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PubMed2006

Role of VraSR in antibiotic resistance and antibiotic-induced stress response in Staphylococcus aureus.

Exposure of Staphylococcus aureus to cell wall inhibitors induces massive overexpression of a number of genes, provided that the VraSR two-component sensory regulatory system is intact. Inactivation of vraS blocks this transcriptional response and also causes a drastic reduction in the levels of resistance to beta-lactam antibiotics and vancomycin. We used an experimental system in which the essential cell wall synthesis gene of S. aureus, pbpB, was put under the control of an isopropyl-beta-d-thiogalactopyranoside-inducible promoter in order to induce reversible perturbations in cell wall synthesis without the use of any cell wall-active inhibitor. Changes in the level of transcription of pbpB were rapidly followed by parallel changes in the vraSR signal, and the abundance of the pbpB transcript was precisely mirrored by the abundance of the transcripts of vraSR and some additional genes that belong to the VraSR regulon. Beta-lactam resistance in S. aureus appears to involve a complex stress response in which VraSR performs the critical role of a sentinel system capable of sensing the perturbation of cell wall synthesis and allowing mobilization of genes that are essential for the generation of a highly resistant phenotype. One of the sites in cell wall synthesis "sensed" by the VraSR system appears to be a step catalyzed by PBP 2.

Anti-Bacterial Agents↗

PubMed2006

Community-acquired methicillin resistant Staphylococcus aureus skin infection.

Staphylococcus aureus is one of the most common pathogens in skin and soft tissue infections, as well as in potentially serious nosocomial infections in patients who acquire it when hospitalized. Penicillin was introduced in the 1940's as an effective treatment against S. aureus. However, shortly after penicillin's introduction, penicillin resistance to S. aureus emerged due to a plasmid-mediated beta-lactamase enzyme. In 1959, a semisynthetic penicillin, methicillin was introduced to overcome the resistance problem. However, within a year, bacteria resistant to methicillin and other penicillinase stable beta-lactams, were present. Worldwide emergence of methicillin-resistant S aureus (MRSA) was established by the 1980's. Since that time, MRSA has become widespread in hospitals and long-term care facilities around the world, accounting for numerous nosocomial infections. Recently, there has been an alarming increase in the incidence of community-acquired MRSA (CA-MRSA). Patients with CA-MRSA began to be reported in the early 1990's and its prevalence has continued to increase. This paper summarizes the current information known about CA-MRSA as it relates to skin infections including populations at risk, clinical presentation, and treatment options.

Community-Acquired Infections↗

PubMed1987

Protein A and coagulase expression in epidemic and non-epidemic Staphylococcus aureus.

Strains of Staphylococcus aureus were divided into groups on the basis of antimicrobial sensitivity and epidemiology and tested for protein A expression in a simple microtitre test, which detected the non-immunological binding of immunoglobulin to protein A on whole cells of S aureus. Isolates of the methicillin resistant strain prevalent in south east England (EMRSA) showed a low expression of protein A compared with the other strains of methicillin resistant S aureus (MRSA), other multiple resistant strains, and sensitive strains. Protein A and coagulase expression in 27 strains of MRSA from 15 countries associated with hospital outbreaks were compared with 27 strains of MRSA from 11 countries reported to be sporadic isolates. Twenty four of the 27 outbreak associated MRSA showed low expression of protein A and high expression of coagulase. Conversely, sporadic strains generally gave higher levels of protein A and a wide variety of coagulase reactions. The results suggest that many epidemic strains of MRSA may have phenotypic characteristics that distinguish them from sporadic strains.

Coagulase↗

PubMed1993

Activation of mucosal V beta 3+ T cells and tissue damage in human small intestine by the bacterial superantigen, Staphylococcus aureus enterotoxin B.

Staphylococcus aureus enterotoxin B (SEB) was added to explants of fetal human intestine in organ culture or administered into the lumen of fetal small intestine prior to culture. Both routes produced a massive increase in lamina propria T cells expressing V beta 3, and to a lesser extent, those expressing V beta 5 and V beta 12. SEB-activated lamina propria T cells produced interleukin-2 and interferon-gamma and T cell activation was accompanied by tissue damage, which was inhibited by FK506.

Antigens, Bacterial↗

PubMed1997

Characteristics of quinolone-induced small colony variants in Staphylococcus aureus.

Exposure of Staphylococcus aureus to 1 x MIC of the quinolone antibiotic pazufloxacin for 24 h, followed by plating on drug-free media, led to the emergence of small colony variants (SCVs) in addition to large colony variants (LCVs). However, following incubation with 0.25 or 4 x MIC of pazufloxacin, only LCVs were obtained. The SCVs were half as susceptible to pazufloxacin or ciprofloxacin as wild-type S. aureus, while the susceptibilities of LCVs were essentially unchanged. The reduced susceptibilities of SCVs did not result from mutations in the quinolone-resistance-determining regions of DNA gyrase and topoisomerase IV, since the sequences of these genes were identical to those of the wild-type. However, the SCVs accumulated pazufloxacin and ciprofloxacin to a lesser degree than did wild-type. Furthermore, their susceptibility to quinolones was almost unaffected by reserpine or verapamil, suggesting that the reduced uptake resulted from decreased permeability, rather than from an active efflux pump. The ability of various quinolones to induce emergence of SCVs in S. aureus, correlated with the presence of carbon-bonded substituents at the C-7 position of a quinoline or naphthyridine nucleus, or with the presence of a benzoxazine nucleus. In conclusion, pazufloxacin-induced SCVs represent a mutant that one might expect to be rapidly eliminated in vivo and, hence, not to survive as a quinolone-resistant pathogen. This finding suggests a novel approach for development of future quinolones.

Animals↗

PubMed2006

A novel Staphylococcus aureus vaccine: iron surface determinant B induces rapid antibody responses in rhesus macaques and specific increased survival in a murine S. aureus sepsis model.

Staphylococcus aureus is a major cause of nosocomial infections worldwide, and the rate of resistance to clinically relevant antibiotics, such as methicillin, is increasing; furthermore, there has been an increase in the number of methicillin-resistant S. aureus community-acquired infections. Effective treatment and prevention strategies are urgently needed. We investigated the potential of the S. aureus surface protein iron surface determinant B (IsdB) as a prophylactic vaccine against S. aureus infection. IsdB is an iron-sequestering protein that is conserved in diverse S. aureus clinical isolates, both methicillin resistant and methicillin sensitive, and it is expressed on the surface of all isolates tested. The vaccine was highly immunogenic in mice when it was formulated with amorphous aluminum hydroxyphosphate sulfate adjuvant, and the resulting antibody responses were associated with reproducible and significant protection in animal models of infection. The specificity of the protective immune responses in mice was demonstrated by using an S. aureus strain deficient for IsdB and HarA, a protein with a high level of identity to IsdB. We also demonstrated that IsdB is highly immunogenic in rhesus macaques, inducing a more-than-fivefold increase in antibody titers after a single immunization. Based on the data presented here, IsdB has excellent prospects for use as a vaccine against S. aureus disease in humans.

Animals↗

PubMed1979

Neutralization of immune complex inhibition of antibody dependent cellular cytotoxicity in vitro by Staphylococcus-aureus protein A.

Staphylococcus-aureus protein A (SPA) incubated with sera containing immune complexes and effector cells increases antibody dependent cellular cytotoxicity (ADCC)and rosette formation. The enhanced ADCC and rosetting is due to SPA functioning as an IgG Fc cellular receptor. SPA binds to the Fc portion of Igg and has much greater affinity for immune complexes than free IgG. SPA bound immune complexes are blocked from attaching to the Fc cellular receptors via a competitive inhibition which neutralizes the inhibitory effect of these complexes on ADCC and rosette formation.

Animals↗

PubMed1992

Beef and dressed chickens as sources of enterotoxigenic Staphylococcus aureus in Nairobi.

Staphylococcus aureus (S. aureus) isolates from beef carcasses, minced beef, and dressed chicken were assayed for production of enterotoxin A, B, C and D using reverse passive agglutination technique. The highest isolation rate was from chickens followed by minced beef. Chickens yielded the highest percentage of enterotoxigenic strains. Staphylococcal enterotoxin C (SEC) was the most frequently produced type from all the three sources while enterotoxin A ranked second and enterotoxin B third. These data show that chickens and minced beef are potential sources of food poisoning staphylococci in Kenya, and that increased handling of the products increases contamination suggesting that man is the major source.

Agglutination Tests↗

PubMed1990

The clinical spectrum of Staphylococcus aureus pulmonary infection.

Staphylococcus aureus causes serious pulmonary infections in adults. Prior descriptions of this entity have depended on diagnosis of expectorated sputum cultures that are often contaminated. To better characterize this infection, we retrospectively reviewed the medical records of 31 adults with S aureus pulmonary infection diagnosed by culture specimens uncontaminated by the upper respiratory flora. Our results support the concept that S aureus pulmonary infections usually occur in older adults (sixth decade or older) with concomitant illnesses that are typically nosocomial. However, in contrast to previous reports, the chest roentgenograms in these patients typically showed multilobar infiltrates (60 percent), predominantly in the lower lobes (64 percent), and often bilateral (48 percent). Pleural involvement (48 percent) was more common than previously reported, and abscess formation (16 percent) occurred infrequently. Sputum cultures were found to be sensitive but nonspecific diagnostic tools. Despite antibiotic therapy, reinfection occurred in 10 percent of patients and the mortality rate was 32 percent.

Adult↗

PubMed1992

[Methicillin-resistant Staphylococcus aureus in dermatology].

Staphylococcus aureus (SA) is among the most important causes of skin infections. The incidence of Methicillin-resistant SA (MRSA) strains isolated from skin and skin structure infections was about 20-40%. In deep-seated pyoderma such as furuncle and furunculosis, MRSA was more frequently isolated than in other type of infectious diseases of the skin. But the incidence was gradually increasing. As to coagulase typing, type IV was most frequently isolated in MRSA. The damaged skin is easily colonized by high numbers of SA on its surface and within hair follicles. Through the indwelling catheters or decubitus SA on the skin could cause easily severe systemic MRSA infections such as sepsis or endocarditis of in-patients.

Humans↗

PubMed1984

Mechanisms of resistance to beta-lactam antibiotics in Staphylococcus aureus.

In vitro, Staphylococcus aureus expresses resistance to beta-lactam antibiotics by beta-lactamase production, methicillin resistance, penicillin tolerance, and deficiency in penicillin binding protein number 3. The clinical significance of all these phenomena is not fully defined. Methicillin resistance is due to a large chromosomal linkage group. The reason for the very high proportion of cultures that produce beta-lactamase is still enigmatic. Selection pressure by penicillins may not be the entire explanation. Plasmids determining beta-lactamase have spread between cultures in vivo. Staphylococcal plasmids can transfer between cells in vitro by transduction, transformation and conjugation. The latter is likely to be the most efficient, occurring without death of the donor nor need to protect the recipient from lysis by normal bacteriophage particles. Conjugation in S. aureus requires bacteriophage genome to be present in either the donor or recipient. We have recently identified distinct genes with donor and recipient function in typing phage 55. Staphylococcal beta-lactamase varies in serotype, extra-cellularity, amount, control of production and substrate specificity. The latter has rarely been reported because it is not detected by routine sensitivity testing for methicillin or penicillin resistance. Of the isoxazolylpenicillins, flucloxacillin was found generally to be most labile to beta-lactamase, and dicloxacillin the most stable with cloxacillin intermediate. However, a few exceptions occurred, and it may be prudent to test specific sensitivity in patients infected with staphylococci. Even methicillin may sometimes be hydrolysed to a significant extent.

Anti-Bacterial Agents↗

PubMed2001

Molecular diversity of live-attenuated prototypic vaccine strains and clinical isolates of Staphylococcus aureus.

Bovine mastitis Staphylococcus aureus isolates and prototypic live-attenuated vaccine strains were analyzed by SmaI pulsed-field gel electrophoresis (PFGE) typing and automated ribotyping. The discriminatory index of these methods was 0.91 and 0.69, respectively. SmaI PFGE typing assigned all laboratory strains into cluster Q, which shared 49% similarity with clusters A and B, and 35% similarity with cluster C. Automated ribotyping placed laboratory strains within ribogroups different from those of bovine isolates. These methods have 70% concordance and permitted identification of the prototypic vaccine background from those of clinical isolates. This information is required before conducting field trials with the vaccine.

Animals↗

PubMed1992

In vivo processing of Staphylococcus aureus lipase.

The Staphylococcus aureus lipase gene encodes a 76-kDa protein. Extracellular lipase purified from culture supernatants is only 45 to 46 kDa, however. We show that the lipase is secreted in vivo as an 82-kDa protein with full enzymatic activity. It is then sequentially processed, both in culture and in cell-free supernatants, to a mature, 45- to 46-kDa protein. Protein sequencing demonstrates that the N-terminal region of the 82-kDa prolipase, comprising 295 amino acids, is cleaved from the central and C-terminal moieties, which contain the active site. A metallocysteine protease is probably responsible for initiating this processing. The extremely hydrophobic, mature lipase is resistant to further protease degradation and retains the full catalytic activity of the prolipase.

Amino Acid Sequence↗

PubMed2002

Inhibition of staphylococcal wound infection and potentiation of antibiotic prophylaxis by a recombinant fragment of the fibronectin-binding protein of Staphylococcus aureus.

Adherence of Staphylococcus aureus to host tissues is a critical step for colonization and initiation of infection. The fibronectin-binding proteins (FnBPs) of S. aureus have been implicated in adherence and internalization in nonprofessional phagocytes. A recombinant fragment of the fibronectin-binding domains (rFnBF) that potently inhibits S. aureus entry into host cells was generated. To test the hypothesis that rFnBF may attenuate the establishment of infection, the ability of intermuscularly administered rFnBF to prevent abscess formation was determined in a guinea pig model of wound infection. rFnBF exhibited dose-dependent inhibition of abscess formation and, at a 100-microg dose, raised the median infective dose approximately 170-fold, compared with the control. In addition, rFnBF potentiated the benefit of prophylaxis with cefazolin. Thus, exogenous administration of the fibronectin-binding domain of FnBP reduces the risk of staphylococcal abscess formation and should be investigated further as a novel agent for prevention of wound infection.

Adhesins, Bacterial↗

PubMed1977

Possible endotoxemia in rabbits after intravenous injection of Staphylococcus aureus enterotoxin B.

Staphylococcus aureus enterotoxin B (SEB) administered intravenously may exert its toxicity by damaging capillary endothelium in the large intestine and, thereby, permit absorption of endotoxin into the circulation. To investigate this possibility, we measured an index of the level of plasma endotoxin. This index was the ability of plasma to cause gelation of limulus amebocyte lysate (GLAL), before and after intravenous administration of SEB (800-1,000 microng/kg of body weight) to 13 rabbits. All samples taken before administration of SEB were negative for GLAL, but GLAL activity was detectable in the plasma of 10 of the rabbits 12 hr after SEB was injected. Only rabbits that developed GLAL activity died; the levels of GLAL in plasma were comparable to those detected by other workers after administration of an intravenous, lethal dose of endotoxin to rabbits.

Animals↗

PubMed2003

Characterization of Staphylococcus aureus enterotoxin L.

Staphylococcus aureus causes a wide variety of diseases. Major virulence factors of this organism include enterotoxins (SEs) that cause both food poisoning and toxic shock syndrome. Recently, a novel SE, tentatively designated SEL, was identified in a pathogenicity island from a bovine mastitis isolate. The toxin had a molecular weight of 26,000 and an isoelectric point of 8.5. Recombinant SEL shared many biological activities with SEs, including superantigenicity, pyrogenicity, enhancement of endotoxin shock, and lethality in rabbits when administered in subcutaneous miniosmotic pumps, but the protein lacked emetic activity. T cells bearing the T-cell receptor beta chain variable regions 5.1, 5.2, 6.7, 16, and 22 were significantly stimulated by recombinant SEL.

Animals↗

PubMed1993

Characteristics and localization of a determinant conferring partial macrolide resistance in Staphylococcus aureus carrying plasmid.

Staphylococcus aureus TPR-27, a clinically isolated strain, showed constitutive resistance to some macrolide antibiotics (erythromycin, oleandomycin, spiramycin, and josamycin), but susceptibility to the other macrolide (tylosin, rokitamycin, and mycinamicin), lincosamide, and streptogramin type B antibiotics (PM-resistance). The PM-resistant strain TPR-27 has carried for visible plasmids. Attempts to eliminate the resistant determinant in terms of ethidium bromide (about 3 micrograms/ml) did not succeed, and every trial to transduce the PM-resistant determinant into rec- mutant ISP105 using phage 80L2 propagated on strain TPR-27 also failed at the frequency of less than 1.1 x 10(-10) transductants per plaque-forming unit. These results suggest that the PM-resistance determinant is localized in chromosomal DNA.

Anti-Bacterial Agents↗

PubMed2005

Staphylococcus aureus bacteremia, Australia.

Staphylococcus aureus bacteremia (SAB) is common and increasing worldwide. A retrospective review was undertaken to quantify the number of cases, their place of acquisition, and the proportions caused by methicillin-resistant S. aureus (MRSA) in 17 hospitals in Australia. Of 3,192 episodes, 1,571 (49%) were community onset. MRSA caused 40% of hospital-onset episodes and 12% of community-onset episodes. The median rate of SAB was 1.48/1,000 admissions (range 0.61-3.24; median rate for hospital-onset SAB was 0.7/1,000 and for community onset 0.8/1,000 admissions). Using these rates, we estimate that approximately 6,900 episodes of SAB occur annually in Australia (35/100,000 population). SAB is common, and a substantial proportion of cases may be preventable. The epidemiology is evolving, with >10% of community-onset SAB now caused by MRSA. This is an emerging infectious disease concern and is likely to impact on empiric antimicrobial drug prescribing in suspected cases of SAB.

Anti-Bacterial Agents↗