Epidemiological studies of clinical and subclinical ovine mastitis in Awassi sheep in northern Jordan

Forty-six Awassi sheep flocks selected by stratified random sampling were subjected to a cross-sectional study to determine the prevalence of intramammary infections, to assess the influence of flock size and parity on the prevalence of somatic cell count (SCC) and to identify major udder pathogens. Of the 3472 udder halves examined, 29.8% had over 10⁶ SCC/ml and 0.03% had dry teats due to chronic mastitis. Flocks with 30–49 milking ewes (small flock size) were much younger (P < 0.001) than flocks with 50–99 ewes (medium) and flocks with ≥ 100 ewes (large). Pairwise analysis of the InSCC of both halves of the udders revealed significant mean differences for small and large flock size (P < 0.05), and for medium and large flock size (P < 0.001). Mean InSCC was lower (P < 0.05) in samples obtained from the left half compared with samples of the right half of the udder. Multiparous ewes had higher (P < 0.001) mean InSCC than primiparous ewes. Also, ewes with twin lambs had higher (P < 0.001) mean InSCC in the right half of the udder compared with single-lamb ewes. Samples collected in January (winter) had lower (P < 0.05) mean InSCC compared with samples collected in June. The most common organisms isolated from subclinical mastitis cases were coagulase-negative Staphylococci (17.8%), E. coli (13.6%), Streptococcus agalactiae (6.8%) and Staphylococcus aureus (6.8%). Of the 46 flocks, 20 were monitored monthly for 9 consecutive months to determine the incidence of clinical mastitis diagnosed by shepherds or/and sheep farmers with major pathogens. The incidence of clinical mastitis (expressed as the number of clinical cases per 100 ewe-months) were 2.1 ± 1.9 (SD), 1.9 ± 1.1, and 1.2 + 2.1 for small, medium and large flocks size strata, respectively. The overall population estimate was 1.7 ± 0.02 cases per 100 ewe-months. The most-common clinical isolates were S. aureus (22% of all clinical isolates) and E. coli (14.2%).     

Factors associated with the presence of Escherichia coli O157 in feedlot-cattle water and feed in the Midwestern USA

Our objective was to generate hypotheses about associations between management, climate, and the presence of Escherichia coli O157 in feedlot–cattle water tanks and in feedlot–cattle feed. Water samples from 710 tanks on 73 feedlots, and feed-samples from a subset of 504 pens on 54 feedlots, in four US states were tested for E. coli O157. Management and climate factors were ascertained by survey and observation. Escherichia coli O157 were isolated from 13% of the water tanks and at least one water tank was positive on 60% of the feedlots. The factors significantly associated with E. coli O157 in water were greater percentage of cattle shedding E. coli O157 in faeces within the same pen, higher concentration of total E. coli in the water, lack of the clarity of the water, the use of fly traps, the reported frequency of rodent sightings in the pen or alley area, and the weather at the time of sampling. Escherichia coli O157 were isolated from 14.9% of the feed samples obtained from the feedbunks. Factors positively associated with E. coli O157 in feed were higher heat index at the time of sampling, the presence of cottonseed meal in the ration, and the feedlot location (state). Coliform counts in feed, presence of E. coli O157 in water tanks and faecal prevalence of E. coli O157 were not associated with the presence of E. coli O157 in feed.     

Antimicrobial-resistance trends in bacterial isolates from companion-animal community practice in the UK

We conducted a longitudinal, retrospective investigation of antimicrobial resistance in bacterial isolates obtained from canine and feline clinical cases in veterinary community practice in UK (1989–1997). Individual-drug resistance was examined using isolates of Escherichia coli and Staphylococcus spp. as Gram-negative and Gram-positive indicator organisms, respectively. The annual prevalence of resistance was calculated for each organism to each of nine (for E. coli) and 11 (for Staphylococcus spp.) selected antimicrobials. The annual prevalence of multiple-drug resistance (MDR) was calculated for E. coli, Proteus spp., Pseudomonas spp., staphylococci and streptococci.

Using a chi-square test for trend, significant rising trends were identified in individual resistance of E. coli to clavulanate-amoxycillin and streptomycin, and in MDR of E. coli, Proteus spp. and Pseudomonas spp.. Declining trends were identified in individual resistance of Staphylococcus spp. to ampicillin and penicillin. Comparison with previously reported results from a contemporaneous investigation of companion-animal hospital patients indicated that selection pressures acting on the two populations overlapped but were not identical.     

Abundance and phenotypic diversity of Escherichia coli isolates with diminished susceptibility to expanded-spectrum cephalosporins in faeces from healthy food animals after slaughter

Antimicrobial resistance (AR) is an increasing phenomenon but its quantitative estimation remains controversial. The classical resistance percentage approach is not well suited to detect either emergence or low levels resistance. One option is to shift the focus from strains to hosts. This approach is applied to test for phenotypic diversity associated with diminished susceptibility to expanded-spectrum cephalosporins (DSESC) in faecal Escherichia coli from healthy food animals in Spain.

We performed E. coli enumeration in faecal samples of broilers (82 pooled samples) and pigs (80 pooled samples) at the slaughterhouse level, using Coli-ID plates alone and supplemented with cefotaxime at two levels (1 and 8 μg/ml). Antimicrobial susceptibility of isolates was tested by the agar diffusion method. Clustering was carried out using these numerical values and Ward and UPGMA methods.

When using plates supplemented with 1 μg/ml of cefotaxime for DSESC E. coli detection, 93% (76/82) of broiler pooled samples and 36% (29/80) pig pooled samples tested positive. When using 8 μg/ml of cefotaxime, 67% (55/82) of broilers and 13% (10/80) of pigs were positive. Nevertheless, the relative abundance of this phenotype was low in both animal species (range 0–4.3%). Irrespective of the clustering method (Ward or UPGMA), a noticeable phenotypic diversity was detected, especially from the plates containing 1 μg/ml of cefotaxime.

We concluded that: (a) E. coli with phenotype DSESC are common in broilers and pigs but are less frequent in pigs, and (b) the host approach is the most appropriate method for antimicrobial resistance assessment when null or very low levels of antimicrobial resistant bacteria are expected.     

Characterization of Escherichia coli isolated from healthy dogs

Five month old dogs from a Midwestern research kennel occasionally developed bloody diarrhea after shipment to other facilities. As previous diagnostic efforts failed to reveal any potential pathogens in feces from normal and diarrheic dogs, Escherichia coli was investigated for select virulence properties that may contribute to the occurrence of bloody diarrhea. Fecal swabs from 52 healthy dogs were examined for E. coli. Two hundred and sixty E. coli-like colonies were screened by PCR for the attaching and effacing (eae) gene, Shiga toxin (stx) genes, and the heat-stable enterotoxin type A (sta) gene. One hundred forty two of the 260 E. coli-like colonies (54.6%) from 43 dogs were eae or sta positive; and 60 of the eae and/or sta positive isolates were examined further. Among the 60 isolates, 23 (38.3%) possessed the eae gene, 32 (53.3%) possessed the sta gene, and five (8.3%) possessed both eae and sta genes (eae⁺/sta⁺). Of the 60 isolates, six sta⁺ and one eae⁺/sta⁺ isolates were hemolytic. When examined in the suckling mouse assay, five of six sta⁺ isolates and three of four eae⁺/sta⁺ isolates gave gut-to-remaining carcass ratios ≥0.083, indicating expression of heat-stable enterotoxin. These enterotoxin-producing isolates belonged to serogroups O42, O170, and O-negative.     

Characterisation of avian pathogenic Escherichia coli (APEC) associated with colisepticaemia compared to faecal isolates from healthy birds

A total of 114 avian pathogenic Escherichia coli (APEC) isolates were collected from cases of colisepticaemia occurring in broilers (77) and layers (37) within Ireland. In addition 45 strains isolated from faeces of healthy birds were included for comparison. All isolates were serogrouped, and examined for known virulence factors, mostly by PCR. The O78 serogroup represented 55 and 27% of broiler and layer colisepticaemic isolates respectively. All isolates were positive for curli fimbriae (crl, csg) and negative for afimbrial adhesin (afa). S-fimbrial (sfa) sequences were present in 8.8% of septicaemic isolates and 8.9% of healthy bird isolates. The majority of E. coli from cases of colisepticaemia (97.4%) and healthy bird (95.6%) isolates were positive for aerobactin (aer), and temperature sensitive haemagglutinin (tsh) was similarly detected in high numbers in 93.9 and 93.3%, respectively. In comparison to E. coli isolates from the faeces of healthy birds, a significantly higher percentage of isolates from septicaemic cases possessed Type 1 fimbriae (fimC) and increased serum survival (iss) gene sequences. Forty-seven (41.2%) isolates from septicaemic birds possessed P-fimbriae (pap) gene sequences, compared with only 15.6% from E. coli isolated from healthy birds. Haemolysin (hlyE) sequences were detected in 46.7% of isolates from healthy birds in comparison with 6.1% of septicaemic isolates. Sequences encoding colicin V (cvaC) were detected in 99.1% of septicaemic isolates and 82.2% of isolates from healthy birds. The K1 capsule was only present in two septicaemic isolates, both taken from layers. Motility was detected in 36.8% of E. coli isolated from cases of septicaemia, compared with 93.3% of isolates from healthy birds. These results demonstrate the presence of 11 virulence genes in E. coli isolated from cases of colisepticaemia within Ireland, and indicate the prevalence of iss and fimC.     

The prevalence and dynamics of Salmonella enterica IIIb 61:k:1,5,(7) in sheep flocks in Norway

Fifty randomly selected sheep flocks from a region in central Norway were sampled in December 1999 to determine the flock prevalence of Salmonella enterica subspecies diarizonae serovar 61:k:1,5,(7) (S. IIIb 61:k:1,5,(7)). From each flock, 15–41 rectal swabs were collected from individual sheep of different age groups and examined for S. IIIb 61:k:1,5,(7). Positive flocks were visited again in January–April and each time, rectal swabs from the same animals were collected and examined for this specific serovar. Seven flocks (14%; 95% CI 6.3–27%) were positive for S. IIIb 61:k:1,5,(7) in December; in all, 10 sheep out of the 1233 (0.8%) were positive at the first sampling. From the seven positive flocks, six, five, six, and nine animals were positive in January, February, March, and April, respectively. Of the total 21 individual sheep tested positive from January to April, 15 were >2 years old (OR_ex=3.26; 1.1–10.2). Six out of the seven positive flocks were large flocks (>117 ewes). Sharing of rams between flocks did not seem to be a risk factor for the presence of S. IIIb 61:k:1,5,(7) in a flock.     

撒坝猪源大肠杆菌高致病性毒力岛诱导病理损伤的超微结构特征

为探究撒坝猪源大肠杆菌（E.coli）高致病性毒力岛（HPI）诱导小鼠病理损伤的超微结构特征,本研究将实验室保存的E.coli HPI阳性株（HPI⁺）和E.coli HPI基因缺失株（^ΔHPI）进行复苏和培养,分别用E.coli HPI⁺、E.coli ^ΔHPI菌株以腹腔接种的方式感染昆明小鼠,检测菌株的半数致死量（50% lethal dose,LD₅₀）,通过HE染色和透射电镜观察并分析菌株对小鼠病理损伤的超微结构特征,利用免疫组织化学标记白细胞介素-1β（interleukin-1β,IL-1β）阳性细胞在被感染小鼠肝脏和肾脏组织中的分布,以反映E.coli HPI⁺及E.coli ^ΔHPI菌株所引起炎症水平的差异。结果显示,E.coli HPI⁺和E.coli ^ΔHPI菌株的半数致死量分别为1×10^7.39和1×10^8.62 CFU/mL;HE染色显示,E.coli感染小鼠后,可见肝脏细胞肿胀、变性,肝窦淤血,肾脏间质淤血,肾小管上皮细胞变性脱落等病理变化;超微结构变化显示,肝脏细胞的完整形态消失,胞核呈不规则形态,线粒体畸形,粗面内质网上核糖体脱落,滑面内质网增生;多数肾小管上皮细胞出现胞核固缩,部分细胞核核仁边移、体积增大,足突融合,系膜细胞间隙变宽。此外,E.coli HPI⁺感染组小鼠于肝脏、肾脏的水肿现象较E.coli ^ΔHPI菌株感染的小鼠更为明显。免疫组化结果显示,大肠杆菌感染小鼠后,IL-1β蛋白主要表达于肝细胞、中央静脉周围、肾间质细胞和肾小管上皮细胞,且E.coli HPI⁺感染组的IL-1β表达量高于E.coli^ΔHPI感染组。综上所述,撒坝猪源E.coli HPI能够调控E.coli对小鼠的致病性,HPI的调控作用可使E.coli对小鼠肝脏、肾脏造成的病变及超微结构变化更明显,并且能够增加小鼠的炎症反应。     

Risk factors for hide contamination of Scottish cattle at slaughter with Escherichia coli O157

In the slaughter processing of cattle, contaminated hides have been identified as one of the major sources of Escherichia coli O157 carcase contamination. Logistic regression analysis was applied to data collected in a large scale study in Scotland involving 222 cattle forming 34 groups sent for slaughter from 30 farms to 10 slaughterhouses. Aspects of individual animal characteristics, farm management practices and slaughterhouse features were examined to identify potential risk factors for hide contamination at harvest. Two models were developed, the first in which slaughterhouse was modelled as a fixed effect, and a second model where slaughterhouse and farm groups were modelled as random effects. In the first model, there was a significantly increased risk of a carcase testing positive for E. coli O157 on the hide if either the hide of the carcase immediately before or after it on the line was contaminated (OR 3.6; 95% CI: 1.4–9.9). If both adjacent carcases had contaminated hides, the odds ratio for the study carcase having a contaminated hide rose to 11.5 (95% CI: 4.4–32.5). If animals were held in lairage, receiving hay as feed appeared to have a protective effect on hide contamination. Transportation to the slaughterhouse by haulier, as opposed to transport by the farmer, was associated with a 5.4 increase in the odds of E. coli O157 contamination. The use of a crush in the lairage, often employed when reading ear tags, was also found to significantly increase the odds of hide contamination with E. coli O157. In the second model, the inclusion of slaughterhouse and farm group as random effects resulted in two of the previously identified factors being associated with hide contamination. If at least one of the adjacent carcases on the line had a contaminated hide, the associated odds ratio was 6.6 (95% CI: 2.8–15.9), which rose to 22.7 (95% CI: 9.3–55.5) if both adjacent hides were contaminated. Receiving hay in lairage was found to be important to the model, although not significant in itself (OR 0.005; 95% CI: 1.2e⁻⁶–20.7). These results suggest that modifiable risk factors for hide contamination exist. However, in order best to reduce the prevalence of hide contamination at slaughter, individual slaughterhouse risk assessment and intervention strategies are appropriate.     

The F18 fimbrial adhesin FedF is highly conserved among F18+Escherichia coli isolates

F18⁺ Escherichia coli cause postweaning diarrhoea and oedema disease in newly weaned piglets. Protection against these diseases can be established by preventing the fimbrial adhesion of these bacteria to the enterocytes of the porcine intestine. To test a vaccine against F18⁺ E. coli consisting of the adhesin of F18 fimbriae, FedF, the conservation of the FedF subunit had to be examined. Therefore, the fedF sequence of 37 F18⁺ E. coli isolates from different countries was determined and compared to the fedF gene of the F18ab reference strain F107/86. The amino acid sequence of the mature FedF from the individual F18⁺ E. coli isolates was 96–100% identical to that from E. coli F107/86, but the overall homology was 90.4%. Hyper variable regions were not found in the FedF sequence. The FedF sequence was conserved over the different countries and between the two antigenic variants, F18ab and F18ac, suggesting that F18ab and F18ac strains have the same receptor. Furthermore, the conserved C-terminal region in the FedF adhesin suggests that the F18 fimbriae, in analogy with type 1 and P pili, are assembled by a donor strand mechanism. In conclusion, the reported conservation of FedF supports the usefulness of the fimbrial adhesin as a subunit vaccine against F18⁺ E. coli infection.     

Fate of pathogenic and nonpathogenic microorganisms during storage of liquid hog manure in Québec

Pathogenic microorganisms in manure represents a potential hazard to human and animal. Few data describing the microbiological content of liquid hog manure intended for spreading are available in the scientific literature. The objective of this project was to verify the presence and estimate the persistence of Escherichia coli, Salmonella spp., Yersinia enterocolitica and Cryptosporidium spp. in liquid hog manure from storages under conditions typical of commercial swine production in Québec. E. coli content of liquid hog manure taken during the spreading period in the 32 hog operations varied between 0 and 5.52 log₁₀ CFU/g with a 95% confidence interval of 3.16–4.23 log₁₀ CFU/g. Salmonella spp., Y. enterocolitica and Cryptosporidium spp. were detected in 37%, 9% and 3% samples, respectively. Under the conditions of this experiment, the predicted number of days required to obtain a 90% reduction of E. coli populations varied between 15 and 26 days, while the predicted storage period necessary to reach undetectable levels was 54–114 days. The maximal persistence of Salmonella observed in this study was 88 days. A 73-day storage time was insufficient for the elimination of Y. enterocolitica.     

Prevalence of intestinal pathogens in Danish finishing pig herds

Our aim was to determine the prevalence of the intestinal bacteria: Lawsonia intracellularis, Brachyspira hyodysenteriae, Serpulina intermedia, Brachyspira innocens, Brachyspira pilosicoli, pathogenic Escherichia coli (serogroups O138, O139, O141 and O149) and Salmonella enterica in Danish finishing pig herds. A total of 79 herds was randomly selected and visited during 1998. From each herd, 20 faecal samples were collected from individual pigs weighing 30–50 kg. Furthermore, 10 pooled pen samples were collected and examined for S. enterica. In total, 1580 faecal samples and 790 pen samples were collected and examined by polymerase chain reaction (PCR) or culture. L. intracellularis was found in 74 herds (93.7%), B. hyodysenteriae in two herds (2.5%), S. intermedia in 10 herds (12.7%), B. innocens in 27 herds (34.2%), B. pilosicoli in 15 herds (19.0%), pathogenic E. coli in 19 herds (24.1%) and S. enterica in eight herds (10.1%). The within-herd prevalences of L. intracellularis and B. hyodysenteriae were 25–30%; the within-herd prevalences of the other agents were 5–10%. Three herds (4%) were not infected with any of the bacteria and 25 herds (32%) were only infected with L. intracellularis.     

东南沿海地区水禽源大肠杆菌耐药表型及耐药基因型的调查

为研究水禽中大肠杆菌的耐药表型及耐药基因型,本研究从中国广东、福建、浙江、江苏和山东5个省市的水禽养殖场及周边环境中采集鸭粪便样品、水样以及土样1 505份,采用选择性培养基和基质辅助激光解吸电离飞行时间(MALDI-TOF-MS)质谱分离鉴定大肠杆菌,采用微量肉汤稀释法检测耐药表型,采用PCR方法筛选大肠杆菌中的25种耐药基因。结果显示,1 505份样品中共分离鉴定出449株大肠杆菌,分离率为29.8%,其中335份来源于粪便,52份来源于土壤,62份来源于水,这些样品中浙江(43.3%)和广东(43.2%)的分离率最高,其次是福建(28.1%)和江苏(23.8%),山东(18.3%)的分离率最低。449株大肠杆菌具有多重耐药性,对氨苄西林、环丙沙星、金霉素、氟苯尼考和磺胺类药物的耐药率分别为90.2%、50.3%、96.7%、87.3%和90.6%,而对替加环素和美罗培南则比较敏感,来源不同省份的大肠杆菌对不同抗菌药呈现出不同的耐药率。PCR检测结果发现,449株大肠杆菌中耐药基因tet(A)检出率最高(88.2%),随后是floR(58.13%)、sul2(57.02%)、tet(B)(53.9%)、cmlA(39.2%)和sul1(36.75%),未检测到qnrA、tet(M)和tet(X)耐药基因的大肠杆菌。在这5个省份中,上述耐药基因在山东省样品中分布均较高,而在浙江省和江苏省样品中分布较低。综上所述,本研究调查了中国东南沿海五省水禽及环境中大肠杆菌的耐药现状,为养殖业抗生素的规范使用提供理论依据。     

同一养殖模式下不同地区猪源大肠杆菌耐药性比较

本试验旨在比较新疆相同养殖模式下不同地区猪源大肠杆菌的耐药情况。分别在某规模化养猪场呼图壁(207份)、玛纳斯(210份)和昌吉(210份)地区采集粪样,共计627份样品,各地区猪源大肠杆菌的分离率均为100.0%。采用微量肉汤稀释法对分离出的大肠杆菌进行临床常用抗菌药物的药敏试验,并通过卡方检验比较3个地区猪源大肠杆菌耐药率的差异。结果显示,呼图壁地区猪源大肠杆菌对安普霉素、阿米卡星、阿莫西林—克拉维酸和头孢噻呋的耐药率均极显著高于另外两地区(P< 0.01);玛纳斯地区猪源大肠杆菌对环丙沙星的耐药率显著高于另外两地区(P< 0.05),对诺氟沙星的耐药率极显著高于另外两地区(P< 0.01);昌吉地区猪源大肠杆菌对诺氟沙星的耐药率极显著高于呼图壁地区(P< 0.01),而对阿莫西林—克拉维酸和氨苄西林的耐药率均显著高于玛纳斯地区(P< 0.05)。呼图壁地区3~8耐菌株占94.7%,玛纳斯地区3~7耐菌株占89.5%,昌吉地区4~8耐菌株占82.4%。不同地区之间3~7耐菌株数差异不显著(P> 0.05)。结果表明,在相同的养殖模式下,不同地区猪源大肠杆菌的耐药情况不同。此外,养殖场猪源大肠杆菌的耐药问题严重,以多药耐药为主,耐药谱型呈多样化。     

犊牛腹泻源大肠杆菌耐药情况及HPI相关基因的检测

本研究旨在明确犊牛腹泻源性大肠杆菌的耐药情况、强毒力岛（HPI）标志基因及相关基因的携带情况，以及大肠杆菌分离株与HPI携带的关系。采集犊牛病理性腹泻样本158份，采用麦康凯培养基和伊红美蓝培养基进行筛选，镜检符合大肠杆菌形态的进行VITEK 2 Compact生化鉴定和PCR鉴定，采用K-B纸片法对大肠杆菌分离株进行药敏试验，应用PCR方法进行分离株HPI相关基因携带情况的检测。结果显示，共分离得到75株大肠杆菌，分离株对阿莫西林、哌拉西林、氨苄西林、头孢唑啉、氟苯尼考、恩诺沙星、四环素的耐药率均>90%，对头孢氨苄、头孢拉定、头孢曲松、环丙沙星、诺氟沙星和氧氟沙星的耐药率均≥ 60.00%，对阿米卡星较敏感，耐药率为9.33%；75株大肠杆菌全部耐3种以上药物，多重耐药（≥ 10）的菌株占85.33%，耐药谱集中在耐14~17种药物，5株对19种药物全部耐药。HPI标志基因irp2的阳性率为100%，其他相关基因fyuA、irp3、irp5、irp8和ytbA的检出率在66.00%以上。综上所述，宁夏地区犊牛腹泻源性大肠杆菌耐药普遍，多重耐药现象严重。     

Comparison of Drug Resistance of E.coli from Pigs in Different Regions under the Same Breeding Mode

In order to compare the resistance of E.coli from pigs of different regions under same breeding mode in Xinjiang, we collected fecal samples from pig farms of Hutubi (207), Manasi (210) and Changji (210) in a certain scale, respectively, a total of 627 samples, and isolation rate of E.coli from fecal samples were all 100.0%.The broth dilution method was used to detect resistance of E.coli to antimicrobials, and we compared the differences of resistance rate of E.coli from pig farms in three regions by chi square test. E.coli from pig farms of Hutubi region to apramycin, amikacin, amoxicillin-clavulanic acid and ceftiofur existed extremely significant differences comparing with another two regions (P< 0.01).E.coli from pig farms of Manasi region to ciprofloxacin existed significant differences comparing with another two regions (P< 0.05), and existed extremely significant differences to norfloxacin (P< 0.01).E.coli from pig farms of Changji region to norfloxacin had extremely significant differences comparing with Hutubi region (P< 0.01), and existed significant differences to amoxicillin-clavulanic acid and ampicillin comparing with Manasi region (P< 0.05).3 to 8 resistant E.coli strains accounted for 94.7% in Hutubi region, 3 to 7 resistant E.coli strains accounted for 89.5% in Manasi region and 4 to 8 resistant E.coli strains accounted for 82.4% in Changji region, respectively.There was no significant difference among different regions on multi-drug resistance (P> 0.05).The results indicated that E.coli from pigs of different regions under the same breeding mode had different characteristics of resistance.In addition, the resistance of E.coli from pigs were very serious and mainly multi-drug resistant, drug resistance patterns were diversified.     

牛源大肠杆菌对秀丽隐杆线虫的致病性研究

为建立牛源大肠杆菌-秀丽隐杆线虫致病模型，本研究从广西南宁、桂林、柳州等地区收集的牛病料中分离出13株大肠杆菌，继而对这些大肠杆菌进行血清学鉴定及小鼠、秀丽隐杆线虫的致病性试验。采用玻片凝集法鉴定大肠杆菌的O血清型，并将13株大肠杆菌培养液以3.0×10⁹ CFU/mL、0.2 mL/10 g体重给小鼠腹腔注射，同时分别喂食N2野生型秀丽隐杆线虫。结果显示，大肠杆菌的O血清型为O127、O126和O44，其中O126为优势血清型（4/13）。致病性结果显示，有11株大肠杆菌能使小鼠致死（致死率为40%~100%），2株大肠杆菌对小鼠没有致死性（致死率为0）。对小鼠有强致病性的大肠杆菌，对线虫的致死率也较高，死亡率在第3~6天最为显著，半数致死时间为3~4.5 d，最长存活时间为9 d；对小鼠不致死的两株大肠杆菌对线虫的致死率也较低，线虫死亡率下降趋势缓慢，半数致死时间为5~6 d，最长存活时间为10~11 d。肠道细菌计数结果显示，大肠杆菌在线虫体内的数量与时间呈线性关系，大肠杆菌不断破坏线虫的免疫系统，从而导致了线虫的死亡。本研究结果表明，大肠杆菌对线虫和小鼠的致病力试验结果一致，说明成功建立了牛源大肠杆菌-秀丽隐杆线虫致病模型，为牛病防治与临床用药提供了依据。     

Associations between management, climate, and Escherichia coli O157 in the faeces of feedlot cattle in the Midwestern USA

Our objective was to generate hypotheses for potential on-farm control strategies for Escherichia coli O157 by identifying associations between management practices and climate, and the presence of E. coli O157 in feedlot cattle. Faeces were obtained from 10,622 cattle in 711 pens on 73 feedlots between May and August 2001. Management and climate information was obtained by questionnaire and observation at the time of sampling. The prevalence of E. coli O157 was 10.2% at the sample level, 52.0% at the pen-level, and 95.9% at the feedlot-level. The factors associated with the presence of E. coli O157 in cattle faeces were the frequency of observing cats in the pens or alleys (most common when observed daily), the presence of E. coli O157 in the water tanks (positive association), the historical use of injectable mass medication (positive association), the use of antibiotics in the ration or water (negative association), the wetness of the pen, number of cattle in the pen (negative association), wind velocity (positive association), and height of the feed bunk (positive association).     

Prevalence and epidemiology of selected enteric infections of livestock in Trinidad

In a study of diarrhoeic and non-diarrhoeic livestock (cattle, pigs and sheep) from 50 farms in Trinidad, the prevalence of bacterial (Campylobacter, Salmonella, Yersinia and Escherichia coli), parasitic (coccidia, Cryptosporidium and enteric helminths) and viral (rotavirus) enteropathogens in faeces or rectal swabs was determined. Occurrence of the enteropathogens was tested for association with age, health status, animal species and mixed infections.

Of 423 diarrhoeic animals tested, Salmonella was isolated from 21 (5.0%), Campylobacter from 191 (45.2%) and Yersinia from three (0.7%), while the corresponding prevalence from 270 non-diarrhoeic controls was eight (3.0%) (χ² 1.19, P = 0.28), 119 (44.1%) (χ² 0.04, P = 0.85) and four (1.5%) (χ² 0.8, P = 0.39), respectively. Verocytotoxigenic E. coli and heat-labile toxin-producing E. coli were isolated from 51 (13.7%) and five (1.3%), respectively, of 373 diarrhoeic animals but the corresponding prevalence from 258 non-diarrhoeic animals was 39 (15.1%) (χ² 0.15, P = 0.7) and five (1.9%) (χ² 0.07, P = 0.8), respectively. Cryptosporidium oocytes were detected in 67 (16.5%) of 406 diarrhoeic animals and from 31 (12.1%) of 257 non-diarrhoeic animals (χ² 2.13, P = 0.15). For 147 diarrhoeic animals tested for coccidia, 64 (43.5%) were positive compared with 34 (37.8%) of 90 non-diarrhoeic animals (χ² 0.54, P = 0.49).

The prevalence of rotavirus infection was significantly (P 0.001, χ² 37.8) higher in diarrhoeic animals (39.9%, 112 of 281) than in non-diarrhoeic animals (13.4%, 26 of 194).     

鸭致病性大肠杆菌分离鉴定及其相关致病性分析

为研究鸭大肠杆菌的致病性及相关生物特性,本试验从西昌市某规模化鸭场采集病料,通过传统分离培养及理化性质鉴定,分离得到27株鸭致病性大肠杆菌。对27株鸭致病性大肠杆菌进行血清型鉴定、药敏试验、相关毒力基因检测。血清型鉴定结果显示,优势血清型为O119、O86、O126、O142和O44,占分离株55.56%。血清型O119占27株鸭致病性大肠杆菌的40.74%,为该鸭场流行的致病血清型。对20种兽医临床常用药物的药敏试验结果显示,27株鸭致病性大肠杆菌均对阿米卡星、庆大霉素和多黏菌素B敏感,对头孢曲松等10种药物较敏感,对利福平等5种药物耐受。大肠杆菌相关毒力基因检测结果显示, iutA、hlyF、Iss、IroN、ompT、fyuA、irp 2、Tsh及papA基因携带率均为100.00%, fimC基因携带率59.26%, K 99基因携带率7.40%。各项研究结果为有效防控鸭大肠杆菌病提供了重要科学依据,并为大肠杆菌深入研究奠定了基础。