CHARACTERIZATION OF A DUPLEX POLYMERASE CHAIN REACTION ASSAY FOR THE DETECTION OF ENTEROTOXIGENIC STRAINS OF STAPHYLOCOCCUS AUREUS

Multiplex PCR method for simultaneous detection of five pathogenic bacteria closely related to foodborne diseases

In this study, we describe a multiplex PCR method for the detection of five food-relevant virulence pathogenicity genes of intestinal pathogens. Five pairs of primers were designed based on nuc gene for Staphylococcus aureus, hlyA gene of Listeria monocytogenes, ipaH gene of Shigella flexneri, lysP gene of Yersinia enterocolitica and tpi gene of Clostridium difficile. Conditions were optimized to amplify fragments of those genes simultaneously in one PCR amplification. After developing and optimizing the multiplex PCR reaction system, the specificity and sensitivity of the multiple PCR assays were evaluated. The optimized program is also applied to retail meat for testing. The result indicated that when the annealing temperature was 54 °C and the primer concentrations of S. aureus, L. monocytogenes, S. flexneri, Y. enterocolitica and C. difficile are 10, 10, 5, 3 and 2 μM, the five strains could expand 484, 345, 204, 156, 88 bp of clear fragments, respectively. So was the multiple PCR in artificially contaminated beef produce. All cultures were cultured and separated by traditional methods. The multiplex PCR method offers a rapid, simple, and accurate identification of pathogens and could be used in food safety investigations, clinical diagnosis as well as for the surveillance of the spreading determinants of pathogens in epidemiological studies.

Prevalence, Antimicrobial Resistance, and Molecular Characterization of Staphylococcus aureus Isolated from Animals, Meats, and Market Environments in Xinjiang, China

Staphylococcus aureus has been recognized as an important foodborne pathogen. However, knowledge about the epidemiology and genetic characteristics of S. aureus in the meat production chain from farm to market is limited. The aim of this study was to investigate the genetic characteristics of S. aureus in animal samples isolated from Xinjiang province farms and farmer' markets, by determining staphylococcal protein A (spa) repeat region and virulence factor typing, and by assessment of antimicrobial resistance. Out of 1324 samples, 128 (9.7%) were positive for S. aureus, 26 (2.0%) of them were identified as methicillin-resistant S. aureus (MRSA) and 88 (6.6%) of them were identified as vancomycin-resistant S. aureus (VRSA). Antimicrobial resistance was determined using the disk diffusion method. S. aureus isolates showed resistance to penicillin G (98.4%), clarithromycin (69.5%), erythromycin (69.5%), vancomycin (68.8%), and tetracycline (67.2%). A total of 80.4% of isolates showed resistance to three or more antimicrobial classes. PCR was used to detect ten virulence genes such as the enterotoxin (sea, seb, and sec), hemolysin (hla and hlb), clumping factor (clfA), and fibronectin-binding proteins A and B (fnbA and fnbB). Our study showed that isolates harbored two or seven virulence genes. All strains encode hla and clfA, and half of them encode hlb and enterotoxin genes. The spa typing results showed that the 128 isolates were grouped into 32 spa types. The main spa types were t127 (22.7%), t2592 (12.5%), t437 (10.9%), and t2616 (10.9%). Notably, isolates of t437 type accounted for 46.2% of the MRSA. Our data indicate that meats in the slaughterhouse and farmers' markets were contaminated with S. aureus. S. aureus virulence genes and spa types were diverse, and its antibiotic resistance was serious. The presence of MRSA and VRSA represents potential public health risks and warrants further investigation regarding the driving factors of such resistance and their transmission to humans.

Evaluating DNA Extraction Methods for Community Profiling of Pig Hindgut Microbial Community

Recovery of high quality PCR-amplifiable DNA has been the general minimal requirement for DNA extraction methods for bulk molecular analysis. However, modern high through-put community profiling technologies are more sensitive to representativeness and reproducibility of DNA extraction method. Here, we assess the impact of three DNA extraction methods (with different levels of extraction harshness) for assessing hindgut microbiomes from pigs fed with different diets (with different physical properties). DNA extraction from each sample was performed in three technical replicates for each extraction method and sequenced by 16S rRNA amplicon sequencing. Host was the primary driver of molecular sequencing outcomes, particularly on samples analysed by wheat based diets, but higher variability, with one failed extraction occurred on samples from a barley fed pig. Based on these results, an effective method will enable reproducible and quality outcomes on a range of samples, whereas an ineffective method will fail to generate extract, but host (rather than extraction method) remains the primary factor.

Genotypes and toxin gene profiles of Staphylococcus aureus clinical isolates from China

A total of 108 S. aureus isolates from 16 major hospitals located in 14 different provinces in China were characterized for the profiles of 18 staphylococcal enterotoxin (SE) genes, 3 exfoliatin genes (eta, etb and etd), and the toxic shock syndrome toxin gene (tsst) by PCR. The genomic diversity of each isolate was also evaluated by pulsed-field gel electrophoresis (PFGE), multilocus sequence typing (MLST), and accessory gene regulator (agr) typing. Of these strains, 90.7% (98/108) harbored toxin genes, in which tsst was the most prevalent toxin gene (48.1%), followed by sea (44.4%), sek (42.6%) and seq (40.7%). The see and etb genes were not found in any of the isolates tested. Because of high-frequency transfer of toxin gene-containing mobile genetic elements between S. aureus strains, a total of 47 different toxin gene combinations were detected, including a complete egc cluster in 19 isolates, co-occurrence of sea, sek and seq in 38 strains, and sec and sel together in 11 strains. Genetic typing by PFGE grouped all the strains into 25 clusters based on 80% similarity. MLST revealed 25 sequence types (ST) which were assigned into 16 clonal complexes (CCs) including 2 new singletons. Among these, 11 new and 6 known STs were first reported in the S. aureus strains from China. Overall, the genotyping results showed high genetic diversity of the strains regardless of their geographical distributions, and no strong correlation between genetic background and toxin genotypes of the strains. For genotyping S. aureus, PFGE appears to be more discriminatory than MLST. However, toxin gene typing combined with PFGE or MLST could increase the discriminatory power of genotyping S. aureus strains.

Phenotypic characterization and prevalence of enterotoxin genes in Staphylococcus aureus isolates from outbreaks of illness in Chengdu City

Staphylococcus aureus produces a spectrum of enterotoxin that is recognized as the main reason for causing staphylococcal food poisoning. The aim of the current study was to investigate the phenotypic characteristics and enterotoxin genotypes of S. aureus isolated from food poisoning sufferers. On the basis of the amplification of 16S rRNA and nuc gene specific to S. aureus assay and the phenotype (hemolytic activity, thermal stable nuclease [Tnase] test, and biofilm formation), all isolates were identified as S. aureus. To genotypically characterize S. aureus isolates, genes encoding staphylococcal enterotoxin (sea, seb, sec, sed, see, seg, seh, sei, sej, sek, sem, sen, ser, and seu) were investigated by using polymerase chain reaction technique. The results showed that the eight isolates of S. aureus had different enterotoxin genotypic characteristics, which was the main cause of food poisoning. One isolate contained 10 enterotoxin genes, and the other 7 isolates carried 3 or more enterotoxin genes. The frequency of the newly identified enterotoxin genes (seg-seu) was higher than classical genes (sea-see). Overall, multi-gene detection rates were 75% (for sek, ser, and seu); 50% (for sea and sem); 37.5% (for sen, seg, and sei); and 12.5% (for seb, sec, sed, and sej), respectively. The see and seh gene were not detected in any isolates. The current study provided the exact distribution of enterotoxin genes in eight S. aureus strains from food poisoning sufferers, which indicated that the pathogenicity of the newly identified enterotoxin should be highlighted. The need for prevention of food poisoning occurrences caused by enterotoxin of S. aureus should be reinforced.

Multiplexed bead-based mesofluidic system for detection of food-borne pathogenic bacteria

In the present study, a simple and rapid multiplexed bead-based mesofluidic system (BMS) was developed for simultaneous detection of food-borne pathogenic bacteria, including Staphylococcus aureus, Vibrio parahaemolyticus, Listeria monocytogenes, Salmonella, Enterobacter sakazakii, Shigella, Escherichia coli O157:H7, and Campylobacter jejuni. This system is based on utilization of isothiocyanate-modified microbeads that are 250 mum in diameter, which were immobilized with specific amino-modified oligonucleotide probes and placed in polydimethylsiloxane microchannels. PCR products from the pathogens studied were pumped into microchannels to hybridize with the oligonucleotide-modified beads, and hybridization signals were detected using a conventional microarray scanner. The short sequences of nucleic acids (21 bases) and PCR products characteristic of bacterial pathogens could be detected at concentrations of 1 pM and 10 nM, respectively. The detection procedure could be performed in less than 30 min with high sensitivity and specificity. The assay was simple and fast, and the limits of quantification were in the range from 500 to 6,000 CFU/ml for the bacterial species studied. The feasibility of identification of food-borne bacteria was investigated with samples contaminated with bacteria, including milk, egg, and meat samples. The results demonstrated that the BMS method can be used for effective detection of multiple pathogens in different foodstuffs.