Distribution of staphylococcal enterotoxin genes among Staphylococcus aureus isolates from poultry and humans with invasive staphylococcal disease

Update on molecular diversity and multipathogenicity of staphylococcal superantigen toxins

Staphylococcal superantigen (SAg) toxins are the most notable virulence factors associated with Staphylococcus aureus, which is a pathogen associated with serious community and hospital acquired infections in humans and various diseases in animals. Recently, SAg toxins have become a superfamily with 29 types, including staphylococcal enterotoxins (SEs) with emetic activity, SE-like toxins (SEls) that do not induce emesis in primate models or have yet not  been tested, and toxic shock syndrome toxin-1 (TSST-1). SEs and SEls can be subdivided into classical types (SEA to SEE) and novel types (SEG to SElY, SE01, SE02, SEl26 and SEl27). The genes of SAg toxins are located in diverse accessory genetic elements and share certain structural and biological properties. SAg toxins are heat-stable proteins that exhibit pyrogenicity, superantigenicity and capacity to induce lethal hypersensitivity to endotoxin in humans and animals. They have multiple pathogenicities that can interfere with normal immune function of host, increase the chances of survival and transmission of pathogenic bacteria in host, consequently contribute to the occurrence and development of various infections, persistent infections or food poisoning. This review focuses on the following aspects of SAg toxins: (1) superfamily members of classic and novelty discovered staphylococcal SAgs; (2) diversity of gene locations and molecular structural characteristics; (3) biological characteristics and activities; (4) multi-pathogenicity of SAgs in animal and human diseases, including bovine mastitis, swine sepsis, abscesses and skin edema in pig, arthritis and septicemia in poultry, and nosocomial infections and food-borne diseases in humans.

Antimicrobial resistances and virulence markers in Methicillin-resistant Staphylococcus aureus from broiler and turkey: A molecular view from farm to fork

Little is known about the characteristics of MRSA occurring along the broiler and turkey production chains. The aim of this study was to characterise and compare MRSA of turkey and broiler origin sampled on different production levels using a DNA microarray and antimicrobial susceptibility testing. Main differences could be observed in the prevalence of the resistance genes erm(C), aacA-aphD and tet(K) and the number of non-wild type strains with minimum inhibitory concentration values (MICs) above the epidemiological cut-off values (ECOFFs) for gentamicin and kanamycin. Overall, MRSA with non-wild type phenotype for the macrolide-lincosamide-streptogramin group, tetracycline, and trimethoprim were found in more than 70% of poultry isolates. Non-wild type isolates carrying the qacC gene conferring resistance to quaternary ammonium compound disinfectants were found at all production stages in similar frequencies. Regarding the presence of enterotoxin genes in poultry-derived MRSA the enterotoxin gene cluster (egc) was only found in Non-CC (clonal complex) 398 strains. Three CC398 strains harboured the genes sed (from turkey at slaughter and broiler meat) and sea-N315 (from a chicken carcass). One Non-CC398 strain isolated from turkey meat was found positive for the seb gene and also enterotoxin production. Similarity analysis based on selected resistance and virulence markers revealed a high clonality among Non-CC398 isolates. Isolates of the same clonal complex clustered together according to their common virulence and resistance profiles. Strains of CC9 were grouped in two subclusters due to different resistance genes. Our results underline, that there are other poultry associated clones of MRSA (mainly CC9 and CC5) besides the predominant CC398 which are similar in both poultry species.

Preliminary study on hazards and critical control points of kokoro, a Nigerian indigenous fermented maize snack

The microbial and proximate composition of an indigenous snack from fermented maize was investigated. Critical control points of milling the raw materials, fermentation pH, processing temperature and time intervals during holdings in processing and storage were evaluated with a view to optimizing the product. The mean total aerobic plate count (TAPC) log₁₀ values for samples of the finished products range from 2.07 ± 0.50 to 4.36 ± 0.10 cfu/g. Mean fungi count log₁₀ was 2.00 ± 0.00 to 3.50 ± 0.50 while mean coliform count 1.04 ± 0.10 log₁₀ cfu/g was detected in one of the sales outlets investigated. Bacterial and fungal species were isolated belonging to the genera Aspergillus, Rhizopus, Penicillium, Fusarium, Cephalosporium, Alternaria, Bacillus, Klebsiella, Staphylococcus, Lactobacillus, Pseudomonas, Proteus and Enterobacter. The moisture content of the samples ranged from 3.41 to 6.75%; fat content was 19.68 to 32.59%; fiber content was 1.84 to 2.78% while protein ranged from 6.76 to 9.23%. The ash and carbohydrate contents ranged from 1.97 to 2.31% and 49.21 to 61.96%, respectively. Based on the specifications by International Commission for Microbiological Specification for Foods (ICMSF), the TAPC counts of the finished products remained at low levels. However, presence of coliforms could prejudice the hygienic quality of these types of products hence, the need for quality control.

Microarray-based characterization of Staphylococcus aureus isolates obtained from chicken carcasses

A total of 34 Staphylococcus aureus isolates from flock-wise pooled chicken neck skin samples collected at two abattoirs during slaughter were characterized with DNA microarray analysis and spa typing. The 20 isolates from abattoir A all belonged to clonal complex (CC) 12 and spa type t160. Of the 14 isolates from abattoir B, 7 belonged to CC5-t3478, 5 to CC12-t160, 1 to CC45-t040, and 1 to CC101-t056. Of the various resistance-associated genes tested, only blaZ/R/I (6 isolates of CC12 and CC101 from abattoir B), sdrM (n = 34), fosB (n = 33), and qacC (n = 22) were detected. None of the isolates harbored genes conferring methicillin resistance. In terms of genes encoding enterotoxins, seb (all isolates of CC12), egc (seg, sei, selm, seln, selo, selu; all isolates of CC5 and CC45), and sea (14 isolates of CC12 and 1 isolate of CC5) were found. In addition, all isolates harbored genes for intracellular adhesion proteins (icaA/C/D) and were positive for cap5 or cap8 (capsule type 5 or 8). Comparison of DNA microarray profiles identified four categories comprising (i) all isolates of CC12, (ii) all isolates of CC5, (iii) the CC45 isolate, and (iv) the CC101 isolate. The high similarity of the isolates from abattoir A could indicate contamination of chicken carcasses with S. aureus persisting on the slaughter equipment, but further investigations are required to elucidate potential contamination routes.

The in vitro anti-pathogenic activity of immunoglobulin concentrates extracted from ovine blood

An immunoglobulin-rich fraction has been prepared from ovine blood in our laboratory. We have investigated its antibacterial activity and binding activity to pathogenic whole cell antigens, lipopolysaccharide (LPS) and staphylococcal enterotoxin B. Ovine immunoglobulin concentrate (OIC) comprised about 73 +/- 2% of IgG and 11 +/- 1% of IgM on a protein basis. It inhibited the growth of all 13 strains of pathogens tested, but the inhibitory activity varied according to bacterial strain. The inhibitory activity of OIC was attributed to the high contents of undenatured immunoglobulin present because its inhibitory activity was destroyed by pepsin digestion and heat treatment (65 degrees C for 30 min). OIC bound to all the Gram-positive and Gram-negative pathogens, regardless of cell wall structure. The highest magnitude of crossreactivity to whole cell antigens was against Staphylococcus epidermidis and Shigella soneii strains (p < 0.001). The binding activity of OIC to LPS obtained from Escherichia coli O111:B4 and Salmonella enterica serotype typhimurium was assessed by enzyme-linked immunosorbent assay and lymphoblast K-562 proliferation assay. OIC bound to LPS with a binding activity that was dependent on OIC concentration and saturable, showing typical hyperbolic curves. For toxin-binding activity, an OIC concentration-dependent trend like that for LPS-binding activity was also observed. This preliminary evidence suggests that the OIC used in this study could be a promising supplement for protecting against pathogenic bacteria.

Molecular diagnostics of clinically important staphylococci

Bacterial species of the genus Staphylococcus known as important human and animal pathogens are the cause of a number of severe infectious diseases. Apart from the major pathogen Staphylococcus aureus, other species until recently considered to be nonpathogenic may also be involved in serious infections. Rapid and accurate identification of the disease-causing agent is therefore prerequisite for disease control and epidemiological surveillance. Modern methods for identification and typing of bacterial species are based on genome analysis and have many advantages compared to phenotypic methods. The genotypic methods currently used in molecular diagnostics of staphylococcal species, particularly of S. aureus, are reviewed. Attention is also paid to new molecular methods with the highest discriminatory power. Efforts made to achieve interlaboratory reproducibility of diagnostic methods are presented.

Evolution of slime production by coagulase-negative staphylococci and enterotoxigenic characteristics of Staphylococcus aureus strains isolated from various human clinical specimens

The present study was designed to determine the slime production of coagulase-negative staphylococci (CoNS) and the enterotoxigenic properties of Staphylococcus aureus strains, and to evaluate the clinical importance of slime-producing CoNS and enterotoxigenic S. aureus strains isolated from various human clinical specimens. For this purpose, a total of 120 Staphylococcus strains were isolated and identified, and further characterized for their slime production and enterotoxigenicity. Of the clinical isolates, 55 (45.8 %) were found to be S. aureus, and the others (54.2 %) were identified as CoNS. Of the CoNS, 20 (16.7 %) were further identified as Staphylococcus hominis, 18 (15 %) as Staphylococcus epidermidis, six (5 %) as Staphylococcus xylosus, six (5 %) as Staphylococcus warneri, five (4.2 %) as Staphylococcus sciuri, four (3.3 %) as Staphylococcus haemolyticus, and two each (1.7 %) as Staphylococcus simulans, Staphylococcus capitis and Staphylococcus saprophyticus, respectively. Thirty-nine (60 %) of 65 CoNS were found to be slime producers. Slime production was observed in all CoNS, except S. capitis, mostly from blood (38.5 %), tracheal aspiration (20.5 %) and urine (12.8 %) specimens. In addition, of the 55 S. aureus isolates, 46 (83.6 %) were found to be enterotoxigenic, and of these S. aureus strains, 39 (84.7 %) were positive for staphylococcal enterotoxin (SE)A. The results of this study showed that the slime-producing CoNS were mostly found in clinical specimens of blood, tracheal aspirate and urine. SEA was the predominant enterotoxin type detected in S. aureus strains from human clinical specimens.

Staphylococcus aureus of phage type 187 isolated from people occurred to be a genes carrier of eneterotoxin C and toxic shock syndrome toxin-1 (TSST-1)

The aim of this study was to examine the genotype properties of Staphylococcus aureus of phage type 187 strains that constitute a separate group among the strains of S. aureus. Sixteen strains were collected from the hospital patients (n=12) and the healthy carriers (n=4) in 13 medical centres in Poland during 1991 and 2005. Biotyping, antibiotic susceptibility, phage typing, detection the genes of enterotoxins and toxic shock syndrome toxin, genotyping of chromosomal DNA by pulsed-field gel electrophoresis (PFGE), also amplification and restriction analysis of the coagulase (coa) and the protein A genes (spa) (PCR/restriction fragment length polymorphism (RFLP)) was tested. The results of this study showed that all staphylococcus of phage type 187 belonged to the human biotype (A) and appeared to be sensitive to all of the tested antibiotics, including methicillin (MSSA). Finding out the toxin genes showed that almost all of them (93.8%) had the enterotoxin C gene (sec) and TSST-1 gene (tst). The PFGE typing proved that the phage type 187 strains (except for one) constitute one PFGE type. These results and the identical restriction patterns in the PCR/RFLP method, also the same biotype, sensitivity to antibiotics and the presence genes of the same type of toxins confirmed that the phage type 187 strains constitute one clone within our country. Additionally, the fact that almost all of them have the enterotoxin genes and tst gene allows to consider them the strains of potentially high virulence.

Comparison of antibiogram, staphylococcal enterotoxin productivity, and coagulase genotypes among Staphylococcus aureus isolated from animal and vegetable sources in Korea

Staphylococcal food poisoning is caused by enterotoxin-producing Staphylococcus aureus. We investigated the prevalence of such organisms in samples of bovine mastitic milk (n = 714), raw meat (n = 139), and vegetables (n = 616). We determined the degrees of relatedness of isolates as indicated by antibiogram, staphylococcal enterotoxin (SE) productivity, and coagulase gene restriction fragment length polymorphism analysis. We examined 297 S. aureus isolates and found SE production in 57 (31.8%), 4 (7.8%), and 49 (73.1%) isolates from raw milk, raw meat, and vegetables, respectively. A high proportion of the isolates obtained from milk produced more than two types of toxins (mainly SEA, SEB, and/or SEC), whereas isolates from raw meat and vegetables primarily produced SEA alone. Most isolates were sensitive to cephalothin (97.6%), gentamicin (80.8%), erythromycin (79.5%), and tetracycline (72.7%), but were resistant to penicillin (90.2%) and ampicillin (88.9%). The proportion of antibiotic-resistant isolates differed according the source of the bacteria; the milk and vegetable isolates were more resistant to penicillin and ampicillin than were the meat isolates (P < 0.05), whereas tetracycline resistance was limited to the milk and vegetables isolates. The coagulase genotypes (I to XII) varied with the source of the organism, and only a few genotypes prevailed in each source: II (42.4%) and IV (24%) types in isolates from milk, IX (35.3%) and XI (45%) from raw meat, and III (40.3%) and XII (32.8%) from vegetables. These findings suggest that remarkable differences exist in antibiogram, SE productivity, and coagulase genotypes, resulting in limited clonal transmission of S. aureus into various food sources. As enterotoxin production only occurs when S. aureus grows to high numbers, staphylococcal food poisoning can be prevented by proper refrigeration.

Identification of Staphylococcus aureus strains negative for enterotoxins A, B and C isolated from bovine mastitis in México

A total of 41 isolates of Staphylococcus aureus obtained from bovine mastitis in 7 different states in Mexico were analyzed by the polymerase chain reaction (PCR) to determine the presence of encoding genes for enterotoxins A, B and C. The oligonucleotides were designed by specific regions of the sea, seb, sec genes. Surprisingly, none of the isolates presented the prospective amplification bands when they were run on agarose gels. On the contrary, reference strains CECT 976 SEA; CECT 5191 SEB; and CECT 4465 SEC showed the prospective amplification products. In order to confirm these results, enterotoxin production A, B, C, D, and E was determined by enzyme linked fluorescent assay (ELFA) using a MiniVIDAS system, on 15 Staphylococcus aureus selected at random from among the 41 isolates. None of the analyzed strains was positive to the test, whereas reference strains enterotoxins producing: CECT 976 SEA; CECT 5191 SEB; CECT 4465 SEC, CECT 4466 SED; CECT 5192 SEE produced concentrations of the toxins detected for this technique. The role of enterotoxins in the pathogenicity of S. aureus in bovine mastitis in Mexico is discussed.

Host- and tissue-specific pathogenic traits of Staphylococcus aureus

Comparative genomics were used to assess genetic differences between Staphylococcus aureus strains derived from infected animals versus colonized or infected humans. A total of 77 veterinary isolates were genetically characterized by high-throughput amplified fragment length polymorphism (AFLP). Bacterial genotypes were introduced in a large AFLP database containing similar information for 1,056 human S. aureus strains. All S. aureus strains isolated from animals in close contact with humans (e.g., pet animals) were predominantly classified in one of the five main clusters of the AFLP database (cluster I). In essence, mastitis-associated strains from animals were categorized separately (cluster IVa) and cosegregated with bacteremia-associated strains from humans. Distribution of only 2 out of 10 different virulence genes differed across the clusters. The gene encoding the toxic shock syndrome protein (tst) was more often encountered among veterinary strains (P < 0.0001) and even more in the mastitis-related strains (P<0.0001) compared to human isolate results. The gene encoding the collagen binding protein (cna) was rarely detected among invasive human strains. The virulence potential, as indicated by the number of virulence genes per strain, did not differ significantly between the human- and animal-related strains. Our data show that invasive infections in pets and humans are usually due to S. aureus strains with the same genetic background. Mastitis-associated S. aureus isolated in diverse farm animal species form a distinct genetic cluster, characterized by an overrepresentation of the toxic shock syndrome toxin superantigen-encoding gene.

Superantigen genes encoded by the egc cluster and SaPIbov are predominant among Staphylococcus aureus isolates from cows, goats, sheep, rabbits and poultry

In recent years several new staphylococcal enterotoxins (SEs) have been described, which currently have largely unknown frequencies of occurrence and roles in human or animal disease. One hundred and ninety-one Staphylococcus aureus isolates from cows (99), goats (39), sheep (23), rabbits (15), chickens (15) and a cat (1) were screened for SE genes sea-see, seg-seo and seq and for the tst gene encoding staphylococcal toxic shock syndrome toxin-1 using multiplex PCRs and individual PCRs for the seb and sek genes. One hundred and ten isolates tested positive for at least one of these 16 superantigen (SAg)-encoding genes. There were statistically significant differences in the frequencies of some of these SAg genes between isolates from different animals. No strain possessed either the sea or see gene. The sec gene was present in 51 isolates, the sed gene in eight and the seb gene in one. The seh gene was found in four strains and the sek and seq genes together in one isolate. The most common combinations of genes were the egc cluster, bearing the seg, sei, sem, sen and seo genes, in 47 isolates, the sec, sel and tst gene combination typical of the SaPIbov pathogenicity island in 44 isolates, the egc cluster lacking the seg gene in 11 isolates, the sed and sej genes in nine isolates, and the sec and tst genes without the sel gene in seven isolates. The higher frequencies of the sec and tst genes together and the lower frequencies of the egc gene cluster among the SAg gene-positive sheep or goat isolates compared to bovine isolates were statistically significant. Of 36 bovine isolates that were mitogenic for human T lymphocytes, four were negative for the 16 SAg genes tested for, while a further 14 gave borderline results in the mitogenicity assay, 12 of which were SAg gene-negative. Twenty-nine strains lacking all the SAg genes did not induce T-cell proliferation. This survey indicates that novel SE genes seg, sei, sel, sem, sen and seo along with the sec and tst genes predominate in S. aureus from animal hosts. The mitogenicity assays indicate that further uncharacterized SAgs may be present in bovine isolates.

PCR-based Detection of Genes encoding Virulence Determinants in Staphylococcus aureus from Birds

The present study was designed to comparatively investigate 19 Staphylococcus aureus strains isolated from specimens of 19 different birds during routine microbiological diagnostics. The S. aureus strains were characterized genotypically by polymerase chain reaction (PCR) amplification using 62 different oligonucleotide primers amplifying genes encoding staphylococcal cell surface proteins, exoproteins and two classes of the accessory gene regulator agr. All 19 investigated S. aureus were positive for the gene segment encoding a S. aureus-specific part of the 23S rRNA, the genes encoding thermostable nuclease (nuc), clumping factor (clfA) and coagulase (coa) and the gene segments encoding the Xr-repetitive region and the immunoglobulin G (IgG)-binding region of protein A (spa). In addition, all tested strains were positive for the genes hla and fnbA and negative for the genes seb, sec, sed, see, sej, tst, eta and etb. The remaining genes, including sbi, hlb, fnbB, ebpS, cna (domains A and B), cap5, cap8, set1, agr class I, agr class II, sea, seg, seh and sei were detected in a variable number of isolates. The presented data give an overview on the distribution of virulence determinants of S. aureus strains isolated from birds. This might be useful to understand the role of these virulence determinants in bird infections.

Evaluation of broiler litter with reference to the microbial composition as assessed by using 16S rRNA and functional gene markers

Very little is known about the microbial composition of animal bedding wastes, including poultry litter, and what is known has been deduced from standard culture methods, by which some fastidious organisms that exist in the environment may not be detected. We evaluated the bacterial composition of poultry litter by using a combination of culture and molecular detection. Total aerobic bacteria in poultry litter were detected by culture at 10(9) CFU/g of material. Enteric bacteria such as Enterococcus spp. and coliforms composed 0.1 and 0.01%, respectively, of the total aerobic cultivatable bacteria in poultry litter; no Salmonella strains were detected by culture. In order to characterize the most abundant bacterial groups, we sequenced 16S ribosomal DNA (rDNA) genes amplified by PCR with microbial community DNA isolated from poultry litter as the template. From the 16S rDNA library, 31 genera were identified. Twelve families or groups were identified with lactobacilli and Salinococcus spp. forming the most abundant groups. In fact, 82% of the total sequences were identified as gram-positive bacteria with 62% of total belonging to low G+C gram-positive groups. In addition to detection of 16S rDNA sequences associated with the expected fecal bacteria present in manure, we detected many bacterial sequences for organisms, such as Globicatella sulfidofaciens, Corynebacterium ammoniagenes, Corynebacterium urealyticum, Clostridium aminovalericum, Arthrobacter sp., and Denitrobacter permanens, that may be involved in the degradation of wood and cycling of nitrogen and sulfur. Several sequences were identified in the library for bacteria associated with disease in humans and poultry such as clostridia, staphylococci, and Bordetella spp. However, specific PCR targeting other human and veterinary pathogens did not detect the presence of Salmonella, pathogenic Escherichia coli, Campylobacter spp., Yersinia spp., Listeria spp., or toxigenic staphylococci. PCR and DNA hybridization revealed the presence of class 1 integrons with gene cassettes that specify resistance to aminoglycosides and chloramphenicol. Only from understanding the microbial community of animal wastes such as poultry litter can we manage animal disease and limit the impact of animal waste on the environment and human and animal health.