Truls Nesbakken

Hazard identification in swine slaughter with respect to foodborne bacteria

Swine slaughter is an open process with many opportunities for the contamination of the pork carcass with potentially pathogenic bacteria; however, it does not contain any point where hazards are completely eliminated. Data on the prevalence of various pathogenic bacteria (Aeromonas hydrophila, Campylobacter coli/jejuni, Listeria monocytogenes, Salmonella spp., Staphylococcus aureus and Yersinia enterocolitica) in pigs, their growth and survival characteristics and ability to become established on the slaughter line are presented. The presentation covers the processing steps from lairage to chilling and is based on swine slaughter practices in Denmark, Norway and Sweden. The major contamination points during swine slaughter are pig-related, such as faecal and pharyngeal, and environmental. HACCP (Hazard Analysis Critical Control Point) and GMP (Good Manufacturing Practice) in swine slaughter must be focused on limiting this spread. The pathogenic bacteria show differences in their general mechanism of distribution. The major contamination source of Campylobacter spp., Salmonella spp. and Y. enterocolitica is the pig, and the contamination of carcasses with these bacteria may be limited, provided that only strict slaughtering procedures are used. Other organisms such as Aeromonas spp., L. moncytogenes/Listeria spp. and S. aureus can be endemic in the processing environment. Since endemic bacteria can be controlled by proper cleaning and disinfection, these organisms are useful as indicators for the success of GMP rules. The following affiliation to CPs or CCPs made for specific steps during slaughter and dressing may serve as a guidance: (i) lairage (CP), (ii) killing (CP), (iii) scalding (CP), (iv) dehairing (CP), (v) singeing/flaming (CP), (vi) polishing (CP), (vii) circumanal incision and removal of the intestines (CCP), (viii) excision of the tongue, pharynx, and in particular the tonsils (CCP), (ix) splitting (CP), (x) post mortem inspection procedures (CCP) and (xi) deboning of the head (CCP).

The storage life of beef and pork packaged in an atmosphere with low carbon monoxide and high carbon dioxide

Ground beef, beef loin steaks and pork chops were packaged in modified atmospheres of 0.4% CO/60% CO(2)/40% N(2) and 70% O(2)/30% CO(2). In addition ground beef was packaged in clipped chub packs, beef loin steaks were vacuum packaged, and pork chops were packaged in an atmosphere of 60% CO(2)/40% N(2) with each pack containing an O(2) absorber. The packs were stored in the dark at 4 or 8°C for up to 21 days. Meat in 0.4% CO/60% CO(2)/40% N(2) had a stable bright red colour that lasted beyond the time of spoilage. The storage lives in this gas mixture at 4°C, as limited by off-odours, were 11, 14 and 21 days for ground beef, beef loin steaks and pork chops, respectively. The 70% O(2)/30% CO(2) atmosphere resulted in an initially bright red to red colour of the meat, but the colour was unstable and off-odours developed rapidly. The off-odours probably were caused by Brochothrix thermosphacta, which grew in all meat types, or by pseudomonads in ground beef. Meat stored in chub packs, vacuum packs or 60% CO(2)/40% N(2) with an O(2) absorber developed off-odours and microflora similar to those of meat in 0.4% CO/60% CO(2)/40% N(2), but with less acceptable appearances. These results show that a low CO/high CO(2) atmosphere is effective for preserving retail-ready meat. ©

Protective cultures inhibit growth of Listeria monocytogenes and Escherichia coli O157:H7 in cooked, sliced, vacuum- and gas-packaged meat.

Contamination of cooked meat products with Listeria monocytogenes poses a constant threat to the meat industry. The aim of this study was therefore to investigate the use of indigenous lactic acid bacteria (LAB) as protective cultures in cooked meat products. Cooked, sliced, vacuum- or gas-packaged ham and servelat sausage from nine meat factories in Norway were inoculated with 10(3) cfu/g of a mixture of three rifampicin resistant (rif-mutant) strains of L. monocytogenes and stored at 8 degrees C for four weeks. Growth of L. monocytogenes and indigenous lactic acid flora was followed throughout the storage period. LAB were isolated from samples where L. monocytogenes failed to grow. Five different strains growing well at 3 degrees C. pH 6.2, with 3% NaCl, and producing moderate amounts of acid were selected for challenge experiments with the rif-resistant strains of L. monocytogenes. a nalidixic acid/streptomycin sulphate-resistant strain of Escherichia coli O157:H7 and a mixture of three rif-resistant strains of Yersinia enterocolitica O:3. All five LAB strains inhibited growth of both L. monocytogenes and E. coli O157:H7. No inhibition of Y. enterocolitica O:3 was observed. A professional taste panel evaluated cooked, sliced, vacuum-packaged ham inoculated with each of the five test strains after storage for 21 days at 8 degrees C. All samples had acceptable sensory properties. The five LAB strains hybridised to a 23S rRNA oligonucleotide probe specific for Lactobacillus sakei. These indigenous LAB may be used as protective cultures to inhibit growth of L. monocytogenes and E. coli O157:H7 in cooked meat products.

Pathways of Listeria monocytogenes contamination in the meat processing industry

One hundred and thirty-three isolates of Listeria monocytogenes from deboned fresh meat, production environment, cold cuts from five meat processing plants and from one plant producing cured dried sausages, were characterized using multilocus enzyme electrophoresis. On the basis of electrophoretically demonstrable allelic variation at 21 enzyme loci, 21 electrophoretic types (ETs) were distinguished. Analysis of the genetic relationships among the 21 ETs revealed two distinct clusters: Cluster A and Cluster B. With the exception of two isolates from one plant, all isolates from deboned fresh meat belonged to Cluster B. During processing of cold cuts, however, isolates belonging to Cluster A became more frequent, and only one of the 37 isolates from cold cuts belonged to Cluster B. In contrast, six of the nine isolates from cured dried sausages had ETs in Cluster B. One clone of Cluster A, ET-6 was isolated from cold cuts in four of six plants. This is one of the ETs most frequently recovered from patients in Norway. Isolates of ET-6 were further characterized using restriction fragment length polymorphism (RFLP) analysis of chromosomal DNA. Six distinct restriction patterns were distinguished among the 44 ET-6 strains. In one plant, four different RFLP patterns could be identified. Two clone variants seemed to have colonized different areas in this plant for at least four years. However, in each of the other plants, all ET-6 isolates had the same RFLP patterns.

Addition of 2.5% lactate and 0.25% acetate controls growth of Listeria monocytogenes in vacuum-packed, sensory-acceptable servelat sausage and cooked ham stored at 4°C

A study of the inhibitory effects of propylparaben and of a combination of lactate and acetate against growth of Listeria monocytogenes in inoculated liquid medium, sliced servelat sausage and cooked ham, were performed using rifampicin resistant Listeria strains in inoculation experiments. A consumer acceptance test of products produced with and without the compounds was also performed. Propylparaben was found to be effective in a model liquid non-fat medium, but was without effect in the actual products. This illustrates the potential pitfalls in translating results from studies in liquid media to fat-containing food products. The combined inhibitory and sensory results showed that a mixture of 2.5% lactate and 0.25% acetate (w/w, calculated on the water phase), could be used to increase the margins of safety for sliced and spreadable vacuum-packed ready-to-eat cooked meat products stored for 4-6 weeks. In addition, strict control of temperature during production and storage is very important.

Industrial application of an antilisterial strain of Lactobacillus sakei as a protective culture and its effect on the sensory acceptability of cooked, sliced, vacuum-packaged meats

The application of a protective lactic acid bacterium (LAB) during the commercial production of cooked meat products is described. The LAB, a strain of Lactobacillus sakei, was previously isolated from cooked ham and inhibited growth of Listeria monocytogenes and Escherichia coli O157:H7 in this product. L. sakei was applied to the cooked products at a concentration of 10(5)-10(6) cfu/g immediately before slicing and vacuum-packaging using a hand-operated spraying bottle. The LAB strain inhibited growth of 10(3) cfu/g of a cocktail of three rifampicin resistant mutant L. monocytogenes strains both at 8 degrees C and 4 degrees C. Consumer acceptance tests of cooked ham and of servelat sausage, a Norwegian non-fermented cooked meat sausage, showed that control and inoculated products were equally acceptable. The products were still acceptable after storage for 28 days at 4 degrees C and, after opening the packages, for a further 5 days at 4 degrees C. The findings presented here confirm that the L. sakei strain is suitable for use as a protective culture and may technically easily be implemented in the commercial production of cooked meat products.

Reduction of Yersinia enterocolitica and Listeria spp. on pig carcasses by enclosure of the rectum during slaughter

By sealing off the rectum with a plastic bag immediately after it had been freed, the spread of Y. enterocolitica O:3/biovar 4 to pig carcasses could be considerably reduced. The organism was recovered from only 0.8% of carcasses when the plastic bag technique was employed. Y. enterocolitica O:3/biovar 4 was recovered from 10% of pig carcasses when eviscerating procedures did not include the use of the plastic bag technique. There was thus an obvious risk of the bacteria further contaminating meat cuts and other meat products. The plastic bag technique was effective both in connection with manual excision of the rectum/low throughput (90 per h), and mechanical freeing of the rectum/high slaughter rate (240 per h). L. monocytogenes was not detected in any of the samples taken from 120 pig carcasses in Norway or from 120 pig carcasses in Sweden. The plastic bag technique was used on half of these pigs. L. innocua was tested for in 120 pigs slaughtered in Sweden. The bacterium was recovered from 33% of the carcasses eviscerated without using a plastic bag, and from 10% of the carcasses in which this technique was employed. The results suggested that there were other, non-faecal, sources of contamination. Other measures in addition to the plastic bag technique are therefore required to limit the spread of Listeria spp. By incorporating the plastic bag technique into the slaughtering procedures, the meat industry would contribute to preventing the dissemination of Y. enterocolitica and other pathogens which spread via the faeces.

Control of Yersinia enterocolitica in pigs at herd level

A higher herd prevalence of antibodies (ELISA) to Yersinia enterocolitica O:3 was found in conventional slaughter production (86.0% seropositive herds) than in conventional farrow-to-finish herds (53.1% seropositive herds). The herd prevalence of antibodies to Y. enterocolitica in multiplying herds (56.1%) was similar to the level in the conventional farrow-to-finish herds. An epidemiological study in conventional pig herds demonstrated that farrow-to-finish production (odds ratio, OR = 0.15) was an important protective factor. Using under-pressure ventilation (OR = 0.33) and manual feeding of slaughter pigs (OR = 0.44) also lowered the herd prevalence. The most expressed risk factor was using an own farm vehicle for transport of slaughter pigs to abattoirs (OR = 12.92). Separation between clean and unclean section in herds (OR = 2.67), daily observations of a cat with kittens on the farm (OR = 2.41) and using straw bedding for slaughter pigs (OR = 2.25) were other factors that increased the risk. In conclusion, the epidemiological data suggest that it is possible to reduce the herd prevalence of Yersinia enterocolitica O:3 by minimising contact between infected herds and non-infected herds. Further, attempts to reduce the prevalence at the top levels of the breeding pyramids may be beneficial for the industry as a whole. The meat industry may use serological tests as a tool to lower the prevalence in the pig population by limiting the contact between seropositive and seronegative herds. However, because of the high prevalence of Y. enterocolitica in pig herds, a strict slaughter hygiene will remain an important means to reduce carcass contamination with Y. enterocolitica O:3 as well as other pathogenic micro-organisms.

A model based on absorbance data on the growth rate of Listeria monocytogenes and including the effects of pH, NaCl, Na-lactate and Na-acetate.

A mathematical model was developed for predicting the growth of L. monocytogenes at 9 degrees C in the presence of 70 ppm sodium nitrite, and at different levels of pH (5.5-6.5), sodium chloride (1.0-4.0%), sodium lactate (0-0.5%) and sodium acetate (0-0.6%). Collection of the growth data was done using absorbance measurements in broth cultures and the absorbance measurement was evaluated. The model was compared to the Food MicroModel, and against the growth of L. monocytogenes in a vacuum-packed meat product stored at 9 degrees C. A linear relationship was obtained, for the absorbance data on different dilutions of the inoculum, in the absorbance interval studied. There was also a linear relationship between the values of the maximum specific growth rates derived from the absorbance and the ones derived from viable count measurements; and corrections were made accordingly. The statistical evaluation showed that all the main factors, i.e. pH, sodium chloride, sodium lactate and sodium acetate were statistically significant for the growth rate of L. monocytogenes. Comparison to the Food MicroModel (FMM) showed a slight underprediction for the developed model (bias = 0.84). The predictions were, on average, within 20% of the FMM predictions (n = 10). Validation against the observed growth of L. monocytogenes inoculated into an emulsion type of sausage (n = 4) also showed a slight underprediction by the model. The predictions were, on average, 16% below the observed values in the sausage (Bias 0.84, Accuracy 1.26).

Comparison between the growth of Yersinia enterocolitica, listeria monocytogenes, escherichia coli O157:H7 and salmonella spp. in ground beef packed by three commercially used packaging techniques.

Growth of the pathogens Yersinia enterocolitica, Listeria monocytogenes, Escherichia coli O157:H7 and strains of Salmonella were compared in ground beef packed in modified atmospheres of 60% CO2/40% N2/0.4% CO (high CO2/low CO mixture), 70% O2/30% CO2 (high O2 mixture) and in chub packs (stuffed in plastic casings). The ground beef was inoculated with rifampicin-resistant or nalidixic acid/streptomycin-resistant strains of the pathogens (final concentration 10(2) - 10(3) bacteria/g) and stored at 4 and 10 degrees C for up to 14 days. At 4 degrees C the shelf life, based on colour stability and background flora development, was prolonged for the high CO2/low CO mixture compared to the two other packaging methods, but at 10 degrees C the shelf life was < 8 days for all the packaging methods. Growth of Y. enterocolitica was nearly totally inhibited both at 4 and 10 degrees C in the high CO2/low CO mixture, while the bacterial numbers in the samples packed in the high O2 mixture increased from about 5 x 10(2) bacteria/g at day 0 to about 10(4) at day 5 at 4 degrees C and to 10(5) at 10 degrees C. Growth in the chub packs was even higher. L. monocytogenes showed very little growth at 4 degrees C in all treatments. At 10 degrees C there was slow growth from about 5 x 10(3) bacteria/g to about 10(4) at day 5 in the high CO2/low CO mixture, while the numbers in the high O2 mixture and the chub packs were about 10 times higher. Growth of E. coli O157:H7 at 10 degrees C in the ground beef was nearly totally inhibited in both the high CO2/low CO mixture and the high O2 mixture. Growth in the chub packs was higher, as the number of bacteria increased 3 log in 5 days. The Salmonella strains (S. typhimurium, S. dublin, S. enteritidis and S. enterica 61:k:1,5,(7)) in the ground beef stored at 10 degrees C for 5 and 7 days grew to a higher number in the high CO2/low CO mixture than in the high O2 mixture. This study shows that the growth of Y. enterocolitica and L. mononcytogenes in ground beef stored in the high CO2 /low CO mixture was not increased as a result of prolonging the shelf life. However, the observed growth of strains of Salmonella at 10 degrees C in this mixture and in chub packs does emphasise the importance of temperature control during storage.