Unveiling Staphylococcus aureus enterotoxin production in dairy products: a review of recent advances to face new challenges

Staphylococcus aureus in Dairy Industry: Enterotoxin Production, Biofilm Formation, and Use of Lactic Acid Bacteria for Its Biocontrol

Staphylococcus aureus is a well-known pathogen capable of producing enterotoxins during bacterial growth in contaminated food, and the ingestion of such preformed toxins is one of the major causes of food poisoning around the world. Nowadays 33 staphylococcal enterotoxins (SEs) and SE-like toxins have been described, but nearly 95% of confirmed foodborne outbreaks are attributed to classical enterotoxins SEA, SEB, SEC, SED, and SEE. The natural habitat of S. aureus includes the skin and mucous membranes of both humans and animals, allowing the contamination of milk, its derivatives, and the processing facilities. S. aureus is well known for the ability to form biofilms in food processing environments, which contributes to its persistence and cross-contamination in food. The biocontrol of S. aureus in foods by lactic acid bacteria (LAB) and their bacteriocins has been studied for many years. Recently, LAB and their metabolites have also been explored for controlling S. aureus biofilms. LAB are used in fermented foods since in ancient times and nowadays characterized strains (or their purified bacteriocin) can be intentionally added to prolong food shelf-life and to control the growth of potentially pathogenic bacteria. Regarding the use of these microorganism and their metabolites (such as organic acids and bacteriocins) to prevent biofilm development or for biofilm removal, it is possible to conclude that a complex network behind the antagonistic activity remains poorly understood at the molecular level. The use of approaches that allow the characterization of these interactions is necessary to enhance our understanding of the mechanisms that govern the inhibitory activity of LAB against S. aureus biofilms in food processing environments.

Investigating lactic acid bacteria genus Lactococcus lactis properties: Antioxidant activity, antibiotic resistance, and antibacterial activity against multidrug-resistant bacteria Staphylococcus aureus

Background

Lactic acid bacteria (LAB) are utilized as a starter culture in the manufacturing of fermented dairy items, as a preservative for various food products, and as a probiotic. In our country, some research has been carried out, even if LAB plays a principal role in food preservation and improves the texture and taste of fermented foods, that is why we tried to evaluate their probiotic effect. The objective of this research was to determine the antibacterial activity of Lactococcus lactis (L. lactis) against Staphylococcus aureus (S. aureus) ATCC 29213, investigate their antioxidant activity, and characterize their sensitivity against 18 antibiotics.

Methods

A total of 23 LAB (L. lactis subsp. cremoris, L. lactis subsp. Lactis diacetylactis, L. lactis subsp. lactis) were isolated from cow's raw milk. The antibacterial activity was performed using two techniques, competition for nutrients and a technique utilizing components nature, using the disk diffusion method. The sensitivity of the studied LAB to different antibiotics was tested on Man rogosa sharp (MRS) agar using commercial antibiotic disks. All strains of LAB were examined for their antioxidant activity. The antioxidant activity of L. lactis was tested by 2,2-diphenyl-1 picrylhydrazyl (DPPH).

Results

The results showed that the MRS medium was more adapted than Muller Hinton Agar (MHA) to investigate the antibacterial activity of L. lactis against S. aureus ATCC 29213. Also, L. lactis exhibited a notable degree of antibacterial activity against S. aureus ATCC 29213. L. Lactis subsp. Lactis displayed higher antibacterial activities, followed by L. lactis ssp. lactis biovar. diacetylactis, and lastly, L. lactis ssp. cremoris against S. aureus ATCC 29213. Lc 26 among all strains of L. lactis showed a high potential antibacterial activity reaching 40 ± 3 mm against S. aureus ATCC 29213. All strains of L. lactis showed a slightly moderate antioxidant activity (10.56 ± 1.28%-26.29 ± 0.05 %). The results of the antibiotic resistance test indicate that all strains of L. lactis were resistant to cefotaxime, sulfamethoxazole-trimethoprim, and streptomycin and were sensitive to Ampicillin, Amoxicillin, Penicillin G, Teicoplanin, Vancomycin, Gentamicin 500, Tetracycline, and Chloramphenicol. These test results indicate that this strain falls within the criteria of not posing any harmful effects on human health. The important antibacterial properties recorded for all L. Lactis strains were derived from the production of antibacterial active metabolites, such as protein, diacetyl, hydrogen peroxide, and lactic acid, together with the fight for nutrients.

Conclusion

This study suggests that the strains of L. lactis could be added as an antibacterial agent against S. aureus ATCC 29213 and can provide an important nutritional property for their antioxidant potential.

Growth of methicillin-resistant Staphylococcus aureus during raw milk soft cheese-production and the inhibitory effect of starter cultures

The consumption of raw milk or raw milk products might be a potential risk factor for the transmission of methicillin-resistant Staphylococcus aureus (MRSA). Therefore, we studied MRSA growth during raw milk soft cheese-production. Furthermore, we investigated the inhibitory effect of four starter cultures (Lactococcus lactis, Lacticaseibacillus rhamnosus, Lactiplantibacillus plantarum, Lactobacillus helveticus) on the growth of MRSA in a spot-agar-assay and in raw milk co-culture following a cheesemaking temperature profile. During the initial phases of raw milk cheese-production, MRSA counts increased by 2 log units. In the ripening phase, MRSA counts only dropped slightly and remained high up to the end of the storage. Comparable MRSA counts were found in the rind and core and strain-specific differences in survival were observed. In the spot-agar-assay, all four starter cultures showed strong or intermediate inhibition of MRSA growth. In contrast, in raw milk, only Lactococcus lactis strongly inhibited MRSA, whereas all other starter cultures only had minor inhibitory effects on MRSA growth. Our results indicate that MRSA follow a similar growth pattern as described for other S. aureus during raw milk soft cheese-production and illustrate the potential use of appropriate starter cultures to inhibit MRSA growth during the production of raw milk cheese.

In vitro co-culture of Clostridium scindens with primary human colonic epithelium protects the epithelium against Staphylococcus aureus

A complex and dynamic network of interactions exists between human gastrointestinal epithelium and intestinal microbiota. Therefore, comprehending intestinal microbe-epithelial cell interactions is critical for the understanding and treatment of intestinal diseases. Primary human colonic epithelial cells derived from a healthy human donor were co-cultured with Clostridium scindens (C. scindens), a probiotic obligate anaerobe; Staphylococcus aureus (S. aureus), a facultative anaerobe and intestinal pathogen; or both bacterial species in tandem. The co-culture hanging basket platform used for these experiments possessed walls of controlled oxygen (O2) permeability to support the formation of an O2 gradient across the intestinal epithelium using cellular O2 consumption, resulting in an anaerobic luminal and aerobic basal compartment. Both the colonic epithelial cells and C. scindens remained viable over 48 h during co-culture. In contrast, co-culture with S. aureus elicited significant damage to colonic epithelial cells within 24 h. To explore the influence of the intestinal pathogen on the epithelium in the presence of the probiotic bacteria, colonic epithelial cells were inoculated sequentially with the two bacterial species. Under these conditions, C. scindens was capable of repressing the production of S. aureus enterotoxin. Surprisingly, although C. scindens converted cholic acid to secondary bile acids in the luminal medium, the growth of S. aureus was not significantly inhibited. Nevertheless, this combination of probiotic and pathogenic bacteria was found to benefit the survival of the colonic epithelial cells compared with co-culture of the epithelial cells with S. aureus alone. This platform thus provides an easy-to-use and low-cost tool to study the interaction between intestinal bacteria and colonic cells in vitro to better understand the interplay of intestinal microbiota with human colonic epithelium.

Effect of biofilm on the survival of Staphylococcus aureus isolated from raw milk in high temperature and drying environment

Microbial contamination in dairy products is a momentous factor affecting food safety. Studies have shown that Staphylococcus aureus, which is an important causative agent of a range of infectious and foodborne diseases, may remain in raw milk after a series of complex processing processes. Although most S. aureus possess biofilm formation capacity, there are few studies concerning the role of biofilm formation of this bacterium in stress tolerance and longtime survival in the dairy products. In this study, we selected 5 S. aureus (RMSA1, RMSA2, RMSA3, RMSA4 and RMSA5) isolates from raw milk and investigated their virulence and biofilm characteristics. Results from biofilm assays showed that all 6 S. aureus strains (5 dairy isolates and 1 human-derived model strain NCTC8325) could form complete biofilms in vitro. The reverse transcription-PCR experiments confirmed that multiple genes related to virulence factors and biofilm formation were expressed in the 6 strains. Furthermore, we simulated the high temperature (at 60 °C for 30 min) and drying pressure (at 37 °C for 24 h) during dairy processing to detect the survival rate of strains culturedunderbiofilm or planktonic condition. The data showed that under high temperature and dry conditions, the survival rates of strains cultured under biofilm conditions were much higher than that of strains cultured under planktonic conditions. In addition, the adversity resistance associated with biofilm formation was more obvious in the milk-isolated strains compared with strain NCTC8325. This study provides evidence regarding the mechanisms of stress resistance of S. aureus strains isolated from raw milk and contribute to prevention of dairy product contamination caused by this bacterium.

Virulence factors and antimicrobial resistance in Staphylococcus aureus isolated from bovine mastitis in Brazil

This study aimed to evaluate virulence factors and genetic markers of antimicrobial resistance in 400 Staphylococcus aureus strains isolated from bovine mastitis in four Brazilian states, as well as to assess the association between these characteristics and field information. Virulence factors and drug resistance genes were identified by PCR screening. Biofilm-forming and hemolytic phenotype were detected using Congo red Tryptic Soy Broth and defibrinated sheep blood agar, respectively. Of all isolates, 83.5% were biofilm-forming and 98.5% strains exhibited biofilm gene icaAD, and a significant association between phenotype and genotype for biofilm was observed (P = 0.0005). Hemolysin genes were observed in 82.85% (hla⁺hlb⁺), 16.5% (hla⁺) and 0.75% (hlb⁺) isolates, whereas the hemolytic phenotype exhibited was complete and incomplete hemolysis in 64.25%, complete in 28.25%, incomplete in 4.75%, and negative in 2.75% of the strains. Virulence factors genes luk, seb, sec, sed, and tst were observed in 3.5%, 0.5%, 1%, 0.25%, and 0.74% isolates, respectively. The gene blaZ was detected in 82.03% of penicillin-resistant isolates, whereas tetK and aac(6')-Ie-aph(2')-Ia were observed in 33.87% and 45.15% of the tetracycline and aminoglycosides-resistant isolates, respectively. Fluoroquinolone resistance gene mepA was detected for the first time in S. aureus from bovine mastitis. Resistance genes tetM (3.22%), tetL (1.61%), ermA (14.29%), ermB (14.29%), ermC (33.3%), ermT (9.52%), ermY (4.76%), msrA (9.52%), and mphC (9.52%) were also detected among resistant isolates. No association between virulence factors or antimicrobial-resistant genes and year of isolation, geographic origin, or antimicrobial resistance profile was observed. Our results showed that S. aureus strains isolated from bovine mastitis in the four Brazilian states sampled are mainly biofilm-forming and hemolytic, whereas virulence genes associated with enterotoxins, luk and tst, were less frequently observed. Moreover, a wide variety of resistance genes that confer resistance to almost all classes of antimicrobial agents approved for use in animals and humans were found. Overall, the data point to a great pathogenic potential of S. aureus associated with bovine mastitis and to the non-negligible risks to public health of staphylococcal infections from animal origin.

Occurrence and Characterization of Enterotoxigenic Staphylococci Isolated from Soft Cheeses in Serbia

A total of 415 cheese samples produced with raw or cooked milk collected from local markets were analysed for the presence of coagulase-positive staphylococci. In 85 (20.48%) samples the presence of coagulase positive staphylococci was detected. The ELFA technique VIDAS SET2 (BioMerieux, France) was used for testing coagulase-positive staphylococci strains to produce classical enterotoxins (SEA, SEB, SEC, SED, SEE), and to determine the enterotoxins in cheese samples. The number of coagulase-positive staphylococci in cheese samples ranged from 1-5.79 log CFU g-1. Out of 85 coagulase-positive strains 26 (30.59%) produced enterotoxins. The presence of genes for the synthesis of staphylococcal enterotoxins (SE) in the obtained extracts of DNA from 26 enterotoxigenic strains was detected by conventional multiplex PCR technique (for genes sea and seb) i.e. the Real-Time PCR technique for genes sec, sed and see. In all 26 strains of coagulase-positive staphylococci (originating from cheeses produced from raw or cooked milk, which were enterotoxin producers) sea was present, and in 24 strains in addition to sea gene, seb was detected. None of the isolates possessed genes for the synthesis of enterotoxin C (SEC), D (SED) and E (SEE). Out of 26 tested cheese samples positive for enterotoxigenic coagulase-positive staphylococci, enterotoxin was detected in 2 (7.69%) samples of sweet-coagulating cheese, in which the number of enterotoxigenic coagulase-positive staphylococci exceeded 5 log CFU g-1. In sweet-coagulating cheeses in which the number of coagulase-positive staphylococci exceeds 5 log CFU g-1 and the pH value was higher than 5.0, enterotoxins may be present in amounts sufficient to cause intoxication.

The effect of protective cultures on Staphylococcus aureus growth and enterotoxin production

Staphylococcus aureus is the causative agent of staphylococcal food poisoning and is a common contaminant in milk. Despite efforts to control S. aureus, recalls and outbreaks continue to occur, highlighting the need for additional interventions. This study determined the potential for protective cultures (PC) that are commercially available to producers to control S. aureus growth in raw milk and attenuate virulence by impeding staphylococcal enterotoxin (SE) production in raw milk and laboratory medium. Cultures of Hafnia alvei and Lactococcus lactis effectively inhibited S. aureus growth in raw milk to counts ~5 log CFU/mL lower than control when cocultured following a cheesemaking time and temperature profile; two cultures of Lactobacillus plantarum inhibited growth to ~1.5 log CFU/mL less than control. Cocultures of S. aureus with Lc. lactis, H. alvei and Lb. plantarum in raw milk reduced SE levels by 24.9%, 62.4%, and 76%, respectively. Lc. lactis also decreased SE production in raw milk in the absence of PC-mediated growth inhibition. Significant reductions in SE production in the absence of pathogen growth inhibition were also achieved in laboratory medium. Together, these results demonstrate the potential for PCs to inhibit S. aureus growth and impede SE production in the absence of growth inhibition.

The protective potential of selected lactic acid bacteria against the most common contaminants in various types of cheese in Egypt

Dairy products, especially cheeses have a great nutritional value and a high consumption level around the world. Considering a widespread consumption of cheeses, there is a growing concern regarding safety and microbiological quality. The current study was designed to conduct a recent evaluation of cheeses microbiological quality. Sixty cheese samples from retailing Egyptian markets were analyzed on different selective microbiological media and 64 bacteria, 35 yeasts and 8 molds were isolated. Out of 60 samples; 26.6% were contaminated with Escherichia coli, 73.3% with Staphylococcus scuiri, 3.33% with Bacillus cereus, 1.66% with Salmonella enterica, and 1.66% with Pseudomonas aeruginosa. The presence of such microorganisms in cheeses referred to the wrong management in cheese manufacturing. These organisms are significant from public health view as they have been associated with the base of human food poisoning. Promising antagonistic behavior was observed using the tested lactic acid bacteria (LAB) either single or in combinations toward the undesired isolates. Lactobacillus helveticus CNRZ 32 (Lb. helveticus) was the most potent culture; recording ≥95% reduction in undesired microbial counts.

Short communication: Characterization of enterotoxin-producing Staphylococcus aureus isolated from mastitic cows

Staphylococcus aureus is not only a common cause of bovine mastitis, but also an agent of food poisoning in humans. In an attempt to determine whether staphylococci causing bovine mastitis could also cause food poisoning, 60 isolates of presumed S. aureus were isolated in the period between March and August 2017 from 3,384 routine, composite, quarter milk samples of individual cows raised on 12 dairy farms in central Italy. Seventeen out of 60 isolates were confirmed as S. aureus after coagulase, thermonuclease, and biochemical tests. These isolates were analyzed by PCR for the presence of the nuc, sea, seb, sec, sed, and see genes. The positive isolates were nuc, 100% (17); sea, 35.29% (6); seb, 5.88% (1); sec, 5.88% (1); sed, 29.41% (5); and see, 47.06% (8). The isolates were also tested with 2 enzyme immunoassay diagnostic kits, one for the screening detection of the production of staphylococcal enterotoxins (SEA, SEB, SEC, SED, SEE) and one for the detection of specific enterotoxin produced by each isolate. Seven out of 17 (41.18%) were enterotoxin producers: 7 produced SEA (41.18%), 1 SEB (5.88%), 1 SEC (5.88%), 5 SED (29.41%), and 6 SEE (35.29%). To further characterize the isolates, they were analyzed by the Kirby Bauer test for susceptibility to 13 antimicrobials (ampicillin, ciprofloxacin, kanamycin, tetracycline, gentamicin, methicillin, nalidixic acid, erythromycin, amoxicillin/clavulanic acid, streptomycin, vancomycin, neomycin, and enrofloxacin), and we detected resistance to ampicillin (52.94%), nalidixic acid (70.59%), erythromycin (5.88%), and amoxicillin/clavulanic acid (17.65%). The isolates were sensitive to the main classes of antimicrobials used for the treatment of bovine subclinical mastitis. The presence of enterotoxin-producing isolates of S. aureus in bovine milk means that a temperature abuse or a breakdown in the thermal treatment of the milk could present a food safety risk, particularly if all enterotoxigenic isolates could potentially produce SEA in milk.

Modeling for Predicting the Time to Detection of Staphylococcal Enterotoxin A in Cooked Chicken Product

Staphylococcal enterotoxins (SEs) produced by Staphylococcus aureus (S. aureus) are the cause of Saphylococcal food poisoning (SFP) outbreaks. Thus, estimation of the time to detection (TTD) of SEs, that is, the time required to reach the SEs detection limit, is essential for food preservation and quantitative risk assessment. This study was conducted to explore an appropriate method to predict the TTD of SEs in cooked chicken product under variable environmental conditions. An S. aureus strain that produces staphylococcal enterotoxin A (SEA) was inoculated into cooked chicken meat. Initial inoculating concentrations (approximately 102, 103, 104 CFU/g) of S. aureus and incubation temperatures (15 ± 1, 22 ± 1, 29 ± 1, and 36 ± 1°C) were chosen as environmental variables. The counting of S. aureus colonies and the detection of SEA were performed every 3 or 6 h during the incubation. The TTD of SEA was considered a response of S. aureus to environmental variables. Linear polynomial regression was used to model the effects of environmental variables on the TTD of SEA. Result showed that the correlation coefficient (R2) of the regressed equation is higher than 0.98, which means the obtained equation was reliable. Moreover, the minimum concentration of S. aureus for producing a detectable amount of SEA under various environmental conditions was approximately 6.32 log CFU/g, which was considered the threshold for S. aureus to produce SEA. Hence, the TTD of SEA could be obtained by calculating the time required to reach the threshold by using an established S. aureus growth predictive model. Both established methods were validated through internal and external validation. The results of graphical comparison, RMSE, SEP, Af , and Bf showed that the accuracy of both methods were acceptable, and linear polynomial regression method showed more accurately.

Presence of Classical Enterotoxin Genes, agr Typing, Antimicrobial Resistance, and Genetic Diversity of Staphylococcus aureus from Milk of Cows with Mastitis in Southern Brazil

Staphylococcus aureus is a common causative agent of bovine mastitis in dairy cows and commonly associated with foodborne disease outbreaks. The aim of this study was to evaluate the presence of enterotoxin genes, agr typing, antimicrobial resistance, and genetic diversity of S. aureus isolated from milk of cows with mastitis in dairy farms from southern Brazil. Results showed that 7 (22.6%) of 31 S. aureus isolates were positive for enterotoxin genes. Specifically, the genes encoding for enterotoxins A ( n = 4), C ( n = 2), and B ( n = 1) were detected. Isolates belonging to the agr group III (10 of 31, 32.2%) and agr group I (7 of 31, 22.5%) were the most common. To our knowledge, this is the first report of both agr I and III in the same S. aureus isolate from milk of cows with bovine mastitis. The antimicrobial resistance test showed that 54% of the isolates were multiresistant to antimicrobial agents. The macrorestriction analysis produced 16 different major SmaI pulsed-field gel electrophoresis patterns, with up to two subpatterns. Moreover, the presence of some S. aureus clones in a distinct area was observed. Although this study characterized a limited number of S. aureus isolates, the presence of classical enterotoxin genes and resistance to multiple antimicrobial agents reinforces the importance of this microorganism to animal and human health. In addition, similar genetic profiles have been identified in distinct geographic areas, suggesting clonal dissemination of S. aureus in dairy herds from southern Brazil.

Short communication: Characterization of Staphylococcus aureus isolated along the raw milk cheese production process in artisan dairies in Italy

Staphylococcus aureus is a common cause of food-borne intoxications. Several staphylococcal food poisoning outbreaks have been linked to consumption of raw milk cheeses and artisanal cheese production. However, information on Staph. aureus isolated from artisanal raw milk cheeses and small-scale dairy production environments is very limited. Therefore, we aimed to characterize Staph. aureus isolated along the artisanal raw milk production chain by determining (1) the population structure, and (2) the presence/absence of enterotoxin genes, mecA/C, and pvl. We collected 276 samples from different production stages (raw milk, whey, curd, brine, drying worktops, and cheese) at 36 artisan dairies in Italy. A total of 102 samples from 25 dairies tested positive for Staph. aureus, with 80% positive samples among the tested artisan cheeses. All isolates were further characterized by spa typing and PCR screening for staphylococcal enterotoxin genes, the mecA/mecC genes characteristic for methicillin-resistant Staph. aureus, and the pvl gene encoding Panton-Valentine leukocidin. The 102 isolates represented 15 different spa types and were assigned to 32 different Staph. aureus strains. The spa type most frequently detected was t2953 (30%), which is associated with genotype B strains causing high within-herd levels of bovine mastitis. In addition, 3 novel spa types (t13269, t13277, and t13278) were identified. Although none of the strains harbored mecA/mecC or pvl, 55% of the isolates exhibited at least one enterotoxin gene. Many strains were present in samples from multiple dairies from different regions and years, highlighting the spread of Staph. aureus in small-scale cheese production plants. Our findings demonstrate that enterotoxigenic Staph. aureus and in particular t2953 (genotype B) isolates commonly occur in artisanal dairies and raw milk cheeses in Italy. It is particularly alarming that 80% of the artisan cheeses sampled in our study were positive for Staph. aureus. These findings stress the need for effective measures preventing staphylococcal food poisoning by limiting Staph. aureus growth and enterotoxin formation along the production chain and in the final product.

Enterotoxin production and antimicrobial susceptibility in Staphylococci isolated from traditional raw milk cheeses in Serbia

This study was undertaken to determine the prevalence of coagulase positive staphylococci (CPS) by examining a total of 71 raw milk cheeses. Additionally, enterotoxigenicity, antimicrobial susceptibility and the presence of mecA and mecC genes in the staphylococcal isolates were investigated. The isolation and enumeration procedure of CPS followed the International Organization for Standardization (ISO) standard. The presumptive staphylococci were identified by matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) using the VITEK MS system. VIDAS® Staph enterotoxin II assay was used for the detection of classical enterotoxins. Antimicrobial susceptibility testing (AST) was accomplished performing the disk diffusion method. All suspected methicillin resistant staphylococci were investigated for the presence of mecA and mecC genes by PCR assay. A high prevalence (87.32%) of CPS was detected in the cheeses at contamination levels up to 5.58 log CFU g^-1. Among 47 staphylococcal isolates screened for enterotoxin production, only one isolate, identified as S. hyicus, was confirmed as being enterotoxigenic. Resistance to penicillin (63.70%) was the most common resistance among the tested Staphylococcus aureus isolates. The dominant phenotypic resistance patterns in coagulase negative staphylococci (CNS) were resistance to ofloxacin and fusidic acid. All CNS isolates were susceptible to the clinically important antibiotics clindamycin, chloramphenicol, gentamicin, linezolid, rifampicin and trimethoprim-sulfamethoxazole. The mecA and mecC genes were not detected. To the best of our knowledge, this is the first study concerning evaluation of the presence of methicillin resistant staphylococci (MRS) in dairy products in Serbia.

Frequência de genes codificadores de toxinas em Staphylococcus aureus isolados de leite de tanques expansão comunitários

RESUMO: A capacidade de produção de toxinas pelo Staphylococcus aureus no leite e produtos derivados está relacionado com surtos de intoxicação alimentar. Objetivou-se nesta pesquisa, estudar a ocorrência de genes que codificam para enterotoxinas estafilocócicas (sea, seb, sed, seg, seh e sei) e toxinas α e β hemolítica (hla e hlb) em S. aureus isolados de 53 amostras de leite de tanques expansão comunitários no Estado de Alagoas, Brasil. Foram identificados 27 isolados (50,94%) como S. aureus pela amplificação do gene nuc. 13/27 isolados (48,1%) foram positivos para pelo menos um gene das enterotoxinas estudadas, sendo as frequências dos genes sea 33,3%, seh 18,5%, sei 11,1% e sed 7,4%; não entanto não foram identificados os genes seb e seg nestas bactérias. Para as toxinas hemolíticas, 51,9% dos isolados portavam ambos genes (hla e hlb), sendo a frequência para o gene hla de 81,5% e para o gene hlb de 51,9%. A frequência de genes das toxinas avaliadas é alta o que constitui um risco potencial para a saúde pública em especial, as enterotoxinas por serem termoestáveis e estarem asssociados com surtos de intoxicação alimentar.

Characterization of Toxin Genes and Antimicrobial Susceptibility of Staphylococcus aureus Isolates in Fishery Products in Iran

Staphylococcus aureus is one of the most common causes of seafood-borne diseases worldwide, which are attributable to the contamination of food by preformed enterotoxins. In this study, a total of 206 (34.3%) Staphylococcus aureus strains were obtained from 600 fish and shrimp samples and were tested for their antimicrobial susceptibility. We assessed the prevalence of the genes responsible for the staphylococcal enterotoxins (SEA, SEB) and toxic shock syndrome toxin 1 (TSST-1) genes. The results indicated that 34% of aqua food samples were contaminated with S. aureus, and 23.8% of these isolates were mec-A-positive. Sixty-four percent of the strains isolated from contaminated seafood was enterotoxigenic S. aureus, and 28.2% of SEs were MRSA-positive. The most prevalent genotype was characterized by the presence of the sea gene (45.2%), followed by the seb gene (18.5%), and the tst gene encoding TSST-1 was found in eight strains (3.9%). Of the 206 S. aureus isolates, 189 strains (84.9%) were resistant to at least one antibiotic. Given the frequent outbreaks of enterotoxigenic MRSA, it is necessary to make revisions to mandatory programmes to facilitate improved hygiene practices during fishing, aquaculture, processing, and sales to prevent the contamination of fishery products in Iran.

Enterotoxin Gene Profile and Molecular Characterization of Staphylococcus aureus Isolates from Bovine Bulk Milk and Milk Products of Tigray Region, Northern Ethiopia

Staphylococcal food poisoning (SFP) is an important foodborne disease worldwide, and milk and milk products are commonly associated with SFP outbreaks. The objectives of this study were to investigate the distribution of staphylococcal enterotoxin (se) genes in Staphylococcus aureus from raw cow's milk and milk products and to assess their genetic background with the spa typing method. Of the 549 samples (297 bulk milk and 162 milk product samples) collected from Tigray region, Northern Ethiopia, 160 (29.1%) were positive for S. aureus, of which 82 (51%) were found to harbor se genes by a modified multiplex PCR. Nine se genes were identified: sea (n = 12), seb (n = 3), sec (n = 3), sed(n = 4), seg (n = 49), seh (n = 2), sei (n = 40), sej (n = 1), and tsst-1 (n = 24). The classical type of genes accounted for 27%. Of the 82 enterotoxigenic isolates, 41.5 and 12.4% harbored two or more se genes, respectively. The highest gene association was observed between sei and seg, whereas sea and seb were always found together with the new types of se genes. Altogether, 18 genotypes of toxin genes were identified, and 33% of the samples contained > 5 log CFU ml(-1) S. aureus. spa typing identified 22 spa types and three novel spa sequences, which showed the high genetic diversity of the isolates. No apparent relationship was observed between spa type and se genes. Of the 25 spa types, 13 (52%) were from raw milk, 3 (12%) from milk products, and 9 (36%) from both types of sample. Types t314 (20.7%,n = 17), t458 (18.3%, n = 15), and t6218 (9.8%, n= 8) were the most common spa types identified and were widely distributed in three of the eight studied localities. This is the first study from the Tigray region to report the high distribution of enterotoxigenic S. aureus with a diversified genetic background from dairy food. The study may provide valuable data for microbial food safety risk assessment, molecular epidemiology, and phylogenetic studies of S. aureus in Ethiopia.

Transcriptomic and metabolic responses of Staphylococcus aureus in mixed culture with Lactobacillus plantarum, Streptococcus thermophilus and Enterococcus durans in milk

Staphylococcus aureus is a major food-borne pathogen due to the production of enterotoxin and is particularly prevalent in contaminated milk and dairy products. The lactic acid bacteria (LAB) are widely used as biocontrol agents in fermented foods which can inhibit pathogenic flora. In our work, we investigated the influence of three strains of LAB (Lactobacillus plantarum, Streptococcus thermophilus and Enterococcus durans) on the relative expression of three enterotoxin genes (sea, sec, sell) and eight virulence and/or regulatory genes (sarA, saeS, codY, srrA, rot, hld/RNAIII, agrA/RNAII, sigB) in two S. aureus strains (MW2 and Sa1612) in TSB and reduced-fat milk (1.5 %) at 30 °C over a 24-h period. The tested LAB and S. aureus strains proved to be mutually non-competitive or only slightly competitive during co-cultivation. In addition, under the above-mentioned conditions, differential gene expression between the S. aureus MW2 and Sa1612 strains was well documented. S. aureus growth was changed in mixed culture with LAB; however, its effect on the repression of sea and sec expression correlated with production of these virulence factors. In comparison, the presence of LAB strains generally inhibited the expression of sec, sell, sarA, seaS, agrA/RNAII and hld/RNAIII genes. The effect of LAB strains presence on the expression of sea, codY, srrA, rot and sigB genes was medium, time, LAB and S. aureus strain specific. SEA and SEC production was significantly reduced in milk compared to TSB in pure culture. After the 24-h cultivation, S. aureus MW2 and Sa1612 SEC production was 187 and 331 times lower in milk compared to TSB, respectively (0.07 and 0.39 ng/mL in milk, versus 13.1 and 129.2 ng/mL in TSB, respectively). At the same time S. aureus MW2 and Sa1612 SEA production was 77 and 68 times lower in milk compared to TSB, respectively (0.99 and 0.17 ng/mL in milk, versus 76.4 and 11.5 ng/mL in TSB, respectively). This study has revealed new insights into the interaction between S. aureus and LAB (L. plantarum, S. thermophilus, E. durans) on the level of the expression and/or production of S. aureus enterotoxins, regulatory and virulence genes in different media, including milk. This study provides data which may improve the quality of food production.

Molecular analysis of Staphylococcus aureus pathogenicity islands (SaPI) and their superantigens combination of food samples

Staphylococcus aureus produces a wide variety of superantigenic activity Staphylococcal enterotoxins (SE) and they are a major cause of food poisoning. These superantigens are associated with mobile genetic elements such as plasmids, prophages and S. aureus pathogenicity islands (SaPI). The presence of well-known eight SaPI integrase and 13 enterotoxin genes (sea, seb, sec, sed, see, seg, seh, sei, sej, sel, sek, seq, and tst) in 93 S. aureus strains were investigated. All S. aureus isolates were characterized by pulsed-field gel electrophoresis (PFGE), and the genes were detected using five sets of multiplex PCR (mPCR). The most predominant toxin genes were sea (19%), seb (15%), sec (54%), sell (48%), selk (46%), selq (52%), seg (22%), and sei (19%). Analysis showed that many S. aureus isolates harbored multiple toxin genes. An mPCR-based assay was developed for the determination of all SaPI and their superantigen gene combinations. Twenty three isolates revealed the gene combination sec, sell and tst, typical of the SaPIbov1 and SaPIn1/m1 pathogenicity islands. Twelve isolates revealed the selk and selq gene combination consistent with SaPI3. Eight isolates exhibited the sec and sell genes without the tst gene typical of SaPImw2. We established a correlation between superantigenic toxin genotypes in S. aureus in terms of combinations of toxin gene-encoding SaPI. These results provide a rapid method for determining superantigenic toxin genotypes in S. aureus strains. A total of 24 PFGE patterns were generated. To our knowledge, this is a first study analyzing the correlation of all known SaPI and their enterotoxins in S. aureus using mPCR.

Impacts of enterotoxin gene cluster-encoded superantigens on local and systemic experimental Staphylococcus aureus infections

Staphylococcus aureus is both a component of the normal skin flora and an important pathogen. It expresses a range of recognized and putative virulence factors, such as enterotoxins with superantigenic properties. Several superantigen genes, i.e., seg, sei, selm, seln, and selo, are encoded by the enterotoxin gene cluster (egc), which is found in the majority of S. aureus isolates. Carriage of egc is associated with fitness of S. aureus in the gut microbiota, but it is not known if it contributes to pathogenicity. We constructed egc+ (functional for the seg, selm, and selo genes) and isogenic egc- S. aureus mutants, and investigated their virulence profiles in murine infection models. No effect of egc was seen in a local skin and soft tissue infection model, but in an invasive infection model, increased weight loss was observed after infection with the egc+ as compared to the egc- mutant. Mortality and arthritis were not affected by egc status. Our data suggest that egc has limited effects on the virulence of S. aureus. It may primarily function as a colonization factor increasing commensal fitness, although it might have some aggravating effects on the infection when the bacteria reach the blood.

Antimicrobial activity of lactic acid bacteria in dairy products and gut: effect on pathogens

The food industry seeks alternatives to satisfy consumer demands of safe foods with a long shelf-life able to maintain the nutritional and organoleptic quality. The application of antimicrobial compounds-producing protective cultures may provide an additional parameter of processing in order to improve the safety and ensure food quality, keeping or enhancing its sensorial characteristics. In addition, strong evidences suggest that certain probiotic strains can confer resistance against infection with enteric pathogens. Several mechanisms have been proposed to support this phenomenon, including antimicrobial compounds secreted by the probiotics, competitive exclusion, or stimulation of the immune system. Recent research has increasingly demonstrated the role of antimicrobial compounds as protective mechanism against intestinal pathogens and therefore certain strains could have an effect on both the food and the gut. In this aspect, the effects of the combination of different strains keep unknown. The development of multistrain probiotic dairy products with good technological properties and with improved characteristics to those shown by the individual strains, able to act not only as protective cultures in foods, but also as probiotics able to exert a protective action against infections, has gained increased interest.

Following pathogen development and gene expression in a food ecosystem: the case of a Staphylococcus aureus isolate in cheese

Human intoxication or infection due to bacterial food contamination constitutes an economic challenge and a public health problem. Information on the in situ distribution and expression of pathogens responsible for this risk is to date lacking, largely because of technical bottlenecks in detecting signals from minority bacterial populations within a complex microbial and physicochemical ecosystem. We simulated the contamination of a real high-risk cheese with a natural food isolate of Staphylococcus aureus, an enterotoxin-producing pathogen responsible for food poisoning. To overcome the problem of a detection limit in a solid matrix, we chose to work with a fluorescent reporter (superfolder green fluorescent protein) that would allow spatiotemporal monitoring of S. aureus populations and targeted gene expression. The combination of complementary techniques revealed that S. aureus localizes preferentially on the cheese surface during ripening. Immunochemistry and confocal laser scanning microscopy enabled us to visualize, in a single image, dairy bacteria and pathogen populations, virulence gene expression, and the toxin produced. This procedure is readily applicable to other genes of interest, other bacteria, and different types of food matrices.

Selection and characterization of DNA aptamers against Staphylococcus aureus enterotoxin C1

Enterotoxins from pathogenic bacteria are known as the main reason that can cause the bacterial foodborne diseases. In this study, aptamers that bound to Staphylococcus aureus enterotoxin C1 (SEC1) with high affinity and selectivity were generated in vitro by twelve rounds of selection based on magnetic separation technology, with a low-level dissociation constant (Kd) value of 65.14 ± 11.64 nmol/L of aptamer C10. Aptamer-based quantification of SEC1 in the food sample by a graphene oxide (GO)-based method was implemented to investigate the potential of the aptamer against SEC1 with a limit of detection of 6 ng/mL. On the basis of this work, biosensors using the selected SEC1 aptamers as new molecular recognition elements could be applied for innovative determinations of SEC1.

Occurrence and antimicrobial resistance of Staphylococcus aureus in bulk tank milk and milk filters

This work is focused on the monitoring of Staphylococcus aureus prevalence in raw milk and milk filters, its antibiotic resistance and detection of methicillin resistant Staphylococcus aureus (MRSA). Samples of raw cow´s milk and milk filters were collected in the period from 2012 till 2014, from 50 dairy farms in the Czech Republic. The total of 261 samples (164 samples of raw milk and 97 milk filters) were cultivated on Baird-Parker agar. Both the typical and atypical colonies were examined by plasmacoagulase test and PCR method was used for detection of species specific fragment SA442 and mecA gene. Standard disk diffusion method was used to determinate resistance to antimicrobial agents. The bacterium Staphylococcus aureus was detected on 25 farms (50%). The antimicrobial resistance showed differences between the farms. Total of 58 samples were positive for Staphylococcus aureus, of which were 37 (14.2%) isolated from raw milk samples and 21 (8.1%) from milk filters. From these samples we isolated 62 Staphylococcus aureus strains, 41 isolates bacteria S. aureus from raw milk (66.1%) and 21 isolates S. aureus from milk filters (33.9%). The presence of antibiotic resistance in Staphylococcus aureus isolates was low, most of them were resistant to amoxicilin. According to the results obtained by the PCR method for the methicillin - resistant S. aureus (MRSA), the mecA gene was present in 6 strains (9.7%), 4 isolates obtained from milk samples (6.5%) and 2 isolates from milk filters (3.2%).  These isolates can be considered as a possible source of resistance genes, which can be spread through the food chain. Nowadays, a globally unfavourable increasing trend of prevalence of methicillin resistant staphylococci strains especially Staphylococcus aureus is being observed worldwide. The improper hygiene and poor farm management practices contributed to the presence of S. aureus in the milk. This may have contributed to the high level of S. aureus isolated. Improving the hygienic conditions of the milking environment and utensils may reduce the prevalence of S. aureus in milk. Objective of this study was monitoring of Staphylococcus aureus prevalence and determine the prevalence rate of antimicrobial resistance of S. aureus isolated from raw milk and milk filters in the Czech Republic.

Occurrence of Methicillin Resistant and Enterotoxigenic Staphylococcus aureus in Traditional Cheeses in the North West of Iran

Traditional dairy products are potential sources of a variety of microorganisms which participate in food poisoning. Staphylococcus aureus is a conspicuous example of toxigenic bacteria causative for food-borne diseases. Moreover, resistance to methicillin is a prominent index in food hygiene studies. In the present study, we have aimed at characterization and identification of enterotoxigenic methicillin resistant S. aureus (MRSA) isolated from traditional cheeses in Azerbaijan region in the northwest of Iran during 2012. A number of phenotypical and molecular assays were utilized for screening of S. aureus. Subsequently, the prevalence of the genes responsible for the five staphylococcal enterotoxins (SEA-SEE) and also methicillin resistance gene was assessed. The outcomes of phenotypical methods were in conformity with those of the molecular procedures. The results indicated that 16% of cheese samples were contaminated by S. aureus. 110 isolates were authenticated by both phenotypical and molecular methods. All of the mentioned isolates were positive for coa, nuc, and 16S rDNA primers. 21% of these isolates were mecA positive and 60.8% of these MRSA were positive for SEs. Regarding the frequent outbreaks of enterotoxigenic MRSA, new hygiene policies and management practices should be considered to increase food safety and avoid extra treatment costs.

TSST-1, enterotoxin and bacteriocin-like substance production by Staphylococcus aureus isolated from foods

The production of Toxic Shock Syndrome Toxin-1 (TSST-1), enterotoxins and bacteriocin-like substances was evaluated in 95 strains of Staphylococcus aureus recovered from raw bovine milk (n=31) and from food samples involved in staphylococcal food poisoning (n=64). Enterotoxigenicity tests with the membrane over agar associated to optimal sensibility plate assays were performed and showed that 96.77% of strains recovered from milk and 95.31% from food samples produced enterotoxins A, B, C, D or TSST-1. Reference strains S. epidermidis, Bacillus cereus, Listeria monocytogenes, Lactobacillus casei, Pseudomonas aeruginosa, S. aureus, Salmonella Typhimurium, Escherichia coli, Enterococcus faecalis and Bacteroides fragilis were used as indicator bacteria in the antagonistic assays, the first five being sensitive to antagonistic substances. Brain heart infusion agar, in pH values ranging from 5.0 to 7.0 in aerobic atmosphere showed to be the optimum condition for antagonistic activity as evaluated with the best producer strains against the most sensitive indicator bacterium, L. monocytogenes. Sensitivity to enzymes confirmed the proteinaceous nature of these substances. Neither bacteriophage activity nor fatty acids were detected and the antagonistic activity was not due to residual chloroform. Results did not establish a positive correlation between the bacteriocinogenic profile and toxigenicity in the tested S. aureus strains.

egc characterization of enterotoxigenic Staphylococcus aureus isolates obtained from raw milk and cheese

Genes encoding staphylococcal enterotoxins (SEs) are carried by mobile genetic elements, and enterotoxin gene clusters (egc) are pathogenicity island-borne structures comprising several SE genes, which are frequently found among clinical Staphylococcus aureus isolates. In the present study, we investigated the distribution and the genetic variability of egc loci in S. aureus strains isolated from raw milk and soft cheese in Minas Gerais, Brazil. Ninety-two isolates were submitted to PCR detection of individual egc-borne SE genes (seg, sei, sem, sen, seo, seu), and egc loci were typed using PCR-RFLP. PCR products of egc positive isolates were sequenced. Ninety-one isolates harbored at least one SE gene, which generated 14 different genotypes. The sei gene was the most widely distributed (97.8%), and was found in combination with seg in 49 isolates (53.3%). Altogether, a complete set of individual egc genes was detected in 37 isolates (40%). However, egc loci were detected by PCR-RFLP in only 4 isolates, and classified as egc1 (n=2), egc3 (n=1), and egc4 (n=1). This investigation demonstrated the low occurrence of the egc in S. aureus isolated from dairy products. However, the frequency of complete sets of individual egc-borne genes reflects either the presence of these SE genes outside egc or the existence of new egc types in these strains.