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Archives of Microbiology (v.192, #8)
Molecular characteristics of community-associated methicillin-resistant Staphylococcus aureus strains for clinical medicine by Paulina Nastaly; Mariusz Grinholc; Krzysztof P. Bielawski (pp. 603-617).
Infections caused by methicillin-resistant S. aureus strains are mainly associated with a hospital setting. However, nowadays, the MRSA infections of non-hospitalized patients are observed more frequently. In order to distinguish them from hospital-associated methicillin-resistant S. aureus (HA-MRSA) strains, given them the name of community-associated methicillin-resistant S. aureus (CA-MRSA). CA-MRSA strains most commonly cause skin infections, but may lead to more severe diseases, and consequently the patient’s death. The molecular markers of CA-MRSA strains are the presence of accessory gene regulator (agr) of group I or III, staphylococcal cassette chromosome mec (SCCmec) type IV, V or VII and genes encoding for Panton–Valentine leukocidin (PVL). In addition, CA-MRSA strains show resistance to β-lactam antibiotics. Studies on the genetic elements of CA-MRSA strains have a key role in the unambiguous identification of strains, monitoring of infections, improving the treatment, work on new antimicrobial agents and understanding the evolution of these pathogens.
Keywords: Accessory gene regulator; CA-MRSA; Epidemiology; Panton–Valentine leukocidin; Staphylococcal cassette chromosome mec ; Virulence
Neutralization of radical toxicity by temperature-dependent modulation of extracellular SOD activity in coral bleaching pathogen Vibrio shiloi and its role as a virulence factor by Malliga Raman Murali; Subramaniya Bharathi Raja; Sivasitambaram Niranjali Devaraj (pp. 619-623).
Vibrio shiloi is the first and well-documented bacterium which causes coral bleaching, particularly, during summer, when seawater temperature is between 26 and 31°C. Coral bleaching is the disruption of the symbiotic association between coral hosts and their photosynthetic microalgae zooxanthellae. This is either due to lowered resistance in corals to infection or increased virulence of the bacterium at the higher sea surface temperature. The concentration of the oxygen and resulting oxygen radicals produced by the zooxanthellae during photosynthesis are highly toxic to bacteria, which also assist corals in resisting the infection. Hence, in this study we examined the effect of different temperatures on the activity of a novel extracellular SOD in V. shiloi. We also partially characterized the SOD and clearly confirmed that the extracellular SOD produced by V. shiloi is Mn–SOD type, as it was not inhibited by H2O2 or KCN. Performing chemical susceptibility killing assay, we confirmed that extracellular SOD may act as first line of defense for the bacteria against the reactive oxygen species. Since, increased activity of novel Mn–SOD at higher temperature, leads to the neutralization of radical toxicity and facilitates the survival of V. shiloi. Hence, the extracellular Mn–SOD may be considered as a virulence factor.
Keywords: Vibrio shiloi ; Mn–SOD; Reactive oxygen species; Chemical susceptible test
The role of fimV and the importance of its tandem repeat copy number in twitching motility, pigment production, and morphology in Legionella pneumophila by David A. Coil; Jozef Anné (pp. 625-631).
Twitching motility, a flagella-independent type of translocation of bacteria over moist surfaces, requires an array of proteins, including FimV. To investigate the role of this protein in twitching motility in Legionella pneumophila, we have generated a knockout mutant of fimV and characterized its phenotypic effects. In addition to a major reduction in twitching motility, deletion of the fimV gene caused a number of other phenotypic effects including decreased protective pigment formation, and it also affected cell morphology. Since fimV contains a variable number of tandem repeats, which can vary according to the origin of a given strain, we have examined the importance of this variability found within the coding region of this gene. By complementing the knockout strain with constructs containing a different number of this tandem repeat, we have been able to also show that repeat copy number is important in the functioning of this gene.
Keywords: FimV; Twitching motility; Type IV pili; Legionella pneumophila ; Tandem repeats
Increased mRNA expression of interferon-induced Mx1 and immunomodulation following oral administration of IFN-α2b-transformed B. longum to mice by Zhijian Yu; Zhongming Zeng; Zhen Huang; Jie Lian; Jin Yang; Qiwen Deng; Weiseng Zeng (pp. 633-638).
We previously constructed an arabinose-inducible recombinant Bifidobacterium longum that could efficiently express secreted IFN-α2b in vitro (Deng et al. in Arch Microbiol 191:681–686, 2009). Here, we investigated the influence of oral pBAD-SPIFN-transformed B. longum on immunomodulation and IFN-induced Mx1 gene transcription in mice. We observed enhanced serum and fecal IFN-α2b concentrations in mice orally administered recombinant B. longum, suggesting a possible Th1 pattern of induction in the spleen and Peyer’s patches. Transcription of the typically IFN-induced antiviral Mx1 gene in the hepatic and intestinal tissues of these mice was also markedly enhanced. In conclusion, oral administration of the recombinant B. longum expressing IFN-α2b might play its roles in the immunomodulation of the mice, and the potential clinical value of this bacterium in the treatment of viral infections needs to be further studied.
Keywords: Bifidobacterium breve ; Peyer’s patch cell; Immunomodulation; Interferon-α2b; Mx1 gene
Isocitrate dehydrogenase isozymes from a psychrotrophic bacterium, Pseudomonas psychrophila by Shougo Matsuo; Haruna Shirai; Yasuhiro Takada (pp. 639-650).
The genes encoding monomer- and dimer-type isocitrate dehydrogenase (IDH) isozymes from a psychrotrophic bacterium, Pseudomonas psychrophila, were cloned and sequenced. Open reading frames of the genes were 2,226 and 1,257 bp in length and corresponded to polypeptides composed of 741 and 418 amino acids, respectively. The deduced amino acid sequences showed high sequence identity with those of psychrophilic bacteria, Colwellia maris and Colwellia psychrerythraea, (about 70% identity) and the respective types of the putative IDH genes from other bacteria of genus Pseudomonas (more than 80% identity). The two genes were located in opposite direction from each other with a spacer of 463 bases in the order of dimeric and monomeric IDH genes on the chromosomal DNA, but analyses of northern blotting and 5′-terminal regions of the mRNAs revealed that they are transcribed independently. The expression of monomer- and dimer-type IDH genes in C. maris are known to be cold- and acetate-inducible, respectively, while only slight inductions by low temperature and/or acetate were observed in the expression of the P. psychrophila monomer- and dimer-type IDH genes. Both of these IDH isozymes overproduced in Escherichia coli showed mesophilic properties, in contrast with monomer- and dimer-type IDHs of C. maris as cold adapted and mesophilic enzymes, respectively. The substitution of Glu55 residue in the P. psychrophila monomeric IDH for Lys, which is the corresponding residue conserved between the cold-adapted monomeric IDHs from C. maris and C. psychrerythraea, by site-directed mutagenesis resulted in the decreased thermostability and the lowered optimum temperature of activity, suggesting that this residue is involved in the mesophilic properties of the P. psychrophila monomeric IDH.
Keywords: Isocitrate dehydrogenase; Isozymes; Psychrotrophic bacterium; Pseudomonas psychrophila ; Site-directed mutagenesis
Physiological responses of Escherichia coli exposed to different heat-stress kinetics by Stéphane Guyot; Laurence Pottier; Eric Ferret; Laurent Gal; Patrick Gervais (pp. 651-661).
The effects of heat-stress kinetics on the viability of Escherichia coli were investigated. Cells were exposed to heat-stress treatments extending from 30 to 50°C, with either a slope (40 min) or a shock (10 s), both followed by a 1-h plateau at 50°C in nutritive medium. A higher survival rate was observed after the slope than after the shock, when both were followed by a plateau, so the heat slope induced a certain degree of thermotolerance. This tolerance was partly (i) linked to de novo protein synthesis during the subsequent plateau phase, and (ii) abolished after rapid cooling from 50 to 30°C, which means that cellular components with rapidly reversible thermal properties are involved in this type of thermotolerance. The heat-slope-induced thermotolerance was chiefly linked to the maintenance of the plasma membrane integrity (preservation of structure, fluidity, and permeability), and not to GroEL or DnaK overexpression. Moreover, the high level of cell mortality induced by the heat shock could be related to changes in the membrane integrity.
Keywords: E. coli ; Heat kinetics; Thermotolerance; Heat-shock proteins; Plasma membrane
Aspartate aminotransferase is involved in cold adaptation in psychrophilic Pseudomonas syringae by V. R. Sundareswaran; Ashish Kumar Singh; Smita Dube; S. Shivaji (pp. 663-672).
CSM2, a cold-sensitive mutant of psychrophilic Pseudomonas syringae, grows like wild-type cells when cultured at 22 and 28°C; but at 4°C, the growth is retarded. In CSM2, AAT (coding for aspartate aminotransferase) is identified as the mutated gene. The expression of AAT in Pseudomonas syringae was transiently enhanced when cells were shifted from 22 to 4°C indicating that AAT is cold-inducible. Complementation of the mutated AAT transformed CSM2 from a cold-sensitive phenotype to a cold-resistant phenotype like the wild-type cells, thus providing evidence for the first time that AAT is required for low-temperature growth.
Keywords: Pseudomonas syringae ; Psychrophilic bacterium; Aspartate aminotransferase; Transposon mutagenesis; Cold-inducible gene
Influence of the Escherichia coli oxyR gene function on λ prophage maintenance by Monika Glinkowska; Joanna M. Łoś; Anna Szambowska; Agata Czyż; Joanna Całkiewicz; Anna Herman-Antosiewicz; Borys Wróbel; Grzegorz Węgrzyn; Alicja Węgrzyn; Marcin Łoś (pp. 673-683).
In Escherichia coli hosts, hydrogen peroxide is one of the factors that may cause induction of λ prophage. Here, we demonstrate that H2O2-mediated λ prophage induction is significantly enhanced in the oxyR mutant host. The mRNA levels for cI gene expression were increased in a λ lysogen in the presence of H2O2. On the other hand, stimulation of the p M promoter by cI857 overproduced from a multicopy plasmid was decreased in the ΔoxyR mutant in the presence of H2O2 but not under normal growth conditions. The purified OxyR protein did bind specifically to the p M promoter region. This binding impaired efficiency of interaction of the cI protein with the OR3 site, while stimulating such a binding to OR2 and OR1 sites, in the regulatory region of the p M promoter. We propose that changes in cI gene expression, perhaps in combination with moderately induced SOS response, may be responsible for enhanced λ prophage induction by hydrogen peroxide in the oxyR mutant. Therefore, OxyR seems to be a factor stimulating λ prophage maintenance under conditions of oxidative stress. This proposal is discussed in the light of efficiency of induction of lambdoid prophages bearing genes coding for Shiga toxins.
Keywords: λ Prophage induction; Shiga toxin-encoding lambdoid phages; OxyR protein; Hydrogen peroxide
Transcriptional regulation of the acetyl-CoA synthetase gene acsA in Pseudomonas aeruginosa by Utta Kretzschmar; Viola Khodaverdi; Lorenz Adrian (pp. 685-690).
Pseudomonas aeruginosa ATCC 17933 is able to oxidize ethanol to acetate under aerobic conditions. The P. aeruginosa acetyl-CoA synthetase (ACS) gene acsA was previously identified, and the ACS enzyme described to be required for growth on ethanol as the sole source of carbon and energy. Here, we investigated the transcriptional regulation of the acsA gene using an acsA::lacZ fusion. Transcription of acsA was regulated by the carbon source, and expression was maximal on ethanol, acetate and propionate. In addition, the induction depended on the response regulator ErdR, which also regulates hierarchically arranged genes for ethanol oxidation. Transcription of the acsA gene was repressed by addition of succinate to an ethanol-containing medium. This repression required Crc, the product of the catabolite repression control gene crc.
Keywords: Acetyl-CoA synthetase; Catabolite repression; Ethanol oxidation; Pseudomonas aeruginosa ; Transcriptional regulation