J.M.A. Snijders

Effect of Fermented Feed on the Microbial Population of the Gastrointestinal Tracts of Pigs

ABSTRACT An in vivo experiment was performed with pigs to study the inhibitory effect of fermented feed on the bacterial population of the gastrointestinal tract. Results demonstrated a significant positive correlation between pH and lactobacilli in the stomach contents of pigs in dry feed as well as in the stomach contents of pigs fed fermented feed. Furthermore, a significant positive correlation between the pH and the numbers of bacteria in the familyEnterobacteriaceae in the contents of the stomach of pigs fed dry feed was found. In the stomach contents of pigs fed fermented feed, a significant negative correlation was found between the concentration of the undissociated form of lactic acid and the numbers of Enterobacteriaceae. The numbers ofEnterobacteriaceae in the contents of the stomach, ileum, cecum, colon, and rectum of pigs fed fermented feed were significantly lower compared with the contents of the stomach, ileum, caecum, colon, and rectum of pigs fed dry feed. The numbers of total lactobacilli were significantly higher in the stomach contents of pigs fed fermented feed and in the ileum contents of one pig group fed fermented feed compared with the contents of pigs fed dry feed. However, the influence of lactobacilli on numbers of Enterobacteriaceae could not be demonstrated. It was concluded that fermented feed influences the bacterial ecology of the gastrointestinal tract and reduces the levels of Enterobacteriaceae in the different parts of the gastrointestinal tract.

Salmonella in slaughter pigs: prevalence, serotypes and critical control points during slaughter in two slaughterhouses

The purpose of this study was to show the distribution of Salmonella in slaughtered pigs and the environment of the slaughterhouse. 1,114 samples of slaughtered pigs (six different samples for Salmonella isolation and one serum sample for ELISA on antibodies per pig) and 477 samples of the slaughterhouse environment were collected in two slaughterhouses on two sampling days per slaughterhouse. Salmonella was isolated from one or more samples of 47% of the pigs. The highest prevalence of Salmonella was observed in rectal content samples (25.6%), whereas the lowest prevalence of Salmonella was observed on the carcasses (1.4%). The prevalence of Salmonella in other samples was: 19.6% in tonsils, 9.3% on livers, 9.3% on tongues, and 9.3% in mesenterial lymphnodes. The prevalence of Salmonella in environmental samples was high in the drain water samples in both slaughterhouses (61%) and on the carcass splitter in one slaughterhouse (33%). Salmonella typhimurium was the most frequently isolated serotype in pig samples and environmental samples in both slaughterhouses: 43% of the Salmonella isolates from pigs and 33% of the Salmonella isolates from the environment was S. typhimurium. The results of this study show that Salmonella prevalences in pigs differ a lot, depending on which part of the pig is sampled. Not all different samples of the pig will become available for human consumption, but collecting more than one sample per pig showed that Salmonella can be found in almost the whole pig. The result of surface samples of carcass and liver gives information about hygiene during the slaughter process; the result of tonsils, lymphnodes and rectal contents, combined with the serological result, gives information about infection of the pig before the slaughter process (on the farm, during transport or in lairage). It can be concluded that results of Salmonella isolation of slaughter pigs should always be carefully interpreted, depending on the type of sample that has been collected.

Salmonella in slaughter pigs: the effect of logistic slaughter procedures of pigs on the prevalence of Salmonella in pork.

A substantial part of the finishing pigs in the Netherlands is infected with Salmonella. Infection of pigs with Salmonella can occur already on the farm. Pigs can also get infected or contaminated during transport, lairage or slaughter. The aim of this study was to evaluate the effect of separating pigs from Salmonella-infected farms from pigs from Salmonella-free farms during transport, lairage and slaughter on the prevalence of Salmonella on pork after slaughter. Two experiments were carried out. In the first experiment, farms were selected to participate, based on serology of the pigs (Dutch Salmonella ELISA). The pigs were slaughtered at the beginning of the day: firstly, sero-negative herds, secondly, sero-positive herds and thirdly, again sero-negative herds. The latter were slaughtered to investigate the effect of a contaminated slaughterline due to a previously slaughtered positive herd. In the second experiment, farms were selected to participate, based on both serology and bacteriology of the pigs on the farm. Two hundred pigs from Salmonella-free farms were slaughtered after 200 pigs from Salmonella-infected farms. Results showed that the prevalence of Salmonella in pork samples of sero-negative herds was lower than in samples of sero-positive herds. Results also showed that Salmonella contamination of carcasses after slaughter was partially caused by Salmonella-infected herds that were slaughtered before, and partially by residential flora of the slaughterhouse. It is concluded that separate slaughter of sero-negative pig herds can be useful to decrease the prevalence of Salmonella-contaminated pork after slaughter. To avoid cross-contamination by residential flora from trucks, lairage and slaughterline, cleaning and disinfection have to be improved.

Monitoring of transmission of Salmonella enterica serovars in pigs using bacteriological and serological detection methods

The standard method to detect Salmonella positive pigs is bacteriological examination of the faeces, but in recent years the use of Salmonella-ELISAs have become available to screen pigs for serological evidence of infection. This study was conducted to monitor the transmission of five different Salmonella enterica serovars (S. Typhimurium, S. Brandenburg, S. Panama, S. Livingstone, and S. Goldcoast) in fattening pigs and to test the feasibility of Salmonella-ELISA, using seeder pigs as a mode of transmission. Serovar dependence in transmission was observed. The Salmonella-ELISA proved to be useful to detect S. Typhimurium and S. Brandenburg in herds but was of limited value to demonstrate S. Livingstone, S. Goldcoast, and S. Panama.

Mechanism of Salmonella reduction in fermented pig feed

To protect consumers from Salmonella infection acquired through the consumption of pork meat, it is necessary to eradicate Salmonella from pork. In order to achieve this, the whole pork production chain should be free from Salmonella, including the pigs at the farm. In epidemiological studies it was concluded that the use of fermented feed plays a significant role in the reduction of Salmonella prevalence in pig farms. However, the mechanism of Salmonella reduction in fermented feed is not known. A controlled feed fermentation was performed using a pure culture of Lactobacillus plantarum, pH reduction, organic acid profiles and bacterial counts were determined. In L plantarum-fermented feed, lactic acid and acetic acid were produced and the pH dropped to a value below 4.0. Antimicrobial products (bacteriocins) could not be detected. The results showed that the produced lactic and acetic acid and the pH in the feed are responsible for Salmonella reduction in fermented feed. L plantarum did not show any other antimicrobial effect on Salmonella

A comparative study of sampling techniques for monitoring carcass contamination

Four bacteriological sampling techniques i.e. the excision, double swab, agar contract and modified agar contact techniques were compared by sampling pig carcasses before and after chilling. As well as assessing the advantages and disadvantages of the techniques particular attention was paid to variation due to the effects of chilling. The agar contact technique cannot be used for determining the contamination of carcasses because too many plates became overcrowded with micro-organisms. Results obtained by the double swab and modified agar technique gave standard deviations which were significantly higher than those of the excision technique. This may indicate a superior repeatability of the excision technique. Statistical analysis of the results showed that chilling influenced the differences between sampling techniques. The excision technique is to be regarded as the most suitable in view of its high accuracy and precision. When the technique is used properly, carcass damage is only small or negligible.

Suggestions for the construction, analysis and use of descriptive epidemiological models for the modernization of meat inspection

There is consensus that scientifically validated, quantitative assessments of actual public health risks are a prerequisite for any sound modernization of current meat inspection procedures. This article outlines how such analyses could be conducted. Approaches that rely heavily upon extrapolations from theoretical dose-effect relationships are inadequate for the assessment of microbiological health risks associated with the production and consumption of meat. The use of highly structured and very elaborate descriptive epidemiological models covering the entire period from stable to table can be considered a promising solution. Health risks can be quantified by means of incidence rates and the influence of risk factors by means of odds ratios and (population) attributable fractions. A great advantage is that when it is not possible to quantify risks exactly, the descriptive models are detailed enough to be used in a hazard analysis critical control point (HACCP)-like approach and for writing validated codes of good manufacturing practice (GMP). There are, however, several conditions which have to be met before risk assessment can become the foundation of safety assurances for meat, such as active legislative support and the setting up of monitoring systems for zoonoses and other health hazards in animals and humans.

Prevention of human diseases by an integrated quality control system

Abstract The efficiency, cost-effectiveness and scientific validity of current ante- and post-mortem meat inspection procedures are doubtful. A new approach is proposed and discussed. Meat and poultry inspection systems need to better address the risks posed by food-borne micro-organisms, particularly pathogens causing inapparent infections in food animals. Microbial agents (particularly bacteria) represent the greatest risk to public health. Intervention should not unduly focus at the abattoir or food processing stage, but also target the risks associated with production stages before the abattoir. It is proposed that producers have to guarantee, e.g. through HACCP-like systems, that their products meet the requirements. When verification of the HACCP-procedures by the competent authority reveals that the HACCP-system is not adequate, the operator or farmer should adapt the procedures. Some examples are described. The establishment of a new European Food Authority (EFA) is expected to contribute to a higher level of consumer health protection, and will help to restore and maintain consumers’ confidence.

Veterinary public health: Human health hazards associated with the administration of antimicrobials to slaughter animals

Summary This article describes the assessment of consumer risks of residues of tetracyclines in slaughter pigs in the Netherlands. The assessed risks were toxic and allergic reactions, and the disturbance of the consumers’ intestinal flora. Toxic and allergic reactions in humans and animals have only been observed at therapeutic doses, affecting between an estimated 1 in 5000 and one 1 in 140,000 individuals exposed. Residues of tetracyclines in pigs are closely associated with treatment with injectable formulations. Established Maximum Residue Levels (MRLs) do not reflect actual consumer risks in case a limit is violated incidentally. For example, when the established MRLs for tetracyclines in meat are exceeded with a factor 400, 40,000, and 200,000, respectively, the actual risk of an adverse drug reaction for the consumer following a single consumption of this meat is maximally 1 in 3 million, 1 in 300,000, and 1 in 8000, respectively. At the current estimated low levels of incidental exposure via pork, the annual risk of negative health effects for a random consumer is estimated at maximally 1 in 33 million. The annual risk that a temporary disturbance of the intestinal flora may also result in a facilitated infection with certain enteropathogens, such as Salmonella spp., is estimated at 1 in 45 million. It is concluded that the current microbiological risks of pork are greater than the risks of residues of tetracyclines as such, and that the control of the microbiological risks of pork should therefore be given first priority.

Human health hazards associated with the administration of antimicrobials to slaughter animals. Part II. An assessment of the risks of resistant bacteria in pigs and pork.

Risks for the consumer regarding the acquisition of resistant bacteria and/or resistance genes via the consumption of pork are discussed. In general, Salmonella spp. and Escherichia coli that originate from animals do not easily transfer their resistance genes to the resident intestinal flora of humans. The prevalence of resistant E. coli in humans seems more associated with being a vegetarian (odds ratio (OR) 1.89) than with the consumption of meat and meat products. Other risk factors are treatment with antimicrobials (OR 2-5), becoming hospitalized (OR 5.93), or working in a health setting (OR 4.38). In the Netherlands, annually an estimated 45,000 people (0-150,000) become a carrier of resistant E. coli and/or resistance genes that ori ginate from pigs, while an estimated 345,000 persons (175,000-600,000) become a carrier of resistant E. coli and/or resistance genes that originate from hospitals, e.g. other patients. Any problems with resistant Salmonella spp. that stem from pigs are, in fact, an integral part of the total problem of food-borne salmonellosis. Sometimes there are outbreaks of a specific multi-resistant clone of S. typhimurium that causes problems in both farm animals and humans. The probability that in the next 30 years there is no or maximally one outbreak of a specific clone that originates from pig herds is estimated at about 75%. Antimicrobials used as a growth promoter can have a measurable influence on the prevalence of resistant bacteria. The likely chain of events regarding avoparcin and the selection and dissemination of resistance against vancomycin in the enterococci gives the impression that the impact of the use of antimicrobials in animals on the prevalence of resistance in humans is largely determined by whether resistance genes are, or become, located on a self-transferable transposon. Furthermore, consumer health risks of antimicrobials used in slaughter pigs are mainly determined by the selection and dissemination of bacterial resistance and much less by the toxicological properties of any residues in pork. It is also concluded that most of the problems with resistant bacteria in humans are associated with the medical use of antimicrobials, and that the impact of particularly the veterinary use of antimicrobials is limited. However, the impact of antimicrobials used as a feed additive appears to be much greater than that of antimicrobials used for strictly veterinary purposes. The use of antimicrobials as a feed additive should therefore be seriously reconsidered.Summary Risks for the consumer regarding the acquisition of resistant bacteria and/or resistance genes via the consumption of pork are discussed. In general, Salmonella spp. and Escherichia coli that originate from animals do not easily transfer their resistance genes to the resident intestinal flora of humans. The prevalence of resistant E. coli in humans seems more associated with being a vegetarian (odds ratio (OR) 1.89) than with the consumption of meat and meat products. Other risk factors are treatment with antimicrobials (OR 2–5), becoming hospitalized (OR 5.93), or working in a health setting (OR 4.38). In the Netherlands, annually an estimated 45,000 people (0–150,000) become a carrier of resistant E. coli and/or resistance genes that originate from pigs, while an estimated 345,000 persons (175,000–600,000) become a carrier of resistant E. coli and/or resistance genes that originate from hospitals, e.g. other patients. Any problems with resistant Salmonella spp. that stem from pigs are, in fact, an integral part of the total problem of food‐borne salmonellosis. Sometimes there are outbreaks of a specific multi‐resistant clone of S. typhimurium that causes problems in both farm animals and humans. The probability that in the next 30 years there is no or maximally one outbreak of a specific clone that originates from pig herds is estimated at about 75%. Antimicrobials used as a growth promoter can have a measurable influence on the prevalence of resistant bacteria. The likely chain of events regarding avoparcin and the selection and dissemination of resistance against vanco‐mycin in the enterococci gives the impression that the impact of the use of antimicrobials in animals on the prevalence of resistance in humans is largely determined by whether resistance genes are, or become, located on a self‐transferable transposon. Furthermore, consumer health risks of antimicrobials used in slaughter pigs are mainly determined by the selection and dissemination of bacterial resistance and much less by the toxicological properties of any residues in pork. It is also concluded that most of the problems with resistant bacteria in humans are associated with the medical use of antimicrobials, and that the impact of particularly the veterinary use of antimicrobials is limited. However, the impact of antimicrobials used as a feed additive appears to be much greater than that of antimicrobials used for strictly veterinary purposes. The use of antimicrobials as a feed additive should therefore be seriously reconsidered.