Ribotype diversity of Listeria monocytogenes strains associated with outbreaks of listeriosis in ruminants

Differentiation between types and strains of Clostridium botulinum by riboprinting

The ability of automated ribotyping to differentiate between major types and individual strains of Clostridium botulinum was tested using the Qualicon Riboprinter Microbial Characterization System. Pure spores of C. botulinum type A, proteolytic type B, nonproteolytic type B, and type E strains were inoculated onto modified anaerobic egg yolk agar and incubated 24 h at 35 degrees C. Plates were rinsed with buffer (2 mM Tris + 20 mM EDTA) to remove vegetative cells that were heated for 10 min at 80 degrees C, treated with a lysing agent, and ribotyped in the Qualicon Riboprinter utilizing the enzyme EcoRI. Riboprint patterns were obtained for 30 strains of the four major types of C. botulinum most commonly involved in human foodborne botulism. Proteolytic strains yielded the best and most consistent results. Fifteen ribogroups were identified among the 31 strains tested. Interestingly, in two cases, a single ribogroup contained patterns from isolates belonging to evolutionarily distinct Clostridium lineages. This degree of differentiation between strains of C. botulinum may be useful in hazard analysis and identification, hazard analysis and critical control point monitoring and validation, environmental monitoring, and in inoculation studies.

Infections and intoxications associated with animal feed and forage which may present a hazard to human health

Animal feed or forage may be the source of a limited number of infections for farm animals that could lead to human illness. Likely organisms include Salmonella enterica, Toxoplasma gondii, Trichinella spiralis and possibly the agent of bovine spongiform encephalopathy. The risk to human health from other infectious agents which may contaminate either feed or forage appear to be either negligible, e.g. Bacillus anthracis and Mycobacterium bovis, or non-existent, e.g. Clostridium botulinum toxin and Listeria monocytogenes. Mycotoxins present in animal feed can result in foods of animal origin also containing them. This risk is well recognized but has yet to be quantified accurately and in some instances the risk may be of theoretical rather than practical importance. Pesticides, agricultural and industrial chemicals, heavy metals and radionuclides may pollute animal feed and forages. The methods available for controlling pollution from these sources are well understood from a technical point of view although the effective implementation of controls can be difficult.

Ribotype analysis of strain distribution in Listeria monocytogenes

Changes in the temporal and spatial patterns of strain distribution for the foodborne pathogen Listeria monocytogenes were studied by ribotyping using the Qualicon Riboprinter system. Ribotype patterns were obtained by using the restriction enzymes EcoRI and PvuII for 72 isolates of L. monocytogenes recovered from smoked salmon samples over a period of 3 years. Each pattern was classified both by comparison to a pattern library and by comparison among the 72 isolate patterns. Eleven EcoRI-based ribogroups and 16 PvuII groups were identified. Eight of the 11 EcoRI ribogroups were found in isolates obtained over a period of >12 months, and 75% of the EcoRI ribogroups that were found in more than one food sample were distributed nationally. Within the set of isolates, there were 26 instances where more than one isolate was obtained from a single food sample. In 35% of these instances, the co-isolates produced different ribotype patterns, indicating that multiple strains of L. monocytogenes commonly coexist in the same environment. Overall, these data indicate that the population of L. monocytogenes consists of a number of widely dispersed strains with little geographic or temporal stratification.

Listeriosis in a Holstein cow

Bovine listeriosis is a sporadie bacterial infection most commonly manifested by encephalitis or meningoencephalitis in adult animals. Cattle fed poorly fermented haylage or corn silage are at increased risk. Mortality is high without early antibiotic and supportive therapy. Listeria monocytogenes can affect many species and is a public health concern.

Use of ribotyping and hemolysin activity to identify highly virulent Streptococcus suis type 2 isolates

Nineteen Streptococcus suis type 2 isolates were evaluated for their virulence in pigs and mice. Of these, seven were determined to be highly virulent in pigs on the basis of clinical sign scores and gross pathology and histopathology results. Clinical sign scores correlated with gross pathology and histopathology scores at P equal to 0.004 and P equal to 0.009, respectively. The virulence of highly virulent isolates in pigs compared somewhat with virulence in mice, but the correlation was not significant. No correlation of virulence was noted among the moderately virulent and avirulent isolates in pigs and mice. Chromosomal DNAs from all S. suis isolates were evaluated by PstI, PvuII, EcoRI, and HaeIII restriction enzyme digestion followed by hybridization with a digoxigenin-11-dUTP-labeled cDNA probe transcribed from 16S and 23S rRNAs from Escherichia coli. The hybridization patterns (ribotypes) varied depending upon the enzyme used, but a significant number of isolates determined to be highly virulent in pigs had unique hybridization patterns compared with those of the moderately virulent and avirulent isolates (P = 0.002). In addition, hemolysin activity showed a high correlation to virulence (P = 0.00008) and ribotype (P = 0.002).

Ribotyping to compare Fusobacterium necrophorum isolates from bovine liver abscesses, ruminal walls, and ruminal contents

Restriction fragment length polymorphism analysis of rRNA genes was employed to genetically compare Fusobacterium necrophorum subsp. necrophorum and F. necrophorum subsp. funduliforme isolates from multiple abscesses of the same liver and isolates from liver abscesses, the ruminal wall, and ruminal contents from the same animal. Four livers with multiple abscesses and samples of ruminal contents, ruminal walls, and liver abscesses were collected from 11 cattle at slaughter. F. necrophorum was isolated from all liver abscesses, nine ruminal walls, and six ruminal content samples. Chromosomal DNA of the isolates was extracted and single or double digested with restriction endonucleases (EcoRI, EcoRV, SalI, and HaeIII); then restriction fragments were hybridized with a digoxigenin-labeled cDNA probe transcribed from a mixture of 16S and 23S rRNAs from Escherichia coli. EcoRI alone or in combination with EcoRV yielded the most discriminating ribopatterns for comparison. Within the subspecies multiple isolates from the same liver were indistinguishable based on the ribopattern obtained with EcoRI. The hybridization patterns of liver abscess isolates were concordant with those of the corresponding isolates from ruminal walls in eight of nine sets of samples. None of the six ruminal content isolates matched either the liver abscess isolates or the ruminal wall isolates. The genetic similarity between the isolates from liver abscesses and ruminal walls supports the hypothesis that F. necrophorum isolates of liver abscesses originate from the rumen.

Manure and microbes: public and animal health problem?

Most environmental concerns about waste management either have focused on the effects of nutrients, especially N and P, on water quality or have emphasized odor problems and air quality. Microbes from manure are often low on the priority list for control and remediation, despite the fact that several outbreaks of gastroenteritis have been traced to livestock operations. The pathogens discussed in this paper include protozoans (Cryptosporidium parvum, Giardia spp.), bacteria (Listeria monocytogenes, Escherichia coli O157:H7, Salmonella spp., and Mycobacterium paratuberculosis), and some enteric viruses. Clinical symptoms, prospects for zoonotic infection, and control methods other than the use of antimicrobials are considered. Recommendations to avoid disease transmission include taking steps to ensure the provision of clean, unstressful environments to reduce disease susceptibility and the careful handling and spreading of manure from animals at high risk for infection, especially young calves. Composting and drying of manure decrease the number of viable pathogens. Environmental controls, such as filter strips, also reduce the risk of water contamination.

Strain-specific differentiation of lactococci in mixed starter culture populations using randomly amplified polymorphic DNA-derived probes

A hydrophobic grid membrane filtration (HGMF) colony hybridization assay was developed that allows strain-specific differentiation of defined bacterial populations. The randomly amplified polymorphic DNA (RAPD) fingerprinting technique was used to identify potential signature nucleic acid sequences unique to each member of a commercial cheese starter culture blend. The blend consisted of two closely related Lactococcus lactis subsp. cremoris strains, 160 and 331, and one L. lactis subsp. lactis strain, 210. Three RAPD primers (OPX 1, OPX 12, and OPX 15) generated a total of 32 products from these isolates, 20 of which were potential strain-specific markers. Southern hybridization analyses revealed, that the RAPD-generated signature sequences OPX15-0.95 and a 0.36-kb HaeIII fragment of OPX1-1.0b were specific for strains 331 and 210, respectively, within the context of the test starter culture blend. These strain-specific probes were used in a HGMF colony hybridization assay. Colony lysis, hybridization, and nonradioactive detection parameters were optimized to allow specific differentiation and quantitation of the target strains in the mixed starter culture population. When the 210 and 331 probes were tested at their optimal hybridization temperatures against single cultures, they detected 100% of the target strain CFUs, without cross-reactivity to the other strains. The probes for strains 210 and 331 also successfully detected their targets in blended cultures even with a high background of the other two strains.

Molecular diagnostics for dairy-borne pathogens

Advances in diagnostic assays based on nucleic acids will revolutionize the ability of the industry to maintain the safety of dairy foods. Two complementary assay formats are explored, one of which permits the rapid detection of bacterial pathogens and the other the identification of reservoirs of these pathogens. The first format is an assay based on the polymerase chain reaction that employs homogeneous detection (TaqMan polymerase chain reaction detection; Perkin Elmer, Applied Biosystems Division, Foster City, CA) of the target sequence. This assay has been applied to the detection of Listeria monocytogenes. A primary problem with current assays that are based on polymerase chain reaction is the complexity of sample handling and the quantification of the initial target number. This fluorogenic assay takes advantage of the endogenous 5',3'-endonuclease activity in Taq DNA polymerase. Approximately 100 samples can be analyzed in 2 to 3 h with a sensitivity of < 50 cells and a dynamic range of > 1000-fold. The TaqMan polymerase chain reaction detection assay is a robust format that is readily applicable to a wide array of other pathogens found in foods and in the environment. The second format is an instrument for automated ribosomal RNA analysis (Riboprinter; DuPont, Wilmington, DE) that can be used to locate the reservoirs harboring the bacterial pathogen. Use of this typing method it has been shown that, although a number of different ribotypes can be isolated from a single environmental sample, only a selected number of these strains apparently have the ability to cause disease. The future of food microbiology lies in the development and integration of molecular methods that can be automated into a testing regimen that extends from the farm to finished products.