The role of Staphylococcal carotenogenesis in resistance to host defense peptides and in vivo virulence in experimental endocarditis model

Complete Genome Sequences of Staphylococcus argenteus Tokyo13064 and Tokyo13069, Isolated from Specimens Obtained during a Food Poisoning Outbreak in Tokyo, Japan

The complete genome sequences of two Staphylococcus argenteus strains, Tokyo13064 and Tokyo13069, isolated from human feces and suspected causative foods during a staphylococcal food poisoning outbreak, consist of 2,750,811-bp and 2,751,556-bp circular chromosomes and 2,543 and 2,548 genome annotation-predicted coding DNA sequences, respectively, with 19 rRNAs, 61 tRNAs, and 1 CRISPR each.

The complete genome sequences of two Staphylococcus argenteus strains, Tokyo13064 and Tokyo13069, isolated from human feces and suspected causative foods during a staphylococcal food poisoning outbreak, consist of 2,750,811-bp and 2,751,556-bp circular chromosomes and 2,543 and 2,548 genome annotation-predicted coding DNA sequences, respectively, with 19 rRNAs, 61 tRNAs, and 1 CRISPR each.

The extracellular loop of the membrane permease VraG interacts with GraS to sense cationic antimicrobial peptides in Staphylococcus aureus

Host defense proteins (HDPs), aka defensins, are a key part of the innate immune system that functions by inserting into the bacterial membranes to form pores to kill invading and colonizing microorganisms. To ensure survival, microorganism such as S. aureus has developed survival strategies to sense and respond to HDPs. One key strategy in S. aureus is a two-component system (TCS) called GraRS coupled to an efflux pump that consists of a membrane permease VraG and an ATPase VraF, analogous to the BceRS-BceAB system of Bacillus subtilis but with distinct differences. While the 9 negatively charged amino acid extracellular loop of the membrane sensor GraS has been shown to be involved in sensing, the major question is how such a small loop can sense diverse HDPs. Mutation analysis in this study divulged that the vraG mutant phenocopied the graS mutant with respect to reduced activation of downstream effector mprF, reduction in surface positive charge and enhanced 2 hr. killing with LL-37 as compared with the parental MRSA strain JE2. In silico analysis revealed VraG contains a single 200-residue extracellular loop (EL) situated between the 7th and 8th transmembrane segments (out of 10). Remarkably, deletion of EL in VraG enhanced mprF expression, augmented surface positive charge and improved survival in LL-37 vs. parent JE2. As the EL of VraG is rich in lysine residues (16%), in contrast to a preponderance of negatively charged aspartic acid residues (3 out of 9) in the EL of GraS, we divulged the role of charge interaction by showing that K380 in the EL of VraG is an important residue that likely interacts with GraS to interfere with GraS-mediated signaling. Bacterial two-hybrid analysis also supported the interaction of EL of VraG with the EL of GraS. Collectively, we demonstrated an interesting facet of efflux pumps whereby the membrane permease disrupts HDP signaling by inhibiting GraS sensing that involves charged residues in the EL of VraG.

Bacterial keratoconjunctivitis caused by Staphylococcus argenteus belonging to sequence type 1223 isolated in Japan

Staphylococcus argenteus, characterized by the formation of non-pigmented (white) colonies, was recently identified as a new lineage separated from Staphylococcus aureus. However, correct identification of this lineage is difficult because of the similar characteristics to S. aureus. Here, we describe the first known case of keratoconjunctivitis due to S. argenteus in a 64-year-old man with diabetes. The symptoms of the patient were not improved by antibiotic therapy using levofloxacin eye drops (15 mg/mL). The conjunctival scraping was cultured, and coagulase-positive staphylococci forming white colonies were detected. Matrix-assisted laser desorption/ionization-time of flight mass spectrometry confirmed the species as S. argenteus with a spectral score of 1.97. After the antibiotic was changed to vancomycin eye drops (10 mg/mL), the patient's symptom clearly improved. Multi-locus sequence typing showed that this isolate belonged to sequence type 1223, which has been predominantly isolated worldwide. Furthermore, this isolate harbored various virulence genes associated with S. aureus, such as staphylococcal enterotoxins and leukocidin. Since only limited information is available for this organism, further studies are needed to establish the epidemiology of S. argenteus.

Schinus terebinthifolia leaf lectin (SteLL) has anti-infective action and modulates the response of Staphylococcus aureus-infected macrophages

Staphylococcus aureus is recognized as an important pathogen causing a wide spectrum of diseases. Here we examined the antimicrobial effects of the lectin isolated from leaves of Schinus terebinthifolia Raddi (SteLL) against S. aureus using in vitro assays and an infection model based on Galleria mellonella larvae. The actions of SteLL on mice macrophages and S. aureus-infected macrophages were also evaluated. SteLL at 16 µg/mL (8 × MIC) increased cell mass and DNA content of S. aureus in relation to untreated bacteria, suggesting that SteLL impairs cell division. Unlike ciprofloxacin, SteLL did not induce the expression of recA, crucial for DNA repair through SOS response. The antimicrobial action of SteLL was partially inhibited by 50 mM N-acetylglucosamine. SteLL reduced staphyloxathin production and increased ciprofloxacin activity towards S. aureus. This lectin also improved the survival of G. mellonella larvae infected with S. aureus. Furthermore, SteLL induced the release of cytokines (IL-6, IL-10, IL-17A, and TNF-α), nitric oxide and superoxide anion by macrophagens. The lectin improved the bactericidal action of macrophages towards S. aureus; while the expression of IL-17A and IFN-γ was downregulated in infected macrophages. These evidences suggest SteLL as important lead molecule in the development of anti-infective agents against S. aureus.

Implications of identifying the recently defined members of the Staphylococcus aureus complex S. argenteus and S. schweitzeri: a position paper of members of the ESCMID Study Group for Staphylococci and Staphylococcal Diseases (ESGS)

BACKGROUND

Staphylococcus argenteus and Staphylococcus schweitzeri, previously known as divergent Staphylococcus aureus clonal lineages, have been recently established as novel, difficult-to-delimit, coagulase-positive species within the S. aureus complex. Methicillin-resistant strains of S. argenteus are known from Australia and the UK. Knowledge of their epidemiology, medical significance and transmission risk is limited and partly contradictory, hampering definitive recommendations. There is mounting evidence that the pathogenicity of S. argenteus is similar to that of 'classical' S. aureus, while as yet no S. schweitzeri infections have been reported.

AIM

To provide decision support on whether and how to distinguish and report both species.

SOURCES

PubMed, searched for S. argenteus and S. schweitzeri.

CONTENT

This position paper reviews the main characteristics of both species and draws conclusions for microbiological diagnostics and surveillance as well as infection prevention and control measures.

IMPLICATIONS

We propose not distinguishing within the S. aureus complex for routine reporting purposes until there is evidence that pathogenicity or clinical outcome differ markedly between the different species. Primarily for research purposes, suitably equipped laboratories are encouraged to differentiate between S. argenteus and S. schweitzeri. Caution is urged if these novel species are explicitly reported. In such cases, a specific comment should be added (i.e. 'member of the S.aureus complex') to prevent confusion with less- or non-pathogenic staphylococci. Prioritizing aspects of patient safety, methicillin-resistant isolates should be handled as recommended for methicillin-resistant Staphylococcus aureus (MRSA). In these cases, the clinician responsible should be directly contacted and informed by the diagnosing microbiological laboratory, as they would be for MRSA. Research is warranted to clarify the epidemiology, clinical impact and implications for infection control of such isolates.

Joint Genomic and Proteomic Analysis Identifies Meta-Trait Characteristics of Virulent and Non-virulent Staphylococcus aureus Strains

Staphylococcus aureus is an opportunistic pathogen of humans and warm-blooded animals and presents a growing threat in terms of multi-drug resistance. Despite numerous studies, the basis of staphylococcal virulence and switching between commensal and pathogenic phenotypes is not fully understood. Using genomics, we show here that S. aureus strains exhibiting virulent (VIR) and non-virulent (NVIR) phenotypes in a chicken embryo infection model genetically fall into two separate groups, with the VIR group being much more cohesive than the NVIR group. Significantly, the genes encoding known staphylococcal virulence factors, such as clumping factors, are either found in different allelic variants in the genomes of NVIR strains (compared to VIR strains) or are inactive pseudogenes. Moreover, the pyruvate carboxylase and gamma-aminobutyrate permease genes, which were previously linked with virulence, are pseudogenized in NVIR strain ch22. Further, we use comprehensive proteomics tools to characterize strains that show opposing phenotypes in a chicken embryo virulence model. VIR strain CH21 had an elevated level of diapolycopene oxygenase involved in staphyloxanthin production (protection against free radicals) and expressed a higher level of immunoglobulin-binding protein Sbi on its surface compared to NVIR strain ch22. Furthermore, joint genomic and proteomic approaches linked the elevated production of superoxide dismutase and DNA-binding protein by NVIR strain ch22 with gene duplications.

Architecture of a Species: Phylogenomics of Staphylococcus aureus

A deluge of whole-genome sequencing has begun to give insights into the patterns and processes of microbial evolution, but genome sequences have accrued in a haphazard manner, with biased sampling of natural variation that is driven largely by medical and epidemiological priorities. For instance, there is a strong bias for sequencing epidemic lineages of methicillin-resistant Staphylococcus aureus (MRSA) over sensitive isolates (methicillin-sensitive S. aureus: MSSA). As more diverse genomes are sequenced the emerging picture is of a highly subdivided species with a handful of relatively clonal groups (complexes) that, at any given moment, dominate in particular geographical regions. The establishment of hegemony of particular clones appears to be a dynamic process of successive waves of replacement of the previously dominant clone. Here we review the phylogenomic structure of a diverse range of S. aureus, including both MRSA and MSSA. We consider the utility of the concept of the 'core' genome and the impact of recombination and horizontal transfer. We argue that whole-genome surveillance of S. aureus populations could lead to better forecasting of antibiotic resistance and virulence of emerging clones, and a better understanding of the elusive biological factors that determine repeated strain replacement.