Mechanisms of action of chemical sporicidal and sporistatic agents

Efficacy of an impression disinfectant solution after repeated use: An in vitro study

Statement of problem

There are very few studies using Benzalkonium Chloride (BAC) as an active disinfection agent for immersion techniques and there are no studies investigating the efficacy of repeated use of a disinfectant solution.

Purpose

This study evaluated an impression disinfectant by testing bacterial contamination of disinfectant batches used in a clinical setting after repeated use.

Materials and methods

Liquid samples were collected from impression disinfectant solutions used to disinfect dental impressions taken at a university dental clinic. The experimental samples (500 ml from 1 L of solution) were collected from teaching and professional clinics and the in-house commercial processing laboratory and stored at room temperature each day of clinic operation over five weeks. To determine to what extent the disinfectant efficacy of the active product decreased over time, the following tests were carried out: a. Inoculation b. Gram staining technique c. Matrix Assisted Laser Desorption/Ionization Mass spectrometry (MALDI- MS). Microbial growth was monitored and photographed. A culture revival was made from colonies grown on sheep blood agar, to isolate pure colonies incubated for 24 h at 37 °C. Each morphologically distinct type of colony was gram stained and MALDI spectrometry analysis was performed using the VITEK MS (BioMerieux Inc.).

Results

Evidence of growth of bacteria was detected in teaching clinics' samples, and no growth from the professional clinic or the commercial laboratory.

Conclusions

The study demonstrated that impression disinfectanat solution tested is effective against common oral bacteria, despite some rare species such as Bacillus circulans, Bacillus horneckiae, Bacillus altitudinis/pumilus and Bacillus cereus showing evidence of survival in solutions used for disinfection of impressions. However, in a high use teaching clinic environment its efficacy deteriorated. Though a second level disinfection protocol in the commercial laboratory-maintained impression disinfection.

Interaction of iodine with Bacillus subtilis spores and spore forms

Buffered solutions of iodine (pH 7.0) were effective against Bacillus subtilis spores, but concentrations and contact times for effective sporicidal action were relatively high. Concentrations of 500 to 1000 ppm available iodine with a contact time of 30-45 min were required to produce a 3-5 log reduction. Treatment of spores with agents which caused progressive extraction of coat protein and cortex hexosamine was associated with increased sensitivity to iodine. Treatment of spores with iodine produced extraction of spore coat protein which was potentiated in the presence of NaOH, but there was no evidence of breakdown of cortex hexosamines or release of dipicolinic acid, either from intact spores or spore protoplasts. Sporicidal concentrations of iodine stimulated the uptake of (32P) phosphate over an initial period of 30-40 min, but phosphate then leaked from the cells; 1000 ppm available iodine produced total loss within 60 min. Results of this investigation are consistent with previous findings which suggest that the resistance of spores to biocides is related to the barrier properties of the spore outer layers and that the sporicidal action of halogen-releasing agents is related to their ability to cause coat and cortex degradation, leading to rehydration of the spore protoplast and allowing diffusion to their site of action on the underlying protoplast.

Interaction of Bacillus subtilis spores with sodium hypochlorite, sodium dichloroisocyanurate and chloramine-T

Solutions of chlorine-releasing agents (CRAs) show varying activity against Bacillus subtilis spores; sodium hypochlorite (NaOCl) shows higher activity than sodium dichloroisocyanurate (NaDCC) which is more active than chloramine-T. Investigations with coat- and cortex-extracted spores indicate that resistance to CRAs depends not only on the spore coat but also the cortex. Whereas extraction of alkali-soluble coat protein increased sensitivity to NaOCl and NaDCC, degradation of coat and cortex material was required to achieve significant activity with chloramine-T. NaOCl (in the presence and absence of NaOH) and NaDCC (in the presence of NaOH only) produced degradation of spore coat and cortex material which may be related to their rapid sporicidal action at low concentrations under these conditions. By contrast, chloramine-T produced no degradation of cortex peptidoglycan and was only effective against normal and alkali-treated spores at high concentrations, requiring extraction of peptidoglycan with urea/dithiothreitol/sodium lauryl sulphate (UDS) or UDS/lysozyme to achieve significant activity at low concentrations. Results suggest that the sporicidal action of CRAs is associated with spore coat and cortex degradation causing rehydration of the protoplast allowing diffusion to the site of action on the underlying protoplast.

Mechanism of resistance of Bacillus subtilis spores to chlorhexidine

Chlorhexidine diacetate (CHA) was rather more sporicidal at 20 degrees C to urea-dithreitol-sodium lauryl sulphate (UDS)-treated spores of Bacillus subtilis NCTC 8236 than to urea-dithiothreitol (UDT)-treated or normal (untreated) spores. UDS spores adsorbed more CHA from solution than did the other two forms. No differences in hydrophobicity, as determined by hydrophobic interaction chromatography (HIC) or bacterial adherence to hydrocarbon (BATH), could be detected between the three spore types. Germinating spores took up much less CHA than did outgrowing spores. Germinating cells were considerably more hydrophobic, as measured by the BATH technique, than outgrowing cells or normal spores. Chlorhexidine diacetate increased the apparent hydrophobicity of the two latter forms, but this effect could be partially reversed by subsequent exposure to a non-ionic surfactant.