Numbers of coliforms, Escherichia coli, F-RNA phage, rotavirus, bovine enteric calicivirus and presence of non-O157 STEC on commercial vacuum packaged beef.

The numbers of coliforms, Escherichia coli, F-RNA coliphages, bovine enteric calicivirus (BEC) and rotavirus (RV) and presence of non-O157 shiga toxigenic E. coli (STEC) were determined on commercial vacuum packaged beef subprimals at the retail level from swabs obtained from the entire surfaces of 150 cuts that originated from federally and provincially registered plants. The prevalence and log mean numbers of E. coli were higher in provincially registered plants than in federally registered plants; 64% vs 20%, respectively, and -0.3 vs -1.22 log cfu/100 cm(2), respectively. In contrast, the prevalence and mean log numbers of F-RNA coliphages were lower for the provincially registered plants than for the federally registered plants; 31% vs 68% and -0.86 vs -0.13 log cfu/100 cm(2), respectively. One E. coli sample tested positive for stx2 and eae. F-RNA coliphages associated with human origin (GII/GIII) were detected in 12% and 30% of samples that originated from provincially and federally registered plants, respectively. RV RNA was detected in 4% of samples while BEC RNA was not detected. Although the infectivity of RV is unknown, the presence of viable F-RNA coliphages suggests that consumers could potentially be at risk when consuming undercooked meat that is contaminated with RV.

Genetic diversity of Escherichia coli recovered from the oral cavity of beef cattle and their relatedness to faecal E. coli.

AIMS: To determine the genetic diversity of generic Escherichia coli recovered from the oral cavities of beef cattle and their relatedness to E. coli isolated from the faeces of cattle during pasture grazing and feedlot finishing. METHODS AND RESULTS: A total of 484 E. coli (248 oral and 236 faecal isolates) were obtained from eight beef cattle after 1 and 5 months of grazing on pasture and after 1 and 5 months in a feedlot. The random amplification of polymorphic DNA (RAPD) method was used to genetically characterize these isolates. The RAPD patterns showed that ca 60% of E. coli recovered from the oral cavities and faeces during pasture and feedlot shared a close genetic relatedness. A number of E. coli with unique RAPD types were also found either in the oral cavities or faeces. Most of the E. coli RAPD types recovered from the oral cavities were shared among animals, but there were also RAPD types which were unique to individual animals. The E. coli populations of the oral cavities were genetically diverse and changed over time. CONCLUSIONS: This study indicates that there are large numbers of E. coli carried in the oral cavities of beef cattle and those E. coli are closely related to strains found in the faeces. The oral cavities of cattle harbour a genetically diverse E. coli population. SIGNIFICANCE AND IMPACT OF THE STUDY: The oral cavity may be an important reservoir of enteric pathogens which may transfer to meat during carcass dressing. A better understanding of the molecular ecology of E. coli in cattle would assist the design of approaches to control pathogenic strains during beef production and processing.

Genotypic analysis of Escherichia coli recovered from product and equipment at a beef-packing plant.

AIMS: To identify sources of Escherichia coli on beef by characterizing strains of the organism on animals, equipment and product at beef-packing plant. METHODS AND RESULTS: Generic E. coli were recovered from hides, carcasses, beef trimmings, conveyers and ground beef during the summer of 2001 (750 isolates) and winter of 2002 (500 isolates). The isolates were characterized by Random Amplification of Polymorphic DNA (RAPD). The numbers of E. coli recovered from dressed carcasses were less than the numbers recovered from hides. The numbers recovered from chilled carcasses were too few for meaningful analysis of the strains present on them but the numbers recovered from trimmings and ground beef were larger. The RAPD patterns showed that the majority of isolates from hides, carcasses, beef trimmings, conveyers and ground beef were of similar RAPD types, but a few unique RAPD types were recovered from only one of those sources. The E. coli populations present on the hides of incoming animals and in the beef-processing environment were highly diverse. Randomly selected E. coli isolates from each of the five sources were further characterized by pulsed-field gel electrophoresis (PFGE). Most genotypes of E. coli defined by PFGE corresponded to the E. coli types defined by RAPD. CONCLUSIONS: The hides of the incoming animals appeared to be only one of the sources of the E. coli on trimmings and in ground beef, as additional sources were apparently present in equipment used for carcass breaking. SIGNIFICANCE AND IMPACT OF THE STUDY: This study indicates that hazardous microbiological contamination of meat may occur after the dressing of carcasses at commercial beef-packing plants, which suggests that attention should be given to the control of the contamination of meat during carcass breaking as well as during the dressing of carcasses.

Evaluation of the ability of lysozyme and nisin to control meat spoilage bacteria.

The antimicrobials lysozyme, nisin, and mixtures of the two were studied to ascertain their abilities to control the growth of the meat-borne spoilage bacteria, Brochothrix thermosphacta B2 and Carnobacterium sp. 845. The goal was to optimize an antimicrobial for potential use in preservation of fresh meats. Their efficacies were evaluated in APT broth, in a meat juice extract and on cores of lean and fat pork tissue. Both lysozyme and nisin alone as well as mixtures of the two effectively inhibited B. thermosphacta B2 at 250 microg/ml in APT broth, the lowest concentration evaluated, for 10 days at 2 degrees C. In the presence of 500 microg/ml lysozyme, B. thermosphacta B2 grew after 12 days incubation. Only 125 microg of antimicrobial/ml was required to inhibit B. thermosphacta B2 for 27 days at 2 degrees C in pork juice. An estimated surface concentration of 130 microg/cm2 of each of the antimicrobials effectively inhibited B. thermosphacta B2 on inoculated cores of fat and lean pork tissue when the cores were incubated in vacuum packages for 6 weeks at 2 degrees C. In APT broth and in pork juice, lysozyme showed no antimicrobial activity against Carnobacterium sp. 845 at concentrations of 500 and 1000 microg/ml, respectively. Nisin and mixtures of the two antimicrobials inhibited Carnobacterium sp. 845 so that its numbers were at least 3 log units lower than untreated samples after 26 and 27 days incubation for APT and pork juice, respectively. The antimicrobial effect was concentration dependent. On lean pork tissue, numbers of Carnobacterium sp. 845 were significantly lower than untreated samples or samples treated with 195 microg/cm2 lysozyme when 260 microg/cm2 of a 1:3 (w/w) ratio of nisin to lysozyme was introduced to the cores. The inhibitory effect lasted for 14 of 42 days incubation in vacuum at 2 degrees C. On fat tissue, both lysozyme alone and the 1:3 nisin/lysozyme mixture inhibited Carnobacterium sp. 845 for 21 days storage in vacuum at 2 degrees C. On fat and lean tissue, mixtures of nisin and lysozyme would be more effective antimicrobials than either nisin or lysozyme alone.

Effect of antemortem feeding regimes on bacterial numbers in the stomachs and ceca of pigs.

Three groups, each of 45 pigs, were either not fasted, fasted for 15 h during lairage at the abattoir, or fasted for 15 h before dispatch from the piggery to the abattoir. Three subgroups, each of 15 pigs from each group, were held at the abattoir for additional times of either 0 to 1 h, 2 to 3 h, or 4 to 5 h. Immediately after slaughter, stomach and cecal contents were collected for pH measurement and enumeration of coliforms, Escherichia coli biotype 1 and lactic acid bacteria (LAB). Stomach pH changed from 4.1 to 3.1 as additional abattoir holding time increased from 0 to 1 h to 4 to 5 h but was unaffected by feed withdrawal (mean pH, 3.5). Cecal pH (range 6.4 to 7.2) increased in response to both treatments. Coliform and E. coli biotype 1 numbers in the stomach, means 4.6 and 4.5 log CFU/g, respectively, were not affected by feed withdrawal but decreased 0.8 log units as additional abattoir holding time increased from 0 to 1 to 4 to 5 h. LAB in the stomach decreased in response to both feed withdrawal and holding at the abattoir. Cecal numbers of coliforms and E. coli biotype 1 increased 0.8 and 1.0 log units to 7.8 and 7.6 log CFU/g, respectively, as a result of feed withdrawal, and 0.6 log units to 7.6 and 7.5 log CFU/g, respectively, as additional abattoir holding time increased to 4 to 5 h. The LAB in the cecum (mean 9.4 log CFU/g) increased slightly with increasing abattoir holding time. In the event of release of stomach or cecal contents onto the meat during carcass dressing, larger numbers of E. coli per g would be released from the ceca and fewer per g from the stomachs of pigs that have had feed withdrawn as compared to pigs not subjected to feed withdrawal.

The use of multiplex PCR reactions to characterize populations of lactic acid bacteria associated with meat spoilage.

A rapid, systematic and reliable approach for identifying lactic acid bacteria associated with meat was developed, allowing for detection of Carnobacterium spp., Lactobacillus curvatus, Lact. sakei and Leuconostoc spp. Polymerase chain reaction primers specific for Carnobacterium and Leuconostoc were created from 16S rRNA oligonucleotide probes and used in combination with species-specific primers for the 16S/23S rRNA spacer region of Lact. curvatus and Lact. sakei in multiplex PCR reactions. The method was used successfully to characterize lactic acid bacteria isolated from a vacuum-packaged pork loin stored at 2 degrees C. Seventy isolates were selected for identification and 52 were determined to be Lact. sakei, while the remaining 18 isolates were identified as Leuconostoc spp.