Norasak Kalchayanand

Interaction of hydrostatic pressure, time and temperature of pressurization and pediocin AcH on inactivation of foodborne bacteria.

High hydrostatic pressure, because it can kill microorganisms, is being investigated for potential use as a nonthermal food preservation method. The objective of this study was to determine the hydrostatic pressurization parameters, pressure, time, and temperature, and a bacteriocin that in combination would destroy 7 to 8 log cycles of pathogenic and spoilage bacterial populations. We suspended cells of Staphylococcus aureus, Listeria monocytogenes, Salmonella typhimurium, Escherichia coli O157:H7, Lactobacillus sake, Leuconostoc mesenteroides, Serratia liquefaciens, and Pseudomonas fluorescens in peptone solution and exposed them to the combination of treatments. The combined parameters used were hydrostatic pressure (138 to 345 MPa), time (5 to 15 min), temperature (25 to 50 degrees C), and pediocin AcH (3,000 AU/ml, final concentration). In general, cell death increased as the pressure, time, or temperature increased; however, the cells developed proportionately greater sensitivity as the pressure increased to 276 MPa and higher and the temperature increased above 35 degrees C. Pressurization for longer than 5 min, especially at lower pressure and temperature ranges, had very little added benefit. Among the four gram-negative species, E. coli O157:H7 was the most resistant to pressurization while among the four gram-positive species, L. sake and L. mesenteroides had greater resistance. The death rate at high pressure (345 MPa) and high temperature (50 degrees C) in combination followed first-order kinetics; at lower pressure and temperature combination it showed a late tailing effect. Estimated D value data indicated that even at 345 MPa and 50 degrees C an 8-log-cycle viability loss could not be achieved within 5 min for all eight species. However, when pediocin AcH was included during pressurization this loss was achieved.

Bacteriocins of Lactic Acid Bacteria in Combination Have Greater Antibacterial Activity

Antibacterial efficiency of two bacteriocins from lactic acid bacteria, pediocin AcH, and nisin was tested individually and in combination against several gram-positive bacterial strains including some involved in food spoilage and foodborne diseases. Pediocin AcH and nisin were more antibacterial in combination than when they were used alone. The principles of this greater antibacterial spectrum have been proposed. Bacteriocins in combinations can be used advantageously to design efficient natural food biopreservative(s).

Transportation and lairage environment effects on prevalence, numbers, and diversity of Escherichia coli O157:H7 on hides and carcasses of beef cattle at processing.

Hide has been established as the main source of carcass contamination during cattle processing; therefore, it is crucial to minimize the amount of Escherichia coli O157:H7 on cattle hides before slaughter. Several potential sources of E. coli O157: H7 are encountered during transportation and in the lairage environment at beef-processing facilities that could increase the prevalence and numbers of E. coli O157:H7 on the hides of cattle. On three separate occasions, samples were obtained from cattle at the feedlot and again after cattle were stunned and exsanguinated at the processing plant (286 total animals). The prevalence of E. coli O157:H7 on hides increased from 50.3 to 94.4% between the time cattle were loaded onto tractor-trailers at the feedlot and the time hides were removed in the processing plant. Before transport, nine animals had E. coli O157:H7 in high numbers (> 0.4 CFU/cm2) on their hides. When sampled at the slaughter facility, the number of animals with high hide numbers had increased to 70. Overall, only 29% of the E. coli O157:H7 isolates collected postharvest (221 of 764) matched pulsed-field gel electrophoresis types collected before transport. The results of this study indicate that transport to and lairage at processing plants can lead to increases in the prevalence and degree of E. coli O157:H7 contamination on hides and the number of E. coli O157:H7 pulsed-field gel electrophoresis types associated with the animals. More study is needed to confirm the mechanism by which additional E. coli O157:H7 strains contaminate cattle hides during transport and lairage and to design interventions to prevent this contamination.

Super shedding of Escherichia coli O157:H7 by cattle and the impact on beef carcass contamination

Beef carcass contamination is a direct result of pathogen transfer from cattle hides harboring organisms such as enterohemorrhagic Escherichia coli. Hide contamination occurs from direct and indirect fecal contamination in cattle production and lairage environments. In each of these environments, individual animals shedding E. coli O157:H7 at high levels (>10(4) CFU/g of feces, hereafter referred to as super shedders) can have a disproportionate effect on cattle hide and subsequent carcass contamination. It is not known what criteria must be met to cause an animal to shed at levels exceeding 10(4) CFU/g. Understanding the factors that play a role in super shedding will aid in minimizing or eliminating the super shedding population. Interventions that would prevent super shedding in the cattle population should reduce E. coli O157:H7 transmission in the production and lairage environments resulting in reduced risk of beef carcass contamination and a safer finished product.

Enumeration of Salmonella and Escherichia coli O157:H7 in ground beef, cattle carcass, hide and faecal samples using direct plating methods†

Aim:u2002 To develop and validate high throughput methods for the direct enumeration of viable and culturable Salmonella and Escherichia coli O157:H7 in ground beef, carcass, hide and faecal (GCHF) samples from cattle.

Spoilage of vacuum-packaged refrigerated beef by Clostridium

A motile, gram-positive, spore forming, anaerobic, psychrotrophic bacterial species, probably from the genus Clostridium , was involved in spoilage of vacuum-packaged refrigerated fresh beef. The spoilage was associated with accumulation of large quantities of foul smelling gas and purge in the bag and loss of color and texture of the meat. Attempts to grow the organism in several laboratory media were not yet successful; however, inoculation of purge from a spoiled sample into a fresh beef, vacuum-packaging and refrigeration storage facilitated growth of this species and produced characteristic spoilage of beef.

Prevalence and level of Escherichia coli O157:H7 in feces and on hides of feedlot steers fed diets with or without wet distillers grains with solubles.

The objective of this study was to determine if wet distillers grains with solubles (WDGS) from corn in diets affected Escherichia coli O157:H7 in growing and finishing cattle; steers (n = 603) were randomly assigned to diets with or without WDGS. Hide and fecal samples were collected monthly (October through June) from each animal for enumeration and enrichment of E. coli O157:H7. In the growing phase (0 or 13.9% WDGS diets), fecal prevalence for E. coli O157:H7 in steers fed a diet with WDGS was twice that of the prevalence in control steers (P < 0.001). In the finishing phase (0 or 40% WDGS diets), the average prevalence in feces (P < 0.001) and on hides (P < 0.001) was higher for cattle fed WDGS. The average percentage of fecal E. coli O157:H7 enumerable samples during the finishing phase for cattle fed WDGS was 2.7% compared with 0.1% for control steers (P < 0.001). The average percentage of E. coli O157:H7 enumerable hide samples was not different between diets, but the cattle fed WDGS had higher levels (P < 0.05) of the pathogen. Animals fed WDGS had higher levels of E. coli (P < 0.001), higher pH values (P < 0.001), and lower concentrations of L-lactate (P < 0.001) in feces than those values of the control steers. These results indicate that feeding 40% WDGS could increase the level and prevalence of E. coli O157:H7 in and on feedlot cattle when E. coli O157:H7 is seasonally low.

Effects of a minimal hide wash cabinet on the levels and prevalence of Escherichia coli O157:H7 and Salmonella on the hides of beef cattle at Slaughter

Harborage of Escherichia coli O157:H7 and Salmonella on animal hides at slaughter is the main source of beef carcass contamination during processing. Given this finding, interventions have been designed and implemented to target the hides of cattle following entry into beef processing plants. Previous interventions targeting hides have not been suitable for all beef processing plants because of cost and space restrictions. In this study, a hide wash cabinet was evaluated to determine whether it was more amenable to widespread use in the beef processing industry, especially for small and medium-size plants. Overall, 101 (35.1%) of 288 beef cattle hides sampled before entry into the hide wash cabinet harbored E. coli O157:H7 at or above the limit of detection (40 CFU/100 cm2). After passage through the hide wash cabinet, only 38 (13.2%) of 288 hides had E. coli O157:H7 levels > or =40 CFU/100 cm2. Before the hide wash cabinet, 50 (17%) of 288 hides harbored E. coli O157:H7 at levels above 100 CFU/100 cm2, with one sample as high as 20,000 CFU/100 cm2. In contrast, only 14 (5%) of 288 hides had E. coli O157:H7 levels above 100 CFU/100 cm2 after hide washing, with the highest being 2000 CFU/100 cm2. These same trends also were found for Salmonella before and after hide washing. These results indicate that the hide wash cabinet described in this study was effective and should provide small and medium-size processing plants with an affordable hide wash intervention strategy.

Characteristics of Psychrotrophic Clostridium laramie Causing Spoilage of Vacuum-packaged Refrigerated Fresh and Roasted Beef

A Clostridium sp., associated with an unusual spoilage of vacuum-packaged refrigerated uncooked (fresh) and roasted beef, was isolated as a pure culture from the spores in spoiled beef. The pure culture was used to study important characteristics and to differentiate it from other clostridial species usually found in beef. The biochemical characteristics, volatile fatty acid and soluble-protein profiles, temperatures and pHs of growth, and temperatures of sporulation, germination, and destruction of the isolate were distinctly different from other Clostridium spp. studied. It is not toxigenic and has 26% guanine plus cytosine. The isolate is a new species and is named Clostridium laramie .

Diversity of Multidrug-Resistant Salmonella enterica Strains Associated with Cattle at Harvest in the United States

ABSTRACT The prevalence and diversity of multidrug-resistant (MDR) Salmonella enterica strains associated with cattle at harvest in the United States were examined. Hides and carcasses of cattle were sampled at processing plants (n = 6) located in four geographically distant regions from July 2005 to April 2006. The mean prevalences of Salmonella on hides, preevisceration carcasses (immediately after hide removal), and postintervention carcasses (in the chiller and after the full complement of interventions) were 89.6%, 50.2%, and 0.8%, respectively. The values for MDR Salmonella enterica strains (defined as those resistant to two or more antimicrobials) as percentages of Salmonella prevalence were 16.7% (95% confidence interval [CI], 8.3 to 25.1%; median percent prevalence, 6.9%), 11.7% (95% CI, 4.4 to 19.0%; median, 4.8%), and 0.33% (95% CI, −0.3 to 0.70%; median, 0%), respectively. In this study, 16,218 Salmonella hide and carcass isolates were screened for antimicrobial resistance. Of these, 978 (6.0%) unique MDR S. enterica isolates were identified and serotyped and their XbaI pulsed-field gel electrophoresis (PFGE) profiles determined. The predominant MDR S. enterica serotypes observed were Newport (53.1%), Typhimurium (16.6%), and Uganda (10.9%). Differences in MDR S. enterica prevalence were detected, and PFGE analysis revealed both epidemic clusters (profiles found in plants in multiple regions/seasons) and endemic clusters (profiles observed in plants in limited regions/seasons) within several of the MDR serotypes examined. Despite these differences, multiple-hurdle processing interventions employed at all plants were found to be quite effective and decreased Salmonella carcass contamination by 98.4% (95% CI, 97.6 to 99.7%).