Exfoliative toxin plasmids of bacteriophage group 2 Staphylococcus aureus: sequence homology

Regulation of Staphylococcus aureus Virulence

Staphylococcus aureus is a Gram-positive opportunistic pathogen that has evolved a complex regulatory network to control virulence. One of the main functions of this interconnected network is to sense various environmental cues and respond by altering the production of virulence factors necessary for survival in the host, including cell surface adhesins and extracellular enzymes and toxins. Of these S. aureus regulatory systems, one of the best studied is the accessory gene regulator (agr), which is a quorum-sensing system that senses the local concentration of a cyclic peptide signaling molecule. This system allows S. aureus to sense its own population density and translate this information into a specific gene expression pattern. Besides agr, this pathogen uses other two-component systems to sense specific cues and coordinates responses with cytoplasmic regulators of the SarA protein family and alternative sigma factors. These divergent regulatory systems integrate the various environmental and host-derived signals into a network that ensures optimal pathogen response to the changing conditions. This article gives an overview of the most important and best-studied S. aureus regulatory systems and summarizes the functions of these regulators during host interactions. The regulatory systems discussed include the agr quorum-sensing system; the SaeRS, SrrAB, and ArlRS two-component systems, the cytoplasmic SarA-family regulators (SarA, Rot, and MgrA); and the alternative sigma factors (SigB and SigH).

A molecular modeling based screening for potential inhibitors to alpha hemolysin from Staphylococcus aureus

Staphylococcus aureus, a Gram-positive bacterium is pathogenic in nature. It is known that secreted toxins remain active after antibiotic treatment. The alpha hemolysin or alpha toxin damages cell membrane and induces apoptosis and degradation of DNA. The titer of alphahemolysin increases and causes hemostasis disturbances, thrombocytopenia, and pulmonary lesions during staphylococcal infection. Therefore, it is of interest to inhibit alpha hemolysin using novel compounds. We used the structure of alpha hemolysin(PDB: 7AHL) to screen structures for 100,000 compounds from the ZINC database using molecular docking with AutoDock VINA. Nine (9) successive hits were then subjected for pharmacokinetic and toxicity properties by PROTOX (a webserver for the prediction of oral toxicities of small molecules) and FAFDrugs (a tool for prediction of ADME and Toxicity). This exercise further identified hit #1 ({[3a-(Dihydroxymethyl)-6-hydroxy-2,2-dimethyl-1,3,4-trioxatetrahydro-2H-pentalen-5- yl]methyl}amino(9H-fluoren-9-yl)acetate with binding affinity: -10.3 kcal/mol) and hit #2 (6-(Dihydroxymethyl)-2-{2-[3- (methylamino)propyl]-2-azatricyclo[9.4.0.03,8]pentadeca-1(11),3,5,7,12,14-hexaen-6-yloxy}tetrahydro-2H-pyran-3,4,5-triol with binding affinity: -9.6 kcal/mol) with acceptable toxicity and ADME properties for potential predicted hemolysin inhibition. These compounds should then be evaluated in vitro using inhibitory studies.

Multiplex PCR for detection of three exfoliative toxin serotype genes in Staphylococcus aureus

Rapid and specific detection of exfoliative toxin (ET)-producing Staphylococcus aureus strains by multiplex polymerase chain reaction (PCR) was used for identification of exfoliative toxin genes in a diverse set of 115 clinical S. aureus strains isolated in 14 Czech cities between 1998 and 2004. Fifty-nine wild-type ET-positive isolates of which 40 strains were the causative agents of toxic epidermolysis in neonates were classified into 4 PCR types. The genes coding for ETA, ETB or ETD were not detected in any of non-ET-producing isolates. The PCR method using the multiplex and specific primer set was shown to be reliable in rapid identification of the exfoliative toxin producing S. aureus and can be used as a convenient tool for hospital epidermolytic infection control.

Molecular typing of exfoliative toxin-producing Staphylococcus aureus strains involved in epidermolytic infections

Genotyping of sixteen exfoliative toxin-producing (ET-positive) strains of Staphylococcus aureus isolated in maternity units of two distant hospitals was accomplished by PFGE, ribotyping, PCR ribotyping, and prophage carriage. Three strains secreted combined ETA + ETB, and the remaining produced ETA and enterotoxin C, or TSST-1. The comparison of various genomic profiles resulted in the identification of nine genotypes. The presence of one prevailing genotype was demonstrated in each hospital. Evidence was given that the outbreak-related ET-positive strains causing the skin disease pemphigus neonatorum disseminated in both the hospitals did not originate from a single source or a common ancestor.

Complete nucleotide sequence of a Staphylococcus aureus exfoliative toxin B plasmid and identification of a novel ADP-ribosyltransferase, EDIN-C

The complete nucleotide sequence of pETB, a 38.2-kb Staphylococcus aureus plasmid encoding the exfoliative toxin B (ETB), was determined. A total of 50 open reading frames were identified on the plasmid genome and, among these, 32 showed sequence similarity to known proteins. pETB contains three copies of IS257, which divide the pETB genome into three regions: (i) a cadmium resistance operon-containing region, (ii) a lantibiotic production gene-containing region, and (iii) the remaining part where genes for plasmid replication and/or maintenance are dispersed. In the third region, genes of various kinds of functions are present among the replication- and maintenance-related genes. They include two virulence-related genes, the etb gene and a gene encoding a novel ADP-ribosyltransferase closely related to EDIN, which belongs to the C3 family of ADP-ribosyltransferases modifying Rho GTPases. They also include genes for a cell wall-anchoring surface protein and a phage resistance protein. Based on the determined sequence of pETB, the genome structures of etb-bearing plasmids (ETB plasmids) from various clinical isolates were analyzed by the PCR scanning method. The data indicate that, although the ETB plasmids are highly heterogeneous in genome size, the fundamental genome organization is well conserved. The size variation of the plasmid is mainly attributed to defined regions which may be hot spots for gene shuffling.

Genetic analysis of the bacteriocin-encoding plasmids pRJ6 and pRJ9 of Staphylococcus aureus by transposon mutagenesis and cloning of genes involved in bacteriocin production

pRJ6 and pRJ9, small Staphylococcus aureus plasmids which code for bacteriocins, exhibited a bactericidal activity against several lactic acid bacteria and strains of Listeria monocytogenes, an important food-borne pathogen. Filter-mating experiments using plasmid derivatives tagged with either Tn551 or Tn917-lac showed that pRJ6, but not pRJ9, could be mobilized by staphylococcal conjugative plasmids. Transposon mutagenesis of both plasmids was also performed. The bacteriocin and immunity structural genes of pRJ6 are part of the same operon, which is located around co-ordinate 4.0, being transcribed from right to left. However, gene cloning experiments using a staphylococcal vector showed some evidence for the involvement of additional functions of pRJ6 in bacteriocin expression. One function involved in pRJ6 mobilization mapped around co-ordinate 5.2, and it appears to be transcribed from left to right. The bactericidal action exerted by strains harbouring pRJ9 appears to reflect the activity of at least two bacteriocins, whose combined action results in a broader spectrum of activity and in a higher antagonistic activity. Gene cloning experiments also supported these assumptions.

The genome of Staphylococcus aureus: a review

The genome of Staphylococcus aureus consists of a single circular chromosome (2.7-2.8 mbp) plus an assortment of extrachromosomal accessory genetic elements: conjugative and nonconjugative plasmids, mobile elements (IS, Tn, Hi), prophages and other variable elements. Plasmids (1-60 kbp) are classified into 4 classes and there are 15 known incompatibility groups. Mobile elements of the genome (0.8-18 kbp) appear in the chromosome or in plasmids of classes II and III. Prophages (45-60 kbp) are integrated in the bacterial chromosome, and they are UV- or mitomycin-inducible. Temperate bacteriophages of S. aureus are members of the Siphoviridae and the serological groups A, B and F occur most frequently. In the paper presented, the characteristics of chromosome, plasmids, transposons and other genetic elements of S. aureus genome are given and an alphabetical list of known genes of this species is included.

Purification and characterization of staphylococcin BacR1, a broad-spectrum bacteriocin

The bacteriocin BacR1 was purified from culture supernatant of Staphylococcus aureus UT0007 by sequential ammonium sulfate precipitation, cation-exchange chromatography, and C4 reverse-phase chromatography steps. Mass spectrographic analysis indicated that the purified peptide has a molecular mass of 3,338 Da. It is resistant to environmental conditions, retaining full biological activity after exposure to pH extremes (pHs 3 to 11), heating at 95 degrees C for 15 min, and exposure to strong chaotropic agents. BacR1 was destroyed with a complete loss of biological activity after digestion with trypsin and proteinase K. Amino acid sequence analysis revealed a high concentration of Asx, Gly, and Pro residues and a high proportion of hydrophobic amino acids. The peptide is bactericidal and kills in a dose-dependent manner, but it does not lyse log-phase cells of Corynebacterium renale, the routine indicator organism for bacteriocin assay. A specific receptor for binding was detected on sensitive cells but not on insensitive cells. Competition assays showed that UV-inactivated cells could protect susceptible cells from antibacterial action. A partial inhibitory spectrum revealed that organisms from the following genera are susceptible: Staphylococcus, Streptococcus, Corynebacterium, Haemophilus, Bordetella, Moraxella, Pasteurella, Neisseria, and Bacillus.

Staphylococcal scalded skin syndrome in two immunocompetent adults caused by exfoliatin B-producing Staphylococcus aureus

An exfoliatin B-producing strain of Staphylococcus aureus was isolated from two adults with typical staphylococcal scalded skin syndrome (SSSS). One patient developed desquamation after a local staphylococcal infection of the hand, and the other developed exfoliation after nosocomially acquired staphylococcal endocarditis. Neither patient was immunocompromised, had evidence of renal insufficiency, or manifested other potential risk factors for SSSS. Purified toxin, isolated from the causative organisms, produced a Nikolsky sign in neonatal mice. The toxins were shown to be exfoliatin B by biochemical and immunologic methods and heretofore had been described only in children with SSSS. Analysis of plasmid DNAs from both strains revealed a 23-megadalton plasmid with identical restriction endonuclease digestion fragments. One isolate belonged to phage group II (3B/3C/6/7/47/54/55), whereas the other isolate belonged to phage groups I and III (7/29/52/52A/53/54/80). The observation that a non-phage group II exfoliatin-producing strain of S. aureus may produce SSSS in adults indicates the need to better define the diagnostic criteria for SSSS. Immunocompetent adults may remain susceptible to some strains of exfoliatin B-producing S. aureus.

Transfer of the plasmid for exfoliative toxin B synthesis in mixed cultures on nitrocellulose membranes

Plasmid pRW002 carries genetic determinants for exfoliative toxin B and bacteriocin R1 synthesis. When a donor strain carrying plasmid pRW002 was mixed with a plasmidless recipient strain on a nitrocellulose membrane in accordance with the procedure used for staphylococcal conjugation, pRW002 was passed to the recipient by mixed-culture transduction. Transfer was inhibited by citrate and serotype B phage antisera but not by DNase I. Cell-to-cell contact was not required, and transfer frequencies increased more than 10-fold in the presence of small concentrations of mitomycin C. These results are consistent with pRW002 transfer in mixed cultures by transduction and not by conjugation or transformation. Immunodiffusion and DNA analyses after agarose gel electrophoresis demonstrated that transductants were exfoliative toxin B producers and housed pRW002. Since mixed-culture transfer has been reported to occur on skin, our results suggest that mixed-culture transduction might be a mechanism for the transfer of genetic determinants for pathogenicity in vivo.

Sequence of the exfoliative toxin B gene of Staphylococcus aureus

We sequenced the Staphylococcus aureus exfoliative toxin B gene contained on a 1.7-kilobase HindIII fragment of plasmid pRW001. The gene was located by comparison of the amino acid sequences of open reading frames with the amino-terminal sequence of exfoliative toxin B and the total amino acid composition of the protein (A.D. Johnson, L. Spero, J.S. Cades, and B.T. De Cicco, Infect. Immun. 24:679-684, 1979). The primary translation product consists of 274 amino acids and contains a 31-amino-acid N-terminal peptide presumably necessary for transport.

Cloning and expression of the exfoliative toxin B gene from Staphylococcus aureus

Exfoliative toxin type B is produced by bacteriophage group II strains of Staphylococcus aureus and is a causative agent of staphylococcal scalded-skin syndrome. In addition to exfoliative toxin B, most isolates also produce a bacteriocin and are immune to the action of the bacteriocin. These phenotypes, as well as resistance to cadmium, were lost after elimination of a 37.5-kilobase plasmid, pRW001, from S. aureus UT0007. Transduction and transformation showed that pRW001 carries the structural genes for four phenotypic characteristics of S. aureus UT0007: (i) exfoliative toxin B production, (ii) bacteriocin production, (iii) bacteriocin immunity, and (iv) resistance to Cd(NO3)2. The exfoliative toxin B structural gene (etb), which is located on a 1.7-kilobase HindIII fragment of pRW001, was cloned in the plasmid pDH5060 and transformed into phage group III S. aureus RN4220. Transformant clones produced extracellular exfoliative toxin B that was biologically active in the neonatal mouse assay. In the Escherichia coli genetic background, the exfoliative toxin B gene was expressed only after being cloned into the positive selection-expression vector pSCC31. The structural gene for cadmium resistance was also isolated on an HindIII fragment of pRW001 cloned in pDH5060. The loci for the exfoliative toxin B gene and the cadmium resistance gene(s) were identified on a restriction map of plasmid pRW001.

Importance of exfoliatin toxin A production by Staphylococcus aureus strains isolated from clustered epidemics of neonatal pustulosis

Clustered epidemics of pustulosis due to Staphylococcus aureus occurred in two geographically distant newborn nurseries. In nurseries A and B an attack rate of pustulosis of 0.8 and 2.0 cases per 100 live births occurred, respectively. Experimental phage type 1046/1116 belonging to phage group II dominated clustered epidemics in nursery A, while group II phage type 3A/3C/55/71 and 3A/3C/55 occurred in nursery B. Other group II strains also occasionally produced clustered epidemics. These epidemic strains were found to be making heat-stable dermal exfoliatin toxin A (ETA) which had a pI of 6.8 and a molecular weight of 32,000 and 33,000. ETA-bearing strains did not make bacteriocin. Children infected with ETA-producing strains developed extensive bullous pustulosis. Surveillance cultures of personnel revealed an ETA-bearing strain in only one person. This strain was not the same phage type as the epidemic cluster. In contrast, ETA-bearing epidemic strains were found in the inanimate environment of both nurseries. ETA protein acts as an important virulence factor in the production of neonatal pustulosis infection and appears to be linked with the ability of S. aureus organisms to stick to the inanimate environment.

Transposon mutagenesis of Pseudomonas aeruginosa exoprotease genes

Transposon Tn5 was used to generate protease-deficient insertion mutants of Pseudomonas aeruginosa. The presence of Tn5 in the chromosome of P. aeruginosa was demonstrated by transduction and DNA-DNA hybridization. The altered protease production and kanamycin resistance were cotransduced into a wild-type P. aeruginosa strain. A radiolabeled probe of Tn5 DNA hybridized to specific BamHI fragments isolated from the insertion mutants. Two independently isolated Tn5 insertion mutants had reduced protease production, partially impaired elastase activity, and no immunologically reactive alkaline protease.

Mutagenesis of extrachromosomal genetic determinants for exfoliative toxin B and bacteriocin R1 synthesis in Staphylococcus aureus after plasmid transfer by protoplast fusion

In previous studies, we have shown that a 27-megadalton plasmid (pRW002) in Staphylococcus aureus contains genetic determinants for exfoliative toxin B (ET B) and bacteriocin (Bac R1) synthesis and Bac R1 resistance. Attempts to transform or transduce this plasmid to S. aureus or Bacillus subtilis recipients were not successful. However, genetic transfer of the plasmid was possible after polyethylene glycol-induced fusion of S. aureus protoplasts containing pRW002 and S. aureus protoplasts lacking this plasmid. Some of the resulting fusants lost the ability to make ET B, Bac R1, or both products. Fusants that were Bac R1-, Bac R1s, ET B- all lacked the 27-megadalton pRW002 plasmid. The largest class of fusants was Bac R1+, Bac R1r, ET B-. Immunodiffusion analyses of ET B extracts from 28 fusants showed that four ET B+ strains were cross-reacting mutants that produced ET B protein that was serologically related to, but not identical to, the wild-type toxin. Results indicated that genetic transfer of pRW002 after protoplast fusion induced molecular rearrangements that resulted in mutation of the genetic determinants for ET B and Bac R1 synthesis. Recombination of chromosomal genes was enhanced after CaCl2 was added to the protoplast-fusion mixture.

Restriction endonuclease map of phage group 2 Staphylococcus aureus exfoliative toxin plasmid

A restriction endonuclease map of the phage group 2 Staphylococcus aureus exfoliative toxin plasmid pRW001 was constructed. The orientation of the restriction endonuclease fragments was determined by a series of single and double enzyme digestions. The location of the deletions found in pRW002, a naturally occurring deletion mutant of the exfoliative toxin plasmid, was determined by comparing the restriction endonuclease fingerprints of the two plasmids. This physical map provided a means for comparing other insertion or deletion mutants of the exfoliative toxin plasmid.