shown to induce attaching effacing lesions in naturally infected animals. However, O157 may induce lesions in deliberate oral inoculation studies and persistence is considered dependent upon the bacterially encoded locus for enterocyte effacement. In concurrent infections in ruminants it is unclear whether non-O157 AEEC contribute either positively or negatively to the persistence of E. coli O157:H7. To investigate this, and prior to animal studies, E. coli O157:H7 NCTC 12900, a non-toxigenic strain that persists in conventionally reared sheep, and non-toxigenic AEEC O26:K60 isolates of sheep origin were tested for adherence to HEp-2 tissue culture alone and in competition one with another. Applied together, both strains adhered in similar numbers but lower than when either was applied separately. Pre-incubation of tissue culture with either one strain reduced significantly (P < 0.05) the extent of adherence of the strain that was applied second. It was particularly noticeable that AEEC O26 when applied first reduced adherence and inhibited microcolony formation, as demonstrated by confocal microscopy, of E. coli O157:H7. The possibility that prior colonisation of a ruminant by non-O157 AEEC such as O26 may antagonise O157 colonisation and persistence in ruminants is discussed.