Microbiological applications of the inactivation of antibiotics and other antimicrobial agents

In Vitro Antimicrobial Susceptibility Testing of Biofilm-Growing Bacteria: Current and Emerging Methods

The antibiotic susceptibility of bacterial pathogens is typically determined based on planktonic cells, as recommended by several international guidelines. However, most of chronic infections - such as those established in wounds, cystic fibrosis lung, and onto indwelling devices - are associated to the formation of biofilms, communities of clustered bacteria attached onto a surface, abiotic or biotic, and embedded in an extracellular matrix produced by the bacteria and complexed with molecules from the host. Sessile microorganisms show significantly increased tolerance/resistance to antibiotics compared with planktonic counterparts. Consequently, antibiotic concentrations used in standard antimicrobial susceptibility tests, although effective against planktonic bacteria in vitro, are not predictive of the concentrations required to eradicate biofilm-related infections, thus leading to treatment failure, chronicization and removal of material in patients with indwelling medical devices.Meeting the need for the in vitro evaluation of biofilm susceptibility to antibiotics, here we reviewed several methods proposed in literature highlighting their advantages and limitations to guide scientists towards an appropriate choice.

Disinfectant testing for veterinary and agricultural applications: A review

Disinfectants for veterinary and livestock use, plus skin antiseptics, are critical elements for the control of infectious agents, including zoonotic and antimicrobial-resistant micro-organisms, in managed animal species. Such agents impact animal welfare, economic performance and human health. Testing of disinfectants is needed for safety, efficacy and quality control. The present review examines the principal types of test (carrier, suspension, surface and field) that have been developed or attempted, plus the features inherent in the respective tests, particularly with respect to variability. Elements of testing that have to be controlled, or which can be manipulated, are discussed in the context of real-world scenarios and anticipated applications. Current national and international testing regimes are considered, with an emphasis on the UK, continental Europe and North America, and with further detail provided in the Supporting Information. Challenges to disinfectant efficacy include: the nature of the biological targets (bacteria, fungi, yeasts, spores, viruses and prions), the need for economical and safe working concentrations, the physical and chemical nature of contaminated surfaces, constraints on contact times and temperatures, the presence of organic soil and other barrier or neutralising substances (including biofilms), and thoroughness of pre-cleaning and disinfectant application. The principal challenges with veterinary disinfectant testing are the control of test variability, and relating test results to likely performance in variable field conditions. Despite some ambitions to develop standardised field tests for disinfectants, aside from skin antiseptic trials the myriad problems such tests pose with respect to cost, reproducibility and generalisability remain intractable.

Comparison of Different Culture Methods for the Detection of Bacillus cereus Group in Cosmetics

BACKGROUND

The U.S. Food and Drug Administration (FDA) Bacteriological Analytical Manual (BAM) reference culture method uses Modified Letheen Broth (MLB) for microbiological analyses for all types of cosmetic products.

OBJECTIVE

This study evaluated the effectiveness of MLB and Tryptone Azolectin Tween (TAT) broths using BAM reference culture method for cosmetics.

METHODS

Pure spore suspensions of B. cereus group members were experimentally spiked (McF: 0.5) into cosmetic products. After an aging period of 72 h, the products were analyzed using MLB and TAT broth. The enumeration of the cells was performed on B. cereus group selective plates Bacillus cereus rapid agar (BACARA) and Mannitol Yolk Polymyxin (MYP) plates.

RESULTS

No statistical difference (p > 0.05) was found for the recovery of cells from the liquid products using either medium (MLB or TAT broth) and the selective plates. In solid/powder products, a combination of Tween 80 and MLB detected significantly more cells (p < 0.05) than combination of Tween 80 and TAT broth. The microbial counts on BACARA showed no significant differences (p > 0.05). However, when assessing cream/oil-based products, the number of cells detected by use of Tween 80/TAT broth was significantly higher than Tween 80/MLB, and MYP showed significantly higher counts than BACARA.

CONCLUSIONS

This study showed that relative effectiveness of MLB vs. TAT for recovering of B. cereus group cells varied depending on the variety of formulation, and combination of preservatives of the tested cosmetic products. The findings suggest additional studies are needed to explore recovery of other relevant microorganisms that may contaminate cream/oil-based cosmetics.

Review: Antimicrobial efficacy validation using in vitro and in vivo testing methods

Pre-clinical antimicrobial validation testing for single and combination products, and parameters that should be considered when testing the antimicrobial performance of a medical device, are discussed. Guidance is provided on key elements required for in vitro and in vivo antimicrobial validation, including validation of microbial growth, microbial recovery, neutralization, and antimicrobial activity. An important consideration, both in terms of practicality and economics, is designing in vitro studies that bridge to in vivo testing: A representative in vitro model is used to generate data on many clinically relevant microorganisms, and then one microorganism is selected for use in in vivo testing. If the in vivo results correlate to the in vitro results, it can reasonably be extrapolated that the same would be true for the remaining microorganisms tested in vitro. Thus, the selection of relevant in vitro models for testing is critical for successful antimicrobial validation testing.

Inactivation of vegetative bacterial threat agents on environmental surfaces

Following a wide-area biological terror attack, numerous decontamination technologies, techniques, and strategies will be required for rapid remediation. Establishing an understanding of how disinfectants will perform under field conditions is of critical importance. The purpose of this study was to determine the efficacy of several liquid decontaminants, when used to inactivate vegetative biological agents on environmental surfaces. Aluminum, carpet, concrete, glass, and wood coupons were inoculated with 1×10(8) CFU of Burkholderia mallei, Francisella tularensis, Vibrio cholerae, or Yersinia pestis. Using spray-based application methods, decontamination was then attempted with pH-adjusted bleach, 1% citric acid, 70% ethanol, quaternary ammonia, or Pine-Sol®. Results indicated that decontamination efficacy varied significantly by decontaminant and organism. Materials such as wood are difficult to decontaminate, even when using sporicides. The data presented here will help responders develop efficacious remediation strategies following a large-scale contamination incident.

Disinfection methods for spores of Bacillus atrophaeus, B. anthracis, Clostridium tetani, C. botulinum and C. difficile

To evaluate disinfection methods for environments contaminated with bioterrorism-associated microorganism (Bacillus anthracis), we performed the following experiments. First, the sporicidal effects of sodium hypochlorite on spores of five bacterial species were evaluated. Bacillus atrophaeus was the most resistant to hypochlorite, followed in order by B. anthracis, Clostridium botulinum and Clostridium tetani, and Clostridium difficile. Subsequently, using B. atrophaeus spores that were the most resistant to hypochlorite, the sporicidal effects of hypochlorite at lower pH by adding vinegar were evaluated. Hypochlorite containing vinegar had far more marked sporicidal effects than hypochlorite alone. Cleaning with 0.5% (5000 ppm) hypochlorite containing vinegar inactivated B. atrophaeus spores attached to vinyl chloride and plywood plates within 15 s, while that not containing vinegar did not inactivate spores attached to cement or plywood plates even after 1 h. Therefore, the surfaces of cement or plywood plates were covered with gauze soaked in 0.5% hypochlorite containing vinegar, and the sporicidal effects were evaluated. B. atrophaeus spores attached to plywood plates were not inactivated even after 6 h, but those attached to cement plates were inactivated within 5 min. On the other hand, covering the surfaces of plywood plates with gauze soaked in 0.3% peracetic acid and gauze soaked in 2% glutaral inactivated B. atrophaeus spores within 5 min and 6 h, respectively. These results suggest that hypochlorite containing vinegar is effective for disinfecting vinyl chloride, tile, and cement plates contaminated with B. anthracis, and peracetic acid is effective for disinfecting plywood plates contaminated with such microorganism.

Microtiter susceptibility testing of microbes growing on peg lids: a miniaturized biofilm model for high-throughput screening

Batch culture of biofilms on peg lids is a versatile method that can be used for microtiter determinations of biofilm antimicrobial susceptibility. In this paper, we describe a core protocol and a set of parameters (surface composition, the rate of rocking or orbital motion, temperature, cultivation time, inoculum size, atmospheric gases and nutritional medium) that can be adjusted to grow single- or multispecies biofilms on peg surfaces. Mature biofilms formed on peg lids can then be fitted into microtiter plates containing test agents. After a suitable exposure time, biofilm cells are disrupted into a recovery medium using sonication. Microbicidal endpoints can be determined qualitatively using optical density measurements or quantitatively using viable cell counting. Once equipment is calibrated and growth conditions are at an optimum, the procedure requires approximately 5 h of work over 4-6 d. This efficient method allows antimicrobial agents and exposure conditions to be tested against biofilms on a high-throughput scale.

Combined Plate Microbial Assay (CPMA): a 6-plate-method for simultaneous first and second level screening of antibacterial residues in meat

This paper proposes an improved high throughput microbial method for the simultaneous performance of first and second level screening for antibacterial residues in meat. It is based on growth inhibition of B. subtilis on agar medium pH 6, 7.2 and 8, of B. cereus on agar medium pH 5.9, of M. luteus on agar medium pH 8 and of E. coli on agar medium pH 7.2 (research or first level screening) and on the use of confirmatory solutions (Pase, Paba, MgSO4) for the identification or second level screening. In kidney control samples, dialysis membranes were interposed between samples and the agar surface to both prevent the action of lysozyme and reduce false positive results. The proposed method detects beta-lactams, sulfonamides, tetracyclines, aminoglycosides, macrolides and quinolones at MRL concentrations and reliably indicates the inhibitor family. Results are obtained in 18-24 h.

High-throughput metal susceptibility testing of microbial biofilms

BACKGROUND

Microbial biofilms exist all over the natural world, a distribution that is paralleled by metal cations and oxyanions. Despite this reality, very few studies have examined how biofilms withstand exposure to these toxic compounds. This article describes a batch culture technique for biofilm and planktonic cell metal susceptibility testing using the MBEC assay. This device is compatible with standard 96-well microtiter plate technology. As part of this method, a two part, metal specific neutralization protocol is summarized. This procedure minimizes residual biological toxicity arising from the carry-over of metals from challenge to recovery media. Neutralization consists of treating cultures with a chemical compound known to react with or to chelate the metal. Treated cultures are plated onto rich agar to allow metal complexes to diffuse into the recovery medium while bacteria remain on top to recover. Two difficulties associated with metal susceptibility testing were the focus of two applications of this technique. First, assays were calibrated to allow comparisons of the susceptibility of different organisms to metals. Second, the effects of exposure time and growth medium composition on the susceptibility of E. coli JM109 biofilms to metals were investigated.

RESULTS

This high-throughput method generated 96-statistically equivalent biofilms in a single device and thus allowed for comparative and combinatorial experiments of media, microbial strains, exposure times and metals. By adjusting growth conditions, it was possible to examine biofilms of different microorganisms that had similar cell densities. In one example, Pseudomonas aeruginosa ATCC 27853 was up to 80 times more resistant to heavy metalloid oxyanions than Escherichia coli TG1. Further, biofilms were up to 133 times more tolerant to tellurite (TeO3(2-)) than corresponding planktonic cultures. Regardless of the growth medium, the tolerance of biofilm and planktonic cell E. coli JM109 to metals was time-dependent.

CONCLUSION

This method results in accurate, easily reproducible comparisons between the susceptibility of planktonic cells and biofilms to metals. Further, it was possible to make direct comparisons of the ability of different microbial strains to withstand metal toxicity. The data presented here also indicate that exposure time is an important variable in metal susceptibility testing of bacteria.

Biofilm susceptibility to metal toxicity

This study compared bacterial biofilm and planktonic cell susceptibility to metal toxicity by evaluating the minimum inhibitory concentration (MIC), the planktonic minimum bactericidal concentration (MBC), and minimum biofilm eradication concentration (MBEC) using the MBEC device. In total, 17 metal cations and oxyanions, chosen to represent groups VIB to VIA of the periodic table, were each tested on biofilm and planktonic cultures of Escherichia coli JM109, Staphylococcus aureus ATCC 29213, and Pseudomonas aeruginosa ATCC 27853. In contrast to control antibiotic assays, where biofilm cultures were 2 to 64 times less susceptible to killing than logarithmically growing planktonic bacteria, metal compounds killed planktonic and biofilm cultures at the same concentration in the vast majority of combinations. Our data indicate that, under the conditions reported, growth in a biofilm does not provide resistance to bacteria against killing by metal cations or oxyanions.

Synthesis and antimicrobial activity of meso-substituted polymethine cyanine dyes

The condensation reaction of equivalent amounts of 2-cyanomethyl benzooxazole or its derivatives with variously substituted aromatic aldehydes gave 2-cyano-styryl benzooxazole or its derivatives. The subsequent reaction of the 2-cyano-styryl benzooxazoles with 2(4)-methyl substituted heterocyclic quaternary salts afforded meso-substituted styryl-2(4)-polymethine cyanines. The condensation reaction of 2-cyanomethyl benzooxazole or its derivatives with alpha-nitroso-beta-naphthol followed by reaction with 2(4)-methyl substituted heterocyclic quaternary salts gave meso-substituted aza-2(4)-polymethine cyanines. The reaction of 2-cyanomethyl benzooxazole or its derivatives with N-methyl heterocyclic quaternary salts followed by the reaction with 2-methylquinolinium methiodide afforded the corresponding meso-substituted trimethine cyanine dyes. Elemental analyses, visible absorption, IR, (1)H NMR spectroscopy, and mass spectra established the structures of these compounds. The relationship between the structure and properties of these dyes has been studied and the solvatochromic behavior of some selected cyanine dyes in organic solvents is discussed. Finally, the antimicrobial activity of selected novel dyes was investigated in vitro using a wide spectrum of microbial strains.

Protocol for evaluating the efficacy of cetylpyridinium chloride as a beef hide intervention

The objective of this study was to establish the necessary protocols and assess the efficacy of cetylpyridinium chloride (CPC) as an antimicrobial intervention on beef cattle hides. Experiments using CPC were conducted to determine (i) the methods of neutralization needed to obtain valid efficacy measurements, (ii) the effect of concentration and dwell time after treatment, (iii) the effect of CPC on hide and carcass microbial populations when cattle were treated at a feedlot and then transported to a processing facility for harvest, and (iv) the effectiveness of spray pressure and two-spray combinations of CPC and water to reduce hide microbial populations. Residual CPC in hide sponge samples prevented bacterial growth. Dey-Engley neutralization media at 7.8% and a centrifugation step were necessary to overcome this problem. All dwell times, ranging from 30 s to 4 h, after 1% CPC application to cattle hides resulted in aerobic plate counts and Enterobacteriaceae counts 1.5 log CFU/100 cm2 lower than controls. The most effective dose of CPC was 1%, which reduced aerobic plate counts and Enterobacteriaceae counts 2 and 1 log CFU/100 cm2, respectively. Low-pressure application of 1% CPC at the feedlot, transport to the processing facility, and harvest within 5 h of application resulted in no effect on Escherichia coli O157 prevalence on hides or preevisceration carcasses. Two high-pressure CPC washes lowered aerobic plate counts and Enterobacteriaceae counts by 4 log CFU/100 cm2, and two medium-pressure CPC washes were only slightly less effective. These results indicate that under the proper conditions, CPC may still be effective for reducing microbial populations on cattle hides. Further study is warranted to determine if this effect will result in reduction of hide-to-carcass contamination during processing.

In vitro action of combinations of selected antimicrobial agents and adult bovine articular cartilage (sesamoid bone)

Anatomically intact articular cartilage in form of sesamoid bones from metacarpophalangeal joints of 2-year-old cows was tested for its influence on the microbicidal effect of the iodophore Betaisodona, the bispyridinamine Octenisept, and the biguanide Lavasept. Comparisons were carried out in Ham's F12 medium with and without 0.2% bovine serum albumin as organic matter loading. The expected abolition of the microbicidal effect of these antiseptics against the test organisms Escherichia coli or Staphylococcus aureus in the presence of sesamoid bone was not evident. Furthermore, sesamoid bone alone demonstrated antibacterial activity against Staphylococcus aureus, which may involve adherence of bacteria to surface constituents of articular cartilage. Final concentrations of 2.5-5% Betaisodona, 5% Octenisept as well as 0.025% Lavasept are effective in killing of 10(8)-10(9) cfu/ml Escherichia coli or Staphylococcus aureus in the presence of sesamoid bone without the reduction of antimicrobial activity expected from binding to CS, which has previously been demonstrated for CS in solution.

A rapid method for assessing the suitability of quenching agents for individual biocides as well as combinations

AIMS

To develop a novel, rapid method for testing the ability of quenching agents to neutralize disinfectants.

METHODS AND RESULTS

Tests were performed to determine the suitability of different neutralizers for a range of disinfectants, using a new method based on the Bioscreen optical density analyser. Results showed that during disinfection tests, efficacy could be over-estimated due to poor, or no, neutralization of the disinfectant after a specified time of exposure to the bacteria. The failure to distinguish adequately between bacteriostatic and bactericidal effects can lead to false results during disinfectant testing. Experiments also showed that dilution of the disinfectant, following exposure to the bacteria, was not always sufficient to stop the activity of the disinfectant for chemicals with low dilution coefficients.

CONCLUSIONS

The quench test proved to be very quick and easy to perform, with results being available within 18 h. Using the Bioscreen, the test is automated and determines whether dilution into a particular neutralizer is able to inactivate a disinfectant within 30 s.

SIGNIFICANCE AND IMPACT OF THE STUDY

This new approach allows the efficacy of quenching agents to be determined, prior to undertaking each disinfection study, and can help in the development of more suitable quenching solutions. The test has also been used to find suitable neutralizers for mixtures of disinfectants which might be used during studies on synergistic biocide combinations.

In vitro action of a combination of selected antimicrobial agents and chondroitin sulfate

Chondroitin sulfate (CS), a highly anionic polymer and the most predominant sulfated glycosaminoglycan in connective tissues, was investigated regarding to its interaction with cationic disinfectants, which are used as antiinfectives in humans. Combinations of cetylpyridiniumchloride (CPC), chlorhexidine (CHex), and polyhexamethylene biguanide (PHMB) with CS, respectively, were prepared and the resulting microbicidal activity of the mixtures was tested in the quantitative suspension test without organic matter. Polyvidone-iodine and Ringer's solution were used as controls. Even precipitated, the resulting test combinations behave differently against Staphylococcus aureus, Enterococcus faecium, Escherichia coli, Pseudomonas aeruginosa, and Candida albicans. CPC/CS demonstrated only microbicidal activity against Gram-positive bacteria, and CHex/CS was more active against Gram-negative bacteria and C. albicans. PHMB/CS, especially in combination with CS-A, only revealed an antimicrobial effect against P. aeruginosa after 60 min action. The interaction of cationic disinfectants with CS showed depending on the investigated microorganism a more or less controlled sustained release manner of the microbicidal agent from the precipitated complex, with the only exception of PHMB in combination with CS-C, which is completely neutralized. Polyvidone-iodine and Ringer's solution were not affected by CS.

Comparative in vitro activity of antiseptics and disinfectants versus clinical isolates of Candida species

OBJECTIVE

To evaluate the in vitro activity of antiseptics and detergents against Candida.

DESIGN

One strain each of Candida albicans, Candida tropicalis, Candida lusitaniae, Candida parapsilosis, Candida kefyr, Candida glabrata, and an American Type Culture Collection strain of Escherichia coli (control) were studied. Clinical isolates were obtained from patients in a bone marrow unit of a large tertiary hospital. Antiseptic and disinfectant agents studied were used in the hospital where isolates were identified for cleaning of inanimate surfaces or hand washing. In vitro susceptibility was determined using a broth macrodilution method with exposure times to antiseptic or disinfectant agent of 15 seconds to 4 minutes and concentrations of agents that ranged from undiluted to 1:10,000 dilution.

SETTING

A 900-bed teaching hospital.

RESULTS

Of disinfectants tested, Vestal and Sparquat inhibited growth of all species at dilutions of < or = 1:100 at all contact times for all species. Clorox showed inhibition of growth at 1:100 dilution after 30 seconds of contact time for all isolates. Of antiseptics studied, Hibiclens inhibited growth of all species except C tropicalis at dilutions of < or = 1:100 at all contact times and for C tropicalis after 60 seconds. Clinidine inhibited growth of all species at dilutions of < or = 1:100 at all contact times for all species with the exception of Cglabrata and C tropicalis, which grew at the undiluted concentration. Ultradex failed to demonstrate killing of any species for any dilutions tested.

CONCLUSIONS

The results of this study show varying degrees of in vitro inhibition of growth by a variety of antiseptics and disinfectants against clinical isolates of Candida species from hospitalized patients.

Efficacy of peroxygen compounds against glutaraldehyde-resistant mycobacteria

BACKGROUND

To prevent cross-infection of patients, semicritical devices must be high-level disinfected by a product capable of destroying mycobacteria. Glutaraldehyde is commonly used; however, recent studies showed that glutaraldehyde-resistant mycobacteria could survive treatment with this chemical for extended exposure times. Our study tested hydrogen peroxide, peracetic acid, and a germicide (Cidex PA, Advanced Sterilization Products, Irvine, Calif) containing a mixture of the 2 peroxygen compounds for their ability to kill both glutaraldehyde-resistant and nonresistant (control) mycobacteria.

METHODS

Bacterial suspensions were exposed to the test chemicals for various periods followed by neutralization and enumeration of survivors.

RESULTS

Hydrogen peroxide at 10% and acidified hydrogen peroxide at 6% had low activity (<4 log reduction in 60 minutes exposure) against glutaraldehyde-resistant strains and slightly higher activity (4 log to 6 log reduction in 60 minutes) against the control strains. Peracetic acid at 0.07% had low to moderate activity (0.6 log to 6 log reduction in 60 minutes) against the resistant organisms and moderate to high activity (4 log to 6 log reduction in 10 minutes) against the control strains. Cidex PA, which contains a mixture of 0.07% peracetic acid and 1% hydrogen peroxide, had high activity (6 log reduction in 10 minutes) against all organisms. Efficacy of 0.8% phenol, a standard reference solution, did not correlate with efficacy of the peroxygen compounds.

CONCLUSIONS

Hydrogen peroxide and peracetic acid had much higher activity toward mycobacteria when combined as a synergistic mixture than when evaluated individually.

Microbial contamination of antiseptics and disinfectants

BACKGROUND

There have been a number of reports on microbial contamination of antiseptics and disinfectants. At present, however, the necessity of measures to prevent contamination do not seem to be fully appreciated. We investigated microbial contamination of antiseptics and disinfectants that are used in our hospital.

METHODS

Fifty-one samples of benzalkonium chloride and chlorhexidine gluconate that were being used in the hospital were examined. Viability of the contaminants detected in these samples was also tested in the agents. Then we examined measures to prevent contamination of these agents.

RESULTS

Microbial contamination was detected at 10(2) to 10(7) CFU/ml in the following samples: 6 of 23 samples of cotton balls soaked in 0.02% benzalkonium chloride kept in a canister for antisepsis and disinfection (26.1%); 7 of 13 samples of 0.02%, benzalkonium chloride or 0.02% chlorhexidine gluconate in an irrigation apparatus kept at 37 degrees C for vaginal douching (53.8%); and 9 of 15 samples of 0.02% benzalkonium chloride or 0.05% chlorhexidine gluconate for storage of suction catheters in a plastic bottle (60%). The major contaminants were Burkholderia cepacia, Pseudomonas aeruginosa, Xanthomonas maltophilia, and Pseudomonas fluorescens. The first two organisms examined grew in the agents. After improvements in the handling of the antiseptics and disinfectants, no microbial contamination was observed.

CONCLUSIONS

It is necessary to check microbial contamination of diluted benzalkonium chloride and diluted chlorhexidine gluconate that are in use. Such products are not recommended as antiseptics.

Bacterial contamination of commercially available ethacridine lactate (acrinol) products

Bacterial contamination of commercially available ethacridine lactate (acrinol) solutions and cotton gauze soaked in ethacridine lactate solution was investigated. Of 56 samples from ethacridine lactate solutions (eight products, seven manufacturers), seven samples (12.5%) of two products (two manufacturers) were contaminated with 10(1)-10(4) colony forming units (cfu)/mL of Burkholderia pickettii. Of 67 samples obtained from gauze soaked in ethacridine lactate solution (seven products, seven manufacturers), 41 (61.2%) of six products (six manufacturers) were contaminated with 10(2)-10(6) cfu/mL of bacteria. The major bacteria detected were Burkholderia cepacia and Burkholderia pickettii. This relatively high incidence of bacterial contamination in commercially available cotton gauze soaked in ethacridine lactate solution may be due to the presence of gauze in ethacridine lactate solution.

Bactericidal activity of skin disinfectants on methicillin-resistant Staphylococcus aureus

We studied bactericidal activity of 10% povidone-iodine, 0.5% chlorhexidine gluconate, and 0.5% chlorhexidine in 80% ethanol on four strains of methicillin-resistant and two strains of methicillin-susceptible Staphylococcus aureus. The pathogen was exposed to each of the disinfectants for 15, 30, 60, 120, and 240 s at room temperature. The inocula from these suspensions were cultured 72 h at 37 degrees C after the antimicrobial activity of the disinfectants in the suspensions was inactivated by 1:1000 dilution with neutralizer. No organism grew in any of the strains after exposure to 0.5% chlorhexidine in 80% ethanol. The 15-, 30-, and 60-s exposure to 10% povidone-iodine reduced the mean colony count by 55.2%, 91.2%, and 96.7%, respectively, and the exposures to 0.5% chlorhexidine gluconate reduced the mean colony count by 37.2%, 77.1%, and 93.3%, respectively. The difference in colony count between disinfectants was significant at 15- and 30-s exposures (P < 0.01 and 0.05, respectively). The results suggest that bactericidal activity of 0.5% chlorhexidine in 80% ethanol is more potent and more rapid against methicillin-susceptible and methicillin-resistant strains of S. aureus.

Methodology for HIV disinfectant testing

Due to the variation in protocols from studies by different workers for the inactivation of HIV by chemical disinfectants, only limited comparisons of the results can be made. These variations include those which apply to disinfectant testing in general, such as the level of organic load and the form of neutralization of the disinfectant, and those which apply particularly to HIV inactivation, such as the method used to detect infectious virus. Our suspension and carrier tests to assess the efficacy of chemical disinfectants against HIV are described and problems with the interpretation and applicability of the results are discussed.

Construction of a bioluminescent mycobacterium and its use for assay of antimycobacterial agents

To show, as a model system, that mycobacteria can express heterologous luciferase genes and that bioluminescence can be a rapid method of measuring antimycobacterial activity, a bioluminescent form of Mycobacterium smegmatis was made by transformation with a Mycobacterium-Escherichia coli shuttle vector containing the luxAB genes from Vibrio harveyi. The antimycobacterial effects of antibiotics and biocides could be assayed in real time by using bioluminescent M. smegmatis.

Factors affecting antibacterial activity of hop compounds and their derivatives

The antibacterial effect of weak acids derived from the hop plant (Humulus lupulus L.) increased with decreasing pH. Analysis of the minimum inhibitory concentration of such compounds against Lactobacillus brevis IFO 3960 over pH 4-7 suggests that undissociated molecules were mainly responsible for inhibition of bacterial growth. The antibacterial activity of trans-isohumulone was ca 20 times greater than that of humulone, 11 times greater than that of colupulone and nine times greater than that of trans-humulinic acid when the degree of ionization was taken into account. Monovalent cations (K+, Na+, NH4+, Rb+, Li+) stimulated antibacterial activity of trans-isohumulone but the effect was smaller than that observed with H+. The response to divalent cations varied: Ca2+ had little effect on antibacterial activity, whereas Mg2+ reduced activity. Lipid materials and beta-cyclodextrin also antagonized the antibacterial action of trans-isohumulone.

Antifungal activity of n-tributyltin acetate against some common yam rot fungi

The antifungal activity of n-tributyltin acetate (TBTA) was examined in relation to combating yam rot disease. TBTA exhibited a significant effect in vitro and in vivo on four yam rot fungal isolates tested. However, the in vitro toxicity of TBTA was drastically reduced when 2.5% Tween 80 was the solvent instead of 25% acetone, as indicated by the MICs of 156.0 and 5.0 micrograms/ml, respectively.

Importance of neutralizers in the stripping fluid in a simulated healthcare personnel handwash

The Food and Drug Administration (FDA) healthcare personnel handwash procedure allows for the use of a non-neutralizing stripping fluid after washing with an antimicrobial handwash product. The antimicrobial in the handwash product can remain active up until the time of neutralization or plating. A modified healthcare personnel handwash procedure using a pigskin substrate and a 4% chlorhexidine gluconate handwash product was used to demonstrate the need for a neutralizer in the stripping fluid. When tests were run with and without neutralizers in the dilution blanks, but with adequate neutralizers in the stripping fluid, there were no significant differences (p greater than .05) between results obtained after five washes or after each wash. When tests were run with a non-neutralizing stripping fluid, significant differences were noticed in the first and the fifth wash (p less than .05), and in the presence or absence of neutralizers in the dilution blanks (p less than .05). The data generated indicate that in order to determine the true activity of an antimicrobial handwash product, an adequate neutralizer should be incorporated into the stripping fluid and not just the dilution media. They also suggest that neutralizer carry-over from the stripping fluid is not a valid concern.

Bacterial spores and chemical sporicidal agents

Bacterial spores are among the most resistant of all living cells to biocides, although the response depends on the stage of sporulation. The development of resistance to some agents such as chlorhexidine occurs much earlier in sporulation than does resistance to glutaraldehyde, which is a very late event. During germination or outgrowth or both, resistance is lost and the cells become as susceptible to biocides as nonsporulating bacteria. Mechanisms of spore resistance to, and the action of, biocides are discussed, and possible means of enhancing antispore activity are considered. The clinical and other uses of sporicidal and sporostatic chemical agents are described.

Influence of two handwashing frequencies on reduction in colonizing flora with three handwashing products used by health care personnel

Four handwashing products (containing either 2% chlorhexidine gluconate, 0.6% parachlorometaxylenol, 0.3% triclosan, or a nonantimicrobial control) at two handwashing frequencies (6 or 18 times/day) were compared with regard to their effectiveness in reducing colonizing hand flora. Eighty adult volunteers were assigned by block randomization to one of the four products and one of the two frequency schedules (n = 10/group) and washed their hands under supervision for 5 consecutive days. There were no significant differences between products in mean log10 colony-forming units after the initial wash (p = 0.61), nor were there significant differences in products after 5 days among subjects washing six times per day. For those who washed 18 times per day, however, the effectiveness of all three antimicrobial soaps was significantly better than that of the control soap (p less than 0.05). Chlorhexidine gluconate produced significantly greater reductions than triclosan or parachlorometaxylenol (p less than 0.05), which were not significantly different from each other. On the basis of these findings an antimicrobial soap is recommended when handwashing frequency is high and a long-term reduction in colonizing flora is desirable. When handwashing frequency is low (6 times/day), there seems to be less advantage of one product over another, although the use of chlorhexidine gluconate resulted in greater reductions at both high and low handwashing frequencies.

Sporicidal activity of local anaesthetics and their binary combinations with preservatives

The sporicidal activity of a 1% solution of five local anaesthetics and five preservatives (cetrimide, chlorocresol, chlorhexidine, phenoxyethanol and phenylmercuric nitrate) at their commonly used concentrations, alone and in binary combinations, was determined against Bacillus subtilis and Aspergillus niger spores at different temperature levels by surface viable count technique. The sporicidal activity of all tested systems was temperature dependent and A. niger spores were much more sensitive to the effect of the test systems than B. subtilis spores. The temperatures at which 99% kill is achieved after 30 min exposure were calculated. For local anaesthetics used singly against A. niger the recorded temperatures were 30 degrees C for amethocaine, 45 degrees C for amylocaine, 43 degrees C for cincochaine, 48 degrees C and 50 degrees C for lignocaine and procaine, respectively. A control temperature of 58 degrees C for saline solution was observed. Much higher temperatures were recorded for B. subtilis spores. Cincochaine was the most effective local anaesthetic with a recorded temperature of 60 degrees C for a 99% kill while amylocaine and amethocaine showed temperatures of 84 and 90 degrees C respectively. Procaine, lignocaine as well as the control saline solution recorded temperatures higher than 100 degrees C. Among the 25 binary combinations of local anaesthetics and preservatives tested, the most pronounced potentiation of the sporicidal activity against fungal spores was recorded with chlorocresol combinations, while other combinations of the four remaining preservatives showed different types of interactions at various temperature levels.

'Cialit' as a tissue preservative: a microbiological assessment

We describe bacterial contamination of a 'Cialit'-preserved cartilage bank which continued after a variety of changes to the harvesting and preservation protocols during a 3-year prospective study. Our results emphasize the importance of adequate tissue bank microbiological screening. Alternative methods of tissue preservation should be considered.

The sporicidal activity and inactivation of chlorhexidine gluconate in aqueous and alcoholic solution

The sporicidal activity of chlorhexidine gluconate in aqueous and alcoholic solution against spores of Bacillus subtilis was examined over a broad temperature range. Activity was not observed at 20 degrees C even with concentrations as high as 10% chlorhexidine. Temperatures of 37 degrees-70 degrees C in combination with such high concentrations were required for reductions in spore viability. No viable spores were recoverable after 4 h contact at 55 degrees C with 10% aqueous chlorhexidine and none after 3 h contact with the alcoholic solution. Because of the high concentrations necessary for activity and the possibility of sporostasis occurring from inefficient chlorhexidine inactivation, existing inactivation systems were examined and modified to obtain satisfactory results. The spores of other Bacillus species examined (B. cereus, B. megaterium and B. stearothermophilus) proved to be considerably less resistant than those of B. subtilis. Presence of organic matter had little effect on the activity.

Sporicidal activity of local anaesthetics and their binary combinations with preservatives

The sporicidal activity of 1% solutions of five local anaesthetics and five preservatives (cetrimide, chlorocresol, chlorhexidine, phenoxyethanol and phenylmercuric nitrate) at their pharmacopeial concentrations, alone and in binary combinations was determined against Bacillus subtilis and Aspergillus niger spores at different temperature levels by the surface viable count technique. The sporicidal activity of all tested systems were temperature dependent. A. niger spores were much more sensitive to the tested systems than B. subtilis spores. The temperature at which 99% of all spores were killed after 30 min exposure time of the anaesthetics were calculated. In case of the local anaesthetics alone against spores of A. niger the recorded temperatures were 30 degrees C for amethocaine, 45 degrees C for both amylocaine and cincochaine, 48 degrees C and 50 degrees C for lignocaine and procaine, respectively, in contrast to 58 degrees C in a control with saline solution. Much higher temperatures were calculated against B. subtilis spores. Cincochaine was the most effective local anaesthetic with a recorded temperature of 60 degrees C, where 99% killing occurred. Amylocaine and amethocaine showed temperatures of 84 degrees C and 90 degrees C, respectively. Procaine, lignocaine as well saline solution as a control caused a 99% killing effect at temperatures higher than 100 degrees C. Among the 25 tested binary combinations of local anaesthetics and preservatives, the highest incidence of potentiation of the sporicidal activity was recorded with chlorocresol combinations, while other combinations of the four remaining preservatives showed different types of interactions at different percentages.

Reversal of the surface effects of chlorhexidine diacetate on cells of Providencia stuartii

Chlorhexidine diacetate (CHA) increased the hydrophobicity of the cell surface of cells of three strains of Providencia stuartii. Removal of at least some of the CHA from the cells by washing them with an appropriate antidote partially reversed the hydrophobicity-increasing action of the biguanide. The effects of other treatments on cell surface hydrophobicity were examined with these strains and, for comparison, with two strains each of Escherichia coli and Pseudomonas aeruginosa: ethylenediamine tetraacetic acid affected all strains, although not to the same extent, whereas thermal injury (55 degrees C) produced marked changes only with the two E. coli strains.