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M J Woodward

Publications and source records attributed to M J Woodward.

At least 19 recordsLinked to original sources
PubMed2006

Sources of variation in the ampicillin-resistant Escherichia coli concentration in the feces of organic broiler chickens.

Currently, there are limited published data for the population dynamics of antimicrobial-resistant commensal bacteria. This study was designed to evaluate both the proportions of the Escherichia coli populations that are resistant to ampicillin at the level of the individual chicken on commercial broiler farms and the feasibility of obtaining repeated measures of fecal E. coli concentrations. Short-term temporal variation in the concentration of fecal E. coli was investigated, and a preliminary assessment was made of potential factors involved in the shedding of high numbers of ampicillin-resistant E. coli by growing birds in the absence of the use of antimicrobial drugs. Multilevel linear regression modeling revealed that the largest component of random variation in log-transformed fecal E. coli concentrations was seen between sampling occasions for individual birds. The incorporation of fixed effects into the model demonstrated that the older, heavier birds in the study were significantly more likely (P = 0.0003) to shed higher numbers of ampicillin-resistant E. coli. This association between increasing weight and high shedding was not seen for the total fecal E. coli population (P = 0.71). This implies that, in the absence of the administration of antimicrobial drugs, the proportion of fecal E. coli that was resistant to ampicillin increased as the birds grew. This study has shown that it is possible to collect quantitative microbiological data on broiler farms and that such data could make valuable contributions to risk assessments concerning the transfer of resistant bacteria between animal and human populations.

Ampicillin↗
PubMed2006

Influence of colostrum deprivation and concurrent Cryptosporidium parvum infection on the colonization and persistence of Escherichia coli O157 : H7 in young lambs.

Escherichia coli O157 : H7 and Cryptosporidium parvum infections of man have been associated with direct contact with small ruminants. Colostrum protects neonates against gastrointestinal pathogens, and orphan lambs, which are common on petting farms, may be deprived of this protection. In a recent study, it was demonstrated that high shedding of E. coli O157 : H7 by an 8-week-old goat kid was associated with coincidental C. parvum infection. Furthermore, both pathogens were co-located in the distal gastrointestinal tract. It was hypothesized that colostrum deprivation and pre-infection with C. parvum predisposed young ruminants to colonization and increased shedding of E. coli O157 : H7. To test this, 21 lambs 5 weeks of age were divided into four groups as follows: (A) colostrum-deprived and inoculated with E. coli O157 : H7, (B) colostrum-deprived and inoculated with C. parvum and then E. coli O157 : H7, (C) conventionally reared and inoculated with E. coli O157 : H7, (D) conventionally reared and inoculated with C. parvum and then E. coli O157 : H7. C. parvum was detected between 8 and 12 days post-inoculation in most of the infected lambs. At 24 h post-inoculation with E. coli O157 : H7, all lambs were shedding between 5 x 10(4) and 5 x 10(7) c.f.u. E. coli O157 : H7 per gram of faeces. E. coli O157 : H7 was shed in higher numbers in the groups pre-inoculated with C. parvum, whether conventionally reared or colostrum-deprived. Interestingly, for the colostrum-deprived lambs on day 3, a significant difference in shedding of E. coli O157 : H7 was observed (P = 0.038), with the lambs inoculated with E. coli alone yielding higher counts than those pre-inoculated with C. parvum. From day 15 onwards, shedding of E. coli O157 : H7 was highest from the colostrum-deprived C. parvum-infected lambs, then (in descending order of shedding) the colostrum-deprived lambs, the conventionally reared lambs infected with C. parvum, and the conventionally reared animals. In total, four animals were euthanized, two at 24 h and two at 96 h post inoculation with E. coli O157 : H7 (two conventionally reared and two colostrum-deprived). All animals euthanized were from groups pre-inoculated with C. parvum prior to challenge with E. coli O157 : H7. On examination of tissues, in three of the four animals examined, multifocal attaching and effacing lesions were observed in the caecum, colon, rectum and at the recto-anal junction, and were confirmed by immunohistochemistry to be associated with E. coli O157 : H7.

Animals↗
PubMed2005

The occurrence of treponemes in contagious ovine digital dermatitis and the characterisation of associated Dichelobacter nodosus.

Contagious ovine digital dermatitis (CODD) is a recently recorded, apparently new infection of the ovine hoof, which differs clinically from footrot caused by Dichelobacter nodosus and which fails to respond well to accepted treatment practices for footrot. Despite the welfare implications of such an infection, very little research has been performed on CODD to date and the aetiology remains confused. Suggestions have been made that there is a potential role for treponemes in the pathogenesis of CODD but that D. nodosus is apparently not involved. Six farms were therefore targeted in this study to provide a more in-depth investigation into the bacterial flora of CODD lesions. Dark ground microscopy, culture and PCR techniques were used, concentrating on the presence of D. nodosus and spirochaetes, particularly those of the genus Treponema. The results demonstrated that isolates of D. nodosus were indeed present in a high percentage (74%) of CODD lesions compared with 31% of apparently healthy feet. The isolates were shown to be of similar virulence type to those reported previously in cases of footrot, and the range of serogroups was also found to be similar to footrot, with serogroup H being prevalent. Treponemes were present in 70% of CODD lesions and 38% of apparently healthy feet, supporting a possible association between CODD and treponemes. However, any further progress on the aetiology of CODD and the potential for novel, effective treatment will depend on an improved ability to culture these organisms routinely in the laboratory thereby enabling their complete characterisation.

Animals↗
PubMed2005

Detection of mutations in Salmonella enterica gyrA, gyrB, parC and parE genes by denaturing high performance liquid chromatography (DHPLC) using standard HPLC instrumentation.

AIMS: Quinolone antibiotics are the agents of choice for treating systemic Salmonella infections. Resistance to quinolones is usually mediated by mutations in the DNA gyrase gene gyrA. Here we report the evaluation of standard HPLC equipment for the detection of mutations (single nucleotide polymorphisms; SNPs) in gyrA, gyrB, parC and parE by denaturing high performance liquid chromatography (DHPLC). METHODS: A panel of Salmonella strains was assembled which comprised those with known different mutations in gyrA (n = 8) and fluoroquinolone-susceptible and -resistant strains (n = 50) that had not been tested for mutations in gyrA. Additionally, antibiotic-susceptible strains of serotypes other than Salmonella enterica serovar Typhimurium strains were examined for serotype-specific mutations in gyrB (n = 4), parC (n = 6) and parE (n = 1). Wild-type (WT) control DNA was prepared from Salmonella Typhimurium NCTC 74. The DNA of respective strains was amplified by PCR using Optimase proofreading DNA polymerase. Duplex DNA samples were analysed using an Agilent A1100 HPLC system with a Varian Helix DNA column. Sequencing was used to validate mutations detected by DHPLC in the strains with unknown mutations. RESULTS: Using this HPLC system, mutations in gyrA, gyrB, parC and parE were readily detected by comparison with control chromatograms. Sequencing confirmed the gyrA predicted mutations as detected by DHPLC in the unknown strains and also confirmed serotype-associated sequence changes in non-Typhimurium serotypes. CONCLUSIONS: The results demonstrated that a non-specialist standard HPLC machine fitted with a generally available column can be used to detect SNPs in gyrA, gyrB, parC and parE genes by DHPLC. Wider applications should be possible.

Amino Acid Substitution↗
PubMed2005

Variable and strain dependent colonisation of chickens by Escherichia coli O157.

The prevalence of enterohaemorrhagic Escherichia coli (EHEC) O157 in poultry is considered minimal compared with other species, especially ruminants. However, deliberate inoculation studies have shown that poultry are readily and persistently infected by this organism but that the mechanism of colonisation is independent of intimin, a recognised factor in host-EHEC interactions in mammalian species, and may be dependent upon flagella. Few strains of EHEC O157 have been tested in poultry and here 1-day-old and 6-week-old chicks were inoculated with seven non-toxigenic E. coli O157 strains in separate experiments. Persistence was measured semi-quantitatively by bacteriological assessment of E. coli O157 cultured from cloacal swabs (shedding score). In the 1-day-old chick model that was monitored for 43 days, all seven strains established well after inoculation. In the 6-week-old chicken model, one strain established and gave consistently high shedding for the duration of the experiment (156 days). Whereas of the remaining six strains, two persisted for 113 days, two persisted for 43 days, one persisted for 22 days and one strain was never detected.

Age Factors↗
PubMed2005

Attaching-effacing bacteria in animals.

Enteric bacteria with a demonstrable or potential ability to form attaching-effacing lesions, so-called attaching-effacing (AE) bacteria, have been found in the intestinal tracts of a wide variety of warm-blooded animal species, including man. In some host species, for example cattle, pigs, rabbits and human beings, attaching-effacing Escherichia coli (AEEC) have an established role as enteropathogens. In other host species, AE bacteria are of less certain significance. With continuing advances in the detection and typing of AE strains, the importance of these bacteria for many hosts is likely to become clearer. The pathogenic effects of AE bacteria result from adhesion to the intestinal mucosa by a variety of mechanisms, culminating in the formation of the characteristic intimate adhesion of the AE lesion. The ability to induce AE lesions is mediated by the co-ordinated expression of some 40 bacterial genes organized within a so-called pathogenicity island, known as the "Locus for Enterocyte Effacement". It is also believed that the production of bacterial toxins, principally Vero toxins, is a significant virulence factor for some AEEC strains. Recent areas of research into AE bacteria include: the use of Citrobacter rodentium to model human AEEC disease; quorum-sensing mechanisms used by AEEC to modulate virulence gene expression; and the potential role of adhesion in the persistent colonization of the intestine by AE bacteria. This review of AE bacteria covers their molecular biology, their occurrence in various animal species, and the diagnosis, pathology and clinical aspects of animal diseases with which they are associated. Reference is made to human pathogens where appropriate. The focus is mainly on natural colonization and disease, but complementary experimental data are also included.

Animals↗
PubMed2005

Naturally acquired attaching and effacing Escherichia coli in sheep.

In a series of experiments involving the inoculation of sheep with Escherichia coli O157:H7, and subsequent detailed histopathological examination of the intestinal mucosa, attaching-effacing (AE) lesions formed by elements of the natural flora were observed in 18% of animals. These incidental AE lesions typically were small and sparse, and were not associated with clinical disease. It was possible to identify further some of the lesional bacteria, revealing that E. coli O115 had formed lesions in one of the seven affected animals, and similarly E. coli O26 had formed some of the lesions in another. As AE strains, source flocks, housing and feed sources were diverse, a common source of lesion-forming bacteria appears to be unlikely. It is postulated that subclinical AE lesions are a mechanism of persistence of AE bacteria in sheep.

Animals↗
PubMed2005

Colonization of 8-week-old conventionally reared goats by Escherichia coli O157 : H7 after oral inoculation.

Enterohaemorrhagic Escherichia coli O157 : H7 infections of man have been associated with consumption of unpasteurized goat's milk and direct contact with kid goats on petting farms, yet little is known about colonization of goats with this organism. To assess the contribution of flagella and intimin of E. coli O157 : H7 in colonization of the goat, 8-week-old conventionally reared goats were inoculated orally in separate experiments with 1x10(10) c.f.u. of a non-verotoxigenic strain of E. coli O157 : H7 (strain NCTC 12900 Nal(r)), an aflagellate derivative (DMB1) and an intimin-deficient derivative (DMB2). At 24 h after inoculation, the three E. coli O157 : H7 strains were shed at approximately 5x10(4) c.f.u. (g faeces)(-1) from all animals. Significantly fewer intimin-deficient bacteria were shed only on days 2 (P = 0.003) and 4 (P = 0.014), whereas from day 7 to 29 there were no differences. Tissues from three animals inoculated with wild-type E. coli O157 : H7 strain NCTC 12900 Nal(r) were sampled at 24, 48 and 96 h after inoculation and the organism was cultured from the large intestine of all three animals and from the duodenum and ileum of the animal examined at 96 h. Tissues were examined histologically but attaching-effacing (AE) lesions were not observed at any intestinal site of the animals examined at 24 or 48 h. However, the animal examined at 96 h, which had uniquely shed approximately 1x10(7) E. coli O157 : H7 (g faeces)(-1) for the preceding 3 days, showed a heavy, diffuse infection with cryptosporidia and abundant, multifocal AE lesions in the distal colon, rectum and at the recto-anal junction. These AE lesions were confirmed by immunohistochemistry to be associated with E. coli O157 : H7.

Adhesins, Bacterial↗
PubMed2005

Effect of the growth promoter avilamycin on emergence and persistence of antimicrobial resistance in enteric bacteria in the pig.

AIM: To assess the effect of the growth promoter avilamycin on emergence and persistence of resistance in enteric bacteria in the pig. METHODS AND RESULTS: Pigs (treated with avilamycin for 3 months and controls) were challenged with multi-resistant Salmonella Typhimurium DT104 and faecal counts were performed for enterococci, Escherichia coli, S. Typhimurium and Campylobacter (before, during and 5 weeks post-treatment). Representative isolates were tested for antibiotic resistance and for the presence of resistance genes. Avilamycin-resistant Enterococci faecalis (speciated by PCR) were isolated from the treated pigs and continued to be detected for the first week after treatment had ceased. The avilamycin-resistance gene was characterized by PCR as the emtA gene and speciation by PCR. MIC profiling confirmed that more than one strain of Ent. faecalis carried this gene. There was no evidence of increased antimicrobial resistance in the E. coli, Salmonella and Campylobacter populations, although there was a higher incidence of tetB positive E. coli in the treated pigs than the controls. CONCLUSION: Although avilamycin selects for resistance in the native enterococci population of the pig, no resistant isolates were detected beyond 1 week post-treatment. This suggests that resistant isolates were unable to persist once selective pressure was removed and were out-competed by the sensitive microflora. SIGNIFICANCE AND IMPACT OF THE STUDY: Our data suggest the risk of resistant isolates becoming carcass contaminants and infecting humans could be minimized by introducing a withdrawal period after using avilamycin and prior to slaughter.

Animal Husbandry↗
PubMed2005

Farm disinfectants select for cyclohexane resistance, a marker of multiple antibiotic resistance, in Escherichia coli.

AIMS: The aim of this study was to determine if three classes of farm disinfectants were able to select for ciprofloxacin or cyclohexane tolerant [indicative of a multiple antibiotic resistance (MAR) phenotype] Escherichia coli and if cyclohexane-tolerant E. coli could be isolated from farms. METHODS AND RESULTS: Chicken slurry containing ca 1 : 99 ratio ciprofloxacin resistant : susceptible E. coli (10 different resistant strains examined) was treated for 24 h with each of the disinfectants and examined for survival of resistant : susceptible strains. Ciprofloxacin-sensitive (n=5) and -resistant (n=5) E. coli were grown with sublethal concentrations of the disinfectants and then plated to agar containing ciprofloxacin or overlaid with cyclohexane. Escherichia coli (n=389) isolated from farms were tested for cyclohexane tolerance. Minimum inhibitory concentrations (MIC) were determined against representative isolates and mutants. The disinfectants did not select for the ciprofloxacin-resistant E. coli in poultry slurry but following growth with each of the three disinfectants, higher numbers (P < or = 0.023) of cyclohexane-tolerant E. coli were isolated and these had a MAR phenotype. Of the 389 farm E. coli tested, only one was cyclohexane tolerant. CONCLUSIONS: It is possible that in a farm environment, E. coli could be exposed to similar concentrations of the disinfectants that are selected for MAR type organisms under these laboratory conditions. SIGNIFICANCE AND IMPACT OF THE STUDY: Data from this study suggest that cyclohexane-resistant E. coli are not common on farms, but in view of the ease of isolating them in the laboratory with farm disinfectants, further investigations on farms are warranted.

Agrochemicals↗
PubMed2004

Characterisation of attaching-effacing Escherichia coli isolated from animals at slaughter in England and Wales.

Escherichia coli isolates were recovered from faecal samples taken from cattle, sheep and pigs at slaughter in England and Wales. Isolates (n = 1227) selected at random from this collection were each hybridised in colony dot-blot experiments with an eae gene probe that presumptively identified attaching-effacing E. coli (AEEC). Of the 99 (8.1%) eae positive isolates 72 were of ovine origin, 24 were of bovine origin and three of porcine origin. None were typed as O157:H7 whereas 78 were assigned to 23 serogroups and 21 were untypable. The most frequently isolated eae positive serogroups were O156 (10), O26 (8), O103 (8), O108 (7) O56 (6) and O168 (6) of which serogroups O103 and O156 only were recovered from all three animal species. In tissue culture adherence assays, 36 representatives of eae positive isolates of all serogroups and host of origin tested induced intimate attachment with varying degrees of actin accumulation and pedestal formation in the HEp-2 cells. The identity of the eae type for these 36 was determined by specific PCR and the most prevalent intimin types were eaebeta (15), eaegamma (12) and eae (4). Isolates were examined by PCR for the presence of other virulence determinants and five possessed stx1 but none possessed stx2. One O115 eae isolate possessed cnf1 and 2, hlyA, etpD and katP genes which is a novel combination of virulence determinants.

Adhesins, Bacterial↗
PubMed2004

The O-antigen of Salmonella enterica serotype Enteritidis PT4: a significant factor in gastrointestinal colonisation of young but not newly hatched chicks.

The lipopolysaccharide of Salmonella and other Gram negative pathogenic species has been implicated as a major virulence determinant and in this study we report the role of LPS of S. Enteritidis in the colonisation and persistent gastrointestinal infection of young poultry. The gene encoding the unique O-antigen ligase, waaL, was mutated by insertional inactivation in a well characterised S. Enteritidis strain, S1400/94. The waaL mutant, designated PCP, produced rough colonies on agar medium, did not agglutinate O9 antiserum, did not produce an LPS ladder on silver stained gels and was serum sensitive. PCP and a nalidixic acid marked derivative of S1400/94 (S1400/94 Nalr) were used to orally challenge young chicks, separately and together in competitive index experiments. At post-mortem examination of 1-day-old chicks challenged S1400/94 Nalr and PCP separately there were no significant differences in the numbers of S1400/94 Nalr and PCP bacteria in tissues sampled on days 1, 2, and 5. By day 42 after challenge S1400/94 Nalr bacteria were recovered in significantly higher numbers than PCP from the caecal contents (P < 0.001). In competitive index studies in the 1-day-old chick PCP colonised, invaded and persisted in lower numbers than S1400/94 Nalr. In 4-week-old chicks challenged separately, PCP bacteria were recovered from all tissues examined in significantly lower numbers than S1400/94 Nalr. In competitive index experiments in 4-week-old chicks, PCP was not detected at any site and at any time point. Therefore, the O-antigen of S. Enteritidis plays an important role in poultry infections although this role is less important in the newly hatched chick.

Age Factors↗
PubMed2004

Effect of triclosan or a phenolic farm disinfectant on the selection of antibiotic-resistant Salmonella enterica.

OBJECTIVE: To determine the effect of growth of five strains of Salmonella enterica and their isogenic multiply antibiotic-resistant (MAR) derivatives with a phenolic farm disinfectant or triclosan (biocides) upon the frequency of mutation to resistance to antibiotics or cyclohexane. METHODS: Strains were grown in broth with or without the biocides and then spread on to agar containing ampicillin, ciprofloxacin or tetracycline each at 4x MIC or agar overlaid with cyclohexane. Incubation was for 24 and 48 h and the frequency of mutation to resistance was calculated for strains with and without prior growth with the biocides. MICs were determined and the presence of mutations in the acrR and marR regions was determined by sequencing and the presence of mutations in gyrA by light-cycler analysis, for a selection of the mutants that arose. RESULTS: The mean frequency of mutation to antibiotic or cyclohexane resistance was increased approximately 10- to 100-fold by prior growth with the phenolic disinfectant or triclosan. The increases were statistically significant for all antibiotics and cyclohexane following exposure to the phenolic disinfectant (P </= 0.013), and for ampicillin and cyclohexane following exposure to triclosan (P </= 0.009). Mutants inhibited by >1 mg/L ciprofloxacin arose only from strains that were MAR. Reduced susceptibility to ciprofloxacin (at 4x MIC for parent strains) alone was associated with mutations in gyrA. MAR mutants did not contain mutations in the acrR or marR region. CONCLUSIONS: These data renew fears that the use of biocides may lead to an increased selective pressure towards antibiotic resistance.

Anti-Bacterial Agents↗
PubMed2004

Mutant prevention concentrations of ciprofloxacin and enrofloxacin for Salmonella enterica.

OBJECTIVES: To determine the mutant prevention concentrations (MPCs) of ciprofloxacin and enrofloxacin against four strains of Salmonella enterica serovar Enteritidis and four strains of S. Typhimurium including one fully susceptible, one multiply resistant (MAR), one GyrA mutant and one GyrA/MAR mutant. Further, to examine mutants arising after exposure to sub-MPC concentrations of the antibiotics for susceptibility to ciprofloxacin and enrofloxacin, and cyclohexane tolerance. METHODS: MICs were determined using the agar dilution method of the BSAC. The MPC was recorded as the lowest concentration of antibiotic to inhibit growth from an inoculum of 10(10) cfu. RESULTS: The MPCs and resulting MPC/MIC ratios of enrofloxacin were generally two- to four-fold higher than for ciprofloxacin. At 24 h for both antibiotics, MPCs were lowest for the fully susceptible strains (0.25-0.5 mg/L), similar for the MAR (1-4 mg/L) and GyrA (2-4 mg/L) mutants and highest for the GyrA/MAR mutants (1-8 mg/L). MPC/MIC ratios at 24 h were 2-16 for all strains except those for the MAR strains without mutation in gyrA where the ratios were 8-64. CONCLUSIONS: The ability to eradicate Salmonella in vivo depends on many factors such as antibiotic susceptibility of the strain, dose and route of administration. It is suggested that these MPC values will be useful when considering dosing strategies. In view of the high MPC/MIC ratio, MAR strains with wild-type gyrA, although susceptible to ciprofloxacin (MICs 0.06-0.13 mg/L), may give rise to treatment failures.

Anti-Infective Agents↗
PubMed2004

Antibiotic resistance genes, integrons and multiple antibiotic resistance in thirty-five serotypes of Salmonella enterica isolated from humans and animals in the UK.

OBJECTIVES: To examine 397 strains of Salmonella enterica of human and animal origin comprising 35 serotypes for the presence of aadB, aphAI-IAB, aadA1, aadA2, bla(Carb(2)) or pse1, bla(Tem), cat1, cat2, dhfr1, floR, strA, sul1, sul2, tetA(A), tetA(B) and tetA(G) genes, the presence of class 1 integrons and the relationship of resistance genes to integrons and antibiotic resistance. RESULTS: Some strains were resistant to ampicillin (91), chloramphenicol (85), gentamicin (2), kanamycin (14), spectinomycin (81), streptomycin (119), sulfadiazine (127), tetracycline (108) and trimethoprim (45); 219 strains were susceptible to all antibiotics. bla(Carb(2)), floR and tetA(G) genes were found in S. Typhimurium isolates and one strain of S. Emek only. Class 1 integrons were found in S. Emek, Haifa, Heidelberg, Mbandaka, Newport, Ohio, Stanley, Virchow and in Typhimurium, mainly phage types DT104 and U302. These strains were generally multi-resistant to up to seven antibiotics. Resistance to between three and six antibiotics was also associated with class 1 integron-negative strains of S. Binza, Dublin, Enteritidis, Hadar, Manhattan, Mbandaka, Montevideo, Newport, Typhimurium DT193 and Virchow. CONCLUSION: The results illustrate specificity of some resistance genes to S. Typhimurium or non- S. Typhimurium serotypes and the involvement of both class 1 integron and non-class 1 integron associated multi-resistance in several serotypes. These data also indicate that the bla(Carb(2)), floR and tetA(G) genes reported in the SG1 region of S. Typhimurium DT104, U302 and some other serotypes are still predominantly limited to S. Typhimurium strains.

Animals↗
PubMed2004

Flagella and curli fimbriae are important for the growth of Salmonella enterica serovars in hen eggs.

Salmonella enterica serovar Enteritidis is unable to multiply in the albumen of fresh eggs and must gain access to the yolk contents in order to multiply to a high level (>10(6) c.f.u. per ml egg contents). As human Salmonella infections resulting from the consumption of infected eggs more frequently involve serovar Enteritidis phage type (PT) 4 than other serovars or PTs, a number of isolates of various S. enterica serovars were examined for their ability to multiply to a high level in eggs over a period of 8 days storage at 20 degrees C. Their behaviour was compared to that of a range of defined fimbrial and flagella mutants of S. Enteritidis. Strains that did not express flagella were unable to multiply in eggs, and those deficient for curli fimbriae, including strains of S. Enteritidis PT6, displayed high-level growth in significantly fewer eggs than those able to express curli. Most S. Enteritidis strains multiplied to a high level in between 5 and 10 % of eggs during 8 days storage. One PT4 strain, though, showed high levels of growth in more than 25 % of eggs over this period, significantly higher than the other PTs or the two other isolates of PT4 tested. This ability may be important for the association of PT4 infection with the consumption of eggs.

Animals↗