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PubMed1992

Biochemical basis of mupirocin resistance in strains of Staphylococcus aureus.

Twenty one strains of Staphylococcus aureus, of varying resistance to mupirocin, were examined in order to determine the mechanism of resistance to this antibiotic; six of these strains were mupirocin sensitive (MIC 0.12-1.0 mg/L) nine moderately resistant strains (MIC 8-256 mg/L) and six highly resistant strains (MIC > 2048 mg/L). Mupirocin showed a time-dependent inhibition of the target enzyme, isoleucyl-tRNA synthetase (IRS); incubation of the antibiotic with this enzyme before adding the substrates markedly increased inhibition in sensitive strains. The IRS I50 values (the antibiotic concentrations which cause a 50% decrease in enzyme activity) correlated well with the MIC values for each strain (P < 0.01). The mean I50 value for sensitive strains was 3.3 x 10(-2) mg/L, in moderately resistant strains it was 1.3 x 10(-1) mg/L and in highly resistant strains it was 7.5 mg/L. No degradation of mupirocin could be detected during extended incubation of the antibiotic with cell free extracts from four resistant S. aureus strains. We conclude that the production of a modified IRS enzyme is the major cause of mupirocin resistance in the strains studied.

Cell-Free System↗
PubMed2006

International dissemination of a high virulence rabbit Staphylococcus aureus clone.

High virulence rabbit Staphylococcus aureus strains cause chronic and spreading problems of mastitis, pododermatitis and subcutaneous abscesses on rabbit flock level, whereas infections with low virulence strains are limited to individual rabbits. In the present report, 13 high virulence rabbit S. aureus strains, selected out of a large collection of strains isolated in five European countries between 1983 and 2004, were genotyped using pulsed-field gel electrophoresis, spa typing, multilocus sequence typing (MLST) and accessory gene regulator (agr) group typing. Two low virulence rabbit S. aureus strains were also included in the study. The results indicate the clonal origin of high virulence rabbit S. aureus strains present in Europe. Furthermore, the results of MLST and spa typing form a basis for international epidemiology of rabbit S. aureus strains, as these DNA sequence-based typing techniques can easily be used for intercentre comparisons.

Animals↗
PubMed1978

Activation of complement by cell surface components of Staphylococcus aureus.

The abilities of intact Staphylococcus aureus H, crude cell walls (CCW), purified cell walls (PCW, peptidoglycan [PG] and covalently linked teichoic acid), peptidoglycan, and cell membranes (CM) to activate the complement system in normal human serum, C2-deficient serum, and immunoglobulin-deficient serum were compared. On a weight basis, PCW was the most active fraction; intact organisms and CCW were about equally effective; and PG was least active in causing complement consumption in normal serum. CM also activated complement but did not give a clear dose-response relationship in the concentrations used. Kinetic studies revealed that C3-C9 consumption occurred at a significantly slower rate in C2-deficient serum, indicating that intact organisms, PCW, and PG may activate the complement system via the classical and alternative pathways in normal serum. C3-C9 consumption was also slower in immunoglobulin-deficient serum than in normal serum, implying that immunoglobulins play a role in attaining maximum rates of complement activation. In all sera studied, PG was less active in complement activation than PCW. These results indicate that a number of cell surface components of S. aureus can play a role in complement activation by this organism and that the presence of teichoic acid has a significant enhancing effect in this regard.

Cell Membrane↗
PubMed1997

Reduced susceptibility of Staphylococcus aureus to vancomycin--Japan, 1996.

Staphylococcus aureus is a virulent microorganism responsible for many serious infections among the general population. Since recognition of vancomycin-resistant enterococci (VRE), the emergence of vancomycin resistance in S. aureus has been anticipated. This report describes the first documented case of infection caused by S. aureus with reduced susceptibility to vancomycin and includes the initial characterization of this isolate (1); the case occurred in a pediatric patient in Japan. The emergence of reduced vancomycin susceptibility in S. aureus increases the possibility that some strains will become fully resistant and that currently available antimicrobial agents will become ineffective for treating infections caused by such strains.

Anti-Bacterial Agents↗
PubMed2005

Heparan sulfate proteoglycans mediate Staphylococcus aureus interactions with intestinal epithelium.

Staphylococcus aureus can be internalized by non-professional phagocytes, and may colonize the intestine in normal and antibiotic-treated individuals. Intestinal colonization may depend on the interactions of S. aureus with the intestinal epithelium. The best described mechanism of S. aureus binding to eukaryotic cells involves S. aureus fibronectin binding proteins (FnBPs), using fibronectin as a bridging molecule to beta1 integrins on the eukaryotic cell surface. Because S. aureus can be internalized by enterocytes, and because S. aureus is known to bind heparan sulfate (HS), we hypothesized that heparan sulfate proteoglycans (HSPGs) widely expressed on epithelia may mediate S. aureus interactions with intestinal epithelial cells. Internalization of S. aureus RN6390 by cultured intestinal epithelial cells was inhibited in a dose-dependent fashion by the HS mimic heparin, and by HS itself. Internalization of S. aureus DU5883, which lacks expression of staphylococcal FnBPs, was also inhibited by heparin. S. aureus adherence to ARH-77 cells, transfected to express the HSPG syndecan-1, was greatly increased when compared to adherence to plasmid control ARH-77 cells which have little detergent extractable HS. In addition, compared to wild-type HS-expressing Chinese hamster ovary (CHO) cells, internalization of S. aureus was decreased using mutant CHO cells with decreased HS expression. These findings are consistent with a model wherein S. aureus internalization by intestinal epithelial cells (and perhaps other epithelia) is mediated by S. aureus binding to the HS moiety of cell-surface HSPGs, and this interaction appears independent of fibronectin binding.

Animals↗
PubMed2004

Characterizing the dynamics of the quorum-sensing system in Staphylococcus aureus.

The virulence determinants of Staphylococcus aureus are expressed in a growth phase-dependent manner governed by the autoinducible quorum-sensing system agr. Activation of the agr system results in a rapid increase in the regulator RNAIII and occurs in response to accumulation of AIP. In order to activate the agr system, a basal transcription of agr components must be assumed. This basal transcription of agr components seems to be stimulated by sarA. To better understand how SarA would affect activation of the agr system by modulating the basal agr activity, a mathematical model for autoactivation of the agr system was set up. The model predicted that the agr system is hysteretic, meaning that the agr system is activated at a specific concentration of autoinducing peptide (AIP), whereas it is inactivated at a specific lower concentration of AIP. According to the model, changing the basal agr activity only had a marginal effect on steady-state levels of RNAIII but changed the sensitivity of the cells to AIP. This was supported by Northern blot analysis of RNAIII in S. aureus mutants with different levels of SarA expression. Since natural antagonistic AIPs have been demonstrated, the effect of adding inhibitors to the system was analyzed.

Adaptation, Physiological↗
PubMed2005

Genomic fingerprinting of bacteriocin-producer strains of Staphylococcus aureus.

Among 363 strains of Staphylococcus aureus, 21 were shown to produce bacteriocins (Bac), antimicrobial peptides with potential biotechnological applications. This collection includes strains which are either isolated from food, patients and healthy cattle, or are involved in subclinical bovine mastitis. From these 21 strains, 17 were shown to carry closely-related 8.0-kb Bac plasmids encoding bacteriocins either identical to or similar to aureocin A70, a bacteriocin able to inhibit strains of Listeria monocytogenes, a food-borne pathogen. Such findings prompted us to investigate the genetic relationships among these Bac+ strains. To obtain more discriminatory results, a combined analysis of AP-PCR, rep-PCR, and a modified PCR technique that we designated SD-PCR was employed. The 17 Bac+ strains harboring 8.0-kb Bac plasmids exhibited seven fingerprint patterns. One such genotype was composed of 8 out of the 11 strains associated with bovine mastitis, which suggests the prevalence of a clone of Bac+ strains involved in this animal infection carrying 8.0-kb Bac plasmids. Our data support the assumption that Bac+ strains of S. aureus carrying genetically related 8.0-kb Bac plasmids do not belong to a single clone. It seems, therefore, that 8.0-kb Bac plasmids have spread horizontally among different S. aureus strains. There also seems to be genetic diversity among the remaining Bac+ strains analyzed.

Bacteriocins↗
PubMed2002

mecA gene is widely disseminated in Staphylococcus aureus population.

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the most important causes of hospital infections worldwide. High-level resistance to methicillin is caused by the mecA gene, which encodes an alternative penicillin-binding protein, PBP 2a. To determine the clonal relationships between methicillin-susceptible S. aureus (MSSA) and MRSA, we typed 1,069 S. aureus isolates (493 MSSA isolates and 576 MRSA isolates), collected mainly in North American and European hospitals between the 1960s and the year 2000, using pulsed-field gel electrophoresis and ribotyping. Of 10 widespread S. aureus lineages recognized, 8 had corresponding mecA-positive strains. Multiresistant MRSA strains are found in hospitals worldwide, while unrelated and more susceptible strains represent less than 1% of the MRSA population. This supports the hypothesis that horizontal transfer plays an important role in the dissemination of the mecA gene in the S. aureus population.

Bacterial Proteins↗
PubMed2000

Molecular population and virulence factor analysis of Staphylococcus aureus from bovine intramammary infection.

Staphylococcus aureus isolates from cows in Ireland (n = 102) and the USA (n = 42) were characterized by RAPD-PCR and analysed for the production of a number of putative virulence factors. Of these strains 63 representative isolates were screened for the corresponding virulence factor genes by PCR or Southern hybridization or both. The isolates were divided into 12 distinct clonal types on the basis of their RAPD fingerprint profiles. Of the isolates, 107 (74.3%) tested positive for clumping factor in a slide agglutination test, all 24 RAPD type 7 isolates being negative for clumping factor. PCR analysis of region R, a repeat region of the clfA gene, revealed eight region-R sizes. There was a strong association between RAPD type and the clfA region-R genotype among Irish isolates. Of the RAPD type 7 isolates, 21 (87.5%) coproduced toxic shock syndrome toxin-1 (TSST-1) and staphylococcal enterotoxin C (SEC). Over 90% of isolates demonstrated haemolytic activity on sheep or rabbit red blood cells and all isolates harboured the gamma-haemolysin (hlg) locus. Of the Irish isolates, all those of RAPD type 7 were sensitive to penicillin G, whereas 86% of RAPD types 4 and 5 strains were resistant. Furthermore, RAPD types 5 and 7 were more likely to be associated with clinical mastitis whereas RAPD type 4 isolates were more often associated with a latent infection. The current study identifies some of the putative virulence factors produced by the predominant clonal types of bovine Staph. aureus that may be considered as components of a vaccine.

Animals↗
PubMed2005

Septic arthritis caused by vancomycin-intermediate Staphylococcus aureus.

Four methicillin-resistant Staphylococcus aureus isolates were consecutively isolated from synovial fluid and a knee wound of a patient with septic arthritis. Determination of the MIC of vancomycin and population analysis confirmed these isolates as vancomycin-intermediate S. aureus (VISA). Results of this study also revealed that cell wall thickness and reduced susceptibility to Triton X-100 were characteristic features of VISA.

Adult↗
PubMed2001

agr expression precedes escape of internalized Staphylococcus aureus from the host endosome.

Staphylococcus aureus is a versatile pathogen capable of causing life-threatening infections. Many of its cell wall and exoproduct virulence determinants are controlled via the accessory gene regulator (agr). Although considered primarily as an extracellular pathogen, it is now recognized that S. aureus can be internalized by epithelial and endothelial cells. Traditional experimental approaches to investigate bacterial internalization are extremely time-consuming and notoriously irreproducible. We present here a new reporter gene method to assess intracellular growth of S. aureus in MAC-T cells that utilizes a gfp-luxABCDE reporter operon under the control of the Bacillus megaterium xylA promoter, which in S. aureus is expressed in a growth-dependent manner. This facilitates assessment of the growth of internalized bacteria in a nondestructive assay. The dual gfp-lux reporter cassette was also evaluated as a reporter of agr expression and used to monitor the temporal induction of agr during the MAC-T internalization process. The data obtained suggest that agr induction occurs prior to endosomal lysis and that agr-regulated exoproteins appear to be required prior to the release and replication of S. aureus within the infected MAC-T cells.

Acyltransferases↗
PubMed1985

Staphylococcus aureus septicaemia treated with cefotaxime.

Staphylococcus aureus strains were exposed in vitro to continuously decreasing cefotaxime concentrations. The initial concentration was approximately 4 X MIC and decreased at t1/2 = 60 min. A reduction in the colony count was seen even after the concentration had dropped below the MIC level. Sixteen patients with blood cultures positive for S. aureus were treated with cefotaxime. Four patient died of underlying diseases. The condition of one patient with staphylococcal endocarditis under treatment with vancomycin in combination with cefotaxime deteriorated when cefotaxime was discontinued, suggesting possible synergism between these two drugs against staphylococci.

Aged↗
PubMed1976

Gentamicin resistance in Staphylococcus aureus.

A clinical isolate of Staphylococcus aureus was resistant to gentamicin, kanamycin, and tobramycin by virtue of the production of a drug-inactivating enzyme. Attempts to establish the cellular location of the genetic determinants for enzyme synthesis have given equivocal results.

Anti-Bacterial Agents↗
PubMed1983

The Staphylococcus aureus receptor for fibronectin.

The Staphylococcus aureus binding site for human fibronectin was determined by unique biologic assays based upon the specific adherence of the bacterium to nasal epithelial cells. Fibronectin treatment of S. aureus caused a reduction in adherence tallies on high granular and fully keratinized cells compared to controls (p less than 0.05; p less than 0.001). Spinous and low granular cells showed no significant differences. The cell wall materials N-acetyl-D-glucosamine, N-acetyl muramic acid, and protein A were unable to inhibit the coupling of fibronectin to S. aureus. Only ribitol teichoic acid had this property. Furthermore, fibronectin could neutralize the adherence-blocking ability of teichoic acid, which affects keratinized cells. Thus, teichoic acid seems to be a receptor for fibronectin.

Binding Sites↗
PubMed2005

Epidemiology, clinical features and management of infections due to community methicillin-resistant Staphylococcus aureus (cMRSA).

Methicillin-resistant Staphylococcus aureus (MRSA) was initially confined to hospitals, but in the late 1970s appeared in the community in the USA, primarily among intravenous drug users. In the 1990s, community MRSA (cMRSA) strains appeared in multiple areas of the world, and spread extensively. Initially, there were problems with the definition of 'community-acquired', which was exacerbated by the fact that if a time-based definition was used without stratification for risk factors, patients with healthcare-associated MRSA would be counted. Some cMRSA strains have entered the hospital environment to cause outbreaks of infection, which has added to the difficulty in separating the two types. cMRSA strains usually possess genes for Panton-Valentine leukocidin (PVL), which is associated with furunculosis and necrotizing pneumonia, and sometimes possess other virulence genes such as those for toxic shock syndrome or exfoliative toxins. Antimicrobial resistance to commonly used topical and oral agents is now appearing in certain cMRSA strains, which is complicating therapy. While cMRSA strains are usually susceptible to most non-beta-lactam antimicrobials, there is a lack of clinical trial data indicating which drugs have superior clinical efficacy. DNA fingerprinting methods have become more sophisticated over the last decade, and have determined that cMRSA strains have probably arisen from virulent methicillin-susceptible strains, most likely by horizontal transfer of methicillin-resistance genes from coagulase negative staphylococci to S. aureus on a limited number of occasions, and these clones have spread extensively throughout the world by person-to-person transmission. In Australia, the dominant cMRSA clones are the Western Australia, Oceania and Queensland strains.

Anti-Bacterial Agents↗
PubMed1996

Purification and characterisation of a plasmin-sensitive surface protein of Staphylococcus aureus.

Certain methicillin-resistant Staphylococcus aureus strains contain a 230-kDa cell-wall protein which is not present on the surface of other staphylococci. The presence of this 230-kDa protein is associated with a negative test result in commercial assays designed to detect fibrinogen-binding proteins and/or protein A on the staphylococcal surface. We have purified and partially characterised the 230-kDa protein from a lysostaphin digest of a non-agglutinating methicillin-resistant S. aureus strain. Partial amino acid sequence data obtained from the purified protein did not reveal any significant similarities to known proteins which indicates that the protein is novel. The 230-kDa protein was very sensitive to proteolysis; soluble plasmin, or plasmin formed on the bacterial-cell surface, rapidly degraded the 230-kDa protein to a 175-kDa form. The finding that the 230-kDa protein bound to lectins allowed its purification by affinity chromatography on immobilised wheat germ agglutinin. Furthermore, the degradation of the 230-kDa protein was associated with an increased adherence of non-agglutinating methicillin-resistant S. aureus cells to solid-phase fibronectin, fibrinogen or IgG.

Agglutination↗
PubMed2003

Enterotoxin production by Staphylococcus aureus isolated from mastitic cows.

Staphylococcus aureus is an important cause of mastitis in cows. The ability of S. aureus strains to produce one or more enterotoxins in milk and dairy products is linked to staphylococcal food poisoning. To determine whether staphylococci causing bovine mastitis could cause human foodborne intoxication, the production of staphylococcal enterotoxins A through D (SEA, SEB, SEC, and SED) by 160 S. aureus isolates was evaluated with the use of a reverse passive latex agglutination enterotoxin kit. All S. aureus strains were isolated over a 9-month period from 2,343 routine submissions of a composite quarter collection of individual mastitic cows at 18 dairy farms in the San Joaquin Valley in California. Prior to enterotoxin detection, isolates were grown by a method that enhances the in vitro synthesis of enterotoxin. Twenty-two of 160 S. aureus isolates produced enterotoxin. Seven produced SEC, 12 produced SED, and 3 produced both SEC and SED. None of the isolates produced SEA or SEB.

Animals↗