Serological identification of enterotoxigenic staphylococci from cheese

Detection of Staphylococcus aureus enterotoxigenic strains in bovine raw milk by reversed passive latex agglutination and multiplex polymerase chain reaction

AIM

This review gives an outline of the assessment of enterotoxigenic Staphylococcus aureus tainting levels in raw milk from different sources in Egypt and characterization of enterotoxigenic strains utilizing a technique in light of PCR to identify genes coding for the production of staphylococcal enterotoxin (SE). The obtained data were compared with results from the application of the reversed passive latex.

MATERIALS AND METHODS

Multiplex PCR and reversed passive latex agglutination (RPLA) were used. A total of 141 samples of raw milk (cow's milk=33, buffalo's milk=58, and bulk tank milk=50) were investigated for S. aureus contamination and tested for enterotoxin genes presence and toxin production.

RESULTS

S. aureus was detected in 23 (16.3%) samples phenotypically and genotypically by amplification of nuc gene. The S. aureus isolates were investigated for SEs genes (sea to see) by multiplex PCR and the toxin production by these isolates was screened by RPLA. SEs genes were detected in six isolates (26.1%) molecularly; see was the most observed gene where detected in all isolates, two isolates harbored seb, and two isolates harbored sec. According to RPLA, three isolates produced SEB and SEC.

CONCLUSION

The study revealed the widespread of S. aureus strains caring genes coding for toxins. The real significance of the presence of these strains or its toxins in raw milk and their possible impact a potential hazard for staphylococcal food poisoning by raw milk consumption. Therefore, detection of enterotoxigenic S. aureus strains in raw milk is necessary for consumer safety.

Peritoneal dialysis-related peritonitis due to coagulase-negative Staphylococcus: a review of 115 cases in a Brazilian center

BACKGROUND AND OBJECTIVES

Coagulase-negative Staphylococcus (CNS) is the most frequent cause of peritoneal dialysis (PD)-related peritonitis in many centers. This study aimed to describe clinical and microbiologic characteristics of 115 CNS episodes and to determine factors influencing the outcome.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This study reviewed the records of 115 CNS peritonitis episodes that occurred in 74 patients between 1994 and 2011 at a single university center. Peritonitis incidences were calculated for three consecutive 6-year periods (P1, 1994-1999; P2, 2000-2005; P3, 2006-2011) and annually. The production of biofilms, enzymes, and toxins was evaluated. Oxacillin resistance was evaluated based on its minimum inhibitory concentration and the presence of the mecA gene.

RESULTS

The overall incidence of CNS peritonitis was 0.15 episodes per patient per year and did not vary over time (0.12, 0.14, and 0.16 for P1, P2, and P3, respectively; P=0.21). The oxacillin resistance rate was 69.6%. Toxin and enzyme production was infrequent and 36.5% of CNS strains presented the gene encoding biofilm production. The presence of icaAD genes associated with biofilm production was predictive of relapses or repeat episodes (odds ratio [OR], 2.82; 95% confidence interval [95% CI], 1.11 to 7.19; P=0.03). Overall, 70 episodes (60.9%) resolved; oxacillin susceptibility (OR, 4.41; 95% CI, 1.48 to 13.17; P=0.01) and vancomycin use as the first treatment (OR, 22.27; 95% CI, 6.16 to 80.53; P<0.001) were the only independent predictors of resolution.

CONCLUSIONS

Oxacillin resistance and vancomycin use as the first treatment strongly influence the resolution rate in CNS peritonitis, which reinforces the validity of the International Society for Peritoneal Dialysis guidelines on monitoring bacterial resistance to define protocols for initial treatment. These results also suggest that the presence of biofilm is a potential cause of repeat peritonitis episodes.

Peritoneal dialysis-related peritonitis due to Staphylococcus aureus: a single-center experience over 15 years

Peritonitis caused by Staphylococcus aureus is a serious complication of peritoneal dialysis (PD), which is associated with poor outcome and high PD failure rates. We reviewed the records of 62 S. aureus peritonitis episodes that occurred between 1996 and 2010 in the dialysis unit of a single university hospital and evaluated the host and bacterial factors influencing peritonitis outcome. Peritonitis incidence was calculated for three subsequent 5-year periods and compared using a Poisson regression model. The production of biofilm, enzymes, and toxins was evaluated. Oxacillin resistance was evaluated based on minimum inhibitory concentration and presence of the mecA gene. Logistic regression was used for the analysis of demographic, clinical, and microbiological factors influencing peritonitis outcome. Resolution and death rates were compared with 117 contemporary coagulase-negative staphylococcus (CoNS) episodes. The incidence of S. aureus peritonitis declined significantly over time from 0.13 in 1996–2000 to 0.04 episodes/patient/year in 2006–2010 (p = 0.03). The oxacillin resistance rate was 11.3%. Toxin and enzyme production was expressive, except for enterotoxin D. Biofilm production was positive in 88.7% of strains. The presence of the mecA gene was associated with a higher frequency of fever and abdominal pain. The logistic regression model showed that diabetes mellitus (p = 0.009) and β-hemolysin production (p = 0.006) were independent predictors of non-resolution of infection. The probability of resolution was higher among patients aged 41 to 60 years than among those >60 years (p = 0.02). A trend to higher death rate was observed for S. aureus episodes (9.7%) compared to CoNS episodes (2.5%), (p = 0.08), whereas resolution rates were similar. Despite the decline in incidence, S. aureus peritonitis remains a serious complication of PD that is associated with a high death rate. The outcome of this infection is negatively influenced by host factors such as age and diabetes mellitus. In addition, β-hemolysin production is predictive of non-resolution of infection, suggesting a pathogenic role of this factor in PD-related S. aureus peritonitis.

The role of virulence factors in the outcome of staphylococcal peritonitis in CAPD patients

Background

Peritonitis continues to be the most frequent cause of peritoneal dialysis (PD) failure, with an important impact on patient mortality. Gram-positive cocci such as Staphylococcus epidermidis, other coagulase-negative staphylococci (CoNS), and Staphylococcus aureus are the most frequent etiological agents of PD-associated peritonitis worldwide. The objective of the present study was to compare peritonitis caused by S. aureus and CoNS and to evaluate the factors influencing outcome.

Methods

Records of 86 new episodes of staphylococcal peritonitis that occurred between 1996 and 2000 in the Dialysis unit of a single university hospital were studied (35 due to S. aureus, 24 to S. epidermidis and 27 to other CoNS). The production of slime, lipase, lecithinase, nuclease (DNAse), thermonuclease (TNAse), α- and β-hemolysin, enterotoxins (SEA, SEB, SEC, SED) and toxic shock syndrome toxin-1 (TSST-1) was studied in S. aureus and CoNS. Antimicrobial susceptibility was evaluated based on the minimal inhibitory concentration determined by the E-test. Outcome predictors were evaluated by two logistic regression models.

Results

The oxacillin susceptibility rate was 85.7% for S. aureus, 41.6% for S. epidermidis, and 51.8% for other CoNS (p = 0.001). Production of toxins and enzymes, except for enterotoxin A and α-hemolysin, was associated with S. aureus episodes (p < 0.001), whereas slime production was positive in 23.5% of CoNS and 8.6% of S. aureus strains (p = 0.0047). The first model did not include enzymes and toxins due to their association with S. aureus. The odds of resolution were 9.5 times higher for S. epidermidis than for S. aureus (p = 0.02) episodes, and were similar for S. epidermidis and other CoNS (p = 0.8). The resolution odds were 68 times higher for non-slime producers (p = 0.001) and were not influenced by oxacillin resistance among vancomycin-treated cases (p = 0.89). In the second model, the resolution rate was similar for S. aureus and S. epidermidis (p = 0.70), and slime (p = 0.001) and α-hemolysin (p = 0.04) production were independent predictors of non-resolution.

Conclusion

Bacterial species and virulence factors rather than antibiotic resistance influence the outcome of staphylococcal peritonitis.

Isolation of exfoliative toxin from Staphylococcus hyicus subsp. hyicus and its exfoliative activity in the piglet

Exfoliative toxin was isolated from the sterile cell-free filtrate of 24 h culture of Staphylococcus hyicus subsp. hyicus strain P-1. The partial purification of exfoliative toxin produced by S. hyicus (shET) was performed by precipitation with 50-80% saturated ammonium sulfate, gel filtration on a Sephadex G-75 column and column chromatography on DEAE-cellulose. Partially purified shET (pp-shET) caused exfoliation in piglets at 8 to 12 h after intradermal or subcutaneous injection. However, heat-treated pp-shET did not cause exfoliation in piglets for up to 24 h after injection. On histopathological examination of the skin at 12 h after injection of pp-shET, an intraepidermal cleavage plane was shown between the stratum corneum and stratum granulosum and at the stratum granulosum.

Bacteriological quality of on-farm manufactured goat cheese

The bacteriological quality of 198 ripened soft or semi-soft goat cheeses obtained from dairy farms and the retail trade was investigated. The cheeses were examined for total counts of aerobic bacteria, coliform bacteria (37 and 44 degrees C respectively), enterococci, coagulase positive staphylococci, Bacillus cereus and Clostridium perfringens. Cheeses obtained from dairy-farms were also determined for pH value. In terms of all tests performed, cheeses made of heat-treated milk with starter culture had the best prospects for fulfilling the criteria for 'fit for consumption'. Cheeses made of raw milk without starter culture made up the most unsatisfactory group from a food-hygiene point of view. Bacteriological guidelines for on-farm manufactured goat cheese are suggested.

Staphylococcal food poisoning from sheep milk cheese

Cheese made from sheep milk was implicated in food-poisoning incidents in December 1984 and January 1985. Bacteriological examination of batches of cheese failed to reveal a viable pathogen but enterotoxin A produced by Staphylococcus aureus was present. This was the first time that enterotoxin was detected in a food produced in the UK which was associated with poisoning and from which viable Staph. aureus could not be isolated. Subsequent detailed examination of milk, yoghurt and cheese from the same producer revealed that contamination with Staph. aureus was associated with post-infection carriage as well as clinical illness in ewes on the farm. Strains producing enterotoxon. A were still intermittently present in the bulk milk used for cheese production nearly 2 years afterwards, apparently in the absence of clinical illness in the sheep. The possible effects of heat treatment are discussed. Any changes in legislation should cover all non-human mammalian milk used for human consumption.

Specificity, cross-reactivity and competition profile of monoclonal antibodies to staphylococcal enterotoxins B and C1 detected by indirect enzyme-linked immunosorbent assays

A group of monoclonal antibodies to the staphylococcal enterotoxins B and C1 without any cross-reactivity to the other known staphylococcal enterotoxins A, C2, C3, D and E was developed. The monoclonal antibodies were compared in competition ELISA's with regard to affinity and epitope recognition. Three different groups could be classified: Group 1, consisting of the MAbs B/3-4 and B/3-8, recognizes in identical manner staphylococcal enterotoxin B. Also group 2 (MAb B/3-5) recognizes only staphylococcal enterotoxin B, yet group 1 and 2 do not compete with each other in the competition ELISA and therefore own different paratopes. Group 3 (MAb C1/2-3 and C1/4-6) reacts exclusively with staphylococcal enterotoxin C1, not even with staphylococcal enterotoxins C2 and C3.

Synthetic oligodeoxyribonucleotide probes for detection of Listeria monocytogenes

A 500-base-pair DNA fragment of a presumptive beta-hemolysin gene of Listeria monocytogenes has been used to identify this organism by a modified colony hybridization technique. We have cloned this DNA fragment into M13 bacteriophage vectors and sequenced it by a dideoxynucleotide sequencing technique. From this sequencing information, several oligodeoxyribonucleotides were synthesized and used as synthetic probes to identify L. monocytogenes. The probes were specific for L. monocytogenes and did not react with any other Listeria strains in a colony hybridization assay. In particular, one of these probes (AD07) was used to detect L. monocytogenes in artificially contaminated raw-milk and soft-cheese samples.

Synthetic enterotoxin B DNA probes for detection of enterotoxigenic Staphylococcus aureus strains

DNA-DNA colony hybridization experiments with three different synthetic probes were carried out with 210 strains of Staphylococcus aureus. The synthetic probes encoded the amino acids 15 to 29 (probe 1), 179 to 192 (probe 2), and 207 to 219 (probe 3) of staphylococcal enterotoxin B (SEB). The amino acid sequences of these parts of SEB are identical to those of SEC1. All 21 SEB-producing strains tested reacted with each of the three probes. Of the 69 SEC-producing strains, 21 reacted with probe 1, none reacted with probe 2, and all 69 reacted with probe 3. With other strains no hybridization signals were obtained. The results presented here show that with a single synthetic DNA probe (probe 3) both SEB- and SEC-producing strains are detectable.

A quantitative study of enterotoxin production by sheep milk staphylococci

Of 124 staphylococcal strains isolated from sheep milk, 78 produced enterotoxin A, B, C, or D when evaluated by an enzyme-linked immunosorbent assay. Enterotoxins A and D, elaborated by 44 and 43 strains, respectively, showed the highest incidence. Enterotoxin production by coagulase-negative strains (one Staphylococcus cohnii, three S. epidermidis, five S. haemolyticus, and four S. xylosus) was detected. Linear and logarithmic-logarithmic regressions of optical density on enterotoxin concentration yielded the best-fitting equations for enterotoxin quantitation. A significantly higher incidence of enterotoxin producers and significantly higher levels of enterotoxins produced were recorded for coagulase-positive, thermostable nuclease-positive, hemolysis-positive, or mannitol-positive strains. Mannitol utilization was the best test for discriminating between enterotoxigenic and nonenterotoxigenic staphylococci.

Growth and enterotoxin production of Staphylococcus aureus in shrimp

Strains of Staphylococcus aureus isolated from shrimp were examined for phage pattern and enterotoxin production; 63% of the strains isolated from North Sea shrimp were typable with the International and additional set of phages, as were 38% of the strains isolated from South-East Asian shrimp. Staphylococcal enterotoxin(s) (SE) were produced by 48% and 35% of strains isolated from North Sea and South-East Asian shrimp respectively. Growth and enterotoxin production by S. aureus in shrimp was examined in storage experiments at 22 degrees C. S. aureus increased by 1-2 log units in 24 h when the organism was only a minor part of the total microflora of shrimp. When S. aureus was an equivalent part of the total flora its numbers increased by 3-4 log units in 24 h. Enterotoxins A and B became detectable when the number of S. aureus exceeded 10(7) per g in aseptically peeled shrimp. Results indicate that S. aureus is able to produce enterotoxin in shrimp, but its production depends upon a number of factors, including the relationship between S. aureus and competitive micro-organisms. It is concluded that the presence of S. aureus on commercially produced shrimp represents a potential hazard to health.

Prevalence of enterotoxigenic staphylococci in nose, throat and skin lesions in meat-workers

The frequency of enterotoxigenic coagulase-positive and coagulase-negative staphylococci in nose and throat and in hand lesions was investigated in 86 meat cutters and dressers. Enterotoxin-producing staphylococci were demonstrated in nasal swabs from 22% of clinically well workers and from 42% of a group with mild coryza. The corresponding rates in throat swabs were 6 and 12%. Four of 16 superficial lesions of the hand harbored enterotoxigenic staphylococci. The implications for contamination of food and outbreaks of staphylococcal food poisoning are discussed.

Incidence and properties of Staphylococcus aureus associated with turkeys during processing and further-processing operations

The incidence of Staphylococcus aureus on turkeys sampled at various stages of processing and further-processing was determined on four occasions at each of three different processing plants. For freshly-slaughtered birds, counts from neck skin varied from plant to plant over the range less than 10(2) to greater than 10(5)/g but in all cases the corresponding counts obtained from carcasses sampled after chilling rarely exceeded 10(3)/g and the same was true for samples of mechanically recovered meat (MRM), the final raw product examined. Despite the limited susceptibility of isolates from the different factories to typing by means of either standard human or poultry bacteriophages (55-94% untypable), evidence was obtained with the aid of biotyping for the presence of both human and animal-derived strains. However, some biotypes isolated from MRM were not detected at earlier stages of processing. At one processing plant, an "indigenous' type of S. aureus was clearly demonstrated. It occurred in high numbers in the defeathering machines (up to 10(5)/swab), was found on carcasses at all subsequent stages of processing over the survey period and was shown to survive routine cleaning and disinfection procedures. Isolates of this type produced unusually large amounts of extracellular "slime' in artificial culture. Two of the three processing plants yielded isolates which were enterotoxigenic. Of 55 strains from Plant 1, 60% produced enterotoxin C and all were of the "indigenous' type. In the case of Plant 2, only two type D- and one type F-producing strain were found.

Enterotoxin production by strains of Staphylococcus aureus isolated from clinical and non-clinical specimens with special reference to enterotoxin F and toxic shock syndrome

Enterotoxin production by strains of Staphylococcus aureus isolated from clinical specimens of human and animal origin and from healthy human carriers was investigated. All nine patients admitted to hospital with symptoms of toxic shock syndrome (TSS) yielded enterotoxin-producing strains of S. aureus. Eight of these produced staphylococcal enterotoxin F (SEF). A significantly smaller proportion of strains (42% of 50 strains tested) isolated from other clinical specimens of hospitalized patients produced SEF. Production of SEF by strains isolated from clinical specimens of animal origin (48 strains) was not observed. Twenty-nine per cent of 24 S. aureus strains isolated from noses of hospital staff produced SEF. This result was not significantly different from that obtained from strains isolated from clinical specimens other than TSS. A similar percentage of strains isolated from healthy human carriers outside hospital produced SEF (25% of 24 strains tested). The results indicated that enterotoxin production, especially that of SEF, is associated with S. aureus isolated from patients suspected of TSS. There was no indication of an association between S. aureus isolated from other staphylococcal infections and SEF production. All strains were phage typed and 79% of the strains belonging to the international phage-group I produced SEF. All strains lysed by phage 187 were found to produce SEF.

Single radial immunodiffusion method for screening Staphylococcal isolates for enterotoxin

A direct system for screening large numbers of staphylococcal isolates for enterotoxin production has been developed. The system employs polyvalent (serotypes A, B, C, D, and E) immunodiffusion assay slides in conjunction with a multiple-culturing system for toxin production. With the combined system, as many as 50 cultures can be screened simultaneously on a single assay slide having a sensitivity of about 0.3 microgram/ml. The system should be useful for detecting potential enterotoxin in foods containing a predominance of non-enterotoxigenic strains.

Quantitative, radial diffusion slide assay for staphylocoagulase

A simple, quantitative radial diffusion assay for staphylocoagulase in culture fluids, using microscope slides coated with a thin layer of agar containing plasma and fibrinogen, was developed. No prior purification of the enzyme was needed, and only small quantities, 7 microliter, were required for each test. This method is particularly suitable for objectively comparing the relative amounts of coagulase produced by different cultures of Staphylococcus aureus.

Pathogenic, enterotoxin-producing staphylococci in mink feed and mink feed raw materials

Samples of 51 mink feeds and 101 raw material batches were analysed for pathogenic staphylococci. Of the feed samples 37 % were contaminated with pathogenic staphylococci, the mean count being 3.02 log CFU (colony forming units)/g and the highest count being 4.48 log CFU/g of feed. Of the raw materials investigated, slaughter-house offals were most frequently contaminated and contained highest counts of S. aureus, 60 % of the samples being positive with a mean log count of 3.86/g and a maximum of 5.70/g. Forty-eight staphylococcal isolates were tested for eniterotoxin production. Toxin A, B or G were produced by eight isolates, A being the most common. None of the isolates produced B or E toxins.

Staphylococcal enterotoxin and thermonuclease production during induced bovine mastitis and the clinical reaction of enterotoxin in udders

Enterotoxin A- and C-producing strains of Staphylococcus aureus and partially and extensively purified enterotoxin A were inoculated into the udder quarters of cows. In the course of experimentally induced mastitis caused by the inoculated S. aureus strain, enterotoxin C but not A was detected in the infected udder. Enterotoxin C was observed in mastitic milk samples at very low S. aureus population levels (10(2) to 10(3) colony-forming units per ml). The results suggest that either the synthesis of enterotoxin C is stimulated in vitro or that growth of S. aureus cells in udders was, in fact, higher than the colony-forming unit values indicated. Thermonuclease was shown to be excreted into mastitic milk at a slower rate than was enterotoxin. An inoculation of 1 microgram of enterotoxin A in autogenic milk returned to the udder caused clinical reactions (swelling, palpation sensitivity, and increase in the level of somatic cells) within 6 h.

The biochemical activity of enterotoxin and non-enterotoxin producing staphylococci

One hundred and sixty-nine staphylococcal strains of human origin have been tested for production of enterotoxin A, B or Ci, coagulase activity, DNase activity, typical growth on ETGP-agar, hemolysin production and the breakdown of mannitol under aerobic conditions. Very good correlation was observed between enterotoxin production and coagulase activity, in that 82 % of the enterotoxin producing strains also synthesized coagulase. The correlation between DNase activity and positive reaction in mannitol to enterotoxin production was also good (80 % of the enterotoxic strains produced both DNase and aerobic acid from mannitol). Of the enterotoxin producing strains 66 % hemolysed bovine erythrocytes and 61 % were ETGP-positive. However, the frequency of hemolysing respectively ETGP-positive but non-enterotoxin producing strains was very high, viz. 46 % respectively 32 %. It is concluded that enterotoxin production can not to a satisfactory degree of security be predicted by means of the other biochemical characters.

Effect of starter culture on staphylococcal enterotoxin and thermonuclease production in dry sausage

Different amounts of enterotoxin A-, B-, and C1-producing staphylococci were added to dry sausage prepared by normal processes, either alone or in conjunction with a starter culture (micrococci and lactobacilli). The sausage was examined after 0, 3, 7, 14, and 30 days for staphylococci, micrococci, and lactobacilli, and measurements were made of water activity, pH, enterotoxin, and thermostable nuclease. The results showed that in the absence of starter culture measurable amounts of enterotoxin A were formed in a 200-g sample of dry sausage in 3 days, the level of Staphylococcus aureus infection being over 10(6) cells/g. Enterotoxin B was not found, although the total number of staphylococci was over 10(8) cells/g. Enterotoxin C1 was observed when the Staphylococcus count was about 8 X 10(7) cells/g, but was no longer detectable after 7 days. The starter culture prevented the production of enterotoxin A in all cases investigated. By contrast, a very high-level inoculation of an enterotoxin C1-producing strain gave a positive result after 3 days of incubation even in the presence of a starter culture. Heat-stable nuclease was observed in all sausages to which enterotoxin-producing staphylococci were added. The cell count determined in a sample of sausage had no definite correlation with the thermonuclease activity of the sample.

Deoxyribonucleic acid base composition and biochemical properties of certain coagulase-negative enterotoxigenic cocci

Eight coagulase-negative, enterotoxigenic strains of cocci and one weakly coagulase-positive strain isolated from a number of different sources, including cases of food poisoning incidents, were evaluated for their relationship to Staphylococcus aureus on the basis of deoxyribonucleic acid (DNA) buoyant density and physiological studies. One strain of cocci produced enterotoxins A and C, two strains produced types B and C, four strains produced only type C, and one strain only type D. The enterotoxin produced by one strain of cocci was serologically untypable. None of the test organisms produced detectable amounts of enterotoxin in broth cultures. The test strains of cocci exhibited the following profile: all produced catalase; all grew anaerobically and fermented glucse; five were sensitive to lysostaphin; the percentage of guanine plus cytosine content of their DNA varied from 32.7 to 37.6; five produced acid from mannitol both aerobically and anaerobically; two formed delta-hemolysin; five produced phosphatase and acetoin; and all produced heat-stable nuclease. None of the organisms exhibited typical characteristics of S. aureus, S. epidermidis, or S. saprophyticus. On the basis of the present data and data reported elsewhere, these organisms should be considered as variants or mutants of S. aureus.

Detecting the enterotoxigenicity of Staphylococcus aureus strains

An optimal sensitivity plate method for examining large number of staphylococcal strains for production of the known enterotoxins (A-E) is presented. Small volumes of relatively concentrated enterotoxin are produced by the semi-solid agar, cellophane-over-agar, or sac culture techniques. Detection of the enterotoxin in the supernatant fluid is accomplished with the optimal sensitivity plate method. In this method small plastic petri dishes (50 mm) were used for a modified Ouchterlony of high sensitivity.

Stomach fermentation in East African Colobus monkeys in their natural state

The microbial fermentation in the stomachs of two monkeys, Colobus polykomos, collected in Kenya, was studied. The gas accumulated within the stomach contained H(2) but no CH(4). Volatile fatty acid concentrations were high, but accumulated acid prevented determination of the fermentation rate in untreated, incubated stomach contents. Upon addition of bicarbonate, a very rapid rate could be demonstrated. Some D- and L-lactate were in the stomach contents. Starchy seeds or fruits rather than leaves appeared to have been consumed. Microscopically, the most prominent microorganisms seen were large, very refringent cocci, possibly Sarcina ventriculi, and various smaller cocci and rods. The 28 cultured strains of bacteria included 14 Staphylococcus, 2 Streptococcus, 10 Propionibacterium, and 2 Peptostreptococcus. The culture count constituted 10 to 20% of the direct count. No protozoa or cellulolytic bacteria were found.

Rapid, sensitive assay for staphylococcal enterotoxin and a comparison of serological methods

Reversed passive hemagglutination was used to assay enterotoxin in culture filtrates and in food samples. With cells tanned and then sensitized with antitoxin globulin and preserved with either formaldehyde or pyruvic aldehyde, as little as 0.0007 mug of enterotoxin was detectable. The results of hemagglutination tests compared well with those obtained by quantitative precipitin tests or by immunodiffusion, but hemagglutination was 50 to 100 times more sensitive than the immunodiffusion technique. In addition, results of the hemagglutination test were available within a few hours, and neither elimination of interfering proteins from food extracts nor concentration of the sample, both of which are necessary for immunodiffusion, was required for this procedure.