Prevalence of Pathogenic Yersinia enterocolitica in Finnish Slaughter Pigs

The prevalence of human pathogenic Yersinia enterocolitica was determined in tonsil and intestinal content samples from 388 healthy fattening pigs at the four biggest Finnish slaughterhouses. These slaughterhouses process 73% of pigs in Finland. Tonsil samples were tested by PCR targeted for yadA, and intestinal samples were cultured. All pathogenic Y. enterocolitica isolates represented bioserotype 4/O:3. The prevalence of Y. enterocolitica in tonsil samples was 60% (95% confidence limit, 55.4 to 65.1%), and its prevalence in intestinal samples was 26% (95% confidence limit, 22.1 to 31.2%). The prevalence of Y. enterocolitica in tonsil and intestinal samples varied between the four slaughterhouses. The tonsil prevalence of Y. enterocolitica was higher in slaughterhouse B, and the prevalence in intestinal content was higher in slaughterhouse C. There were more positive results in both tonsil and intestinal samples in pigs coming from fattening farms than in pigs coming from farrowing-and-fattening farms. A seasonal variation was observed in the prevalence of Y. enterocolitica in intestinal samples, with the highest prevalence during July and August, but no seasonal variation was detected in tonsil samples.

Isolation and characterization of Yersinia-specific bacteriophages from pig stools in Finland

AIMS

Bacteriophages infect bacteria, and they are present everywhere in the world including the intestinal tracts of animals. Yersiniosis is a common foodborne infection caused by Yersinia enterocolitica and Yersinia pseudotuberculosis. As these bacteria are frequently isolated from pigs, we wanted to know whether Yersinia-specific bacteriophages are also present in the pig stools and, if so, whether there is a positive or negative association between the prevalence of the Yersinia phages and the pathogenic Yersinia in the stool samples.

METHODS AND RESULTS

Altogether 793 pig stool samples collected between November 2010 and March 2012 from 14 Finnish pig farms were screened for the presence of bacteriophages able to infect Y. enterocolitica serotype O:3, O:5,27 or O:9 strains, or Y. pseudotuberculosis serotype O:1a, O:1b or O:3 strains. Yersinia phages were isolated from 90 samples from eight farms. Yersinia enterocolitica O:3 was infected by 59 phages, 28 phages infected serotypes O:3 and O:5,27, and eight phages infected serotypes O:3, O:5,27 and O:9, and Y. pseudotuberculosis O:1a by eight phages. Many phages originating from pigs in the same farm were identical based on their restriction enzyme digestion patterns; 20 clearly different phages were selected for further characterization. Host ranges of these phages were tested with 94 Yersinia strains. Six of the phages infected eight strains, 13 phages infected three strains, and one phage infected only one strain, indicating that the phages had a relatively narrow host range.

CONCLUSIONS

There was a clear association between the presence of the host bacteria and specific phages in the stools.

SIGNIFICANCE AND IMPACT OF THE STUDY

The isolated bacteriophages may have potential as biocontrol agents for yersiniosis in both humans and pigs in future, and as alternatives or in addition to antibiotics. To our knowledge, this is the first reported isolation of Yersinia-specific phages from pig stool samples.

Introduction of infected animals to herds is an important route for the spread of Yersinia enterocolitica infection between pig farms

Altogether, 369 pathogenic Yersinia enterocolitica isolates from 1,118 fecal samples collected from 22 pig farms of different production types were characterized by biotyping, serotyping, and genotyping using multiple-locus variable-number tandem repeats analysis. We investigated the distribution of the different genotypes at the farm level and their association with different farm conditions. Pigs were found to carry and transmit Y. enterocolitica between farms, because the same genotypes were found on farms that had previously transported the pigs between them. The purchase of new animals for the farms associated significantly with the number of different multiple-locus variable-number tandem repeats analysis types of Y. enterocolitica found within a farm. Some genotypes seemed to persist on farms for years. The results of this study show that pigs purchased from infected herds transmit Y. enterocolitica infection between farms. Certain pig farms may act as long-term sources of infection.

Determination of pH in meat

The pH of 80 beef and 120 pork muscles was determined electrometrically using different electrode systems and different presentations of samples; that is, directly from the muscle, from a meat-water mixture and from a meat homogenate. The results showed statistically significant differences (p < 0·001). Differences between electrodes appear to be greater than the differences due to the different presentations of the meat samples. Certain methods gave systematically lower or higher pH values than others. On the other hand, these differences were not very large and the repeatability of each method was low. On the basis of the results, however, no pH measurement method could be considered better than the others. Further harmonization of the methods used for pH measurement of meat is still needed.

Special treatment during slaughtering in Finland of cattle carrying an excessive load of dung; Meat hygienic aspects

The aim of the study was to evaluate the microbiological consequences of the Finnish special hide regulations. These were agreed upon, by a committee including members representing meat production, industry and the state, to reduce the number of cattle carrying excessive loads of dung. The changes in the number of excessively dungy cattle in one beef abattoir have been recorded since the adoption of the special rules. The effect of excessive dunginess of the hide on microbial contamination of the carcasses was measured in the same abattoir using excision sampling technique. From 1983 to 1990 the proportion of excessively dungy cattle has decreased 85%, with the majority of them arriving from October to March. Excess dunginess resulted in statistically significantly increased microbial contamination at both sampling sites. Results indicate that the regulations are reasonable from the point of view of meat hygiene and that, for commercial-scale slaughtering, the drawbacks caused by the excess dunginess of the hide cannot be compensated for by greater care in the work procedures.

Two cases of food-borne botulism in Finland caused by conserved olives, October 2011

In October 2011 in Finland, two persons fell ill with symptoms compatible with botulism after having eaten conserved olives stuffed with almonds. One of these two died. Clostridium botulinum type B and its neurotoxin were detected in the implicated olives by PCR and mouse bioassay, respectively. The olives were traced back to an Italian manufacturer and withdrawn from the market. The public and other European countries were informed through media and Europe-wide notifications.

cspB encodes a major cold shock protein in Clostridium botulinum ATCC 3502

The relative expression of three cold shock protein coding genes (cspA, cspB and cspC) of Clostridium botulinum ATCC 3502 was studied with quantitative RT-PCR analysis following a cold shock shift from 37 °C to 15 °C. A significant increase in the relative expression of all three genes was observed upon the temperature downshift. To validate these findings, single-gene insertional inactivation of cspA, cspB and cspC was undertaken with the ClosTron gene knock-out system. In growth experiments, mutations in cspB or cspC, but not cspA, resulted in a cold-sensitive phenotype. No growth of the cspB mutant was observed at 15°C over a ten day period, whereas at 20 °C the growth rate was 70% lower than that of wild type strain. The growth rate of cspC mutant was 70% and 80% lower than the growth rate of the wild type strain at 15 °C and 20 °C, respectively. At 37 °C the growth of cspB mutant did not differ from, but the growth rate of cspC mutant was 30% lower than, that of the wild type strain. The cspA mutant grew somewhat faster than the wild type strain at all studied temperatures. Since the inactivation of cspB resulted in the most prominent defect in growth at low temperatures, we suggest that cspB encodes the major cold shock protein of C. botulinum ATCC 3502. Understanding the mechanisms behind cold tolerance of C. botulinum helps to evaluate the safety risks this foodborne pathogen poses in the modern food industry.

Fur animal botulism hazard due to feed

To assess the botulism hazard in fur animal feed production, 236 fur animal feed components and feed samples were analysed for Clostridium botulinum by detecting BoNT-encoding genes (botA, botB, botC, botE or botF) by PCR and for sulphite-reducing clostridia (SRC) by iron sulphite agar. The quality of the hazard analysis of critical control points (HACCP) -based in-house control system (IHCS) was evaluated with respect to botulism risk in feed plants (n=32). The overall prevalence of C. botulinum was 13% in different feed components and 5% in feed. The estimated MPN count of C. botulinum in feed components was 6.4 × 10(3)/kg at the highest and was shown to poorly correlate with SRC count. The critical control points in IHCSs were variable, and control limits were improperly set in most feed-producing plants. C. botulinum possesses a persistent safety hazard for fur animals by feed production, and control practices should be reassessed.

Botulism and hot-smoked whitefish: a family cluster of type E botulism in France, September 2009

A family cluster of three cases of type E botulism were identified in south-east France in September 2009. The suspected food source of infection was a vacuum packed hot-smoked whitefish of Canadian origin purchased by the family during a visit to Finland and consumed several weeks later in France on the day prior to symptom onset. No leftover fish was available to confirm this hypothesis. Vacuum packed hot-smoked whitefish has previously been associated with cases of type E botulism in multiple countries, including Finland, Germany, the United States and Israel.

Distribution of virF/lcrF-positive Yersinia pseudotuberculosis serotype O:3 at farm level

The distribution and persistence of pathogenic, virF/lcrF-positive Yersinia pseudotuberculosis were investigated in pigs and in the pig house environment during rearing to determine possible contamination routes of early infections. Based on Y. pseudotuberculosis-positive tonsils of slaughter pigs in our previous study, Y. pseudotuberculosis-positive animals were traced back to the farms. Eight farms were visited from 6-10 months later, and a total of 155 pooled and six individual faecal samples from pigs and 116 pooled environmental samples were collected for analysis by different culture methods. Four of the eight farms were found to be Y. pseudotuberculosis-positive. All positive faecal samples were obtained from fattening pigs, with prevalence varying from 5% to 71% on positive farms. Sows, boars and suckling piglets were Y. pseudotuberculosis-negative on all farms. Most Y. pseudotuberculosis-positive farms (three of four) were on a one-site production system, which had a higher prevalence of Y. pseudotuberculosis (5-26%) among fattening pigs than the all-in, all-out system (1-5%). All Y. pseudotuberculosis isolates belonged to serotype O:3 and carried the virF/lcrF gene on the virulence plasmid. Biotypes 2 and 3 were involved, the latter in one isolate and not being previously reported in pigs. Altogether 53 isolates from 16 positive samples were characterized with pulsed-field gel electrophoresis (PFGE). Using SpeI, NotI and XbaI enzymes, four, three and two different PFGE patterns were obtained respectively. A total of nine different genotypes were identified when the profiles of the enzymes were combined. The most common genotypes were gIV, found on three, and gXII, found on two of the four Y. pseudotuberculosis-positive farms. The same genotypes previously detected in pig tonsils were present in pig faeces from the same farm, indicating that some Y. pseudotuberculosis strains can persist in the pig house environment.

Acid and heat tolerance of persistent and nonpersistent Listeria monocytogenes food plant strains

AIMS

Acid and heat tolerance of 17 persistent and 23 nonpersistent Listeria monocytogenes strains, recovered from three meat-processing plants, were investigated.

METHODS AND RESULTS

The isolates were genotyped by pulsed-field gel electrophoresis and categorized into persistent strains according to the frequency of the strain and duration of the contamination. The persistent and nonpersistent strains were challenged to acidic conditions (pH 2.4 for 2 h, 1 mol l(-1) HCl were used to acidify the suspension) and to heat (55 degrees C for 40 min) to receive a reduction in cell count. Listeria monocytogenes strains showed large variation in acid tolerance (over 6 log units) and in heat tolerance (3 log units). The persistent strains showed higher tolerance to acidic conditions than the nonpersistent strains (Student's t-test, P = 0.02), but significant differences in heat tolerance between persistent and nonpersistent strains were not observed.

CONCLUSIONS

The results indicate that acid tolerance may have an effect on the persistence of L. monocytogenes contamination.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study highlights the fact that there are great differences in acid and heat tolerances between L. monocytogenes strains, and the preventive measures should be designed to be effective against the most tolerant strains.

Listeria monocytogenes is common in wild birds in Helsinki region and genotypes are frequently similar with those found along the food chain

AIMS

To evaluate the prevalence and genetic diversity of Listeria monocytogenes in wild birds and to compare the genotypes with isolates previously collected from foods and food processing environments.

METHODS AND RESULTS

Samples of wild birds' faeces (n = 212) were collected from a municipal landfill site and from urban areas in the Helsinki region and analysed by two-step enrichment and plating onto L. monocytogenes-selective agar. The overall prevalence of L. monocytogenes in bird faeces was 36% (95% CI 30-43%), and prevalence on the landfill site was significantly higher. All isolates were analysed with pulsed-field gel electrophoresis and compared with the L. monocytogenes profiles in an existing collection. Similar pulsotypes were found in birds and in isolates collected along the food chain.

CONCLUSIONS

Birds commonly carry L. monocytogenes, and strains are frequently similar with those detected in foods and food processing environments. Thus, birds may disseminate L. monocytogenes in nature and may also contaminate foods when entering the food processing environments and outdoor market places.

SIGNIFICANCE AND IMPACT OF THE STUDY

Populations of L. monocytogenes in wild birds and along the food processing chain overlap. Our findings add to the epidemiological data on this significant foodborne pathogen.

Botulism associated with vacuum-packed smoked whitefish in Finland, June-July 2006

On 29 June 2006, a 65 year old woman fell ill with vomiting and diarrhoea in southern Finland

Multiplex PCR assay for toxinotyping Clostridium perfringens isolates obtained from Finnish broiler chickens

AIMS

The aim of the study was to determine the presence of genes coding for alpha (cpa), beta (cpb), epsilon (etx), iota (iA) and enterotoxin (cpe) from Clostridium perfringens broiler chicken isolates, using multiplex PCR assay established in the study.

METHODS AND RESULTS

The multiplex PCR assay was shown to be specific when tested with 10 C. perfringens strains representing different toxin types, and 15 strains of other bacterial species. All 118 broiler chicken C. perfringens isolates were shown to carry the cpa gene but not cpb, etx, iap or cpe genes, signifying that all isolates represented type A and were cpe-negative.

CONCLUSIONS

The assay established in the study enables the simultaneous detection of the major toxin genes and the cpe gene from C. perfringens isolates.

SIGNIFICANCE AND IMPACT OF THE STUDY

The present study offers a new primer pair for detecting cpa, combined with a multiplex PCR assay. In addition, the study provides data of the presence of different toxin genes in C. perfringens isolates obtained from broiler chickens.

Listeria monocytogenes occurrence and characterization in meat-producing plants

AIMS

The prevalence, level of contamination and epidemiological profile of Listeria monocytogenes were investigated in two meat-producing plants during a 20-month period.

METHODS AND RESULTS

Sampling for L. monocytogenes was carried out in a cattle slaughterhouse (n = 72) and a swine meat-processing plant (n = 68) during a 20-month period. Swabs and food samples were analysed with the most probable number (MPN) technique for L. monocytogenes and the isolated strains were characterized by AscI-restriction analysis pulsed-field gel electrophoresis (REA-PFGE). Contamination of meat and meat products was always at low level (below 50 MPN per gram). The seven L. monocytogenes positive samples isolated in the bovine slaughterhouse yielded strains with the same REA-PFGE profile. However, the seven strains isolated in the swine meat processing plant showed six different profiles. Two of them showed indistinguishable profiles with L. monocytogenes strains collected from other meat processing facilities located in the same area.

SIGNIFICANCE AND IMPACT OF THE STUDY

The genotyping method is a valuable tool to investigate contamination sources. The study of REA-PFGE profiles indicated that environmental contamination was probably responsible for the persistence of over 16 months of one strain of L. monocytogenes in the cattle slaughterhouse. Several meat suppliers could be responsible for the contamination in the pig meat processing facility, and this is confirmed by the finding of some identical strain in other meat processing facilities located in the same area.

Different Yersinia enterocolitica 4:O3 genotypes found in pig tonsils in Southern Germany and Finland

The distribution of different genotypes of Y. enterocolitica 4:O3 strains recovered from pig tonsils in Southern Germany and Finland in 1999-2000 was investigated. A total of 96 and 207 Y. enterococolitica 4:O3 isolates recovered from 47 and 66 tonsils of finishing pigs in Germany and Finland, respectively, were characterised with PFGE using NotI enzyme. In all, 39 different NotI profiles were obtained, only one of which, NB1, was found in both Germany and Finland. All strains were further characterised with ApaI and XhoI enzymes. When the 54 German and 74 Finnish strains were characterised with all three enzymes, 51 genotypes were obtained. The 23 genotypes found in German strains differed from the 28 found in Finnish strains. These results indicate that Y. enterocolitica 4:O3 genotypes have a differential geographical distribution and thus can be used in epidemiological studies.

Characterisation of sucrose-negative Yersinia enterocolitica 4/O:3 isolates recovered from pig tonsils

Sucrose-negative Yersinia enterocolitica isolates of bioserotype 4/O:3 have been recovered for the first time. They were found in 2% of the tonsils of clinically healthy fattening pigs. These sucrose-negative Y. enterocolitica isolates could not be differentiated from Y. kristensenii isolates using API 20E; thus, they were identified using PCR and sequencing. Using pulsed-field gel electrophoresis (PFGE). NotI profiles of sucrose-negative Y. enterocolitica 4/O:3 isolates showed a high similarity to sucrose-positive Y. enterocolitica 4/O:3 isolates. This study demonstrated that sucrose-negative Y. enterocolitica 4/O:3 isolates of porcine origin can harbour virulence genes; plasmid-encoded virulence markers were found in 8 out of 11 isolates and all isolates contained chromosomal-encoded virulence markers. Thus, the pathogenicity of sucrose-negative Yersinia isolates should always be assessed.

A high prevalence of Clostridium botulinum type E in Finnish freshwater and Baltic Sea sediment samples

The distribution of Clostridium botulinum serotypes A, B, E and F in aquatic environments of the Baltic Sea and Finnish mainland was examined. A total of 110 samples were tested with a neurotoxin-specific PCR assay. Clostridium botulinum type E was found in 81% of sea and 61% of freshwater samples. No other toxinotypes were found. Spore counts were quantified by the most probable number method, Cl. botulinum type E kg(-1) averaging 940 in sea and 370 in freshwater samples. The overall prevalence and spore counts of Cl. botulinum type E in aquatic sediments correlated significantly with offshore bottom oxygen content, depth, and bioturbation activity, whereas there was no correlation with bottom water temperature. These findings indicate the possibility of Cl. botulinum type E multiplication or at least, suitable conditions for spore survival, in anoxic sediments.

Multiplex PCR assay for detection and identification of Clostridium botulinum types A, B, E, and F in food and fecal material

Botulism is diagnosed by detecting botulinum neurotoxin and Clostridium botulinum cells in the patient and in suspected food samples. In this study, a multiplex PCR assay for the detection of Clostridium botulinum types A, B, E, and F in food and fecal material was developed. The method employs four new primer pairs with equal melting temperatures, each being specific to botulinum neurotoxin gene type A, B, E, or F, and enables a simultaneous detection of the four serotypes. A total of 43 C. botulinum strains and 18 strains of other bacterial species were tested. DNA amplification fragments of 782 bp for C. botulinum type A alone, 205 bp for type B alone, 389 bp for type E alone, and 543 bp for type F alone were obtained. Other bacterial species, including C. sporogenes and the nontoxigenic nonproteolytic C. botulinum-like organisms, did not yield a PCR product. Sensitivity of the PCR for types A, E, and F was 10(2) cells and for type B was 10 cells per reaction mixture. With a two-step enrichment, the detection limit in food and fecal samples varied from 10(-2) spore/g for types A, B, and F to 10(-1) spore/g of sample material for type E. Of 72 natural food samples investigated, two were shown to contain C. botulinum type A, two contained type B, and one contained type E. The assay is sensitive and specific and provides a marked improvement in the PCR diagnostics of C. botulinum.

Microbiological quality and shelf-life of vacuum-packaged 'gravad' rainbow trout stored at 3 and 8 degrees C

Microbiological and sensory changes of vacuum-packaged 'gravad' rainbow trout slices were studied during storage at 3 and 8 degrees C. At the time of spoilage, after 27 and 20 days of storage at 3 and 8 degrees C, respectively, both mesophilic viable counts (MVC) and psychrotrophic viable counts (PVC) reached 10(6)-10(7) cfu/g at 3 degrees C and 10(7)-10(5) cfu/g at 8 degrees C. H2S-producing bacteria constituted a high proportion of the PVCs and lactic acid bacteria (LAB) counts were lower than the other determined bacterial counts. Sensory scores decreased with increasing MVC and PVC. The judges considered samples unfit for human consumption at MVC and PVC levels exceeding 10(6) and 10(7) cfu/g for samples stored at 3 and 8 degrees C, respectively. At respective levels of 10(7) and 10(8) cfu/g, most of the samples were deemed unfit. The main reasons for sensory rejection at both storage temperatures were the lack of the typical product odour or an ammonia off-odour and colour change to dark violet. The shelf-lives of the rainbow trout slices based on microbiological and sensory analyses were 20 days and 18 days at 3 and 8 degrees C, respectively.

High prevalence of Yersinia enterocolitica 4:O3 on pig offal in southern Germany: a slaughtering technique problem

Prevalence and contamination routes of pathogenic Yersinia enterocolitica were studied in Southern Germany. Tonsil and faeces samples of 50 fattening pigs, 140 offal samples and 120 minced meat samples were examined. Pig and offal samples were collected from a slaughterhouse approved by the European Union, and minced meat samples from two large meat factories. Yersinia enterocolitica was isolated using direct plating, overnight enrichment and selective enrichment in MRB and ITC broth. The isolates were bio- and serotyped, and pathogenicity was studied using two plasmid-encoded virulence markers: calcium dependence and Congo red absorption. The genotypes were studied with pulsed-field gel electrophoresis using NotI enzyme. Prevalence of pathogenic Y. enterocolitica 4:O3 was 60% and 10% in tonsils and faeces of fattening pigs, respectively. Besides tonsils, prevalence of pathogenic Y. enterocolitica 4:O3 was also high in other pluck set samples, including tongues, lungs, hearts, diaphragms and livers. However, the highest isolation rate was obtained from the tonsils. Kidneys, which were not attached to the pluck set and did not hang together with tonsils on the rack, had the lowest isolation rate. Yersinia enterocolitica 4:O3 was isolated from 12% of minced meat samples. A total of 25 NotI profiles were obtained from porcine samples. The most common genotype, NBI, found in tonsils was also the most common type recovered from offal and minced meat samples. The high contamination rate of tonsils, and the indistinguishable NotI profiles obtained from tonsils and offal indicate that the tonsils contaminate offal when they are removed and hung on the rack together. When the head, with the tonsils and tongue, is not removed prior to evisceration and is not handled and inspected separately, it is difficult to control the spread of Y. enterocolitica 4:O3 from tonsils to the carcass, and subsequently, to meat.

Correspondence of genotypes of sporadic Yersinia enterocolitica bioserotype 4/O:3 strains from human and porcine sources

The sources and transmission routes of sporadic Yersinia enterocolitica bioserotype 4/O:3 infections in Finland were studied. A total of 212 human strains were compared with 334 non-human strains, including 163 strains from pig slaughterhouses, 164 strains from retail outlets and 7 strains from pet animals. All strains were characterized using pulsed-field gel electrophoresis (PFGE) with NotI enzyme. When the 194 human and 287 non-human strains of 22 identical NotI profiles were further characterized with ApaI and XhoI enzymes, 126 genotypes (DI = 094) were distinguished. Of all 212 human strains, 80% were genetically indistinguishable from the strains found in samples of pig origin when characterized with the three enzymes. A major contamination source of sporadic Y. enterocolitica 4/O:3 infections was revealed to be edible pig offal: 71% of the human strains were indistinguishable from the strains isolated from tongues, livers, kidneys and hearts of pigs. These results reveal that in Finland contaminated pig offal is an important vehiclein the transmission of Y. enterocolitica bioserotype 4/O:3 from slaughterhouses to humans.

Prevalence of Listeria monocytogenes in broilers at the abattoir, processing plant, and retail level

The environment and products from two broiler abattoirs and processing plants and raw broiler pieces at the retail level were sampled for Listeria monocytogenes in order to evaluate the contamination level of the broiler carcasses and products. Sampling started in the slaughtering process and finished with raw broiler meat or ready-to-eat cooked product. Sampling sites positive for L. monocytogenes at the broiler abattoir were the air chiller, the skin-removing machine, and the conveyor belt leading to the packaging area. The L monocytogenes contamination rate varied from 1 to 19% between the two plants studied. Furthermore, 62% (38 of 61) of the raw broiler pieces, bought from retail stores, were positive for L. monocytogenes. Altogether, 136 L. monocytogenes isolates were obtained for serotyping and pulsed-field gel electrophoresis (PFGE) characterization performed with two rare-cutting enzymes (ApaI and AscI). Altogether three serotypes (1/2a, 1/2c, and 4b) and 14 different PFGE types were obtained using information provided from both ApaI and AscI patterns for discrimination basis. The two broiler abattoirs studied did not share the same PFGE types. However, the same PFGE types found in the raw broiler pieces at the retail level were also found in the broiler abattoirs where the broilers had been slaughtered.

Inhibition of growth of nonproteolytic Clostridium botulinum type B in sous vide cooked meat products is achieved by using thermal processing but not nisin

The safety of refrigerated processed foods of extended durability (REPFEDs) with respect to nonproteolytic Clostridium botulinum is under continuous evaluation. In the present study, mild (P7.0(85.0) values 0 to 2 min [P, pasteurization value; z-value 7.0 degrees C; reference temperature 85.0 degrees C]) and increased (P7.0(85.0) values 67 to 515 min) heat treatments were evaluated in relation to survival of nonproteolytic C. botulinum type B spores in sous vide processed ground beef and pork cubes. The use of two concentrations of nisin in inhibition of growth and toxin production by nonproteolytic C. botulinum in the same products was also evaluated. A total of 96 samples were heat processed and analyzed for C. botulinum by BoNT/B gene-specific polmerase chain reaction and for botulinum toxin by a mouse bioassay after storage of 14 to 28 days at 4 and 8 degrees C. Predictably, after mild processing all samples of both products showed botulinal growth, and one ground beef sample became toxic at 8 degrees C. The increased heat processing, equivalent to 67 min at 85 degrees C. resulted in growth but not toxin production of C. botulinum in one ground beef sample in 21 days at 8 degrees C: in the pork cube samples no growth was detected. The increased heating of both products resulted in higher sensory quality than the milder heat treatment. Nisin did not inhibit the growth of nonproteolytic C. botulinum in either product; growth was detected in both products at 4 and 8 degrees C, and ground beef became toxic with all nisin levels within 21 to 28 days at 8 degrees C. Aerobic and lactic acid bacterial counts were reduced by the addition of nisin at 4 degrees C. The study demonstrates that the mild processing temperatures commonly employed in sous vide technology do not eliminate nonproteolytic C. botulinum type B spores. The intensity of each heat treatment needs to be carefully evaluated individually for each product to ensure product safety in relation to nonproteolytic C. botulinum.

Transmission of Yersinia enterocolitica 4/O:3 to pets via contaminated pork

AIMS

This study was conducted to investigate sources of Yersinia enterocolitica 4/O:3 infections in dogs and cats.

METHODS AND RESULTS

Transmission of Y. enterocolitica 4/O:3 to pets via contaminated pork was studied using PFGE with NotI, ApaI and XhoI enzymes. A total of 132 isolates, of which 16 were from cat and dog faeces and 116 from raw pork samples, were recovered in Finland during 1998-99. Cat 1, whose diet consisted mostly of raw pig hearts and kidneys, excreted Y. enterocolitica 4/O:3 of genotype G4. This predominant genotype was also found in isolates recovered from the pig heart, liver, kidney, tongue and ear, and minced pork samples. Dog 2, which was fed raw minced pork, excreted Y. enterocolitica of genotype G13. This genotype was also identified in isolates recovered from the pig heart, kidney and tongue, and minced pork samples.

CONCLUSION

These results show that raw pork can be an important source of Yersinia enterocolitica 4/O:3 infections in dogs and cats.

SIGNIFICANCE AND IMPACT OF THE STUDY

Raw pork should not be given to pets.

Lactobacillus alimentarius: a specific spoilage organism in marinated herring

Spoilage characterised by bulging of lids and gas formation affected various product lots of different marinated herring types. Microbiological analyses resulted in growth on MRS and Rogosa SL agar. Altogether, 206 randomly selected colonies from two unspoiled and ten spoiled samples were characterised using phenotypical key tests and a 16 + 23S rRNA gene-based RFLP identification database. L. alimentarius was found to be the specific spoilage organism in all samples. All isolates obtained from the different product types were of the same clonal type. The slight rise in pH value together with marked gas production suggested a rare lactic acid bacteria spoilage type called 'protein swell'. L. alimentarius has not been previously associated with herring spoilage.

Listeria monocytogenes contamination pattern in pig slaughterhouses

Ten low-capacity slaughterhouses were examined for Listeria by collecting a total of 373 samples, of which 50, 250, and 73 were taken from carcasses, pluck sets, and the slaughterhouse environment, respectively. Six slaughterhouses and 9% of all samples were positive for Listeria monocytogenes. Of the samples taken from pluck sets, 9% were positive for L. monocytogenes, the highest prevalence occurring in tongue and tonsil samples, at 14% and 12%, respectively. Six of 50 (12%) carcasses were contaminated with L. monocytogenes. In the slaughterhouse environment, L. monocytogenes was detected in two, one, one, and one sample originating from the saws, drain, door, and table, respectively. Carcasses were contaminated with L. monocytogenes in those two slaughterhouses, where the mechanical saws, used for both brisket and back splitting, were also positive for L. monocytogenes. A total of 58 L. monocytogenes isolates were characterized by pulsed-field gel electrophoresis typing. The isolates were divided into 18 pulsotypes, 15 of which were detected in pluck sets. In two slaughterhouses, where the carcasses were contaminated with L. monocytogenes, the same pulsotypes were also recovered from splitting saws. In addition, identical pulsotypes were recovered from pluck sets. Our findings indicate that L. monocytogenes of tongue and tonsil origin may contaminate the slaughtering equipment that may in turn spread the pathogen to carcasses. Thus, it is of the utmost importance to follow good manufacturing practices and to have efficient cleaning and disinfection procedures to prevent equipment being contaminated with L. monocytogenes.

An outbreak of Listeria monocytogenes serotype 3a infections from butter in Finland

In February 1999, an outbreak of listeriosis caused by Listeria monocytogenes serotype 3a occurred in Finland. All isolates were identical. The outbreak strain was first isolated in 1997 in dairy butter. This dairy began delivery to a tertiary care hospital (TCH) in June 1998. From June 1998 to April 1999, 25 case patients were identified (20 with sepsis, 4 with meningitis, and 1 with abscess; 6 patients died). Patients with the outbreak strain were more likely to have been admitted to the TCH than were patients with other strains of L. monocytogenes (60% vs. 8%; odds ratio, 17.3; 95% confidence interval, 2.8-136.8). Case patients admitted to the TCH had been hospitalized longer before cultures tested positive than had matched controls (median, 31 vs. 10 days; P=.008). An investigation found the outbreak strain in packaged butter served at the TCH and at the source dairy. Recall of the product ended the outbreak.

Safety evaluation of sous vide-processed products with respect to nonproteolytic Clostridium botulinum by use of challenge studies and predictive microbiological models

Sixteen different types of sous vide-processed products were evaluated for safety with respect to nonproteolytic group II Clostridium botulinum by using challenge tests with low (2. 0-log-CFU/kg) and high (5.3-log-CFU/kg) inocula and two currently available predictive microbiological models, Food MicroModel (FMM) and Pathogen Modeling Program (PMP). After thermal processing, the products were stored at 4 and 8 degrees C and examined for the presence of botulinal spores and neurotoxin on the sell-by date and 7 days after the sell-by date. Most of the thermal processes were found to be inadequate for eliminating spores, even in low-inoculum samples. Only 2 of the 16 products were found to be negative for botulinal spores and neurotoxin at both sampling times. Two products at the high inoculum level showed toxigenesis during storage at 8 degrees C, one of them at the sell-by date. The predictions generated by both the FMM thermal death model and the FMM and PMP growth models were found to be inconsistent with the observed results in a majority of the challenges. The inaccurate predictions were caused by the limited number and range of the controlling factors in the models. Based on this study, it was concluded that the safety of sous vide products needs to be carefully evaluated product by product. Time-temperature combinations used in thermal treatments should be reevaluated to increase the efficiency of processing, and the use of additional antibotulinal hurdles, such as biopreservatives, should be assessed.

Contamination of carcasses, offals, and the environment with yadA-positive Yersinia enterocolitica in a pig slaughterhouse

This study was carried out in order to evaluate the contamination of the pig-slaughtering line with pathogenic Yersinia enterocolitica carrying the yadA gene. A total of 292 samples were collected from the slaughterhouse; 131 swab samples from pig carcasses, ears, livers, kidneys, and hearts; 89 swab samples from the environment; and 72 sedimentation samples from the air. All surface samples were studied with both the polymerase chain reaction (PCR) and culture methods. The contamination rate of edible pig offals was high with both methods. Using PCR, the detection rates of yadA-positive Y. enterocolitica for livers, kidneys, and hearts were 38, 86, and 63%, respectively, and using the culture method, the detection rates were 31, 69, and 50%, respectively. Pathogenic Y. enterocolitica was also detected from different environmental sites in the slaughterhouse. Using PCR, 13% of the surface samples from the environment were contaminated with yadA-positive Y. enterocolitica. PCR-positive samples were found on the brisket saw, the hook from which the pluck set (heart, lungs, esophagus, trachea, diaphragm, liver, kidneys, and tongue with tonsils) hang, the knife used for evisceration, the floors in the eviscerating area and the weighing area, the meat-cutting table, the aprons used by trimming workers, the computer used in the meat-inspection area, and the coffeemaker used by slaughterhouse workers. The respective detection rate (6%) was considerably lower when we used the culture method. Pathogenic Y. enterocolitica was isolated from the air in the bleeding area. Bioserotype 4/O:3 was the only pathogenic bioserotype isolated in this study. A total of 113 isolates of type 4/O:3 were characterized with pulsed-field gel electrophoresis using NotI and XbaI digests. By combining these profiles, nine different pulsotypes were obtained, the most common of which (1a) was found in 19 (61%) of 31 samples from different sites. This is the same type that has dominated in pig tonsils, which suggests that tonsils may be the source of Y. enterocolitica contamination in the slaughterhouse. The four pulsotypes (1a, 4g, 6g, and 19q) found on edible offals were the same as those found in tonsils, which supports our hypothesis that tonsils are the contamination source for the liver, heart, and kidneys.

Efficient subtyping of Yersinia enterocolitica bioserotype 4/O:3 with pulsed-field gel electrophoresis

The purpose of this study was to evaluate the efficiency of pulsed-field gel electrophoresis (PFGE) for differentiation of isolates of Yersinia enterocolitica bioserotype 4/O:3 recovered from pig tongues at retail level in the Helsinki area during October and November of 1996. NotI generated 15 different PFGE patterns for 128 isolates. The discriminatory index did not exceed 74% due to the presence of two predominant PFGE-types, NA1 (58/128) and NB1 (25/128). After preliminary investigations with 35 enzymes, ApaI, XbaI, XhoI and SpeI were chosen for further characterization of the isolates. The discriminatory index increased from 74% to 93% and the number of different genotypes from 15 to 30 when isolates with the same PFGE pattern with NotI were further characterized with ApaI and XhoI, indicating that PFGE can be an efficient technique for characterization of bioserotype 4/O:3.

Characterisation of lactic acid bacteria from spoiled, vacuum-packaged, cold-smoked rainbow trout using ribotyping

A total of 405 lactic acid bacteria (LAB) isolated from spoiled, vacuum-packaged, salted, sodium nitrite- or potassium nitrate-treated, cold-smoked rainbow trout stored at 4 degrees C or 8 degrees C were characterised and identified using a molecular method. The isolates were initially classified according to their restriction endonuclease profiles using HindIII and EcoRI restriction endonucleases and further characterised by rRNA gene restriction patterns (ribotypes). Numerical analysis of these ribopatterns was performed together with 19 reference LAB strain patterns in order to identify the isolates to species level. The strains were divided with HindIII and EcoRI ribopatterns into ten and nine clusters at the similarity level of 65% and 50%, respectively. The Leuconostoc-clusters and the Lb. sakei/Lb. curvatus-clusters formed the two main groups. Only one isolate was identified as Lactobacillus plantarum and no Carnobacterium strains were discovered. For both enzymes, the 35 isolates possessing six individual ribotypes and forming five clusters could not be identified further with the reference strains used. The relative proportion of Leuconostoc mesenteroides subsp. mesenteroides was higher in all samples stored at 4 degrees C. Most of the Leuconostoc citreum were found in the samples stored at 8 degrees C, and particularly in the nitrite-treated samples.

rRNA gene RFLP as an identification tool for Corynebacterium species

The value of rRNA gene RFLP analysis (ribotyping) as a tool for Corynebacterium and Turicella species identification was evaluated. Seventy-four strains representing 26 different species or subspecies were analysed by BstEII, SmaI and SphI ribotyping. Numerical analysis of the resulting rDNA banding patterns was performed by Dice coefficient correlation in order to establish a database for species identification. In general, most of the strains belonging to the same species clustered together. Interestingly, BstEII clustering of many species followed known phylogenetic lineages. This was not evident with the more heterogeneous SmaI and SphI patterns. The SmaI patterns contained a 1800 bp band in the digests of all species studied with the exception of Corynebacterium urealyticum. SphI digestion resulted in the most heterogeneous patterns. The information provided by all three enzymes was considered essential for the reliable linking of strains of unknown identity with defined species in the database. It is concluded that ribotyping provides an useful tool for screening and characterization of potentially new Corynebacterium species.

Characterisation of Clostridium botulinum groups I and II by randomly amplified polymorphic DNA analysis and repetitive element sequence-based PCR

Random amplified polymorphic DNA analysis (RAPD) and repetitive element sequence-based PCR (rep-PCR) were evaluated with respect to their applicability to characterise Clostridium botulinum group I and II strains, the species causing human botulism. Fifteen group I and 21 group II strains of various geographical and temporal origins were characterised with four single arbitrary RAPD primers at low stringency amplification conditions and with a degenerate REP primer pair at moderately stringent conditions. Ready-To-Go RAPD Analysis Beads and Ready-To-Go PCR Beads were used for PCR reactions with RAPD and rep-PCR, respectively. Arbitrary primer OPJ 6 yielded the most discriminating patterns, and distinguished group II C. botulinum serotypes at the strain level. Group I strains were mainly discriminated at the serotype level. The discriminatory power of rep-PCR was found to be inferior to that of RAPD. The REP1R-Dt and REP2R-Dt primer pair generated group I- and II-specific fragments and arbitrary primer OPJ 13 produced a serotype E-specific fragment. The use of pre-dispensed and pre-optimised beads attributed to highly reproducible results. As compared to more time-consuming typing methods, such as pulsed-field gel electrophoresis (PFGE), both RAPD and rep-PCR were characterised by rapid performance and a typeability of 100%.

Molecular analysis of Pseudomonas aeruginosa: epidemiological investigation of mastitis outbreaks in Irish dairy herds

Pseudomonas aeruginosa is a pathogen in both humans and animals. This bacterium, most often associated with respiratory infections in cystic fibrosis patients, was found to be the causative agent in bovine mastitis outbreaks among 11 Irish dairy herds. Epidemiological findings suggested that the infection was spread to all herds by teat wipes that had been contaminated with this organism. Two molecular-typing strategies were used in an attempt to determine the genomic relationship(s), if any, of the P. aeruginosa strains isolated from the various herds and to verify whether the same strain was responsible for each outbreak. Thirty-six isolates from the mastitis outbreaks were tested and compared to fourteen clinical isolates from Cork University Hospital. With one exception, all outbreak-linked strains produced identical patterns when ribotyped with ClaI and PvuII enzymes. Eight of the clinical isolates gave the same ClaI ribotype pattern as the mastitis-causing strains. However, PvuII proved more discriminatory, with only the outbreak isolates producing identical patterns. Similar results were obtained with RW3A-primed DNA amplification fingerprinting, with all outbreak isolates except one displaying the same fingerprint array. The clinical strains produced several fingerprint patterns, all of which were different from those of the mastitis-causing isolates. Fine-resolution DNA fingerprinting with a fluorescence-labelled RW3A primer also identified a number of low-molecular-weight polymorphisms that would have remained undetected by conventional methods. These data support the view that the same P. aeruginosa strain was responsible for the mastitis outbreaks in all 11 herds.

Biodiversity of Clostridium botulinum type E strains isolated from fish and fishery products

The genetic biodiversity of Clostridium botulinum type E strains was studied by pulsed-field gel electrophoresis (PFGE) with two macrorestriction enzymes (SmaI-XmaI and XhoI) and by randomly amplified polymorphic DNA (RAPD) analysis with two primers (OPJ 6 and OPJ 13) to characterize 67 Finnish isolates from fresh fish and fishery products, 15 German isolates from farmed fish, and 10 isolates of North American or North Atlantic origin derived mainly from different types of seafood. The effects of fish species, processing, and geographical origin on the epidemiology of the isolates were evaluated. Cluster analysis based on macrorestriction profiles was performed to study the genetic relationships of the isolates. PFGE and RAPD analyses were combined and resulted in the identification of 62 different subtypes among the 92 type E isolates analyzed. High genetic biodiversity among the isolates was observed regardless of their source. Finnish and North American or North Atlantic isolates did not form distinctly discernible clusters, in contrast with the genetically homogeneous group of German isolates. On the other hand, indistinguishable or closely related genetic profiles among epidemiologically unrelated samples were detected. It was concluded that the high genetic variation was probably a result of a lack of strong selection factors that would influence the evolution of type E. The wide genetic biodiversity observed among type E isolates indicates the value of DNA-based typing methods as a tool in contamination studies in the food industry and in investigations of botulism outbreaks.

Predicted and observed growth and toxigenesis by Clostridium botulinum type E in vacuum-packaged fishery product challenge tests

The observed growth and toxigenesis by Clostridium botulinum type E in vacuum-packaged unprocessed, raw pickled and cold-smoked rainbow trout stored at slightly abusive temperatures were compared to predictions generated by two currently available predictive microbiological programs, Food MicroModel and Pathogen Modelling Program. In unprocessed fish there was only a 2 log increase in type E cell count at the time the toxicity first occurred after 2 weeks storage at 8 degrees C. Neither growth or toxin production was observed in raw pickled fish with a NaCl concentration of 6.7% (w/v) during 6 weeks storage at 6 degrees C. In cold-smoked fish with a NaCl level of 3.2% (w/v) toxic samples were detected after 3 and 4 weeks storage at 8 degrees C and 4 degrees C, respectively, without any increase in type E count. Both models were hampered by limitations to controlling environmental factors set by the programs which also had an adverse effect on the reliability of predictions. Most predictions generated by the models were inconsistent with the results observed in the challenge studies. In certain situations, the models seemed to be 'fail-safe', in that, the growth rate predicted from the model was faster or a predicted time to toxicity shorter than that which actually occurred in the food. In other situations, the predictions showed the product to be safe when it was not. The results demonstrate the need for further development and rigorous validation of the models before they are accepted for wider use by inspecting officials and the food industry.

Ribotyping as an identification tool for Clostridium botulinum strains causing human botulism

Ribotyping was used for characterisation of 68 Clostridium botulinum strains and five related Clostridium species to determine the applicability of this method for identification of species causing human botulism. Thirteen restriction enzymes were initially tested for suitability for ribotyping of C. botulinum, of which EcoRI and HindIII were selected. Both enzymes clearly differentiated between proteolytic (group I) and a nonproteolytic (group II) strains of C. botulinum, and can be recommended for Group/species identification. Using a commercial software package (GelCompar), a numerical analysis of the discriminatory abilities of EcoRI and HindIII ribotyping within and between the two C. botulinum groups was performed. EcoRI had the higher discriminatory index (0.982), but the ribopatterns generated with group II strains were partly muddled and difficult to interpret. All HindIII ribopatterns were easy to analyse and the discriminatory index for all strains was almost equally high (0.954), whereas this enzyme did not discriminate well between group I isolates. The Clostridium strains diverged at 35+/-13% (mean+/-standard deviation) Dice similarity in dendrograms based on cluster analysis of the ribotyping results. These findings are in good agreement with taxonomical ribotyping studies with other bacterial genera, indicating that ribotyping is a highly suitable method for C. botulinum species identification.

High prevalence of yadA-positive Yersinia enterocolitica in pig tongues and minced meat at the retail level in Finland

Polymerase chain reaction (PCR) was used to determine the prevalence of yadA-positive Yersinia enterocolitica in pig tongues and minced meat at the retail level in Finland and to confirm the yadA-positive Y. enterocolitica isolates recovered from the same samples using the conventional culture method. A total of 51 pig tongues purchased at 12 retail outlets and 255 minced meat samples purchased at 40 retail outlets in the Helsinki area were studied. The prevalence of Y. enterocolitica carrying the yadA gene was 92% in pig tongues and 25% in minced meat using PCR and 78% in tongues and 2% in minced meat with the culture method. The prevalence of yadA-positive tongues was higher (98%) when both PCR- and culture-positive results were included because Y. enterocolitica carrying the yadA gene could also be isolated in three PCR-negative tongue samples. In the minced meat samples, all PCR-negative samples were also culture-negative. With the culture method, 66 of 80 yadA-positive isolates in 38 tongues and all yadA-positive isolates (4) in four minced meat samples were recovered after selective enrichment. A total of 92 isolates of Y. enterocolitica bioserotype 4/O:3 in tongues and 5 isolates in minced meat were found, of which 13% in tongues and 20% in minced meat did not carry the yadA gene.

Sources of Listeria monocytogenes contamination in a cold-smoked rainbow trout processing plant detected by pulsed-field gel electrophoresis typing

Sites of Listeria monocytogenes contamination in a cold-smoked rainbow trout (Oncorhynchus mykiss) processing plant were detected by sampling the production line, environment, and fish at different production stages. Two lots were monitored. The frequency of raw fish samples containing L. monocytogenes was low. During processing, the frequency of fish contaminated with L. monocytogenes clearly rose after brining, and the most contaminated sites of the processing plant were the brining and postbrining areas. A total of 303 isolates from the raw fish, product, and the environment were characterized by pulsed-field gel electrophoresis (PFGE). PFGE yielded nine pulsotypes, which formed four clusters. The predominating L. monocytogenes pulsotypes of the final product were associated with brining and slicing, whereas contaminants of raw fish were not detected in the final product. Air-mediated contamination in the plant could not be proved. In accordance with these results, an L. monocytogenes eradication program was planned. The use of hot steam, hot air, and hot water seemed to be useful in eliminating L. monocytogenes. None of the control samples taken in the 5 months after the eradication program was implemented contained L. monocytogenes.

The spoilage flora of vacuum-packaged, sodium nitrite or potassium nitrate treated, cold-smoked rainbow trout stored at 4 degrees C or 8 degrees C

The spoilage flora of vacuum-packaged, salted, cold-smoked rainbow trout fillets, with or without the addition of nitrate or nitrite, stored at 4 degrees C and 8 degrees C, was studied. Of 620 isolates, lactic acid bacteria were the major fraction (76%), predominating in all samples of spoiled product. However, the phenotypical tests used were insufficient to identify the lactic acid bacteria to the species level. Gram-positive, catalase-positive cocci, gram-negative, oxidase-negative rods and gram-negative, oxidase-positive rods were found in 6%, 16% and 2% of the samples, respectively. Of 39 gram-positive, catalase-positive cocci, 29 were identified as staphylococci and 10 as micrococci. Eighty-five isolates were found to belong to the family Enterobacteriaceae, with 45 of those being Serratia plymuthica. Eleven isolates from the nitrate treated samples stored at 8 degrees C were identified as Pseudomonas aeruginosa. The occurrence of P. aeruginosa and staphylococci in the nitrate-containing samples, stored at 8 degrees C, may cause problems with respect to the safety of the product. The types of lactic acid and other bacteria in the spoilage flora were generally reduced by the addition of nitrate or nitrite to fillets.

Prevalence of Clostridium botulinum in Finnish trout farms: pulsed-field gel electrophoresis typing reveals extensive genetic diversity among type E isolates

The distribution of Clostridium botulinum serotypes A, B, E, and F in Finnish trout farms was examined. A total of 333 samples were tested with a neurotoxin-specific PCR assay. C. botulinum type E was found in 68% of the farm sediment samples, in 15% of the fish intestinal samples, and in 5% of the fish skin samples. No other serotypes were found. The spore counts determined by the most-probable-number method were considerably higher for the sediments than for the fish intestines and skin; the average values were 2,020, 166, and 310 C. botulinum type E spores kg-1, respectively. The contamination rates in traditional freshwater ponds and marine net cages were high, but in concrete ponds equipped with sediment suction devices the contamination rates were significantly lower. Pulsed-field gel electrophoresis (PFGE) typing of 42 isolates obtained in this survey and 12 North American reference strains generated 28 pulsotypes upon visual inspection, suggesting that there was extensive genetic diversity and that the discriminatory power of PFGE typing in C. botulinum type E was high. A numerical analysis of SmaI-XmaI macrorestriction profiles confirmed these findings, as it divided the 54 isolates into 15 clusters at a similarity level of 76%. For this material, this level of similarity corresponded to a three-band difference in the macrorestriction profiles, which indicated that there is no genotypic proof of a close epidemiological relationship among the clusters.