A simulated oral hygiene model to determine the efficacy of repeated exposure of amine oxide on the viability of Streptococcus mutans biofilms.

The use of biocide in oral care products is important for controlling microbial pathogens. However, the use of biofilm tests that investigate repeated exposure to biocide, to mimic in situ treatment, has rarely been reported in the literature. The present study describes the application of a biofilm-based efficacy protocol, for testing the effect of repeated exposure to antimicrobials on biofilm, in an attempt to mimic oral care regimens. The activity of different treatment regimens, including repeated exposure to amine oxide (AO; C(10)-C(16)-alkyldimethyl N-oxides; 1.1% v/v), was conducted against 16-h Streptococcus mutans biofilms grown on hydroxyapatite disks. Single exposure to AO alone produced a 3 log(10) reduction in microbial count, but when combined with mechanical removal, a 5 log(10) reduction in microbial count was observed. Treatments incorporating repeated exposure to AO reduced the microbial count below the level of detection, even when exposure to AO was interspersed with recovery periods. The presence of organic load produced an additional 2 log(10) reduction in the microbial count. This study showed that the application of a biofilm-based efficacy protocol to mimic oral care regimens allowed the reproducible testing of repeated antimicrobial exposures against bacterial biofilm. In addition, AO was confirmed to be an excellent biocide for eliminating S. mutans biofilms and could therefore be beneficial in oral care formulations.

Effects of ortho-phthalaldehyde, glutaraldehyde and chlorhexidine diacetate on Mycobacterium chelonae and Mycobacterium abscessus strains with modified permeability.

The mechanisms of the mycobactericidal action of ortho-phthalaldehyde (OPA), glutaraldehyde (GTA) and chlorhexidine diacetate (CHA) were investigated using mycobacterial spheroplasts of two reference strains, Mycobacterium chelonae NCTC 946, Mycobacterium abscessus NCTC 10882 and two GTA-resistant strains, M. chelonae Epping and M. chelonae Harefield. Transmission electron microscopy of the spheroplasts revealed an altered cell wall structure compared with the parent cells. Structural alterations resulting from the spheroplasting process were in part correlated to a loss of lipid content. Low concentrations of CHA induced protein coagulation in M. chelonae NCTC 946 spheroplasts, which also exhibited the highest loss of free non-polar lipids. Higher concentrations of CHA were required to produce similar results to the other spheroplasts investigated in which there was a less substantial decrease in lipid content. OPA (0.5% w/v) readily penetrated the residual cell wall and cytoplasmic membrane, producing significant protein coagulation in M. chelonae NCTC 946. GTA (0.5% v/v) induced a similar effect but to a lesser extent. Pre-treatment of the spheroplasts with OPA and GTA and their subsequent suspension in water demonstrated that GTA was a more potent cross-linking agent. This protective effect of GTA results from extensive cross-linking of amino and/or sulphydryl side-chain groups of proteins. The rapid mycobactericidal effect of OPA probably arises from its more efficient penetration across biological membranes. Mycobacterial spheroplasts represented a useful cellular model with an altered cell wall permeability. This study also showed the importance of the mycobacterial cell wall in conferring intrinsic resistance to CHA.

Influence of the charge of low molecular weight proteins on their efficacy of filtration and/or adsorption on dialysis membranes with different intrinsic properties.

Hemodialysis membranes eliminate by filtration low-molecular-weight toxic metabolites (urea and creatinine) with minimum interactions between blood components and the membrane itself. However, the ability of a membrane to adsorb specific proteins could be beneficial if the accumulation of these same proteins is implicated in the genesis of a pathological condition. Beta-amyloidosis which accompanies the elevation of beta2-microglobulin (11.8 kDa) in the plasma of dialysed patients is one such condition (Biochem. Biophys. Res. Commun. 129 (3) (1985) 701-706: Lancet 1 (1986) 1240-1311). To determine whether increases in plasma beta2-microglobulin levels were due to differences in filtration efficacy of the membrane used and/or to certain characteristics of this protein, e.g. its charge (pI 5.7) the adsorption and filtration of [3H] beta2-microglobulin and [3H] lysozyme of similar MW 14.5 kDa, but pI: 10.8 were compared on different membranes. It was found that, neither [3H] beta2-microglobulin nor [3H] lysozyme are removed by cuprophan, whereas over 75% of beta2-microglobulin is removed by filtration on polyacrylonitrile, polyacrylonitrile-polyethyleneimine, polysulfone and >95% by adsorption to polymethylmethacrylate-BK. For lysozyme, removal by adsorption is >95% on polyacrylonitrile and polyacrylonitrile-polyethyleneimine, 72% on polymethylmethacrylate-BK and by filtration is 95% on polysulfone. Hemodialysis membranes must therefore not simply be considered as filters of low-molecular-weight metabolites but should be equally assessed for their capacity to eliminate potentially deleterious low-molecular-weight plasma proteins.

Comparison of the mycobactericidal activity of ortho- phthalaldehyde, glutaraldehyde and other dialdehydes by a quantitative suspension test.

The mycobactericidal activity of various dialdehydes has been assessed by a quantitative suspension test in both 'clean' and 'dirty' conditions. Test organisms consisted of glutaraldehyde (GTA)-sensitive strains of Mycobacterium chelonae NCTC 946, M. abscessus NCTC 10882, two GTA-resistant M. chelonae strains and M. terrae NCTC 10856 (a proposed M. tuberculosis surrogate). The aldehydes tested were a new high-level disinfectant, ortho-phthalaldehyde (OPA) at 0.5% (v/v) unadjusted pH 6.5 and pH 8, GTA at 0.5% (v/v) pH 8, glyoxal at 0.5% (v/v) pH 8 and 10% (v/v) unadjusted pH 2.8, malonaldehyde sodium salt (NaMDA) at 0.5% (w/v) pH 8 and 10% (w/v) unadjusted pH 7.5 and succinaldehyde at 0.5% (v/v) pH 8. Results showed that 0.5% acidic and alkaline OPA were rapidly mycobactericidal, under both 'clean' and 'dirty' conditions, and more importantly were active against GTA-resistant strains. The washer disinfector isolates of M. chelonae were, as expected, extremely resistant to 0.5% GTA which was slowly mycobactericidal against the other strains. Glyoxal, NaMDA and succinaldehyde were ineffective against all the strains investigated. However, a high concentration of glyoxal exhibited a slow mycobactericidal activity except with M. terrae NCTC 10856, but this was not observed with NaMDA. This evaluation, using a quantitative suspension test based on a European standard, supported the claim that OPA is an effective choice as a high-level disinfectant for medical devices.

Combined exogenous surfactant and inhaled nitric oxide therapy for lung ischemia-reperfusion injury in minipigs.

BACKGROUND: The combined application of exogenous surfactant and inhaled nitric oxide was evaluated for prevention of ischemia-reperfusion injury of the lung. METHODS: Left lungs were selectively perfused in 18 minipigs in situ with cold preservation solution. After 90 min of warm ischemia, the lungs were reperfused and the right pulmonary artery and bronchus were ligated (control group, n=6). Exogenous surfactant was instilled via bronchoscopy during ischemia (surfactant group, n=6). In a third group, surfactant was applied, followed by administration of inhaled nitric oxide (surfactant+NO group, n=6). Hemodynamic and respiratory parameters were recorded for 7 hr, and bronchoalveolar lavage fluid (BALF) was obtained before and after reperfusion for measurement of surface tension, small aggregate/large aggregate ratio, protein and phospholipid contents, and a differential cell count. RESULTS: Control group animals survived for 3.7+/-1.4 hr. In both surfactant-treated groups, five out of six animals survived the observation period (P<0.001). Dynamic compliance of the lung was decreased in control animals (P<0.001). In the surfactant+NO group, arterial PO2 was higher than in both other groups (P<0.001). BALF cell count and histology showed reduced neutrophil infiltration in surfactant+NO-treated lungs. Surface tension assessed in BALF with a pulsating bubble surfactometer was severely impaired in control animals (gammamin, 14.82+/-9.95 mN/m), but maintained in surfactant-treated (gammamin, 1.11+/-0.56 mN/m) and surfactant+NO-treated animals (gammamin, 3.90+/-2.35 mN/m, P=0.02). CONCLUSIONS: Administration of exogenous surfactant in lung reperfusion injury results in improved lung compliance. The addition of inhaled NO improves arterial oxygenation and reduces neutrophil extravasation compared with surfactant treatment alone.