The pYV plasmid of Yersinia encodes a lipoprotein, YlpA, related to TraT

A series of lipoproteins was detected in the membrane fraction of Yersinia enterocolitica W227, a typical strain from serotype O:9. At least two of them, YlpA and YlpB, are encoded by the pYV plasmid. The sequence of ylpA reveals the presence of a typical lipoprotein signal peptide. The mature YlpA protein would be 223 residues long with a calculated molecular weight of 23798 for the proteic moiety of the molecule. YlpA shares 88% identical residues with the TraT protein encoded by plasmid pED208, 80% identity with TraT proteins encoded by plasmids R100 and F, and 77% identity with the TraT protein encoded by the virulence plasmid of Salmonella typhimurium. The ylpA gene hybridized with the pYV plasmid of Yersinia pseudotuberculosis, suggesting that this gene is conserved among Yersinia spp. The production of YlpA is controlled by virF and only occurs at 37 degrees C in the absence of Ca2+ ions. This co-regulation with the yop genes suggests that ylpA is a virulence determinant. However, mutations in ylpA clearly affect neither the resistance to human serum nor the virulence for intravenously inoculated mice.     

Evidence that mycoplasmas, gram-negative bacteria, and certain gram-positive bacteria share a similar protein antigen.

It was demonstrated that mycoplasmas, gram-negative bacteria, and certain gram-positive bacteria share a similar protein antigen with a molecular weight ranging from 42,000 to 48,000. Western blotting (immunoblotting) with an antibody specific to a 43-kDa membrane protein of Mycoplasma fermentans showed the existence of this protein antigen in all Mycoplasma spp. tested (14 species), Acholeplasma laidlawii (1 strain), and gram-negative bacteria (8 species) but only in Staphylococcus aureus of four gram-positive species tested. Neither Ureaplasma urealyticum nor mammalian cell cultures showed any cross-reactions with this antibody. These proteins were found in both cytoplasmic and membrane fractions of mycoplasma cells but were not exposed on the surface of mycoplasmal or bacterial cells.     

Perspectives on interactions between lactoferrin and bacteria.

Lactoferrin has long been recognized for its antimicrobial properties, initially attributed primarily to iron sequestration. It has since become apparent that interaction between the host and bacteria is modulated by a complex series of interactions between lactoferrin and bacteria, lactoferrin and bacterial products, and lactoferrin and host cells. The primary focus of this review is the interaction between lactoferrin and bacteria, but interactions with the lactoferrin-derived cationic peptide lactoferricin will also be discussed. We will summarize what is currently known about the interaction between lactoferrin (or lactoferricin) and surface or secreted bacterial components, comment on the potential physiological relevance of the findings, and identify key questions that remain unanswered.     

Taxonomic position and seasonal variations in marine neritic environment of some gram-negative antibiotic-producing bacteria.

Six marine bacteria which synthesize macromolecular antibiotics were isolated from neritic waters on the French Mediterranean coast, and their frequency recorded over two successive years. They appeared in relatively large numbers during the period August to December, and can be identified as marine pseudomonads; however, the low guaninecytosine ratio of their DNA, lack of catalase and specific self-inhibition are not compatible with the characteristics of the genus Pseudomonas. Two produced violacein, usually synthesized by bacteria belonging to the genus Chromobacterium. Their taxonomic position is discussed.     

The role of carotenoids and their derivatives in mediating interactions between insects and their environment

Carotenoids are long conjugated isoprenoid molecules derived mainly from plants and microbial organisms. They are highly diverse, with over 700 identified structures, and are widespread in nature. In addition to their fundamental roles as light-harvesting molecules in photosynthesis, carotenoids serve a variety of functions including visual and colouring pigments, antioxidants and hormone precursors. Although the functions of carotenoids are relatively well studied in plants and vertebrates, studies are severely lacking in insect systems. There is a particular dearth of knowledge on how carotenoids move among trophic levels, influence insect multitrophic interactions and affect evolutionary outcomes. This review explores the known and potential roles that carotenoids and their derivatives have in mediating the ecological interaction of insects with their environment. Throughout the review, we highlight how the fundamental roles of carotenoids in insect physiology might be linked to ecological and evolutionary processes.     

Natural transfer of conjugative transposon Tn916 between gram-positive and gram-negative bacteria.

The conjugative streptococcal transposon Tn916 was found to transfer naturally between a variety of gram-positive and gram-negative eubacteria. Enterococcus faecalis hosting the transposon could serve as a donor for Alcaligenes eutrophus, Citrobacter freundii, and Escherichia coli at frequencies of 10(-6) to 10(-8). No transfer was observed with several phototrophic species. Mating of an E. coli strain carrying Tn916 yielded transconjugants with Bacillus subtilis, Clostridium acetobutylicum, Enterococcus faecalis, and Streptococcus lactis subsp. diacetylactis at frequencies of 10(-4) to 10(-6). Acetobacterium woodii was the only gram-positive organism tested that did not accept the transposon from a gram-negative donor. The results prove the ability of conjugative transposable elements such as Tn916 for natural cross-species gene transfer, thus potentially contributing to bacterial evolution.     

Replication of plasmids in gram-negative bacteria.

Replication of plasmid deoxyribonucleic acid (DNA) is dependent on three stages: initiation, elongation, and termination. The first stage, initiation, depends on plasmid-encoded properties such as the replication origin and, in most cases, the replication initiation protein (Rep protein). In recent years the understanding of initiation and regulation of plasmid replication in Escherichia coli has increased considerably, but it is only for the ColE1-type plasmids that significant biochemical data about the initial priming reaction of DNA synthesis exist. Detailed models have been developed for the initiation and regulation of ColE1 replication. For other plasmids, such as pSC101, some hypotheses for priming mechanisms and replication initiation are presented. These hypotheses are based on experimental evidence and speculative comparisons with other systems, e.g., the chromosomal origin of E. coli. In most cases, knowledge concerning plasmid replication is limited to regulation mechanisms. These mechanisms coordinate plasmid replication to the host cell cycle, and they also seem to determine the host range of a plasmid. Most plasmids studied exhibit a narrow host range, limited to E. coli and related bacteria. In contrast, some others, such as the IncP plasmid RK2 and the IncQ plasmid RSF1010, are able to replicate in nearly all gram-negative bacteria. This broad host range may depend on the correct expression of the essential rep genes, which may be mediated by a complex regulatory mechanism (RK2) or by the use of different promoters (RSF1010). Alternatively or additionally, owing to the structure of their origin and/or to different forms of their replication initiation proteins, broad-host-range plasmids may adapt better to the host enzymes that participate in initiation. Furthermore, a broad host range can result when replication initiation is independent of host proteins, as is found in the priming reaction of RSF1010.     

Phospholipase D activity of gram-negative bacteria.

A phospholipase hydrolyzing cardiolipin to phosphatidic acid and phosphatidyl glycerol was characterized in gram-negative bacteria but was absent in preparations of gram-positive bacteria, Saccharomyces cerevisiae, and rat liver mitochondria. In cell-free extracts of Escherichia coli, Salmonella typhimurium, Proteus vulgaris, and Pseudomonase aeruginosa, this cardiolipin-hydrolyzing enzyme had similar pH and Mg2+ requirements and displayed a specificity which excluded phosphatidyl glycerol and phosphatidyl ethanolamine as substrates.     

Interaction of chitosans and their N-acylated derivatives with lipopolysaccharide of gram-negative bacteria

The interactions of lipopolysaccharide (LPS) with the natural polycation chitosan and its derivatives--high molecular weight chitosans (80 kD) with different degree of acetylation, low molecular weight chitosan (15 kD), acylated oligochitosan (5.5 kD) and chitooligosaccharides (biose, triose, and tetraose)--were studied using ligand-enzyme solid-phase assay. The LPS-binding activity of chitosans (80 kD) decreased with increase in acetylation degree. Affinity of LPS interaction with chitosans increased after introduction of a fatty acid residue at the reducing end of chitosan. Activity of N-monoacylated chitooligosaccharides decreased in the order: oligochitosan --> tetra- > tri- --> disaccharides. The three-dimensional structures of complexes of R-LPS and chitosans with different degree of acetylation, chitooligosaccharides, and their N-monoacylated derivatives were generated by molecular modeling. The number of bonds stabilizing the complexes and the energy of LPS binding with chitosans decreased with increase in acetate group content in chitosans and resulted in changing of binding sites. It was shown that binding sites of chitooligosaccharides on R-LPS overlapped and chitooligosaccharide binding energies increased with increase in number of monosaccharide residues in chitosan molecules. The input of the hydrophobic fragment in complex formation energy is most prominent for complexes in water phase and is due to the hydrophobic interaction of chitooligosaccharide acyl fragment with fatty acid residues of LPS.     

Genetic exchange between bacteria in the environment.

Nucleotide sequence analysis, and more recently whole genome analysis, shows that bacterial evolution has often proceeded by horizontal gene flow between different species and genera. In bacteria, gene transfer takes place by transformation, transduction, or conjugation and this review examines the roles of these gene transfer processes, between different bacteria, in a wide variety of ecological niches in the natural environment. This knowledge is necessary for our understanding of plasmid evolution and ecology, as well as for risk assessment. The rise and spread of multiple antibiotic resistance plasmids in medically important bacteria are consequences of intergeneric gene transfer coupled to the selective pressures posed by the increasing use and misuse of antibiotics in medicine and animal feedstuffs. Similarly, the evolution of degradative plasmids is a response to the increasing presence of xenobiotic pollutants in soil and water. Finally, our understanding of the role of horizontal gene transfer in the environment is essential for the evaluation of the possible consequences of the deliberate environmental release of natural or recombinant bacteria for agricultural and bioremediation purposes.     

Analysis of functional regions of YPM, a superantigen derived from gram-negative bacteria.

The bacterial superantigens, staphylococcal enterotoxins and streptococcal pyrogenic exotoxins, are grouped in a family by the conservation of amino acid sequence and polypeptide folding patterns. In the case of Yersinia pseudotuberculosis-derived mitogen (YPM), however, there is no noticeable homology with this family, although many of the in vitro functional features conform to the criteria for a superantigen. To study the mode of action of YPM at the molecular level, we first generated a number of YPM point mutants with reduced T-cell proliferative activity using random mutagenesis and localized the amino acid positions involved in either major histocompatibility complex class II or T-cell receptor Vbeta-interaction. Plotting the elucidated positions on the hydrophilicity profile suggested that they reside mostly on the outer portion of the molecule. We also report that the two cysteines positioned almost at opposing ends of the YPM molecule are connected by an S-S bond the destruction of which causes fatal damage. Finally, we obtained evidence that YPM partially competes with staphylococcal enterotoxin E for human leukocyte antigen-DR binding. This raises the question of whether these different types of superantigens have acquired the same function by genetic convergence or originated from a common ancestral gene.     

Relationship between exopolysaccharide production and protein-tyrosine phosphorylation in gram-negative bacteria

The phosphorylation of proteins at tyrosine residues is known to play a key role in the control of numerous fundamental processes in animal systems. In contrast, the biological significance of protein-tyrosine phosphorylation in bacteria, which has only been recognised recently, is still unclear. Here, we have analysed the role in Escherichia coli cells of an autophosphorylating protein-tyrosine kinase, Wzc, and a phosphotyrosine-protein phosphatase, Wzb, by performing knock-out experiments on the corresponding genes, wzc and wzb, and looking at the metabolic consequences induced. The results demonstrate that the phosphorylation of Wzc, as regulated by Wzb, is directly connected with the production of a particular capsular polysaccharide, colanic acid. Thus, when Wzc is phosphorylated on tyrosine, no colanic acid is synthesised by bacteria, but when dephosphorylated by Wzb, colanic acid is produced. This process is rather specific to the pair of proteins Wzc/Wzb. Indeed, a much lesser effect, if any, on colanic acid synthesis is observed when knock-out experiments are performed on another pair of genes, etk and etp, which also encode respectively a protein-tyrosine kinase, Etk, and a phosphotyrosine-protein phosphatase, Etp, in E. coli. In addition, the analysis of the phosphorylation reaction at the molecular level reveals differences between Gram-negative and Gram-positive bacteria, namely in the number of protein components required for this reaction to occur.     

Etiology of nosocomial surgical infections caused by gram-negative bacteria, and profile of their antibiotic resistance

Microbiological monitoring of microbial landscape of gram-negative bacteria--etiological agents of nosocomial surgical infections--was performed as well as their level of antibiotic resistance was studied. Two hundred forty-four strains were isolated. Antimicrobial susceptibility was assessed by the method of serial microdilutions. Spectrum of Gram-negative microorganisms was represented by 3 groups: fermenting (62.7%), nonfermenting (34.8%), and nonidentified microbes (2.5%). Spectrum of gram-negative etiological agents of nosocomial surgical infections was represented mainly by Pseudomonas aeruginosa, Acinetobacter baumanii, Escherichia coli, and Klebsiella. Most active antibacterial drugs against studied strains were carbapenems (imipenem and meropenem).     

Bactericidal activities of lysozyme and aprotinin against gram-negative and gram-positive bacteria related to their basic character.

Bactericidal properties of aprotinin, a proteinase inhibitor and possibly a defence molecule in bovine species, and of chicken egg white lysozyme, known as muramidase, were investigated. Incubation of various bacteria in the presence of either aprotinin or lysozyme showed that both proteins killed Gram-positive as well as Gram-negative bacteria without addition of complement or EDTA. Denaturation of the two proteins by dithiothreitol did not lead to loss of their bactericidal potency. Electron microscopic examination of Escherichia coli incubated either with lysozyme or aprotinin revealed that the bacterial cytoplasms gradually disintegrated. Both aprotinin and lysozyme were demonstrated within the affected cytoplasm by immunogold labelling. The results suggest that the bactericidal potency of lysozyme is not only due to muramidase activity but also to its cationic and hydrophobic properties. The bactericidal activity of aprotinin is probably also related to both these properties rather than to its activity as proteinase inhibitor.     

Comparative surface-to-hand and fingertip-to-mouth transfer efficiency of gram-positive bacteria,gram-negative bacteria,and phage

AIMS: To determine the transfer efficiency of micro-organisms from fomites to hands and the subsequent transfer from the fingertip to the lip. METHODS AND RESULTS: Volunteers hands were sampled after the normal usage of fomites seeded with a pooled culture of a Gram-positive bacterium (Micrococcus luteus), a Gram-negative bacterium (Serratia rubidea) and phage PRD-1 (Period A). Activities included wringing out a dishcloth/sponge, turning on/off a kitchen faucet, cutting up a carrot, making hamburger patties, holding a phone receiver, and removing laundry from the washing machine. Transfer efficiencies were 38.47% to 65.80% and 27.59% to 40.03% for the phone receiver and faucet, respectively. Transfer efficiencies from porous fomites were <0.01%. In most cases, M.luteus was transferred most efficiently, followed by phage PRD-1 and S. rubidea. When the volunteers' fingertips were inoculated with the pooled organisms and held to the lip area (Period B), transfer rates of 40.99%, 33.97%, and 33.90% occurred with M. luteus, S. rubidea, and PRD-1, respectively. CONCLUSIONS: The highest bacteral transfer rates from fomites to the hands were seen with the hard, non-porous surfaces. Even with low transfer rates, the numbers of bacteria transferred to the hands were still high (up to 10(6) cells). Transfer of bacteria from the fingertip to the lip is similar to that observed from hard surfaces to hands. SIGNIFICANCE AND IMPACT OF THE STUDY: Infectious doses of pathogens may be transferred to the mouth after handling an everyday contaminated household object.