Isolation and characterization of Staphylococcus argenteus strains from retail foods and slaughterhouses in Japan

Genomic analysis and identification of a novel superantigen, SargEY, in Staphylococcus argenteus isolated from atopic dermatitis lesions

During surveillance of Staphylococcus aureus in lesions from patients with atopic dermatitis (AD), we isolated Staphylococcus argenteus, a species registered in 2011 as a new member of the genus Staphylococcus and previously considered a lineage of S. aureus. Genome sequence comparisons between S. argenteus isolates and representative S. aureus clinical isolates from various origins revealed that the S. argenteus genome from AD patients closely resembles that of S. aureus causing skin infections. We previously reported that 17%-22% of S. aureus isolated from skin infections produce staphylococcal enterotoxin Y (SEY), which predominantly induces T-cell proliferation via the T-cell receptor (TCR) Vα pathway. Complete genome sequencing of S. argenteus isolates revealed a gene encoding a protein similar to superantigen SEY, designated as SargEY, on its chromosome. Population structure analysis of S. argenteus revealed that these isolates are ST2250 lineage, which was the only lineage positive for the SEY-like gene among S. argenteus. Recombinant SargEY demonstrated immunological cross-reactivity with anti-SEY serum. SargEY could induce proliferation of human CD4+ and CD8+ T cells, as well as production of TNF-α and IFN-γ. SargEY showed emetic activity in a marmoset monkey model. SargEY and SET (a phylogenetically close but uncharacterized SE) revealed their dependency on TCR Vα in inducing human T-cell proliferation. Additionally, TCR sequencing revealed other previously undescribed Vα repertoires induced by SEH. SargEY and SEY may play roles in exacerbating the respective toxin-producing strains in AD.

IMPORTANCE

Staphylococcus aureus is frequently isolated from active lesions of atopic dermatitis (AD) patients. We reported that 17%-22% of S. aureus isolated from AD patients produced a novel superantigen staphylococcal enterotoxin Y (SEY). Unlike many S. aureus superantigens that activate T cells via T-cell receptor (TCR) Vß, SEY activates T cells via TCR Vα and stimulates cytokine secretion. Staphylococcus argenteus was isolated from AD patients during the surveillance for S. aureus. Phylogenetic comparison of the genome indicated that the isolate was very similar to S. aureus causing skin infections. The isolate encoded a SEY-like protein, designated SargEY, which, like SEY, activated T cells via the TCR Vα. ST2250 is the only lineage positive for SargEY gene. ST2250 S. argenteus harboring a superantigen SargEY gene may be a novel staphylococcal clone that infects human skin and is involved in the exacerbation of AD.

Prevalence of Staphylococcus argenteus among food handlers, kitchen utensils, and food samples in Japan

Staphylococcus argenteus has received increased attention from an aspect of food safety since several food poisoning outbreaks caused by the bacterium were reported in Japan. However, S. argenteus prevalence among food handlers and utensils has not yet been investigated. In this study, we investigated S. argenteus prevalence among a collection of coagulase-positive staphylococci (CPS) that were isolated during food sanitary inspections in Japan. Out of a total of 191 CPS isolates, 14 were identified as S. argenteus. One was isolated from shelled shrimp, nine were isolated from food handlers' hand swabs, and four were isolated from kitchen utensils. Whole-genome sequencing revealed that transmission of S. argenteus from human hands to utensils was possible. Though all 14 isolates were negative for the pvl and tst-1 genes, 6 harbored the seb gene. Only 21.4% of S. argenteus isolates were resistant to antibiotics, while 62.1% of the S. aureus isolates from the same sources were confirmed to be resistant. To the best of our knowledge, this is the first report to demonstrate possible transmission of S. argenteus from food handlers to utensils in food-processing environments.

A look at staphylococci from the one health perspective

Staphylococcus aureus and other staphylococcal species are resident and transient multihost colonizers as well as conditional pathogens. Especially S. aureus represents an excellent model bacterium for the "One Health" concept because of its dynamics at the human-animal interface and versatility with respect to host adaptation. The development of antimicrobial resistance plays another integral part. This overview will focus on studies at the human-animal interface with respect to livestock farming and to companion animals, as well as on staphylococci in wildlife. In this context transmissions of staphylococci and of antimicrobial resistance genes between animals and humans are of particular significance.

Prevalence and characterization of Staphylococcus aureus and Staphylococcus argenteus isolated from rice and flour products in Guangdong, China

Staphylococcus aureus and Staphylococcus argenteus have been implicated in food poisoning outbreaks, and have been found in various types of food products according to our previous study. Rice and flour products are popular and widely consumed around the world. However, limited data are available on the microbial safety of S. aureus in rice and flour products, and S. argenteus has never been reported. Thus, this study aimed to investigate the contamination of S. aureus and S. argenteus in 250 fresh rice and flour product samples from five cities in Guangdong, China. According to qualitative and quantitative analyses, 68 (27.2 %) and 11 (4.4 %) samples were positive for S. aureus and S. argenteus, including 9 samples that exceeded 100 MPN/g. For antibiotics susceptibility tests in 16 antibiotics, the S. aureus isolates exhibited higher rates of resistance and multidrug resistance than S. argenteus. The S. aureus and S. argenteus isolates were mainly resistant to penicillin (70.21 %; 79.17 %), tetracycline (20.21 %; 58.33 %) and azithromycin (19.68 %, 8.33 %). However, the other antibiotic resistance rates were <10 %. Furthermore, the genetic background of the isolates was analyzed by whole-genome sequencing (WGS). As a result, the S. aureus isolates were divided into 18 known sequence types (STs) and 4 novel STs (ST7675, ST7679, ST7680 and ST7682), which mainly belonged to ST188 (20.6 %) and ST6 (14.7 %). The S. argenteus isolates mainly belonged to ST2250 (90.9 %), with a novel type (ST7683). In total, 36 and 16 antibiotic resistance genes (ARGs) were found in S. aureus and S. argenteus isolates, respectively. In addition, 91 virulence genes (VFs) were detected in S. aureus isolates as well as 90 % of core VFs were similar to S. argenteus. More than 20 % of the S. aureus isolates carried the classic enterotoxin gene (sea-sec), but chp, cna and map were free in all S. argenteus isolates. Importantly, 33.8 % of S. aureus isolates belonged to the immune evasion cluster (IEC) type B, whereas most of S. argenteus isolates (90.9 %) belong to IEC type E. According to the phylogenetic analysis, the S. aureus and S. argenteus isolates in fresh rice and flour products may indicate loss or acquisition of ARGs and VFs to survive and adapt to the environment. Our study confirmed the presence of S. argenteus in rice and flour products at first and focused on the multi-dimensional systematic comparative analysis of S. aureus and S. argenteus to reveal their ubiquity and similarities or differences, and provide more accurate and effective basic information for follow-up monitoring and tracking.

Prevalence and Characteristics of Invasive Staphylococcus argenteus among Patients with Bacteremia in Hong Kong

Staphylococcus argenteus is a novel Staphylococcus species derived from Staphylococcus aureus. Information on the prevalence and genetic characteristics of invasive S. argenteus in Asia is limited. In this study, 275 invasive S. aureus complex strains were retrieved from blood culture specimens in Hong Kong and re-analyzed using MALDI-TOF mass spectrometry and an in-house multiplex real-time PCR for S. argenteus. The prevalence of invasive S. argenteus in Hong Kong was found to be 4.0% (11/275). These strains were primarily susceptible to commonly used antibiotics, except penicillin. Whole-genome sequencing revealed the circulation of three S. argenteus genotypes (ST-2250, ST-1223, and ST-2854) in Hong Kong, with ST-2250 and ST-1223 being the predominant genotypes. The local ST-2250 and ST-1223 strains showed close phylogenetic relationships with isolates from mainland China. Antimicrobial-resistant genes (fosB, tet-38, mepA, blaI, blaZ) could be found in nearly all local S. argenteus strains. The ST-1223 and ST-2250 genotypes carried multiple staphylococcal enterotoxin genes that could cause food poisoning and toxic shock syndrome. The CRISPR/Cas locus was observed only in the ST-2250 strains. This study provides the first report on the molecular epidemiology of invasive S. argenteus in Hong Kong, and further analysis is needed to understand its transmission reservoir.

First report of enterotoxigenic Staphylococcus argenteus as a foodborne pathogen

Staphylococcal enterotoxins preformed in food are the causative agents of staphylococcal food poisoning outbreaks (SFPO). In this study we characterised in depth two coagulase-positive non-pigmented staphylococci involved in two independent outbreaks that occurred in France. While indistinguishable from Staphylococcus aureus using PCR methods and growth phenotype comparisons, both isolates were identified as Staphylococcus argenteus by whole genome sequencing. The genomes were analysed for the presence of enterotoxin genes, whose expression was determined in laboratory medium and, for the first time, in artificially-contaminated milk samples by using liquid chromatography-mass spectrometry and ELISA methods. The concentration measured for the SEB toxin in milk (0.67 ng/ml) was comparable to concentrations reported for other types of enterotoxins behind SFPO. From a collection of publicly available genomes, we performed an unprecedented systematic investigation of the enterotoxin gene set of S. argenteus, including variants and pseudogenes. The most prevalent genes were sex, followed by sel26, sel27 and sey. The egc cluster was less frequent and most of the time carried a dysfunctional seg gene. Our results shed light on the enterotoxigenic properties of S. argenteus, and emphasize the importance in monitoring of S. argenteus as an emerging foodborne pathogen.

Bacteriophage-based nano-biosensors for the fast impedimetric determination of pathogens in food samples

The early and rapid detection of pathogenic microorganisms is of critical importance in addressing serious public health issues. Here, a new bacteriophage-based nano-biosensor was constructed and the electrochemical impedimetric method was fully optimized and applied for the quantitative detection of Escherichia coli O157:H7 in food samples. The impact of using a nanocomposite consisting of gold nanoparticles (AuNPs), multi-walled carbon nanotubes (MWCNTs), and tungsten oxide nanostructures (WO₃) on the electrochemical performance of disposable screen printed electrodes was identified using the cyclic voltammetry and electrochemical impedance spectroscopy. The use nanomaterials enabled high capturing sensitivity against the targeting bacterial host cells with the limit of detection of 3.0 CFU/ml. Moreover, selectivity of the covalently immobilized active phage was tested against several non-targeting bacterial strains, where a high specificity was achieved. Thus, the targeting foodborne pathogen was successfully detected in food samples with high specificity, and the sensor provided an excellent recovery rate ranging from 90.0 to 108%. Accordingly, the newly developed phage-biosensor is recommended as a disposable label-free impedimetric biosensor for the quick and real-time monitoring of food quality.

First Report of a Methicillin-Resistant, High-Level Mupirocin-Resistant Staphylococcus argenteus

We describe the identification of a methicillin-resistant, high-level mupirocin-resistant Staphylococcus argenteus. The isolate (1801221) was characterized as t6675-ST2250-SCCmecIVc, and whole-genome sequencing revealed that the isolate possessed two plasmids. One plasmid (34,870 bp), designated p1_1801221 with rep23, harboured the mupirocin resistance (mupA) gene. The second plasmid (20,644 bp), assigned as p2_1801221 with rep5a and rep16, carried the resistance determinants for penicillin (blaZ) and cadmium (cadD). Phylogenetic analysis revealed that the isolate clustered with the European ST2250 lineage. The overall high similarity of both plasmids in S. argenteus with published DNA sequences of Staphylococcus aureus plasmids strongly suggests an interspecies transfer. The pathogenic potential, community and nosocomial spread, and acquisition of antibiotic resistance gene determinants, including the mupA gene by S. argenteus, highlight its clinical significance and the need for its correct identification.

Canine Staphylococcus argenteus: Case Report from The Netherlands

Staphylococcus argenteus has been reported worldwide in humans, while reported non-human cases are sparse. Its complete epidemiology, alongside its infectivity and pathogenicity in humans and non-humans, remain to be clarified. Here, we describe the first reported canine Staphylococcus argenteus, causing a deep wound infection in a Labrador retriever after orthopedic surgery. The closed genome is reported, with phylogenic and genetic analyses, as well as extensive phenotypic antimicrobial susceptibility testing for human and veterinary antibiotics. No genetic explanation could be found for its interaction with a canine host, underscoring the intrinsic multispecies pathogenicity and potential (anthropo-)zoonotic spread of Staphylococcus argenteus.