Epidemiology of Salmonella on the Paws and in the Faeces of Free-Ranging Raccoons (Procyon Lotor) in Southern Ontario, Canada

Raccoons are common in urban and rural environments and can carry a wide range of bacteria, including Salmonella, that can negatively affect human and livestock health. Although previous studies have reported that raccoons shed a variety of Salmonella serovars in their faeces, it is unknown whether Salmonella is carried on raccoon paws. Our objective was to compare the prevalence of Salmonella on the paws and in the faeces of raccoons in south-western Ontario. Raccoons were sampled in a repeat cross-sectional study on five swine farms and five conservation areas from May to October 2012. A total of 416 paired faecal and paw samples were collected from 285 individual raccoons. Salmonella was detected in 18% (75/416; 95% CI, 14-22%) and 27% (111/416; 95% CI, 22-31%) of paw and faecal samples, respectively. Salmonella was detected only on paws in 8% (35/416; 95% CI, 5.9-11.5%), only in faeces in 17% (71/416; 95% CI, 13.6-21.0%) and on both paws and in faeces in 10% (40/416; 95% CI, 7.0-12.9%) of raccoon captures. Multilevel logistic regression models were used to examine associations between the presence of Salmonella and age (adult, juvenile), sex (male, female), location type (swine farm, conservation area), sample type (faeces, paw) and season (May-July and August-October). Random intercepts were included to account for clustering by individual animal and location. Significant differences, that varied by sample type and season, were noted in the prevalence of Salmonella carriage between sexes. Raccoons can carry Salmonella serovars known to infect humans and livestock on their paws and/or in their faeces and therefore have the potential to mechanically and biologically disseminate Salmonella among livestock facilities and human recreational areas.

Horizontally Transferred Genetic Elements and Their Role in Pathogenesis of Bacterial Disease

This article reviews the roles that laterally transferred genes (LTG) play in the virulence of bacterial pathogens. The features of LTG that allow them to be recognized in bacterial genomes are described, and the mechanisms by which LTG are transferred between and within bacteria are reviewed. Genes on plasmids, integrative and conjugative elements, prophages, and pathogenicity islands are highlighted. Virulence genes that are frequently laterally transferred include genes for bacterial adherence to host cells, type 3 secretion systems, toxins, iron acquisition, and antimicrobial resistance. The specific roles of LTG in pathogenesis are illustrated by specific reference to Escherichia coli, Salmonella, pyogenic streptococci, and Clostridium perfringens.

Salmonella serovars and antimicrobial resistance profiles in beef cattle, slaughterhouse personnel and slaughterhouse environment in ethiopia

The present study was undertaken to determine the occurrence, distribution and antimicrobial resistance profiles of Salmonella serovars in slaughter beef cattle, slaughterhouse environment and personnel engaged in flaying and evisceration during slaughtering process. A total of 800 samples (each sample type, n = 100) consisting of swabs from hides, slaughterhouse personnel hands at flaying and evisceration, rumen and caecal contents, mesenteric lymph nodes, carcasses and holding pens were collected. Of the total 100 beef cattle examined, 14% were Salmonella positive in caecal content and/or mesenteric lymph nodes. Of the various samples analysed, Salmonella was detected in 31% of hides, 19% of rumen contents, 8% of mesenteric lymph nodes, 6% of caecal contents, 2% of carcass swabs, 9% of palm swabs taken from the hands of personnel in the slaughterhouse during flaying (7%) and evisceration (2%), and in 12% of holding pen swabs. The Salmonella isolates (n = 87) belonged to eight different serovars of which S. Anatum (n = 54) and S. Newport (19) were the major serovars and both serovars were detected in all sample sources except in carcass swabs. Eighteen of the 87 (20.7%) Salmonella serovars consisting of Newport (n = 14), Anatum (n = 3) and Eastbourne (n = 1) were resistant to one or more antimicrobials. Among the antimicrobial resistant Salmonella serovars, S. Newport was multidrug resistant (15.6%) and exhibited resistance to streptomycin, sulphisoxazole and tetracycline.

Evaluation of the risks of shedding Salmonellae and other potential pathogens by therapy dogs fed raw diets in Ontario and Alberta

Dogs that participate in animal-assisted interventions (AAIs), often called 'therapy dogs', commonly interact with humans whose immune systems are not functioning optimally. The advisability of feeding raw meat (including poultry) to these animals remains a highly contentious issue, in spite of increasing evidence that raw meat is frequently contaminated with Salmonella. We set out to determine if consuming raw meat influences the risk of therapy dogs shedding Salmonella and other pathogens. Two hundred healthy therapy dogs from Ontario and Alberta were enrolled. Between May 2005 and November 2006, fecal specimens were collected from each dog every 2 months for 1 year, along with a log of places visited, antimicrobial use within the home, dog health status and diet. Specimens were cultured for Salmonella, methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant enterococci (VRE), extended-spectrum cephalosporinase (ESC) Escherichia coli and Clostridium difficile. Forty (20%) of the dogs were reported to have been fed raw meat at some point during the year. The incidence rate of Salmonella shedding in the raw meat-fed dogs was 0.61 cases/dog-year, compared with 0.08 cases/dog-year in dogs that were not fed raw meat (P<0.001). Controlling for therapy dog group, the repeated measures, and pig ear consumption and diarrhoea in the 2 months prior to specimen submission, dogs that consumed raw meat were significantly more likely to test positive for Salmonella at least once during the year than dogs that did not eat raw meat [odds ratio (OR) 22.7; 95% confidence interval (CI) 3.1-58.8; P<0.001]. Specific Salmonella serovars were more common among dogs that consumed raw meat versus those that did not include S. Typhimurium, S. Heidelberg and S. Kentucky. Raw meat consumption was also significantly associated with shedding ESC E. coli (OR 17.2; 95% CI 9.4-32.3). No associations between C. difficile, MRSA or VRE and consumption of raw meat were detected. We recommend that dogs fed raw meat should be excluded from AAI programmes, particularly when the programmes involve interaction with humans at high risk of infection or adverse sequelae attributable to infection. Furthermore, although AAI dogs may not be representative of the general population of dogs, we also recommend that feeding of raw meat to dogs is to be avoided in homes where immunocompromised people live.

Factors associated with cross-contamination of hides of Scottish cattle by Escherichia coli O157

The putative source of hide contamination for 236 cattle in Scotland followed from the farm through to slaughter was determined using phage and verocytotoxin type data. The majority of cattle (84%) were found to have subtypes of Escherichia coli O157 on their hide that had not been found previously in any animal from the farm of origin, strongly suggesting that contamination occurred once animals had left the farm of origin. Using logistic regression analysis, several variables and factors were found to be strongly associated (P < 0.01) with cross-contamination of cattle hides at the univariate level; commercial transport to slaughter, transport with other animals, use of a crush, line automation, and increasing slaughterhouse throughput were all risk factors, while feeding hay in lairage, processing an animal earlier in a slaughter cohort, and cleaning the landing area poststunning were protective. In the multivariable model, with the slaughterhouse and the farm group included as random effects, factors associated with the cross-contamination of cattle hides were identified. Transport to the slaughterhouse by a commercial hauler had a borderline-significant association with increased odds of an animal having a cross-contaminated hide (odds ratio [OR] [95% confidence interval (CI)] = 5.7 [0.99, 33.0]; P = 0.05). At the slaughterhouse, providing hay to cattle waiting in lairage (OR [95% CI] = 0.04 [<0.01, 1.04]; P = 0.05) and cleaning the landing area (OR [95% CI] = 0.03 [<0.01, 1.15,]; P = 0.06) also had a borderline-significant association with decreased odds of an animal having a cross-contaminated hide. Although the prevalence of carcass contamination remains very low, targeted intervention at the preslaughter stage may have the potential to reduce further the risk to public health.

Characterization of Clostridium difficile strains isolated from patients in Ontario, Canada, from 2004 to 2006

Clostridium difficile is the bacterium most commonly surmised to cause antimicrobial- and hospital-associated diarrhea in developed countries worldwide, and such infections are thought to be increasing in frequency and severity. A laboratory-based study was carried out to characterize C. difficile strains isolated from persons in Ontario, Canada, during 2004 to 2006 according to toxin type (enterotoxin A, cytotoxin B, and binary toxin [CDT]), tcdC gene characterization, ribotyping, pulsed-field gel electrophoresis, and toxinotyping. Clostridium difficile was isolated from 1,080/1,152 (94%) samples from 21 diagnostic laboratories. Isolates with toxin profiles A(+) B(+) CDT(-), A(+) B(+) CDT(+), A(-) B(+) CDT(-), and A(-) B(+) CDT(+) accounted for 63%, 34%, 2.4%, and 0.6% of isolates, respectively. Alterations in tcdC were detected in six different ribotypes, including ribotype 027. A total of 39 different ribotypes were identified, with ribotype 027/North American pulsotype 1 (NAP1), an internationally recognized outbreak strain associated with severe disease, being the second most common ribotype (19% of isolates). Transient resistance to metronidazole was identified in 19 (1.8%) isolates. While a large number of ribotypes were found, a few predominated across the province. The high prevalence and wide distribution of ribotype 027/NAP1 are disconcerting in view of the severity of disease associated with it.

Genetic diversity of Clostridium perfringens isolated from healthy broiler chickens at a commercial farm

Clostridium perfringens is an important commensal and bacterial pathogen of many animal species. It has particular significance in poultry, where it may cause necrotic enteritis. Our objective was to characterize the population diversity of C. perfringens colonizing healthy birds, and to observe how diversity changed over time. Isolates were obtained from broiler chicken cecal samples in two barns on a single farm, on days 7, 14, 22, 27, 30 and 34 of a single 42-day rearing cycle. Bacitracin was used as a feed additive in one of the barns and withdrawn from the second barn for the duration of the experiment. Each isolate was typed using pulsed-field gel electrophoresis (PFGE) using SmaI restriction endonuclease. A total of 205 cecal isolates from 49 birds were typed, as well as 93 isolates from the barn environment (bedding, drinking water and feces). Eight major PFGE types and 17 subtypes were found in the 298 total isolates. The results show that an optimal sampling strategy would involve a large number of birds, with only a few isolates sampled per bird. The diversity of C. perfringens in this study appears to be low within a single bird, and increases as the bird matures. There was no significant difference in genetic diversity between the two barns. In addition, isolates from fresh fecal samples appear to represent the cecal C. perfringens population accurately, although this was not proven statistically. Antimicrobial susceptibility testing was performed on selected isolates (n=41) representing a cross-section of PFGE types. Based on minimum inhibitory concentration distributions, 95% of the isolates tested were deemed resistant to bacitracin, with a 16 microg/mL breakpoint. Three new cpb2 (beta2 toxin gene) variants were found in the study.

Typing of Clostridium perfringens by multiple-locus variable number of tandem repeats analysis

Clostridium perfringens is a well-characterized bacterial species which can be both commensal and pathogenic in humans and many animals. Genetic typing of the bacterium is often used for molecular epidemiological purposes, and can be useful for observing population structures as well. Analysis of the variable number of tandem repeats (VNTRs) within the genome, called multiple-locus VNTR analysis (MLVA) provides genetic information useful for molecular typing. A MLVA typing method has been developed recently by Sawires and Songer [Sawires, Y.S., Songer, J.G., 2005. Multiple-locus variable-number tandem repeat analysis for strain typing of Clostridium perfringens. Anaerobe 11, 262-272] for C. perfringens. A novel MLVA protocol is described here, with the aim of investigating the discriminatory potential of the method, and to obtain preliminary data on the population structure of C. perfringens from a wide variety of C. perfringens sources. This protocol uses new loci in noncoding regions of the chromosome, and also makes use of capillary electrophoresis for more precise results and for high-throughput typing. DNA sequencing of amplicons was performed to ensure inclusion of conserved tandem repeats within each locus. Fifty-four epidemiologically unrelated isolates from a local collection obtained from 11 different animal species were typed at 6 loci. Thirty-five unique MLVA types were obtained, resulting in a Simpson's index of diversity of 0.975. Epidemiologically related isolates (n=27) previously typed by pulsed-field gel electrophoresis (PFGE) were also examined with MLVA and the congruency of the two methods was found to be very high. All 81 isolates were successfully typed with MLVA, and polymerase chain reactions (PCR) were automated using robotics and 96-well plates, with PCR product sizes determined using capillary electrophoresis. Reproducibility was also shown to be very high.

Acquisition of resistance to extended-spectrum cephalosporins by Salmonella enterica subsp. enterica serovar Newport and Escherichia coli in the turkey poult intestinal tract

Salmonella enterica subsp. enterica serovar Newport resistant to the extended-spectrum cephalosporins (ESCs) and other antimicrobials causes septicemic salmonellosis in humans and animals and is increasingly isolated from humans, animals, foods, and environmental sources. Mechanisms whereby serovar Newport bacteria become resistant to ESCs and other classes of antimicrobials while inhabiting the intestinal tract are not well understood. The present study shows that 25.3% of serovar Newport strains isolated from the turkey poult intestinal tract after the animals were dosed with Escherichia coli harboring a large conjugative plasmid encoding the CMY-2 beta-lactamase and other drug resistance determinants acquired the plasmid and its associated drug resistance genes. The conjugative plasmid containing the cmy-2 gene was transferred not only from the donor E. coli to Salmonella serovar Newport but also to another E. coli serotype present in the intestinal tract. Laboratory studies showed that the plasmid could be readily transferred between serovar Newport and E. coli intestinal isolates. Administration of a single dose of ceftiofur, used to prevent septicemic colibacillosis, to 1-day-old turkeys did not result in the isolation of ceftiofur-resistant E. coli or Salmonella serovar Newport. There was a remarkable association between serotype, drug resistance, and plasmid profile among the E. coli strains isolated from the poults. This study shows that Salmonella serovar Newport can become resistant to ESCs and other antibiotics by acquiring a conjugative drug resistance plasmid from E. coli in the intestines.

Brucellosis and Q-fever seroprevalences of nomadic pastoralists and their livestock in Chad

As a part of a research-and-action partnership between public health and veterinary medicine, the relationships between the seroprevalences of brucellosis and Q-fever in humans and livestock were evaluated in three nomadic communities of Chad (Fulani cattle breeders, and Arab camel and cattle breeders). Nomad camps were visited between April 1999 and April 2000. A total of 860 human and 1637 animal sera were tested for antibodies against Brucella spp., and 368 human and 613 animal sera for Coxiella burnetii. The same indirect ELISA was used for livestock and human sera, and the test characteristics for its use on human sera were evaluated. Twenty-eight people were seropositive for brucellosis (seroprevalence 3.8%). Brucella seroprevalence was higher in cattle (7%) than other livestock, and brucellosis seropositivity was a significant factor for abortion in cattle (OR=2.8). No correlation was found between human brucellosis serostatus and camp proportions of seropositive animals. Q-fever-seropositive blood samples were taken from 11 Arab camel and 4 Arab cattle breeders (seroprevalence 1%). Being a camel breeder was associated with Q-fever seropositivity in humans (OR=9). Camels had the highest Q-fever seroprevalence (80%) among livestock species. Although there was high-risk human behaviour for the acquisition of brucellosis and Q-fever from livestock through raw-milk consumption (98%) and contact with placentas of livestock (62%), we concluded that seroprevalences in humans were relatively low (likely due to limited active foci in livestock).

Immunohistochemical localization of Clostridium perfringens beta2-toxin in the gastrointestinal tract of horses

Clostridia-associated intestinal disease in horses was generally reported to be due to infection with Clostridium perfringens type A, which harbors the cpa-encoded alpha-toxin. A recent study demonstrated a high incidence of beta2-toxigenic C. perfringens in horses suffering or dying from typhlocolitis, suggesting that this novel type of C. perfringens might play an important role in typhlocolitis and possibly other equine intestinal diseases. A retrospective study was conducted to assess the presence of the beta2-toxin in tissues of the equine gastrointestinal tract. Monospecific polyclonal antibodies against recombinant beta2-toxin were produced in rabbits and used to demonstrate the beta2-toxin in sections of the gastrointestinal tract by immunohistochemical methods. Sections from 69 horses were stained and beta2-toxin was observed immunohistochemically in 40 animals. Sections from the stomach, small intestine, and large intestine were positive. Immunopositivity for beta2-toxin was significantly associated with presence of beta2-toxigenic bacteria. This investigation demonstrates local production of beta2-toxin and suggests that immunohistochemistry using antitoxin antibodies represents a useful diagnostic method in those cases where isolation of bacteria and polymerase chain reaction typing is not feasible. Although the association between the presence of beta2-toxin and development of gastrointestinal disease in horses remains uncertain, the findings of this study indicate that the potential causal relationship warrants further investigation.

Verocytotoxin-producing Escherichia coli in patients with diarrhoea in Switzerland

The present study was conducted between October 1996 and October 1998 to estimate the frequency of verocytotoxin-producing Escherichia coli among outpatients with diarrhoea in Switzerland. Among 3,041 subjects studied, 16 (0.5%) verocytotoxin-producing Escherichia coli infections were identified. Eleven cases were in infants and children </= 6 years of age. In 15 cases, a verocytotoxin-producing Escherichia coli strain was isolated. These strains belonged to 11 different serotypes, and only two were serogroup O157. In five cases, the infection was probably acquired outside Switzerland. Verocytotoxin-producing Escherichia coli apparently play a minor role in the aetiology of diarrhoeal disease in adult outpatients in Switzerland, but they are important pathogens in preschool children in whom the most severe symptoms are observed.

[The necrotizing enteritis by Clostridium perfringens type C in piglets: II. Molecular epidemiology study]

Investigations were performed on shedding of C. perfringens in sows from four different pig farms. In two farms where no outbreaks of necrotizing enteritis had been observed, no strains of C. perfringens producing beta-toxin were detected in the faeces of sows. In contrast, C. perfringens strains producing beta-toxin were detected in sows on both farms suffering outbreaks of acute necrotizing enteritis. Strains of C. perfringens producing beta-toxin were invariably positive for the beta 2-toxin gene. However, strains carrying the beta 2-toxin gene only (i.e. negative for beta-toxin) were present in animals on all farms with roughly similar frequencies (mean 28.2% carriers). Some sows carried C. perfringens strains of both toxin genotypes simultaneously. Whereas these data further support the role of betatoxin as a cause of necrotizing enteritis, the role of beta 2-toxin in intestinal disease of piglets remains unclear. To establish the role of faecal shedding vs. environmental contamination as reservoirs of C. perfringens type C, strains were isolated from teats and feedlot trough swabs (toxin genotype beta/beta 2), as well as from fodder (genotype beta 2). However, sows carried this pathogen intermittently and in small numbers. This renders an individual, reliable diagnosis of carrier sows very difficult. Ribotyping of 34 C. perfringens isolates of different toxin genotypes showed five distinct profiles. Different toxin genotypes can belong to the same ribotype, and the same toxin genotype can be present in different ribotypes. Thus, even if a majority (79.4%) of strains investigated in a limited geographic region belonged to ribotype 1, ribotyping offered discrimination of strains beyond toxin typing.

A Swiss case-control study to assess Neospora caninum-associated bovine abortions by PCR, histopathology and serology

Neospora caninum is one of the most frequent infectious organisms causing abortion in cattle worldwide. The present case-control study was designed to assess the importance of bovine neosporosis for causing abortion in Swiss cattle and to identify selected risk factors. Infection was primarily diagnosed by a N. caninum-specific PCR and serology, complemented with histopathology and immunohistochemistry. A total of 113 case and 113 corresponding control-farms were studied for 1.5 year. During this time period, 242 abortions were reported and referred for bacteriological, virological, parasitological and pathohistological examinations. N. caninum was detected by PCR in the brains of 21% of all aborted fetuses. Microscopic lesions indicative for cerebral protozoa infection were detected in 84% of PCR-positive fetal brains. Bovine viral diarrhea virus (BVDV) was demonstrated in 7% of the cases, and bacterial infections were detected in 4% of the abortions. One or more N. caninum-abortions occurred in 20% of the herds (41 case-farms and 3 control-farms). Serological examination of aborting mother cows revealed a significantly higher percentage of N. caninum-seropositive animals (44%) in comparison to the prevalence in a randomly selected population (12%). However, in eight cases (4% of all investigated abortions) seronegative cows aborted N. caninum PCR-positive fetuses, and in 50 cases the fetus remained negative although the respective mother cow was N. caninum-seropositive. Repetitive serological investigations (at a 3-12 months interval) of 3551 cows from case- and control-farms showed a decrease of the overall N. caninum-seroprevalence from 17 to 12%. Ninety out of 3008 seronegative animals were converted to N. caninum-seropositivity. Conversely, 212 out of 543 initially seropositive animals became seronegative for their second serum sample. The obtained data underlined the importance of N. caninum as a causative agent for abortion in Swiss cattle. Furthermore, PCR was confirmed to be a valuable diagnostic tool for the primary diagnosis of N. caninum in aborted fetuses. On the other hand, the value of serology appears to be hampered by the temporal instability of N. caninum antibody concentrations in adult cattle, including especially seronegativity of some individual animals. Thus, seronegativity in a mother cow or heifer does not exclude N. caninum-associated abortions.

Antimicrobial growth promoter ban and resistance to macrolides and vancomycin in enterococci from pigs

Ninety-six enterococcus isolates from fecal samples of pigs receiving tylosin as an antimicrobial growth promoter and 59 isolates obtained in the same farms 5 to 6 months after the ban of antimicrobial growth promoters in Switzerland were tested for susceptibility to nine antimicrobial agents. A clear decrease in resistance to macrolides, lincosamides, and tetracycline was visible after the ban. Vancomycin-resistant Enterococcus faecium belonged to the same clonal lineage as vancomycin-resistant isolates previously isolated from Danish pigs.

[The current antimicrobial resistance situation in Swiss veterinary medicine]

Antimicrobial susceptibility data (n = 1501) and bacterial isolates (n = 258) of important bacterial pathogens from animals were collected in collaboration with eight Swiss laboratories from May 1999 to February 2000. Using these data, the antimicrobial resistance situation could be assessed for the following bacterial species: Escherichia coli, Salmonella, Haemophilus parasuis, Actinobacillus pleuropneumoniae, Pasteurella multocida, Mannheimia haemolytica, Bordetella bronchiseptica, Campylobacter jejuni, Pseudomonas aeruginosa, Staphylococcus aureus, Staphylococcus intermedius, Streptococci, and enterococci. Differences in the distribution of resistance between animal species could be evidenced in E. coli and salmonella. Some resistance frequency data were compared with those obtained in 1980. A significant increase of resistance frequency was observed for several antibiotics. This includes in particular an increase of ampicillin, gentamicin, and cotrimoxazole resistance in E. coli. A similar increase was observed in salmonella for ampicillin, streptomycin, sulfonamides, and nalidixic acid. Staphylococci from dogs (S. intermedius and S. aureus) also presented a clear increase of resistance for penicillin, neomycin, sulfonamides, cotrimoxazole, and erythromycin. Finally, a comparison with data from abroad shows that the antibiotic resistance situation in Switzerland is relatively favorable.

Transmission of opportunistic pathogens in a veterinary teaching hospital

Acinetobacter baumannii, Enterococcus faecalis, Enterococcus faecium, and Staphylococcus intermedius isolates from infected surgical wounds and other types of infections in a veterinary teaching hospital were typed by pulsed field gel electrophoresis. A first cluster of infections with a multiresistant A. baumannii strain was observed in dogs and cats in 1998-1999. This strain disappeared after cleaning and disinfection of the companion animals intensive care unit. It was followed in 2000 by a second multiresistant strain, which caused another cluster of infections and was also transmitted to a patient in the nearby horse clinic. Transmission of a multiresistant E. faecium strain between two cats with surgical wound infections was also observed during the same period. No multiresistant S. intermedius strain was observed during this time and transmission of this organism between patients did not seem to occur. The present study demonstrates the potential for hospital nosocomial resistance problems in veterinary medicine similar to those encountered in human medicine. The results suggest that the epidemiology of nosocomial infections with A. baumannii and E. faecium may differ from that of S. intermedius infections and that preventive measures may have to be adapted to the problem organism.

Molecular epidemiology and genetic linkage of macrolide and aminoglycoside resistance in Staphylococcus intermedius of canine origin

A collection of 77 Staphylococcus intermedius isolates from dogs and cats in Switzerland was examined for resistance to erythromycin. Resistance profiles for 14 additional antibiotics were compared between erythromycin-resistant and susceptible isolates. A resistance prevalence of 27% for erythromycin was observed in the population under study. Complete correlation between resistance to erythromycin, and to spiramycin, streptomycin, and neomycin was observed. The erythromycin-resistant isolates all had a reduced susceptibility to clindamycin when compared to the erythromycin-susceptible isolates. Both constitutive and inducible resistance phenotypes were observed for clindamycin. Ribotyping showed that macrolide-aminoglycoside resistance was randomly distributed among unrelated strains. This suggests that this particular resistance profile is not related to a single bacterial clone but to the horizontal transfer of resistance gene clusters in S. intermedius populations. The erythromycin-resistant isolates were all carrying erm(B), but not erm(A), erm(C), or msr(A). The erm(B) gene was physically linked to Tn5405-like elements known as resistance determinants for streptomycin, streptothricin, neomycin and kanamycin. Analysis of the region flanking erm(B) showed the presence of two different groups of erm(B)-Tn5405-like elements in the S. intermedius population examined and of elements found in Gram-positive species other than staphylococci. This strongly suggests that erm(B) or the whole erm(B)-Tn5405-like elements in S. intermedius originate from other bacterial species, possibly from enterococci.

Phylogenetic analysis of Pasteurella multocida subspecies and molecular identification of feline P. multocida subsp. septica by 16S rRNA gene sequencing

Pasteurella multocida is commonly found in the oral cavity of cats and dogs. In humans it is known as an opportunistic pathogen after bites from these animals. Phenotypic identification of P. multocida based on biochemical reactions is often limited and usually only done on a species level, even though 3 subspecies are described. For molecular taxonomy and diagnostic purposes a phylogenetic analysis of the three subspecies of P. multocida based on their 16S rRNA (rrs) gene sequence was therefore carried out. We found P. multocida subsp. septica on a distinguished branch on the phylogenetic tree of Pasteurellaceae, due to a 1.5% divergence of its rrs gene compared to the two other, more closely related subspecies multocida and gallicida. This phylogenetic divergence can be used for the identification of P. multocida subsp. septica by rrs gene determination since they form a phylogenetically well isolated and defined group as shown with a set of feline isolates. Comparison to routine phenotypic identification shows the advantage of the sequence-based identification over conventional methods. It is therefore helpful for future unambiguous identification and molecular taxonomy of P. multocida as well as for epidemiological investigations.

Molecular identification and epidemiological tracing of Pasteurella multocida meningitis in a baby

We report a case of Pasteurella multocida meningitis in a 1-month-old baby exposed to close contact with two dogs and a cat but without any known history of injury by these animals. 16S rRNA gene sequencing of the isolate from the baby allowed identification at the subspecies level and pointed to the cat as a possible source of infection. Molecular typing of Pasteurella isolates from the animals, from the baby, and from unrelated animals clearly confirmed that the cat harbored the same P. multocida subsp. septica strain on its tonsils as the one isolated from the cerebrospinal fluid of the baby. This case stresses the necessity of informing susceptible hosts at risk of contracting zoonotic agents about some basic hygiene rules when keeping pets. In addition, this study illustrates the usefulness of molecular methods for identification and epidemiological tracing of Pasteurella isolates.

Target genes for virulence assessment of Escherichia coli isolates from water, food and the environment

The widespread species Escherichia coli includes a broad variety of different types, ranging from highly pathogenic strains causing worldwide outbreaks of severe disease to avirulent isolates which are part of the normal intestinal flora or which are well characterized and safe laboratory strains. The pathogenicity of a given E. coli strain is mainly determined by specific virulence factors which include adhesins, invasins, toxins and capsule. They are often organized in large genetic blocks either on the chromosome ('pathogenicity islands'), on large plasmids or on phages and can be transmitted horizontally between strains. In this review we summarize the current knowledge of the virulence attributes which determine the pathogenic potential of E. coli strains and the methodology available to assess the virulence of E. coli isolates. We also focus on a recently developed procedure based on a broad-range detection system for E. coli-specific virulence genes that makes it possible to determine the potential pathogenicity and its nature in E. coli strains from various sources. This makes it possible to determine the pathotype of E. coli strains in medical diagnostics, to assess the virulence and health risks of E. coli contaminating water, food and the environment and to study potential reservoirs of virulence genes which might contribute to the emergence of new forms of pathogenic E. coli.

Evolution of virulence factors in Shiga-toxin-producing Escherichia coli

The major demonstrated or putative virulence factors of Shiga-toxin-producing Escherichia coli (STEC) are the Shiga toxins, products of the locus of enterocyte effacement, and products encoded by the EHEC-hemolysin plasmid. Molecular analysis shows that STEC acquired the majority of these virulence factors by horizontal transfer of genetic material. In the case of Shiga toxins, the phages encoding them are probably responsible for this transfer. For the locus of enterocyte effacement, however, it is not clear how often this transfer took place and which parts of the locus were involved in this transfer. The large EHEC-hemolysin plasmid is clearly a mosaic structure, which arose from multiple recombination events with foreign DNA. Two lineages of this plasmid can be distinguished, one of which is associated with chromosomally encoded virulence factors. Despite the wealth of information available, further comparative studies are needed to decipher definitively the evolution of virulence in STEC.

Associations between virulence factors of Shiga toxin-producing Escherichia coli and disease in humans

Associations between known or putative virulence factors of Shiga toxin-producing Escherichia coli and disease in humans were investigated. Univariate analysis and multivariate logistic regression analysis of a set of 237 isolates from 118 serotypes showed significant associations between the presence of genes for intimin (eae) and Shiga toxin 2 (stx2) and isolates from serotypes reported in humans. Similar associations were found with isolates from serotypes reported in hemorrhagic colitis and hemolytic-uremic syndrome. The enterohemorrhagic E. coli (EHEC) hemolysin gene was significantly associated with isolates from serotypes found in severe diseases in univariate analysis but not in multivariate logistic regression models. A strong association between the intimin and EHEC-hemolysin genes may explain the lack of statistical significance of EHEC hemolysin in these multivariate models, but a true lack of biological significance of the hemolysin in humans or in disease cannot be excluded. This result warrants further investigations of this topic. Multivariate analysis revealed an interaction between the eae and stx2 genes, thus supporting the hypothesis of the synergism between the adhesin intimin and Shiga toxin 2. A strong statistical association was observed between the stx2 gene and severity of disease for a set of 112 human isolates from eight major serotypes. A comparison of 77 isolates of bovine origin and 91 human isolates belonging to six major serotypes showed significant associations of the genes for Shiga toxin 1 and EspP protease with bovine isolates and an increased adherence on HEp-2 cell cultures for human isolates, particularly from diarrheic patients and healthy persons.

Association of enterohemorrhagic Escherichia coli hemolysin with serotypes of shiga-like-toxin-producing Escherichia coli of human and bovine origins

In this study we investigated whether the enterohemorrhagic Escherichia coli (EHEC) hemolysin gene ehxA could be used as an indicator of pathogenicity in Shiga-like-toxin-producing Escherichia coli (SLTEC) isolates. The isolates in a collection of 770 SLTEC strains of human and bovine origins were assigned to group 1 (230 human and 138 bovine SLTEC isolates belonging to serotypes frequently implicated in human disease), group 2 (85 human and 183 bovine isolates belonging to serotypes less frequently implicated in disease), and group 3 (134 bovine isolates belonging to serotypes not implicated in disease). PCR amplification was used to examine all of the SLTEC isolates for the presence of ehxA and the virulence-associated genes eae, slt-I, and slt-II. The percentages of human isolates in groups 1 and 2 that were positive for ehxA were 89 and 46%, respectively, and the percentages of bovine isolates in groups 1 to 3 that were positive for ehxA were 89, 51, and 52%, respectively. The percentages of human isolates in groups 1 and 2 that were positive for eae were 92 and 27%, respectively, and the percentages of bovine isolates in groups 1 to 3 that were positive for eae were 78, 15, and 19%, respectively. The frequencies of both ehxA and eae were significantly higher for group 1 isolates than for group 2 isolates. The presence of the ehxA gene was associated with serotype, as was the presence of the eae gene. Some serotypes, such as O117:H4, lacked both eae and ehxA and have been associated with severe disease, but only infrequently. The slt-I genes were more frequent in group 1 isolates than in group 2 isolates, and the slt-II genes were more frequent in group 2 isolates than in group 1 isolates. In a second experiment we determined the occurrence of the ehxA and slt genes in E. coli isolated from bovine feces. Fecal samples from 175 animals were streaked onto washed sheep erythrocyte agar plates. Eight E. coli-like colonies representing all of the morphological types were transferred to MacConkey agar. A total of 1, 080 E. coli isolates were examined, and the ehxA gene was detected in 12 independent strains, only 3 of which were positive for slt. We concluded that the ehxA gene was less correlated with virulence than the eae gene was and that EHEC hemolysin alone has limited value for screening bovine feces for pathogenic SLTEC because of presence of the ehxA gene in bovine isolates that are not SLTEC.

Evolution of enterohemorrhagic Escherichia coli hemolysin plasmids and the locus for enterocyte effacement in shiga toxin-producing E. coli

This study assessed the diversity of the enterohemorrhagic Escherichia coli (EHEC) hemolysin gene (ehxA) in a variety of Shiga toxin-producing E. coli (STEC) serotypes and the relationship between ehxA types and virulence markers on the locus for enterocyte effacement (LEE). Restriction fragment length polymorphism of the ehxA gene and flanking sequences and of the E. coli attaching and effacing (eae) gene was determined for 79 EHEC hemolysin-positive STEC isolates of 37 serotypes. Two main groups of EHEC hemolysin sequences and associated plasmids, which corresponded to the eae-positive and the eae-negative isolates, were delineated. Comparisons of the ehxA gene sequences of representative isolates of each group showed that this gene and the rest of the EHEC hemolysin operon are highly conserved. Digestion of an ehxA PCR product with the restriction endonuclease TaqI showed a unique restriction pattern for eae-negative isolates and another one for isolates of serotypes O157:H7 and O157:NM. A conserved fragment of 5.6 kb with four potential open reading frames was identified on the EHEC hemolysin plasmid of eae-positive STEC. Phylogenetic analysis of a subset of 27 STEC isolates, one enteropathogenic E. coli isolate, and a K-12 reference isolate showed that eae-positive STEC isolates all belong to a single evolutionary lineage and that the EHEC hemolysin plasmid and the ehxA gene evolved within this lineage without recent horizontal transfer. However, the eae gene and the LEE appear to have been transferred horizontally within this STEC lineage on several occasions. The reasons for the lack of transfer or maintenance of the LEE in other STEC lineages are not clear and require further study.

Comparison of PCR-based DNA fingerprinting techniques for the identification of Listeria species and their use for atypical Listeria isolates

Four PCR-based DNA fingerprinting techniques were compared for their ability to identify at the species level a heterogeneous collection of isolates belonging to the six valid Listeria species. 16S rDNA-RFLP analysis identified all species and 16S rDNA-SSCP analysis identified almost all species. Also, isolates with unusual biochemical characteristics and/or unusual antigenic composition could be identified correctly. rRNA-intracistronic length polymorphism analysis suffered from high intraspecific variability, a limited number of fragments per profile, and small length differences between the spacers of different species. tRNA-intergenic length polymorphism analysis resulted in identification of all isolates but one, when fluorescent DNA capillary electrophoresis was used such that fragment length differences of 1 bp could be resolved. The four techniques yielded comparable results relevant to the taxonomy of Listeria. They all indicate a high degree of genetic relatedness between L. innocua and L. welshimeri, homogeneity of L. grayi, distinct but clear relatedness of L. grayi to the other Listeria species, a clear distinction between the two subspecies of L. ivanovii, and a clear distinction between Listeria isolates and isolates from closely related taxa or from species which are phenotypically difficult to distinguish from Listeria. New sequence determination of the 16S rRNA gene was necessary to obtain sequences in accordance with the findings of 16S rDNA-RFLP analysis.

Widespread geographic distribution of oral Candida dubliniensis strains in human immunodeficiency virus-infected individuals

Candida dubliniensis is a recently identified chlamydospore-positive yeast species associated with oral candidiasis in human immunodeficiency virus (HIV)-infected (HIV+) patients and is closely related to Candida albicans. Several recent reports have described atypical oral Candida isolates with phenotypic and genetic properties similar to those of C. dubliniensis. In this study 10 atypical chlamydospore-positive oral isolates from HIV+ patients in Switzerland, the United Kingdom, and Argentina and 1 isolate from an HIV-negative Irish subject were compared to reference strains of C. albicans and Candida stellatoidea and reference strains of C. dubliniensis recovered from Irish and Australian HIV+ individuals. All 11 isolates were phenotypically and genetically similar to and phylogenetically identical to C. dubliniensis. These findings demonstrate that the geographical distribution of C. dubliniensis is widespread, and it is likely that it is a significant constituent of the normal oral flora with the potential to cause oral candidiasis, particularly in immunocompromised patients.

Typing Listeria monocytogenes isolates from fish products and human listeriosis cases

Seventy-two Listeria monocytogenes isolates originating from 10 different fish products of 12 producers and 47 isolates from human listeriosis cases were typed by serotyping and multilocus enzyme electrophoresis. Seventy-five of these isolates were further subtyped by restriction analysis of genomic DNA with the enzyme XhoI and by pulsed-field gel electrophoresis using the enzymes ApaI and SmaI. The results show that several L. monocytogenes clones identified by multilocus enzyme electrophoresis are frequently found in fish products of different origins. One of these clones is the same as another previously shown to be frequently associated with meat and meat products. The epidemic-associated electrophoretic type 1 was only rarely found in fish products. No association was found between any type of fish product and a particular lineage of L. monocytogenes. Both long-term persistence of a strain and simultaneous presence of several clearly distinct strains in the products of single producers were observed. The comparison of L. monocytogenes isolates from human clinical listeriosis cases in Switzerland and those from imported fish products by use of multilocus enzyme electrophoresis showed that they do not form two clearly distinct lineages but nevertheless belong to two separate populations. None of the 48 subtypes distinguished by the combination of all four typing methods could be found in both populations of human origin and those of fish origin.

The WHO multicenter study on Listeria monocytogenes subtyping: random amplification of polymorphic DNA (RAPD)

As part of a WHO multicenter study on Listeria monocytogenes subtyping methods the random amplification of polymorphic DNA (RAPD)-technique was evaluated. Six participants were asked to use a standard protocol to analyse a set of 80 L. monocytogenes strains. This set contained 22 groups of epidemiologically linked isolates and 11 pairs of duplicate strains. Using three different 10-mer primers the median reproducibility of the RAPD-results obtained by the six participants was 86.5% (range 0-100%). Failure in reproducibility was mainly due to results obtained with one particular primer. The number of epidemiological groups found to be homogeneous varied from 1-22 (median 16). However, for some groups an inhomogeneity was found by the majority of participants. The overall correlation between the results from the different participants ranged from 32 to 85%.

High-frequency endonuclease (REA) typing: results from the WHO collaborative study group on subtyping of Listeria monocytogenes

Eighty isolates of Listeria monocytogenes were typed by high-frequency restriction endonuclease analysis. Two laboratories participated in the study with two restriction enzymes each. The enzymes used were EcoRI, Hae1II, HhaI. and its isoschizomer Cfo1. EcoRI was less discriminatory than the other enzymes. The profiles generated by Hha1 and CfoI were not fully stable for some closely related isolates. The size and the number of restriction bands generated by Hha1 in one laboratory and its isoschizomer Cfo1 in another laboratory were directly comparable. This indicates that REA-typing may be used as a definitive typing method for Listeria monocytogenes if the typing procedure is standardized. The stability of the REA-types needs further elucidation in order to establish firm differentiation criteria for comparison of isolates.

Multilocus enzyme electrophoresis for characterization of Listeria monocytogenes isolates: results of an international comparative study

Multilocus enzyme electrophoresis (MEE) is a standard technique that is used to elucidate the epidemiology of a variety of bacterial species. Recently, the method has been employed by several laboratories for investigations of clinical and foodborne isolates of Listeria monocytogenes. To assess the sensitivity and reproducibility of MEE in characterising L. monocytogenes isolates for epidemiological purposes and, ultimately, to agree on a standard protocol, seven laboratories participated in a blinded study of 80 strains. The strain collection included both epidemiologically related and unrelated isolates. Each laboratory used its own protocol for MEE. The number of enzymes that were assayed by the laboratories ranged from 8 to 23, and the total number of identified electrophoretic types (ETs) varied between 14 and 25. Of the II pairs of duplicate strains, the number of pairs recognised as identical by the seven laboratories ranged from 3 to 10 (median = 8). From 10 to 18 (median = 15) of the 22 groups of epidemiological related strains were recognised as homogeneous by the different laboratories. The discriminatory power of the method, calculated using Simpson's index of diversity for 69 strains (80 strains minus the 11 duplicates), ranged from 0.827 to 0.925. This relatively low discriminatory power is a consequence of a somewhat low genetic diversity of L. monocytogenes compared to other bacterial species. Efforts should be pursued to standardise the method in order to improve the intra- and inter-laboratory reproducibility.

Subtyping Listeria monocytogenes isolates genetically related to the Swiss epidemic clone

Macrorestriction analysis by pulsed-field gel electrophoresis was used to assess the diversity of strains within the epidemic-associated electrophoretic type 1 (ET1) clone of Listeria monocytogenes. For this purpose, a total of 144 isolates from Switzerland shown by multilocus enzyme electrophoresis to belong to the ET1 were examined. These isolates were subtyped by macrorestriction analysis using the enzymes ApaI and SmaI and field inversion gel electrophoresis. Among these 144 isolates, 45 were isolated in human listeriosis cases of the postepidemic period of 1988 to 1993 and 44 were isolated in animal listeriosis cases of the same period. Forty-seven isolates were from the epidemic period of 1983 to 1987, and eight additional isolates were from cattle from two different farms. Twenty-nine different subtypes could be identified among the 144 isolates tested. Five major subtypes were found more frequently than the others during the postepidemic period, both in humans and in animals. Two of these subtypes had been previously implicated in outbreaks of listeriosis, thus suggesting that particular pulsed-field gel electrophoresis subtypes may be frequently associated with disease in humans and animals. Two of these frequent subtypes were also suspected to be related to small clusters of listeriosis cases during the postepidemic period. The results obtained by typing epidemiologically related isolates from different animals within the same farms and from different body sites of a given patient confirmed the potential of macrorestriction analysis for epidemiological studies restricted to short periods of time and to small number of isolates. The analysis of 47 isolates related to the Swiss listeriosis epidemic period of 1983 to 1987 and the use of Southern blotting and hybridization experiments show that the interpretation of relatedness between isolates presenting slightly different macrorestriction patterns may be more complex than commonly accepted. In such cases, careful interpretation of the potential molecular mechanisms leading to the differences observed between patterns is necessary.

Typing of Listeria monocytogenes by monocin and phage receptors

One hundred strains of Listeria monocytogenes from both sporadic and epidemic cases were typed by monocin production combined with phage receptor and reverse phage receptor methods. The monocin-phage combination gave 72 types with 100% typability and 97% reproducibility. The results were compared to those of serotyping, phage typing, ribotyping, multilocus enzyme electrophoresis, restriction enzyme analysis and RAPD (random amplification of polymorphic DNA). The monocin/phage types were comparable in terms of discrimination with other methods for epidemiological investigations. The index of discrimination of using the monocin typing and phage receptor/reverse phage receptor method combination (0.99) for both the 87 epidemiologically unrelated strains and the epidemiologically important serogroup 4 strains was the highest of the seven different methods analysed. This combination of methods was simple, highly discriminatory and reproducible and can be carried out in a non-specialized laboratory. However, like most of the other Listeria typing methods, both the method and the indicator test strains need to be standardized.

Typing Candida albicans oral isolates from human immunodeficiency virus-infected patients by multilocus enzyme electrophoresis and DNA fingerprinting

A total of 189 Candida albicans isolates have been typed by multilocus enzyme electrophoresis. The results obtained confirm the clonal mode of reproduction of C. albicans. The C. albicans populations found in the oropharynx of human immunodeficiency virus (HIV)-infected patients, in the oropharynx of healthy carriers, or in association with invasive candidiasis could not be distinguished. No clone or group of clones could be associated with the appearance of clinical disorders or with a reduced in vitro susceptibility to the antifungal agent fluconazole. Multiple and sequential oral isolates from 24 HIV-infected patients were also typed by restriction enzyme analysis with the enzymes EcoRI and HinfI and by use of the Ca3 repetitive probe. The results obtained by the combination of all three typing methods show that all but one patient each carried a unique major C. albicans clone in their oropharynx. The 21 patients with sequential isolates had the same C. albicans clones in their throats during recurrent oropharyngeal candidiasis episodes, independently of clinical status or of changes of in vitro susceptibility to fluconazole. Finally, several isolates of the same C. albicans clone found simultaneously in the oropharynx of a patient may present different levels of susceptibility to fluconazole.

Cluster of oral atypical Candida albicans isolates in a group of human immunodeficiency virus-positive drug users

Twenty-one chlamydospore-forming and germ tube-positive Candida albicans clinical isolates from 15 human immunodeficiency virus (HIV)-positive and 3 HIV-negative patients were examined by two different genetic methods. Multilocus enzyme electrophoresis and hybridization with the C. albicans-specific Ca3 probe showed that such isolates can be split into two genetically distinct groups that can be clearly distinguished. One group mainly contained strains with atypical sugar assimilation patterns and could be distinguished from the other group by the absence of intracellular beta-glucosidase activity. All 13 strains belonging to this group were isolated from the oral cavities of asymptomatic HIV-positive drug users and may be less pathogenic than the eight strains from the other group isolated either from HIV-positive patients with oropharyngeal candidiasis or from HIV-negative patients with invasive candidiasis.

Typing Listeria monocytogenes: a comparison of random amplification of polymorphic DNA with 5 other methods

One hundred Listeria monocytogenes strains were typed by random amplification of polymorphic DNA (RAPD) with three different primers, and the results were compared with those obtained by serotyping, ribotyping, multilocus enzyme electrophoresis, restriction enzyme analysis and phage typing. The RAPD patterns of strains appear to be stable during epidemics even over periods of several years. Reproducibility of the RAPD patterns was good. The discriminatory power of RAPD typing was the best among all the methods tested. RAPD is therefore a very promising tool in the study of listeriosis epidemiology. However, the problems related to the standardization of the technique first have to be resolved before the wide use of RAPD is possible.

Delineation of Borrelia burgdorferi sensu stricto, Borrelia garinii sp. nov., and group VS461 associated with Lyme borreliosis

We studied 48 Borrelia isolates that were associated with Lyme borreliosis or were isolated from ticks and identified three DNA relatedness groups by using the S1 nuclease method. The three DNA groups (genospecies) were associated with specific rRNA gene restriction patterns, protein electrophoresis patterns, and patterns of reactivity with murine monoclonal antibodies. Genospecies I corresponded to Borrelia burgdorferi sensu stricto since it contained the type strain of this species (strain ATCC 35210); this genospecies included 28 isolates from Europe and the United States. Genospecies II was named Borrelia garinii sp. nov. and included 13 isolates from Europe and Japan. Genospecies III (group VS461) included seven isolates from Europe and Japan.

Population genetic analysis of Borrelia burgdorferi isolates by multilocus enzyme electrophoresis

Fifty Borellia burgdorferi strains isolated from humans and ticks in Europe and the United States were analyzed by multilocus enzyme electrophoresis. Eleven genetic loci were characterized on the basis of the electrophoretic mobilities of their products. Ten loci were polymorphic. The average number of alleles per locus was 5.9, with a mean genetic diversity of 0.673 among electrophoretic types (ETs). The strains were grouped into 35 ETs constituting three main divisions (I, II, and III) separated at a genetic distance greater than 0.75. Divisions I, II, and III contained 13, 6, and 16 ETs, respectively. These findings, together with previous data from DNA hybridization and restriction enzyme analysis of rRNA genes, suggest that divisions I, II, and III may represent three distinct genomic species. All three divisions contained human clinical ETs. However, in division I, which includes the ET of the type strain of B. burgdorferi, the human pathogenic ETs constituted a single clone. The ETs of division I were from west-central Europe and the United States, whereas divisions II and III contained ETs from west-central and northern Europe but not from the United States. Finally, our data show that the genetic structure of B. burgdorferi populations is clonal.

Assignment of Listeria grayi and Listeria murrayi to a single species, Listeria grayi, with a revised description of Listeria grayi

The genomic relatedness between Listeria grayi and Listeria murrayi was reevaluated by using DNA-DNA hybridization, multilocus enzyme electrophoresis, and rRNA restriction fragment length polymorphism techniques. The high levels of similarity observed between the strains of these two species confirmed the data published since 1973 and indicated that they should be considered members of a single species. On grounds of priority, the species should be named L. grayi.

Typing of human, animal, food, and environmental isolates of Listeria monocytogenes by multilocus enzyme electrophoresis

In order to elucidate some aspects of the epidemiology of listeriosis in Switzerland, 181 strains of Listeria monocytogenes isolated from humans, animals, food, and the environment have been analyzed by multilocus enzyme electrophoresis at 21 enzyme loci. The clone responsible for several recent food-borne outbreaks in Switzerland and in North America (marked by electrophoretic type 1 and serovar 4b) has been found frequently among strains isolated from animals. Thus, animals may represent a major source of diffusion of this clone in the environment and in food, in which it has been found only sporadically, however. Two other unrelated clones (including strains belonging to serovars 1/2b and 1/2c) have often been isolated from meat but not from animals. These findings indicate that contamination of meat with L. monocytogenes might originate mainly from the environment in which it is processed rather than from animals themselves. This could explain the differences in the distribution of L. monocytogenes serovars isolated from meat and from animals.