Bacteria

About: Bacteria is a research topic. Over the lifetime, 23676 publications have been published within this topic receiving 715990 citations. The topic is also known as: eubacteria.

Bactericidal effects of non-thermal argon plasma in vitro, in biofilms and in the animal model of infected wounds.

Abstract: Non-thermal (low-temperature) physical plasma is under intensive study as an alternative approach to control superficial wound and skin infections when the effectiveness of chemical agents is weak due to natural pathogen or biofilm resistance. The purpose of this study was to test the individual susceptibility of pathogenic bacteria to non-thermal argon plasma and to measure the effectiveness of plasma treatments against bacteria in biofilms and on wound surfaces. Overall, Gram-negative bacteria were more susceptible to plasma treatment than Gram-positive bacteria. For the Gram-negative bacteria Pseudomonas aeruginosa, Burkholderia cenocepacia and Escherichia coli, there were no survivors among the initial 105 c.f.u. after a 5 min plasma treatment. The susceptibility of Gram-positive bacteria was species- and strain-specific. Streptococcus pyogenes was the most resistant with 17 % survival of the initial 105 c.f.u. after a 5 min plasma treatment. Staphylococcus aureus had a strain-dependent resistance with 0 and 10 % survival from 105 c.f.u. of the Sa 78 and ATCC 6538 strains, respectively. Staphylococcus epidermidis and Enterococcus faecium had medium resistance. Non-ionized argon gas was not bactericidal. Biofilms partly protected bacteria, with the efficiency of protection dependent on biofilm thickness. Bacteria in deeper biofilm layers survived better after the plasma treatment. A rat model of a superficial slash wound infected with P. aeruginosa and the plasma-sensitive Staphylococcus aureus strain Sa 78 was used to assess the efficiency of argon plasma treatment. A 10 min treatment significantly reduced bacterial loads on the wound surface. A 5-day course of daily plasma treatments eliminated P. aeruginosa from the plasma-treated animals 2 days earlier than from the control ones. A statistically significant increase in the rate of wound closure was observed in plasma-treated animals after the third day of the course. Wound healing in plasma-treated animals slowed down after the course had been completed. Overall, the results show considerable potential for non-thermal argon plasma in eliminating pathogenic bacteria from biofilms and wound surfaces.

Morphological and compositional changes in a planktonic bacterial community in response to enhanced protozoan grazing.

Abstract: We analyzed changes in bacterioplankton morphology and composition during enhanced protozoan grazing by image analysis and fluorescent in situ hybridization with group-specific rRNA-targeted oligonucleotide probes. Enclosure experiments were conducted in a small, fishless freshwater pond which was dominated by the cladoceran Daphnia magna. The removal of metazooplankton enhanced protozoan grazing pressure and triggered a microbial succession from fast-growing small bacteria to larger grazing-resistant morphotypes. These were mainly different types of filamentous bacteria which correlated in biomass with the population development of heterotrophic nanoflagellates (HNF). Small bacterial rods and cocci, which showed increased proportion after removal of Daphnia and doubling times of 6 to 11 h, belonged nearly exclusively to the beta subdivision of the class Proteobacteria and the Cytophaga-Flavobacterium cluster. The majority of this newly produced bacterial biomass was rapidly consumed by HNF. In contrast, the proportion of bacteria belonging to the gamma and alpha subdivisions of the Proteobacteria increased throughout the experiment. The alpha subdivision consisted mainly of rods that were 3 to 6 μm in length, which probably exceeded the size range of bacteria edible by protozoa. Initially, these organisms accounted for less than 1% of total bacteria, but after 72 h they became the predominant group of the bacterial assemblage. Other types of grazing-resistant, filamentous bacteria were also found within the beta subdivision of Proteobacteria and the Cytophaga-Flavobacterium cluster. We conclude that the predation regimen is a major structuring force for the bacterial community composition in this system. Protozoan grazing resulted in shifts of the morphological as well as the taxonomic composition of the bacterial assemblage. Grazing-resistant filamentous bacteria can develop within different phylogenetic groups of bacteria, and formerly underepresented taxa might become a dominant group when protozoan predation is the major selective pressure.

Mechanism of electrical enhancement of efficacy of antibiotics in killing biofilm bacteria.

Abstract: The bioelectric effect, in which electric fields are used to enhance the efficacy of biocides and antibiotics in killing biofilm bacteria, has been shown to reduce the very high concentrations of these antibacterial agents needed to kill biofilm bacteria to levels very close to those needed to kill planktonic (floating) bacteria of the same species. In this report, we show that biofilm bacteria are readily killed by an antibiotic on all areas of the active electrodes and on the surfaces of conductive elements that lie within the electric field but do not themselves function as electrodes. Considerations of electrode geometry indicate that very low (< 100 microA/cm2) current densities may be effective in this electrical enhancement of antibiotic efficacy against biofilm bacteria, and flow experiments indicate that this bioelectric effect does not appear to depend entirely on the possible local electrochemical generation of antibacterial molecules or ions. These data are expected to facilitate the use of the bioelectric effect in the prevention and treatment of device-related bacterial infections that are caused by bacteria that grow in biofilms and thereby frustrate antibiotic chemotherapy.

The assimilation of amino-acids by bacteria. XV. Actions of antibiotics on nucleic acid and protein synthesis in Staphylococcus aureus.

Abstract: In previous papers of this series, experimental conditions have been described which will enable the following processes to be studied in washed suspensions of Staphylococcus aureus (Micrococcus pyogenes var. aureus): internal accumulation of free glutamic acid (Gale, 1947 a, b), extracellular accumulation of peptides containing glutamic acid (Gale & Van Halteren, 1951), accumulation of combined glutamic acid within the cells (Gale, 1951 b) and synthesis of protein and nucleic acid (Gale & Folkes, 1953). Aureomycin and chloramphenicol inhibit the increase of cellular combined glutamate at lower concentrations than those necessary to prevent the accumulation of free glutamic acid within the cells, whereas sodium azide, 2:4-dinitrophenol and 8-hydroxyquinoline affect these processes to approximately the same extent (Gale & Paine, 1951). Penicillin and bacitracin have no effect upon the accumulation of free or combined glutamic acid in washed suspensions of cells, but if either of these antibiotics is added to the growth medium an hour before harvesting, the resulting cells are unable to accumulate either free or combined glutamic acid (Gale & Taylor, 1947; Gale & Paine, 1951; Paine, 1951). Hotchkiss (1950) has described a disorganization of protein synthesis by penicillin which results, under the conditions of his experiments, in extracellular accumulation of peptides when Staph. aureus is incubated with amino-acid mixtures. Mitchell & Moyle (1951) followed the nucleic acid content of Staph. aureus during normal growth and in the presence of penicillin. During the normal phase of accelerated growth they found that nucleic acid reproduced more rapidly than cell dry weight, suggesting that nucleic acid controlled the rate of cell synthesis. A disturbance of nucleic acid metabolism occurred in the presence ofpenicillin and was accompanied by an intracellular accumulation of extractable nucleotides. Krampitz & Werkman (1947) and Gros & Macheboeuf (1948a, b) have previously described inhibitions of nucleic acid metabolism in bacterial cells by high concentrations of penicillin, while Gros, Beljanski & Macheboeuf (1951) have found that penicillin inhibits the breakdown of guanosine by sensitive strains of Staph. aureus. Park & Johnson (1949) described the accumulation of labile phosphate compounds in Staph. aureus growing in the presence of penicillin, and Park (1952) identified three substances accumulating under these conditions; one of these is a derivative of uridine-5'-pyrophosphate and an N-acetylaminosugar, and the other two possess the same basic structure in combination with either L-alanine or a peptide containing L-lysine, Dglutamic acid and DL-alanine.

Gram-positive bacteria are potent inducers of monocytic interleukin-12 (IL-12) while gram-negative bacteria preferentially stimulate IL-10 production.

Abstract: Interleukin-10 (IL-10) and IL-12 are two cytokines secreted by monocytes/macrophages in response to bacterial products which have largely opposite effects on the immune system. IL-12 activates cytotoxicity and gamma interferon (IFN-gamma) secretion by T cells and NK cells, whereas IL-10 inhibits these functions. In the present study, the capacities of gram-positive and gram-negative bacteria to induce IL-10 and IL-12 were compared. Monocytes from blood donors were stimulated with UV-killed bacteria from each of seven gram-positive and seven gram-negative bacterial species representing both aerobic and anaerobic commensals and pathogens. Gram-positive bacteria induced much more IL-12 than did gram-negative bacteria (median, 3,500 versus 120 pg/ml at an optimal dose of 25 bacteria/cell; P < 0.001), whereas gram-negative bacteria preferentially stimulated secretion of IL-10 (650 versus 200 pg/ml; P < 0.001). Gram-positive species also induced stronger major histocompatibility complex class II-restricted IFN-gamma production in unfractionated blood mononuclear cells than did gram-negative species (12,000 versus 3,600 pg/ml; P < 0.001). The poor IL-12-inducing capacity of gram-negative bacteria was not remediated by addition of blocking anti-IL-10 antibodies to the cultures. No isolated bacterial component could be identified that mimicked the potent induction of IL-12 by whole gram-positive bacteria, whereas purified LPS induced IL-10. The results suggest that gram-positive bacteria induce a cytokine pattern that promotes Th1 effector functions.