Staphylococcal Food Poisoning Outbreaks Research Articles

Effects of Growth at Low Water Activity on the Thermal Tolerance of Staphylococcus aureus

Staphylococcus aureus is the most osmotolerant foodborne pathogen, and outbreaks of staphylococcal food poisoning are often linked to foods of reduced water activity (aw) values. While it is generally known that the thermal tolerance of microorganisms increases as the aw of the heating menstruum is decreased, surprisingly little research has examined the influence of growth medium aw on microbial thermal tolerance. In the present study, we show that growth of S. aureus at an aw value of 0.94 leads to the development of dramatically enhanced thermal tolerance (i.e., less than 1 log reduction after heating for 20 min at 60°C). We further show that the identity of the accumulated compatible solute within cells grown at low aw can also influence the overall level of thermal tolerance of S. aureus. Finally, we provide evidence that the synthesis of general stress and/or osmotic stress proteins is required for the development of enhanced thermal tolerance of S. aureus at low aw.

Staphylococcal Food Poisoning Caused by Imported Canned Mushrooms

From February through April 1989, four outbreaks of staphylococcal food poisoning in the United States were associated with eating mushrooms canned in the People's Republic of China (PRC). In the four outbreaks, 99 persons who ate at a suspect facility developed gastrointestinal symptoms within 24 h, including 18 who were hospitalized. Illness was associated with eating mushrooms at a university cafeteria (relative risk [RR] = 53.0), a hospital cafeteria (RR = 13.8), a pizzeria (odds ratio [OR] = infinity), and a restaurant (OR = infinity) (all P < .0001). Staphylococcal enterotoxin A was found by ELISA in mushrooms at the sites of two outbreaks and in unopened cans from the three plants thought to have produced mushrooms implicated in outbreaks. These investigations led to multistate recalls and a US Food and Drug Administration order to restrict entry into the United States of all mushrooms produced in the PRC; until this action, the United States imported approximately 50 million pounds yearly.

Murine monoclonal antibodies reactive with staphylococcal enterotoxins A, B, C2, D, and E

By fusion of mouse spleen cells immunized with five different staphylococcal enterotoxins (SEA, SEB, SEC2, SED, and SEE) with myeloma cells, we obtained 15 hybridomas producing monoclonal antibodies (mAbs). Four mAbs were reactive with both SEA and SEE, whereas 8 mAbs were reactive with SEB and SEC2. One mAb reacted with SEA, SED, and SEE. The other two mAbs were found to be reactive with all five serotypes of SEs. The mAbs specific for five serotypes of SEs were found to be most reactive with SED, reactive with SEA, and slightly less reactive with SEB, SEC2, and SEE. Those mAbs with specificities for all serotypes of SEs may be valuable to prepare immunoadsorbent(s) for isolation of SEs and to detect SEs in foods and clinical specimens involved in outbreaks of staphylococcal food poisoning.

Murine monoclonal antibodies reactive with staphylococcal enterotoxins A, B, C2, D, and E

By fusion of mouse spleen cells immunized with five different staphylococcal enterotoxins (SEA, SEB, SEC2, SED, and SEE) with myeloma cells, we obtained 15 hybridomas producing monoclonal antibodies (mAbs). Four mAbs were reactive with both SEA and SEE, whereas 8 mAbs were reactive with SEB and SEC2. One mAb reacted with SEA, SED, and SEE. The other two mAbs were found to be reactive with all five serotypes of SEs. The mAbs specific for five serotypes of SEs were found to be most reactive with SED, reactive with SEA, and slightly less reactive with SEB, SEC2, and SEE. Those mAbs with specificities for all serotypes of SEs may be valuable to prepare immunoadsorbent(s) for isolation of SEs and to detect SEs in foods and clinical specimens involved in outbreaks of staphylococcal food poisoning.

Analytical methods for Staphylococcus aureus

The staphylococcal enterotoxins are relatively low molecular weight proteins, 27000 to 29000 Da (Bergdoll, 1979). They are produced by the staphylococci, primarily Staphylococcus aureus, although the newer species, Staphylococcus intermedius and Staphylococcus hyicus have been reported to be enterotoxigenic (Adesiyun et al., 1984; Fukuda et al., 1984). The guideline followed for many years in the Food Research Institute to determine whether staphylococci might produce enterotoxin was to determine whether the particular strain produced either coagulase or thermonuclease (TNase). Formerly, both S. intermedius and S. hyicus would have been classified as S. aureus. Therefore, if we follow the current species classification, we cannot confine our testing of staphylococcal strains to S. aureus alone. To my knowledge, no one is currently working on the identification of additional enterotoxins although we do know that unidentified ones do exist. This is very difficult to accomplish because a specific biological test such as the monkey feeding test is necessary to identify the enterotoxin (Surgalla et al., 1953). Apparently, only about five percent of staphylococcal food poisoning outbreaks are due to unidentified enterotoxins. The enterotoxins that have been identified so far are classified as enterotoxins A (SEA), B (SEB), C 1 (SEC1), C~ (SEC2), C 3 (SEC3), D (SED) and E (SEE). The enterotoxin Cs are very closely related and can be identified by their cross-reactions with antibodies prepared against any one of the SECs. The other enterotoxins are identified by antibodies specific for each of the enterotoxins, although cross-reactions between SEB and the SECs (Lee et al., 1980) and SEA and SEE (Lee et al., 1978) do exist. Monoclonal antibodies have been prepared that are useful in the sandwich ELISA for the detection of SEB, SECs, SEA and SEE by one set of two antibodies for each group. Efforts to prepare monoclonal antibodies that cross-react with SEA, SED and SEE were generally unsuccessful, although an

Staphylococcus aureus: Production of Extracellular Compounds and Behavior in Foods - A Review

Growth of Staphylococcus aureus is accompanied by production of such extracellular compounds as hemolysins, nuclease, coagulase, lipase, and enterotoxins. Enterotoxins that can cause food poisoning are produced by about one-third of the coagulase-positive strains of S. aureus. The enterotoxins are a heterogeneous group of heat-stable, water-soluble, single-chain globular proteins having a molecular weight between 28,000 and 35,000 daltons. Production of enterotoxin by appropriate strains of S. aureus is affected by the nutritional quality and pH of the substrate, temperature, atmosphere, sodium chloride (and hence water activity), other chemicals, and competing microorganisms. Outbreaks of staphylococcal food poisoning most often are associated with processed red meats, poultry products (especially chicken salad), sauces, dairy products (especially cheeses), and custard- or cream-filled bakery products. Ham and associated products often are involved in as many as 30% of outbreaks of staphylococcal food poisoning. Most outbreaks result from the combined effects of contamination of the food, often through unsanitary handling, with S. aureus and holding the food at the wrong temperature thus allowing growth and synthesis of enterotoxin by the pathogen.

Estimation of human dose of staphylococcal enterotoxin A from a large outbreak of staphylococcal food poisoning involving chocolate milk

An outbreak of gastroenteritis in a school district in the United States was determined to be staphylococcal food poisoning due to 2% chocolate milk containing staphylococcal enterotoxin A (SEA). Twelve one-half pint (approx 0.28 l) cartons of the 2% chocolate milk from this outbreak were analyzed for the quantity of SEA present in the milk. The amount of SEA in the cartons varied from 94 to 184 ng with the average being 144 ng (mean = 139±45). The attack rate for vomiting among those who consumed more than one carton was greater (38.3%) than among those who consumed only one carton (31.5%) with the highest attack rate among those who consumed three or more cartons (44.4%).

Nasal carriage of Staphylococcus species by food handlers

On the basis of a variety of physiological, biochemical and morphological characteristics, 201 staphylococcal strains were identified to species level. All of the cultures were isolated from the anterior nares of food handlers. 83 strains produced coagulase and 88 produced thermonuclease. Amongst the coagulase-positive cultures, 80 belonged to the species Staphylococcus aureus and 3 could not be identified. These latter strains showed similar properties and were related to S. intermedius. S. epidermidis was the coagulase-negative species most frequently found (97 strains), followed by S. capitis (10 strains), S. saprophyticus (3 strains), S. hyicus subsp. chromogenes (2 strains), S. hominis (1 strain), S. haemolyticus (1 strain) and S. warneri (1 strain). The remaining 3 coagulase-negative strains were thermonuclease producers and one of them was identified as S. aureus. The quantitative estimations showed that most of the species isolated were present in large populations, S. aureus giving the highest counts. The strains of S. saprophyticus, novobiocin resistant species associated with animals, and S. hyicus subsp. chromogenes were isolated from food handlers woking with animals and foods derived from animals (abattoirs and butchers' shops). The possible role of food handlers in the epidemiology of staphylococcal food poisoning outbreaks is also discussed.

International outbreak of staphylococcal food poisoning caused by contaminated lasagne.

An outbreak of staphylococcal food poisoning in Europe caused by contaminated lasagne was detected and monitored by both national and international surveillance systems. The common source was a pasta-producing factory in Italy and high levels of Staphylococcus aureus were detected in packets of dried lasagne distributed in Luxembourg, the UK, France and Italy. Forty-seven cases were reported in the UK. Outbreaks of staphylococcal food poisoning attributed to mishandling during the food processing stage are uncommon and pasta as the food vehicle is rare. Prompt recognition of the outbreak and rapid identification of the food vehicle enabled most of the consignment to be withdrawn from the market.

The use of a sandwich ELISA for the detection of staphylococcal enterotoxin A in foods from outbreaks of food poisoning.

Foods from outbreaks of food poisoning were examined for the presence of staphylococcal enterotoxin A (SEA) by a sandwich ELISA using microtitre trays as the solid phase and SEA antibodies raised in sheep. The presence of SEA was confirmed by neutralization tests. The toxin was detected in 12 of 15 foods from separate outbreaks of staphylococcal food poisoning; all 15 foods contained a strain of Staphylococcus aureus which produced SEA. For most foods a simple extraction procedure without a concentration step was sufficient to detect the toxin. The method was semi-quantitative and recoveries of SEA added to control foods varied from 30 to 80%. The foods from outbreaks contained between 1 and 10 micrograms of SEA/100 g. SEA was not found in foods from 21 outbreaks in which an SEA-producing strain of Staph. aureus was not isolated.

Enterotoxigenicity of Staphylococcus intermedius strains isolated from dogs.

Dogs (n = 100) were examined for the presence of enterotoxigenic Staphylococcus intermedius. Enterotoxigenic strains were isolated from the nasal cavities of 43 (43.0%) out of 100 dogs. Of the 50 enterotoxigenic strains isolated, 23 (46.0%) produced enterotoxin A, 17 (34.0%) enterotoxins A and C, 8 (16.0%) enterotoxin C, and only two (4.0%) enterotoxins A and B. The amount of enterotoxin produced on semisolid brain heart infusion medium by the 17 enterotoxin A producing strains of S. intermedius was 10-160 ng per ml. Enterotoxin A production by S. intermedius strains was ony one tenth to one hundredth of that of S. aureus strains from staphylococcal food poisoning outbreaks.

Enterotoxin production by strains of Staphylococcus aureus isolated from animals and main in Nigeria

Enterotoxin production by 194 strains of Straphylococcus aureaus isolated from animals and man was investigated. The organisms were also classified into biotypes, irrespective of sources. Human biotypes isolated from people had the highest proportion of enterotoxigenic strains (39%). The animal biotypes isolated from human beings were not enterotoxinenic, but 8.8% of the human biotypes isolated from animals yielded enterotoxin. About 18% of the animal biotypes isolated from animals were enterotoxigenic, while 25% of the untypable biotypes from all the sources investigated were enterotoxin producers. The predominant enterotoxins were A and B, with A accounting for 55%5% of the entrotoxins produced by human biotypes. Enterotoxins A, B and C were produced by some animal biotypes, and three canine biotypes produced enterotoxin combinations, BE, CE and ABE, respectively. From goat isolates, only four of the caprine biotypes were enterotoxigenic, including the only isolate producing enterotoxins B, C and E. The isolates obtained from horses and chickens were non-enterotoxigenic regardless of the biotypes. It is concluded that strains producing enterotoxins A and B may be responsible for outbreaks of staphylococcal food poisoning in Nigeria. The close association between man and his animals in this environment may account for the high prevalence (47%) of human biotypes in animals.

CLINICAL ASPECTS OF OUTBREAK OF STAPHYLOCOCCAL FOOD POISONING DURING AIR TRAVEL

An outbreak of staphylococcal food poisoning among 364 charter-flight passengers and crew members is described. Symptoms appeared just before landing, about an hour after a meal containing contaminated ham had been served. 143 passengers were admitted to hospital. 1 patient developed acute anuria and 1 had hemiplegia and aphasia; both recovered. Fever and bloody stools were recorded with unusual frequency.

STAPHYLOCOCCUS AUREUS AND STAPHYLOCOCCAL FOOD INTOXICATIONS. A REVIEW: III. STAPHYLOCOCCI IN DAIRY FOODS , , ,

Dairy products have been associated with several rather large outbreaks of staphylococcal food poisoning. These include eight related outbreaks in England and 19 in Puerto Rico which involved dry milk, an outbreak that affected people over a widespread area of the United States caused by Cheddar cheese, and a 200-case outbreak traced to Cheddar cheese consumed in an Iowa institution. These and other outbreaks of staphylococcal food intoxications are reviewed in this paper. Surveys which have been conducted to determine the incidence of staphylococci in dairy foods are also discussed. These studies show that it is not uncommon for raw milk and cheese to contain detectable numbers of coagulase-positive Staphylococcus aureus. Finally, information is presented on the behavior of staphylococci in dairy products. Most of the work deals with growth of and enterotoxin production by S. aureus in milk and cheese. Growth of staphylococci in these foods is favored by the presence of low numbers of other organisms and is increasingly restricted as the pH decreases.

Enterotoxigenicity of Staphylococcus aureus cultures isolated from acute cases of bovine mastitis.

To determine whether staphylococci causing bovine mastitis are potential causes of human intoxications, 142 cultures identified as etiological agents of acute cases and 18 cultures causing chronic cases of staphylococcal mastitis were obtained from investigators in the United States and Canada, examined microscopically, and tested for carbohydrate utilization, terminal pH, catalase, coagulase, egg yolk hydrolysis, gelatin hydrolysis, cytochrome oxidase, urease production, nitrate reduction, micrococcal nuclease, phage type, and enterotoxin production. Three cultures were not confirmed as Staphylococcus aureus. Of the 157 S. aureus cultures, 23 produced staphylococcal enterotoxins. Although a direct relationship between staphylococcal mastitis and outbreaks of staphylococcal food poisoning was not proved, results indicated that staphylococcal infections of the bovine mammary gland represent a significant reservoir of enterotoxigenic strains of S. aureus.

Enterotoxigenicity of Staphylococcus aureus Cultures Isolated from Acute Cases of Bovine Mastitis

To determine whether staphylococci causing bovine mastitis are potential causes of human intoxications, 142 cultures identified as etiological agents of acute cases and 18 cultures causing chronic cases of staphylococcal mastitis were obtained from investigators in the United States and Canada, examined microscopically, and tested for carbohydrate utilization, terminal pH, catalase, coagulase, egg yolk hydrolysis, gelatin hydrolysis, cytochrome oxidase, urease production, nitrate reduction, micrococcal nuclease, phage type, and enterotoxin production. Three cultures were not confirmed as Staphylococcus aureus. Of the 157 S. aureus cultures, 23 produced staphylococcal enterotoxins. Although a direct relationship between staphylococcal mastitis and outbreaks of staphylococcal food poisoning was not proved, results indicated that staphylococcal infections of the bovine mammary gland represent a significant reservoir of enterotoxigenic strains of S. aureus.

DETECTION OF STAPHYLOCOCCAL ENTEROTOXIN IN FOOD.

Methods are described for the extraction and serological detection of trace amounts of enterotoxins A and B in foods incriminated in outbreaks of staphylococcal food poisoning. Evidence is presented for the probable applicability of the methods for the detection of unidentified enterotoxins.

Detection of Staphylococcal Enterotoxin in Food

Methods are described for the extraction and serological detection of trace amounts of enterotoxins A and B in foods incriminated in outbreaks of staphylococcal food poisoning. Evidence is presented for the probable applicability of the methods for the detection of unidentified enterotoxins.

Bacteria Associated with Giblets of Commercially Processed Turkeys

CONTAMINATED products made from turkey meat are important sources of food borne intoxications and infections. Dack (1962) reported that turkeys accounted for 14 of 137 outbreaks of staphylococcal food poisoning during the years 1956–1961. According to Dauer (1961) turkey meat was associated with four outbreaks involving 350 cases of salmonellosis and eight outbreaks responsible for 682 cases of staphylococcal food poisoning in 1960.The most probable source of salmonellae on turkey carcasses has been reported to be the viscera and intestinal contents (Gunderson et al., 1954). Morris and Ayres (1960) recovered Salmonella spp. from only 12 of 2,500 samples taken in a federally inspected turkey processing plant. None of the positive cultures were recovered from the carcass surface after evisceration or from the drainage from giblets. Sadler et al. (1961) isolated Salmonella species from 2.4% of the intestinal or cecal samples of turkeys on the processing line.Incidence and…

Control of Staphylococcal Food Poisoning

STAPHYLOCOCCAL food poisoning is overwhelmingly the most prevalent of foodborne infections in the United States. The need for improved methods of controlling the disease is indicated by the number of outbreaks reported in the annual summaries of disease outbreaks, which show little evidence of decrease in incidence (1-4). Factors responsible for outbreaks of staphylococcal food poisoning have not been clearly defined. It is difficult, if not impossible, to determine those conditions required to render food poisonous because no satisfactory laboratory test has been found for the presence of staphylococcus enterotoxin in food (5-7). At present, the only means of clarifying these factors appears to be through analysis of unselected outbreaks of this disease. Ninety-five outbreaks of staphylococcal food poisoning in 1955 and 1956, reported in the weekly communicable disease summaries issued by the Public Health Service, were surveyed. More complete data on 89 of them were obtained from the State, county, and city health officers reporting the incidents.