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Query: UMLS:C0348321 (Haemophilus)
 15,372 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We compared the sensitivities of oral and nonoral isolates of Actinobacillus actinomycetemcomitans, Haemophilus segnis, H. aphrophilus, and H. paraphrophilus to the bactericidal action of reagent hydrogen peroxide (H2O2). Susceptibility to a range of H2O2 concentrations (10(-6) to 10(-3) M) was assessed by incubating bacterial suspensions for 1 h at 37 degrees C in the presence of H2O2 and plating on chocolate agar to determine the concentration of H2O2 that would produce a 50% reduction in CFU (50% lethal dose). As a group, A. actinomycetemcomitans was more resistant to H2O2 than the oral haemophili, and H. aphrophilus was much more sensitive than all other organisms tested. The range of 50% lethal dose values for A. actinomycetemcomitans was between 8.5 X 10(-5) and 10(-3) M H2O2 or above. In contrast, H. aphrophilus exhibited 50% lethal dose values from below 1 X 10(-6) to 3.4 X 10(-4) M H2O2. The resistance of A. actinomycetemcomitans to H2O2 may be sufficient to protect these organisms from direct H2O2-mediated killing by host phagocytes.
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PMID:Resistance of Actinobacillus actinomycetemcomitans and differential susceptibility of oral Haemophilus species to the bactericidal effects of hydrogen peroxide. 650 Jul 6

A selective medium, malachite green bacitracin agar, was developed for the isolation of Actinobacillus actinomycetemcomitans from subgingival plaque of periodontally diseased patients. The medium consisted of Trypticase soy agar 40 gm/liter, bacitracin 128 micrograms/ml, malachite green 8 micrograms/ml and 5% defibrinated sheep blood. The medium, when incubated in an atmosphere of air plus 10% CO2 for 5 days, permitted greater than 80% recovery of pure cultures of A. actinomycetemcomitans when compared with a nonselective medium. The most frequent contaminant in plaque samples from different clinical conditions was Haemophilus aphrophilus. Decomposition of H2O2 was useful in differentiating these two species. Clinical studies employing the malachite green bacitracin medium revealed a significant association between the presence of the organism, A. actinomycetemcomitans and juvenile periodontitis.
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PMID:A selective medium for Actinobacillus actinomycetemcomitans and the incidence of the organism in juvenile periodontitis. 702 38

Earlier studies have demonstrated that pure cultures of oral streptococci produce hydrogen peroxide but none has found any free peroxide in dental plaque or salivary sediment despite streptococci being major components of their mixed bacterial populations. The absence of peroxide in plaque and sediment could be due to the dominance of its destruction over its formation by bacterial constituents. To identify which of the oral bacteria might be involved in such a possibility, pure cultures of 27 different oral bacteria were surveyed (as well as dental plaque and sediment) for their peroxide-forming and peroxide-removing capabilities. Peroxide production was measured for each of the pure cultures by incubation with glucose at low and high substrate concentrations (2.8 and 28.0 mM) for 4 h and with the pH kept at 7.0 by a pH-stat. Removal of hydrogen peroxide was assessed in similar experiments where peroxide at 0, 29.4, 147.2 or 294.4 mM [0, 0.1, 0.5 and 1% (w/v)] replaced the glucose. Hydrogen peroxide formation was seen with only three of the bacteria tested, Streptococcus sanguis I and II (sanguis and oralis), and Strep. mitior (mitis biotype I); levels of hydrogen peroxide between 2.2 and 9.8 mM were produced when these micro-organisms were grown aerobically and 1.1 and 3.9 mM when grown anaerobically. Earlier reports indicate that such levels were usually sufficient to inhibit the growth of many plaque bacteria. The amounts formed were similar at the two glucose levels tested, suggesting that maximum peroxide production is reached at low glucose concentration. None of the three peroxide-producing organisms was able to utilize hydrogen peroxide but five of the other 24 tested, Neisseria sicca, Haemophilus segnis, H. parainfluenzae, Actinomyces viscosus and Staphylococcus epidermidis, could readily do so, as could the mixed bacteria in salivary sediment and dental plaque, both of which contain relatively high numbers of these peroxide-utilizing micro-organisms. The ability of the bacteria in plaque and sediment to degrade hydrogen peroxide was considerable and extremely rapid; peroxide removal and usually complete within the first 15 min of the incubation even when its initial level was as high as 294.4 mM. This almost overwhelming ability to remove peroxide was confirmed when peroxide-producing and -using cultures were mixed and when each of eight salivary sediments was incubated with glucose and with peroxide at concentrations up to 294.4 mM. In the glucose incubations, no hydrogen peroxide was observed, indicating dominance of microbial peroxide removers over hydrogen peroxide producers.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Bacteria in human mouths involved in the production and utilization of hydrogen peroxide. 748 77

An inverse correlation between colonization of the human nasopharynx by Streptococcus pneumoniae and Haemophilus influenzae, both common upper respiratory pathogens, has been reported. Studies were undertaken to determine if either of these organisms produces substances which inhibit growth of the other. Culture supernatants from S. pneumoniae inhibited growth of H. influenzae, whereas culture supernatants from H. influenzae had no effect on the growth of S. pneumoniae. Moreover, coculture of S. pneumoniae and H. influenzae led to a rapid decrease in viable counts of H. influenzae. The addition of purified catalase prevented killing of H. influenzae in coculture experiments, suggesting that hydrogen peroxide may be responsible for this bactericidal activity. H. influenzae was killed by concentrations of hydrogen peroxide similar to that produced by S. pneumoniae. Hydrogen peroxide is produced by the pneumococcus through the action of pyruvate oxidase (SpxB) under conditions of aerobic growth. Both an spxB mutant and a naturally occurring variant of S. pneumoniae, which is downregulated in SpxB expression, were unable to kill H. influenzae. A catalase-reversible inhibitory effect of S. pneumoniae on the growth of the respiratory tract pathogens Moraxella catarrhalis and Neisseria meningitidis was also observed. Elevated hydrogen peroxide production, therefore, may be a means by which S. pneumoniae is able to inhibit a variety of competing organisms in the aerobic environment of the upper respiratory tract.
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PMID:Inhibitory and bactericidal effects of hydrogen peroxide production by Streptococcus pneumoniae on other inhabitants of the upper respiratory tract. 1085 13

Glutathione is an abundant and ubiquitous low-molecular-weight thiol that may play a role in many cellular processes, including protection against the deleterious effects of reactive oxygen species. We address here the role of glutathione in protection against hydrogen peroxide (H2O2) in Haemophilus influenzae and show that glutathione and catalase provide overlapping defense systems. H. influenzae is naturally glutathione deficient and imports glutathione from the growth medium. Mutant H. influenzae lacking catalase and cultured in glutathione-deficient minimal medium is completely devoid of H2O2 scavenging activity and, accordingly, substantial amounts of H2O2 accumulate in the growth medium. H. influenzae generates H2O2 at rates similar to those reported for Escherichia coli, but the toxicity of this harmful metabolite is averted by glutathione-based H2O2 removal, which appears to be the primary system for protection against H2O2 endogenously generated during aerobic respiration. When H2O2 concentrations exceed low micromolar levels, the hktE gene-encoded catalase becomes the predominant scavenger. The requirement for glutathione in protection against oxidative stress is analogous to that in higher and lower eukaryotes but is unlike the situation in other bacteria in which glutathione is dispensable for aerobic growth during both normal and oxidative stress conditions.
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PMID:Glutathione and catalase provide overlapping defenses for protection against respiration-generated hydrogen peroxide in Haemophilus influenzae. 1294 8

The Gram-negative commensal bacterium nontypeable Haemophilus influenzae (NTHI) can cause respiratory tract diseases that include otitis media, sinusitis, exacerbations of chronic obstructive pulmonary disease, and bronchitis. During colonization and infection, NTHI withstands oxidative stress generated by reactive oxygen species produced endogenously, by the host, and by other copathogens and flora. These reactive oxygen species include superoxide, hydrogen peroxide (H2O2), and hydroxyl radicals, whose killing is amplified by iron via the Fenton reaction. We previously identified genes that encode proteins with putative roles in protection of the NTHI isolate strain 86-028NP against oxidative stress. These include catalase (HktE), peroxiredoxin/glutaredoxin (PgdX), and a ferritin-like protein (Dps). Strains were generated with mutations in hktE, pgdX, and dps. The hktE mutant and a pgdX hktE double mutant were more sensitive than the parent to killing by H2O2. Conversely, the pgdX mutant was more resistant to H2O2 due to increased catalase activity. Supporting the role of killing via the Fenton reaction, binding of iron by Dps significantly mitigated the effect of H2O2-mediated killing. NTHI thus utilizes several effectors to resist oxidative stress, and regulation of free iron is critical to this protection. These mechanisms will be important for successful colonization and infection by this opportunistic human pathogen.
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PMID:Overlapping and complementary oxidative stress defense mechanisms in nontypeable Haemophilus influenzae. 2536 97


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