Distribution of enterotoxin genes among carriage- and infection-associated isolates of Staphylococcus aureus

Investigation of Various Toxigenic Genes and Antibiotic and Disinfectant Resistance Profiles of Staphylococcus aureus Originating from Raw Milk

This study investigated the toxigenic genes and antimicrobial resistance profiles of Staphylococcus aureus strains isolated from 260 raw milk samples collected from dairy farms in Türkiye. The results indicated that 60.7% of staphylococcal enterotoxin genes (sea, seb, sed, seg, sei, sej, sek, seq, sem, seo, and seu) and 21.4% of the tst and eta genes were positive, with most enterotoxin-positive samples carrying more than one gene. The sec, see, seh, sel, sen, sep, and etb genes were not identified in any samples. The prevalence of antibiotic resistance genes (mecA, blaR, blaI, blaZ, vanA, ermT, tetK, aac/aph, ant, dfrA, tcaR, IS256, and IS257) was high at 89.2%, with bla being the most frequently detected gene (75%). The mecA gene was present in 14.2% of samples, while tcaR was detected in 78.5%. Nevertheless, the mecC was not identified. Disinfectant resistance genes (qacA/B, qacC, qacJ, smr) were detected in 21.4% of the samples. The results of the disk diffusion test showed that 64.2% of strains were resistant to penicillin G and ampicillin, with additional resistance found for cefoxitin, teicoplanin, levofloxacin, norfloxacin, and other antibiotics. These findings highlight a significant public health and food safety risk associated with raw milk due to the presence of S. aureus strains with toxigenic genes and high antimicrobial resistance.

Identification and characterization of Staphylococcus argenteus from Indonesia

BACKGROUND

In 2015, Staphylococcus argenteus was reported for the first time as a novel species of the Staphylococcus aureus complex. While S. argenteus has been found in many countries, its presence in Indonesia has not been reported yet. Our aim is to confirm S. argenteus presence in Indonesia, describe its characteristics and analyze its genomic diversity.

METHODS

The S. aureus isolates used in this study were collected from patients with skin and soft tissue infections in Indonesia, between July 2009 to February 2010. Randomly selected isolates were recultured from -80 C° stocks and analyzed using matrix-assisted laser desorption/ionization - time of flight (MALDI-TOF). Isolates identified as S. argenteus, S. roterodami, or S. schweitzeri and S. aureus with a low score in the MALDI-TOF analysis were analyzed by a real-time PCR targeting the nucA gene able to identify true S. argenteus. Isolates identified as S. argenteus were further characterized by whole genome sequencing. Vitek®2 (bioMérieux) was used for antimicrobial susceptibility testing.

RESULTS

Fifteen isolates were identified as S. argenteus, with the majority belonging to ST2250. Two pairs of isolates proved to be identical by core genome multilocus sequence typing analysis. Most isolates were susceptible to all antibiotics tested, except for seven isolates (46.7 %) that were resistant to benzylpenicillin, and one isolate was resistant to tetracycline (6.7 %). The presence of resistance genes blaZ and tet(45) correlated with these findings. Notably, the sey enterotoxin gene was prevalent in 80 % of the isolates. Other virulence factor genes were less prevalent. Plasmid replicon types in S. argenteus were also known to S. aureus.

CONCLUSION

Our study reveals the occurrence of S. argenteus in Indonesia. The diversity within Indonesian S. argenteus matches the global diversity of S. argenteus. Identical isolates between patients indicate potential transmission events. A lower prevalence of a broad panel of virulence factors suggests that S. argenteus is less virulent than S. aureus.

Antimicrobial Resistance, Enterotoxin and mec Gene Profiles of Staphylococcus aureus Associated with Beef-Based Protein Sources from KwaZulu-Natal Province, South Africa

Annually, approximately 23,000 cases of food poisoning by Staphylococcus aureus enterotoxins are reported worldwide. The aim of this study was to determine the occurrence and characterize S. aureus on beef and beef products in South Africa. Organ meats (n = 169), raw processed meat (n = 110), raw intact (n = 53), and ready-to-eat meats (n = 68) were obtained from 25 retail outlets. S. aureus was isolated and enumerated according to the ISO 6888-1 method. Identification of the strains was performed by MALDI-TOF MS. The antimicrobial resistance was determined using the disc diffusion test. The presence of methicillin-resistance genes and the staphylococcal enterotoxin genes was determined by PCR. Prevalence was low (13/400; CI 1.7–5) and all but one positive sample were from organ meats. Eight isolates were resistant to at least one antibiotic. Two isolates carried the mecC gene. All the isolates tested positive for seg, seh, sei, and sep, whilst 53.8% were positive for sea. None of the isolates was positive for ser, sej, seb, sec, or sed. The prevalence of S. aureus was low, with organ meats being the most contaminated. The presence of mecC-positive MRSA and of enterotoxins warrants further investigation and risk assessment.

Clonal Diversity, Antimicrobial Susceptibility and Presence of Genes Encoding Virulence Factors in Staphylococcus aureus Strains Isolated from Cut Wound Infections

The aim of the study was to evaluate the clonal relatedness and antimicrobial susceptibility in 52 Staphylococcus aureus strains isolated from cut wound infections in non-related community patients and to determine the presence of selected virulence genes. To analyse the clonal relatedness of investigated strains, pulsed-field gel electrophoresis (PFGE) of macrorestricted DNA fragments was conducted. Antimicrobial susceptibility testing was performed using the AST-P644 card in the VITEK 2 Compact system. All strains were tested for the presence of selected virulence genes using Single and Multiplex PCR. All isolates were classified into 15 PFGE genotypes and seven unique patterns. The vast majority of investigated S. aureus strains were susceptible to all tested antimicrobial agents. Among examined S. aureus strains, 24 combinations of virulence factors were identified. 62.5% of S. aureus strains contained various egc types, alone or together with other staphylococcal enterotoxin genes. A high percentage (86.5%) of isolates harboured superantigen genes. The most frequent enterotoxin gene identified was encoding for sep. All S. aureus strains were classified as agr-positive, and the most frequent agr gene was agr-1. Our results indicate that all examined strains isolated from cut wound infections demonstrated high clonal diversity, diversified gene distribution and good susceptibility to antimicrobial agents.

Bacterial Carriage of Genes Encoding Fibronectin-Binding Proteins Is Associated with Long-Term Persistence of Staphylococcus aureus in the Nasal and Gut Microbiota of Infants

Staphylococcus aureus can colonize both the anterior nares and the gastrointestinal tract. However, colonization at these sites in the same individuals has not been studied, and the traits that facilitate colonization and persistence at these sites have not been compared. Samples from the nostrils and feces collected on 9 occasions from 3 days to 3 years of age in 65 infants were cultured; 54 samples yielded S. aureus. The numbers of nasal and fecal S. aureus strains increased rapidly during the first weeks and were similar at 1 month of age (>40% of infants colonized). Thereafter, nasal carriage declined, while fecal carriage remained high during the first year of life. Individual strains were identified, and their colonization patterns were related to their carriage of genes encoding adhesins and superantigenic toxins. Strains retrieved from both the nose and gut (n = 44) of an infant were 4.5 times more likely to colonize long term (≥3 weeks at both sites) than strains found only in the rectum/feces (n = 56) or only in the nose (n = 32) (P ≤ 0.001). Gut colonization was significantly associated with carriage of the fnbA gene, and long-term colonization at either site was associated with carriage of fnbA and fnbB. In summary, gut colonization by S. aureus was more common than nasal carriage by S. aureus in the studied infants. Gut strains may provide a reservoir for invasive disease in vulnerable individuals. Fibronectin-binding adhesins and other virulence factors may facilitate commensal colonization and confer pathogenic potential.

IMPORTANCES. aureus may cause severe infections and frequently colonizes the nose. Nasal carriage of S. aureus increases 3-fold the risk of invasive S. aureus infection. S. aureus is also commonly found in the gut microbiota of infants and young children. However, the relationships between the adhesins and other virulence factors of S. aureus strains and its abilities to colonize the nostrils and gut of infants are not well understood. Our study explores the simultaneous colonization by S. aureus of the nasal and intestinal tracts of newborn infants through 3 years of follow-up. We identify bacterial virulence traits that appear to facilitate persistent colonization of the nose and gut by S. aureus. This expands our current knowledge of the interplay between bacterial commensalism and pathogenicity. Moreover, it may contribute to the development of targeted strategies for combating S. aureus infection.

The mice’s hematological effect of given the Staphylococcus aureus and Persea americana

Staphylococcus aureus is often the cause of various diseases and food poisoning in animals and humans. Avocado seeds (Persea americana, Mill) contain important compounds that have antimicrobial activity. This study aimed to observe the hematological dynamics of mice (Mus musculus domesticus) infected with S. aureus and induced by P. americana extract. BALB/c male mice aged 12 weeks were divided into 6 groups of 5 in each group, named K-1, K-2, K-3, K-4, K-5, and K-6. All groups were infected with S. aureus 1x108 CFU cell/mL intraperitoneally (IP) on day 0. After the blood sample was taken, then K-1 was given a single dose of tetracyclin 130 mg/kg BW, K-2 was given 130 mg/kb BW oferythromycin, K-3 was given aquabidest (placebo), K-4 was given P. americana extract 300 mg/kg BW, K-5 at a dose 600 mg/kg BW and K-6 at a dose 1200 mg/kg BW. The treatment was given for 7 consecutive days, then a second blood sample was taken and analyzed with the VetScan-HM5 analyzer and interpreted. It was concluded that S. aureus infection caused leukopenia and was potentially followed by lymphopenia, neutrophilia, and monocytosis. The occurrence of microcytosis can lead to anemia, which can be categorized as microcytic hypochromic or normocytic normochromic. Administration of P. americana extract at a dose 300 mg/kg BW (K-4) for 7 days after S. aureus infection was found to be effective in improving hematological values in mice back to normal.

Occurrence and enterotoxin gene profiles of Staphylococcus aureus isolated from retail chicken meat

The present study was conducted to evaluate the prevalence and enterotoxin gene profiles of Staphylococcus aureus isolated from 120 chicken meat marketed in retail outlets of Chennai, India. It was observed that total of 120 meat samples collected from different retail outlets, 66.67% (80/120) of the samples were positive for the presence of S. aureus based on biochemical characterization and species specific PCR based on thermonuclease gene (nuc). Enterotoxin gene profiling of the isolates for 9 genes (sea- sej) revealed that 52.50% (42/80) of the isolates in the present study were enterotoxigenic harboring either one or more gene. It was evident that majority of the isolates harbored seb, followed by seg, sei, sec, sed and sej either alone or in combination. None of the isolates harbored sea, see and seh either alone or in combination. The results of the study clearly indicated higher prevalence of enterotoxigenic S. aureus in retail meat marketed in Chennai, India indicating the potential of retail chicken meat to act as vehicle for food borne intoxication and a major public health threat.

Elimination of Staphylococcus aureus nasal carriage in intensive care patients lowers infection rates

This study surveys the clinical relevance of the nasal Staphylococcus aureus colonization status on intensive care unit (ICU)-acquired S. aureus infections and compares molecular characteristics of isolates from the nose and infectious sites. The 390 patients included comprised 278 non-carriers and 112 carriers. Among the carriers, 56 were decolonized with mupirocin. Decolonization was verified through a second (negative) culture. Spa typing and virulence gene profiling were performed for all isolates. Twenty six S. aureus infections were detected in the carriage group and 20 in the non-carriage group. Eighteen of these 26 (69.2%) infections were among carriers, and 8 of these 26 (30.8%) infections occurred among decolonized carriers (p = 0.02). Overall, 31/112 (27.7%) of the colonized patients and 25/46 (60.1%) of infection were due to methicillin-resistant S. aureus (MRSA). The highest frequency virulence genes were sea and hlg (both 100%) in nasal isolates and sea, hlg, fnb, and clf (100%) for infectious isolates. t030 was the most abundant spa type overall. S. aureus carriers were more likely to develop S. aureus infection compared with decolonized and non-carrying patients. The sources of ICU S. aureus infection appear to be exogenous mostly, and a predominant clone (spa type 030) plays an important role. We confirm that nasal mupirocin treatment prevents ICU infections even when there is an increased prevalence of nosocomial MRSA.

Comparative Secretome Analyses of Human and Zoonotic Staphylococcus aureus Isolates CC8, CC22, and CC398

The spread of methicillin-resistant Staphylococcus aureus (MRSA) in the community, hospitals and in livestock is mediated by highly diverse virulence factors that include secreted toxins, superantigens, enzymes and surface-associated adhesins allowing host adaptation and colonization. Here, we combined proteogenomics, secretome and phenotype analyses to compare the secreted virulence factors in selected S. aureus isolates of the dominant human- and livestock-associated genetic lineages CC8, CC22, and CC398. The proteogenomic comparison revealed 2181 core genes and 1306 accessory genes in 18 S. aureus isolates reflecting the high genome diversity. Using secretome analysis, we identified 869 secreted proteins with 538 commons in eight isolates of CC8, CC22, and CC398. These include 64 predicted extracellular and 37 cell surface proteins that account for 82.4% of total secretome abundance. Among the top 10 most abundantly secreted virulence factors are the major autolysins (Atl, IsaA, Sle1, SAUPAN006375000), lipases and lipoteichoic acid hydrolases (Lip, Geh, LtaS), cytolytic toxins (Hla, Hlb, PSMβ1) and proteases (SspB). The CC398 isolates showed lower secretion of cell wall proteins, but higher secretion of α- and β-hemolysins (Hla, Hlb) which correlated with an increased Agr activity and strong hemolysis. CC398 strains were further characterized by lower biofilm formation and staphyloxanthin levels because of decreased SigB activity. Overall, comparative secretome analyses revealed CC8- or CC22-specific enterotoxin and Spl protease secretion as well as Agr- and SigB-controlled differences in exotoxin and surface protein secretion between human-specific and zoonotic lineages of S. aureus.

High prevalence of methicillin resistant and enterotoxin gene-positive Staphylococcus aureus among nasally colonized food handlers in central Iran

This study defined the prevalence of enterotoxin gene-positive Staphylococcus aureus strains among food handlers and non-food processing healthy nasal S. aureus carriers in central Iran. Meticillin-resistant S. aureus (MRSA) strains were diagnosed by cefoxitin disk diffusion. PCR was used to detect the mecA, Sa442, and enterotoxin genes. Out of the 1113 food handlers, 224 (20.1%) were nasal carriers of S. aureus and 157 (70.1%) of these isolates were positive for one or more enterotoxin genes. The most prevalent enterotoxin gene was sei (40.2%), followed by seg (35.3%), sea (23.5%), seb (15.2%), sec (5.5%), and seh (2.7%). See and sed genes were not found. Sixty seven (42.7%) of enterotoxin gene-positive isolates possessed a single enterotoxin gene, and 64 (40.8%), 23 (14.7%), and 3 (1.9%) contained two, three, or four enterotoxin genes, respectively. The most frequently detected gene combination was sei/seg (n = 35, 22.3%). Thirty seven (16.5%) isolates were diagnosed as MRSA, and 27 (73%) of these strains were positive for at least one enterotoxin gene. Out of 546 healthy controls, 100 individuals were identified as S. aureus nasal carriers; among the strains, 39 (39%) were positive for at least one enterotoxin gene. Only one (1%) CA-MRSA was identified among the strains from the volunteers. A high prevalence of meticillin resistant and enterotoxin-positive S. aureus were documented in food handlers. We suggest that this may be due to the frequent handling of contaminated foodstuffs and that this is possibly related to the elevated frequencies of acquired staphylococcal food poisoning in this population.

Basis of Virulence in Enterotoxin-Mediated Staphylococcal Food Poisoning

The Staphylococcus aureus enterotoxins are a superfamily of secreted virulence factors that share structural and functional similarities and possess potent superantigenic activity causing disruptions in adaptive immunity. The enterotoxins can be separated into two groups; the classical (SEA-SEE) and the newer (SEG-SElY and counting) enterotoxin groups. Many members from both these groups contribute to the pathogenesis of several serious human diseases, including toxic shock syndrome, pneumonia, and sepsis-related infections. Additionally, many members demonstrate emetic activity and are frequently responsible for food poisoning outbreaks. Due to their robust tolerance to denaturing, the enterotoxins retain activity in food contaminated previously with S. aureus. The genes encoding the enterotoxins are found mostly on a variety of different mobile genetic elements. Therefore, the presence of enterotoxins can vary widely among different S. aureus isolates. Additionally, the enterotoxins are regulated by multiple, and often overlapping, regulatory pathways, which are influenced by environmental factors. In this review, we also will focus on the newer enterotoxins (SEG-SElY), which matter for the role of S. aureus as an enteropathogen, and summarize our current knowledge on their prevalence in recent food poisoning outbreaks. Finally, we will review the current literature regarding the key elements that govern the complex regulation of enterotoxins, the molecular mechanisms underlying their enterotoxigenic, superantigenic, and immunomodulatory functions, and discuss how these activities may collectively contribute to the overall manifestation of staphylococcal food poisoning.

Genomic differences between nasal Staphylococcus aureus from hog slaughterhouse workers and their communities

New human pathogens can emerge from the livestock-human interface and spread into human populations through many pathways including livestock products. Occupational contact with livestock is a risk factor for exposure to those pathogens and may cause further spreading of those pathogens in the community. The current study used whole genome sequencing to explore nasal Staphylococcus aureus obtained from hog slaughterhouse workers and their community members, all of whom resided in a livestock-dense region in rural North Carolina. Sequence data were analyzed for lineage distribution, pathogenicity-related genomic features, and mobile genetic elements. We observed evidence of nasal S. aureus differences between hog workers and non-workers. Nasal S. aureus from hog workers showed a greater lineage diversity than nasal S. aureus from community residents. Hog worker isolates were less likely to carry the φSa3 prophage and human-specific immune evasion cluster genes than community resident isolates (φSa3 prophage: 54.5% vs. 91.7%, Benjamini-Hochberg (BH) corrected p = 0.035; immune evasion cluster genes: 66.7% vs. 100%, BH p = 0.021). Hog worker isolates had a lower prevalence and diversity of enterotoxins than community resident isolates, particularly lacking the enterotoxin gene cluster (39.4% vs. 70.8%, BH p = 0.125). Moreover, hog worker isolates harbored more diverse antibiotic resistance genes, with a higher prevalence of carriage of multiple resistance genes, than community resident isolates (75.8% vs. 29.2%, BH p = 0.021). Phylogenetic analysis of all ST5 isolates, the most abundant lineage in the collection, further supported separation of isolates from hog workers and non-workers. Together, our observations suggest impact of occupational contact with livestock on nasal S. aureus colonization and highlight the need for further research on the complex epidemiology of S. aureus at the livestock-human interface.

Staphylococcus aureus and Methicillin-Resistant Staphylococcus aureus in Workers in the Food Industry

Staphylococcus aureus is part of the common flora on the skin and mucous membranes of mammals and approximately 20–30% of humans are persistently colonized, mainly by mostly susceptible human-adapted isolates. In contrast, colonization with methicillin-resistant S. aureus is rare (approximately 1%), predominantly transient and associated with prior contact to the health care system. Additionally, in recent years livestock-associated S. aureus clones contributed to colonization in humans, especially in those working in close contact to farm animals. A considerable percentage of colonizing S. aureus isolates is equipped with enterotoxin genes. Humans carrying enterotoxigenic isolates represent a contamination source when handling food, thus generating a continuous risk of S. aureus food intoxication. Molecular characterization of isolates colonizing humans and obtained from food, respectively, enables the tracing of food-related outbreaks back to the source of food intoxication. We will summarize current knowledge about the S. aureus population colonizing humans, including those in close contact to animals and food, respectively. Additionally, we will review data on the molecular characterization of S. aureus isolates related to staphylococcal foodborne disease and the elucidation of staphylococcal foodborne outbreaks. Staphylococcal food poisoning is a common foodborne disease, mediated by the ingestion of enterotoxins produced by enterotoxigenic strains of S. aureus. For several outbreaks of foodborne S. aureus disease, colonized personnel could be identified as the source of food contamination. However, because of the widespread occurrence of enterotoxigenic strains as human colonizers and the often transient nature of colonization, the source of contamination cannot always be identified unambiguously. Therefore, compliance with hygiene measures is the most important requirement to prevent food contamination by both human colonization and environmental S. aureus reservoirs.

Comparison of antibiotic resistance, virulence gene profiles, and pathogenicity of methicillin-resistant and methicillin-susceptible Staphylococcus aureus using a Caenorhabditis elegans infection model

OBJECTIVES

This study compared the presence of 35 virulence genes, resistance phenotypes to 11 anti-staphylococcal antibiotics, and pathogenicity in methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-susceptible S. aureus (MSSA).

METHODS

Multiplex PCR analysis was used to differentiate Staphylococcus aureus isolates (n = 102) based on characterization of the Staphylococcal Cassette Chromosome mec (SCCmec). Singleplex and multiplex PCR assays targeting 35 virulence determinants were used to analyze the virulence repertoire of S. aureus. In vitro activities of the antibiotics were determined by the disk-diffusion method. The pathogenicity of representative isolates was assessed using Caenorhabditis elegans survival assays. Significance in virulence distribution and antibiotic resistance phenotypes was assessed using the Chi-squared tests. Kaplan-Meier survival estimates were used to analyze nematode survival and significance of survival rates evaluated using the log-rank test.

RESULTS

Except for sei (staphylococcal enterotoxin I) (P  =  0·027), all other virulence genes were not significantly associated with MRSA. Resistance to clindamycin (P  =  0·03), tetracycline (P  =  0·048), trimethoprim/sulfamethoxazole (P  =  0·038), and oxacillin (P  =  0·004) was significantly associated with MRSA. Survival assay showed MSSA having a lower median lifespan of 3 days than MRSA that had a median lifespan of 6 days. The difference in the killing time of MRSA and MSSA was significant (P < 0·001).

CONCLUSION

While antibiotic resistance was significantly associated with MRSA, there was no preferential distribution of the virulence genes. The quicker killing potential of MSSA compared to MRSA suggests that carriage of virulence determinants per se does not determine pathogenicity in S. aureus. Pathogenicity is impacted by other factors, possibly antibiotic resistance.

A pooling-based genomewide association study identifies genetic variants associated with Staphylococcus aureus colonization in chronic rhinosinusitis patients

BACKGROUND

Staphylococcus aureus (S. aureus) has been implicated in the pathogenesis of chronic rhinosinusitis (CRS). However, host factors contributing to susceptibility to S. aureus colonization in CRS remain unknown. We wish to investigate, using a pooled genomewide association study (pGWAS), single-nucleotide polymorphisms (SNPs) associated with S. aureus carriage in CRS patients.

METHODS

An existing population of 408 CRS patients and 190 controls was prospectively recruited for genetic association studies. All CRS patients had an endoscopic swab culture as part of phenotyping. A pGWAS compared DNA pools from patients with and without S. aureus colonization using the Illumina HumanHap 1M BeadChip, which interrogates 1 million SNPs. Top-ranked SNPs associated with S. aureus colonization were selected according to biallelic differences and silhouette rank, and confirmed by individual genotyping using the Sequenom platform. PLINK software was used for genetic association tests. Ingenuity pathway analysis was used to identify canonical and signaling pathways enriched for genes neighboring associated SNPs, as well as identification of the underlying biological mechanisms.

RESULTS

Thirty-nine top priority SNPs were selected for individual genotyping. Out of 39 SNPs, 23 were associated (p < 0.05) with S. aureus colonization in CRS patients. These SNPs are located within or near 21 genes reported to be implicated in several diseases, endocytic internalization, and bacterial recognition.

CONCLUSION

These results suggest novel host genetic factors influencing susceptibility to S. aureus colonization in CRS. Identifying implicated mechanisms may offer new insights into pathogenesis of CRS.

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

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

Longitudinal genetic analyses of Staphylococcus aureus nasal carriage dynamics in a diverse population

Background

Staphylococcus aureus (SA) nasal colonization plays a critical role in the pathogenesis of staphylococcal infections and SA eradication from the nares has proven to be effective in reducing endogenous infections. To understand SA nasal colonization and its relation with consequent disease, assessment of nasal carriage dynamics and genotypic diversity among a diverse population is a necessity.

Results

We have performed extensive longitudinal monitoring of SA nasal carriage isolates in 109 healthy individuals over a period of up to three years. Longitudinal sampling revealed that 24% of the individuals were persistent SA nasal carriers while 32% were intermittent. To assess the genetic relatedness between different SA isolates within our cohort, multi locus sequence typing (MLST) was performed. MLST revealed that not only were strains colonizing intermittent and persistent nasal carriers genetically similar, belonging to the same clonal complexes, but strain changes within the same host were also observed over time for both types of carriers. More highly discriminating genetic analyses using the hypervariable regions of staphylococcal protein A and clumping factor B virulence genes revealed no preferential colonization of specific SA strains in persistent or intermittent carriers. Moreover, we observed that a subset of persistent and intermittent carriers retained clinically relevant community-acquired methicillin-resistant SA (CA-MRSA) strains in their nares over time.

Conclusions

The findings of this study provides added perspective on the nasal carriage dynamics between strains colonizing persistent and intermittent carriers; an area currently in need of assessment given that persistent carriers are at greater risk of autoinfection than intermittent carriers.

Staphylococcus aureus nasal carriage in a Moroccan dialysis center and isolates characterization

Staphylococcus aureus, which has its ecological niche in the anterior nares, has been shown to cause a variety of infectious diseases mainly for patients in hemodialysis units. We performed this study to evaluate the prevalence of nasal S. aureus carriage among hemodialysis outpatients, to determine the antimicrobial susceptibility of isolates, to characterize the virulence genes, and to identify associated risk factors. Nares swab specimens were obtained from 70 outpatients on hemodialysis between March and June 2010. Samples were plated immediately onto S. aureus specific media and pattern of antibacterial sensitivity was determined using disk diffusion method. Polymerase chain reaction was used to detect nuc, mecA, and genes encoding staphylococcal toxins. Medical record of patients was explored to determine S.aureus carriage risk factors. Nasal screening identified 42.9% S. aureus carriers with only one (3.3%) methicillin-resistant S. aureus isolate. Among the methicillin-susceptible S. aureus isolates, high rate of penicillin resistance (81.8%) has been detected. The identified risk factors were male gender and age ≤ 30 years. Research of virulence factors showed a high genetic diversity among the 30 S. aureus isolates. Twenty-one (70%) of them had at least one virulence gene, of which 3.3% were Panton-Valentine leukocidin (lukS/F-PV) genes. S. aureus carriage must be screened for at regular intervals in hemodialysis patients. Setting up a bacterial surveillance system is one of the strategies to understand the epidemiology of methicillin-resistant S. aureus, to guide local antibiotic policy and prevent spread of antibiotic-resistant S. aureus.

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

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

Exoproteome of Staphylococcus aureus reveals putative determinants of nasal carriage

Due to the increasing prevalence of nosocomial and community-acquired antibiotic resistant Staphylococcus aureus (SA), understanding the determinants of SA nasal carriage has become a major imperative. Previous research has revealed many host and bacterial factors that contribute to SA nasal carriage. To assess bacterial factors that facilitate nasal carriage, we compared the exoproteome of a nasal carrier strain of SA to a genetically similar noncarrier strain. Additionally, the carrier strain biofilm exoproteome was also compared against its planktonic counterpart. Using high throughput proteomics, it was observed that the carrier strain of SA secretes a greater number of proteins that may promote successful colonization of the human nose, including cell attachment and immunoevasive proteins, than the noncarrier strain. Similarly, SA carrier strain biofilm exoproteome contains a greater number of immunoevasive proteins than its planktonic counterpart. Analysis of the most abundant immunoevasive proteins revealed that Staphylococcal protein A was present at significantly higher levels in carrier than in noncarrier strains of SA, suggesting an association with nasal carriage. While further analyses of specific differences between carrier and noncarrier strains of SA are required, many of the differentially expressed proteins identified can be considered to be putative determinants of nasal carriage.

Staphylococcus aureus nasal carriage and its contributing factors

Staphylococcus aureus is a medically important pathogen that is often acquired from hospital settings (nosocomial) as well as from the community (community acquired). Bacteria that reside in anterior nares of hosts serve as reservoirs for both the spread of the pathogen and predispose the host to subsequent infections. Here, we will review the extent and variability of nasal carriage, and the possible causative factors--both from the host and the bacterium. We also discuss the existing molecular typing techniques used for studying variations among strains of S. aureus. Finally, we discuss the possible areas of studies that are open in this field. Given the pathogen's importance in healthcare setting, such areas of study vary vastly, from fundamental research to applied medical care and use of alternative medical regimes for control of S. aureus nasal carriage. Unsurprisingly, our conclusions also underscore the importance of making policy decisions based on local ethnic and socioeconomic population structure.

Associations between enterotoxin gene cluster types egc1, egc2 and egc3, agr types, enterotoxin and enterotoxin-like gene profiles, and molecular typing characteristics of human nasal carriage and animal isolates of Staphylococcus aureus

Twenty genes encoding enterotoxin and enterotoxin-like proteins have been described in Staphylococcus aureus strains. Five of these occur commonly in the enterotoxin gene cluster (egc: selo, selm, sei, seln and seg). In the sei-seln intergenic region, two pseudogenes, psient1 and psient2, can be present or an additional gene designated selu or a variant selu(v). Whilst frequencies of loci bearing pseudogenes (egc1) or the selu gene (egc2) have been reported, the distinction between selu-bearing and selu(v)-bearing (egc3) loci has rarely been made. A PCR-RFLP procedure involving cleavage of the sei-seln intergenic region by restriction endonuclease BbvI or TseI was developed that allowed differentiation of selu(+) and selu(v)(+) loci. In addition, PCR primers were designed to yield a 203 bp amplimer for sequencing of a selu or selu(v) intragenic region, which encompassed ten signature nucleotide differences. A total of 43 egc(+) human nasal isolates and 53 egc(+) bovine, ovine, caprine, leporine and gallinaceous isolates were egc typed and agr typed. None of the animal isolates was of agr type III. A total of 12 out of 17 egc3(+) human nasal isolates were of agr type III, the other 5 being agr type I. On the basis of representative multilocus sequence typing, agr type III/egc3(+) strains belonged to CC30. Human nasal isolates bearing an egc1 locus were distributed evenly across agr types I, II and III. Only two nasal isolates had an egc2 locus. All 14 agr type IV isolates, only 1 of which was of human origin, possessed an egc2 locus. The agr IV nasal isolate was fusidic acid sensitive and was found to be ST123 (CC121). There were strong associations between bovine, leporine and gallinaceous S. aureus clonal types and egc locus types. The PCR-RFLP procedure was used to screen an additional 45 S. aureus isolates from dogs, cats, rats, pigs and horses for egc locus types. Of these, 33 were egc(-). Six equine isolates were selu(+). One canine and three porcine isolates possessed pseudogenes psient1 and psient2. One porcine and one canine isolate each had the selu(v) gene. Putative relationships between disease-causing propensity and egc type need (re-)evaluation.

Genome sequencing and analysis reveals possible determinants of Staphylococcus aureus nasal carriage

Background

Nasal carriage of Staphylococcus aureus is a major risk factor in clinical and community settings due to the range of etiologies caused by the organism. We have identified unique immunological and ultrastructural properties associated with nasal carriage isolates denoting a role for bacterial factors in nasal carriage. However, despite extensive molecular level characterizations by several groups suggesting factors necessary for colonization on nasal epithelium, genetic determinants of nasal carriage are unknown. Herein, we have set a genomic foundation for unraveling the bacterial determinants of nasal carriage in S. aureus.

Results

MLST analysis revealed no lineage specific differences between carrier and non-carrier strains suggesting a role for mobile genetic elements. We completely sequenced a model carrier isolate (D30) and a model non-carrier strain (930918-3) to identify differential gene content. Comparison revealed the presence of 84 genes unique to the carrier strain and strongly suggests a role for Type VII secretion systems in nasal carriage. These genes, along with a putative pathogenicity island (SaPIBov) present uniquely in the carrier strains are likely important in affecting carriage. Further, PCR-based genotyping of other clinical isolates for a specific subset of these 84 genes raise the possibility of nasal carriage being caused by multiple gene sets.

Conclusion

Our data suggest that carriage is likely a heterogeneic phenotypic trait and implies a role for nucleotide level polymorphism in carriage. Complete genome level analyses of multiple carriage strains of S. aureus will be important in clarifying molecular determinants of S. aureus nasal carriage.

Molecular typing of nasal carriage isolates of Staphylococcus aureus from an Irish university student population based on toxin gene PCR, agr locus types and multiple locus, variable number tandem repeat analysis

Forty-eight Staphylococcus aureus isolates collected from a young, healthy, Irish university student population from 1995 to 2004 were screened for 16 enterotoxin (SE) and enterotoxin-like (SEl) genes (sea-see, seg-sei, selj-selo, selq, selu), and for the toxic shock toxin syndrome toxin-1 gene, tst. All of the isolates harboured at least one SE or SEl gene and 66.7 % possessed a classical SE gene (sea, seb, sec), the commonest being the seb gene. Most of the isolates (85.4 %) had a complete egc locus (selo, selm, sei, seln, seg). The intergenic sei-seln region of the egc locus was typed by PCR-RFLP in 34 isolates, 15 possessing pseudogenes psient1 and psient2 and 19 having the selu gene. The seh and sell genes, the selk-selq gene combination, and the tst gene were each found in <15 % of isolates. The agr genotype distribution was agr type III, 37.5 %; agr type I, 35.4 %; agr type II, 25 %; and agr type IV, 2.1 %. There was no association between SE-SEl genotype and agr type. All tst gene-positive isolates were of agr type III and harboured a classical SE gene. Multiple locus, variable number tandem repeat analysis (MLVA) produced 47 different patterns. While the sdr locus was present in all isolates, half of them lacked one or two of the sdr gene amplimers. Twenty isolates harboured the bbp gene, its presence being associated with agr type III, but not with the SE-SEl gene profile. The agr types of isolates were associated with MLVA subclusters. Selective MLST analysis revealed seven novel sequence types and a new aroE allele. Five clonal clusters (CCs), including CCs comprising major pandemic clones CC30, CC5 and CC22 and minor lineages CC6 and CC9, and three singletons were identified.