Meticillin-resistant Staphylococcus aureus with a novel mecA homologue in human and bovine populations in the UK and Denmark: a descriptive study

Background

Animals can act as a reservoir and source for the emergence of novel meticillin-resistant Staphylococcus aureus (MRSA) clones in human beings. Here, we report the discovery of a strain of S aureus (LGA251) isolated from bulk milk that was phenotypically resistant to meticillin but tested negative for the mecA gene and a preliminary investigation of the extent to which such strains are present in bovine and human populations.

Methods

Isolates of bovine MRSA were obtained from the Veterinary Laboratories Agency in the UK, and isolates of human MRSA were obtained from diagnostic or reference laboratories (two in the UK and one in Denmark). From these collections, we searched for mecA PCR-negative bovine and human S aureus isolates showing phenotypic meticillin resistance. We used whole-genome sequencing to establish the genetic basis for the observed antibiotic resistance.

Findings

A divergent mecA homologue (mecA_LGA251) was discovered in the LGA251 genome located in a novel staphylococcal cassette chromosome mec element, designated type-XI SCCmec. The mecA_LGA251 was 70% identical to S aureus mecA homologues and was initially detected in 15 S aureus isolates from dairy cattle in England. These isolates were from three different multilocus sequence type lineages (CC130, CC705, and ST425); spa type t843 (associated with CC130) was identified in 60% of bovine isolates. When human mecA-negative MRSA isolates were tested, the mecA_LGA251 homologue was identified in 12 of 16 isolates from Scotland, 15 of 26 from England, and 24 of 32 from Denmark. As in cows, t843 was the most common spa type detected in human beings.

Interpretation

Although routine culture and antimicrobial susceptibility testing will identify S aureus isolates with this novel mecA homologue as meticillin resistant, present confirmatory methods will not identify them as MRSA. New diagnostic guidelines for the detection of MRSA should consider the inclusion of tests for mecA_LGA251.

Funding

Department for Environment, Food and Rural Affairs, Higher Education Funding Council for England, Isaac Newton Trust (University of Cambridge), and the Wellcome Trust.

Production effects related to mastitis and mastitis economics in dairy cattle herds

Mastitis is the most prevalent production disease in dairy herds world-wide and is responsible for several production effects. Milk yield and composition can be affected by a more or less severe short-term depression and, in case of no cure, by a long-acting effect, and, sometimes, an overlapping effect to the next lactation. Summary values in the literature for losses of milk production were proposed at 375 kg for a clinical case (5% at the lactation level) and at 0.5 kg per 2-fold increase of crude SCC of a cow. Due to the withdrawal period after treatment, composition changes in milk can almost be neglected in economic calculations. Lethality rate for clinical mastitis is very low on the average, while anticipated culling occurs more frequently after clinical and subclinical mastitis (relative risk between 1.5 and 5.0). The economics of mastitis needs to be addressed at the farm level and, per se, depends on local and regional epidemiological, managerial and economic conditions. To assess the direct economic impact of mastitis, costs (i.e. extra resource use) and losses (i.e. reduced revenues) have to be aggregated. To support decision making for udder health control, it is necessary to use a marginal approach, based on the comparison of the losses avoided and the additional costs of modified plans, compared to the existing ones.

Purification and characterization of angiotensin I-converting enzyme inhibitors from sour milk

The inhibitory activity of angiotensin I-converting enzyme in milk increased during fermentation with the Calpis sour milk starter containing Lactobacillus helveticus and Saccharomyces cerevisiae. Two kinds of peptides inhibitory to angiotensin I-converting enzyme were purified from the sour milk by using four-step HPLC. The amino acid sequences of these inhibitors were identified as Val-Pro-Pro and Ile-Pro-Pro. The concentrations of peptides providing 50% inhibition of angiotensin I-converting enzyme were 9 and 5 microM, respectively. Most of the inhibitory activity in sour milk was attributed to these two peptides.

Foodborne pathogens in milk and the dairy farm environment: food safety and public health implications

Milk and products derived from milk of dairy cows can harbor a variety of microorganisms and can be important sources of foodborne pathogens. The presence of foodborne pathogens in milk is due to direct contact with contaminated sources in the dairy farm environment and to excretion from the udder of an infected animal. Most milk is pasteurized, so why should the dairy industry be concerned about the microbial quality of bulk tank milk? There are several valid reasons, including (1) outbreaks of disease in humans have been traced to the consumption of unpasteurized milk and have also been traced back to pasteurized milk, (2) unpasteurized milk is consumed directly by dairy producers, farm employees, and their families, neighbors, and raw milk advocates, (3) unpasteurized milk is consumed directly by a large segment of the population via consumption of several types of cheeses manufactured from unpasteurized milk, (4) entry of foodborne pathogens via contaminated raw milk into dairy food processing plants can lead to persistence of these pathogens in biofilms, and subsequent contamination of processed milk products and exposure of consumers to pathogenic bacteria, (5) pasteurization may not destroy all foodborne pathogens in milk, and (6) inadequate or faulty pasteurization will not destroy all foodborne pathogens. Furthermore, pathogens such as Listeria monocytogenes can survive and thrive in post-pasteurization processing environments, thus leading to recontamination of dairy products. These pathways pose a risk to the consumer from direct exposure to foodborne pathogens present in unpasteurized dairy products as well as dairy products that become re-contaminated after pasteurization. The purpose of this communication is to review literature published on the prevalence of bacterial foodborne pathogens in milk and in the dairy environment, and to discuss public health and food safety issues associated with foodborne pathogens found in the dairy environment. Information presented supports the model in which the presence of pathogens depends on ingestion of contaminated feed followed by amplification in bovine hosts and fecal dissemination in the farm environment. The final outcome of this cycle is a constantly maintained reservoir of foodborne pathogens that can reach humans by direct contact, ingestion of raw contaminated milk or cheese, or contamination during the processing of milk products. Isolation of bacterial pathogens with similar biotypes from dairy farms and from outbreaks of human disease substantiates this hypothesis.

A fermented milk high in bioactive peptides has a blood pressure-lowering effect in hypertensive subjects

BACKGROUND

Angiotensin-converting enzyme (ACE; EC 3.4.15.1) plays a dual role in the regulation of hypertension: it catalyzes the production of the vasoconstrictor angiotensin II and it inactivates the vasodilator bradykinin. By inhibiting these processes, ACE inhibitors have antihypertensive effects. Peptides derived from milk proteins can have ACE-inhibiting properties and may thus be used as antihypertensive components.

OBJECTIVE

We evaluated the long-term blood pressure-lowering effect of milk fermented by Lactobacillus helveticus LBK-16H in hypertensive subjects.

DESIGN

In a randomized placebo-controlled study, 39 hypertensive patients received 150 mL/d of either L. helveticus LBK-16H fermented milk or a control product for 21 wk after a 2-wk run-in period. During the run-in period, the average baseline diastolic and systolic blood pressure values were 155 and 97 mm Hg, respectively, in the test product group and 152 and 96 mm Hg, respectively, in the control group. After the run-in period, blood pressure was measured at home on the same day every week with the use of an automatic blood pressure recorder.

RESULTS

There was a mean difference of 6.7 +/- 3.0 mm Hg in systolic blood pressure (P = 0.030) and of 3.6 +/- 1.9 mm Hg (P = 0.059) in diastolic blood pressure between the test product and control groups. Demographic factors had no significant effect on the responses.

CONCLUSION

L. helveticus LBK-16H fermented milk containing bioactive peptides in normal daily use has a blood pressure-lowering effect in hypertensive subjects.

Bioactive milk peptides: a prospectus

Bioactive peptides have been identified within the amino acid sequences of native milk proteins. Hydrolytic reactions, such as those catalyzed by digestive enzymes, result in their release. These peptides directly influence numerous biological processes evoking behavioral, gastrointestinal, hormonal, immunological, neurological, and nutritional responses. The specific bioreactions associated with each physiological class have been well characterized. Herein, we review the scientific literature and attempt to stimulate consideration of the continued use of bioactive peptides and their expanded development as a commercial product. Several applications have already evolved. For example, phosphopeptides derived from casein fractions are currently used as both dietary and pharmaceutical supplements. Potentially, the addition of bioactive peptides to food products could improve consumer safety as a result of their antimicrobial properties. Lastly, bioactive peptides may function as health care products, providing therapeutic value for either treatment of infection or prevention of disease.

Monitoring udder health and milk quality using somatic cell counts

In this article the use of somatic cell counts for monitoring udder health and milk quality is discussed. Somatic cell count dynamics at quarter, cow, herd and population level are discussed and illustrated with examples. Quarter and cow somatic cell counts directly represent the inflammatory status of the mammary gland. Herd and population somatic cell count are related to the inflammatory process in individual cows but much more reflect the udder health status of the herd and the quality of the raw milk in the herd and the population. Application of monitoring tools in herd health management are illustrated using a case study. Understanding infection dynamics requires precise longitudinal data. Monitoring tools are required to find the areas of risk in the herd. It is inevitable that more complete udder health programs and monitoring systems are to be developed and implemented. These programs are necessarily dynamic and complex. Implementation of complete udder health programs should be accompanied by research efforts to further fine-tune these complete udder health control and monitoring programs.

Variation in biofilm formation among strains of Listeria monocytogenes

Contamination of food by Listeria monocytogenes is thought to occur most frequently in food-processing environments where cells persist due to their ability to attach to stainless steel and other surfaces. Once attached these cells may produce multicellular biofilms that are resistant to disinfection and from which cells can become detached and contaminate food products. Because there is a correlation between virulence and serotype (and thus phylogenetic division) of L. monocytogenes, it is important to determine if there is a link between biofilm formation and disease incidence for L. monocytogenes. Eighty L. monocytogenes isolates were screened for biofilm formation to determine if there is a robust relationship between biofilm formation, phylogenic division, and persistence in the environment. Statistically significant differences were detected between phylogenetic divisions. Increased biofilm formation was observed in Division II strains (serotypes 1/2a and 1/2c), which are not normally associated with food-borne outbreaks. Differences in biofilm formation were also detected between persistent and nonpersistent strains isolated from bulk milk samples, with persistent strains showing increased biofilm formation relative to nonpersistent strains. There were no significant differences detected among serotypes. Exopolysaccharide production correlated with cell adherence for high-biofilm-producing strains. Scanning electron microscopy showed that a high-biofilm-forming strain produced a dense, three-dimensional structure, whereas a low-biofilm-forming strain produced a thin, patchy biofilm. These data are consistent with data on persistent strains forming biofilms but do not support a consistent relationship between enhanced biofilm formation and disease incidence.

Vip3A, a novel Bacillus thuringiensis vegetative insecticidal protein with a wide spectrum of activities against lepidopteran insects

A novel vegetative insecticidal gene, vip3A(a), whose gene product shows activity against lepidopteran insect larvae including black cutworm (Agrotis ipsilon), fall armyworm (Spodoptera frugiperda), beet armyworm (Spodoptera exigua), tobacco budworm (Heliothis virescens), and corn earworm (Helicoverpa zea) has been isolated from Bacillus thuringiensis strain AB88. VIP3-insecticidal gene homologues have been detected in approximately 15% of Bacillus strains analyzed. The sequence of the vip3A(b) gene, a homologue of vip3A(a) isolated from B. thuringiensis strain AB424 is also reported. Vip3A(a) and (b) proteins confer upon Escherichia coli insecticidal activity against the lepidopteran insect larvae mentioned above. The sequence of the gene predicts a 791-amino acid (88.5 kDa) protein that contains no homology with known proteins. Vip3A insecticidal proteins are secreted without N-terminal processing. Unlike the B. thuringiensis 5-endotoxins, whose expression is restricted to sporulation, Vip3A insecticidal proteins are expressed in the vegetative stage of growth starting at mid-log phase as well as during sporulation. Vip3A represents a novel class of proteins insecticidal to lepidopteran insect larvae.

Implication of milk and milk products in food-borne diseases in France and in different industrialised countries

A study was carried out to estimate the proportion of diseases due to milk and milk products among food-borne diseases recorded in France and in other countries since 1980. Particular attention was given to whether the milk involved was heat-treated or not. Four etiologic agents were considered: Salmonella spp., Staphylococcus aureus, Listeria monocytogenes, and pathogenic Escherichia coli. An overview of food-borne disease annual reports from seven countries indicated that milk and milk products were implicated in 1-5% of the total bacterial outbreaks; however, details about the type of product and milk involved were usually not provided. When considering 60 outbreaks and four single cases described in the literature and implicating milk and milk products, confirmed or suspected food vehicles were distributed as follows: milk, 39.1%, cheese, 53.1%, other milk products, 7.8%. Overall, 32.8% of the food vehicles were made from pasteurised milk; 37.5% from raw milk; 10.9% from milk stated as "unpasteurised"; and 18.8% from unspecified milk. Salmonella spp. were responsible for 29 outbreaks, L. monocytogenes for 10 outbreaks and four well-documented single cases, pathogenic E. coli for 11 outbreaks, and S. aureus for 10 outbreaks. Analysis of unpublished data about food-borne disease outbreaks, listeriosis excluded, collected by the coordinator of the French surveillance system from 1992 to 1997, revealed 69 documented outbreaks for which milk and milk products were confirmed as the vehicle by the isolation of the etiologic agent. The food vehicles were distributed as follows: milk, 10%; cheese, 87%; others, 3%. UHT milk accounted for 1.5%, raw milk and raw milk products for 48%, and milk and milk products from unspecified milk for 50.5% of the 69 outbreaks. S. aureus was by far the most frequent pathogen associated with these outbreaks (85.5% of the outbreaks), followed by Salmonella (10.1%). This study demonstrates the limitations of the surveillance systems and the difficulties in estimating the contribution of milk and milk products to food-borne diseases. In particular, it was not possible to find out in many outbreaks what heat treatment, if any, the milk had undergone.

An outbreak of gastroenteritis and fever due to Listeria monocytogenes in milk

BACKGROUND

After an outbreak of gastroenteritis and fever among persons who attended a picnic in Illinois, chocolate milk served at the picnic was found to be contaminated with Listeria monocytogenes.

METHODS

In investigating this outbreak, we interviewed the people who attended the picnic about what they ate and their symptoms. Surveillance for invasive listeriosis was initiated in the states that receive milk from the implicated dairy. Stool and milk samples were cultured for L. monocytogenes. Serum samples were tested for IgG antibody to listeriolysin O.

RESULTS

Forty-five persons had symptoms that met the case definition for illness due to L. monocytogenes, and cultures of stool from 11 persons yielded the organism. Illness in the week after the picnic was associated with the consumption of chocolate milk. The most common symptoms were diarrhea (present in 79 percent of the cases) and fever (72 percent). Four persons were hospitalized. The median incubation period for infection was 20 hours (range, 9 to 32), and persons who became ill had elevated levels of antibody to listeriolysin O. Isolates from stool specimens from patients who became ill after the picnic, from sterile sites in three additional patients identified by surveillance, from the implicated chocolate milk, and from a tank drain at the dairy were all serotype 1/2b and were indistinguishable on multilocus enzyme electrophoresis, ribotyping, and DNA macrorestriction analysis.

CONCLUSIONS

L. monocytogenes is a cause of gastroenteritis with fever, and sporadic cases of invasive listeriosis may be due to unrecognized outbreaks caused by contaminated food.

Effect of long-term consumption of a probiotic bacterium, Lactobacillus rhamnosus GG, in milk on dental caries and caries risk in children

Lactobacillus rhamnosus GG, ATCC (LGG), has shown antagonism to many bacteria including mutans streptococci. This randomized, double-blind, placebo-controlled intervention study was designed to examine whether milk containing LGG has an effect on caries and the risk of caries in children when compared with normal milk. 594 children, 1-6 years old, from 18 municipal day-care centres were included. The children received the milk with meals from coded containers 5 days a week in the day-care centres for 7 months. The children's oral health was recorded at baseline and at the end, using WHO criteria. The caries risk was calculated based on clinical and microbiological data, comprising mutans streptococcus levels from dental plaque and saliva. The risk was classified as high if the child had a dmft/DMFT or initial caries score >0, and a mutans streptococcus count > or = 10(5) CFU/ml. The results showed less dental caries in the LGG group and lower mutans streptococcus counts at the end of the study. LGG was found to reduce the risk of caries significantly (OR = 0.56, p = 0.01; controlled for age and gender, OR = 0.51, p = 0.004). The effect was particularly clear in the 3- to 4-year-olds. Thus, milk containing the probiotic LGG bacteria may have beneficial effects on children's dental health.

Growth of Listeria monocytogenes at refrigeration temperatures

The growth of three strains of Listeria monocytogenes at refrigeration temperatures (-0.5 to 9.3 degrees C) in chicken broth and/or UHT milk was determined using a rocking temperature gradient incubator. Minimum growth temperatures ranged from -0.1 to -0.4 degree C for the three strains. Lag times of 1-3 d and 3 to greater than 34 d were observed with incubation at 5 and 0 degrees C respectively. Corresponding generation times ranged from 13-24 h at 5 degrees C and 62-131 h at 0 degree C. The type of culture medium had an influence on both the rate and extent of growth. Incubation of cultures at 4 degrees C before inoculation caused a marked reduction in the lag time when compared with cultures which had been previously incubated at 30 degrees C.

Isolation of Escherichia coli serotype O157:H7 and other Shiga-like-toxin-producing E. coli from dairy cattle

We examined 1,266 fecal specimens from healthy cattle during the investigations of two sporadic cases of hemolytic uremic syndrome associated with raw milk consumption and an outbreak of gastroenteritis and hemolytic uremic syndrome caused by Escherichia coli serotype O157:H7. We collected specimens from heifers, calves, and adult cows on 22 farms, in a stockyard, and in a packing house. We also collected 3 raw hamburger specimens from a restaurant and 23 raw milk samples from two farms. All specimens were examined for E. coli O157:H7 by using sorbitol-MacConkey agar, H immobilization, O157 agglutination, and tissue culture cytotoxicity. E. coli O157:H7 was isolated from 16 heifers or calves and 1 adult cow on 22 farms, 1 stockyard calf, 2 beef specimens, and 1 raw milk sample. Selected fecal specimens were also examined for the presence of other Shiga-like-toxin-producing E. coli (SLTEC) by testing polymyxin B extracts of colony sweeps and then testing individual colonies for toxin production. SLTEC other than O157 was isolated from 8 of 10 farms investigated and from the stockyard; 8% of adult cows and 19% of heifers and calves were positive for SLTEC. Several animals were positive for SLTEC by colony sweep only. This investigation demonstrates that dairy cattle are a reservoir of E. coli O157:H7 and other SLTEC.

Ability of dairy strains of lactic acid bacteria to bind a common food carcinogen, aflatoxin B1

This study was conducted to examine the ability of selected dairy strains of lactic acid bacteria to remove aflatoxin B1 (AFB1) from liquid media. Both Lactobacillus rhamnosus strain GG (LBGG) and L. rhamnosus strain LC-705 (LC705) can significantly (P > 0.05) remove AFB1 when compared with that by other strains of either Gram-positive or Gram-negative bacteria. Removal of AFB1 by LBGG and LC705 was a rapid process with approximately 80% AFB1 removed at 0 hr. Removal of AFB1 by these two strains was both temperature and bacterial concentration dependent.

Immunomodulation of human blood cells following the ingestion of lactic acid bacteria

Because of the lack of data that convincingly show immunomodulatory properties of lactic acid bacteria in humans, a study was performed in which healthy volunteers were divided into two groups and given a fermented milk product supplemented with Lactobacillus acidophilus strain La1 or Bifidobacterium bifidum strain Bb 12 for 3 wk. Blood was sampled throughout the study to assess changes in lymphocyte subsets or leukocyte phagocytic activity following consumption of the fermented products. No modifications of lymphocyte subpopulations were detected. In contrast, phagocytosis of Escherichia coli sp. in vitro was enhanced after the administration of both fermented products. The increment in phagocytosis was coincident with fecal colonization by the lactic acid bacteria and persisted for 6 wk after ingestion of the fermented products. By this time, the fecal lactobacilli and bifidobacteria had returned to concentrations prior to consumption. Nonspecific, anti-infective mechanisms of defense can be enhanced by the ingestion of specific lactic acid bacteria strains. These strains can be used as nutritional supplements to improve the immune function of particular age groups, i.e., the neonate or the elderly, for which these functions are diminished.

Antimicrobial activity of plant essential oils using food model media: efficacy, synergistic potential and interactions with food components

The aim of this study was to optimise the antimicrobial efficacy of plant essential oils (EOs) for control of Listeria spp. and spoilage bacteria using food model media based on lettuce, meat and milk. The EOs evaluated were lemon balm, marjoram, oregano and thyme and their minimum inhibitory concentrations (MIC) were determined against Enterobacter spp., Listeria spp., Lactobacillus spp., and Pseudomonas spp. using the agar dilution method and/or the absorbance based microplate assay. MICs were significantly lower in lettuce and beef media than in TSB. Listeria strains were more sensitive than spoilage bacteria, and oregano and thyme were the most active EOs. EO combinations were investigated using the checkerboard method and Oregano combined with thyme had additive effects against spoilage organisms. Combining lemon balm with thyme yielded additive activity against Listeria strains. The effect of simple sugars and pH on antimicrobial efficacy of oregano and thyme was assessed in a beef extract and tomato serum model media. EOs retained greater efficacy at pH 5 and 2.32% sugar, but sugar concentrations above 5% did not negatively impact EO efficacy. In addition to proven antimicrobial efficacy, careful selection and investigation of EOs appropriate to the sensory profile of foods and composition of the food system is required. This work shows that EOs might be more effective against food-borne pathogens and spoilage bacteria when applied to foods containing a high protein level at acidic pH, as well as moderate levels of simple sugars.

Survival of lactic acid bacteria in a dynamic model of the stomach and small intestine: validation and the effects of bile

This study was conducted to validate a dynamic model of the stomach and small intestine to quantify the survival of lactic acid bacteria and to assess the influence of gastrointestinal secretions. The survival of a single strain of each of the following species, Bifidobacterium bifidum, Lactobacillus acidophilus, Lactobacillus bulgaricus, and Streptococcus thermophilus, was measured under physiological conditions (e.g., peristalsis, changes in pH, and changes in concentrations of enzymes and bile) and were compared with data obtained from humans. No significant differences were found between the in vitro and in vivo data, indicating that the model has a predictive value for the survival of these bacteria in humans. The survival of these strains of lactic acid bacteria in the gastrointestinal model was investigated under two different conditions in the small intestine: simulation of physiological secretion of bile and low bile secretion. Reductions in viability were significantly different between the bacterial species. The dose-response effect of bile on the survival of the tested bacteria was significant, demonstrating the bactericidal effect of bile salts. This study demonstrates the differences among bacterial species in their sensitivity to gastric and intestinal secretions.

Enhancement of immunity in the elderly by dietary supplementation with the probiotic Bifidobacterium lactis HN019

BACKGROUND

The aging process can lead to a decline in cellular immunity. Therefore, the elderly could benefit from safe and effective interventions that restore cellular immune functions.

OBJECTIVE

We determined whether dietary supplementation with the known immunostimulating probiotic Bifidobacterium lactis HN019 could enhance aspects of cellular immunity in elderly subjects.

DESIGN

Thirty healthy elderly volunteers (age range: 63-84 y; median: 69 y) participated in a 3-stage dietary supplementation trial lasting 9 wk. During stage 1 (run-in), subjects consumed low-fat milk (200 mL twice daily for 3 wk) as a base-diet control. During stage 2 (intervention), they consumed milk supplemented with B. lactis HN019 in a typical dose (5 x 10(10) organisms/d) or a low dose (5 x 10(9) organisms/d) for 3 wk. During stage 3 (washout), they consumed low-fat milk for 3 wk. Changes in the relative proportions of leukocyte subsets and ex vivo leukocyte phagocytic and tumor-cell-killing activity were determined longitudinally by assaying peripheral blood samples.

RESULTS

Increases in the proportions of total, helper (CD4(+)), and activated (CD25(+)) T lymphocytes and natural killer cells were measured in the subjects' blood after consumption of B. lactis HN019. The ex vivo phagocytic capacity of mononuclear and polymorphonuclear phagocytes and the tumoricidal activity of natural killer cells were also elevated after B. lactis HN019 consumption. The greatest changes in immunity were found in subjects who had poor pretreatment immune responses. In general, the 2 doses of B. lactis HN019 had similar effectiveness.

CONCLUSION

B. lactis HN019 could be an effective probiotic dietary supplement for enhancing some aspects of cellular immunity in the elderly.

Molecular epidemiology of mastitis pathogens of dairy cattle and comparative relevance to humans

Mastitis, inflammation of the mammary gland, can be caused by a wide range of organisms, including gram-negative and gram-positive bacteria, mycoplasmas and algae. Many microbial species that are common causes of bovine mastitis, such as Escherichia coli, Klebsiella pneumoniae, Streptococcus agalactiae and Staphylococcus aureus also occur as commensals or pathogens of humans whereas other causative species, such as Streptococcus uberis, Streptococcus dysgalactiae subsp. dysgalactiae or Staphylococcus chromogenes, are almost exclusively found in animals. A wide range of molecular typing methods have been used in the past two decades to investigate the epidemiology of bovine mastitis at the subspecies level. These include comparative typing methods that are based on electrophoretic banding patterns, library typing methods that are based on the sequence of selected genes, virulence gene arrays and whole genome sequencing projects. The strain distribution of mastitis pathogens has been investigated within individual animals and across animals, herds, countries and host species, with consideration of the mammary gland, other animal or human body sites, and environmental sources. Molecular epidemiological studies have contributed considerably to our understanding of sources, transmission routes, and prognosis for many bovine mastitis pathogens and to our understanding of mechanisms of host-adaptation and disease causation. In this review, we summarize knowledge gleaned from two decades of molecular epidemiological studies of mastitis pathogens in dairy cattle and discuss aspects of comparative relevance to human medicine.

A maternally inherited superantigen encoded by a mammary tumour virus

A collection of superantigens, molecules which in combination with class II major histocompatibility complex (MHC) engage T cells bearing particular V beta chains as part of their alpha beta receptors, have recently been described. The mouse self superantigen, Mls-1a, for example, in conjunction with many MHC class II proteins, engages mouse T cells bearing V beta 6, 7, 8.1 and 9, almost regardless of the sequences of the other variable components of the receptors on the T cells. Two types of superantigen have been identified so far: first, superantigens encoded in the mouse genome, such as Mls-1a; second, superantigens produced by bacteria, such as the staphylococcal enterotoxins. Although the latter type of superantigens are in many cases known to be proteins of about 220 amino acids, nothing is known about the structures of any of the superantigens encoded in mouse. Here we describe the properties of a new mouse superantigen. The antigen is maternally transmitted in milk and is probably encoded by a mammary tumour virus (MTV). Given the known genetic linkage between at least one of the mouse genomic superantigens and endogenous MTV integration sites, it is tempting to speculate that the superantigen described here and some of the endogenous mouse superantigens are encoded by MTVs.

Epidemic Yersinia enterocolitica infection due to contaminated chocolate milk

In September and October, 1976, an outbreak of illness due to chocolate milk contaminated with Yersinia enterocolitica resulted in hospitalization of 36 children, 16 of whom had appendectomies. Infection with Y. enterocolitica serotype 0:8 was demonstrated in 38 ill persons. Sixty-one per cent of the persons who were infected had a titer greater than 1:160 OH agglutinins to serotype 8 yersinia, whereas 48 per cent of the hospitalized children had a fourfold change in agglutinin titer. An epidemiologic investigation demonstrated that illness was associated with drinking of chocolate milk purchased in school cafeterias, and Y. enterocolitica 0:8 was subsequently isolated from the milk. The investigation suggested that the bacterium was introduced at the dairy during the mixing by hand of chocolate syrup with previously pasteurized milk.

An extensive outbreak of staphylococcal food poisoning due to low-fat milk in Japan: estimation of enterotoxin A in the incriminated milk and powdered skim milk

An extensive outbreak of staphylococcal food poisoning occurred in Kansai district in Japan. As many as 13,420 cases frequently ingested dairy products manufactured by a factory in Osaka City. The main ingredient of these dairy products was powdered skim milk manufactured by a factory in Hokkaido. Staphylococcal enterotoxin A (SEA) (< or = 0.38 ng/ml) was detected in low-fat milk and approx. 3.7 ng/g in powdered skim milk. The total intake of SEA per capita was estimated mostly at approx. 20-100 ng. The assumed attack rate was considerably lower than those reported in previous outbreaks. SEA exposed at least twice to pasteurization at 130 degrees C for 4 or 2 s retained both immunological and biological activities, although it had been partially inactivated. The present outbreak was unusual in that the thermal processes had destroyed staphylococci in milk but SEA had retained enough activity to cause intoxication.