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At least 1,153 records · Page 64Linked to original sources
PubMed2001

Optimization of the PCR for detection of Staphylococcus aureus nuc gene in bovine milk.

Staphylococcus aureus is an economically important and a major mastitis-causing pathogen that also poses food safety and antimicrobial resistance threats. Substances in mastitic milk inhibit the Taq DNA polymerase reaction (Taq PCR) making it of limited use for detecting S. aureus mastitis. In the study reported here, a set of oligonucleotide primers of 21 and 24 bases was used in Taq-PCR to amplify DNA from S. aureus (isolates from bovine mastitis). A specific amplicon of 270 bp was generated as predicted. Replacing Taq DNA polymerase with Thermus thermophilus (Tth) DNA polymerase alone (Tth-PCR) raised the sensitivity of S. aureus detection in milk from experimentally infected cows from 65 to 80%. Combining the use of Tth DNA polymerase and the purification of crude DNA extract using Chelex-100 before PCR raised the sensitivity to 100%. In a random survey involving 100 milk samples from cattle not infected with S. aureus, the test was 100% specific. With milk samples from clinical cases of bovine mastitis, 100% sensitivity and specificity were also observed. It is concluded that Tth-PCR on milk samples with the purification of crude DNA extracts using Chelex-100 is as sensitive as but faster than conventional milk bacteriological culture techniques and is highly specific. The modified PCR correlates with elevated somatic cell counts, detects evidence of chronic and resolving infection based on S. aureus-specific DNA and circumvents the endogenous inhibitory effects of milk.

Animals↗
PubMed1998

[Methicillin-resistant Staphylococcus aureus in Dakar].

This study was carried out at the Fann University Hospital Center in Dakar, Senegal between 1994 and 1996. The purpose was to assess the prevalence of methicillin-resistant Staphylococcus aureus and to propose alternative treatments. A total of 149 stains of Staphylococcus aureus were isolated from a variety of clinical specimens. Sensitivity to various antibiotics was tested by the disc diffusion technique (anti-biogram). Resistance to methicillin was evaluated by the oxacillin disc diffusion technique on Mueller-Hinton agar containing 5% NaCl. The prevalence of methicillin resistance was 66.4%. All strains of Staphylococcus aureus were sensitive to vancomycin. Other highly effective antibiotics included fucidic acid (94%), aminoglycosides (91%), cotrimoxazol (89.6%), and norfloxacin (84.5%). Most strains (70.6%) presented a wide profile against macrolides and related groups. The LSa phenotype (resistance to lincosamines and streptogramines) was the predominant resistant phenotype. The results of this study indicate that the prevalence of methicillin-resistant Staphylococcus aureus is increasing in Senegal. Since these strains respond well to chloramphenicol and cotrimoxazole, clinicians are advised to use these drugs as an alternative first-line treatment.

Methicillin Resistance↗
PubMed1996

Sternoclavicular joint septic arthritis with small-colony variant Staphylococcus aureus.

Small-colony variants of Staphylococcus aureus may cause invasive disease in adults that is prolonged and refractory to standard therapies. We present a case of sternoclavicular arthritis with small-colony variant S. aureus that occurred in an 11-year-old child and discuss the importance of identification of these variants in the clinical microbiology laboratory.

Anti-Bacterial Agents↗
PubMed1978

Cleavage maps of a tetracycline plasmid from Staphylococcus aureus.

The cleavage maps of a Staphylococcus aureus plasmid, pSN1 (2.75 megadaltons), conferring tetracycline resistance, were determined. Cleavage maps are given for HpaI and HindIII restriction endonucleases by using the single HpaII site as a reference point. Nucleases EcoRI, BamHI, SalI, and HaeIII have no sites on this plasmid.

DNA Restriction Enzymes↗
PubMed1995

Surface-associated proteins from Staphylococcus aureus demonstrate potent bone resorbing activity.

Staphylococcus aureus infections are associated with rapid bone destruction in conditions such as osteomyelitis, bacterial arthritis, and infected orthopedic implant failure. How this bacterium induces bone destruction has not been defined. In studies of the role of oral Gram-negative bacteria in periodontal pathology, we have established that cell surface-associated proteins (SAPs) are potent stimulators of bone resorption. The surface-associated components from S. aureus have now been isolated and demonstrated to be extremely potent stimulators of bone resorption in the murine calvarial bone resorption assay. Bone resorption appears to be due to proteins, is not the result of contamination with lipoteichoic acid or muramyl dipeptide, and is potently inhibited by indomethacin and can be completely blocked by high concentrations of interleukin-1 receptor antagonist or TN3-19.12, a neutralizing monoclonal antibody to murine TNF. The SAP fraction can stimulate fibroblasts or monocytes to release osteolytic cytokines, but only at high concentrations. Fractionation of the SAPs by high performance liquid chromatography demonstrated that a number of fractions were osteolytically active. The most active contained a heterodimeric protein of molecular weight 32-36 kD. The presence of this osteolytically active surface-associated fraction may account for the bone resorption associated with local infection with S. aureus.

Animals↗
PubMed2006

Identification of different clonal complexes and diverse amino acid substitutions in penicillin-binding protein 2 (PBP2) associated with borderline oxacillin resistance in Canadian Staphylococcus aureus isolates.

Borderline oxacillin-resistant Staphylococcus aureus (BORSA) exhibit oxacillin MIC values of 1-8 microg ml(-1), but lack mecA, which encodes the low-affinity penicillin-binding protein (PBP)2a. The relationship of the BORSA phenotype with specific genetic backgrounds was assessed, as well as amino acid sequence variation in the normal PBP2. Among 38 BORSA, 26 had a common PFGE profile of genomic DNA, and were multilocus sequence type (ST)25. The other isolates were genetically diverse. Complete pbp2 sequences were determined for three BORSA, corresponding to ST25, ST1 and ST47, which were selected on the basis of lacking blaZ-encoded beta-lactamase. The essential transpeptidase-domain-encoding segment of pbp2 was also sequenced from seven additional ST25 isolates. Amino acid substitutions occurred in the transpeptidase domain of all BORSA, irrespective of clonal type. A Gln(629)-->Pro substitution was common to all ST25 BORSA, but most could be distinguished from one another by additional unique substitutions in the transpeptidase domain. The ST1 and ST47 isolates also possessed unique substitutions in the transpeptidase domain. Plasmid-mediated expression of pbp2 from an ST25 or ST1 isolate in S. aureus RN6390 increased its oxacillin MIC from 0.25 to 4 microg ml(-1), while pbp2 from a susceptible strain, ATCC 25923, had no effect. Therefore, different amino acid substitutions in PBP2 of diverse BORSA lineages contribute to borderline resistance. The predominant ST25 lineage was not related to any of the five clonal complexes that contain meticillin-resistant S. aureus (MRSA), suggesting that ST25 cannot readily acquire mecA-mediated resistance.

Amino Acid Substitution↗
PubMed2000

Molecular cloning and analysis of a putative siderophore ABC transporter from Staphylococcus aureus.

From a mass-excised Staphylococcus aureus lambdaZapII expression library, we cloned an operon encoding a novel ABC transporter with significant homology to bacterial siderophore transporter systems. The operon encodes four genes designated sstA, -B, -C, and -D encoding two putative cytoplasmic membrane proteins (sstA and sstB), an ATPase (sstC), and a membrane-bound 38-kDa lipoprotein (sstD). The sst operon is preceded by two putative Fur boxes, which indicated that expression of the sst operon was likely to be iron dependent. SstD was overexpressed in Escherichia coli, purified by Triton X-114 phase partitioning, and used to generate monospecific antisera in rats. Immunoblotting studies located SstD in the membrane fraction of S. aureus and showed that expression of the lipoprotein was reduced under iron-rich growth conditions. Triton X-114 partitioning studies on isolated membranes provided additional biochemical evidence that SstD in S. aureus is a lipoprotein. Immunoreactive polypeptides of approximately 38 kDa were detected in a wide range of staphylococcal species, but no antigenic homolog was detected in Bacillus subtilis. Expression of SstD in vivo was confirmed by immunoblotting studies with S. aureus recovered from a rat intraperitoneal chamber implant model. To further define the contribution of SstD in promoting growth of S. aureus in vitro and in vivo, we used antisense RNA technology to modulate expression of SstD. Expression of antisense sstD RNA in S. aureus resulted in a decrease in SstD expression under both iron-rich and iron-restricted growth conditions. However, this reduction in SstD levels did not affect the growth of S. aureus in vitro in an iron-limited growth medium or when grown in an intraperitoneal rat chamber implant model in vivo.

ATP-Binding Cassette Transporters↗
PubMed2003

The sigma B regulon influences internalization of Staphylococcus aureus by osteoblasts.

Individual strains of Staphylococcus aureus have different capacities to become internalized by osteoblasts. Here we report that the levels of sigma(B) expressed by S. aureus correlate with the capacity of this bacterium to be internalized by osteoblasts. However, sigma(B) is not essential for internalization and does not necessarily account for the differences in the capacities of strains to be internalized.

Bacterial Proteins↗
PubMed2006

Comparative bactericidal activities of daptomycin and vancomycin against glycopeptide-intermediate Staphylococcus aureus (GISA) and heterogeneous GISA isolates.

Staphylococcus aureus strains from the U.S. SENTRY Antimicrobial Surveillance Program, 2002-2003, glycopeptide-intermediate S. aureus (GISA) strains, and heterogeneous GISA (hGISA) strains were used to compare bactericidal activities of daptomycin and vancomycin using MICs and minimum bactericidal concentrations. Glycopeptide-susceptible S. aureus and hGISA strains were further studied by using time-kill curves. For all isolates, the daptomycin MIC50 and MIC90 are four times lower and the log drops in viable counts at 6 h and 24 h are significantly greater than those for vancomycin.

Anti-Bacterial Agents↗
PubMed2001

Teicoplanin stress-selected mutations increasing sigma(B) activity in Staphylococcus aureus.

A natural rsbU mutant of Staphylococcus aureus, unable to activate the alternative transcription factor sigma(B) via the RsbU pathway and therefore forming unpigmented colonies, produced first-step teicoplanin-resistant mutants upon selection for growth in the presence of teicoplanin, of which the majority were of an intense orange color. By using an asp23 promoter-luciferase fusion as an indicator, the pigmented mutants were shown to express increased sigma(B) activity. Increased sigma(B) activity was associated with point mutations in rsbW, releasing sigma(B) from sequestration by the anti-sigma factor RsbW, or to promoter mutations increasing the sigma(B)/RsbW ratio. Genetic manipulations involving the sigB operon suggested that the mutations within the operon were associated with the increase in teicoplanin resistance. The upregulation of sigma(B) suggests that a sigma(B)-controlled gene(s) is directly or indirectly involved in the development of teicoplanin resistance in S. aureus. Carotenoids do not contribute to teicoplanin resistance, since inactivation of the dehydrosqualene synthase gene crtM abolished pigment formation without affecting teicoplanin resistance. The relevant sigma(B)-controlled target genes involved in teicoplanin resistance remain to be identified.

Anti-Bacterial Agents↗
PubMed2000

Beware of short-course therapy for Staphylococcus aureus bacteremia without a removable cause.

Staphylococcus aureus bacteremia has long been known to cause significant morbidity and mortality. The optimal treatment of this disease has evolved over the years. Recently, criteria have been established for the use of shorter courses of antibiotic therapy in certain patients, most notably those with an easily removed source of the bacteremia. We present the case of a 55-year-old man with S aureus bacteremia unrelated to an intravascular device. He was treated with "short-course" antibiotic therapy, and lumbar diskitis and an epidural abscess developed.

Anti-Bacterial Agents↗
PubMed2006

Pneumonia and new methicillin-resistant Staphylococcus aureus clone.

Necrotizing pneumonia caused by Staphylococcus aureus strains carrying the Panton-Valentin leukocidin gene is a newly described disease entity. We report a new fatal case of necrotizing pneumonia. An S. aureus strain with an agr1 allele and of a new sequence type 377 was recovered, representing a new, emerging, community-acquired methicillin-resistant clone.

Bacterial Toxins↗
PubMed1998

Transmembrane topology and histidine protein kinase activity of AgrC, the agr signal receptor in Staphylococcus aureus.

The agr P2 operon in Staphylococcus aureus codes for the elements of a density-sensing cassette made up of a typical two-component signalling system and its corresponding inducer. It is postulated that the autoinducer, a post-translationally modified octapeptide generated from the AgrD peptide, interacts with a receptor protein, coded by agrC, to transmit a signal via AgrA regulating expression of staphylococcal virulence genes through expression of agr RNA III. We show by analysis of PhoA fusions that AgrC is a transmembrane protein, and confirm using Western blotting that a 46 kDa protein corresponding to AgrC is present in the bacterial membrane. This protein is autophosphorylated on a histidine residue only in response to supernatants from an agr+ strain, and can also respond to the purified native octapeptide. A recombinant fusion protein where most of the N-terminal region of AgrC is replaced by the Escherichia coli maltose-binding protein is also autophosphorylated in response to stimulation by agr+ supernatants or purified octapeptide. We conclude that AgrC is the sensor molecule of a typical two-component signal system in S. aureus, and that the ligand-binding site of AgrC is probably located in the third extracellular loop of the protein.

Bacterial Proteins↗
PubMed2005

Fibrinogen and fibronectin binding cooperate for valve infection and invasion in Staphylococcus aureus experimental endocarditis.

The expression of Staphylococcus aureus adhesins in Lactococcus lactis identified clumping factor A (ClfA) and fibronectin-binding protein A (FnBPA) as critical for valve colonization in rats with experimental endocarditis. This study further analyzed their role in disease evolution. Infected animals were followed for 3 d. ClfA-positive lactococci successfully colonized damaged valves, but were spontaneously eradicated over 48 h. In contrast, FnBPA-positive lactococci progressively increased bacterial titers in vegetations and spleens. At imaging, ClfA-positive lactococci were restricted to the vegetations, whereas FnBPA-positive lactococci also invaded the adjacent endothelium. This reflected the capacity of FnBPA to trigger cell internalization in vitro. Because FnBPA carries both fibrinogen- and fibronectin-binding domains, we tested the role of these functionalities by deleting the fibrinogen-binding domain of FnBPA and supplementing it with the fibrinogen-binding domain of ClfA in cis or in trans. Deletion of the fibrinogen-binding domain of FnBPA did not alter fibronectin binding and cell internalization in vitro. However, it totally abrogated valve infectivity in vivo. This ability was restored in cis by inserting the fibrinogen-binding domain of ClfA into truncated FnBPA, and in trans by coexpressing full-length ClfA and truncated FnBPA on two separate plasmids. Thus, fibrinogen and fibronectin binding could cooperate for S. aureus valve colonization and endothelial invasion in vivo.

Adhesins, Bacterial↗
PubMed1993

Meningitis due to Staphylococcus aureus in children.

Meningitis due to Staphylococcus aureus is uncommon, occurring primarily in patients with known preexisting abnormalities of the CNS (including patients who have undergone previous neurosurgery or trauma). We reviewed our experience with meningitis due to S. aureus in children seen at two medical centers. Among the 40 patients, 32 (80%) had a known predisposing abnormality of the CNS at the time of diagnosis of S. aureus meningitis; all of these 32 patients had had recent neurosurgery, most for placement or revision of a ventriculoperitoneal shunt. Eight patients had no known predisposing CNS abnormality. Four of these eight patients were known to be immunocompromised. The other four patients all had an occult CNS abnormality demonstrated during subsequent workup. Our series demonstrates that when the diagnosis of S. aureus meningitis is made in the absence of a known predisposing CNS abnormality or immunologic defect, then a timely search for an occult CNS abnormality should be undertaken.

Brain Abscess↗
PubMed2000

Identification of a fmtA-like gene that has similarity to other PBPs and beta-lactamases in Staphylococcus aureus.

We identified a gene from Staphylococcus aureus, flp (fmtA-like protein), encoding a protein of 489 amino acid residues with a molecular mass of 56.4 kDa. The deduced amino acid sequence shows similarity to previously characterized penicillin binding proteins (PBPs) and FmtA of S. aureus (one of the factors which affect methicillin resistance). FLP protein has three motifs, which are conserved in PBPs and beta-lactamases, suggesting that it might be associated with cell wall synthesis. Recombinant FLP protein, however, lacks penicillin binding activity, and the inactivation of flp in two methicillin-resistant S. aureus strains did not cause a reduction in the methicillin resistance.

Amino Acid Motifs↗