Diversity of Salmonella serotypes in cull (market) dairy cows at slaughter.

OBJECTIVE: To determine the diversity of Salmonella serotypes isolated from a large population of cull (market) dairy cows at slaughter. DESIGN: Cross-sectional study. SAMPLE POPULATION: Salmonella organisms isolated from the cecal-colon contents of 5,087 market dairy cows. PROCEDURE: During winter and summer 1996, cecal-colon contents of cull dairy cows at slaughter were obtained from 5 US slaughter establishments. Specimens were subjected to microbiologic culturing for Salmonella spp at 1 laboratory. Identified isolates were compared with Salmonella isolation lists published by the Centers for Disease Control and Prevention (CDC) and the National Veterinary Services Laboratory (NVSL) for approximately the same period. The Simpson diversity index was used to calculate the likelihood that Salmonella isolates selected randomly by establishment were different. RESULTS: Of 58 Salmonella serotypes identified, Salmonella ser. Montevideo was the most prevalent. Two of the top 10 CDC serotypes identified from in 1996, Salmonella ser. Typhimurium and S Montevideo, appeared on our top 10 list; 8 of the top 10 were found on NVSL listings. Thirty-one of 59 S. Typhimurium isolates were identified as DT104 and found at a west slaughter establishment, 30 during the winter and 1 during the summer. The greatest diversity of serotypes was at a southeast establishment during the summer; the least diversity was at a central establishment in the winter. CONCLUSIONS AND CLINICAL RELEVANCE: 58 Salmonella serotypes were isolated from market dairy cows at slaughter and could pose a threat for food-borne illness. Salmonella Montevideo was the most frequently isolated serotype and may contribute substantially to salmonellosis in dairy cattle.

Prevalence of Salmonella spp in cull (market) dairy cows at slaughter.

OBJECTIVE: To determine the prevalence of Salmonella spp in the cecal-colon contents of cull (market) dairy cows at slaughter because of potential public health ramifications. DESIGN: Survey study. SAMPLE POPULATION: Cecal-colon contents collected from 5,087 cull (market) dairy cows at slaughter at 5 slaughter establishments across the United States. PROCEDURE: During 2 periods of the year, winter (January and February) and summer (July through September), 5 cull (market) cow slaughter establishments in the United States--west (WE), southeast (SEE), central (CE), north central (NCE), and south central (SCE)--establishments were visited, and cecal-colon contents of cull dairy cows were obtained at the time of slaughter. Samples were examined by microbiologic culture at a single laboratory for Salmonella spp. RESULTS: Salmonella spp were detected in 23.1% of cecal-colon content samples from cull dairy cows across the 5 slaughter establishments. The highest site prevalence (54.5%) was detected at the WE during the summer period, whereas the lowest was found at the CE during the summer (4.3%) and at the NCE during the winter (4.5%). Considerable variation in the daily prevalence of Salmonella spp was found, particularly at the WE and the SCE. Salmonella spp were isolated from 93% of cecal-colon contents collected on a summer day at the WE. CONCLUSIONS AND CLINICAL RELEVANCE: Results strongly suggest that there is a high prevalence of Salmonella spp in cull dairy cows at slaughter, which could burden Hazard Analysis Critical Control Point programs implemented in slaughter establishments. Procedures to reduce Salmonella load at the dairy farm and during transport to slaughter could reduce the risk of spread during the slaughter process.

Preharvest food safety.

Preharvest food safety is essential for the protection of our food supply. The production and transport of livestock and poultry play an integral part in the safety of these food products. The goals of this safety assurance include freedom from pathogenic microorganisms, disease, and parasites, and from potentially harmful residues and physical hazards. Its functions should be based on hazard analysis and critical control points from producer to slaughter plant with emphasis on prevention of identifiable hazards rather than on removal of contaminated products. The production goal is to minimize infection and insure freedom from potentially harmful residues and physical hazards. The marketing goal is control of exposure to pathogens and stress. Both groups should have functional hazard analysis and critical control points management programs which include personnel training and certification of producers. These programs must cover production procedures, chemical usage, feeding, treatment practices, drug usage, assembly and transportation, and animal identification. Plans must use risk assessment principles, and the procedures must be defined. Other elements would include preslaughter certification, environmental protection, control of chemical hazards, live-animal drug-testing procedures, and identification of physical hazards.

New Advances in Humane Slaughter of Meat Animals.

On June 18, 1985, the U.S. Department of Agriculture approved a new method of humane slaughter for meat animals - "electrical slaughter" or deep stunning. In this method, the heart is stopped by cardiac arrest. The amount of blood loss and quality of the meat is the same as in conventional slaughter. Heart stoppage practically eliminates blood splashing and speckling.

Effect of Chloride Salts and Nitrite on Survival of Trichina Larvae and Other Properties of Pork Sausages.

Two experiments were conducted using trichinae-infected pork shoulders. In the first experiment, samples of ground pork shoulder were allocated to the following treatments: (a) sodium nitrite levels of 0, 75 or 150 ppm, and (b) chloride salt levels of 2.5% sodium chloride, 3.18% potassium chloride, 1.35% magnesium chloride and 1.58% calcium chloride (for the latter three chloride salts, ionic strengths equivalent to that of 2.5% sodium chloride were used). In the second experiment, samples of ground pork shoulder were allocated to treatments in which 0, 25, 50, 75 or 100% of the sodium chloride was replaced with a 70:30 mixture of magnesium chloride: potassium chloride. Pork sausage links were made and stored for 12 d in a refrigerated display case. All chloride salts numerically reduced total plate counts compared to controls (no added salts) and calcium chloride or magnesium chloride significantly reduced total plate counts (P<.05). However, addition of sodium nitrite (75 or 150 ppm) did not affect total plate counts. Percentages of dead trichina larvae (visually determined) were greater (P<.05) for potassium chloride and sodium chloride than for magnesium or calcium chloride. However, in the second study when salts of equivalent ionic strengths were not used, replacement of sodium chloride with a 70:30 mixture of magnesium chloride: potassium chloride did not affect (increase or decrease) pH, total plate count or juice-loss during cooking. Percentages of dead trichina larvae increased for the 75 and 100% replacement levels when compared to controls.

Effect of Sodium Chloride Concentration, Water Activity, Fermentation Method and Drying Time on the Viability of Trichinella spiralis in Genoa Salami.

Pork from pigs experimentally infected with Trichinella spiralis was used to manufacture Genoa salami. In Experiment I, Genoa salami was formulated to include: (a) in-going sodium chloride of 2.00 or 3.33% based on raw meat weight; (b) either commercial starter culture or no starter culture and held for fermentation at either 35°C (95°F) or 46.1 °C (115°F). Lower water activity (aw) was found (P<0.0001) in salami manufactured either with 3.33% salt or processed by high fermentation temperature. Lower pH values resulted from use of a starter culture. An interaction between salt concentration and fermentation temperature was seen after 20 days of drying. Salt concentration appeared to exert a definite effect of trichina viability. In Experiment II, Genoa salami was formulated to include: (a) in-going sodium chloride of 0.00, 1.67 or 3.33% based on raw meat weight; (b) all salami contained starter culture and held for fermentation at 46.1 °C. Salami made with 3.33% salt had higher pH and lower aw values than did that made with no or 1.67% salt. The salt content and drying time interaction was greatest in salami made with 3.33% salt. The 3.33% salt content also appeared to exert a definite effect on trichina viability.

Effects of Sodium Nitrite, Sodium Chloride, Heating and Freezing on Survival of Trichinae in Hams.

Two experiments were conducted to determine the effects of sodium chloride, sodium nitrite, heating and/or freezing on viability of trichinae in hams. The most effective treatment for destroying trichinae consisted of pumping hams with a curing solution containing 2.6% sodium chloride and 156 ppm sodium nitrite followed by heating of hams to 43.3°C. Six days of storage at -29°C were required to achieve 100% destruction of trichinae for control (not pumped, not heated) hams. Seven, 8 and 8 d, respectively, were required to achieve 100% destruction of trichinae for those hams that were not heated but pumped without sodium chloride or sodium nitrite, or those that were pumped with solutions containing either 1.6% sodium chloride and 120 ppm sodium nitrite or 2.6% sodium chloride and 156 ppm sodium nitrite.

Isolation of Yersinia enterocolitica from Pig Tonsils.

Yersinia enterocolitica serotype 0:5 was isolated from the tonsils of 8 of 27 butcher hogs subjected to normal slaughtering procedures. Isolation through enrichment in cold mannitol broth or a bile medium at 4 C for 10-60 days was equally effective. Enrichment in modified Rappaport broth at 25 C for longer than 2 days sharply decreased recovery of Y. enterocolitica from tonsils. The type of enrichment medium also had a marked effect on the recovery efficiency of different strains of Y. enterocolitica from ground meat.

Biotypes of Brucella abortus and their value in epidemiologic studies of infected cattle herds.

Four Texas cattle herds containing cows infected with either Brucella abortus biotype 1, 2, or 4 were studied to determine the probability of transmission of Brucella between adjacent cattle herds, the most probable means by which Brucella was introduced into the herds, and the relative frequency of strain 19 isolation from vaccinated cattle. A total of 1,935 cattle in the four herds were tested for brucellosis; 339 reactors were identified, and isolations of B abortus were made from 143. The biotype of B abortus was used to determine that purchased cattle or reentry of bred heifers into the herds was probably responsible for introducing B abortus and that the biotype was not readily transmitted to adjacent herds. Three (9%) of 32 B abortus isolations from adult-vaccinated cattle were strain 19. The data supported the hypothesis that biotypes can be useful in determining the source of B abortus for cattle and in differentiating field and vaccine strain infections in adult-vaccinated cattle.

Reduction of Salmonella and fecal contamination of pork during swine slaughter.

Experiments were designed to reduce Salmonella and fecal contamination of pork, using several sanitizing methods and agents. Sanitizing the hauling vehicle and holding pens with chlorine or quaternary ammonium compounds proved ineffective in reducing carcass contamination. When the eviscerator wore a plastic glove and sanitized his knife in 82-C water before using it on each carcass, contamination was reduced about 50%. Sanitizing the eviscerator's knife in 500-ppm chlorine solution adjusted to a pH of 6.0, or in 25-ppm iodine solution reduced contamination approximately 75%.