Genetic analysis of Staphylococcus aureus from intravenous drug user lesions

Approach to the Patient with a Skin and Soft Tissue Infection

The diagnosis of a skin and soft tissue infection (SSTI) requires careful attention to a patient's history, physical examination, and diagnostic test results. We review for many bacterial, viral, fungal, and parasitic pathogens that cause SSTIs the clues for reaching a diagnosis, including reported past medical history, hobbies and behaviors, travel, insect bites, exposure to other people and to animals, environmental exposures to water, soil, or sand, as well as the anatomic site of skin lesions, their morphology on examination, and their evolution over time. Laboratory and radiographic tests are discussed that may be used to confirm a specific diagnosis.

Quorum sensing-mediated regulation of staphylococcal virulence and antibiotic resistance

ABSTRACT: 

Accessory gene regulator (agr)-mediated quorum sensing plays a central role in staphylococcal pathogenesis. It primarily upregulates secreted virulence factors and downregulates cell surface proteins, thereby governing invasiveness of staphylococci and cell dispersal from biofilms. Except for α- and β-PSMs, which are directly controlled by AgrA, the effector functions of agr are primarily mediated by RNAIII, a regulatory RNA encoded by this operon. agr phenotype and expression considerably influence the chronicity of an infection. It has also been linked with altered susceptibility of Staphylococcus aureus against antibiotics. Four classes of S. aureus and Staphylococcus epidermidis AIPs exist based on sequence variation, and lead to inter-strain and species cross-inhibition. Certain agr classes have been associated with specific clonal complexes, disease syndromes and intermediate-susceptibility to glycopeptides. It is also being investigated as a prophylactic and therapeutic target. This article describes the presently available literature regarding the role of agr in S. aureus and S. epidermidis infections.

Population structure and exotoxin gene content of methicillin-susceptible Staphylococcus aureus from Spanish healthy carriers

The population structure of 111 methicillin-susceptible Staphylococcus aureus (MSSA), recovered in Spain from healthy and risk-free carriers was investigated using pulsed-field gel electrophoresis (PFGE), spa (staphylococcal protein A) typing, multi locus sequence typing (MLST) and the accessory gene regulator (agr). Results from the different techniques were highly concordant, and revealed twelve clonal complexes (CCs): CC30 (27%), CC5 (18.9%), CC45 (16.2%), CC15 (11.7%), CC25 (8.1%), CC1, CC9 (3.6% each), CC59, CC97 and CC121 (2.7% each), CC72 (1.8%) and CC8 (0.9%). Isolates with genetic backgrounds of hospital-acquired MSSA were detected and, consistent with the ability of diverse MSSA to act as recipients of the SCCmec cassette, a MSSA isolate from a healthy carrier shared the ST, spa-type and agr-type of a MRSA clone recovered in a hospital of the same region. All except two fragments of the PGFE-profiles of these isolates were identical, and the differential fragment of the MRSA carried mecA. Analyses of the exotoxin gene content of the nasal isolates revealed an increase in the number of exotoxin genes over time. This, together with the detection of lukPV and the high frequency of tst, exfoliatin and enterotoxin genes, is worrisome and requires further surveillance.

Population genetic structures of Staphylococcus aureus isolates from cats and dogs in Japan

We determined the population genetic structures of feline and canine Staphylococcus aureus strains in Japan by multilocus sequence typing (MLST). Ecological analyses suggested that multiple feline-related S. aureus clones, including ST133, naturally occur as commensals and can cause endogenous infections in felines. In contrast, S. aureus populations do not likely include any clone that exhibits tropism in domestic dogs. Even if S. aureus infections occur in dogs, the pathologies are likely exogenous infections.

Roles of Toll-like receptor 2 (TLR2) and superantigens on adaptive immune responses during CNS staphylococcal infection

Staphylococcus aureus is a common etiologic agent of brain abscesses and possesses numerous virulence factors that manipulate host immunity. One example is superantigens (SAG) that clonally expand T cell subsets bearing specific Vβ receptors. Toll-like receptor 2 (TLR2) is one receptor implicated in S. aureus recognition. However, the interplay between TLR2, SAG, and adaptive immunity during brain abscess formation has not yet been investigated and could reveal novel insights into host-pathogen interactions for regulating protective immunity. A comprehensive analysis of abscess-associated T cell populations in TLR2 KO and WT mice was performed following infection with a S. aureus clinical isolate. Both natural killer T (NKT) and γδ T cell infiltrates were increased in brain abscesses of TLR2 KO mice and produced more IL-17 and IFN-γ compared to WT populations, which could have resulted from elevated bacterial burdens observed in these animals. Analysis of SAG-reactive T cells revealed a predominant Vβ(8.1,8.2) infiltrate reactive with staphylococcal enterotoxin B (SEB), whereas SEA-reactive Vβ(11) T cells were less numerous. Brain abscesses of TLR2 KO mice had fewer Vβ(8.1,8.2) and Vβ(11) T cells and produced less TNF-α and IFN-γ compared to WT animals. Treatment of primary microglia with purified SEB augmented TNF-α production in response to the TLR2 ligand Pam3Cys, which may serve to amplify proinflammatory cascades during CNS S. aureus infection. Collectively, these studies demonstrate that TLR2 impacts adaptive immunity to S. aureus infection and modulates SAG responses.

Shooting up: the interface of microbial infections and drug abuse

Illicit drug control has been on the global agenda for more than a century. Infections have long been recognized as one of the most serious complications of drug abuse. Drug users are susceptible to pulmonary, endovascular, skin and soft tissue, bone and joint, and sexually transmitted infections caused by a wide range of bacterial, viral, fungal and protozoal pathogens. In addition, injection drug users are at increased risk for parenterally acquired infections such as human immunodeficiency virus, hepatitis B virus, hepatitis C virus, tetanus and malaria. Factors related to drug use, such as unsterile injection practices, contaminated drug paraphernalia and drug adulterants, increase the exposure to microbial pathogens. Illicit drugs also affect several components of the complex immune system and thus modulate host immunity. In addition, lifestyle practices such as multiple sexual partners, overcrowded housing arrangements and malnutrition serve as co-factors in increasing the risk of infection. In this review we present an overview of the unique aspects of microbial pathogenesis, immune modulation and common infections associated with drug use. We have restricted the definition of drug abuse to the use of illegal drugs (such as opiates, marijuana, cocaine, heroin and amphetamines), not including alcohol and nicotine.

Characterization of infecting strains and superantigen-neutralizing antibodies in Staphylococcus aureus bacteremia

Staphylococcus aureus superantigens (SAgs) are highly potent T cell mitogens. Antibodies against non-enterotoxin gene cluster (non-egc) SAgs are common in healthy adults, whereas neutralizing antibodies against egc SAgs are rare. We investigated the infecting S. aureus strains and the anti-SAg antibody response during S. aureus bacteremia (SAB). This prospective clinical study (www.clinicaltrials.gov, NCT00548002) included 43 injection drug users (IDUs) and 44 group-matched nonaddicts with SAB. spa genotypes and SAg gene patterns (multiplex PCR) of the S. aureus isolates were determined. The neutralizing capacities of sera obtained at the acute phase and the convalescent phase of SAB were tested against the SAg cocktail of the respective infecting strain and a panel of recombinant SAgs. The lineages CC59 and CC30 were more prevalent among bacteremia strains from IDUs than among strains from nonaddicts. SAg gene patterns in isolates from IDUs and nonaddicts were similar. At the acute phase of bacteremia, IDUs had more neutralizing antibodies against non-egc SAgs than did nonaddicts. Antibody titers frequently increased during infection. In contrast, there were no neutralizing antibodies against egc SAgs at disease onset and such antibodies were not induced by SAB. SAB triggers an antibody response only against non-egc SAgs. Preimmunization in IDU patients is probably due to previous exposure to the infecting strain.

Panton-Valentine leukocidin (PVL)-positive methicillin-susceptible and resistant Staphylococcus aureus in Taiwan: identification of oxacillin-susceptible mecA-positive methicillin-resistant S. aureus

Methicillin-resistant Staphylococcus aureus (MRSA) arises when methicillin-susceptible S. aureus (MSSA) acquires the staphylococcal cassette chromosome mec (SCCmec). Most pvl-positive MRSA in Taiwan belong to ST59 lineage and carry SCCmec V. The genetic profiles of 51 MSSA were compared with those of 80 MRSA from the same hospitals. Nine pvl-positive MSSA (oxacillin MIC < or = 2 microg/mL) shared >80% similarity in pulsed field gel electrophoresis pattern with 17 pvl-positive SCCmec V MRSA. Further investigation found that 5 of these 9 isolates were MRSA by cefoxitin and carried SCCmec V. All 26 pvl-positive isolates had very similar genetic profile (ST59, protein A clonal complex [spa-CC] c2:441/437, and agr group I). The success of the ST59:SCCmec V MRSA may be due in part to its heterogeneous and borderline resistance to methicillin, which may be missed by testing only oxacillin, with subsequent exposure to beta-lactams causing the emergence of more resistant subpopulations.

The emergence of meticillin-resistant Staphylococcus aureus among injecting drug users

OBJECTIVE

To quantify an observed increase in meticillin-resistant Staphylococcus aureus (MRSA) infections in injecting drug users (IDUs) and, using genetic analysis and clinical presentation, contrast findings with those from previous studies in Brighton to further understanding of the clinical epidemiology and underlying molecular biology associated with the increase.

METHODS

From 2006 to 2008, isolates of S. aureus were collected, together with clinical details from infected IDUs. Isolates were characterised using antibiotic susceptibilities, multilocus-sequence typing (MLST) and spa typing. The molecular epidemiology and patterns of clinical presentation were compared with results from 1999-2000 to 2000-2003.

RESULTS

From 2006 to 2008, 18/37 (49%) of clinical isolates from IDUs were MRSA compared with 4/59 (7%) in 2000-2003 and 0/48 (0%) in 1999-2000. Despite this increase, hospital attendances by IDUs for treatment of infection dropped from 3.2 to 1.1 patients per month. MLST showed a shift in population structure towards a single MRSA clone, ST1, rather than epidemic hospital-associated strains.

CONCLUSION

In IDUs between 2000-2003 and 2006-2008, an increase occurred in the percentage of community-associated S. aureus isolates showing meticillin-resistance, but hospital attendances decreased. IDUs may act as a focus for the emergence of resistant S. aureus strains.

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.

Clonal distribution of superantigen genes in clinical Staphylococcus aureus isolates

Staphylococcus aureus is both a successful human commensal and a major pathogen. The elucidation of the molecular determinants of virulence, in particular assessment of the contributions of the genetic background versus those of mobile genetic elements (MGEs), has proved difficult in this variable species. To address this, we simultaneously determined the genetic backgrounds (spa typing) and the distributions of all 19 known superantigens and the exfoliative toxins A and D (multiplex PCR) as markers for MGEs. Methicillin- sensitive S. aureus strains from Pomerania, 107 nasal and 88 blood culture isolates, were investigated. All superantigen-encoding MGEs were linked more or less tightly to the genetic background. Thus, each S. aureus clonal complex was characterized by a typical repertoire of superantigen and exfoliative toxin genes. However, within each S. aureus clonal complex and even within the same spa type, virulence gene profiles varied remarkably. Therefore, virulence genes of nasal and blood culture isolates were separately compared in each clonal complex. The results indicated a role in infection for the MGE harboring the exfoliative toxin D gene. In contrast, there was no association of superantigen genes with bloodstream invasion. In summary, we show here that the simultaneous assessment of virulence gene profiles and the genetic background increases the discriminatory power of genetic investigations into the mechanisms of S. aureus pathogenesis.

Characterization of the epidemic European fusidic acid-resistant impetigo clone of Staphylococcus aureus

Resistance to the antibiotic fusidic acid in European strains of Staphylococcus aureus causing impetigo has increased in recent years. This increase appears to have resulted from clonal expansion of a strain we have designated the epidemic European fusidic acid-resistant impetigo clone (EEFIC), which carries the fusidic acid resistance determinant fusB on its chromosome. To understand better the properties of the EEFIC responsible for its success, we have performed detailed phenotypic and genotypic characterization of this clone. Molecular typing revealed the EEFIC to be ST123, spa type t171, and agr type IV and therefore unrelated to earlier prevalent fusB(+) strains found in the United Kingdom. EEFIC strains exhibited resistance to fusidic acid, penicillin, and, in some cases, erythromycin, which are all used in the treatment of impetigo. PCR analysis of the EEFIC and complete DNA sequencing of the 39.3 Kb plasmid it harbors identified genes encoding several toxins previously implicated in impetigo (exfoliative toxins A and B and EDIN-C). The location of fusB was mapped on the chromosome and found to be associated with a novel 16.6-kb genomic island integrated downstream of groEL. Although this element is related to classical staphylococcal pathogenicity islands, it does not encode any known virulence factors and consequently has been designated SaRI(fusB) (for "S. aureus resistance island carrying fusB").

Molecular analysis of Staphylococcus aureus isolates associated with staphylococcal food poisoning in South Korea

AIMS

To investigate the molecular epidemiological study of Staphylococcus aureus from staphylococcal food poisoning (SFP) incidents in South Korea.

METHODS AND RESULTS

Three hundred and thirty-two strains isolated from ten provinces between June 1999 and January 2002 were characterized by staphylococcal enterotoxin genes, toxic shock syndrome toxin 1 (tst) gene, and exfoliative toxin genes. Toxin genotypes were sea-seh (n=197), sea (n=51), sea-seg-sei (n=14), seg-sei (n=10), seb (n=10), seb-sed-seg-sei-sej (n=3), sea-seg-seh-sei (n=1), sea-seb (n=1), sea-sec (n=1), seg-sei plus eta (n=4), and sea-seg-sei plus tst (n=40). Most of the strains could be classified into three clusters of pulsed-field gel electrophoresis (PFGE) types A and B with coagulase type VII and type E with coagulase type IV. Of the ten sequence types (ST), ST1, ST59, and ST30 were frequently showed by multilocus sequence typing.

CONCLUSIONS

The strain belonging to PFGE pattern A with sea-seh gene, coagulase VII, and ST1 was the most epidemic clone of SFP incidents in Korea.

The phylogeny of Staphylococcus aureus - which genes make the best intra-species markers?

The ability to make informed decisions on the suitability of alternative marker loci is central for population and epidemiological investigations. This issue was addressed using Staphylococcus aureus as a model population by generating nucleotide sequence data from 33 gene fragments in a representative sample of 30 strains. Supplementing the data with pre-existing multilocus sequence typing data, an intra-species tree based on approximately 17.8 kb of sequence was reconstructed and the goodness of fit of each individual gene tree was computed. No strong association was noted between gene function per se and phylogenetic reliability, but it is suggested that candidate loci should possess at least the average degree of nucleotide diversity for all genes in the genome. In the case of S. aureus this threshold is >1 % mean pairwise diversity.

Comparative Prevalence of Superantigen Genes in Staphylococcus aureus Isolates Causing Sepsis With and Without Septic Shock

BACKGROUND

Staphylococcus aureus superantigens are associated with the pathogenesis of toxic shock syndrome, but their involvement in septic shock is unknown.

METHODS

We compared the distribution of 11 superantigen genes in S. aureus blood culture isolates obtained from patients with sepsis who did and did not have septic shock (19 and 61 patients, respectively), as well as from patients with suppurative infections (101 patients) and patients with colonization (25 patients).

RESULTS

The prevalence of the enterotoxin A gene (sea) increased significantly with the severity of infection (P<.001), whereas the prevalence of the enterotoxin gene cluster (egc) decreased significantly (P=.009).

CONCLUSION

Enterotoxin A (SEA) might play a key role in sea-positive S. aureus sepsis by triggering over-expression of inflammatory mediators associated with shock. Novel treatments targeting superantigens, especially the sea gene, might be beneficial in the treatment of S. aureus sepsis.