Various Species Of Gram-negative Bacteria Research Articles

Epidemiology of β-Lactamase-Producing Staphylococci and Gram Negative Bacteria as Cause of Clinical Bovine Mastitis in Tunisia.

The aim of this study was to determine the species distribution of Staphylococcus, Gram negative bacteria (GNB) and the occurrence of Methicillin Resistant Staphylococci (MRS) and Extended-Spectrum β-lactamase- (ESBL-) producing GNB. Bacterial culture of 300 clinical mastitis milk samples from 30 different farms across different regions of Tunisia during four seasons was realized. The obtained results showed the presence of high frequency of the tested samples with a positive growth for bacteria (64%). In addition a high recovery rate of Staphylococci and/or GNB in these clinical mastitis milk samples (87%) was detected. In addition, a high percentage of GNB (68.2%) compared to Staphylococcus species (32%) was noted. Moreover, a significant variation of the number of these bacteria according to the farm location, the seasons, and cows age was detected. The highest percentage was observed in the North of Tunisia during the winter and the spring seasons in adult cows with a dominance of GNB growth. Coagulase negative Staphylococci (CNS) (n=11) and GNB (n=16) species were identified. Escherichia coli (E. coli) was the most frequently found bacterium followed by Klebsiella pneumoniae. The dominant Staphylococcus isolates was S. xylosus followed by S. aureus the major pathogen isolated. Methicillin resistance was confirmed by the presence of the mecA gene in 3 S. aureus and 14 CNS isolates; all of these isolates were lacking the mecC gene. Various species of GNB, resistant to cefotaxime, were detected (n=15). ESBLs were detected on selective medium in 10 E. coli and 4 K. pneumoniae. All ESBL producers strains carry the blaCTX-M. The presence of different resistant mastitis pathogens in dairy farms may complicate therapeutic options and contaminated animals could become zoonotic agent reservoir for human.

Use of rhamnolipid biosurfactant for membrane biofouling prevention and cleaning

Rhamnolipids were evaluated as biofouling reducing agents in this study. The permeability of the bacterial outer membrane was increased by rhamnolipids while the growth rate of Pseudomonas aeruginosa was not affected. The surface hydrophobicity was increased through the release of lipopolysaccharides and extracellular polymeric substances from the outer cell membrane. Rhamnolipids were evaluated as agents for the prevention and cleaning of biofilms. A high degree of biofilm detachment was observed when the rhamnolipids were used as a cleaning agent. In addition, effective biofilm reduction occurred when rhamnolipids were applied to various species of Gram-negative bacteria isolated from seawater samples. Biofilm reduction using rhamnolipids was comparable to commercially available surfactants. In addition, 20% of the water flux was increased after rhamnolipid treatment (300 μg ml−1, 6 h exposure time) in a dead-end filtration system. Rhamnolipids appear to have promise as biological agents for reducing membrane biofouling.

Emergence of Extended-Spectrum β-Lactamase PER-1 in Proteus vulgaris and Providencia stuartii Isolates from Algiers, Algeria

PER β-lactamases are one of the rarer extended-spectrum β-lactamase (ESBL) families; however, their prevalence is increasing more and more. Two PER types have been described previously (1, 3-7). In addition, sequences for PER-3, -4, and -5 from Aeromonas punctata, Proteus vulgaris, and Acinetobacter baumannii are available in the GenBank database (accession no. {type:entrez-nucleotide,attrs:{text:AY740681,term_id:52858431,term_text:AY740681}}AY740681, {type:entrez-nucleotide,attrs:{text:EU748544,term_id:190364828,term_text:EU748544}}EU748544, and {type:entrez-nucleotide,attrs:{text:EU687473,term_id:188988410,term_text:EU687473}}EU687473); however, no data are published. PER-1 was mainly detected in Europe and was particularly widespread in Turkey (5) and Asia (3), while PER-2 occurred in South America, mostly in Argentina (7). Data on the diffusion of this ESBL gene in Africa are virtually nonexistent. Furthermore, the host genera of the blaPER-1 gene are usually Pseudomonas, Acinetobacter, and Providencia (1, 5). We report the emergence of the PER-1 ESBL in Proteus vulgaris and Providencia stuartii in clinical isolates from an Algiers public hospital. Five isolates of P. vulgaris (n = 4) and P. stuartii (n = 1) were collected in 2007 by the bacteriology laboratory of Beni Messous hospital from urine and blood specimens and identified by the API 20E system (bioMerieux, Marcy l'Etoile, France). Antimicrobial susceptibility testing by the disk diffusion method and Etest (AB Biodisk, Solna, Sweden) showed that the five isolates were resistant to ceftazidime (MIC ≥ 256 μg/ml). Intermediate resistance to piperacillin, cefotaxime, and cefepime (MIC = 8 to 32 μg/ml) were also observed. All isolates tested were susceptible to imipenem (Table ​(Table1).1). Finally, a marked synergetic effect between clavulanic acid and ceftazidime, indicative of the production of an ESBL, was observed. PCR analysis using primers previously described (5) and sequencing revealed the presence of blaPER-1. Enterobacterial repetitive intergenic consensus-PCR typing was performed as described previously (2) for the four ESBL producers belonging to the P. vulgaris species. Similar enterobacterial repetitive intergenic consensus-PCR patterns were observed, suggesting clearly that the P. vulgaris isolates are genetically related; thus, clonal expansion is probable. TABLE 1. MICs of antimicrobial agents for the PER-1-producing isolates and corresponding transconjugantsa Conjugation studies, with ceftazidime selection (10 μg/ml) and Escherichia coli J53 (rifampin resistant) as the recipient, showed that the blaPER-1 gene was transferable and located on a 100-kb plasmid, which also conferred resistance to trimethoprim, trimethoprim-sulfamethoxazole, and kanamycin for the four P. vulgaris isolates but only trimethoprim for the P. stuartii isolate. Regarding the genetic environment, PCRs were performed according to the schematic map described previously (5). The upstream region of blaPER-1 was explored using primers PER.D and PER.extA designed in that study. We observed that ISPa12 was present in the five isolates of our study and genetically linked to blaPER-1. However, PCRs failed to identify ISPa13 in all of our isolates. The epidemiological data regarding ESBLs available for Algeria report the presence of only CTX-M-3, CTX-M-15, SHV-12, and VEB-1 in various species of gram-negative bacteria (2). This first report of PER-1 in two enterobacterial species from Algiers indicates that the blaPER-1 gene has spread south of the Mediterranean and perhaps even to Africa.

Activation of interleukin-1 receptor-associated kinase by gram-negative flagellin.

Flagellin from various species of gram-negative bacteria activates monocytes to produce proinflammatory cytokines. We have analyzed the pathway by which Salmonella enteritidis flagellin (FliC) activates murine and human monocyte/macrophage-like cell lines. Since lipopolysaccharide (LPS), the principal immune stimulatory component of gram-negative bacteria, is known to signal through Toll-like receptor 4 (TLR4), we tested the possibility that FliC also signals via TLR4. When murine HeNC2 cells were stimulated with LPS in the presence of a neutralizing anti-TLR4 monoclonal antibody, tumor necrosis factor alpha (TNF-alpha) and nitric oxide (NO) production were markedly reduced. In contrast, FliC-mediated TNF-alpha and NO production were minimally affected by the anti-TLR4 antibody. Furthermore, FliC, unlike LPS, stimulated TNF-alpha production in the TLR4 mutant cell line, GG2EE, indicating that TLR4 is not essential for FliC-mediated signaling. To test the possibility that FliC signals via another TLR, we measured FliC-mediated activation of interleukin-1 (IL-1) receptor-associated kinase (IRAK), a central component in IL-1R/TLR signaling. FliC induced IRAK activation in HeNC2 and GG2EE cells as well as in the human promonocytic cell line THP-1. IRAK activation was rapid in HeNC2 cells, with maximal activity observed after 5 min of treatment with FliC. In addition, FliC-mediated IRAK activation exhibited the same concentration dependence as was demonstrated for the induction of TNF-alpha. These results represent the first demonstration of IRAK activation by a purified bacterial protein and strongly suggest that a TLR distinct from TLR4 is involved in the macrophage inflammatory response to FliC.

Molecular mechanisms of polymyxin B-membrane interactions: direct correlation between surface charge density and self-promoted transport.

We have studied the interaction of the polycationic peptide antibiotic polymyxin B (PMB) with asymmetric planar bilayer membranes via electrical measurements. The bilayers were of different compositions, including those of the lipid matrices of the outer membranes of various species of Gram-negative bacteria. One leaflet, representing the bacterial inner leaflet, consisted of a phospholipid mixture (PL; phosphatidylethanolamine, -glycerol, and diphosphatidylglycerol in a molar ratio of 81:17:2). The other (outer) leaflet consisted either of lipopolysaccharide (LPS) from deep rough mutants of PMB-sensitive (Escherichia coli F515) or -resistant strains (Proteus mirabilis R45), glycosphingolipid (GSL-1) from Sphingomonas paucimobilis IAM 12576, or phospholipids (phosphatidylglycerol, diphytanoyl-phosphatidylcholine). In all membrane systems, the addition of PMB to the outer leaflet led to the induction of current fluctuations due to transient membrane lesions. The minimal PMB concentration required for the induction of the lesions and their size correlated with the charge of the lipid molecules. In the membrane system resembling the lipid matrix of a PMB-sensitive strain (F515 LPS/PL), the diameters of the lesions were large enough (d = 2.4 nm +/- 8%) to allow PMB molecules to permeate (self-promoted transport), but in all other systems they were too small. A comparison of these phenomena with membrane effects induced by detergents (dodecyltriphenylphosphonium bromide, dodecyltrimethylammonium bromide, sodiumdodecylsulfate) revealed a detergent-like mechanism of the PMB-membrane interaction.

Investigation into the fluidity of lipopolysaccharide and free lipid A membrane systems by Fourier‐transform infrared spectroscopy and differential scanning calorimetry

The phase behaviour, particularly the fluidity within each phase state and the transitions between them, of lipopolysaccharides and of their lipid moiety, free lipid A, of various species of Gram-negative bacteria, especially of Salmonella minnesota and Escherichia coli, has been investigated by applying mainly Fourier-transform infrared spectroscopy and differential scanning calorimetry. For enterobacterial strains, the transition temperatures of the gel----liquid crystalline (beta----alpha) phase transition of the hydrocarbon chains in dependence on the length of the sugar moiety are highest for free lipids A (around 45 degrees C) and lowest for deep rough mutant lipopolysaccharides (around 30 degrees C). Evaluating certain infrared active vibration bands of the hydrocarbon moiety, mainly the symmetric stretching vibration of the methylene groups around 2850 cm-1, it was found that, in the gel state, the acyl chains of lipopolysaccharides and free lipid A have a higher fluidity as compared with saturated and the same fluidity as compared with unsaturated phospholipids. This 'partial fluidization' of lipopolysaccharide below the transition temperature correlates with its reduced enthalpy change at that temperature compared to phospholipids with the same chain length. The fluidity depends strongly on ambient conditions, i.e. on the Mg2+ and H+ content: higher Mg2+ concentrations and low pH values make the acyl chains of free lipid A and lipopolysaccharide preparations significantly more rigid and also partially increase the transition temperature. The influence of Mg2+ is highest for free lipid A and decreases with increasing length of the sugar side chain within the lipopolysaccharide molecules, whereas the effect of a low pH is similar for all preparations. At basic pH, a fluidization of the lipopolysaccharide and lipid A acyl chains and a decrease in transition temperature take place. Free lipid A and all investigated rough mutant lipopolysaccharides exhibit an extremely strong lyotropic behaviour in the beta----alpha melting enthalpy but not in the value of the transition temperature. The phase transition is distinctly expressed only at water concentrations higher than 50-60%. A further increase of the water content still leads to an increase in the phase-transition enthalpy, particularly for lipopolysaccharides with a more complete sugar moiety. The fluidity of the hydrocarbon chains is shown to be an important parameter with respect to the expression of biological activities.(ABSTRACT TRUNCATED AT 400 WORDS)

Transformation of various species of gram-negative bacteria belonging to 11 different genera by electroporation.

We have undertaken a systematic study to test the transformation of various species of gram-negative bacteria using the electroporation method. The data obtained show very clearly that a great variety of gram-negative bacteria--15 different species belonging to 11 different genera--including freshly isolated wild-type strains can be transformed efficiently by use of the electric-field mediated transformation technique. These include species of the families Enterobacteriaceae, Pseudomonadaceae, Rhizobiaceae, photosynthetic bacteria and strains for which transformation could not be achieved, up to now, by other methods.

Susceptibility of Gram-negative bacteria to β-lactam antibiotics and rapid characterization of β-lactamase activity

Various species of Gram-negative bacteria were tested for susceptibility to β-lactam antibiotics and for production of β-lactamase. The rapid cephalosporin 87/312 visual test was more sensitive than either the acidometric or the iodometric test; the iodometric test was least sensitive. Characteristic β-lactamase hydrolysis product patterns were obtained by scanning mixtures of β-lactamase-producing bacteria and cephalosporin substrates. β-Lactamase could not be detected on bacterial cells by fluorescent antibody techniques. The presence of β-lactamase can be correlated with minimal inhibitory concentrations of β-lactam antibiotics only in certain Gram-negative bacilli.

Nalidixic acid: an antibacterial paradox.

Nalidixic acid was found to be most bactericidal against various species of gram-negative bacteria at 50 to 200 mug/ml. With all species tested, increases in the concentration of nalidixic acid above this range reduced, rather than increased, its bactericidal effect so that, at levels in the region of 400 mug/ml, the drug was relatively bacteriostatic. Therefore, the mode of action of nalidixic acid at various concentrations was investigated. It was found that at the most bactericidal concentration deoxyribonucleic acid synthesis, but no ribonucleic acid (RNA) or protein synthesis, was inhibited. However at higher concentrations, where the drug is least bactericidal, both RNA and protein synthesis were found to be inhibited. Results are presented which suggest that the protein synthesis inhibition is a secondary manifestation of the ability of the drug to inhibit RNA synthesis, and that of RNA synthesis is most likely the second target site for the action of the drug when bacteria are exposed to it in high concentrations. The clinical implications of these findings are discussed.