Bioactive glass has found extensive application as an orthopedic and dental graft material and most recently also as a tissue engineering scaffold. Here we report an initial investigation of the in vitro antibacterial properties of AgBG, a novel bioactive glass composition doped with Ag 2 O. The bacteriostatic and bactericidal properties of this new material and of two other bioactive glass compositions, 45S5 Bioglass and BG, have been studied by using Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus as test microorganisms. Concentrations of AgBG in the range of 0.05 to 0.20 mg of AgBG per ml of culture medium were found to inhibit the growth of these bacteria. Not only was AgBG bacteriostatic, but it also elicited a rapid bactericidal action. A complete bactericidal effect was elicited within the first hours of incubation at AgBG concentrations of 10 mg ml ؊1 . 45S5 Bioglass and BG had no effect on bacterial growth or viability. The antibacterial action of AgBG is attributed exclusively to the leaching of Ag ؉ ions from the glass matrix. Analytical measurements rule out any contribution to AgBG-mediated bacterial killing by changes in pH or ionic strength or the dissolution of other ionic species from the biomaterials. Our observations of the dissolution profiles of Ag ؉ from AgBG in the presence and absence of bacteria are consistent with silver accumulation by the bacteria.Bioactive glasses are special glass systems which are generally composed of SiO 2 , CaO, P 2 O 5 , and Na 2 O. They can be produced by the traditional melting process or by the more versatile sol-gel process (14, 15). The bioactive behavior of these glasses is defined as the ability to bond to soft and hard tissues by means of a series of reactions, which produces a strong, compliant interface between the glass and the tissue (14). Due to their high level of tissue integration and regeneration (15, 34), bioactive glasses have been used clinically in a variety of situations. Bioactive glass devices are now available to treat conductive deafness and alveolar ridge resorption and bone loss due to periodontal disease and to fill cystic and surgically created defects, particularly in craniomaxillofacial sites (19,25,33).The material under investigation in the present work is a novel bioactive glass system composed of SiO 2 , CaO, P 2 O 5 , and Ag 2 O. The introduction of Ag 2 O into the bioactive glass composition is aimed at minimizing the risk of microbial contamination through the potential antimicrobial activity of the leaching Ag ϩ ions (7, 13). The introduction of silver has recently become one of the preferred methods to confer microbial resiliency on biomedical materials and devices (1,6,17,18,21), since the incidence of biomaterial-centered infections is one of the main causes of revision surgery (12). The production of the material via the sol-gel process allows the tailoring of the textural characteristics of the matrix in order to obtain a controlled Ag ϩ delivery system. Here we report an initial investigation of ...

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SummaryThe structural genes for the cyanide-insensitive terminal oxidase (CIO) of Pseudomonas aeruginosa were sequenced. The locus comprised two open reading frames, cioA and cioB, coding for gene products of 488 and 335 amino acid residues with predicted molecular masses of 54 241 and 37 016 Da respectively. These genes were encoded by a 2.7 kb transcript and probably comprise an operon. Upstream of a major transcriptional start site is a ¹10 promoter region and, approximately at nucleotides ¹50 and þ13, there are sequences homologous to the binding site of the transcriptional regulator Anr. The deduced amino acid sequences of CioA and CioB are homologous to the cytochrome bd quinol oxidases of Escherichia coli and Azotobacter vinelandii. However, no cytochrome d -like signals were found in wild-type P. aeruginosa strains. An atypical cytochrome d -like signal was seen under low-aeration growth conditions but only in strains in which the cioAB genes were present on a high-copy-number plasmid. The appearance of these cytochrome d -like signals was not paralleled by a concomitant increase in CIO activity. These data support the hypothesis that the CIO of P. aeruginosa does not contain haem d. This raises the possibility that there is a family of bacterial quinol oxidases related to the cytochrome bd of E. coli that can differ in their haem composition from the E. coli paradigm.

Conditions were investigated that promote the formation of 'non-culturable' (NC) cells of Mycobacterium (Myc.) smegmatis in stationary phase. After cultivation in a rich medium, or under conditions that may be considered optimal for bacterial growth, or starvation for carbon, nitrogen or phosphorus, bacteria failed to enter a NC state. However, when grown under suboptimal conditions, resulting in a reduced growth rate or maximal cell concentration (e.g. in modified Hartman's-de Bont medium), bacteria adopted a stable NC state after 3-4 days incubation in stationary phase. Such conditions are not specific as purF and devR mutants of Myc. smegmatis also showed (transient) loss of culturability following growth to stationary phase in an optimized medium, but under oxygen-limited conditions. The behaviour of the same mutants in oxygen-sufficient but nutrient-inappropriate medium (modified Hartman's-de Bont medium) was similar to that of the wild-type (adoption of a stable NC state). It is hypothesized that adoption of a NC state may represent an adaptive response of the bacteria, grown under conditions when their metabolism is significantly compromised due to the simultaneous action of several factors, such as usage of inappropriate nutrients or low oxygen availability or impairment of a particular metabolic pathway. NC cells of wild-type Myc. smegmatis resume growth when transferred to a suitable resuscitation medium. Significantly, resuscitation was observed when either recombinant Rpf protein or supernatant derived from a growing bacterial culture was incorporated into the resuscitation medium. Moreover, co-culture with Micrococcus (Mcc.) luteus cells (producing and secreting Rpf) also permitted resuscitation. Isogenic strains of Myc. smegmatis harbouring plasmids containing the Mcc. luteus rpf gene also adopt a similar NC state after growth to stationary phase in modified Hartman's-de Bont medium. However, in contrast to the behaviour noted above, these strains resuscitated spontaneously when transferred to the resuscitation medium, presumably because they are able to resume endogenous synthesis of Mcc. luteus Rpf. Resuscitation was not observed in the control strain harbouring a plasmid lacking Mcc. luteus rpf. In contrast to wild-type, the NC cells of purF and devR mutants obtained under oxygen-limited conditions resuscitate spontaneously, presumably because the heterogeneous population contains some residual viable cells that continue to make Rpf-like proteins.

Cyclic di-adenosine monophosphate (c-di-AMP) is a recently discovered signaling molecule important for the survival of Firmicutes, a large bacterial group that includes notable pathogens such as Staphylococcus aureus. However, the exact role of this molecule has not been identified. dacA, the S. aureus gene encoding the diadenylate cyclase enzyme required for c-di-AMP production, cannot be deleted when bacterial cells are grown in rich medium, indicating that c-di-AMP is required for growth in this condition. Here, we report that an S. aureus dacA mutant can be generated in chemically defined medium. Consistent with previous findings, this mutant had a severe growth defect when cultured in rich medium. Using this growth defect in rich medium, we selected for suppressor strains with improved growth to identify c-di-AMP–requiring pathways. Mutations bypassing the essentiality of dacA were identified in alsT and opuD, encoding a predicted amino acid and osmolyte transporter, the latter of which we show here to be the main glycine betaine–uptake system in S. aureus. Inactivation of these transporters likely prevents the excessive osmolyte and amino acid accumulation in the cell, providing further evidence for a key role of c-di-AMP in osmotic regulation. Suppressor mutations were also obtained in hepS, hemB, ctaA, and qoxB, coding proteins required for respiration. Furthermore, we show that dacA is dispensable for growth in anaerobic conditions. Together, these findings reveal an essential role for the c-di-AMP signaling network in aerobic, but not anaerobic, respiration in S. aureus.

In patients with cystic fibrosis (CF) and non-CF bronchiectasis, Pseudomonas aeruginosa is the most important respiratory pathogen. It is able to synthesise hydrogen cyanide, a potent inhibitor of cellular respiration.The present study investigated whether cyanide is present in the sputum of CF and non-CF bronchiectasis patients infected with P. aeruginosa, and whether the detection of cyanide affected lung function. Cyanide was measured in sputum using a cyanide ion selective electrode.Cyanide was detected in sputum from 15 out of 25 CF and non-CF bronchiectasis patients with current P. aeruginosa infection; however, it was not detected in any of the 10 patients without this organism. Maximum levels were 130 mM (mean¡SE 72¡6.6 mM). Concurrent lung function data were available on all 21 P. aeruginosa-infected CF patients; the group with measurable sputum cyanide (n511) was not different from those without (n510) on the basis of age or sex. However, those with detectable cyanide had significantly poorer lung function than those without (forced expiratory volume in one second (% predicted) 26.8¡3.8 versus 46.0¡6.7%; forced vital capacity (% pred) 44.4¡4.9 versus 60.1¡7.7%).Cyanide is detectable in sputum from cystic fibrosis and non-cystic fibrosis bronchiectasis patients infected with Pseudomonas aeruginosa, and is also associated with impaired lung function.

The regulation of the cyanide-insensitive oxidase (CIO) in Pseudomonas aeruginosa, a bacterium that can synthesize HCN, is reported. The expression of a cioA-lacZ transcriptional fusion, CioA protein levels and CIO activity were low in exponential phase but induced about fivefold upon entry into stationary phase. Varying the O 2 transfer coefficient from 11?5 h 21 to 87?4 h 21 had no effect on CIO expression and no correlation was observed between CIO induction and the dissolved O 2 levels in the growth medium. However, a mutant deleted for the O 2 -sensitive transcriptional regulator ANR derepressed CIO expression in an O 2 -sensitive manner, with the highest induction occurring under low-O 2 conditions. Therefore, CIO expression can respond to a signal generated by low O 2 levels, but this response is normally kept in check by ANR repression. ANR may play an important role in preventing overexpression of the CIO in relation to other terminal oxidases. A component present in spent culture medium was able to induce CIO expression. However, experiments with purified N-butanoyl-L-homoserine lactone or N-(3-oxododecanoyl)homoserine lactone ruled out a role for these quorum-sensing molecules in the control of CIO expression. Cyanide was a potent inducer of the CIO at physiologically relevant concentrations and experiments using spent culture medium from a DhcnB mutant, which is unable to synthesize cyanide, showed that cyanide was the inducing factor present in P. aeruginosa spent culture medium. However, the finding that in a DhcnB mutant cioA-lacZ expression was induced normally upon entry into stationary phase indicated that cyanide was not the endogenous inducer of the terminal oxidase. The authors suggest that the failure of O 2 to have an effect on CIO expression in the wild-type can be explained either by the requirement for an additional, stationary-phase-specific inducing signal or by the loss of an exponential-phase-specific repressing signal. INTRODUCTIONPseudomonas aeruginosa is an opportunistic pathogen that causes a variety of nosocomial infections, including pneumonia, urinary tract infections, surgical wound infections, and bloodstream infections (for a review see Deretic, 2000). It causes life-threatening illness in patients with cystic fibrosis. Initially, P. aeruginosa colonizes the airways with other pathogens such as Haemophilus influenzae and Staphylococcus aureus. However, in most of these patients chronic lung disease develops in which the bacterial population consists almost exclusively of P. aeruginosa in the form of biofilms (Govan & Deretic, 1996). P. aeruginosa is a facultative anaerobe that preferentially obtains its energy via aerobic respiration, but it is well adapted to conditions of limited O 2 supply (Palleroni, 1984;Davies et al., 1989). It is capable of anaerobic growth with nitrate as a terminal electron acceptor and in the absence of nitrate it is able to ferment arginine, generating ATP by substrate-level phosphorylation (Palleroni, 1984;Davies et al., 1989;Van der Wauven et ...

We identified a response regulator in Mycobacterium smegmatis which plays an important role in adaptation to oxygen-starved stationary phase. The regulator exhibits strong sequence similarity to DevR/Rv3133c of M. tuberculosis. The structural gene is present on a multigene locus, which also encodes a sensor kinase. A devR mutant of M. smegmatis was adept at surviving growth arrest initiated by either carbon or nitrogen starvation. However, its culturability decreased several orders of magnitude below that of the wild type under oxygenstarved stationary-phase conditions. Two-dimensional gel analysis revealed that a number of oxygen starvation-inducible proteins were not expressed in the devR mutant. Three of these proteins are universal stress proteins, one of which is encoded directly upstream of devR. Another protein closely resembles a proposed nitroreductase, while a fifth protein corresponds to the ␣-crystallin (HspX) orthologue of M. smegmatis. None of the three universal stress proteins or nitroreductase, and a considerably lower amount of HspX was detected in carbon-starved wild-type cultures. A fusion of the hspX promoter to gfp demonstrated that DevR directs gene expression when M. smegmatis enters stationary phase brought about, in particular, by oxygen starvation. To our knowledge, this is the first time a role for a two-component response regulator in the control of universal stress protein expression has been shown. Notably, the devR mutant was 10 4 -fold more sensitive than wild type to heat stress. We conclude that DevR is a stationary-phase regulator required for adaptation to oxygen starvation and resistance to heat stress in M. smegmatis.