Energy dispersive analysis of X-rays study of the distribution of chlorhexidine diacetate and cetylpyridinium chloride on the Pseudomonas aeruginosa bacteriophage F116

Biocides--resistance, cross-resistance mechanisms and assessment

IMPORTANCE OF THE FIELD

Antibiotic resistance in bacterial pathogens has increased worldwide leading to treatment failures. Concerns have been raised about the use of biocides as a contributing factor to the risk of antimicrobial resistance (AMR) development. In vitro studies demonstrating increase in resistance have often been cited as evidence for increased risks. It is therefore important to understand the mechanisms of resistance employed by bacteria toward biocides used in consumer products and their potential to impart cross-resistance to therapeutic antibiotics.

AREAS COVERED

In this review, the mechanisms of resistance and cross-resistance reported in the literature toward biocides commonly used in consumer products are summarized. The physiological and molecular techniques used in describing and examining these mechanisms are reviewed and application of these techniques for systematic assessment of biocides for their potential to develop resistance and/or cross-resistance is discussed.

EXPERT OPINION

The guidelines in the usage of biocides in household or industrial purpose should be monitored and regulated to avoid the emergence of any MDR strains. The genetic and molecular methods to monitor the resistance development to biocides should be developed and included in preclinical and clinical studies.

Differential actions of chlorhexidine on the cell wall of Bacillus subtilis and Escherichia coli

Chlorhexidine is a chlorinated phenolic disinfectant used commonly in mouthwash for its action against bacteria. However, a comparative study of the action of chlorhexidine on the cell morphology of gram-positive and gram-negative bacteria is lacking. In this study, the actions of chlorhexidine on the cell morphology were identified with the aids of electron microscopy. After exposure to chlorhexidine, numerous spots of indentation on the cell wall were found in both Bacillus subtilis and Escherichia coli. The number of indentation spots increased with time of incubation and increasing chlorhexidine concentration. Interestingly, the dented spots found in B. subtilis appeared mainly at the hemispherical caps of the cells, while in E. coli the dented spots were found all over the cells. After being exposed to chlorhexidine for a prolonged period, leakage of cellular contents and subsequent ghost cells were observed, especially from B subtilis. By using 2-D gel/MS-MS analysis, five proteins related to purine nucleoside interconversion and metabolism were preferentially induced in the cell wall of E. coli, while three proteins related to stress response and four others in amino acid biosynthesis were up-regulated in the cell wall materials of B. subtilis. The localized morphological damages together with the biochemical and protein analysis of the chlorhexidine-treated cells suggest that chlorhexidine may act on the differentially distributed lipids in the cell membranes/wall of B. subtilis and E. coli.

Polyhexamethylene biguanide exposure leads to viral aggregation

AIMS

This study reports the activity of two biguanides against MS2 bacteriophage used as a surrogate virus for nonenveloped mammalian viruses and provides an explanation as to their apparent limited efficacy.

METHODS AND RESULTS

When tested in a standard suspension test, two polyhexamethylene biguanides (PHMB), VANTOCIL TG and COSMOCIL CQ, reduced the viability of MS2 by only 1-2 log(10) PFU ml(-1). Exposure time up to 30 min did not affect the activity of the biguanides, although both PHMB were shown to strongly interact with MS2 proteins.

CONCLUSIONS

Inactivation kinetics and change in virus hydrophobicity suggested that PHMB induces the formation of viral aggregates. This hypothesis was supported using dynamic light scattering that showed an increase in viral aggregates sizes (up to 500 nm) in a concentration-dependent manner.

SIGNIFICANCE AND IMPACT OF THE STUDY

It has been reported that viral aggregation is responsible for virus survival to the biocide exposure. Here, this might be the case, because the virucidal activity of the biguanides was modest and viral aggregation important. The formation of viral aggregates during virus exposure to PHMB was unlikely to overestimate the virucidal potential of the biguanides.

Cytological changes in chlorhexidine-resistant isolates of Pseudomonas stutzeri

Transmission electron microscopy (TEM), scanning electron microscopy (SEM) and energy-dispersive analysis of X-ray (EDAX) have been used to examine chlorhexidine diacetate (CHA)-sensitive and -resistant isolates of Pseudomonas stutzeri and to determine the effects of CHA on the cells. Significant differences were observed in the structure, size and elemental composition of CHA-sensitive and -resistant cells. Treatment with CHA produced considerably greater changes in CHA-sensitive cells, with widespread peeling of the outer membrane, a substantial loss of cytoplasmic electron-dense material and extensive lysis. Cells from the resistant isolates showed no blebbing of the outer membrane and no structural damage. X-ray mapping confirmed the difference in CHA uptake between CHA-sensitive and CHA-resistant cells. It is proposed that changes in the outer membrane form a major mechanism of resistance to CHA in P. stutzeri.

X-ray microanalysis of chlorine and phosphorus content in biguanide-treated Acanthamoeba castellanii

Energy dispersive analysis of X-rays (EDAX) was used to study the effects of chlorhexidine diacetate (CHA) and polyhexamethylene biguanide (PHMB) on Acanthamoeba castellanii. A high variation of elements occurred in untreated individual cells and only two elements, Cl (a biocide marker) and P, were investigated. X-ray dot mapping of untreated trophozoites and cysts revealed that Cl in cells was uniformly distributed throughout the cytoplasm, whereas P was less dense in the vacuoles. X-ray dots of Cl in biocide-treated trophozoites and cysts appeared denser and evenly distributed within the cells as the biguanide concentration increased. Quantitative analysis of either CHA or PHMB within the cells using Cl as an elemental marker was unsatisfactory because of the high Cl levels in untreated cells. The apparent increases of P in some experiments with treated cells might be associated with reduced permeability, protein coagulation or aggregation of phospholipids.

Antiseptics and disinfectants: activity, action, and resistance

Antiseptics and disinfectants are extensively used in hospitals and other health care settings for a variety of topical and hard-surface applications. A wide variety of active chemical agents (biocides) are found in these products, many of which have been used for hundreds of years, including alcohols, phenols, iodine, and chlorine. Most of these active agents demonstrate broad-spectrum antimicrobial activity; however, little is known about the mode of action of these agents in comparison to antibiotics. This review considers what is known about the mode of action and spectrum of activity of antiseptics and disinfectants. The widespread use of these products has prompted some speculation on the development of microbial resistance, in particular whether antibiotic resistance is induced by antiseptics or disinfectants. Known mechanisms of microbial resistance (both intrinsic and acquired) to biocides are reviewed, with emphasis on the clinical implications of these reports.