Reduced susceptibility of methicillin-resistant Staphylococcus aureus to cetylpyridinium chloride and chlorhexidine

Ionic Liquids: Emerging Antimicrobial Agents

Antimicrobial resistance has become a serious threat to global health. New antimicrobials are thus urgently needed. Ionic liquids (ILs), salts consisting of organic cations and anions with melting points less than 100°C, have been recently found to be promising in antimicrobial field as they may disrupt the bacterial wall and membrane and consequently lead to cell leakage and death. Different types of antimicrobial ILs are introduced in the review, including cationic, polymeric, and anionic ILs. Being the main type of the antimicrobial ILs, the review focuses on the structure and the antimicrobial mechanisms of cationic ILs. The quantitative structure-activity relationship (QSAR) models of the cationic ILs are also included. Increase in alkyl chain length and lipophilicity is beneficial to increase the antimicrobial effects of cationic ILs. Polymeric ILs are homopolymers of monomer ILs or copolymers of ILs and other monomers. They have great potential in the field of antibiotics as they provide stronger antimicrobial effects than the sum of the monomer ILs. Anionic ILs are composed of existing anionic antibiotics and organic cations, being capable to enhance the solubility and bioavailability of the original form. Nonetheless, the medical application of antimicrobial ILs is limited by the toxicity. The structural optimization aided by QSAR model and combination with existing antibiotics may provide a solution to this problem and expand the application range of ILs in antimicrobial field.

Bacterial resistance to antiseptics and disinfectants – minireview

The appearance of bacterial resistance to disinfectants and antiseptics is an issue of substantial health concern, resulting in low efficiency of epidemic control activities and emergence of microorganisms with cross-resistance to antibiotics and biocides. A synopsis of the main mechanisms of development of resistance to biocides is presented. The emphasis is placed to health risks and impact on medical practice. The main methods for detection of resistance, and prevention measures of key importance for its control are outlined.

Cetylpyridinium Chloride: Mechanism of Action, Antimicrobial Efficacy in Biofilms, and Potential Risks of Resistance

Antimicrobial resistance is a serious issue for public health care all over the world. While resistance toward antibiotics has attracted strong interest among researchers and the general public over the last 2 decades, the directly related problem of resistance toward antiseptics and biocides has been somewhat left untended. In the field of dentistry, antiseptics are routinely used in professional care, but they are also included in lots of oral care products such as mouthwashes or dentifrices, which are easily available for consumers over-the-counter. Despite this fact, there is little awareness among the dental community about potential risks of the widespread, unreflected, and potentially even needless use of antiseptics in oral care. Cetylpyridinium chloride (CPC), a quaternary ammonium compound, which was first described in 1939, is one of the most commonly used antiseptics in oral care products and included in a wide range of over-the-counter products such as mouthwashes and dentifrices. The aim of the present review is to summarize the current literature on CPC, particularly focusing on its mechanism of action, its antimicrobial efficacy toward biofilms, and on potential risks of resistance toward this antiseptic as well as underlying mechanisms. Furthermore, this work aims to raise awareness among the dental community about the risk of resistance toward antiseptics in general.

Presence of Qac genes in clinical isolates of methicillin-resistant and methicillin-susceptible Staphylococcus pseudintermedius and their impact on chlorhexidine digluconate susceptibility

OBJECTIVE

To evaluate the presence of quaternary ammonium compound (QAC) (resistance genes, qac A/B, smr, qacG, and qacJ, in clinical isolates of methicillin-susceptible Staphylococcus pseudintermedius (MSSP) and methicillin-resistant S pseudintermedius (MRSP) from dogs and the impact on in vitro chlorhexidine susceptibility.

STUDY DESIGN

Experimental in vitro study.

SAMPLE POPULATION

Seventy isolates from dogs colonized or infected with MRSP (n = 50) or MSSP (n = 20).

METHODS

Agar dilution was used to determine the minimum inhibitory concentration (MIC) of chlorhexidine digluconate. Real-time polymerase chain reaction was used to detect the presence of QAC resistance genes, qacA/B, smr, qacG, and qacJ genes.

RESULTS

One or more qac genes were identified in 52 of 70 (74%) isolates. Overall, there was no association between chlorhexidine MIC and the presence of one or more qac genes (P = .85) or the presence of qacA/B (P = .31), smr (P = .72) or qacJ (P = .93) individually. There was an association between qacG and MIC (P = .012), with a median MIC of 1.5 μg/mL for isolates possessing this gene and 1 μg/mL for those not possessing it.

CONCLUSION

Quaternary ammonium compound resistance genes were present in MRSP and MSSP isolates. With the exception of qacG, the presence of these genes was not associated with increased MIC. All isolates exhibited MIC 5000 to 80 000 times lower than the concentration recommended for use.

CLINICAL SIGNIFICANCE

Despite the presence of QAC genes, chlorhexidine digluconate should be effective against MRSP and MSSP if used correctly.

Synthesis and Antibacterial Activity of Ionic Liquids and Organic Salts Based on Penicillin G and Amoxicillin hydrolysate Derivatives against Resistant Bacteria

The preparation and characterization of ionic liquids and organic salts (OSILs) that contain anionic penicillin G [secoPen] and amoxicillin [seco-Amx] hydrolysate derivatives and their in vitro antibacterial activity against sensitive and resistant Escherichia coli and Staphylococcus aureus strains is reported. Eleven hydrolyzed β-lactam-OSILs were obtained after precipitation in moderate-to-high yields via the neutralization of the basic ammonia buffer of antibiotics with different cation hydroxide salts. The obtained minimum inhibitory concentration (MIC) data of the prepared compounds showed a relative decrease of the inhibitory concentrations (RDIC) in the order of 100 in the case of [C₂OHMIM][seco-Pen] against sensitive S. aureus ATCC25923 and, most strikingly, higher than 1000 with [C₁₆Pyr][seco-Amx] against methicillin-resistant Staphylococcus aureus (MRSA) ATCC 43300. These outstanding in vitro results showcase that a straightforward transformation of standard antibiotics into hydrolyzed organic salts can dramatically change the pharmaceutical activity of a drug, including giving rise to potent formulations of antibiotics against deadly bacteria strains.

Inhibitory effects of silybin on the efflux pump of methicillin‑resistant Staphylococcus aureus

Bacterial multidrug resistance efflux systems serve an important role in antimicrobial resistance. Thus, identifying novel and effective efflux pump inhibitors that are safe with no adverse side effects is urgently required. Silybin is a flavonolignan component of the extract from the milk thistle seed. To order to investigate the mechanism by which silybin inhibits the efflux system of methicillin-resistant Staphylococcus aureus (MRSA), antimicrobial susceptibility testing and the double-plate method were used to evaluate the effect of silybin on MRSA41577. The ability of silybin to inhibit the efflux of ciprofloxacin from MRSA was evaluated by performing a fluorescence assay. Reverse transcription-quantitative polymerase chain reaction analysis revealed that silybin reduced the expression of the quinolone resistance protein NorA (norA) and quaternary ammonium resistance proteins A/B (qacA/B) efflux genes in MRSA. This suggested that silybin may effectively inhibit the efflux system of MRSA41577. Compared with the control, MRSA41577 treated with silybin for 16 h exhibited a 36 and 49% reduction in the expression of norA and qacA/B, respectively. Inhibition of the expression of these genes by silybin restored the sensitivity of MRSA41577 to antibiotics, indicating that efflux pump inhibitors, which act by inhibiting the efflux system of MRSA, may disrupt the MRSA resistance to antibiotics, rendering the bacteria sensitive to these drugs.

Phenotypic chlorhexidine and triclosan susceptibility in clinical Staphylococcus aureus isolates in Australia

Antiseptics such as chlorhexidine gluconate and triclosan are widely used in healthcare settings for both skin antisepsis and decolonisation of Staphylococcus aureus. We determined the minimum inhibitory concentration (MIC) of 198 methicillin susceptible and resistant Staphylococcus aureus clinical isolates to both chlorhexidine and triclosan using an agar dilution method. Of these, 10% (19/198) showed a raised MIC to chlorhexidine and 3% (6/198) showed an elevated MIC to triclosan. The multilocus sequence type (MLST) of each isolate was predicted using a binary method, and although ST93-MRSA-IV was the most common, ST22-MRSA-IV was shown to have statistically higher chlorhexidine MIC values compared with non ST22-MRSA-IV isolates (z = -8.7, p < 0.01). Additionally, isolates from patients known to have failed decolonisation were included and did not demonstrate elevated MIC to the decolonisation antiseptic. Monitoring for non-susceptibility of clinical isolates to biocides is important to determine trends, and may have clinical implications in terms of sub-lethal concentration in residues and concomitant antibiotic resistance.

The Two-Component System ChtRS Contributes to Chlorhexidine Tolerance in Enterococcus faecium

Enterococcus faecium is one of the primary causes of nosocomial infections. Disinfectants are commonly used to prevent infections with multidrug-resistant E. faecium in hospitals. Worryingly, E. faecium strains that exhibit tolerance to disinfectants have already been described. We aimed to identify and characterize E. faecium genes that contribute to tolerance to the disinfectant chlorhexidine (CHX). We used a transposon mutant library, constructed in a multidrug-resistant E. faecium bloodstream isolate, to perform a genome-wide screen to identify genetic determinants involved in tolerance to CHX. We identified a putative two-component system (2CS), composed of a putative sensor histidine kinase (ChtS) and a cognate DNA-binding response regulator (ChtR), which contributed to CHX tolerance in E. faecium Targeted chtR and chtS deletion mutants exhibited compromised growth in the presence of CHX. Growth of the chtR and chtS mutants was also affected in the presence of the antibiotic bacitracin. The CHX- and bacitracin-tolerant phenotype of E. faecium E1162 was linked to a unique, nonsynonymous single nucleotide polymorphism in chtR Transmission electron microscopy showed that upon challenge with CHX, the ΔchtR and ΔchtS mutants failed to divide properly and formed long chains. Normal growth and cell morphology were restored when the mutations were complemented in trans Morphological abnormalities were also observed upon exposure of the ΔchtR and ΔchtS mutants to bacitracin. The tolerance to both chlorhexidine and bacitracin provided by ChtRS in E. faecium highlights the overlap between responses to disinfectants and antibiotics and the potential for the development of cross-tolerance for these classes of antimicrobials.

Oral care with 0.12% chlorhexidine for the prevention of ventilator-associated pneumonia in critically ill children: randomised, controlled and double blind trial

PURPOSE

To test the effectiveness of oral care with 0.12% chlorhexidine in decreasing ventilator-associated pneumonia in critically ill children.

METHODS

Prospective, randomised, controlled, double-blind clinical trial performed in a paediatric critical care unit at a university hospital. The sample was composed of 96 mechanically ventilated children randomly allocated to the chlorhexidine group (oral care with a toothbrush and an antiseptic gel twice a day) and the placebo group (oral care with a toothbrush and a non-antiseptic gel twice a day). Microbiological analyses of oropharyngeal and tracheal secretions were performed 24, 48 and 96h after intubation. Chi-square, Fischer's exact and Mann-Whitney tests were applied (p≤0.05).

RESULTS

The chlorhexidine group was composed of 46 children, and the placebo group consisted of 50 children. Within these samples, 15 (32.6%) children in the chlorhexidine group and 16 (32.0%) children in the placebo group developed ventilator-associated pneumonia (p=0.949). Children in the chlorhexidine group without potentially pathogenic microflora in their oropharynx 24h after mechanical ventilation presented with fewer episodes of ventilator-associated pneumonia (p=0.019). The pathogen colonization profile of children with ventilator-associated pneumonia in the chlorhexidine group included Klebsiella pneumoniae, Escherichia coli, and Pseudomonas aeruginosa. In the placebo group, Pseudomonas aeruginosa and Escherichia coli were the predominant potentially pathogenic microorganisms. The intervention did not influence paediatric intensive care unit mortality (p=0.425), hospital length of stay (p=0.143), or paediatric intensive care unit length of stay (p=0.177).

CONCLUSIONS

The use of 0.12% chlorhexidine did not significantly modify the VAP incidence in a sample of mechanically ventilated children.

Minimum inhibitory (MIC) and minimum microbicidal concentration (MMC) of polihexanide and triclosan against antibiotic sensitive and resistant Staphylococcus aureus and Escherichia coli strains

BACKGROUND

An in-vitro study was conducted investigating the antimicrobial efficacy of polihexanide and triclosan against clinical isolates and reference laboratory strains of Staphylococcus aureus and Escherichia coli.

METHODS

The minimal inhibitory concentration (MIC) and the minimal microbicidal concentration (MMC) were determined following DIN 58940-81 using a micro-dilution assay and a quantitative suspension test following EN 1040. Polihexanide was tested in polyethylene glycol 4000, triclosan in aqueous solutions.

RESULTS

Against all tested strains the MIC of polihexanide ranged between 1-2 µg/mL. For triclosan the MICs varied depending on strains ranging between 0.5 µg/mL for the reference strains and 64 µg/mL for two clinical isolates. A logRF >5 without and logRF >3 with 0.2% albumin burden was achieved at 0.6 µg/mL triclosan. One exception was S. aureus strain H-5-24, where a triclosan concentration of 0.6 µg/mL required 1 minute without and 10 minutes with albumin burden to achieve the same logRFs. Polihexanide achieved a logRF >5 without and logRF >3 with albumin burden at a concentration of 0.6 µg/mL within 30 sec. The exception was the North-German epidemic MRSA strain, were an application time of 5 minutes was required.

CONCLUSION

The clinical isolates of E. coli generally showed higher MICs against triclosan, both in the micro-dilution assay as well in the quantitative suspension test than comparable reference laboratory strains. For polihexanide and triclosan strain dependant susceptibility was shown. However, both antimicrobial compounds are effective when used in concentrations common in practice.

The efficacy of silver dressings and antibiotics on MRSA and MSSA isolated from burn patients

In this study our objectives were (1) to investigate whether meticillin-resistant Staphylococcus aureus (MRSA) showed an increased tolerance to silver wound dressings compared with meticillin-sensitive S. aureus (MSSA); and (2) to evaluate the effects of bacterial phenotypic states of MRSA and MSSA, and pH, on the activity of silver wound dressings and two antibiotics, ampicillin and clindamycin. Twenty MRSA strains and 10 MSSA strains isolated from burns patients in South Africa were evaluated for their susceptibility to a silver alginate and a silver carboxymethyl cellulose wound dressing, employing a corrected zone of inhibition assay, conducted on Mueller Hinton agar and a poloxamer-based biofilm model. When exposed to the two silver dressings, all 30 S. aureus strains showed susceptibility. Possible enhanced antimicrobial efficacy of the silver dressings occurred when pH was lowered to 5.5, compared with a pH of 7.0. When all S. aureus were grown in the biofilm phenotypic state and exposed to both silver dressings and antibiotics, enhanced tolerance was noted. Susceptibility to silver was overall higher for MRSA when compared with MSSA. This study showed that the effect of pH and bacterial phenotypic state must be considered when the antimicrobial activity of silver wound dressings is being investigated. It is evident from the data generated that both pH and the bacterial phenotypic state are factors that induce changes that affect both antimicrobial performance and bacterial susceptibility.

Central line bundle implementation in US intensive care units and impact on bloodstream infections

BACKGROUND

Central line-associated bloodstream infections (CLABSI) represent a serious patient safety issue. To prevent these infections, bundled interventions are increasingly recommended. We examine the extent of adoption of Central Line (CL) Bundle elements throughout US intensive care units (ICU) and determine their effectiveness in preventing CLABSIs.

METHODOLOGY/PRINCIPAL FINDINGS

In this cross-sectional study, National Healthcare Safety Network (NHSN) hospitals provided the following: ICU-specific NHSN-reported rates of CLABSI/1,000 central line days; policies and compliance rates regarding bundle components; and other setting characteristics. In 250 hospitals the mean CLABSI rate was 2.1 per 1000 central line days and 49% reported having a written CL Bundle policy. However, of those that monitored compliance, only 38% reported very high compliance with the CL Bundle. Only when an ICU had a policy, monitored compliance, and had ≥ 95% compliance did CLABSI rates decrease. Complying with any one of three CL Bundle elements resulted in decreased CLABSI rates (β = -1.029, p = 0.015). If an ICU without good bundle compliance achieved high compliance with any one bundle element, we estimated that its CLABSI rate would decrease by 38%.

CONCLUSIONS/SIGNIFICANCE

In NHSN hospitals across the US, the CL Bundle is associated with lower infection rates only when compliance is high. Hospitals must target improving bundle implementation and compliance as opposed to simply instituting policies.

Effect of subinhibitory concentrations of benzalkonium chloride on the competitiveness of Pseudomonas aeruginosa grown in continuous culture

This study investigates the link between adaptation to biocides and antibiotics in Pseudomonas aeruginosa. An enrichment continuous culture of P. aeruginosa NCIMB 10421 (MIC 25 mg BKC l−1) was operated (D=0.04 h−1, 792 h) with added benzalkonium chloride (BKC). A derivative, PA-29 (696 h), demonstrated a >12-fold decrease in sensitivity to the biocide (MIC >350 mg BKC l−1). The variant demonstrated a 256-fold increase in resistance to ciprofloxacin, with a mutation in the gyrA gene (Thr-83→Ile). Similarly, culturing of the original strain in a continuous-culture system with ciprofloxacin selection pressure led to the evolution of BKC-adapted populations (MIC 100 mg BKC l−1). Efflux pump activity predominantly contributed to the developed phenotype of PA-29. An amino acid substitution (Val-51→Ala) in nfxB, the Mex efflux system regulator gene, was observed for PA-29. Overexpression of both MexAB-OprM and MexCD-OprJ was recorded for PA-29. Similarly, mexR, a repressor of the Mex system, was downregulated. Competition studies were carried out in continuous culture between PA-29 and the original strain (in the presence of subinhibitory concentrations of BKC). The outcome of competition was influenced by the concentration of biocide used and the nature of limiting nutrient. The inclusion of 1 mg BKC l−1 in the medium feed was sufficient to select (S=0.011) for the BKC-adapted strain in magnesium-limited culture. Conversely, the presence of 10 mg BKC l−1 in the medium supply was insufficient to select for the same organism (S=−0.017) in the glucose-limited culture. These results indicate the importance of environmental conditions on selection and maintenance of biocide adaptation.

Evaluation of the effectiveness of common hospital hand disinfectants against methicillin-resistant Staphylococcus aureus, glycopeptide-intermediate S. aureus, and heterogeneous glycopeptide-intermediate S. aureus

BACKGROUND

The presence of methicillin-resistant Staphylococcus aureus (MRSA) and glycopeptide-intermediate S. aureus (GISA) in hospitals poses a significant challenge to hospital infection control teams. The use of disinfectants for both surface and hand cleaning is an essential part of the infection control measures.

OBJECTIVE

To evaluate the effectiveness of common hospital hand disinfectants against MRSA, GISA, and heterogeneous GISA (hGISA).

METHODS

For methicillin-susceptible S. aureus (MSSA), MRSA, GISA, and hGISA, the levels of susceptibility to hand disinfectants and their active ingredients were determined. Suspension tests were performed on commercial handwashing products.

RESULTS

Minimum inhibitory concentrations (MICs) of 2-propanol, chlorhexidine, and hexachlorophene were similar for all phenotypes. The MICs of cetrimide and triclosan were higher for the MRSA, GISA, and hGISA strains than for the MSSA strain. The MICs for the chlorhexidine-containing agents Hibisol and Hibiscrub (AstraZeneca) and for the propanol-containing agent Sterillium (Medline) were 1-2-fold lower for the MSSA strains than for the MRSA, GISA, and hGISA strains. Suspension tests showed that the GISA and hGISA strains were less susceptible to the triclosan-containing agent Aquasept (SSL) than were the MRSA and MSSA strains, with resistance increasing with glycopeptide resistance. Products containing Betadine (Purdue) were more effective against the GISA and hGISA strains than against the MRSA and MSSA strains, especially after the strain was exposed to the product for 30 seconds.

CONCLUSIONS

Using the EN 1040 standard criteria for the performance of disinfectants, we determined that all agents, except 50% Aquasept for hGISA and 0.33% hexachlorophene for GISA, performed effectively. However, the GISA and hGISA strains were less susceptible to triclosan-containing products, compared with the MRSA stains, but were more susceptible to products containing Betadine.

Oral care interventions and oropharyngeal colonization in children receiving mechanical ventilation

BACKGROUND

Recent progress in identification of oral microorganisms has shown that the oropharynx can be a site of origin for dissemination of pathogenic organisms to distant body sites, such as the lungs.

OBJECTIVE

To compare the oropharyngeal microbiological profile, duration of mechanical ventilation, and length of stay in the intensive care unit of children receiving mechanical ventilation who had pharmacological or nonpharmacological oral care.

METHODS

A randomized and controlled study was performed in a pediatric intensive unit in São Paulo, Brazil. A total of 56 children were randomly assigned to an experimental group (n=27, 48%) that received oral care with use of 0.12% chlorhexidine digluconate or a control group (n=29, 52%) that received oral care without an antiseptic. Oropharyngeal secretions were collected and cultured on days 0, 2, and 4, and at discharge.

RESULTS

The 2 groups had similar demographic characteristics, preexisting underlying diseases, and pharmacological, nutritional, and ventilatory support. Gram-negative bacteria were the predominant pathogens: Acinetobacter baumannii, Pseudomonas aeruginosa, Klebsiella pneumoniae, and Enter-obacter species. The 2 groups did not differ significantly in the colonization of normal (P= .72) or pathogenic (P= .62) flora, in the duration of mechanical ventilation (P= .67), or in length of stay in the intensive care (P= .22).

CONCLUSION

Use of chlorhexidine combined with nonpharmacological oral care did not decrease the colonization profile, duration of mechanical ventilation, or length of stay in critically ill children receiving mechanical ventilation.

Povidone-iodine: use in hand disinfection, skin preparation and antiseptic irrigation

Iodine and its antibacterial properties have been used for the prevention or management of wound infections for over 150 years. However, the use of solutions (tincture) of iodine has been replaced by the widespread use of povidone-iodine, a water-soluble compound, which is a combination of molecular iodine and polyvinylpyrrolidone. The resultant broad spectrum of antimicrobial activity is well documented and its efficacy, particularly in relation to resistant micro-organisms such as methicillin-resistant Staphylococcus aureus, has been shown. In the clinical environment, there is no general agreement regarding the 'best' antiseptic and the practice varies widely. This article reviews the studies that have assessed the efficacy of povidone-iodine in hand disinfection and skin preparation and its use as an antiseptic irrigant. Although there is a distinct lack of well-designed, randomised controlled trials evaluating antiseptic efficacy, selection should be based on the next best available evidence. This evidence suggests that the use of povidone-iodine as an agent of choice is dependent on the clinical need but is also likely to be influenced by personal preference.

MRSA and the environment: implications for comprehensive control measures

Environmental contamination with methicillin-resistant Staphylococcus aureus (MRSA) is established soon after colonized or infected patients become resident. There are many studies that detail the mechanisms of spread and environmental survival of methicillin-susceptible Staphylococcus aureus (MSSA); this knowledge translates directly into the same findings for MRSA. The potential ubiquity of MRSA in a health-care setting poses challenges for decontamination. Whereas patients and medical staff are important sources for MRSA spread, the environmental burden may contribute significantly in various contexts. Effective control measures must therefore include consideration for MRSA in the environment.

Bacterial resistance to biocides in the healthcare environment: should it be of genuine concern?

The emergence of bacterial resistance following exposure in healthcare facilities has been a recurrent topic of interest over the last 10 years. The overwhelming and increasing body of evidence from studies in vitro showed that bacteria have an immense capacity to respond to chemical stress brought upon by biocides. Empirically two major types of mechanisms have been described: intrinsic and acquired. However, the increasing documented response from bacteria exposed to biocide in conditions close to those found in practice suggests that intrinsic resistance does not adequately describe bacterial survival mechanisms, and that other terms such as biofilm resistance and environmental resistance would be therefore more appropriate. In addition, such terms are more relevant when describing in-situ conditions. The lack of evidence of bacterial resistance in practice and the inability to correlate emerging bacterial resistance from in-vitro experiments with practical situations is a major drawback when attempting to ascertain whether emerging bacterial resistance in healthcare facilities is of genuine concern. Microbial resistance to high or in-use concentration of biocides has been described in practice, although it remains uncommon. The efficacy of biocides in eliminating bacterial contaminants within healthcare facilities has to be questioned with the widespread and increasing use of products containing low concentrations of biocide or possessing low bactericidal activity, as is the selection of less susceptible bacteria following such exposure.

Resistance to disinfectants in epidemiologically defined clinical isolates of Acinetobacter baumannii

Decreased susceptibility to biocides may contribute to epidemic spread of Acinetobacter baumannii in the hospital. This study was conducted to evaluate the susceptibility of different clinical A. baumannii strains to disinfectants. Twenty A. baumannii strains were examined, ten of which were outbreak-related and ten that were sporadic. Clinical isolates were selected on the basis of demonstrating a unique pulsed-field gel electrophoresis pattern. The in-vitro activities of propanol, combination of 1-propanol, 2-propanol and mecetronium ethylsulphate, polyvinylpyrrolidone (PVP)-iodine, triclosan and chlorhexidine were determined using a broth macrodilution method. Exposure times to the disinfectant ranged from 15 s to 2 min and concentrations ranged from undiluted to a 1:4000 dilution in order to investigate the impact of inadvertent dilution that might occur in clinical practice. Five American Type Culture Collection (ATCC) type strains (A. baumannii, Escherichia coli, Pseudomonas aeruginosa, Enterococcus faecalis and Staphylococcus aureus) were used as controls. All disinfectants inhibited growth of all isolates at concentrations and contact times recommended by the respective manufacturer. With most of the disinfectants tested, a relevant number of viable bacteria remained if contact times < 30s or diluted agents were used. No significant differences in susceptibility between outbreak-related and sporadic strains were detected, but larger studies would be required to confirm this. Resistance to currently used disinfectants is probably not a major factor in the epidemic spread of A. baumannii. However, even minor deviations from the recommended procedures leading to decreased concentrations or exposure times may play a role in nosocomial cross-transmission.

Use of germicides in the home and the healthcare setting: is there a relationship between germicide use and antibiotic resistance?

BACKGROUND

The spread of antibiotic-resistant pathogens represents an increasing threat in healthcare facilities. Concern has been expressed that the use of surface disinfectants and antiseptics may select for antibiotic-resistant pathogens.

OBJECTIVE

To review the scientific literature on whether there is a link between use of germicides (ie, disinfectants and antiseptics) and bacterial resistance to antibiotics. In addition, we will review whether antibiotic-resistant bacteria exhibit altered susceptibility to germicides that are recommended for use as disinfectants or antiseptics.

DESIGN

A review of the appropriate scientific literature.

RESULTS

In the laboratory, it has been possible to develop bacterial mutants with reduced susceptibility to disinfectants and antiseptics that also demonstrate decreased susceptibility to antibiotics. However, the antibiotic resistance described was not clinically relevant because the test organism was rarely a human pathogen, the altered level of antimicrobial susceptibility was within achievable serum levels for the antibiotic, or the antibiotic tested was not clinically used to treat the study pathogen. Similarly, wild-type strains with reduced susceptibility to disinfectants (principally, quaternary ammonium compounds) and antiseptics (principally, triclosan) have been reported. However, because the concentration of disinfectants used in the healthcare setting greatly exceeds the concentration required to kill strains with reduced susceptibility to disinfectants, the clinical relevance of these observations is questionable.

CONCLUSION

To date, there is no evidence that using recommended antiseptics or disinfectants selects for antibiotic-resistant organisms in nature. Disinfectants and antiseptics should be used when there are scientific studies demonstrating benefit or when there is a strong theoretical rationale for using germicides.

Does microbial resistance to biocides create a hazard to food hygiene?

Numerous reports are available on microbial resistance to antibiotics as well as to biocides. Instances of cross-resistance between these substance groups have been reported. Resistance, which is a genetically determined phenomenon, has to be distinguished from phenotypic adaptation processes, which are not hereditary. Adaptation can be avoided by rigorous cleaning and disinfection, avoiding concentrations of disinfectants below the microbicidal concentration. Resistance phenomena have to be divided into intrinsic and acquired resistance. Intrinsic resistance is the naturally greater resistance of certain microbial species compared to others. The term acquired resistance is used if certain strains of a microbial species differ significantly in their susceptibility to biocides compared to the average of this species. An overview of existing reports of resistance to different biocidal substances is given. In most of these reports, resistance is defined as an elevated minimum inhibitory concentration. The relevance of these data for disinfection processes, where microbicidal concentrations are applied, is discussed. Rotational use of different types of disinfectants, to avoid development of resistance, has been discussed controversially. Because of the unspecific mechanism of action of biocides, and the lack of scientific evidence for its need, rotational use of disinfectants is not recommended. In conclusion the risk of hazards in food production and processing caused by resistance to biocides is regarded as low.

Guidelines for the prophylaxis and treatment of methicillin-resistant Staphylococcus aureus (MRSA) infections in the UK

These evidence-based guidelines have been produced after a literature review of the treatment and prophylaxis of methicillin-resistant Staphylococcus aureus (MRSA) infection. The guidelines were further informed by antibiotic susceptibility data on MRSA from the UK. Recommendations are given for the treatment of common infections caused by MRSA, elimination of MRSA from carriage sites and prophylaxis of surgical site infection. There are several antibiotics currently available that are suitable for use in the management of this problem and potentially useful new agents are continuing to emerge.

In vitro activity of a novel compound, the metal ion chelating agent AQ+, against clinical isolates of Staphylococcus aureus

OBJECTIVES

To determine the efficacy of a novel antimicrobial compound, AQ+, against a genetically heterogeneous collection comprising 213 Staphylococcus aureus isolates from global sources. AQ+ is an aqueous preparation containing 0.5% 8-hydroxyquinoline.

METHODS

MICs were found for all the isolates tested using the BSAC microdilution method. Time-kill studies were performed according to NCCLS guidelines. Transmission electron microscopy (TEM) was used to view the ultrastructural effects of AQ+.

RESULTS

AQ+ was shown to strongly inhibit the growth of all isolates with a median MIC of 0.25% at a pH optimum of 9.2. Lowering the pH to 7.5 gave an approximately 4-fold reduction in efficacy and at pH 5.5 there was an approximately 8-fold reduction in efficacy. Methicillin-resistant S. aureus (MRSA) as well as vancomycin-intermediate S. aureus were shown to be as equally susceptible to AQ+ as methicillin-susceptible S. aureus. Time-kill curves for AQ+ were similar to those for gentamicin. TEM showed that AQ+ actively disrupts the cell wall of S. aureus leading to cell lysis.

CONCLUSIONS

These results suggest that AQ+ has strong antimicrobial activity and may be useful in preparations to reduce nasal and skin carriage of MRSA.

[Activity of antiseptic catheter lubricants against methicillin-resistant Staphylococcus aureus (MRSA)]

In recent years, general and urinary tract infections caused by methicillin-resistant Staphylococcus aureus (MRSA) have became an increasing problem worldwide. Catheterization of the urinary bladder is one of the most significant risk factors for MRSA contamination of the urine. In vitro tests have documented the antimicrobial activity of the catheter lubricants Instillagel and Endosgel against MRSA specimens within 5 min. These findings support recommending the use of these lubricants in high-risk patients in hospitals and old people's homes for prophylaxis of MRSA bacteriuria.

Potential impact of increased use of biocides in consumer products on prevalence of antibiotic resistance

There has recently been much controversy surrounding the increased use of antibacterial substances in a wide range of consumer products and the possibility that, as with antibiotics, indiscriminate use of biocides might contribute to the overall pattern of susceptibility in the general environment and in the clinic. Such speculation, based on the isolation of resistant mutants from in vitro monoculture experiments, is not reflected by an emergence of biocide-resistant strains in vivo. This review provides a broad coverage of the biocide and resistance literature and evaluates the potential risks, perceived from such laboratory monoculture experiments, against evidence gathered over 50 years of field studies. An explanation for the continued effectiveness of broad-spectrum biocidal agents against the decline in efficacy of therapeutic agents is provided based on the fitness costs of resistance and the ubiquity of naturally occurring substances that possess antibacterial effect. While we conclude from this review of the literature that the incorporation of antibacterial agents into a widening sphere of personal products has had little or no impact on the patterns of microbial susceptibility observed in the environment, the associated risks remain finite. The use of such products should therefore be associated with a clear demonstration of added value either to consumer health or to the product life. Hygienic products should therefore be targeted to applications for which the risks have been established.

Association between intensity of chlorhexidine use and micro-organisms of reduced susceptibility in a hospital environment

The potential for emergence of resistance to biocides has been a concern in recent years. This study tested whether an association exists between the intensity of chlorhexidine use and chlorhexidine susceptibility of micro-organisms isolated from patients in different clinical areas in an acute-care general hospital. Organisms frequently involved in nosocomial infections in the hospital were chosen for study over a six week period: Staphylococcus aureus (60 isolates), coagulase-negative staphylococci (48), Klebsiella pneumoniae (32), Pseudomonas aeruginosa (60), Acinetobacter baumannii (16) and Candida albicans (35). An index of chlorhexidine exposure for each clinical unit was derived for the year preceding organism collection. Chlorhexidine susceptibility was evaluated using agar incorporation minimum inhibitory concentrations (MICs) and disk diffusion. A statistically significant inverse correlation was shown between intensity of chlorhexidine use and the overall susceptibility of all study organisms taken together. There was no association when individual taxa were considered. These findings must be interpreted with caution considering that greater use of chlorhexidine is likely to occur in difficult clinical disciplines where antibiotic use, invasive procedures and other intensive care-related procedures, cross-infection and immunosuppression are all potential confounding factors. There was an excellent correlation between MICs and disk testing, suggesting that disk diffusion might be useful in studies involving more than one biocide.

Antibiotic resistance as an indicator of bacterial chlorhexidine susceptibility

The antibiotic and chlorhexidine (CHX) susceptibility of 70 distinct clinical isolates: Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Acinetobacter baumannii, Staphylococcus aureus (not MRSA), Streptococcus pyogenes and Enterococcus faecalis (10 of each) were tested using minimal bactericidal (MBC) and/or minimal inhibitory (MIC) concentrations. Non-fermentative bacteria tolerated CHX at high concentrations; Gram-positive cocci, especially S. pyogenes, were the most susceptible. We found a good correlation between CHX and antibiotic susceptibility in both MIC and MBC among Gram-negative bacteria, and mainly in MBC among Gram-positive bacteria. Resistance to ciprofloxacin, imipenem, cefotaxime, ceftazidime, gentamicin and aztreonam appeared to indicate increased CHX resistance among Gram-negative bacteria. This finding gives clinicians the ability to predict CHX susceptibility according to routine antibiotic resistance testing.

Effectiveness of hand-cleansing agents for removing methicillin-resistant Staphylococcus aureus from contaminated hands

OBJECTIVE

The effectiveness of hand-cleansing agents in removing a hospital strain of methicillin-resistant Staphylococcus aureus from artificially contaminated hands of five volunteers was studied.

DESIGN

The products used were plain liquid soap, ethyl alcohol 70% (by weight), 10% povidone-iodine liquid soap (PVP-I), and chlorhexidine gluconate (4%) detergent. The experiments were performed using a Latin square statistical design, with two 5x4 randomized blocks. The removal rates of S aureus cells from contaminated fingertips were estimated by analysis of variance, the response variable being the log10 reduction factor (RF), ie, log10 of the initial counts minus log10 of the final counts. In the first and second blocks, the fingertips of the volunteers were contaminated in mean with 3.76 log10 colony-forming units ([CFU] light-contamination hand) and 6.82 log10 CFU (heavy-contamination hand), respectively.

RESULTS

In the first block, there were significant differences between treatments (P<.05). The 10% PVP-I (RF, 3.76) and 70% ethyl alcohol (RF, 3.51) had significantly higher removal rates than plain liquid soap (RF, 1.96) and 4% chlorhexidine (RF, 1.91). In the second block, 10% PVP-I (RF, 4.39) and 70% ethyl alcohol (RF, 3.27) also were significantly more effective than plain liquid soap (RF, 1.77) and 4% chlorhexidine (RF, 1.37; P<.05). Plain liquid soap was significantly more effective than chlorhexidine (4%) detergent.

CONCLUSIONS

The results suggest that 10% PVP-I and 70% ethyl alcohol may be the most effective hand-cleansing agents for removing methicillin-resistant S aureus strain from either lightly or heavily contaminated hands.

Development of resistance to chlorhexidine diacetate in Pseudomonas aeruginosa and the effect of a "residual" concentration

Stable resistance in Pseudomonas aeruginosa NCIMB 10421 was obtained by step-wise exposure to gradually increasing concentrations of chlorhexidine diacetate (CHX). Repeated exposure to a proposed "residual" (sub-MIC) concentration of CHX also created stable resistance. Resistance was also developed by a single exposure to the "residual" concentration of CHX, but this was unstable. Similar experiments with Escherichia coli and CHX or cetylpyridinium chloride resulted in no significant increase in resistance. Antibiotic susceptibility profiles of the CHX-resistant P. aeruginosa cultures showed no cross-resistance, although some of the cultures were resistant to benzalkonium chloride.

Evaluation of chlorhexidine and povidone iodine activity against methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus faecalis using a surface test

Most published studies of the activity of biocides against methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE) have been based on suspension tests. This study was undertaken to provide information on the effect of chlorhexidine and povidone iodine on bacteria dried on to surfaces, a situation in which biocide activity is known to be reduced. The inactivation of MRSA (10 strains), methicillin-sensitive Staphylococcus aureus (MSSA, 10 strains), VRE (nine strains) and vancomycin-sensitive Enterococcus faecalis (VSE, 10 strains) by 0.5% aqueous chlorhexidine gluconate or 10% povidone iodine was evaluated by applying the European surface test method. Povidone iodine was equally active against resistant and sensitive strains of both species with microbicidal effects (ME), i.e. the log(10)concentration of micro-organisms compared with controls treated with distilled water, after 1.5 min of 3.14 and 3.49 for VRE and VSE respectively, and 3.47 and 3.78 for MRSA and MSSA. Chlorhexidine was equally active against VRE and VSE (ME 3.37 vs. 3. 56 after 7 min, respectively), but was significantly less active against MRSA as opposed to MSSA (ME 3.07 vs. 3.83 after 10 min, P= 0. 017).

Antibiotic and biocide resistance in methicillin-resistant Staphylococcus aureus and vancomycin-resistant enterococcus

Concern has been growing regarding the potential of antibiotic and disinfectant co-resistance in clinically important bacteria. In this study, the susceptibilities of methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-sensitive Staphylococcus aureus (MSSA) to chlorhexidine (CHX), the quaternary ammonium compounds cetylpyridinium chloride (CPC) and benzalkonium chloride (BC), triclosan, dibromopropamidine isethionate (DBPI) and triclocarban were compared. MRSA exhibited low-level resistance to CHX and the QACs, with MICs of 1.5 to 3-fold (CHX), and 2 to 4-fold (QACs) higher than MSSA. However, the MIC values for MRSA ranged between 0.025 (the MIC of MSSA) and 1 microg/mL with triclosan, and between <5 (the MIC of MSSA) and 75 microg/mL with DPBI. Nevertheless, these strains remain relatively sensitive to most of these antimicrobial agents. The bactericidal efficacy of CHX, CPC and DBPI (with the exception of one strain) correlated with their MIC value. This was not observed using triclosan; MRSA and MSSA strains were equally susceptible to its killing effect, regardless of MIC. The permeabilizing agent, ethylenediamine tetraacetic acid (EDTA) was unable to potentiate the antibacterial activities of the biocides against any of the strains tested. Attempts to select for staphylococcal strains with increased resistance to triclosan, CPC or CHX, using disc diffusion, step-wise broth, or repeated exposure/recovery technique, were only partially successful, and resistance was found to be unstable. The susceptibilities of vancomycin-resistant enterococcus (VRE) and vancomycin-sensitive enterococcus (VSE) to the biocides were also compared and found to be similar both in terms of MIC testing and time-kill studies.

Susceptibility in vitro of Helicobacter pylori to cetylpyridinium chloride

The antimicrobial agent cetylpyridinium chloride (CPC) which is used in therapy of oro-pharyngeal infections and for antiseptic treatment of the oral cavity is active against different bacterial species. Determination of the minimal inhibitory concentration (MIC) using the agar dilution technique revealed that the gastric pathogen Helicobacter pylori in vitro is highly susceptible to CPC as indicated by an MIC of 10 microM (3.4 microg ml(-1)) which was significantly lower than the MIC of CPC against other bacterial species, which were analyzed in comparison to H. pylori. Bacteria of the genus Campylobacter, various Streptococcus spp., Staphylococcus aureus and Escherichia coli showed higher MICs ranging from 100 microM to 2 mM. In summary, this finding renders CPC-containing drugs candidates possibly useful for eradication or for the prevention of transmission of the gastric pathogen.

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.

Antiseptics: a forgotten weapon in the control of antibiotic resistant bacteria in hospital and community settings?

The aim of this study was to ascertain the activity of a selection of widely-used antiseptic/disinfectant agents against antibiotic resistant bacteria and strains isolated from patients infected with clinically significant species. Four antiseptic agents (Dettol, Dettol Hospital Concentrate, Savlon and Betadine) were tested against Staphylococcus aureus, Methicillin Resistant S. aureus (MRSA), Enterococcus hirae, Vancomicin Resistant Enterococcus sp (VRE), Escherichia coli and E. coli 0157. The antiseptics were applied at recommended use dilutions and at a half and a quarter of those concentrations in a standard suspension test (EST). Organic material was added to mimic the presence of blood, protein and other such contaminants to be found in the clinical situation. All antiseptics tested were effective against both the antibiotic sensitive and antibiotic resistant strains of S. aureus and E. hirae as well as normal and clinical strains of E. coli at recommended concentrations. All but Betadine were also effective against the antibiotic resistant bacteria at a half and a quarter of normal concentration. The iodine containing antiseptic, however, failed the test against MRSA at a half normal concentration and showed virtually no activity against MRSA at a quarter normal concentration.