Studies on the mechanisms of the sporicidal action of ortho-phthalaldehyde

Synthesis, In Silico, and Biological Applications of Novel Heteroleptic Copper (II) Complex of Natural Product-Based Semicarbazone Ligands

Recently, heteroleptic coordination between essential metallic elements with semicarbazone-based derivatives attracts more consideration for the varied ranges of bioactivities. Semicarbazone-based moiety holding azomethine (C=N) group become flexible ligands, forming stable complexes. Through a stirring and reflux technique, a novel heteroleptic complex of copper (II) was synthesized by reacting two semicarbazone-based derivative ligands, ortho-phthalaldehyde disemicarbazone (L1) and dehydrozingerone semicarbazone (L2), with copper chloride salt in 1 : 1 : 1 molar ratio. Magnetic moment measurement, elemental analyzer, thermogravimetric (TGA) analysis, and several spectroscopic techniques were applied to describe the prepared compounds. The disc diffusion and DPPH methods were actually used to investigate the antibacterial and antiradical potentials, respectively. The obtained data indicates the ligand (L1) has good mean inhibition zones on Staphylococcus aureus (12.42 ± 0.00 mm) and S. pyogenes (11.64 ± 0.12 mm) bacteria. The heteroleptic [Cu(L1) (L2)] complex displayed higher antibacterial actions (13.67 ± 0.52 mm) on Streptococcus pyogenes bacteria. The [Cu(L1) (L2)] complex also shows better antiradical potential (63.7%). Furthermore, the docking result of prepared compounds on S. aureus gyrase confirms the ligands (L1 and L2) and the complex potential molecules possess the smallest binding potential of −8.0 to −8.4 kcal/mol. A higher value was achieved by [Cu(L1) (L2)] complex (−8.4 kcal/mol). Thus, this study indicates an insight towards combining semicarbazone form derivatives of natural source origin with a synthetic compound as ligands through metal coordination could enhance bioactivity.

On the Disinfection of Electrochemical Aptamer-Based Sensors

Electrochemical aptamer-based (EAB) sensors encompass the only biosensor approach yet reported that is simultaneously: (1) independent of the chemical or enzymatic reactivity of its target, rendering it general; (2) continuous and real-time; and (3) selective enough to deploy in situ in the living body. Consistent with this, in vivo EAB sensors supporting the seconds-resolved, real-time measurement of multiple drugs and metabolites have been reported, suggesting the approach may prove of value in biomedical research and the diagnosis, treatment, and monitoring of disease. However, to apply these devices in long-duration animal models, much less in human patients, requires that they be free of any significant pathogen load. Thus motivated, here we have characterized the compatibility of EAB sensors with standard sterilization and high-level disinfection techniques. Doing so, we find that, while many lead to significant sensor degradation, treatment with CIDEX OPA (0.55% ortho-phthalaldehyde) leads to effective disinfection without causing any detectable loss in sensor performance.

Sporicidal mechanism of the combination of ortho-phthalaldehyde and benzyldimethyldodecylammonium chloride as a disinfectant against the Bacillus subtilis spores

Previous studies have shown that the combination disinfectant, Ortho-phthalaldehyde and benzyldimethyldodecylammonium chloride (ODB), can effectively kill a variety of microorganisms, such as Escherichia coli, Staphylococcus aureus, and Candida albicans. To observe the sporicidal ability and mechanism of ODB for spores, Bacillus subtilis spores were used as the research object in this experiment. TEM images revealed that ODB destroyed the integrity of the coat, cortex, and inner membrane of the spores after 0.5-h treatment, and the nuclear material was also broken and exuded after 4-h treatment. The broken structure led to the release of dipicolinic acid (DPA) in large amount. The results show that B. subtilis spores can be effetely killed by ODB through destroying the structure of the spores.

Persister cells in a biofilm treated with a biocide

This study investigated the physiology and behaviour following treatment with ortho-phthalaldehyde (OPA), of Pseudomonas fluorescens in both the planktonic and sessile states. Steady-state biofilms and planktonic cells were collected from a bioreactor and their extracellular polymeric substances (EPS) were extracted using a method that did not destroy the cells. Cell structure and physiology after EPS extraction were compared in terms of respiratory activity, morphology, cell protein and polysaccharide content, and expression of the outer membrane proteins (OMP). Significant differences were found between the physiological parameters analysed. Planktonic cells were more metabolically active, and contained greater amounts of proteins and polysaccharides than biofilm cells. Moreover, biofilm formation promoted the expression of distinct OMP. Additional experiments were performed with cells after EPS extraction in order to compare the susceptibility of planktonic and biofilm cells to OPA. Cells were completely inactivated after exposure to the biocide (minimum bactericidal concentration, MBC = 0.55 ± 0.20 mM for planktonic cells; MBC = 1.7 ± 0.30 mM for biofilm cells). After treatment, the potential of inactivated cells to recover from antimicrobial exposure was evaluated over time. Planktonic cells remained inactive over 48 h while cells from biofilms recovered 24 h after exposure to OPA, and the number of viable and culturable cells increased over time. The MBC of the recovered biofilm cells after a second exposure to OPA was 0.58 ± 0.40 mM, a concentration similar to the MBC of planktonic cells. This study demonstrates that persister cells may survive in biocide-treated biofilms, even in the absence of EPS.

Innate resistance to sporicides and potential failure to decontaminate

Bacterial spores are frequently intrinsically resistant to biocides and only a number of alkylating and oxidising biocides are sporicidal under certain conditions. Activity against spores is affected by several key factors such as concentration, exposure time, soiling, and the types of surface to be treated. Sporicidal efficacy is usually achieved after an exposure time of several minutes with a high concentration of a biocide. Failure to understand these factors will result in decreased sporicide activity and spore survival. Sporicides in healthcare settings are used for surface disinfection and for the high level disinfection of certain medical devices (e.g. endoscopes). With efficacy data in mind, sporicidal activity should be achieved for the disinfection of medical devices where both high concentration and long exposure time occur. However, for the disinfection of environmental surfaces, high concentration is not recommended, nor is long exposure time achievable. In this case, sporicidal activity is severely reduced and spore survival following treatment is to be expected and contributes to the explanation of spore persistence on surfaces.

Antimicrobial mechanisms of ortho-phthalaldehyde action

Biocides generally have multiple biochemical targets. Such a feature easily entangles the analysis of the mechanisms of antimicrobial action. In this study, the action of the dialdehyde biocide ortho-phtalaldehyde (OPA), on bacteria, was investigated using the Gram-negative Pseudomonas fluorescens. The targets of the biocide action were studied using different bacterial physiological indices. The respiratory activity, membrane permeabilization, physico-chemical characterization of the bacterial surfaces, outer membrane proteins (OMP) expression, concomitant influence of pH, contact time and presence of bovine serum albumin (BSA) on respiratory activity, morphological changes and OPA-DNA interactions were assessed for different OPA concentrations. With the process conditions used, the minimum inhibitory concentration was 1500 mg/l, the concentration to promote total loss of bacterial culturability was 65 mg/l and the concentration needed to inactivate respiratory activity was 80 mg/l. These data are evidence that culturability and respiratory activity were markedly affected by the biocide. OPA lead, moreover, to a significant change in cell surface hydrophobicity and induced propidium iodide uptake. Such results suggest cytoplasmic membrane damage, although no release of ATP was detected. At pH 5, the bactericidal action of OPA was stronger, though not influenced by BSA presence. Nevertheless, at pH 9, BSA noticeably (p < 0.05) impaired biocide action. A time-dependent effect in OPA action was evident when contemplating respiratory activity variation, mainly for the lower exposure times. Scanning electron microscopy allowed to detect bacterial morphological changes, translated on cellular elongation, for OPA concentrations higher than 100 mg/l. Interferences at DNA level were, however, restricted to extreme biocide concentrations. The overall bactericidal events occurred without detectable OMP expression changes. In conclusion, the results indicated a sequence of events responsible for the antimicrobial action of OPA: it binds to membrane receptors due to cross-linkage; impairs the membrane functions allowing the biocide to enter through the permeabilized membrane; it interacts with intracellular reactive molecules, such as RNA, compromising the growth cycle of the cells and, at last, with DNA.

Spores of Bacillus subtilis: their resistance to and killing by radiation, heat and chemicals

A number of mechanisms are responsible for the resistance of spores of Bacillus species to heat, radiation and chemicals and for spore killing by these agents. Spore resistance to wet heat is determined largely by the water content of spore core, which is much lower than that in the growing cell protoplast. A lower core water content generally gives more wet heat-resistant spores. The level and type of spore core mineral ions and the intrinsic stability of total spore proteins also play a role in spore wet heat resistance, and the saturation of spore DNA with alpha/beta-type small, acid-soluble spore proteins (SASP) protects DNA against wet heat damage. However, how wet heat kills spores is not clear, although it is not through DNA damage. The alpha/beta-type SASP are also important in spore resistance to dry heat, as is DNA repair in spore outgrowth, as Bacillus subtilis spores are killed by dry heat via DNA damage. Both UV and gamma-radiation also kill spores via DNA damage. The mechanism of spore resistance to gamma-radiation is not well understood, although the alpha/beta-type SASP are not involved. In contrast, spore UV resistance is due largely to an alteration in spore DNA photochemistry caused by the binding of alpha/beta-type SASP to the DNA, and to a lesser extent to the photosensitizing action of the spore core's large pool of dipicolinic acid. UV irradiation of spores at 254 nm does not generate the cyclobutane dimers (CPDs) and (6-4)-photoproducts (64PPs) formed between adjacent pyrimidines in growing cells, but rather a thymidyl-thymidine adduct termed spore photoproduct (SP). While SP is formed in spores with approximately the same quantum efficiency as that for generation of CPDs and 64PPs in growing cells, SP is repaired rapidly and efficiently in spore outgrowth by a number of repair systems, at least one of which is specific for SP. Some chemicals (e.g. nitrous acid, formaldehyde) again kill spores by DNA damage, while others, in particular oxidizing agents, appear to damage the spore's inner membrane so that this membrane ruptures upon spore germination and outgrowth. There are also other agents such as glutaraldehyde for which the mechanism of spore killing is unclear. Factors important in spore chemical resistance vary with the chemical, but include: (i) the spore coat proteins that likely react with and detoxify chemical agents; (ii) the relative impermeability of the spore's inner membrane that restricts access of exogenous chemicals to the spore core; (iii) the protection of spore DNA by its saturation with alpha/beta-type SASP; and (iv) DNA repair for agents that kill spores via DNA damage. Given the importance of the killing of spores of Bacillus species in the food and medical products industry, a deeper understanding of the mechanisms of spore resistance and killing may lead to improved methods for spore destruction.

Use of a new alginate film test to study the bactericidal efficacy of the high-level disinfectant ortho-phthalaldehyde

OBJECTIVES

To evaluate the merit of a new alginate efficacy film test to determine the bactericidal activity of the high-level disinfectant ortho-phthalaldehyde (OPA).

METHODS

The efficacy of OPA was investigated using a new sodium alginate surface film test against Mycobacterium chelonae NCIMB 1474 and Epping, and Pseudomonas aeruginosa NCIMB 10421 under different test conditions.

RESULTS

OPA was highly bactericidal against P. aeruginosa but its mycobactericidal efficacy was seriously reduced and produced >or=5 log reductions only at a concentration of 0.5% (w/v) within 30-60 min without organic load.

CONCLUSIONS

The sodium alginate film efficacy was reproducible between repeats. Inactivation results depended upon the concentration of OPA, contact time, the presence of an organic load and the bacterial genera.

Mechanisms of killing of Bacillus subtilis spores by Decon and OxoneTM, two general decontaminants for biological agents

AIMS

To determine the mechanisms of Bacillus subtilis spore killing by and resistance to the general biological decontamination agents, Decon and Oxone.

METHODS AND RESULTS

Spores of B. subtilis treated with Decon or Oxone did not accumulate DNA damage and were not mutagenized. Spore killing by these agents was increased if spores were decoated. Spores prepared at higher temperatures were more resistant to these agents, consistent with a major role for spore coats in this resistance. Neither Decon nor Oxone released the spore core's depot of dipicolinic acid (DPA), but Decon- and Oxone-treated spores more readily released DPA upon a subsequent normally sublethal heat treatment. Decon- and Oxone-killed spores initiated germination with dodecylamine more rapidly than untreated spores, but could not complete germination triggered by nutrients or Ca(2+)-DPA and did not degrade their peptidoglycan cortex. However, lysozyme treatment did not recover these spores.

CONCLUSIONS

Decon and Oxone do not kill B. subtilis spores by DNA damage, and a major factor in spore resistance to these agents is the spore coat. Spore killing by both agents renders spores defective in germination, possibly because of damage to the inner membrane of spore.

SIGNIFICANCE AND IMPACT OF STUDY

These results provide information on the mechanisms of the killing of bacterial spores by Decon and Oxone.

Mechanisms of killing of Bacillus subtilis spores by hypochlorite and chlorine dioxide

AIMS

To determine the mechanisms of Bacillus subtilis spore killing by hypochlorite and chlorine dioxide, and its resistance against them.

METHODS AND RESULTS

Spores of B. subtilis treated with hypochlorite or chlorine dioxide did not accumulate damage to their DNA, as spores with or without the two major DNA protective alpha/beta-type small, acid soluble spore proteins exhibited similar sensitivity to these chemicals; these agents also did not cause spore mutagenesis and their efficacy in spore killing was not increased by the absence of a major DNA repair pathway. Spore killing by these two chemicals was greatly increased if spores were first chemically decoated or if spores carried a mutation in a gene encoding a protein essential for assembly of many spore coat proteins. Spores prepared at a higher temperature were also much more resistant to these agents. Neither hypochlorite nor chlorine dioxide treatment caused release of the spore core's large depot of dipicolinic acid (DPA), but hypochlorite- and chlorine dioxide-treated spores much more readily released DPA upon a subsequent normally sub-lethal heat treatment than did untreated spores. Hypochlorite-killed spores could not initiate the germination process with either nutrients or a 1 : 1 chelate of Ca2+-DPA, and these spores could not be recovered by lysozyme treatment. Chlorine dioxide-treated spores also did not germinate with Ca2+-DPA and could not be recovered by lysozyme treatment, but did germinate with nutrients. However, while germinated chlorine dioxide-killed spores released DPA and degraded their peptidoglycan cortex, they did not initiate metabolism and many of these germinated spores were dead as determined by a viability stain that discriminates live cells from dead ones on the basis of their permeability properties.

CONCLUSIONS

Hypochlorite and chlorine dioxide do not kill B. subtilis spores by DNA damage, and a major factor in spore resistance to these agents appears to be the spore coat. Spore killing by hypochlorite appears to render spores defective in germination, possibly because of severe damage to the spore's inner membrane. While chlorine dioxide-killed spores can undergo the initial steps in spore germination, these germinated spores can go no further in this process probably because of some type of membrane damage.

SIGNIFICANCE AND IMPACT OF THE STUDY

These results provide information on the mechanisms of the killing of bacterial spores by hypochlorite and chlorine dioxide.

Studies on the mechanism of killing of Bacillus subtilis spores by hydrogen peroxide

AIMS

To determine the mechanism of killing of Bacillus subtilis spores by hydrogen peroxide.

METHODS AND RESULTS

Killing of spores of B. subtilis with hydrogen peroxide caused no release of dipicolinic acid (DPA) and hydrogen peroxide-killed spores were not appreciably sensitized for DPA release upon a subsequent heat treatment. Hydrogen peroxide-killed spores appeared to initiate germination normally, released DPA and hydrolysed significant amounts of their cortex. However, the germinated killed spores did not swell, did not accumulate ATP or reduced flavin mononucleotide and the cores of these germinated spores were not accessible to nucleic acid stains.

CONCLUSIONS

These data indicate that treatment with hydrogen peroxide results in spores in which the core cannot swell properly during spore germination.

SIGNIFICANCE AND IMPACT OF THE STUDY

The results provide further information on the mechanism of killing of spores of Bacillus species by hydrogen peroxide.