Antiseptics and disinfectants: activity, action, and resistance

Antiplaque biocides and bacterial resistance: a review

Modern dentistry emphasizes the importance of dental plaque control to improve oral health. The use of oral care formulations with antiplaque biocides plays a crucial role in patient-directed approaches for plaque control. The antiplaque efficacies of these formulations have been extensively studied in many long-term clinical studies designed in accordance with well-accepted guidelines. The results from these studies conclusively demonstrate that long-term use of oral care formulations with well-known antiplaque biocides such as chlorhexidine and triclosan reduce supragingival plaque and gingivitis. This review summarizes microbiological results from clinical studies conducted with oral care formulations containing antiplaque biocides. Results from a number of long-term clinical studies conducted under real-life use conditions indicate no adverse alterations in the bacteria found in dental plaque or emergent microbial resistance. Additionally, microbial sampling of dental plaque subsequent to extended use of antiplaque biocides reveals no increase in resistant microflora. Large numbers of common oral bacteria isolated from patients using chlorhexidine indicate no increase in microbial resistance to chlorhexidine or to commonly used antibiotics. The effects of antiplaque biocides containing oral care formulations on dental plaque that exists naturally as a biofilm are examined. These formulations contain biocide, surfactants, polymers and other components that are effective against the biofilm. In summary, the results of studies on the real-life use of oral care formulations with antiplaque biocides show no emergence of resistant microflora or alterations of the oral microbiota, while such formulations have been found to provide the benefits of reducing plaque and gingivitis.

Activity of disinfectants against Gram-negative bacilli isolated from patients undergoing lung transplantation for cystic fibrosis

Lung transplant recipients with cystic fibrosis are frequently colonized with antibiotic-resistant bacteria. We evaluated the in vitro activity of 5 disinfectants frequently used in cardiac surgery against strains of Burkholderia cepacia and Pseudomonas aeruginosa isolated from patients undergoing sequential single lung transplantation. Our results suggest that the activity of Taurolin and Noxyflex is superior to conventional disinfectants.

Postadaptational resistance to benzalkonium chloride and subsequent physicochemical modifications of Listeria monocytogenes

Many studies have demonstrated that bacteria, including Listeria monocytogenes, are capable of adapting to disinfectants used in industrial settings after prolonged exposure to sublethal concentrations. However, the consequent alterations of the cell surface due to sanitizer adaptation of this pathogen are not fully understood. Two resistant and four sensitive L. monocytogenes strains from different sources were progressively subcultured with increasing sublethal concentrations of a surfactant, benzalkonium chloride (BC). To evaluate the effects of acquired tolerance to BC, parent and adapted strains were compared by using several morphological and physiological tests. Sensitive strains showed at least a fivefold increase in the MIC, while the MIC doubled for resistant strains after the adaptation period. The hydrophobicities of cells of parent and adapted strains were similar. Serological testing indicated that antigen types 1 and 4 were both present on the cell surface of adapted cells. The data suggest that efflux pumps are the major mechanism of adaptation in sensitive strains and are less important in originally resistant isolates. A different, unknown mechanism was responsible for the original tolerance of resistant isolates. In an originally resistant strain, there was a slight shift in the fatty acid profile after adaptation, whereas sensitive strains had similar profiles. Electron micrographs revealed morphological differences after adaptation. The changes in cell surface antigens, efflux pump utilization, and fatty acid profiles suggest that different mechanisms are used by resistant and sensitive strains for adaptation to BC.

Chlorhexidine resistance in antibiotic-resistant bacteria isolated from the surfaces of dispensers of soap containing chlorhexidine

Bacterial contamination with pan-resistant Acinetobacter and Klebsiella, multidrug-resistant Pseudomonas, and methicillin-resistant Staphylococcus aureus (MRSA) was noted on the surfaces of dispensers of hand soap with 2% chlorhexidine. Gram-negative isolates could multiply in the presence of 1% chlorhexidine. In contrast, MRSA was inhibited in vitro by chlorhexidine at concentrations as low as 0.0019%.

Pine oil cleaner-resistant Staphylococcus aureus: reduced susceptibility to vancomycin and oxacillin and involvement of SigB

Mutants of Staphylococcus aureus strain COL resistant to a household pine oil cleaner (POC) were isolated on laboratory media containing POC. S. aureus mutants expressing the POC resistance (POC(r)) phenotype also demonstrate reduced susceptibility to the cell wall-active antibiotics vancomycin and oxacillin. The POC(r) phenotype is reliant on the S. aureus alternative transcription factor SigB, since inactivation of sigB abolished expression of elevated POC resistance and the reductions in vancomycin and oxacillin susceptibilities. The isolation of suppressor mutants of COLsigB::kan, which maintain the sigB::kan allele, indicates that the POC(r) phenotype can also be expressed to a lesser degree via a sigB-independent mechanism. These results bolster a growing body of reports suggesting that common disinfectants can select for bacteria with reduced susceptibilities to antibiotics. A series of in vitro-selected glycopeptide-intermediate S. aureus (GISA) isolates also expressed reductions in POC susceptibility compared to parent strains. Viewed collectively, our evidence suggests that mutations leading to the POC(r) phenotype may also be involved with the mechanism that leads to the GISA phenotype.

Action of chlorhexidine digluconate against yeast and filamentous forms in an early-stage Candida albicans biofilm

An in situ method for sensitive detection of differences in the action of chlorhexidine against subpopulations of cells in Candida albicans biofilms is described. Detection relies on monitoring the kinetics of propidium iodide (PI) penetration into the cytoplasm of individual cells during dosing with chlorhexidine. Accurate estimation of the time for delivery of the dosing concentration to the substratum was facilitated by using a flow cell system for which transport to the interfacial region was previously characterized. A model was developed to quantify rates of PI penetration based on the shape of the kinetic data curves. Yeast were seeded onto the substratum, and biofilm formation was monitored microscopically for 3 h. During this period a portion of the yeast germinated, producing filamentous forms (both hyphae and pseudohyphae). When the population was subdivided on the basis of cell morphology, rates of PI penetration into filamentous forms appeared to be substantially higher than for yeast forms. Based on the model, rates of penetration were assigned to individual cells. These data indicated that the difference in rates between the two subpopulations was statistically significant (unpaired t test, P < 0.0001). A histogram of rates and analysis of variance indicated that rates were approximately equally distributed among different filamentous forms and between apical and subapical segments of filamentous forms.

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.

Frequency of disinfectant resistance genes and genetic linkage with beta-lactamase transposon Tn552 among clinical staphylococci

A total of 61 strains of Staphylococcus aureus and 177 coagulase-negative staphylococcal strains were isolated from the blood of patients with bloodstream infections and from the skin of both children under cancer treatment and human immunodeficiency virus-positive patients. The MIC analyses revealed that 118 isolates (50%) were resistant to quaternary ammonium compound-based disinfectant benzalkonium chloride (BC). The frequencies of resistance to a range of antibiotics were significantly higher among BC-resistant staphylococci than among BC-sensitive staphylococci. Of 78 BC-resistant staphylococcal isolates, plasmid DNA from 65 (83%), 2 (3%), 43 (55%), and 15 (19%) isolates hybridized to qacA or -B (qacA/B), qacC, blaZ, and tetK probes, respectively. The qacA/B and blaZ probes hybridized to the same plasmid in 19 (24%) staphylococcal strains. The plasmids harboring both qacA/B and blaZ genes varied from approximately 20 to 40 kb. The Staphylococcus epidermidis Fol62 isolate, harboring multiresistance plasmid pMS62, contained qacA/B and blaZ together with tetK. Molecular and genetic studies indicated different structural arrangements of blaZ and qacA/B, including variable intergenic distances and transcriptional directions of the two genes on the same plasmid within the strains. The different organizations may be due to the presence of various genetic elements involved in cointegration, recombination, and rearrangements. These results indicate that qac resistance genes are common and that linkage between resistance to disinfectants and penicillin resistance occurs frequently in clinical isolates in Norway. Moreover, the higher frequency of antibiotic resistance among BC-resistant strains indicates that the presence of either resistance determinant selects for the other during antimicrobial therapy and disinfection in hospitals.

Adaptive resistance to benzalkonium chloride, amikacin and tobramycin: the effect on susceptibility to other antimicrobials

AIMS

To produce strains of antimicrobial-resistant Pseudomonas aeruginosa via adaptation to benzalkonium chloride, amikacin and tobramycin and to then examine the incidence, or otherwise, of cross-resistance between antibiotics and between antibiotics and benzalkonium chloride.

METHODS AND RESULTS

Adaptation was obtained by progressive subculturing in subinhibitory concentrations of the antimicrobials. Pseudomonas aeruginosa NCIMB 10421 adapted to grow in high concentrations of benzalkonium chloride (BC) had lower MIC to antibiotics than the wild type, whereas Ps. aeruginosa adapted to grow in antibiotics had greater MIC to benzalkonium by a small degree.

CONCLUSIONS

Adaptive resistance to BC of Ps. aeruginosa generally produced cultures with a decrease in resistance to several antibiotics. Adaptive resistance to the aminoglycosides Ak and Tm produced a low-level increase in tolerance to BC. The adaptive mechanisms of resistance appear to be different for the different types of antimicrobials used.

SIGNIFICANCE AND IMPACT OF THE STUDY

The relationships between biocide and antibiotic resistance are complex. It appears, from this study, that an organism resistant to a common biocide can become sensitive to antibiotics, but the converse was not true. Could this observation be used in a strategy to alleviate antibiotic resistance?

Analysis of the properties of spores of Bacillus subtilis prepared at different temperatures

AIMS

To determine the effect of sporulation temperature on Bacillus subtilis spore resistance and spore composition.

METHODS AND RESULTS

Bacillus subtilis spores prepared at temperatures from 22 to 48 degrees C had identical amounts of dipicolinic acid and small, acid-soluble proteins but the core water content was lower in spores prepared at higher temperatures. As expected from this latter finding, spores prepared at higher temperatures were more resistant to wet heat than were spores prepared at lower temperatures. Spores prepared at higher temperatures were also more resistant to hydrogen peroxide, Betadine, formaldehyde, glutaraldehyde and a superoxidized water, Sterilox. However, spores prepared at high and low temperatures exhibited nearly identical resistance to u.v. radiation and dry heat. The cortex peptidoglycan in spores prepared at different temperatures showed very little difference in structure with only a small, albeit significant, increase in the percentage of muramic acid with a crosslink in spores prepared at higher temperatures. In contrast, there were readily detectable differences in the levels of coat proteins in spores prepared at different temperatures and the levels of at least one coat protein, CotA, fell significantly as the sporulation temperature increased. However, this latter change was not due to a reduction in cotA gene expression at higher temperatures.

CONCLUSIONS

The temperature of sporulation affects a number of spore properties, including resistance to many different stress factors, and also results in significant alterations in the spore coat and cortex composition.

SIGNIFICANCE AND IMPACT OF THE STUDY

The precise conditions for the formation of B. subtilis spores have a large effect on many spore properties.

Comparison of adhesion of the food spoilage bacterium Shewanella putrefaciens to stainless steel and silver surfaces

AIMS

To compare the number of attached Shewanella putrefaciens on stainless steel with different silver surfaces, thus evaluating whether silver surfaces could contribute to a higher hygienic status in the food industry.

METHODS AND RESULTS

Bacterial adhesion to three types of silver surface (new silver, tarnished silver and sulphide-treated silver) was compared with adhesion to stainless steel (AISI 316) using the Malthus indirect conductance method to estimate the number of cfu cm(-2). The number of attached bacteria on new silver surfaces was lower than on steel for samples taken after 24 h. However, this was not statistically significant (P > 0.05). The numbers of attached bacteria were consistently lower when tarnished silver surfaces were compared with stainless steel and some, but not all, experiments showed statistical significance (P < 0.05). Treating new silver with sulphide to reproduce a tarnished silver surface did not result in a similar lowering of adhering cells when compared with steel (P > 0.05).

CONCLUSIONS

New or tarnished silver surfaces caused a slight reduction in numbers of attached bacteria; however, the difference was only sometimes statistically significant.

SIGNIFICANCE AND IMPACT OF THE STUDY

The lack of reproducibility in differences in numbers adhering to the different surfaces and lack of statistical significance between numbers of adhered viable bacteria do not indicate that the tested silver surfaces can be used to improve hygienic characteristics of surfaces in the food industry.

Genetic linkage between resistance to quaternary ammonium compounds and beta-lactam antibiotics in food-related Staphylococcus spp

Little is known about the occurrence of antimicrobial resistance determinants in staphylococci isolated from food and food processing industries. Quaternary ammonium compound (QAC)-resistant coagulase-negative staphylococci (CNS) isolated from food and food-processing industries were investigated for the presence of genetic determinants (qacA/B and qacC/smr) encoding resistance to the QAC benzalkonium chloride (BC), several antibiotic resistance genes, and staphylococcal insertion sequences IS257 and IS256. Six qacA/B-harboring strains were resistant to penicillin and hybridized to a blaZ probe. The qacA/B and blaZ probes hybridized to plasmids of similar size in three isolates. Molecular and genetic characterization of the 23-kb plasmid (pST6) of Staphylococcus epidermidis St.6 revealed the presence of qacB adjacent to an incomplete beta-lactamase transposon Tn552 encoding the gene cluster blaZ, blaR, and blaI. Sequence analysis of flanking regions and the intergenic region between blaZ and qacB revealed the presence of IS257 downstream of blaZ as well as sin and binR between blaZ and qacB. In the three other BC and penicillin-resistant strains, the qacA/B and blaZ genes were located on separate plasmids. A qacC harboring S. epidermidis strain (St.17) also hybridized to tetK (tetracycline resistance) and ermB (erythromycin resistance) genes. The individual genes were located on separate plasmids, suggesting no linkage between QAC and antibiotic resistance determinants. Plasmid-free Staphylococcus aureus RN4220 allowed uptake of the pST6 plasmid DNA, indicating that the resistance genes could potentially be transferred to pathogens under selective stress. In conclusion, presence of both resistance determinants could lead to co-selection during antimicrobial therapy or disinfection in hospitals or in food industries.

Effectiveness of chemical sanitizers against Campylobacter jejuni-containing biofilms

Survival of Campylobacter jejuni in mixed-culture biofilms was determined after treatment with chemical sanitizers including chlorine, quaternary ammonia, peracetic acid (PAA), and a PAA/peroctanoic acid mixture (PAA/POA). Biofilm-producing bacteria (gram-positive rods, Y1 and W1) were isolated from chicken house nipple drinkers. A meat plant isolate (Pseudomonas sp.) was also included as a biofilm producer. Two-day-old biofilms grown on polyvinyl chloride (PVC) plastic coupons in R2A broth at 12 degrees C were incubated with 10(6) CFU/ml C jejuni for 6 h to allow attachment. The coupons were then rinsed and incubated in fresh media for an additional 24 h. C. jejuni-containing biofilms were detached by vortexing with glass beads in modified brucella broth, which was then enumerated for C. jejuni on selective/differential media. The presence of biofilm enhanced (P < 0.01) the attachment and survival of C. jejuni After the 24-h incubation, only 20 CFU/cm2 of C. jejuni were recovered from the control without biofilms compared to 2,500 to 5,000 CFU/cm2 in samples with preexisting biofilms. The presence of biofilm microflora decreased (P < 0.01) the effectiveness of sanitizers against C. jejuni. Chlorine was the most effective sanitizer since it completely inactivated C. jejuni in the biofilms after treatment at 50 ppm for 45 s. C. jejuni in biofilms was susceptible to all sanitizers tested but was not completely inactivated by treatment with quaternary ammonia, PAA, or PAA/POA mixture at 50 and 200 ppm for 45 s.

Structure-based classification of antibacterial activity

The aim of this study was to develop a simple quantitative structure-activity relationship (QSAR) for the classification and prediction of antibacterial activity, so as to enable in silico screening. To this end a database of 661 compounds, classified according to whether they had antibacterial activity, and for which a total of 167 physicochemical and structural descriptors were calculated, was analyzed. To identify descriptors that allowed separation of the two classes (i.e. those compounds with and without antibacterial activity), analysis of variance was utilized and models were developed using linear discriminant and binary logistic regression analyses. Model predictivity was assessed and validated by the random removal of 30% of the compounds to form a test set, for which predictions were made from the model. The results of the analyses indicated that six descriptors, accounting for hydrophobicity and inter- and intramolecular hydrogen bonding, provided excellent separation of the data. Logistic regression analysis was shown to model the data slightly more accurately than discriminant analysis.

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

AIMS

To determine the mechanism of killing of spores of Bacillus subtilis by ortho-phthalaldehyde (OPA), an aromatic dialdehyde currently in use as an antimicrobial agent.

METHODS AND RESULTS

OPA is sporicidal, although spores are much more OPA resistant than are vegetative cells. Bacillus subtilis mutants deficient in DNA repair, spore DNA protection and spore coat assembly have been used to show that (i) the coat appears to be a major component of spore OPA resistance, which is acquired late in sporulation of B. subtilis at the time of spore coat maturation, and (ii) B. subtilis spores are not killed by OPA through DNA damage but by elimination of spore germination. Furthermore, OPA-treated spores that cannot germinate are not recovered by artificial germinants or by treatment with NaOH or lysozyme.

CONCLUSIONS

OPA appears to kill spores by blocking the spore germination process.

SIGNIFICANCE AND IMPACT OF THE STUDY

This work provides information on the mechanism of spore resistance to, and spore killing by, the disinfectant, OPA.

Mechanisms contributing to hypochlorous acid resistance of a Salmonella isolate from a poultry-processing plant

AIMS

We have recently reported the isolation of Salmonella that have acquired tolerance to hypochlorous acid (HOCl) (Mokgatla et al. 1998). The aim of this work was to investigate possible protective mechanisms involved in the increased tolerance to HOCl of a selected resistant strain.

METHODS AND RESULTS

One resistant (Salmonella 104) and one sensitive (Salmonella 81) isolate in exponential phase were exposed to HOCl at a final active concentration of 28 mg l(-1). Cultures were assayed for superoxide dismutase and catalase activity, as well as for four membrane-bound dehydrogenases (malate, lactate, glutamate and glucose-6-phosphate dehydrogenase). The degree of single-strand breaks in genomic DNA was analysed and lipopolysaccharide profiles determined. The resistant Salmonella isolate differed from the sensitive isolate in a number of ways. It responded within 10 min of exposure by producing catalase and decreasing the activity levels of four membrane-bound dehydrogenases. This combination would lead to lower levels of hydroxyl radicals and singlet oxygen, moieties thought to be integrally involved in the antibacterial action of HOCl. Furthermore, the resistant strain did not display the same degree of DNA damage as did the sensitive strain.

CONCLUSIONS

Strain 104 is believed to grow in the presence of 28 mg l(-1) HOCl by protecting itself against HOCl by decreasing the levels of species that could react with HOCl to generate toxic reactive oxygen radicals and by improved DNA damage repair mechanisms.

SIGNIFICANCE AND IMPACT OF THE STUDY

The occurrence of Salmonella able to grow in the presence of 28 mg l(-1) HOCl is of relevance to the food-processing and drinking water treatment industries as these strains would survive sanitation regimes.

Cloning of a cation efflux pump gene associated with chlorhexidine resistance in Klebsiella pneumoniae

Expression libraries of a chlorhexidine-resistant Klebsiella pneumoniae strain were constructed and transformed into Escherichia coli XLOLR. Twenty chlorhexidine-resistant transformants were obtained after selection. All clones contained a novel 903-nucleotide locus. Its sequences were compatible with a cation efflux pump, and the locus was thus designated as cepA. Retransformation using cepA-containing plasmids conferred chlorhexidine resistance to both XLOLR and a chlorhexidine-sensitive K. pneumoniae strain. Therefore, CepA is associated with chlorhexidine resistance and may act as a cation efflux pump.

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.

Mechanisms of killing spores of Bacillus subtilis by acid, alkali and ethanol

AIMS

To determine the mechanisms of killing of Bacillus subtilis spores by ethanol or strong acid or alkali.

METHODS AND RESULTS

Killing of B. subtilis spores by ethanol or strong acid or alkali was not through DNA damage and the spore coats did not protect spores against these agents. Spores treated with ethanol or acid released their dipicolinic acid (DPA) in parallel with spore killing and the core wet density of ethanol- or acid-killed spores fell to a value close to that for untreated spores lacking DPA. The core regions of spores killed by these two agents were stained by nucleic acid stains that do not penetrate into the core of untreated spores and acid-killed spores appeared to have ruptured. Spores killed by these two agents also did not germinate in nutrient and non-nutrient germinants and were not recovered by lysozyme treatment. Spores killed by alkali did not lose their DPA, did not exhibit a decrease in their core wet density and their cores were not stained by nucleic acid stains. Alkali-killed spores released their DPA upon initiation of spore germination, but did not initiate metabolism and degraded their cortex very poorly. However, spores apparently killed by alkali were recovered by lysozyme treatment.

CONCLUSIONS

The data suggest that spore killing by ethanol and strong acid involves the disruption of a spore permeability barrier, while spore killing by strong alkali is due to the inactivation of spore cortex lytic enzymes.

SIGNIFICANCE AND IMPACT OF THE STUDY

The results provide further information on the mechanisms of spore killing by various chemicals.

A survey of reprocessing methods, residual viable bioburden, and soil levels in patient-ready endoscopic retrograde choliangiopancreatography duodenoscopes used in Canadian centers

OBJECTIVES

To obtain information about current reprocessing practices and to obtain samples from the biopsy channel to quantitate soil levels and bioburden in patient-ready flexible duodenoscopes used for endoscopic retrograde choliangiopancreatography (ERCP).

DESIGN

Participating centers were sent a questionnaire and a kit for on-site collection of samples from the biopsy channel of the duodenoscope.

SETTING

Thirty-seven hospitals from across Canada participated. The only criterion was that they currently used and reprocessed flexible duodenoscopes for ERCP procedures.

METHODS

The questionnaire obtained information on reprocessing practices. The kit included a detailed instruction booklet outlining sample collection and all of the tubes, sterile water, and brushes needed for it. Samples were collected on-site from all ERCP scopes in each center on Monday morning and shipped by overnight courier on ice to the research center. Each sample was assayed by routine microbiologic methods for total viable count and protein, blood, carbohydrate, and endotoxin levels.

RESULTS

Microbial overgrowth was present in 7% of 119 scope samples. Cleaning appeared to be reasonably well done in most of the centers, and 43% of the centers were in total compliance with basic national guidelines. The data from the scope samples indicated that there was significantly greater buildup of protein, carbohydrate, and endotoxin associated with ERCP scopes from centers using glutaraldehyde, compared with those using peracetic acid. Carbohydrate was the soil component detected most frequently and in the highest concentration in scope channels.

CONCLUSIONS

Although cleaning was generally well done, areas for improvement included ensuring the availability of written reprocessing protocols, immersion of scopes during manual cleaning, use of adequate fluid volume for rinsing, adequate drying of scopes prior to storage, and the separation of ERCP valves from scopes during storage.

Efficacy of instrumentation techniques and irrigation regimens in reducing the bacterial population within root canals

The purpose of this study was to compare the in vitro intracanal bacterial reduction produced by using two instrumentation techniques and different irrigation methods. Root canals inoculated with Enterococcus faecalis were prepared by using the following techniques and irrigants: alternated rotary motions (ARM) technique, hand nickel-titanium files and 2.5% sodium hypochlorite (NaOCl) as irrigant; ARM technique and combined irrigation with 2.5% NaOCl and citric acid; ARM technique and combined irrigation with 2.5% NaOCl and 2% chlorhexidine gluconate; and Greater Taper rotary files, using 2.5% NaOCl as irrigant. Controls were instrumented by using the ARM technique and irrigated with sterile saline. Canals were sampled before and after preparation. After serial dilution, samples were plated onto Mitis-Salivarius agar, and the colony forming units that were grown were counted. All test techniques and solutions significantly reduced the number of bacterial cells within the root canal (p < 0.05). There was no significant difference between the experimental groups (p > 0.05). Nonetheless, all of them were significantly more effective than the control group (p < 0.05). These findings support the importance of using antimicrobial irrigants during the chemomechanical preparation, regardless of the solutions or instrumentation techniques used.

Microbial overgrowth in water perfusion equipment for esophageal/rectal motility

BACKGROUND

There are few data on microbial levels in water used during the assessment of GI motility. Patients undergoing such procedures may be ingesting water with unacceptably high levels of bacteria.

METHODS

Samples of water from the reservoir and tubing from water perfusion motility equipment were taken and quantitatively assessed to determine the concentration of viable aerobic and facultative microorganisms. Interventions were evaluated to determine which reprocessing schedule ensures absence of overgrowth by microbes within the system during storage.

RESULTS

Bacterial overgrowth can occur in manometry systems with bacterial levels of greater than 10(4) colony-forming units (cfu)/mL in the water from both the reservoir and the tubing. Organisms detected included Serratia marcescens, Burkholderia species, and other gram-negative nonfermentors. Eradication of these organisms was difficult, and the only intervention that consistently ensured bacterial water levels below 200 cfu/mL (i.e., within potable water guidelines) was retrofitting of the pump/tubing with new components combined with a monthly hydrogen peroxide decontamination protocol and a daily drying protocol.

CONCLUSIONS

The entire tubing path of motility equipment must be stored dry to prevent microbial overgrowth. Additionally, implementation of a motility equipment quality assurance program with water testing 3 to 4 times per year is recommended to ensure that overgrowth is not a problem.

Biological weapons--a primer for microbiologists

Biological weapons are not new. Biological agents have been used as instruments of warfare and terror for thousands of years to produce fear and harm in humans, animals, and plants. Because they are invisible, silent, odorless, and tasteless, biological agents may be used as an ultimate weapon-easy to disperse and inexpensive to produce. Individuals in a laboratory or research environment can be protected against potentially hazardous biological agents by using engineering controls, good laboratory and microbiological techniques, personal protective equipment, decontamination procedures, and common sense. In the field or during a response to an incident, only personal protective measures, equipment, and decontamination procedures may be available. In either scenario, an immediate evaluation of the situation is foremost, applying risk management procedures to control the risks affecting health, safety, and the environment. The microbiologist and biological safety professional can provide a practical assessment of the biological weapons incident to responsible officials in order to help address microbiological and safety issues, minimize fear and concerns of those responding to the incident, and help manage individuals potentially exposed to a threat agent.

Killing of spores of Bacillus subtilis by peroxynitrite appears to be caused by membrane damage

During an infection of a higher eukaryote, dormant spores of a Bacillus species have been previously shown to be present in cells that can generate the toxic agent peroxynitrite (PON). Dormant spores of Bacillus subtilis were much more resistant to killing by PON than were growing cells, and spore-coat alteration or removal greatly decreased PON resistance. Spores were not killed by PON through DNA damage and lost no dipicolinic acid (DPA) during PON treatment. However, PON-killed spores lost DPA during subsequent heat treatments that caused much less DPA release from untreated spores. Although dead, the PON-killed spores germinated and initiated metabolism but never went through outgrowth; the great majority of germinated PON-killed spores also took up propidium iodide, indicating that they had suffered significant membrane damage and were dead. Together these data suggest that spore killing by PON is through some type of damage to the spore's inner membrane.

Analysis of the killing of spores of Bacillus subtilis by a new disinfectant, Sterilox

AIMS

To determine the mechanism whereby the new disinfectant Sterilox kills spores of Bacillus subtilis.

METHODS AND RESULTS

Bacillus subtilis spores were readily killed by Sterilox and spore resistance to this agent was due in large part to the spore coats. Spore killing by Sterilox was not through DNA damage, released essentially no spore dipicolinic acid and Sterilox-killed spores underwent the early steps in spore germination, including dipicolinic acid release, cortex degradation and initiation of metabolism. However, these germinated spores never swelled and many had altered permeability properties.

CONCLUSIONS

We suggest that Sterilox treatment kills dormant spores by oxidatively modifying the inner membrane of the spores such that this membrane becomes non-functional in the germinated spore leading to spore death.

SIGNIFICANCE AND IMPACT OF THE STUDY

This work provides information on the mechanism of spore resistance to and spore killing by a new disinfectant.

The relationships and susceptibilities of some industrial, laboratory and clinical isolates of Pseudomonas aeruginosa to some antibiotics and biocides

AIMS

To provide evidence to support or refute the hypothesis that cross-resistance between antibiotics and biocides can occur.

METHODS AND RESULTS

Fifty-five strains of Pseudomonas aeruginosa were tested for their resistance to anti-pseudomonal antibacterials. Twenty clinical, 19 industrial and 16 culture collection isolates were used. The MIC was found for the antibiotics amikacin, ceftazidime, ciprofloxacin, gentamycin, ticarcillin, tobramycin, imipenem and polymyxin B. The MIC was also found for the biocides benzalkonium chloride and chlorhexidine. The analysis of the data was based on the production of a normal distribution of the log (MIC) plots for each antimicrobial. Strains were then labelled as resistant, intermediate or sensitive based on the mean and standard deviation of the distributions.

CONCLUSIONS

In general the clinical isolates were the most recalcitrant organisms, with the industrial isolates being the most sensitive.

SIGNIFICANCE AND IMPACT OF THE STUDY

The work shows that antibiotic/biocide correlations do occur, especially with clinical strains. That such correlations were not found with industrial isolates suggests that the clinical environment is responsible for the correlation. We could infer that it is the selective pressure of antibiotic usage that differentiates the clinical environment from the industrial.

Plasmid-borne smr gene causes resistance to quaternary ammonium compounds in bovine Staphylococcus aureus

Resistance to quaternary ammonium compounds (QAC) in staphylococci is common in hospital environments and has been described in the food industry. Little is known about staphylococcal QAC resistance associated with animal disease, although such disinfectants are widely used in veterinary medicine. In order to investigate the occurrence of QAC resistance in staphylococci isolated from QAC-exposed animals, 32 penicillin- and tetracycline-resistant and 23 penicillin- and tetracycline-susceptible Staphylococcus aureus isolates collected from milk from cows with mastitis during a 4-year period were selected for QAC susceptibility studies and genetic characterization. The isolates originated from four different herds that used a common pasture with a joint milking parlor in the summer. During the pasture season, a teat cream containing the QAC cetyltrimethylammonium bromide had been used daily for more than 10 years for mastitis control. Three of the penicillin- and tetracycline-resistant isolates, which were recovered from three different cows during a 20-month period, were resistant to QAC. Plasmid analysis, PCR, and DNA sequencing revealed a novel plasmid of 2,239 bp containing the smr gene. The plasmid, designated pNVH99, has similarities to small, smr-containing staphylococcal plasmids previously found in human and food isolates. pNVH99 is a new member of the pC194 family of rolling-circle replication plasmids. The three QAC-resistant isolates, as well as 28 of the 29 remaining penicillin- and tetracycline-resistant isolates, were indistinguishable by pulsed-field gel electrophoresis. The study indicates that the occurrence and spread of QAC-resistant S. aureus among dairy cows may be a problem that needs further investigation.

[Esophageal manometry: equipment cleaning and disinfection with glutaraldehyde]

BACKGROUND

Many publications have emphasized the need of proper cleaning, disinfection and sterilization process for reused materials intended to prevent cross infections. As the endoscope the esophageal manometry catheters are considered as semicritical materials and must be free of microrganisms.

AIM

To standardize the esophageal manometry materials cleaning and disinfection process to guarantee the safety of patients when reusing semicritical materials. It was based on international protocols and according to recommendations of the Hospital Infection Control Commission of the "Hospital de Clinicas de Porto Alegre", Porto Alegre, RS, Brazil.

MATERIALS AND METHODS

Enzymatic detergent was used for catheter cleaning, followed by immersion with 2% glutaraldehyde solution during 20 minutes for high-level disinfection. The water reservatory was kept clean and dry to prevent microorganisms proliferation.

CONCLUSIONS

The high level disinfection with 2% glutaraldehyde, preceded by enzymatic detergent cleaning, is a safe and simple technique that avoids cross infection in the esophageal manometry equipment. This care must be taken after each manometric procedure. The transducers must be resterilized in ethylene oxide. The professionals of this area must work in concordance with the Hospital Infection Control Commission, being acquainted with the country laws and regulations and keeping sterilizing process and materials updated.

The efficacy of chemical agents in cleaning and disinfection programs

BACKGROUND

Due to the growing number of outbreaks of infection in hospital nurseries, it becomes essential to set up a sanitation program that indicates that the appropriate chemical agent was chosen for application in the most effective way.

METHOD

For the purpose of evaluating the efficacy of a chemical agent, the minimum inhibitory concentration (MIC) was reached by the classic method of successive broth dilutions. The reference bacteria utilized were Bacillus subtilis var. globigii ATCC 9372, Bacillus stearothermophilus ATCC 7953, Escherichia coli ATCC 25922, Staphylococcus aureus ATCC 25923. The strains of Enterobacter cloacae IAL 1976 (Adolfo Lutz Institute), Serratia marcescens IAL 1478 and Acinetobactev calcoaceticus IAL 124 (ATCC 19606), were isolated from material collected from babies involved in outbreaks of infection in hospital nurseries.

RESULTS

The MIC intervals, which reduced bacteria populations over 08 log10, were: 59 to 156 mg/L of quaternarium ammonium compounds (QACs); 63 to 10000 mg/L of chlorhexidine digluconate; 1375 to 3250 mg/L of glutaraldehyde; 39 to 246 mg/L of formaldehyde; 43750 to 87500 mg/L of isopropanol or ethanol; 1250 to 6250 mg/L of iodine in polyvinyl-pyrolidone complexes, 150 to 4491 mg/L of chlorine-releasing-agents (CRAs); 469 to 2500 mg/L of hydrogen peroxide; and, 2310 to 18500 mg/L of peracetic acid.

CONCLUSIONS

Chlorhexidine showed non inhibitory activity over germinating spores. A. calcoaceticus, was observed to show resistance to the majority of the agents tested, followed by E. cloacae and S. marcescens.

An investigation into the efficacy of hatchery disinfectants against strains of Staphylococcus aureus associated with the poultry industry

The efficacy of 18 commercial disinfectants was investigated using the type strain, isolate 24 (I. 24), of pulsed-field gel electrophoresis pattern related Staphylococcus aureus that have shown to be associated with clinical disease in Northern Ireland broilers. Eight quartenary ammonium compound (QAC), four peroxygen, three amphoteric (AMP), one phenolic along with two chlorine-based disinfectants were tested at their manufacturer's recommended concentration (MRC) and at three 10-fold dilutions of the MRC. The efficacy of disinfectants against I. 24 was assessed in conditions with no hatchery organic matter (HOM) and in conditions with no HOM present. In addition, 17 S. aureus strains, related and non-related to I. 24 and obtained from the poultry industry were screened for any increase in resistance relative to I. 24. All disinfectants were effective against all test strains when tested in the absence of HOM. Products from the QAC and peroxygen groups were the most potent. The performance of all disinfectants was reduced in the presence of HOM. Under these conditions all chlorine-based, two out of three AMP, and one out of eight QAC disinfectants were not effective against I. 24 when tested at the MRC. The results emphasise the importance of proper application on appropriate areas, using the correct concentration and exposure time for the disinfectant.

Triclosan: a widely used biocide and its link to antibiotics

Triclosan is the active ingredient in a multitude of health care and consumer products with germicidal properties, which have flooded the market in recent years in response to the public's fear of communicable bacteria. Although originally thought to kill bacteria by attacking multiple cellular targets, triclosan was recently shown to target a specific bacterial fatty acid biosynthetic enzyme, enoyl-[acyl-carrier protein] reductase, in Gram-negative and Gram-positive bacteria, as well as in the Mycobacteria. Triclosan resistance mechanisms include target mutations, increased target expression, active efflux from the cell, and enzymatic inactivation/degradation. These are the same types of mechanisms involved in antibiotic resistance and some of them account for the observed cross-resistance with antibiotics in laboratory isolates. Therefore, there is a link between triclosan and antibiotics, and the widespread use of triclosan-containing antiseptics and disinfectants may indeed aid in development of microbial resistance, in particular cross-resistance to antibiotics.

Mechanisms of bacterial insusceptibility to biocides

Bacterial insusceptibility to biocides is of two types, intrinsic and acquired. Intrinsic insusceptibility is a natural property of an organism and is shown by bacterial spores, mycobacteria, and gram-negative bacilli. Cellular impermeability is a major factor, and in some cases active efflux pumps play an important role. A special example is that of phenotypic (physiological) adaptation to intrinsic resistance found in bacteria present in biofilms. Acquired resistance arises through mutation or via the acquisition of plasmids or transposons; efflux of biocide is a major mechanism, although plasmid-mediated inactivation has also been shown to occur. An additional aspect that must be considered is the stringent response elicited in bacteria on exposure to inimical agencies. There is a possible linkage between certain biocides and antibiotic resistance under experimental conditions.

Nosocomial transmission of imipenem-resistant Pseudomonas aeruginosa following bronchoscopy associated with improper connection to the Steris System 1 processor

OBJECTIVE

To assess nosocomial transmission of imipenem-resistant Pseudomonas aeruginosa (IRPA) following bronchoscopy during August through October 1998.

DESIGN

Traditional and molecular epidemiological investigation of a case series.

SETTING

University-affiliated community hospital.

PATIENTS

18 patients with IRPA bronchial-wash isolates.

INTERVENTIONS

We reviewed clinical data, performed environmental cultures and molecular analysis of all IRPA isolates, and observed disinfection of bronchoscopes.

RESULTS

Of 18 patients who had IRPA isolated from bronchoscopic or postbronchoscopic specimens, 13 underwent bronchoscopy for possible malignancy or undiagnosed pulmonary infiltrates. Following bronchoscopy, 3 patients continued to have IRPA isolated from sputum and demonstrated clinical evidence of infection requiring specific antimicrobial therapy. The remaining 15 patients had no further IRPA isolated and remained clinically well 3 months following bronchoscopy. Pulsed-field gel electrophoresis revealed that all strains except one were >95% related. STERIS SYSTEM 1 had been implemented in July 1998 as an automatic endoscope reprocessor (AER) for all endoscopes and bronchoscopes. Inspection of bronchoscope sterilization cycles revealed incorrect connectors joining the bronchoscope suction channel to the STERIS SYSTEM 1 processor, obstructing peracetic acid flow through the bronchoscope lumen. No malfunction warning was received, and spore strips remained negative.

CONCLUSIONS

The similarity of diverse connectors and limited training by the manufacturer regarding AER for bronchoscopes were the two factors responsible for the outbreak. Appropriate connections were implemented, and there was no further bronchoscope contamination. We suggest active surveillance of all bronchoscopy specimen cultures, standardization of connectors of various scopes and automated processors, and systematic education of staff by manufacturers with periodic on-site observation.

A new hydrogen peroxide--based medical-device detergent with germicidal properties: comparison with enzymatic cleaners

BACKGROUND

The objective of this study was to evaluate the efficacy of the cleaning and bacterial killing ability of a new non-enzyme-based formulation (killing detergent solution [KDS]) compared with commercially available enzymatic detergents that included Metrizyme (Metrex Research Division of Sybron Canada Ltd. Morrisburg, Ontario) and Gzyme (Germiphene Corp, Brantford, Ontario). KDS is a hydrogen peroxide-based detergent formulation that combines cleaning efficacy with the ability to kill microorganisms. The KDS formulation helps ensure the protection of the health care worker from infectious risk during the soaking and cleaning stages of medical device reprocessing and reduces the bioburden on devices before sterilization/disinfection.

METHODS

Test organisms that included Enterococcus faecalis, Salmonella choleraesuis, Staphylococcus aureus, and Pseudomonas aeruginosa were suspended in artificial test soil (ATS-B; patent submitted), inoculated at 10(6) colonyforming units per carrier and dried overnight before detergent exposure. The ATS-B mimics the blood, protein, carbohydrate, and endotoxin levels of patient-used medical devices. Plastic lumen carriers and a flexible colonoscope were used for surface and simulated-use testing, respectively.

RESULTS

The results for the microbial challenge dried onto polyvinyl chloride (PVC) carriers demonstrated that the ability of KDS to remove protein, blood, carbohydrate, and endotoxin from surface test carriers was as effective as the enzyme detergents that were evaluated. Furthermore, KDS was able to effect approximately a 5-Log(10) reduction in microbial loads with a 3-minute exposure at room temperature, whereas none of the other detergents were as effective. In simulated-use testing of a soiled colonoscope, KDS was significantly better at ensuring microbial killing compared with Gzyme and Metrizyme and was equivalent to the enzymatic detergents in cleaning ability.

CONCLUSIONS

In summary the KDS has excellent microbial-killing ability in 3-minute exposures at room temperature and cleans as well as the existing enzymatic detergent formulations that were tested.

Biocides, drug resistance and microbial evolution

Antimicrobial biocides are widely used in critical human health situations in which rigorous infection control is needed. Increasingly, biocidal agents are being marketed for home use, although there is little evidence that they significantly improve home hygiene. Biocide resistance mechanisms share many themes with antibiotic resistance mechanisms.

Resistance to antibiotics and biocides among non-fermenting Gram-negative bacteria

OBJECTIVE

To investigate the antibiotic and biocide susceptibilities of clinical isolates of rarely encountered Gram-negative, non-fermenting bacteria.

METHODS

Thirty Gram-negative non-fermenting bacterial strains were isolated from blood cultures of oncology patients. These were studied for their resistance to 11 antibiotics. Their susceptibilities to seven biocides used in hospitals were also examined.

RESULTS

Isolates of Stenotrophomonas maltophilia and Ochrobactrum anthropi were generally resistant to at least five of the antibiotics, whereas isolates of Comamonas acidivorans, Flavobacterium oryzihabitans, Aeromonas hydrophila, Sphingobacterium spiritivorum, Acinetobacter junii and Acinetobacter lwoffi were generally sensitive to at least nine of the antibiotics. Trovafloxacin and trimethoprim-sulfamethoxazole were the most effective antibacterial agents tested, with 0% and 7%, respectively, of isolates being resistant, whereas 63% of isolates were resistant to aztreonam. Some isolates, sensitive to meropenem and/or ceftazidime in vitro, possessed very high MBC/MIC ratios for these beta-lactams. Two out of three biocides used in hospital pharmacies showed lethal activity towards all strains tested when used at less than one-third of their recommended in-use concentration. Proceine 40 failed to give a 5 log reduction in bacterial cell number for the isolates tested when used at its "in-use" concentration. A concentration of > 500 mg/L chlorhexidine was required to achieve a 5 log reduction for the same isolates.

CONCLUSIONS

We have examined the antibiotic susceptibilities of non-fermenting Gram-negative bacterial strains isolated from immunocompromised patients. Despite being sensitive to certain antibiotics in vitro, some isolates were still able to cause serious bacteremia. We have also reported for the first time the susceptibilities of non-fermenting Gram-negative bacteria to common biocides used in hospital infection control, and have shown that some strains are able to persist at the "in-use" concentration of particular biocides. It is therefore important to study further this particular group of organisms, and, in particular, to examine whether there exists a link between resistance to antibiotics and resistance to biocides.

Wound colonization and infection: the role of topical antimicrobials

Infection and bacterial colonization are important factors in compromised wound healing, particularly in chronic wounds. The current "best practice" for controlling these factors is still unclear. Systemic antibiotics are generally accepted as being the preferred choice for treating infection, provided that ischaemia does not interfere. However, their widespread systemic and topical use is leading to the emergence of resistant bacterial strains such as methicillin-resistant Staphylococcus aureus. Colonization of wounds presents a double problem: possible delayed healing if out of balance with the immune system; and as a source for cross-infection. Managing colonization is not yet defined in best practice. The judicious use of dressings, notably those containing certain antiseptic agents, can be valuable in infection control and in promoting healing. This review states the case for taking the antiseptic route as part of the concerted approach to local wound management and infection control.