Differentiation of toxigenic Staphylococcus aureus in staphylococcal isolates from prepared and frozen foods by combined arbitrarily primed polymerase chain reaction and DNA probe

In prepared and frozen flamenquín and hake fish fingers Staphylococcus aureus as sanitary hazards have been detected. In the present work, a combined method that includes an arbitrarily primed PCR (AP-PCR) and a mixed DNA probe hybridisation designed for the enterotoxigenic genes sea, seb, sec, and sed will be assayed to differentiate enterotoxigenic S. aureus from other staphylococcal species isolated during the processing of prepared and frozen foods. From the protocols tested for the AP-PCR, the highest number of amplification bands showing the best resolution was achieved at 30 degrees C annealing and 35 degrees C extension temperatures. Several staphylococci identified by a biochemical test as S. aureus showed in the AP-PCR analysis different banding patterns to the references S. aureus. The isolates, were investigated by slot blot hybridisation for genes encoding A, B, C, and D staphylococcal enterotoxins to determine their enterotoxigenic potential. Several isolates characterised by the AP-PCR analysis as S. aureus hybridised with the DNA probe mixture. The combined AP-PCR and DNA probe hybridisation assayed was able to differentiate toxigenic S. aureus from other staphylococcal species from prepared and frozen foods. This method could be considered as microbial quality assurance in these products.     

Determination of Enterotoxigenic and Methicillin Resistant Staphylococcus aureus in Ice Cream

The aim of this study was to determine the prevalence of enterotoxigenic and methicillin‐resistant Staphylococcus aureus in ice creams. After culture‐based identification of isolates, the presence of 16S rRNA and nuc was confirmed by mPCR. S. aureus was identified in 18 of 56 fruity (32.1%), 4 of 32 vanilla (12.5%), and 1 of 12 chocolate (8.3%) ice creams. S. aureus was identified as 38 isolates in 23 ice cream samples by culture‐based techniques, but only 35 isolates were confirmed by PCR as S. aureus. To determine the enterotoxigenic properties of PCR‐confirmed S. aureus isolates, a toxin detection kit was used (SET RPLA®). Of the 12 enterotoxigenic S. aureus isolates, 9 SEB (75%), 1 SED (8.3%), 1 SEB+SED (8.3%), and 1 SEA+SEB+SED (8.3%) expressing isolates were found. The presence of enterotoxin genes (sea, seb, sed) was identified in 13 (37.1%) out of 35 isolates by the mPCR technique. In the ice cream isolates, the sea, seb, and sed genes were detected: 1 sea (7.6%), 9 seb (69.2%), 1 sed (7.6%), 1 seb+sed (7.6%), and 1 sea+seb+sed (7.6%), respectively. The sec gene was not detected in any of these isolates. One of the 35 (2.8%) S. aureus strain was mecA positive.     

Differentiation of Clostridium perfringens and Clostridium botulinum from non‐toxigenic clostridia,isolated from prepared and frozen foods by PCR‐DAN based methods

During the elaboration process of prepared and frozen foods, Clostridium sp. have been reported. From those microorganisms, C. perfringensand C. botulinum may pose a high risk for the consumers. To avoid these pathogenic organisms an HACCP program should be implemented, but in addition sensitive and moderately time consuming microbiological methods for monitoring C. perfringens and C. boulinum should be established. In this work, an RFLP analysis of the 16S rDNA will be developed to differentiate C. perfringens from other Clostridium sp. In addition, a PCR protocol, will be assayed to detect C. botulinum. Both two methods will be compared with biochemical characterization by API system. The restriction analysis of the 16S rDNA with Taq I and RsaI showed at least the same sensitivity to differentiate C. perfringensfrom clostridial isolates as biochemical identification. However, the former method takes only 8–10 h of analysis as compared with 24–48 h required for biochemical characterization. With the specific PCR protocol to detect C. botulinum a band of 1.1 kbp was obtained derived from the specific amplification of BoNT genes, taking 6–8 h for analysis. Both two molecular DNA based methods should be considered as verification techniques of pathogenic clostridia in the HACCP program.     

Prevalence and Characteristics of Enterotoxin B‐Producing Staphylococcus aureus Isolated from Food Sources: A Particular Cluster of ST188 Strains was Identified

The aim of this study was to investigate the prevalence and characteristics of staphylococcal enterotoxin B (SEB) producing Staphylococcus aureus (S. aureus) isolated from food sources. A total of 412 S. aureus isolates were recovered from 1970 milk and dairy samples (n = 236) and 2450 meat samples (n = 176) in China from 2009 to 2014. Of the 412 isolates, 124 isolates were tested positive for 1 or more classical staphylococcal enterotoxin (SE) genes using PCR, and 31 isolates were positive for seb gene and further proved to be SEB‐producing. Four SE profiles were observed among 31 SEB‐producing isolates when investigated using ELISA kit, that is, SEB (16 isolates), SEA+SEB (6 isolates), SEB+SEC (6 isolates), and SEB+SED (3 isolates). Thirteen sequence types (STs) were identified in the 31 SEB‐producing S. aureus isolates using multilocus sequence typing (MLST). The 3 most detected STs were ST1 (7 isolates), ST188 (6 isolates), ST59 (3 isolates). Two distinct clusters were identified by pulsed‐field gel electrophoresis (PFGE), each of which showed excellent consistency with ST188 and ST1 achieved by MLST, respectively. In summary, this study reveals that various SE profiles are observed in SEB‐producing S. aureus isolates and the great part of SEB‐producing S. aureus isolates are showed as clusters. Especially, a particular cluster of ST188 strains was observed in SEB‐producing S. aureus isolates which was associated with outbreaks of SFP and needs further attention.     

Distribution of newly described enterotoxin-like genes in <Emphasis Type="Italic">Staphylococcus aureus</Emphasis> isolated from ready-to-eat foods in Korea

To investigate the distribution of staphylococcal enterotoxin-like (SEl) genes in Staphylococcus aureus from food, a total of 154 S. aureus isolates from ready-to-eat (RTE) foods in Korea were analyzed by mutiplex PCR for the detection of the following 9 staphylococcal enterotoxin-like genes; sek, sel, sem, sen, seo, sep, seq, ser, and seu. Seventy-nine isolates (51.3%) were found to have at least one of SEl genes. The major SEl genes were sek, sem, sen, and seq. Other SEl genes found in the isolates were seo (21 isolates, 13.6%), seu (12 isolates, 7.8%), sep (8 isolates, 5.2%), sel (7 isolates, 4.5%), and ser (2 isolates, 1.3%). Most (95%) of the isolates with staphylococcal enterotoxin (SE) genes were also carried SEl genes. The genes seg, sei, sem, and sen were all detected in the same isolates. Ninety-seven % of isolates with seg+sei+sem+sen also contained seo or seu. Ninety-four % of isolates with sea+seh were found to coexist with sek+seq. The toxic shock syndrome toxin gene, tst-1, was found in all isolates with egc-2, including seg, sei, sem, sen, and seu. The coexistence of SE and SEl genes in S. aureus isolates from RTE foods can be explained by the mobile genetic elements. Because of the mobile genetic element, SE and SEl genes of S. aureus in foods may be transferable to nontoxigenic S. aureus and other food pathogens. Additional studies must be conducted to prevent spread of pathogenic genes such as enterotoxin gene.     

Benefits of the Combined Use of Immunological- and PCR-Based Methods for Determination of Staphylococcal Enterotoxin Food Safety Criteria in Cheeses

The aim of this study, performed under official controls, was to assess the relationship between the content of staphylococcal enterotoxins SEA to SEE in cheese samples and the enterotoxigenic potential of Staphylococcus aureus isolates. The level of correlation may further underline the benefit of using complementary approaches based on immunological tests and the PCR method to improve the diagnosis for determination of staphylococcal enterotoxin food safety criteria in cheeses submitted to official controls and own checks.     

Comparison of the enterotoxigenic types,toxic shock syndrome toxin I (TSST-1) strains and antibiotic susceptibilities for enterotoxigenicStaphylococcus aureusstrains isolated from food and clinical samples

The distribution of enterotoxin types and toxic shock syndrome toxin I (TSST-1) strains for 176Staphylococcus aureusstrains obtained from food samples and 62S. aureusstrains isolated from clinical samples were compared. It was found that for both the food and clinical isolates, staphylococcal enterotoxin A (SEA) strains accounted for the major part (75% and 45% of the total enterotoxigenic strains for food and clinical isolates, respectively) followed by SEB or SEAB, SEC and SED strains. For food isolates, none of theS. aureusstrains was TSST-1 strain while for clinical isolates, three strains (1 SEC, 1 SED and 1 SEAB strain) were found to be TSST-1 strains. When susceptibilities for these enterotoxigenicS. aureusstrains to antibiotics, such as penicillin, oxacillin, vancomycin, methicillin, streptomycin, tetracycline, gentamycin and kanamycin were compared, results showed that 51.6% of the food isolates were resistant to penicillin G only but sensitive to the other antibiotics tested. Also, 8 of the 64 enterotoxigenic strains isolated from food samples were all sensitive to antibiotics while none of the enterotoxigenic strains from clinical samples showed this antibiotic susceptibility pattern. No methicillin resistantS. aureus(MRSA) strains could be found among the food isolates. On the other hand, the majority (42.4%) of the enterotoxigenicS. aureusstrains from clinical samples were penicillin and/or other antibiotics resistant MRSA strains. Since MRSA strains often posed the therapeutic problem, the MRSA strains were further confirmed by PCR assay using the primers specific formecA gene. It was found that results obtained from the disc agar diffusion method and the PCR method were the same.     

Characterization for enterotoxin production,virulence factors,and antibiotic susceptibility of Staphylococcus aureus isolates from various foods in Portugal

Staphylococcus aureus represents a public health challenge worldwide. The aim of this study was the characterization of different food isolates of S. aureus on the basis of their production of enterotoxins, hemolysins and resistance to antibiotics. A total of 148 coagulase-positive staphylococcal strains isolated from different food origins were identified to the species level. By multiplex PCR, 69% of the isolates were shown to be enterotoxigenic (SEs); the most common were sea seg, sea seg sei and seg sei. According to CLSI [CLSI, Clinical and Laboratory Standards Institute, 2007. Performance Standards for Antimicrobial Susceptibility Testing; Fifteenth Informational Supplement. CLSI document M100-S15. Clinical and Laboratory Standards Institute, Wayne, PA], 38% of the isolates were resistant to oxacillin (≥6 μg/mL; MRSA positives) but only 0.68% showed the presence of mecA gene. 70 and 73% of the S. aureus strains were resistant to β-lactams, ampicillin and penicillin, respectively. The virulence pattern was demonstrated to be origin and strain dependent. These findings emphasise the need to prevent the presence of S. aureus strains and SEs production in foods.     

Detection of Enterotoxigenic Staphylococcus aureus in Raw Milk and Dairy Products by Multiplex PCR

Abstract: The aim of this study was to investigate the prevalence of enterotoxigenic Staphylococcus aureus in 122 samples, including 60 raw milk, 32 white cheese, 10 kashar cheese, 10 butter, and 10 ice cream samples obtained from Samsun province, Turkey. In this study, S. aureus was detected in 64 samples, including raw milk (45/60; 75%), white cheese (12/32; 37.5%), kashar cheese (3/10; 30%), butter (3/10; 30%), and ice cream (1/10; 10%) samples. A total of 81 isolates were identified as S. aureus by PCR with the presence of 16S rRNA and nuc genes. The presence of genes encoding the staphylococcal enterotoxins (SEs) SEA, SEB, SEC, and SED was detected by multiplex PCR. According to the analysis, seven isolates from the raw milk samples (7/51; 13.7%) were enterotoxigenic; five of them produced SEA (5/7; 71.4%), one produced SEB (1/7; 14.2%), and one produced SEA+SEB (1/7; 14.2%). Four isolates from the white cheese samples (4/21; 19%) produced the SEA (1/4; 25%), SEC (1/4; 25%), SED (1/4; 25%), and SEA+SED (1/4; 25%) toxins. Two isolates from the kashar cheese samples (2/4; 50%) were found to be enterotoxigenic; one produced SEA (1/2; 50%) and the other produced SED (1/2; 50%). One isolate from the butter samples (1/4; 25%) showed enterotoxigenic character (SEB, 1/1; 100%). The products were found to be potentially hazardous to public health because of the fact that levels of contamination were higher than 105–106 cfu/g ml in 39% (25/64, 17 raw milk, 7 white cheese, and 1 butter) of the analyzed samples.     

Rapid whole protein quantification of staphylococcal enterotoxin B by liquid chromatography

Food poisoning caused by Staphylococcus aureus is one of the most important foodborne diseases in the world. The ability of these bacteria to produce one or more enterotoxins in milk and dairy products is linked to staphylococcal food poisoning. Enterotoxin B (SEB) is an exotoxin produced by S. aureus and is one of the compounds most frequently involved in staphylococcal food poisoning worldwide. In this work, 20 samples of milk collected from restaurants have been studied for the presence of S. aureus enterotoxigenic strains. All the isolates from milk samples have been analysed by liquid chromatography-coupled with diode array detector for the rapid identification and quantification of SEB as intact protein. Limit of detection and limit of quantification values were 0.5 and 1 μg/mL, respectively. S. aureus was found in 35% of analysed samples but only one of them was an enterotoxigenic strain, which produced staphylococcal enterotoxin B at levels of 3.6 μg/mL.     

Prevalence of staphylococcal enterotoxins, toxin genes and genetic-relatedness of foodborne Staphylococcus aureus strains isolated in the Marmara Region of Turkey

Staphylococcus aureus is a major foodborne pathogen and it has the ability to produce a number of extracellular toxins. We analyzed 1070 food samples obtained from retail markets and dairy farms in the Marmara Region of Turkey for the presence of S. aureus. Out of 147 isolates, 92 (62.6%) were enterotoxigenic. PCR was used to investigate the presence of staphylococcal enterotoxin genes (sea, seb, sec, sed, see, seg, seh, sei, sej, sek, sel, sem, sen, seo, sep, seq and seu), exfoliative toxin genes (eta and etb) and the toxic − shock syndrome toxin gene (tst). The PCR results showed that 53.3% of the isolates contained staphylococcal enterotoxin-like (SEl) toxin genes (seg, seh, sei, sej, sek, sel, sem, sen, seo, sep, seq and seu) which were more frequent than classical enterotoxin genes (sea to see). Furthermore, seo, sei, sem, seg, seu and sec were found in 37.0, 32.7, 30.4, 29.3, 29.3 and 27.2% of the isolates, respectively. The tst gene was detected and confirmed by DNA sequencing in 9 isolates. The presence of eta and etb were not found in the isolates. Enterotoxigenic capabilities of isolates with SEA-SEE were investigated by ELISA. Enterotoxigenic S. aureus isolates produced one to three enterotoxins, with the most frequently produced types being enterotoxin A and C. There was a correlation of 72.1% between production of a specific toxin and the presence of the respective genes. PFGE analysis was used to identify genetic-relatedness of enterotoxigenic S. aureus isolates and the results revealed that 13 groups of isolates from different or the same origin that contained the same genes showed 100% homology with indistinguishable band patterns. The other enterotoxigenic isolates showed related band patterns with 72-86% homology in sea-, 61-90% homology in sec-, 80-96% homology in seh-, and 69-96% homology in sep-positive isolates. To our knowledge, this is the first study to examine enterotoxins and related gene contents of S. aureus food isolates in the Marmara Region of Turkey.     

Differentiation of Clostridium perfringens and Clostridium botulinum from non-toxigenic clostridia, isolated from prepared and frozen foods by PCR-DAN based methods

During the elaboration process of prepared and frozen foods, Clostridium sp. have been reported. From those microorganisms, C. perfringens and C. botulinum may pose a high risk for the consumers. To avoid these pathogenic organisms an HACCP program should be implemented, but in addition sensitive and moderately time consuming microbiological methods for monitoring C. perfringens and C. boulinum should be established. In this work, an RFLP analysis of the 16S rDNA will be developed to differentiate C. perfringens from other Clostridium sp. In addition, a PCR protocol, will be assayed to detect C. botulinum. Both two methods will be compared with biochemical characterization by API system. The restriction analysis of the 16S rDNA with Taq I and Rsa I showed at least the same sensitivity to differentiate C. perfringens from clostridial isolates as biochemical identification. However, the former method takes only 8-10 h of analysis as compared with 24-48 h required for biochemical characterization. With the specific PCR protocol to detect C. botulinum a band of 1.1 kbp was obtained derived from the specific amplification of BoNT genes, taking 6-8 h for analysis. Both two molecular DNA based methods should be considered as verification techniques of pathogenic clostridia in the HACCP program.     

DETECTION OF STAPHYLOCOCCAL ENTEROTOXIN A FROM RICOTTA CHEESE BY CELL CULTURE

Staphylococcal food poisoning (SFP) is a very common foodborne disease. Milk and dairy products are frequently contaminated with enterotoxigenic Staphylococcus aureus, which are often involved in SFP. These foods may become contaminated owing to subclinical staphylococcal mastitis or during handling, storage and trade. For sanitary purposes, an effective approach is to detect the staphylococcal enterotoxins directly in foods, rather than detect, count and type the isolated S. aureus strains, because the toxin is the causative agent of foodborne illness. This paper illustrates a cell‐based bioassay that uses the PEB (bovine embryo lung cells) cell line to detect staphylococcal enterotoxin type A (SEA) directly from artificially contaminated ricotta cheese. The test was able to detect SEA in the contaminated samples after 24 and 48 h of incubation at 37C, while results were uncertain when the samples were incubated for 72 h. The test proved to be easy to use and rapidly provided results.     

Phenotypic and Genotypic Antimicrobial Resistance Traits of Foodborne Staphylococcus aureus Isolates from Shanghai

Staphylococcus aureus is a recognized pathogen in humans, which causes nosocomial infections and food poisoning. The transmission of antibiotic resistant S. aureus (ARSA), especially methicillin‐resistant S. aureus, between food products and humans has become a serious problem. Hence, it is necessary to monitor S. aureus through the food supply chain. In this study, the disk diffusion method and epsilometer test were performed to determine the prevalence of ARSA in 78 foodborne isolates using 18 antibiotics. The highest resistance frequency was found for penicillin G (74.4%), followed by erythromycin (59.0%) and clindamycin (44.9%), whereas no vancomycin‐resistant isolates were found. The 78 isolates could be subtyped into 31 resistance profiles and 11 clusters based on their antimicrobial susceptibility. Furthermore, Polymerase chain reaction (PCR) screening for the presence of 13 genes conferring antibiotic resistance was conducted. The presence of resistance genes was relatively high: bla_TEM (80.8%), ermB (41.0%), grlA (38.5%), ermC (35.9%), and aac6’/aph2” (35.9%). The incidence of antibiotic resistance was significantly correlated to food types (p = 0.018), with isolates from meat and raw milk more resistant to antibiotics than those from frozen food and vegetables.     

Emergence of methicillin-resistant Staphylococcus aureus (MRSA) ST8 in raw milk and traditional dairy products in the Tizi Ouzou area of Algeria

Staphylococcus aureus is one of the leading causes of food-borne illness worldwide. Raw milk and dairy products are often contaminated with enterotoxigenic strains of this bacterium. Some of these strains carry antimicrobial resistance, leading to a potential risk for consumers. The aim of this study was to characterize S. aureus strains circulating in raw milk and traditional dairy products for carriage of staphylococcal enterotoxin (se) genes and antimicrobial resistance. Overall, 62 out of 270 samples (23%) were contaminated with S. aureus, and 69 S. aureus strains were identified. We studied the enterotoxin genes using 2 multiplex PCR targeting 11 se genes. Seventeen (24.6%) isolates carried one or more genes encoding for staphylococcal enterotoxins. The most commonly detected se genes were seb and sep, followed by seh, sea, and see. Using the disk diffusion method, we found that resistance to penicillin G and tetracycline was the most common. Eleven isolates of methicillin-resistant S. aureus (MRSA) carried the mecA gene. All MRSA isolates belonged to the same spa type (t024) and sequence type (ST8), and carried the seb and sep enterotoxin genes. However, none of them carried the Panton Valentine leukocidin gene (lukF/S-PV). The presence of enterotoxigenic S. aureus strains, including MRSA, in raw milk and dairy products, raises a serious public health concern, because these strains may cause food poisoning outbreaks, be disseminated to the population, or both.     

Molecular and phenotypic characterization of Staphylococcus aureus strains isolated from carcass swabs and carcass drips of chickens slaughtered in the informal market in Gauteng Province,South Africa

The study was conducted to characterize Staphylococcus aureus strains from swabs and drips of dressed chicken carcasses sold at outlets in six townships in the informal market in Gauteng province, South Africa, using molecular and phenotypic methods. Seven genes (6 toxins and 1 antimicrobial resistance) comprising staphylococcal enterotoxin A (SEA), B (SEB), C (SEC), D (SED), exfoliative toxin A, toxic shock syndrome toxin, and MecA encoding methicillin resistance were assayed using polymerase chain reaction. The resistance of the S. aureus strains to 18 antimicrobial agents was determined using the disk diffusion method. The frequency of detection of the six toxin genes was sea (52.2%), followed by seb (10.9%), sec (6.5%), sed (2.2%), eta (93.5%), and tst (19.6%). The mecA gene was detected in 4.3% of the isolates. The predominant profiles of toxin genes detected were sea-eta (37.0%). All 63 isolates of S. aureus were resistant to one or more antimicrobial agents. The frequency of resistance was high to spectinomycin (98.4%), nalidixic acid (85.7%), and penicillin (84.1%), but low to gentamycin (1.6%) and cefotaxime (1.6%). The high frequency of toxin genes and antimicrobial resistance gene observed in S. aureus isolates from chicken could pose a challenge to food safety and may have therapeutic and zoonotic implications.     

Enterotoxin-producing Staphylococcus aureus genotype B as a major contaminant in Swiss raw milk cheese

The objective of this study was to characterize Staphylococcus aureus isolates from Swiss raw milk cheeses that had been found to be contaminated with coagulase-positive staphylococci and to estimate the frequency of the various genotypes, in particular the mastitis-associated Staph. aureus genotype B (GTB). The isolates were also tested for staphylococcal enterotoxin (SE) genes and other virulence factors. From 623 coagulase-positive staphylococci isolated from 78 contaminated raw milk cheeses, 609 were found to be Staphylococcus aureus. Genotyping of all Staph. aureus isolates was performed by PCR amplification of the 16S–23S rRNA intergenic spacer region, as this method was used previously to differentiate between mastitis subtypes associated with their clinical outcome. In total, 20 different genotypes were obtained and the 5 most frequently occurring genotypes were distributed in 6.4% or more of the samples. The enterotoxin-producing Staph. aureus GTB, known for its high contagiousness and increased pathogenicity in Swiss mastitis herds, was found to be the most abundant subtype at the sample level (71.8%) as well as among the isolates (62.0%). A subset of 107 isolates of the different genotypes were analyzed for the presence of SE genes and revealed 9 different SE gene patterns, with sed being most frequently detected and 26% being PCR-negative for SE genes. Almost all isolates of the major contaminant GTB contained the SE gene pattern sed, sej, ser, with half of them additionally carrying sea. Production of SE in vitro was consistent with the SE genes detected in most of the cases; however, some isolated GTB did not produce SEA. Staphylococcus aureus Protein A (spa) typing revealed 30 different subtypes and most GTB isolates belonged to the bovine spa type t2953; GTB/t2953 was linked among other subtypes to SE production in cheese and staphylococcal intoxication cases. Furthermore, 1 of the 623 isolates was a methicillin-resistant Staph. aureus, which was an seh-carrying Staph. aureus spa type tbl 0635 (non-GTB). We conclude that control and reduction of enterotoxigenic Staph. aureus GTB in dairy herds in Switzerland will not only prevent economic losses at the farm level but also improve the safety of raw milk cheeses; distribution of methicillin-resistant Staph. aureus via raw milk cheese is of less concern.     

A Study on the Growth Potential of Staphylococcus aureus In Boletus edulis, A Wild Edible Mushroom, Prompted by a Food Poisoning Outbreak

A dish of Boletus edulis, a wild edible mushroom, in vinegar caused staphylococcal food poisoning in 13 of 35 diners in a restaurant. Enterotoxicosis was confirmed by detection of toxins A and D in the dish. Staphylococcus aureus growth potential in B. edulis was studied by inoculating fresh and frozen and thawed bolete with S. aureus strains VTTE 530, 757, 793 and 805 and storing for 3 days at 15 and/or 21°C. Essentially no staphylococcal growth was observed in frozen and thawed mushrooms contaminated with strains 530, 793 or 805 and stored at 15 or 21°C. In fresh B. edulis the same strains showed slight growth at 21°C. Frozen and thawed bolete inoculated with strains 530 and 757 (isolated from mushroom soup, nonenterotoxigenic) supported staphylococcal growth in 2 days at 21°C from a level of 4.8±10⁴ and 5.4±10³ to 2.0±10⁶ and 7.0±10₇ cfu/g, respectively. Enterotoxin was not detected in these samples.     

Staphylococcus aureus Identification Characteristics and Enterotoxigenicity

Enterotoxigenicity and conventional tests for identification of Staphylococcus aureus were correlated for strains of staphylococci isolated from foods. These strains were examined for enterotoxin production, colonial morphology on Baird-Parker agar, coagulase activity with rabbit and pig plasma, thermostable nuclease (TNase) production, lysostaphin sensitivity and anaerobic utilization of glucose and mannitol. Enterotoxins A,B,C,D, and E were produced singly or in combination by 100 of the S. aureus strains; 51 strains produced no enterotoxin. False-negative rates in identifying the enterotoxigenic group as typical S. aureus were as follows: 11% for colonial morphology on Baird-Parker agar, 8% for coagulase activity with Difco rabbit plasma, 7% for TNase production, 4% for lysostaphin sensitivity and 2% and 4%, respectively, for the anaerobic utilization of glucose and mannitol. Consequently, none of these tests was reliable for differentiating toxigenic from nontoxigenic S. aureus..