High prevalence of pathogenic Yersinia enterocolitica in pig cheeks.

Samples from pork cuts for minced meat and cheeks from processing plants and a slaughterhouse, and modified atmosphere (MA) packaged pork from retail were studied to estimate the prevalence of pathogenic, i.e. virulence plasmid bearing, Yersinia enterocolitica and Yersinia pseudotuberculosis in pork, as well as to quantify pathogenic Y. enterocolitica in pork cuts. Pathogenic (virF-positive) Y. enterocolitica was isolated from 17 pig cheeks (23%) but not from any of the MA-packaged 54 retail pork samples and only from one of the 155 pork cut (0.6%). Most (16/17) of the cheek samples were contaminated with pathogenic Y. enterocolitica 4/O:3 and one with bioserotype 2/O:9. No Y. pseudotuberculosis was isolated. The prevalence of pathogenic Y. enterocolitica was clearly higher (39%) in 155 pork cuts when studied with nested PCR targeting yadA on the virulence plasmid pYV although the contamination level was low varying between 0.1 and 1.6 MPN/g. Raw pork cuts and especially pig cheeks may serve as possible sources for yersiniosis caused by pathogenic Y. enterocolitica.

Listeria monocytogenes contamination in pork can originate from farms.

The presence of Listeria monocytogenes in the pork production chain was followed from farm to slaughterhouse by examining the farm and slaughterhouse levels in the same 364 pigs, and finally by analyzing the cut meats from the same pig lots. Both organic and conventional farms were included in the study. Altogether, 1,962 samples were collected, and the 424 L. monocytogenes isolates were analyzed by pulsed-field gel electrophoresis. The results from microbial analyses were combined with data from an on-farm observation and a questionnaire to clarify the associations between farm factors and prevalence of L. monocytogenes. The prevalence of L. monocytogenes was 11, 1, 1, 24, 5, 1, and 4% in feed and litter, rectal swabs, intestinal contents, tonsils, pluck sets (including lungs, heart, liver, and kidney), carcasses, and meat cuts, respectively. The prevalence was significantly higher in organic than in conventional pig production at the farm and slaughterhouse level, but not in meat cuts. Similar L. monocytogenes genotypes were recovered in different steps of the production chain in pigs originating from the same farm. Specific farm management factors, i.e., large group size, contact with pet and pest animals, manure treatment, use of coarse feed, access to outdoor area, hygiene practices, and drinking from the trough, influenced the presence of L. monocytogenes in pigs. L. monocytogenes was present in the production chain, and transmission of the pathogen was possible throughout the chain, from the farm to pork. Good farm-level practices can therefore be utilized to reduce the prevalence of this pathogen.

The temporal, PFGE and resistance pattern associations suggest that poultry products are only a minor source of human infections in western Finland.

In order to compare human and retail poultry meat thermophilic Campylobacter isolates originating in a regional area in Western Finland, minimum inhibitory concentration (MICs) for six antimicrobials (96 isolates) and pulsed-field gel electrophoresis (PFGE) (102 isolates) were analysed. Campylobacter spp. were detected in 10.5% out of 305 fresh poultry products studied; 29 (90.5%) isolates were identified as Campylobacter jejuni. Among the 70 human isolates, 66 (94.3%) isolates were identified as C. jejuni. Only one C. jejuni domestic poultry isolate showed resistance (ampicillin), whereas domestic human C. jejuni isolates were more commonly resistant to ciprofloxacin, nalidixic acid, ampicillin and tetracycline. The resistance in foreign human isolates was significantly more common than among domestic isolates. PFGE analysis with KpnI restriction enzyme resulted in 59 different PFGE types among the poultry and human isolates. Three types were detected first in poultry meat and thereafter during the following month in domestic human samples, whereas the other conjoint types were detected only after many months. This study suggests that poultry products play only a minor role in human campylobacteriosis in the study area and that the resistance found in domestic human isolates is not likely related to retail poultry meat products.

Contamination of carcasses with human pathogenic Yersinia enterocolitica 4/O:3 originates from pigs infected on farms.

Pigs are considered as a major reservoir of human pathogenic Yersinia enterocolitica and a source of human yersiniosis. However, the transmission route of Y. enterocolitica from farm to pork is still unclear. The transmission of pathogenic Y. enterocolitica from pigs to carcasses and pluck sets was investigated by collecting samples from 364 individual ear-tagged pigs on the farm and at the slaughterhouse. In addition, isolated strains were analyzed, using pulsed-field gel electrophoresis. Isolation of similar genotypes of pathogenic Y. enterocolitica 4/O:3 in animals on the farm and at the slaughterhouse and in carcasses shows that carcass contamination originates from the strains a pig carries during the fattening period. Direct contamination from the carrier pig to its subsequent pluck set is also the primary contamination route for pluck sets, but cross-contamination appears to have a larger impact on pluck set contamination than on carcasses. In this study, the within-farm prevalence of pathogenic Y. enterocolitica varied from 0% to 100%, indicating specific farm factors affect the prevalence of Y. enterocolitica in pigs. The association of farm factors with the high prevalence of pathogenic Y. enterocolitica on farms was studied for the first time, using correlation and two-level logistic regression analyses. Specific farm factors, i.e. drinking from a nipple, absence of coarse feed or bedding for slaughter pigs, and no access of pest animals to pig house, were associated with a high prevalence of pathogenic Y. enterocolitica 4/O:3.

Reviewing the undergraduate veterinary curriculum in Finland for control tasks in veterinary public health.

To review and develop the undergraduate veterinary curriculum on official control in veterinary public health, an electronic survey was sent to 204 Finnish veterinarians employed in the field of food hygiene in 2005. The response rate was 44%. Most frequently cited as strengths of the current curriculum were extensive education and good knowledge. Respondents considered the main challenges in their work to be a wide field of activity, organizational changes, financial resources, organization of substitutes, and collaboration with decision makers. Of the 23 items to be included in the undergraduate curriculum, therefore, respondents prioritized state and local decision making, the role of the public servant, and leadership and management in the area of social factors; in the field of practical control work, in-house control systems, organizations and responsibilities, control techniques, and planning and targeting of controls were prioritized. Of areas traditionally covered in the undergraduate curriculum, legislation; legal proceedings and implications of controls; risks to human, animal, and plant health; and hazards in feed, animal, and food production were stated to be the most important. Although respondents were generally content with their career choice, veterinary public health tasks were not their first choice of career path immediately after graduation. Based on these findings, more attention should be focused on social aspects and practical training in official control in the undergraduate veterinary curriculum. The survey results also highlight the contrasts between society's needs and veterinarians' motivations and career-path expectations, which pose a significant challenge for future curricula.

Transmission of Yersinia pseudotuberculosis in the pork production chain from farm to slaughterhouse.

The transmission of Yersinia pseudotuberculosis in the pork production chain was followed from farm to slaughterhouse by studying the same 364 pigs from different production systems at farm and slaughterhouse levels. In all, 1,785 samples were collected, and the isolated Y. pseudotuberculosis strains were analyzed by pulsed-field gel electrophoresis. The results of microbial sampling were combined with data from an on-farm observation and questionnaire study to elucidate the associations between farm factors and the prevalence of Y. pseudotuberculosis. Following the same pigs in the production chain from farm to slaughterhouse, we were able to show similar Y. pseudotuberculosis genotypes in live animals, pluck sets (containing tongue, tonsils, esophagus, trachea, heart, lungs, diaphragm, liver, and kidneys), and carcasses and to conclude that Y. pseudotuberculosis contamination originates from the farms, is transported to slaughterhouses with pigs, and transfers to pluck sets and carcasses in the slaughter process. The study also showed that the high prevalence of Y. pseudotuberculosis in live pigs predisposes carcasses and pluck sets to contamination. When production types and capacities were compared, the prevalence of Y. pseudotuberculosis was higher in organic production than in conventional production and on conventional farms with high rather than low production capacity. We were also able to associate specific farm factors with the prevalence of Y. pseudotuberculosis by using a questionnaire and on-farm observations. On farms, contact with pest animals and the outside environment and a rise in the number of pigs on the farm appear to increase the prevalence of Y. pseudotuberculosis.

Use of results of microbiological analyses for risk-based control of Listeria monocytogenes in marinated broiler legs.

Microbial risk assessment provides a means of estimating consumer risks associated with food products. The methods can also be applied at the plant level. In this study results of microbiological analyses were used to develop a robust single plant level risk assessment. Furthermore, the prevalence and numbers of Listeria monocytogenes in marinated broiler legs in Finland were estimated. These estimates were based on information on the prevalence, numbers and genotypes of L. monocytogenes in 186 marinated broiler legs from 41 retail stores. The products were from three main Finnish producers, which produce 90% of all marinated broiler legs sold in Finland. The prevalence and numbers of L. monocytogenes were estimated by Monte Carlo simulation using WinBUGS, but the model is applicable to any software featuring standard probability distributions. The estimated mean annual number of L. monocytogenes-positive broiler legs sold in Finland was 7.2x10(6) with a 95% credible interval (CI) 6.7x10(6)-7.7x10(6). That would be 34%+/-1% of the marinated broiler legs sold in Finland. The mean number of L. monocytogenes in marinated broiler legs estimated at the sell-by-date was 2 CFU/g, with a 95% CI of 0-14 CFU/g. Producer-specific L. monocytogenes strains were recovered from the products throughout the year, which emphasizes the importance of characterizing the isolates and identifying strains that may cause problems as part of risk assessment studies. As the levels of L. monocytogenes were low, the risk of acquiring listeriosis from these products proved to be insignificant. Consequently there was no need for a thorough national level risk assessment. However, an approach using worst-case and average point estimates was applied to produce an example of single producer level risk assessment based on limited data. This assessment also indicated that the risk from these products was low. The risk-based approach presented in this work can provide estimation of public health risk on which control measures at the plant level can be based.

Costs of two alternative Salmonella control policies in Finnish broiler production.

BACKGROUND: Costs and benefits of two Salmonella control policies for broiler production were described and compared. The control options were the Zoonosis Directive 92/117/EC and the more intense strategy, the Finnish Salmonella Control Programme (FSCP). METHODS: The comparison included the Salmonella control costs in primary and secondary production and the direct and indirect losses due to Salmonella infections in humans in 2000. RESULTS: The total annual costs of the FSCP were calculated to be 990 400 EUR (0.02 euro/kg broiler meat). The average control costs in the broiler production chain were seven times higher with the FSCP than with the Zoonosis Directive alone. However, the public health costs were 33 times higher with the Zoonosis Directive alone. The value of one prevented loss of life per year exceeded the annual control costs of the FSCP. CONCLUSION: Due to significant savings in public health costs compared to costs of FSCP, the FSCP was found to be economically feasible.

Studying the effects of POs and MCs on the Salmonella ALOP with a quantitative risk assessment model for beef production.

The Finnish Salmonella Control Programme and the special guarantees (SG) of import concerning Salmonella in the beef production chain were examined within the risk analysis framework. The appropriate level of protection (ALOP de facto since not referred to as ALOP in regulation), performance objectives (PO), and microbiological criteria (MC) were identified along the beef production chain. A quantitative microbiological risk assessment (QMRA) model using the Bayesian probabilistic method was developed for the beef chain to evaluate the capability of different POs to contribute to the ALOP. The influence of SGs was studied as an intervention protecting Finnish consumers. The QMRA made it possible to translate an ALOP without a stated food safety objective (FSO) to POs when implemented for both ready-to-eat (RTE) and non-RTE products. According to the results, the Finnish ALOP de facto for beef, beef preparations and products (10 human Salmonella cases/100,000) was reached in all of the years 1996-2004. However, if the prevalence at the slaughter, domestic cut beef, and retail levels would increase to the level of POs set (maximum 1%), the ALOP de facto would be exceeded by a factor of roughly two. On the other hand, the zero tolerance applied to MCs would keep the true Salmonella prevalence at production steps with POs clearly below 1%, and the ALOP would then be achievable. The influence of SGs on the total exposure was so small (average 0.1% added to the total prevalence of beef-derived foods at retail) that their relevance may be doubted with the current amount and Salmonella prevalence in beef-derived imports. On the other hand, a change in import profile could increase the protective effect of the SGs. Although practical follow-up has to be carried out as apparent prevalences, the objectives and criteria should be estimated as true prevalences and incidences with quantified uncertainties in order to achieve a sound, transparent scientific-based understanding of the risk. The QMRA model developed here provided a useful tool for studying the connection between the ALOP and other targets in the production chain.

Estimation of true Salmonella prevalence jointly in cattle herd and animal populations using Bayesian hierarchical modeling.

The Finnish salmonella control program (FSCP) for beef production is based on both randomized and selective testing of herds and animals. Sampling of individual animals in abattoirs is randomized. Herds are selectively tested for salmonella on the basis of clinical symptoms and/or other factors. Risk assessment of FSCP is inherently difficult due to the complexity of the complete data set, especially if the detailed labeling of the testing types is lost. However, for a risk assessment of the whole production chain, methods for exploiting all available data should be considered. For this purpose, a hierarchical Bayesian model of true salmonella prevalence was constructed to combine information at different levels of aggregation: herds in geographical regions and individual animals arriving for slaughter. The conditional (municipality specific) probability of selection of a herd for testing was modeled given the underlying true infection status of the herd and information about the general sampling activity in the specific region. The model also accounted for the overall sensitivity of the sampling methods, both at the herd and at the animal level. In 1999, the 95% posterior probability intervals of true salmonella prevalence in the herd population, in individual cattle, and in slaughter animal populations were [0.54%, 1.4%] (mode 0.8%), [0.15%, 0.39%] (mode 0.2%), and [0.12%, 0.36%] (mode 0.2%), respectively. The results will be further exploited in other risk assessments focusing on the subsequent parts of the beef production chain, and in evaluation of the FSCP.

A probabilistic transmission model of Salmonella in the primary broiler production chain.

Annual data from the Finnish National Salmonella Control Programme were used to build up a probabilistic transmission model of salmonella in the primary broiler production chain. The data set consisted of information on grandparent, parent, and broiler flock populations. A probabilistic model was developed to describe the unknown true prevalences, vertical and horizontal transmissions, as well as the dynamical model of infections. By combining these with the observed data, the posterior probability distributions of the unknown parameters and variables could be derived. Predictive distributions were derived for the true number of infected broiler flocks under the adopted intervention scheme and these were compared with the predictions under no intervention. With the model, the effect of the intervention used in the programme, i.e., eliminating salmonella positive breeding flocks, could be quantitatively assessed. The 95% probability interval of the posterior predictive distribution for (broiler) flock prevalence under current (1999) situation was [1.3%-17.4%] (no intervention), and [0.9%-5.8%] (with intervention). In the scenario of one infected grandparent flock, these were [2.8%-43.1%] and [1.0%-5.9%], respectively. Computations were performed using WinBUGS and Matlab softwares.

A Less Hazardous Enrichment Broth for Listeria without Cycloheximide and Acriflavine.

The hazardous substances cycloheximide and acriflavine are used as selective agents in standard listeria enrichment broths. This study was undertaken to develop a less hazardous listeria enrichment broth in order to avoid occupational-safety and waste-management problems. The replacement of cycloheximide (50 mg/l) and acriflavine (15 mg/l) with natamycin (25 mg/l), moxalactam (10 mg/l) and bacitracin (20 mg/l) did not inhibit the growth of Listeria monocytogenes . Furthermore, most of the competing microbial strains were suppressed equally well or better in this less hazardous modification than in a standard broth.

Histamine and Tyramine Production by a Lactobacillus Strain Subjected to External pH Decrease.

The preservative effect of fermentation is based on the pH decrease during processing. However, most studies conceming the influence of pH on the formation of biogenic amines have been made in broths with different initial pH values. A histamine- and tyramine-positive Lactobacillus strain isolated from dry sausage was added at an initial level of 3.9- to 4.4-logl0 CFU/ml and incubated on a shaker at room temperature (20.0°C) for 6 days. The pH was decreased in histidine- or tyrosine-fortified MRS broth by adding glucono-delta-lactone (GDL) or lactic acid during the incubation. The external acidification decreased the growth and the production of histamine and tyramine by the strain. GDL was more effective as a preventative than lactic acid. According to these results, a rapid pH decrease resulting in decreased growth of amine-positive lactic acid bacteria in the beginning of fermentation may be a means of preventing the formation of high levels of amines in foods.

The Effect of GDL-induced pH Decrease on the Formation of Biogenic Amines in Meat.

The effect of pH on the formation of biogenic amines has mainly been studied in broths in which pH has been fixed before incubation. However, in the fermentation of dry sausage, pH quite rapidly decreases from the initial value to a certain level. In this study glucono-delta-lactone (GDL) was used to decrease pH in meat, Six minced meat samples were each divided into three portions (A-C): 0% (A), 0.5% (B), or 1.0% (C) of GDL was added and the samples were incubated at 20-22°C for 7 d. The amounts of biogenic amines (histamine, tyramine, putrescine, cadaverine, phenylethylamine, tryptamine, spermine, and spermidine) as well as pH, water activity, and the bacterial counts of lactic acid bacteria, fecal streptococci, coliforms, and total plate count were measured. Addition of GDL resulted in a significant decrease in pH and in the levels of histamine and putrescine as well as in the levels of fecal streptococci, coliforms, and total plate counts. Of 87 fecal streptococci, seven Enterococcus faecalis strains produced tyramine. All the coliforms and related strains isolated from violet red bile agar produced tyramine, putrescine, and cadaverine on agar plates. However, the proportion of histamine-positive strains of these strains, especially Hafnia alvei , increased from 0 to 57% during the incubation. The rate and level of pH decrease clearly affected amine formation in meat, indicating that the levels of, e.g., histamine produced could be decreased by optimizing the pH decrease during fermentation. Addition of GDL facilitates study of the effect of pH decrease without interactions between the starter culture and contaminant flora.