Molecular analysis of Staphylococcus aureus isolates associated with staphylococcal food poisoning in South Korea

Molecular characterization and antibiotic resistance of Staphylococcus aureus strains isolated from patients with diarrhea in Korea between the years 2007 and 2022

To investigate the molecular characteristics and antibiotic resistance of Staphylococcus aureus isolates from patients with diarrhea in Korea, 327 S. aureus strains were collected between 2007 and 2022. The presence of staphylococcal enterotoxin (SE) and toxic shock syndrome toxin-1 (TSST-1) genes in S. aureus isolates was determined by PCR. The highest expression of the TSST-1 gene was found in the GIMNO type (43.1% of GIMNO type). GIMNO type (Type I) refers to each staphylococcal enterotoxin (SE) gene gene (initials of genes): G = seg; I = sei; M = selm; N = seln; O = selo. Moreover, Type I isolates showed a significantly higher resistance to most antibiotics. A total of 195 GIMNO-type S. aureus strains were analyzed using multilocus sequence typing (MLST), and 18 unique sequence types (STs) were identified. The most frequent sequence type was ST72 (36.9%), followed by ST5 (22.1%) and ST30 (16.9%). Interestingly, ST72 strains showed a higher prevalence of MRSA than the other STs. In conclusion, our results were the first reported for S. aureus strains in Korea, which significantly expanded S. aureus genotype information for the surveillance of pathogenic S. aureus and may provide important epidemiological information to resolve several infectious diseases caused by S. aureus.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10068-023-01478-9.

Coordination of prophage and global regulator leads to high enterotoxin production in staphylococcal food poisoning-associated lineage

Staphylococcus species in food produce Staphylococcal enterotoxins (SEs) that cause Staphylococcal food poisoning (SFP). More than 20 SE types have been reported, among which Staphylococcal enterotoxin A (SEA) has been recognized as one of the most important SEs associated with SFP. However, the regulatory mechanisms underlying its production remain unclear. Previously, we identified a major SFP clone in Japan, CC81 subtype-1, which exhibits high SEA production. In this study, we attempted to identify the factors contributing to this phenomenon. Thus, we demonstrated that the attenuation of the activity of endogenous regulator, Staphylococcal accessory regulator S (SarS), and the lysogenization of a high SEA-producing phage contributed to this phenomenon in CC81 subtype-1. Furthermore, our results indicated that SarS could directly bind to the promoter upstream of the sea gene and suppress SEA expression; this low SarS repression activity was identified as one of the reasons for the high SEA production observed. Therefore, we revealed that both exogenous and endogenous factors may probably contribute to the high SEA production. Our results confirmed that SE production is a fundamental and critical factor in SFP and clarified the associated production mechanism while enhancing our understanding as to why a specific clone frequently causes SFP.

IMPORTANCE

The importance of this study lies in its unveiling of a molecular regulatory mechanism associated with the most important food poisoning toxin and the evolution of Staphylococcal food poisoning (SFP)-associated clone. SFP is primarily caused by Staphylococcus aureus, with Staphylococcal enterotoxin A (SEA) being commonly involved in many cases. Thus, SEA has been recognized as a major toxin type. However, despite almost a century since its discovery, the complete mechanism of SEA production is as yet unknown. In this study, we analyzed an SEA-producing SFP clone isolated in East Asia and discovered that this strain, besides acquiring the high SEA-producing phage, exhibits remarkably high SEA production due to the low activity of SarS, an intrinsic regulatory factor. This is the first report documenting the evolution of the SFP clone through the coordinated action of exogenous mobile genetic factors and endogenous regulators on this notorious toxin.

Comparative genomic analysis of antibiotic resistance and virulence genes in Staphylococcus aureus isolates from patients and retail meat

Introduction

Staphylococcus aureus is a significant human pathogen that poses a threat to public health due to its association with foodborne contamination and a variety of infections. The factors contributing to the pathogenicity of S. aureus include virulence, drug resistance, and toxin production, making it essential to monitor their prevalence and genetic profiles. This study investigated and compared the genomic characteristics of S. aureus isolates from retail meat and patients in Saudi Arabia.

Methods

A total of 136 S. aureus isolates were obtained between October 2021 and June 2022:84 from patients and 53 from meat samples in Riyadh, Saudi Arabia. S. aureus isolates were identified using conventional methods and MALDI-TOF MS, and methicillin-resistant S. aureus (MRSA) was identified using VITEK2 and BD Phoenix systems. MRSA was confirmed phenotypically using chromogenic agar, and genotypically by detecting mecA. Genomic data were analyzed using BactopiaV2 pipeline, local BLAST, and MLST databases.

Results

Antibiotic resistance genes were prevalent in both meat and patient S. aureus isolates, with high prevalence of tet38, blaZ, and fosB. Notably, all S. aureus isolates from patients carried multidrug-resistant (MDR) genes, and a high percentage of S. aureus isolates from meat also harbored MDR genes. Phenotypically, 43% of the S. aureus isolates from meat and 100% of the patients' isolates were MDR. Enterotoxin genes, including selX, sem, and sei, exhibited high compatibility between meat and patient S. aureus isolates. Virulence genes such as cap, hly/hla, sbi, and isd were found in all S. aureus isolates from both sources.

Conclusion

Our study established a genetic connection between S. aureus isolates from meat and patients, showing shared antibiotic resistance and virulence genes. The presence of these genes in meat derived isolates underscores its role as a reservoir. Genomic relatedness also suggests potential transmission of resistance between different settings. These findings emphasize the necessity for a comprehensive approach to monitor and control S. aureus infections in both animals and humans.

Genomic analysis of foodborne Staphylococcus aureus obtained from unannounced food inspections between 2012 and 2021 in East China

Staphylococcus aureus is a significant cause of foodborne illness in China. Our investigation concentrated on the genetic characterization of foodborne S. aureus identified during unannounced inspections conducted in Suzhou from 2012 to 2021. Dominant clones included clonal complex (CC) 1, CC398, CC188, and CC7, with CC398 notably increasing in 2020-2021. The isolates commonly contained 1-3 plasmids, with rep5a (48.55%) and rep16 (44.51%) predominating. A concerning 24.3% showed multidrug resistance, particularly to penam (blaZ and mecA) and fosfomycin (fosB), with resistance rates rising from 32.7% to 53.3%, potentially linked to the increase in CC types like CC5, CC20, and CC25. Most isolates carried genes for virulence factors such as aureolysin, hemolysin, staphylokinase, and staphylococcal complement inhibitor. A significant increase in virulence genes, especially the enterotoxin gene sea, was observed, possibly associated with shifts in CC1 and CC7 prevalence. This underscores the necessity for ongoing surveillance to understand the genomic traits of S. aureus in ensuring food safety.

Occurrence, Antibiotic Susceptibility, Biofilm Formation and Molecular Characterization of Staphylococcus aureus Isolated from Raw Shrimp in China

The aim of this study was to determine the prevalence and characterization of Staphylococcus aureus isolated from 145 shrimp samples from 39 cities in China. The results show that 41 samples (28%) from 24 cities were positive, and most of the positive samples (39/41, 95.1%) were less than 110 MPN/g. Antimicrobial susceptibility testing showed that only seven isolates were susceptible to all 24 antibiotics, whereas 65.1% were multidrug-resistant. Antibiotic resistance genes that confer resistance to β-lactams, aminoglycosides, tetracycline, macrolides, lincosamides and streptogramin B (MLSB), trimethoprim, fosfomycin and streptothricin antibiotics were detected. All S. aureus isolates had the ability to produce biofilm and harbored most of the biofilm-related genes. Genes encoding one or more of the important virulence factors staphylococcal enterotoxins (sea, seb and sec), toxic shock syndrome toxin 1 (tsst-1) and Panton-Valentine leukocidin (PVL) were detected in 47.6% (30/63) of the S. aureus isolates. Molecular typing showed that ST15-t085 (27.0%, 17/63), ST1-t127 (14.3%, 9/63) and ST188-t189 (11.1%, 7/63) were the dominant genetic types. The finding of this study provides the first comprehensive surveillance on the incidence of S. aureus in raw shrimp in China. Some retained genotypes found in this food have been linked to human infections around the world.

A food poisoning caused by ST7 Staphylococcal aureus harboring sea gene in Hainan province, China

ST7 Staphylococcus aureus is highly prevalent in humans, pigs, as well as food in China; however, staphylococcal food poisoning (SFP) caused by this ST type has rarely been reported. On May 13, 2017, an SFP outbreak caused by ST7 S. aureus strains occurred in two campuses of a kindergarten in Hainan Province, China. We investigated the genomic characteristics and phylogenetic analysis of ST7 SFP strains combined with the 91 ST7 food-borne strains from 12 provinces in China by performing whole-genome sequencing (WGS). There was clear phylogenetic clustering of seven SFP isolates. Six antibiotic genes including blaZ, ANT (4′)-Ib, tetK, lnuA, norA, and lmrS were present in all SFP strains and also showed a higher prevalence rate in 91 food-borne strains. A multiple resistance plasmid pDC53285 was present in SFP strain DC53285. Among 27 enterotoxin genes, only sea and selx were found in all SFP strains. A ФSa3int prophage containing type A immune evasion cluster (sea, scn, sak, and chp) was identified in SFP strain. In conclusion, we concluded that this SFP event was caused by the contamination of cakes with ST7 S. aureus. This study indicated the potential risk of new emergencing ST7 clone for SFP.

First report of the presence of enterotoxin gene in coagulase-negative staphylococci recovered from meat of snails (Achatina achatina)

Introduction

It has been suggested that coagulase-negative staphylococci can serve as reservoirs of virulence genes for other bacteria. This study assessed the presence of such genes in selected isolates recovered from meat of the giant African snail (Achatina achatina).

Material and Methods

Virulence genes were detected using a polymerase chain reaction targeting specific primers. Two representative isolates were identified using 16S rRNA gene sequencing.

Results

The results showed that the staphylococcal enterotoxin A gene (sea) was present in five out of the eight isolates studied. The isolates expressed resistance mainly to three antibiotics: chloramphenicol, norfloxacin and cloxacillin in descending order of incidence. Most importantly, the Staphylococcus sciuri isolate NEDU 181, in addition to being resistant to the three aforementioned antibiotics, also harboured the sea gene.

Conclusion

Our findings demonstrate, for the first time, the presence of toxigenic and antibiotic-resistant coagulase-negative Staphylococcus spp. in commercially-available fresh snail meat. With staphylococcal enterotoxin A known to survive cooking temperature, this presents a food safety concern.

Comparative genomics of bovine mastitis-origin Staphylococcus aureus strains classified into prevalent human genotypes

Humans may serve as a reservoir host of Staphylococcus aureus, resulting in transmission to animals. Previously, we used RNA polymerase beta subunit gene (rpoB)-based genotyping and classified S. aureus strains into rpoB sequence types (RSTs). According to our previous work, the predominant genotypes of S. aureus in humans and cows differ in Korea, but some predominant genotypes (RST4-1 and RST2-1) in humans have been isolated from bovine mastitis. Therefore, it needs to be determined whether some strains of the predominant human genotypes have adapted to or caused occasional infections in cows. We determined the whole genome sequences of 2 bovine mastitis-origin strains, PMB179 (RST4-1) and PMB196 (RST2-1), and performed comparative genomics with the corresponding RST4-1 and RST2-1 S. aureus strains in the NCBI database. We identified 257 and 180 pseudogenes among 131 RST4-1 and 54 RST2-1 strains, respectively, for the comparison of pseudogene profiles. RST4-1 strains shared more common pseudogenes than RST2-1 strains, and some epidemiologically related strains shared common pseudogenes. However, most of the pseudogenes were strain-specific, and diverse pseudogene profiles were apparent in both the RST4-1 and RST2-1 strains. Furthermore, analysis of the mobile genetic elements, virulence genes, and antibiotic resistance genes revealed no molecular markers to differentiate PMB179 and PMB196 from human strains. Interestingly, the collective comparison of RST4-1 or RST2-1 strains revealed cumulative acquisition steps of genomic islands and antibiotic resistance genes. In conclusion, our data support PMB179 and PMB196 causing occasional infections that result in bovine mastitis.

Genotypic Characteristics and Correlation of Epidemiology of Staphylococcus aureus in Healthy Pigs, Diseased Pigs, and Environment

China is one of the largest producers of pigs and pork in the world. However, large-scale studies on pig-associated Staphylococcus aureus in relation to healthy pigs, diseased pigs and environment are scarce. The objective of the present study was to characterize and compare S. aureus isolates from healthy pigs, diseased pigs and environment through antimicrobial susceptibility testing, multiple locus sequence typing, spa typing, and antimicrobial resistance gene screening. Results showed all isolates were susceptible to linezolid and vancomycin. However, 66.7% (104/156) isolates were multidrug-resistant by displaying resistance to three or more antibiotics and high rates of resistance to penicillin, tetracycline, clindamycin, and clarithromycin were observed. Of the 20 multilocus sequence types (STs) identified among the isolates, ST9, ST188, and ST7 were most commonly isolated from healthy pigs and environment, while ST1 was most commonly isolated from diseased pigs. In total, 17 spa types were represented among the isolates, while t4792 was most commonly isolated from diseased pigs and t899, t189 were most commonly isolated from healthy pigs and environment. In conclusion, the genotypic and epidemiology characteristics observed among the isolates suggest pigs and pork could be important players in S. aureus dissemination.

Characterization of Oxacillin-Susceptible mecA-Positive Staphylococcus aureus from Food Poisoning Outbreaks and Retail Foods in China

In this study, we explored the prevalence of oxacillin-susceptible mecA-positive Staphylococcus aureus (OS-MRSA) in staphylococcal food poisoning outbreak isolates and foodborne isolates, and then investigated their molecular characteristics, classical staphylococcal enterotoxins (SEs), and drug resistance. Eight (2.9%) of 275 isolates from food poisoning outbreaks and 7 (3.8%) of 184 isolates from retail foods were identified as OS-MRSA isolates. Among the 15 OS-MRSA isolates, the most frequently detected toxin genes were hld (100%), hla (93.3%), pvl (80.0%), and hlb (46.7%) followed by seg and seq (33.3%, each), hlg (26.7%), seb and hlgv (20.0%, each), sec, seh, sel, sep, and tst (13.3%, each), and sei, sem, sen, and seo (6.7%, each). None of isolates carried other tested virulence genes. The most frequently detected classical SEs were SEB and SEC (26.7%, each), followed by SEA and SEE (20.0%, each), and SED (6.7%). Resistance was most frequently observed in ampicillin, penicillin, and cefoxitin (100%, each), followed by trimethoprim/sulfamethoxazole (93.3%), erythromycin (73.3%), amoxicillin/clavulanic acid (46.7%), tetracyclines (26.7%), and ciprofloxacin (6.7%). All isolates were susceptible to other tested antibiotics. A dominant molecular type belonged to ST398-IVa-t034 (26.7%), followed by ST59-IVa-t437 (20.0%), ST88-III-t14340 and ST1-IVa-t114 (13.3%, each), and ST5-II-t002, ST630-t4549, ST5-II, and ST4495-t10738 (6.7%, each). Our findings indicated that OS-MRSA strains had a low prevalence rate among outbreak strains and foodborne strains, which frequently harbored SCCmec IVa, and carried a variety of toxin genes, and also expressed numerous classical SEs. In addition, all OS-MRSA isolates were susceptible to the majority of antibacterial agents except β-lactam. Our study is the first to report that OS-MRSA isolates are associated with food poisoning outbreaks worldwide.

B. A. Zaki H, S. Tolba K, A. Yassin N. Staphylococcus aureus and enterotoxin A relative gene expression in beef meat after lactic acid treatment and storage at different temperatures

The Staphylococcus aureus enterotoxin A (sea) is the toxin mostly involved in Staphylococcus aureus (S. aureus) food poisoning. In this study, the effect of different lactic acid (LA) concentrations (LA 1% and 2%) and temperatures (4 oC, 25 oC, and 37 oC) on S. aureus growth and relative sea expression in fresh meat cuts were studied. Real-Time RT-PCR used to determine the relative sea expression. Fresh meat cuts were inoculated with 105 CFU/g of S. aureus producing enterotoxin A. S. aureus growth and relative sea expression were regularly tested for 48 hours. The growth of S. aureus was decreased by one log CFU/g than control sample using 1% LA and 2% LA 2% (5.32 ± 3.76 log CFU/g, 4.38 ± 3.00 log CFU/g and 4.54 ± 3.18 log CFU/g respectively) at zero time. Relative expression of the sea gene in both LA concentrations was lower than control. Moreover, both lactic acid concentrations had effect on relative sea gene expression at all examined hours, especially at 4 oC compared to control samples. The higher the lactic acid concentration, the lower the S. aureus enterotoxin A relative expression was.

Methicillin-Resistant Staphylococcus aureus in Seafood: Prevalence, Laboratory Detection, Clonal Nature, and Control in Seafood Chain

Methicillin-resistant Staphylococcus aureus (MRSA), a versatile pathogen bearing multiple virulence determinants, is increasingly being detected in various food-producing animals, including fish. In addition, it is a potential food poisoning agent. MRSA is not an inherent microbiota of fish; its presence is attributed to pre- or postharvest contamination through fish handlers, water, ice, and processing equipment. Several reviews have been written on MRSA in clinical as well as the food animal-producing sector, but information specific to MRSA in seafood is scant. This review puts forth insights on MRSA detection in seafood, antibiotic resistance, diversity of clones in seafood, and possible control measures in seafood production chain. Emphasis has been given on assessing the variations in the protocols employed for isolation and identification in different food matrices and lay the foundation for researchers to develop optimized procedure.

Characterization of an Unusual Foodborne Illness Including an Outbreak and Sporadic Illness Caused by Three Bacterial Pathogens Via a Takeaway Service

Takeaway food services are an emerging business in China and have a potential impact on food safety. An unusual foodborne illness associated with takeaway food delivered through a logistics company on August 27, 2018 is reported. Epidemiological investigations showed that 28 patients from 2 companies were diagnosed with gastroenteritis symptoms. The major symptoms included nausea (24, 85.71%), vomiting (24, 85.71%), diarrhea (22, 78.57%), and abdominal pain (22, 78.75%). Laboratory investigations showed that six Staphylococcus aureus isolates, three Salmonella enteria serovar livingstone isolates, and one Vibrio parahaemolyticus isolate were detected. Six S. aureus isolates were detected from one patient, food, and a food handler, and all six S. aureus isolates had the same pulsed-field gel electrophoresis (PFGE) pattern and multilocus sequence typing (MLST) genotype. Staphylococcal enterotoxin A was detected from food and the six S. aureus isolates. These results confirmed that S. aureus isolates were the major agent causing this foodborne illness. Three Salmonella isolates with the same PFGE pattern and MLST genotype were detected from patients. This was the first time that Salmonella isolates have been identified as causing a foodborne disease outbreak in China. Only one O4:K8 serotype of V. parahaemolyticus with the tdh gene isolate was detected from one patient. These results confirmed that this was an unusual foodborne illness that included an outbreak associated with two different pathogens and a third pathogen sporadic illness. Takeaway services pose a risk to public health because they have the potential to distribute contaminated products over a large geographic area within a short time. Therefore, more attention should be paid to prevent and control foodborne illnesses caused by contaminated food from takeaway services.

The Role of Regulatory Mechanisms and Environmental Parameters in Staphylococcal Food Poisoning and Resulting Challenges to Risk Assessment

Prevention, prediction, control, and handling of bacterial foodborne diseases - an ongoing, serious, and costly concern worldwide - are continually facing a wide array of difficulties. Not the least due to that food matrices, highly variable and complex, can impact virulence expression in diverse and unpredictable ways. This review aims to present a comprehensive overview of challenges related to the presence of enterotoxigenic Staphylococcus aureus in the food production chain. It focuses on characteristics, expression, and regulation of the highly stable staphylococcal enterotoxins and in particular staphylococcal enterotoxin A (SEA). Together with the robustness of the pathogen under diverse environmental conditions and the range of possible entry routes into the food chain, this poses some of the biggest challenges in the control of SFP. Furthermore, the emergence of new enterotoxins, found to be connected with SFP, brings new questions around their regulatory mechanisms and expression in different food environments. The appearance of increasing amounts of antibiotic resistant strains found in food is also highlighted. Finally, potentials and limitations of implementing existing risk assessment models are discussed. Various quantitative microbial risk assessment approaches have attempted to quantify the growth of the bacterium and production of disease causing levels of toxin under various food chain and domestic food handling scenarios. This requires employment of predictive modeling tools, quantifying the spatiotemporal population dynamics of S. aureus in response to intrinsic and extrinsic food properties. In this context, the armory of predictive modeling employs both kinetic and probabilistic models to estimate the levels that potentiate toxin production, the time needed to reach that levels, and overall, the likelihood of toxin production. Following risk assessment, the main challenge to mitigate the risk of S. aureus intoxication is first to prevent growth of the organism and then to hamper the production of enterotoxins, or at least prevent the accumulation of high levels (e.g., >10-20 ng) in food. The necessity for continued studies indeed becomes apparent based on the challenges to understand, control, and predict enterotoxin production in relation to the food environment. Different types of food, preservatives, processing, and packaging conditions; regulatory networks; and different staphylococcal enterotoxin-producing S. aureus strains need to be further explored to obtain more complete knowledge about the virulence of this intriguing pathogen.

Genotypes, Enterotoxin Gene Profiles, and Antimicrobial Resistance of Staphylococcus aureus Associated with Foodborne Outbreaks in Hangzhou, China

Staphylococcal food poisoning is an illness caused by the consumption of food that contains sufficient amounts of one or more enterotoxins. In the present study, a total of 37 S. aureus isolates were recovered from leftover food, swabs from a kitchen environment, and patient feces associated with four foodborne outbreaks that occurred in Hangzhou, southeast China, and were characterized by multilocus sequence typing (MLST), spa typing, pulse-field gel electrophoresis (PFGE), and antimicrobial susceptibility. Classical enterotoxin and enterotoxin-like genes were profiled by PCR analysis. ST6-t304 was the most common clone (40.54%), followed by ST2315-t11687 (32.43%). Six clusters (A to F) were divided based on PFGE patterns, and Clusters A and C were the most common types, constituting 86.49% of all isolates. Moreover, sea was the most frequently identified enterotoxin gene (81.08%), followed by the combination of seg-sei-selm-seln-sleo-selu and sec-sell (each 48.65%). Five isolates also harbored the exotoxin cluster sed-selj-ser. In addition, resistance to penicillin (97.30%), erythromycin (37.85), tetracycline (32.43%), clindamycin, gentamicin, and sulfamethoxazole (each 10.81%) was observed. Our research demonstrated the link between leftover foods and patients by molecular typing and detecting the profiles of enterotoxin or enterotoxin-like genes in human and food isolates. S. aureus maintains an extensive repertoire of enterotoxins and drug resistance genes that could cause potential health threats to consumers.

Study on the Growth and Enterotoxin Production by Staphylococcus aureus in Canned Meat before Retorting

Possible contamination by Staphylococcus aureus of the production environment and of the meat of a canned meat production factory was analysed. A total of 108 samples were taken from nine critical control points, 13 of them were positive for S. aureus. None of the isolates produced enterotoxins. To determine how much time can elapse between can seaming and sterilisation in the autoclave without any risk of enterotoxin production by S. aureus, the growth and enterotoxin production of three enterotoxin A producing strains of S. aureus (one ATCC strain and two field strains) in canned meat before sterilisation was investigated at three different temperatures (37, 20 and 10 °C). Two types of meat were used, one with and one without sodium nitrite. In the canned products, the spiked bacteria spread throughout the meat and reached high levels. Enterotoxin production was shown to start 10 hours after incubation at 37 °C and after 48 h after incubation at 20 °C; the production of enterotoxin was always detected in the transition between the exponential and the stationary growth phase. At 10 °C, the enterotoxin was never detected. The statistical analysis of the data showed that the difference between the two different types of meat was not statistically significant (p value > 0.05). Since it is well known that following heat treatment, staphylococcal enterotoxins, although still active (in in vivo assays), can be undetectable (loss of serological recognition) depending on the food matrix and pH, it is quite difficult to foresee the impact of heat treatment on enterotoxin activity. Therefore, although the bacteria are eliminated, the toxins may remain and cause food poisoning. The significance of the results of this study towards implementing good manufacturing practices and hazard analysis critical control points in a canned meat factory are discussed with reference to the management of pre-retorting steps after seaming.

Toxin gene profiles, genetic diversity, antimicrobial resistance, and coagulase type of Staphylococcus aureus from cream-filled bakery products

We determined the toxin gene profile, toxin production, antibiotic resistance coagulase serotype, and genetic diversity of 42 coagulase-positive Staphylococcus aureus (CPS) isolates collected from 1,464 cream-filled bakery products in Korea. Among the CPS isolates, 37 (88.1%) produced enterotoxin genes in combination with another toxin; 26 (61.9%) of the strains were positive for sea, 1 (2.4%) for sea-seb, and 4 (9.5%) for sea-sec. Among the strains showing antibiotic resistance, 28 (66.7%) showed resistance to only one antibiotic, whereas nine (21.4%) showed resistance to multiple antibiotics: 4 (9.5%) strains were both mecA-positive and oxacillin-resistant. Most strains are resistant to at least one antibiotic-benzyl penicillin. The CPS isolates were classified into eight coagulase serotypes. This information will be valuable for assessing the capability risks of CPS food poisoning, contributing a better known of the epidemiology result associated with CPS contamination in bakery products.

Occurrence and Characterization of Methicillin Resistant Staphylococcus aureus in Processed Raw Foods and Ready-to-Eat Foods in an Urban Setting of a Developing Country

Infections by methicillin-resistant Staphylococcus aureus (MRSA) are gradually increasing in the community. In this study, we investigated a total of 162 food samples including 112 ready-to-eat (RTE) foods and 40 processed raw meat and fish samples collected from retail vendors in Dhaka, Bangladesh and determined the occurrence of toxigenic S. aureus and MRSA. Around 22% of samples were positive for S. aureus, RTE foods being more positive (23%) than the processed raw meat/fish samples (18%). Among 35 S. aureus isolates, 74% were resistant to erythromycin, 49% to ciprofloxacin and around 30% to oxacillin and cefoxitin. Around 37% of isolates were resistant to ≥3 classes of antibiotics and 26% of isolates (n = 9) were identified as MRSA. Majority of the isolates were positive for enterotoxin genes (74%), followed by pvl gene (71%), toxic shock syndrome toxin (tsst) gene (17%) and exfoliative toxin genes (11%). Multi locus sequence typing (MLST) of 9 MRSA isolates identified four different types such as ST80 (n = 3), ST6 (n = 2), ST239 (n = 2) and ST361 (n = 2). spa typing of MRSA isolates revealed seven different types including t1198 (n = 2), t315 (n = 2), t037 (n = 1), t275 (n = 1), t304 (n = 1), t8731 (n = 1) and t10546 (n = 1). To our knowledge, this is the first report entailing baseline data on the occurrence of MRSA in RTE foods in Dhaka highlighting a potential public health risk to street food consumers.

Dialogue between Staphylococcus aureus SA15 and Lactococcus garvieae strains experiencing oxidative stress

Background

Staphylococcus aureus is an important foodborne pathogen. Lactococcus garvieae is a lactic acid bacterium found in dairy products; some of its strains are able to inhibit S. aureus growth by producing H₂O₂. Three strains of L. garvieae from different origins were tested for their ability to inhibit S. aureus SA15 growth. Two conditions were tested, one in which H₂O₂ was produced (high aeration) and another one in which it was not detected (low aeration). Several S. aureus genes related to stress, H₂O₂-response and virulence were examined in order to compare their level of expression depending on the inoculated L. garvieae strain. Simultaneous L. garvieae H₂O₂ metabolism gene expression was followed.

Results

The results showed that under high aeration condition, L. garvieae strains producing H₂O₂ (N201 and CL-1183) inhibited S. aureus SA15 growth and impaired its ability to deal with hydrogen peroxide by repressing H₂O₂-degrading genes. L. garvieae strains induced overexpression of S. aureus stress-response genes while cell division genes and virulence genes were repressed. A catalase treatment partially or completely restored the SA15 growth. In addition, the H₂O₂ non-producing L. garvieae strain (Lg2) did not cause any growth inhibition. The SA15 stress-response genes were down-regulated and cell division genes expression was not affected. Under low aeration condition, while none of the strains tested exhibited H₂O₂-production, the 3 L. garvieae strains inhibited S. aureus SA15 growth, but to a lesser extent than under high aeration condition.

Conclusion

Taken together, these results suggest a L. garvieae strain-specific anti-staphylococcal mechanism and an H₂O₂ involvement in at least two of the tested L. garvieae strains.

Electronic supplementary material

The online version of this article (10.1186/s12866-018-1340-3) contains supplementary material, which is available to authorized users.

Clinical and Molecular Characterization of Panton-Valentine Leukocidin-Positive Invasive Staphylococcus aureus Infections in Korea

AIM

Panton-Valentine leukocidin (PVL) is a virulent cytotoxin and an indicator of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) infection. In this study, we evaluated the prevalence and clinical and molecular characteristics of PVL-positive invasive S. aureus (ISA) infections in Korea.

RESULTS

A collection of 1,962 nonduplicate clinical isolates were screened for multilocus sequence typing, staphylococcal cassette chromosome mec (SCCmec), accessory gene regulator typing, major toxins, and antimicrobial susceptibility. Twenty-eight (1.4%) PVL-positive S. aureus samples were found; of them 19 (67.9%) were MRSA (8 CA and 11 healthcare-associated infections). Seventeen patients (60.7%) were men (median age: 63 years; range: 13-93 years) and 12 patients (42.9%) had no underlying comorbidities. The most common infections were skin and skin structure infection (SSSI) and pneumonia. The 30-day mortality rate was 37.0%. The most common PVL-positive MRSA clones were ST8-SCCmec IVa and ST30-SCCmec IVc along with their single-locus variants. Antimicrobial susceptibility and toxin-gene profile differed according to the clone.

CONCLUSIONS

ISA infections caused by PVL-positive strains are rare in Korea, with the two most common infections being SSSI and pneumonia. Our findings indicated that several PVL-positive MRSA clones, predominantly ST8-SCCmecIVa and ST30-SCCmecIVc, were circulating and causing sporadic cases of ISA infections in the community and hospital settings.

Prevalence of Enterotoxigenic Staphylococcus aureus and Shiga Toxin Producing Escherichia coli in Fish in Egypt: Quality Parameters and Public Health Hazard

This study investigated the prevalence of Staphylococcus aureus enterotoxin genes and shiga toxin -producing Escherichia coli (STEC) in fish and evaluated quality parameters of examined fish. A total of 150 fish samples belonging to 6 species (25/each species) were cultured on Baird-Parker agar and eosin methylene blue agar. Staphylococcal enterotoxin genes and virulence genes (stx1, stx2, and eaeA genes) in E. coli serotypes were determined by multiplex PCR. Aerobic plate count (APC), Enterobacteriaceae count, coliform count, and Pseudomonas count were performed. Also, levels of total volatile base nitrogen and histamine in fish were determined. The prevalence of S. aureus ranged from 4% to 36% and count from 2 to 4 log₁₀CFU/g. The sed, sea, and seb genes in S. aureus isolates were detected with percentages of 40%, 26.6%, and 20%, respectively. The E. coli serotype O26 carried stx1, stx2, and eaeA. The APCs, Enterobacteriaceae counts, and Pseudomonas counts ranged from 5.1 to 7.2, from 2.01 to 3.9, and from 2.1 to 3.1 log₁₀ CFU/g, respectively. The most probable number (MPN) of coliform ranged from 1.3 to 3.6 log₁₀/g. Levels of total volatile basic nitrogen and histamine ranged from 29.2 to 12.2 and from 0.6 to 4.6 mg/100 g, respectively. Also, the value of thiobarbituric acid was highly significant (1.1 ± 0.084 mg MDA/kg) in Trachurus mediterraneus samples compared with those levels obtained from other fish species. Our findings concluded that those fish species could constitute a public health hazard as fish are reservoirs for enterotoxigenic S. aureus and Shiga toxin producing E. coli strains. This study highlighted the importance of screening of fish for enterotoxigenic S. aureus strains and STEC isolates, and also assessing the quality parameters of fish.

Characterization of Staphylococcus aureus Isolated from Food Products in Western Algeria

The current study aimed to characterize Staphylococcus aureus isolates from foodstuffs collected from western Algeria. A total of 153 S. aureus isolates from various raw and processed foods were obtained and identified using matrix-assisted laser desorption and ionization time-of-flight mass spectrometry. Isolates were characterized by antimicrobial susceptibility testing and toxin gene detection. Methicillin-resistant Staphylococcus aureus (MRSA) isolates were identified by detection of the mecA gene and characterized by staphylococcal cassette chromosome mec (SCCmec) typing. We found that 30.9% (153/495) of food samples were contaminated with S. aureus. Thirty-three (21.5%) S. aureus isolates were identified as MRSA, and 16.9% (26/153) carried the mecA gene. Three SCCmec types were identified of which type IV was the most common (69.2%) followed by type V (15.3%) and type II (7.6%). Two MRSA isolates were not typable with SCCmec typing. None of the examined isolates harbored mecC. Furthermore, 14.3% (22/153) of the isolates were toxigenic S. aureus. The cytotoxin gene pvl was detected in 11.1% of the S. aureus isolates. This gene was more commonly detected (76.4%) in MRSA isolates than in methicillin-suceptible Staphylococcus aureus (MSSA) isolates. The tsst-1 gene coding for toxic shock syndrome toxin was isolated rarely (3.2%) and only in MSSA isolates. According to disk diffusion test results, 70 isolates were resistant to only one antimicrobial drug, and 51 (33.3%) isolates were multidrug resistant. Other 32 isolates were susceptible to all antibiotics. Our study highlights, for the first time, a high prevalence of multidrug-resistant S. aureus isolates carrying pvl or tsst-1 found in food products in Algeria. The risk of MRSA transmission through the food chain cannot be disregarded, particularly in uncooked foods.

Multilocus Sequence Typing and Virulence-Associated Gene Profile Analysis of Staphylococcus aureus Isolates From Retail Ready-to-Eat Food in China

The aim of this study was to characterize the subtypes and virulence profiles of 69 Staphylococcus aureus isolates obtained from retail ready-to-eat food in China. The isolates were analyzed using multilocus sequence typing (MLST) and polymerase chain reaction (PCR) analysis of important virulence factor genes, including the staphylococcal enterotoxin (SE) genes (sea, seb, sec, sed, see, seg, seh, sei, sej), the exfoliative toxin genes (eta and etb), the toxic shock syndrome toxin-1 gene (tst), and the Panton-Valentine leucocidin-encoding gene (pvl). The isolates encompassed 26 different sequence types (STs), including four new STs (ST3482, ST3484, ST3485, ST3504), clustered in three clonal complexes and 17 singletons. The most prevalent STs were ST1, ST6, and ST15, constituting 34.8% of all isolates. Most STs (15/26, 57.7%) detected have previously been associated with human infections. All 13 toxin genes examined were detected in the S. aureus isolates, with 84.1% of isolates containing toxin genes. The three most prevalent toxin genes were seb (36.2%), sea (33.3%), and seg (33.3%). The classical SE genes (sea–see), which contribute significantly to staphylococcal food poisoning (SFP), were detected in 72.5% of the S. aureus isolates. In addition, pvl, eta, etb, and tst were found in 11.6, 10.1, 10.1, and 7.2% of the S. aureus isolates, respectively. Strains ST6 carrying sea and ST1 harboring sec-seh enterotoxin profile, which are the two most common clones associated with SFP, were also frequently detected in the food samples in this study. This study indicates that these S. aureus isolates present in Chinese ready-to-eat food represents a potential public health risk. These data are valuable for epidemiological studies, risk management, and public health strategies.

Contamination sources, biofilm-forming ability and biocide resistance of Staphylococcus aureus in tilapia-processing facilities

The major contamination sources, biofilm-forming ability and biocide resistance of Staphylococcus aureus in tilapia-processing plants were evaluated. Twenty-five processing control points were analysed twice in two factories, including whole tilapias, frozen fillets, water and food-contact surfaces. No final product was contaminated with S. aureus. However, high concentrations of S. aureus carrying enterotoxin ( se) genes were found in several processing points of both factories due to the application of inadequate hygienic and handling procedures, which generate a high risk of cross-contamination of the tilapia fillets with staphylococcal enterotoxins. Nine S. aureus strains were characterized by RAPD-PCR using primers AP-7, ERIC-2 and S. A wide diversity of se gene profiles was detected, most strains being multi- se-carriers. All S. aureus strains showed high biofilm-forming ability on stainless steel and polystyrene. Biofilm-forming ability was correlated with the presence of fliC H7 and the type of origin surface (metallic or plastic). A marked resistance of S. aureus to peracetic acid and sodium hypochlorite was also observed, required doses being higher than those recommended by manufacturers to be eradicated. Case-by-case approaches are thus recommended to determine the sources and degree of contamination present in each factory, which would allow applying precise responses that avoid, or at least reduce, the presence of bacterial pathogens and the emergence of antimicrobial resistance.

Humoral immune consequences of Staphylococcus aureus ST239-associated bacteremia

The humoral immune responses against 46 different staphylococcal antigens in 27 bacteremia patients infected by clonally related methicillin-resistant Staphylococcus aureus (MRSA) strains of a single sequence type (ST) 239 were investigated. A group of non-infected patients (n = 31) hospitalized for different reasons served as controls. All strains were confirmed as ST 239 by S. aureus and mecA-specific PCR, spa, and multi-locus sequence typing (MLST). In each bacteremia patient, a unique pattern of S. aureus antigen-specific immune responses after infection was observed. Antibody levels among bacteremia patients were significantly higher than controls for HlgB (P = 0.001), LukD (P = 0.009), LukF (P = 0.0001), SEA (P = 0.0001), SEB (P = 0.011), SEC (P = 0.010), SEQ (P = 0.049), IsaA (P = 0.043), IsdA (P = 0.038), IsdH (P = 0.01), SdrD (P = 0.001), SdrE (P = 0.046), EsxA (P = 0.0001), and SA0104 (P = 0.0001). On the other hand, the antibody levels were significantly higher among controls for SSL3 (P = 0.009), SSL9 (P = 0.002), and SSL10 (P = 0.007) when the IgG level on the day of infection was compared with that measured on the day of admission. Diversity was observed in the immune response against the antigens. However, a set of antigens (IsaA, IsdA, IsdH, SdrD, and HlgB) triggered a similar type of immune response in different individuals. We suggest that these antigens could be considered when developing a multi-component (passive) vaccine. SEA and/or its specific antibodies seem to play a critical role during ST239 MRSA bacteremia and SEA-targeted therapy may be a strategy to be considered.

Staphylococcus aureus in Some Brazilian Dairy Industries: Changes of Contamination and Diversity

Staphylococcus aureus, a major food-poisoning pathogen, is a common contaminant in dairy industries worldwide, including in Brazil. We determined the occurrence of S. aureus in five dairies in Brazil over 8 months. Of 421 samples, 31 (7.4%) were positive for S. aureus and prevalence varied from 0 to 63.3% between dairies. Sixty-six isolates from the 31 samples were typed by Multi-Locus Sequence Typing to determine if these isolates were persistent or continuously reintroduced. Seven known sequence types (STs), ST1, ST5, ST30, ST97, ST126, ST188 and ST398, and four new ST were identified, ST3531, ST3540, ST3562 and ST3534. Clonal complex (CC) 1 (including the four new ST), known as an epidemic clone, was the dominant CC. However, there were no indications of persistence of particular ST. The resistance toward 11 antibiotic compounds was assessed. Twelve profiles were generated with 75.8% of strains being sensitive to all antibiotic classes and no Methicillin-resistant S. aureus (MRSA) strains were found. The enterotoxin-encoding genes involved in food-poisoning, e.g., sea, sed, see, and seg were targeted by PCR. The two toxin-encoding genes, sed and see, were not detected. Only three strains (4.5%) harbored seg and two of these also harbored sea. Despite the isolates being Methicillin-sensitive S. aureus (MSSA), the presence of CC1 clones in the processing environment, including some harboring enterotoxin encoding genes, is of concern and hygiene must have high priority to reduce contamination.

Prevalence of Staphylococcal Enterotoxins in Ready-to-Eat Foods Sold in Istanbul

The aim of this study was to investigate the prevalence of staphylococcal enterotoxins (SEs) in ready-to-eat (RTE) foods sold in Istanbul, Turkey. A total of 5,241 samples were randomly collected from various caterers, hotels, and restaurants from 2014 to 2016. The samples were classified into four groups: (i) various cooked RTE meat and vegetable meals, (ii) various RTE salads, charcuterie, and cold appetizers, (iii) various cooked RTE bakery products (pasta, pastries, pizza, pita, ravioli, etc.), and (iv) any cooked RTE sweets and desserts (pudding, custard, cream, ashura, etc.). The samples were examined for the presence of SEs by 3M Tecra Staph Enterotoxin Visual Immunoassay method, which is a manual enzyme-linked immunosorbent assay method. Among all samples, only 1 (0.019%) RTE meal (vegetable meal with meat) was found to be contaminated with SEs, a good result in terms of staphylococcal food poisoning risk and public health.

Complete Sequence of a Staphylococcus aureus Clonal Complex 81 Strain, the Dominant Lineage in Food Poisoning Outbreaks in Japan

Staphylococcus aureus No. 10 is an isolate from a staphylococcal food poisoning outbreak in Japan, classified as clonal complex 81 subtype 1. It preferentially produces larger quantities of staphylococcal enterotoxin A (SEA) and staphylococcal enterotoxin H (SEH) in foods and media. Here, we report the complete annotated genome sequence of the chromosome and a plasmid.

Diagnosis and management of Panton-Valentine leukocidin toxin associated Staphylococcus aureus infection: an update

The incidence of invasive Staphylococcus aureus (SA) infection has increased in the past decade and is associated with poor outcomes and high mortality rates. Of all the virulence factors, Panton-Valentine Leukocidin (PVL) has received the greatest attention. PVL producing SA strains are more likely to produce severe skin and soft tissue infections (SSTIs) and necrotizing pneumonia. This review focuses on the current evidence on PVL-SA virulence, epidemiology, clinical disease and treatment with relevance to healthcare in India.

Analysis of virulence genes and accessory gene regulator (agr) types among methicillin-resistant Staphylococcus aureus strains in Iran

OBJECTIVES

Methicillin-resistant Staphylococcus aureus (MRSA) strains are a major cause of hospital-acquired infections and are considered a serious public health concern. MRSA isolates have abundant virulence factors that are the basis for their pathogenicity. The accessory gene regulator (agr) locus co-ordinates the expression of these genes. The aim of this study was to determine the presence and frequency of various virulence genes encoding enterotoxins and adhesins as well as to identify agr specificity groups in MRSA isolates.

METHODS

This descriptive study included a total of 296 MRSA strains isolated from clinical samples collected in Tehran Heart Center (Tehran, Iran) between October 2004 and March 2013. Following DNA extraction, PCR-based assays were used to evaluate the presence of various virulence genes. IBM SPSS Statistics for Windows v.21.0 was used for statistical analysis.

RESULTS

The results indicated that the most frequent toxin genes were see (120/296; 40.5%), followed by sea (79/296; 26.7%); the other genes were encoded less frequently. The presence of seb and seh was not found in any of the isolates. Furthermore, the most frequent adhesin genes were clfA, spa, cna, map/eap and bbp, found in 281 (94.9%), 275 (92.9%), 267 (90.2%), 265 (89.5%) and 264 (89.2%) isolates, respectively. The majority of isolates belonged to agr group I (53.0%), followed by agr group III (1.4%). None of the isolates belonged to agr group II.

CONCLUSIONS

The relatively high frequency of various virulence genes suggests the emergence and pathogenic potential of MRSA isolates containing these genes in the study area.

Identification and measurement of staphylococcal enterotoxin-like protein I (SEll) secretion from Staphylococcus aureus clinical isolate

AIMS

Staphylococcus aureus (Staph. aureus) produces a wide variety of staphylococcal enterotoxins (SEs) and staphylococcal enterotoxin-like (SEl) proteins, which are the most causative agents of staphylococcal food poisoning. In contrast to classical SEs (SEA to SEE), the relationship between the novel SEs/SEls (SEG to SElX) and staphylococcal food poisoning is not elucidated. This study is aimed to establish a system to detect staphylococcal enterotoxin-like protein I (SElI) for analysis of staphylococcal food poisoning.

METHODS AND RESULTS

SElI was characterized in a Staph. aureus clinical isolate associated with food poisoning; there was an amino acid substitution Thr145Ala compared to previously identified SEI from Staph. aureus 04-02981. Subsequently, SElI was expressed, purified, and the poly- and monoclonal antibodies against it were prepared. Using these antibodies, a highly sensitive sandwich enzyme-linked immunosorbent assay (ELISA) that specifically detected and measured SElI secretion from the Staph. aureus clinical isolate in LB medium, milk and bloodstream was developed.

CONCLUSIONS

The ELISA system has been successfully applied for analysing SElI secretion in vivo and in vitro.

SIGNIFICANCE AND IMPACT OF THE STUDY

The highly sensitive ELISA should make it attractive for quantifying SElI in food hygiene supervision and clinical diagnosis in near future.

Prevalence of Staphylococcus aureus and Methicillin-Resistant Staphylococcus aureus in Retail Ready-to-Eat Foods in China

Staphylococcus aureus, particularly methicillin-resistant S.aureus (MRSA), is a life-threatening pathogen in humans, and its presence in food is a public health concern. MRSA has been identified in foods in China, but little information is available regarding MRSA in ready-to-eat (RTE) foods. We aimed to investigate the prevalence of S. aureus and MRSA in Chinese retail RTE foods. All isolated S. aureus were tested for antimicrobial susceptibility, and MRSA isolates were further characterized by multilocus sequence typing (MLST) and staphylococcal cassette chromosome mec (SCCmec) typing. Of the 550 RTE foods collected from 2011 to 2014, 69 (12.5%) were positive for S. aureus. Contamination levels were mostly in the range of 0.3–10 most probable number (MPN)/g, with five samples exceeding 10 MPN/g. Of the 69 S. aureus isolates, seven were identified as MRSA by cefoxitin disc diffusion test. Six isolates were mecA-positive, while no mecC-positive isolates were identified. In total, 75.8% (47/62) of the methicillin-susceptible S. aureus isolates and all of the MRSA isolates were resistant to three or more antibiotics. Amongst the MRSA isolates, four were identified as community-acquired strains (ST59-MRSA-IVa (n = 2), ST338-MRSA-V, ST1-MRSA-V), while one was a livestock-associated strain (ST9, harboring an unreported SCCmec type 2C2). One novel sequence type was identified (ST3239), the SCCmec gene of which could not be typed. Overall, our findings showed that Chinese retail RTE foods are likely vehicles for transmission of multidrug-resistant S. aureus and MRSA lineages. This is a serious public health risk and highlights the need to implement good hygiene practices.

Characterization of Staphylococcus aureus faecal isolates associated with food-borne disease in Korea

AIMS

To characterize Staphylococcus aureus faecal isolates from people suspected to be infected with food poisoning by using antimicrobial susceptibility testing and molecular techniques.

METHODS AND RESULTS

A total of 340 Staph. aureus isolates from 6226 people suspected to be infected with food poisoning were identified and characterized by biochemical methods, antimicrobial susceptibility testing and PCR. Samples were obtained from January 2006 to December 2008 from the National Notifiable Diseases Surveillance System at the Research Institute of Public Health and Environment in Seoul Metropolitan, Korea. All strains carried at least one of the eight staphylococcal enterotoxin (se) genes tested and a total of 27 se profiles were produced; the most frequent se profile was seg-sei and the next was sea. Among the total isolates, 36 methicillin-resistant Staphylococcus aureus (MRSAs) isolates were further analysed by multilocus sequence typing (MLST), Staphylococcal cassette chromosome mec (SCCmec) typing, pulsed-field gel electrophoresis (PFGE) and PCR detection for pvl. ST72-SCCmec type IV was the most predominant clone (27 isolates, 75%) followed by ST1-SCCmec type IV (five isolates, 13·8%), ST20-SCCmec type IV (one isolate, 2·8%), ST493-SCCmec type IV (one isolate, 2·8%), ST903-SCCmec type IV (one isolate, 2·8%) and ST5-SCCmec type II (one isolate, 2·8%). By PFGE typing, MRSAs isolated during the same period were grouped together although they were isolated from different regions. None of MRSAs had PVL gene and nine MRSAs were multidrug resistant.

CONCLUSIONS

Analysis of MRSAs by MLST, SCCmec typing, PFGE and pvl detection showed that the majority of strain associated with food-borne diseases belonged to a Korean community-acquired (CA) MRSA clone with ST72-SCCmec type IV-PVL negative-SEG/SEI and its variations while one strain was hospital-acquired (HA) MRSA.

SIGNIFICANCE AND IMPACT OF THE STUDY

CA-MRSA clone which possessed ST72-SCCmec type IV-PVL negative-SEG/SEI was spread most commonly among MRSAs that were associated with food-borne diseases. This is the first report of ST903 strain in Korea.

Contamination of beef products with staphylococcal classical enterotoxins in Egypt and Saudi Arabia

Food-borne pathogens are of high concern for public health and food safety. Staphylococcus aureus food poisoning is one of the most economically devastating types of food poisoning globally. The purpose of this study was to detect staphylococcal classical enterotoxins (SEs) in processed beef from Kingdom of Saudi Arabia (KSA) and Egypt. In the present investigation a total of 250 random processed meat samples (50 each of minced meat, beef burger, beef sausage, beef kofta and beef luncheon) were collected from different super markets in the study area. Using conventional cultural methods, samples were cultured for isolation and identification of S. aureus. Multiplex PCR was used to detect SEs of the classical type SEA, SEB, SEC and SED from isolates. The percentage presence of S. aureus in minced meat, beef burger, beef sausage, beef kofta and beef luncheon was 38%, 22%, 30%, 32% and 12%, respectively. Multiplex PCR indicated that all examined samples contain different types of classical staphylococcal enterotoxins and only minced meat samples contained all four types of toxins. Multiplex PCR is efficient in detection of SEs from food and may be used in tracing of toxins to promote food hygiene. Implications of contamination of processed meat to food hygiene in the study area are highlighted.

Virulence Factors and Antibiotic Susceptibility of Staphylococcus aureus Isolates in Ready-to-Eat Foods: Detection of S. aureus Contamination and a High Prevalence of Virulence Genes

Staphylococcus aureus is one of the leading causes of food poisoning. Its pathogenicity results from the possession of virulence genes that produce different toxins which result in self-limiting to severe illness often requiring hospitalization. In this study of 200 sushi and sashimi samples, S. aureus contamination was confirmed in 26% of the food samples. The S. aureus isolates were further characterized for virulence genes and antibiotic susceptibility. A high incidence of virulence genes was identified in 96.2% of the isolates and 20 different virulence gene profiles were confirmed. DNA amplification showed that 30.8% (16/52) of the S. aureus carried at least one SE gene which causes staphylococcal food poisoning. The most common enterotoxin gene was seg (11.5%) and the egc cluster was detected in 5.8% of the isolates. A combination of hla and hld was the most prevalent coexistence virulence genes and accounted for 59.6% of all isolates. Antibiotic resistance studies showed tetracycline resistance to be the most common at 28.8% while multi-drug resistance was found to be low at 3.8%. In conclusion, the high rate of S. aureus in the sampled sushi and sashimi indicates the need for food safety guidelines.

Prevalence of Staphylococcus aureus in Imported Fish and Correlations between Antibiotic Resistance and Enterotoxigenicity

A total of 156 Staphylococcus aureus isolates were obtained from 330 imported fresh fish samples from three countries. Selective media were used for the isolation of S. aureus, and the isolates were confirmed by PCR. The isolates were tested for mecA gene, antibiotic resistance, and enterotoxin genes (sea, seb, sec, sed, see, seg, seh, and sei). Most isolates carried sea, seg, and sei genes, and seg-sei was the most frequent enterotoxin profile. About 88.5% of the S. aureus exhibited resistance to at least one antibiotic. High resistance to penicillin and ampicillin; low resistance to tetracycline, erythromycin, rifampin, and clindamycin; and very low resistance to cefotaxime, amoxicillin-clavulanic acid, gentamicin, and ciprofloxacin were exhibited by S. aureus from the three countries. In addition, some antibiotic resistance exhibited a strong correlation (P ≤ 0.01) with enterotoxigenicity in S. aureus. The study concluded that the large amount of globally traded fish increases the possibility of intercontinental transmission of enterotoxigenic and multidrug-resistant S. aureus through fish and highlights the potential influence of local fish handling and processing on consumer health worldwide. The introduction of periodic training in food safety and hygiene is essential to increase fish handlers' awareness of good hygienic practices in handling fish. These findings also enrich the ongoing debate about the risk of methicillin- and multidrug-resistant S. aureus as a foodborne pathogen compared with drug-susceptible S. aureus.

Enterotoxin-Encoding Genes in Staphylococcus spp. from Food Handlers in a University Restaurant

Food handlers carrying enterotoxin-producing Staphylococcus are a potential source of food poisoning. The aim of this study was to analyze genes encoding enterotoxins in coagulase-positive Staphylococcus (CoPS) and coagulase-negative Staphylococcus (CoNS) isolated from the anterior nostrils and hands of food handlers at a university restaurant in the city of Natal, Northeast Brazil. Thirty food handlers were screened for the study. The isolates were subjected to Gram staining, a bacitracin sensitivity test, mannitol fermentation, and catalase and coagulase tests. CoNS and CoPS strains were subsequently identified by a Vitek 2 System (BioMerieux, France) and various biochemical tests. Polymerase chain reaction was used to detect genes for enterotoxins A, B, C, D, E, G, H, and I (sea, seb, sec, sed, see, seg, seh, and sei) and a disc-diffusion method was used to determine susceptibility to several classes of antimicrobials. All food handlers presented staphylococci on their hands and/or noses. The study found 58 Staphylococcus spp., of which 20.7% were CoPS and 79.3% were CoNS. S. epidermidis was the most prevalent species. Twenty-nine staphylococci (50%) were positive for one or more enterotoxin genes, and the most prevalent genes were seg and sei, each with a frequency of 29.3%. Indeed, CoNS encoded a high percentage of enterotoxin genes (43.5%). However, S. aureus encoded even more enterotoxin genes (75%). Most isolates showed sensitivity to the antibiotics used for testing, except for penicillin (only 35% sensitive). The results from this study reinforce that coagulase-negative as well as coagulase-positive staphylococci isolated from food handlers are capable of genotypic enterotoxigenicity.

Positive Regulation of Staphylococcal Enterotoxin H by Rot (Repressor of Toxin) Protein and Its Importance in Clonal Complex 81 Subtype 1 Lineage-Related Food Poisoning

We previously demonstrated the clonal complex 81 (CC81) subtype 1 lineage is the major staphylococcal food poisoning (SFP)-associated lineage in Japan (Y. Sato'o et al., J Clin Microbiol 52:2637-2640, 2014, http://dx.doi.org/10.1128/JCM.00661-14). Strains of this lineage produce staphylococcal enterotoxin H (SEH) in addition to SEA. However, an evaluation of the risk for the recently reported SEH has not been sufficiently conducted. We first searched for staphylococcal enterotoxin (SE) genes and SE proteins in milk samples that caused a large SFP outbreak in Japan. Only SEA and SEH were detected, while there were several SE genes detected in the samples. We next designed an experimental model using a meat product to assess the productivity of SEs and found that only SEA and SEH were detectably produced in situ. Therefore, we investigated the regulation of SEH production using a CC81 subtype 1 isolate. Through mutant analysis of global regulators, we found the repressor of toxin (Rot) functioned oppositely as a stimulator of SEH production. SEA production was not affected by Rot. seh mRNA expression correlated with rot both in media and on the meat product, and the Rot protein was shown to directly bind to the seh promoter. The seh promoter sequence was predicted to form a loop structure and to hide the RNA polymerase binding sequences. We propose Rot binds to the promoter sequence of seh and unfolds the secondary structure that may lead the RNA polymerase to bind the promoter, and then seh mRNA transcription begins. This alternative Rot regulation for SEH may contribute to sufficient toxin production by the CC81 subtype 1 lineage in foods to induce SFP.

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.

Development of an indirect competitive enzyme-linked immunosorbent assay based on the multiepitope peptide for the synchronous detection of staphylococcal enterotoxin A and G proteins in milk

Staphylococcal food poisoning (SFP), one of the most common foodborne diseases, results from ingestion of staphylococcal enterotoxins (SEs) in foods. In our previous studies, we found that SEA and SEG were two predominant SE proteins produced by milkacquired S. aureus isolates. Here, a tandemly arranged multiepitope peptide (named SEAGepis) was designed with six linear B-cell epitopes derived from SEA or SEG and was heterologously expressed. The SEAGepis-specific antibody was prepared by immunizing rabbit with rSEAGepis. Then, an indirect competitive enzyme-linked immunosorbent assay (ic-ELISA) based on rSEAGepis and the corresponding antibody was developed to simultaneously detect SEA and SEG. Under the optimized conditions, the ic-ELISA standard curve for rSEAGepis was constructed in the concentration range of 0.5 to 512 ng/ml, and the average coefficients of variation of intra- and interassay were 4.28 and 5.61% during six standard concentrations. The average half-maximal inhibitory concentration was 5.07 ng/ml, and the limit of detection at a signal-to-noise ratio of 3 was 0.52 ng/ml. The anti-rSEAGepis antibody displayed over 90% cross-reactivity with SEA and SEG but less than 0.5% cross-reactivity with other enterotoxins. Artificially contaminated milk with different concentrations of rSEAGepis, SEA, and SEG was detected by the established ic-ELISA; the recoveries of rSEAGepis, SEA, and SEG were 91.1 to 157.5%, 90.3 to 134.5%, and 89.1 to 117.5%, respectively, with a coefficient of variation below 12%. These results demonstrated that the newly established ic-ELISA possessed high sensitivity, specificity, stability, and accuracy and could potentially be a useful analytical method for synchronous detection of SEA and SEG in milk.

Staphylococcus aureus ST6-t701 isolates from food-poisoning outbreaks (2006-2013) in Xi'an, China

The aim of the study was to investigate the molecular epidemiologic of Staphylococcus aureus isolated from seven staphylococcal food-poisoning (SFP) outbreaks between 2006 and 2013 in Xi'an, northwest China. A total of seven S. aureus isolates associated with seven SFP outbreaks were obtained and characterized by determining the multilocus sequence typing, spa typing, pulsed-field gel electrophoresis (PFGE), antimicrobial susceptibility, toxin and resistant genes. The results showed that S. aureus ST6-t701 (71.4%) was the most predominant clone, followed by ST5-t002 and ST59-t172 (each 14.3%). Seven different PFGE patterns were obtained. Moreover, resistance was most frequently observed to trimethoprim and penicillin (each 71.4%), followed by erythromycin (28.6%), ampicillin, clindamycin, and tetracycline (each 14.3%). All strains were susceptible to chloramphenicol, cefoxitin, oxacillin, amikacin, and vancomycin. Three of seven strains displayed resistance to three or more antimicrobials. Resistance genes were found as follows: linA/linA' (100%), blaZ (85.7%), tet(K), ermC, ermT, and ermB (each 14.3%). Other resistant genes were not detected. In addition, the most frequently identified exotoxin genes were seu, lukED, hla, hlb, hld (each 100%), followed by hlg and hlgv (each 85.7%), lukPV (71.4%), sea (57.1%), see (42.9%), etd (28.6%), and seb, sec, sed, sej, and sek (each 14.3%). The results indicated that S. aureus ST6-t701, with a high prevalence in the northwest of China, exhibited multidrug resistance and harbored multiple toxin and resistance genes. Therefore, strict hygienic and preventative measures should be taken in order to avoid the contamination of food by S. aureus and toxin production in foods.

Genetic diversity and virulence potential of Staphylococcus aureus isolates from raw and processed food commodities in Shanghai

The risk of zoonotic transmission to humans highlights the need to understand the molecular ecology of Staphylococcus aureus in foods. In this study, 142 S. aureus isolates obtained from various raw and processed foods from Shanghai, China were characterized to determine their genetic diversity and virulence gene content. A total of 16 clonal complexes (CCs), 34 staphylococcal protein A (spa) types, and 6 accessory gene regulator (agr) allelic groups were identified and analyzed among the 142 S. aureus isolates. Among these, the genotype CC188-t189-agr Ι was the most prevalent, constituting 28.2% of all isolates. The presence of virulence genes encoding 20 staphylococcal enterotoxins (se), toxic shock syndrome toxin (tsst1), exfoliative toxins (eta, etb, and etd), Panton-Valentine leukocidin (lukS-PV and lukF-PV), as well as methicillin resistance gene (mecA), was determined by PCR. Of these S. aureus isolates, 72.5% harbored toxin genes, in which the most frequent toxin gene was sep (43.7%), followed by sej (26.1%) and pvl (21.1%). In contrast, see, ses, set, tsst1, etb, and etd were not found in any of the isolates tested. Eight S. aureus isolates (5.6%, 8/142), seven from raw milk and one from frozen food, were mecA positive and resistant to oxacillin, thus were MRSA. The 142 S. aureus isolates displayed 52 different toxin gene profiles. Although no direct association was found between toxin gene profile and the S. aureus genotype, the isolates belonging to CC5, CC9, CC20, CC50, and CC72 clonal lineages in general carried more toxin genes (>5) compared with the isolates in other CCs. It was also revealed that raw milk and raw meat were the major sources of isolates containing multiple toxin genes. S. aureus isolates from food that were genetically highly related, displayed diverse toxin gene profiles, implying the significant role of horizontal gene transfer in the emergence of highly toxigenic S. aureus isolates.