Comparisons of enrichment methods (with or without antibiotics and with or without a preenrichment step) using gram-negative (GN) broth or tryptic soy broth (TSB) were conducted with feeds inoculated with Escherichia coli O157:H7. TSB was more sensitive than GN broth, and TSB with a preenrichment step followed by TSB with antibiotics was more sensitive than plain TSB enrichment, in detecting E. coli O157 in inoculated feeds. Feed samples were collected from feed bunks from 54 feedlots to determine the prevalence of E. coli O157 in cattle feeds. TSB preenrichment followed by TSB with antibiotics and the standard GN broth enrichment were used for each feed sample. All samples underwent immunomagnetic separation and were plated onto sorbitol MacConkey agar with cefixime and potassium tellurite. Identification of E. coli O157 was based on indole production, positive latex agglutination for O157 antigen, API 20E test strip results, PCR for the eaeA gene, and the presence of at least one Shiga toxin. E. coli O157 was detected in 52 of 504 feed samples (10.3%) by using GN broth enrichment and in 46 of 504 feed samples (9.1%) by using TSB followed by TSB supplemented with cefixime and vancomycin. E. coli O157 was detected in 75 of 504 feed bunk samples (14.9%) by one or both methods. There was no correlation between E. coli O157 prevalence and generic coliform counts in feeds. The prevalence of E. coli O157 in cattle feed warrants further studies to increase our knowledge of the on-farm ecology of E. coli O157 in order to develop strategies to prevent food-borne disease in humans.The source of Escherichia coli O157 that colonizes cattle is unknown. Feeds commonly contain coliforms (7) and generic E. coli (25), suggesting fecal contamination of feedstuffs. Individual cattle can be transiently colonized and shed E. coli O157 in their feces (15) for 30 to 60 days (3). The reported prevalence in cattle has generally been low in winter and high in summer (1,15,29), although some studies have found similar prevalences in winter and summer (11). On a herd basis, fecal shedding usually occurs in clusters, followed by relatively longer periods of low or no fecal shedding (13, 15). E. coli O157 can survive for an extended period in bovine feces (18,33), providing opportunity for feed contamination.E. coli O157 has rarely been detected in cattle feeds; in two previous studies, it was not detected (14, 25) and in a third it was detected in only 3 out of 32 (9.4%) feed samples taken from a farm over a 5-month period (36). Recently, 0.5% of feeds that were purchased and stored in certain farms were found to contain E. coli O157 (11). Certain conditions appear to support growth of generic E. coli and E. coli O157 in cattle feeds, such as increased concentrations of lactate and decreased concentrations of propionate (25) and high pH in poorly fermented silage (7). This ability of E. coli O157 to survive and grow in feed under appropriate conditions (7, 25), as well as the temporal clustering of fecal shedding in cattle, suggests that c...
In this setting, administration of the Salmonella Newport SRP vaccine in feedlot cattle had no effect on fecal prevalence of Salmonella bacteria or cattle health and performance.
Our objective was to define and compare pulsed-field gel electrophoresis (PFGE) profiles of Escherichia coli O157 isolated from cattle feces and carcass samples to evaluate relationships between beef carcass contamination and fecal shedding of E. coli O157 at harvest. We used PFGE separation of Xba1-digested DNA to characterize E. coli O157 isolates (n = 174) from preevisceration carcasses (n = 39) and feces (n = 135) that were recovered from 37 E. coli O157-positive truckloads sampled at a commercial abattoir. Semiquantitative fecal culture techniques differentiated high-shedding, low-shedding, and negative cattle. Among all isolates, there were 17 PFGE types (95% homology) and 37 subtypes (100% homology). Specific subtypes were detected on multiple occasions and from different sample types within loads, among loads, and among days. Seventeen subtypes were recovered from carcasses; most were also recovered from feces of high-shedding cattle (13) and low-shedding cattle (14). Within truckload, the percentages of carcass isolates that were identical to high-shedder or low-shedder fecal isolates, as determined by PFGE, were 69.2% and 46.0%, respectively, whereas among different truckloads within the same study day, the percentages of carcass isolates that were the same subtype as high-shedder or low-shedder fecal isolates were 35.3% and 58.8%, respectively. Our results suggest that cattle feces from both low- and high-shedders pose a potential risk for E. coli O157 contamination of carcasses. Truckload may be an important factor in the potential transmission of E. coli O157, but isolates from carcasses also may be similar to those from feces of cattle on different truckloads and harvest days.
There are many factors (i.e. renal physiology, hepatic metabolism, etc.) between species that could lead to modifications in the pharmacokinetics and thus possibly changes in the therapeutic interval of a compound (Short, 1994). The dosage regimens in New World camelids is often determined with little information regarding the pharmacokinetics or unique physiology in llamas and alpacas.Doramectin (Dectomax Ò Pour-on, Pfizer Inc., New York, NY, USA) is an avermectin endectocide (Goudie et al., 1993) approved for topical use in cattle. Topical (pour-on) administration has the advantages of being easier to administer and lacks injection site lesions. The pharmacokinetic parameters of the topical doramectin in cattle after a single, 0.5 mg/kg administration were: t 1/2 of 9.8 days, maximum plasma concentration (C max ) of 12.2 ng/mL, time of C max (T max ) of 4.3 days, mean residence time (MRT) of 12.8 days, and detectable plasma concentrations 40 days postadministration (Gayrard et al., 1999).The objective of this project was to determine the pharmacokinetics of a single, 0.5 mg/kg dose of topically administered doramectin in llamas and alpacas. This will assist with determining possible differences in topical doramectin pharmacokinetics between these two species of New World camelids. Seven llamas (Lama glama) and seven alpacas (Lama pacos) were obtained from commercial sources and had not been treated with an avermectin/ milbemycin within 30 days prior to the start of the study. The animals were housed outdoors with water and hay available ad libitum. The procedures described below were approved by the Kansas State University Animal Care and Use Committee.Complete blood counts and serum biochemical panels were carried out prior to drug administration. The animals were clipped along the dorsal midline; leaving approximately 0.6 cm fiber length on the animal from the withers to the ischium. All animals received doramectin at a dose of 500 lg/kg, which is the same dose approved in the US for topical treatment in cattle. Blood samples were collected via jugular venipuncture prior to dosing and at 0.5, 1, 2, 3, 4, 5, 6, 7, 9, 11, 14, 17, 20, 25, 30, 35, and 40 days postdose. Blood samples (10 mL) were collected into evacuated tubes containing Li heparin and centrifuged to obtain plasma.Samples were analyzed using modifications of previously described methods (Stout et al., 1994;Nowakowski et al., 1995) via liquid chromatography/mass spectrometry. The assay was validated for plasma from both species. There were no species effects on recovery, precision, or accuracy. Recovery of doramectin was >96% across the range of the assay (0.25-20 ng/ mL). Intra-day precision was ±10% with an accuracy ±13% of intended values with inter-day precision of ±5.6% with an accuracy of ±8.9%. A daily assay run was rejected if more than two of the six QCs for a given standard curve were >15% of their intended value or if both QCs at a single concentration were >15% of their intended concentration, the run was reassayed with fresh extraction...
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