Modeling COVID-19 infection risks for a single hand-to-fomite scenario and potential risk reductions offered by surface disinfection

We used a quantitative microbial risk assessment approach to relate log₁₀ disinfection reductions of SARS-CoV-2 bioburden to COVID-19 infection risks. Under low viral bioburden, minimal log₁₀ reductions may be needed to reduce infection risks for a single hand-to-fomite touch to levels lower than 1:1,000,000, as a risk comparison point. For higher viral bioburden conditions, log₁₀ reductions of more than 2 may be needed to achieve median infection risks of less than 1:1,000,000.

Reducing antibiotic prescribing and addressing the global problem of antibiotic resistance by targeted hygiene in the home and everyday life settings: A position paper

Antimicrobial resistance (AMR) continues to threaten global health. Although global and national AMR action plans are in place, infection prevention and control is primarily discussed in the context of health care facilities with home and everyday life settings barely addressed. As seen with the recent global SARS-CoV-2 pandemic, everyday hygiene measures can play an important role in containing the threat from infectious microorganisms. This position paper has been developed following a meeting of global experts in London, 2019. It presents evidence that home and community settings are important for infection transmission and also the acquisition and spread of AMR. It also demonstrates that the targeted hygiene approach offers a framework for maximizing protection against colonization and infections, thereby reducing antibiotic prescribing and minimizing selection pressure for the development of antibiotic resistance. If combined with the provision of clean water and sanitation, targeted hygiene can reduce the circulation of resistant bacteria in homes and communities, regardless of a country's Human Development Index (overall social and economic development). Achieving a reduction of AMR strains in health care settings requires a mirrored reduction in the community. The authors call upon national and international policy makers, health agencies, and health care professionals to further recognize the importance of targeted hygiene in the home and everyday life settings for preventing and controlling infection, in a unified quest to tackle AMR.

Developing an Evidence-Based Approach to Domestic Hygiene Which Protects Against Infection Whilst Also Addressing Sustainability Issues

Changes in recent years mean that preventing infection through hygiene in home and everyday life has become increasingly important. In developing and promoting home and everyday life hygiene, a number of issues which represent a barrier to change need to be addressed and balanced against the need for effective hygiene. These include environmental and toxicity issues, and concerns about antibiotic resistance and whether we have become “too clean”. Education of the public is key, but this can only be achieved if hygiene practice is based on a simple, plausible approach to hygiene, which health professionals and the public can relate to. This in turn needs to be underpinned by an evidence base which demonstrates to health professionals and other hygiene stakeholders who communicate with the public that the procedures and products which they advise are capable of reducing infection risks to an acceptable level, with sustainable use of resource necessary to deliver hygiene such as water, heat, microbiocides etc. The purpose of this paper is to outline a multimodal targeted approach to home and everyday life hygiene based on risk management. This includes a framework for developing effective and sustainable hygiene practices, including hand hygiene, surface hygiene and laundering practices.

Time to abandon the hygiene hypothesis: new perspectives on allergic disease, the human microbiome, infectious disease prevention and the role of targeted hygiene

Aims:

To review the burden of allergic and infectious diseases and the evidence for a link to microbial exposure, the human microbiome and immune system, and to assess whether we could develop lifestyles which reconnect us with exposures which could reduce the risk of allergic disease while also protecting against infectious disease.

Methods:

Using methodology based on the Delphi technique, six experts in infectious and allergic disease were surveyed to allow for elicitation of group judgement and consensus view on issues pertinent to the aim.

Results:

Key themes emerged where evidence shows that interaction with microbes that inhabit the natural environment and human microbiome plays an essential role in immune regulation. Changes in lifestyle and environmental exposure, rapid urbanisation, altered diet and antibiotic use have had profound effects on the human microbiome, leading to failure of immunotolerance and increased risk of allergic disease. Although evidence supports the concept of immune regulation driven by microbe–host interactions, the term ‘hygiene hypothesis’ is a misleading misnomer. There is no good evidence that hygiene, as the public understands, is responsible for the clinically relevant changes to microbial exposures.

Conclusion:

Evidence suggests a combination of strategies, including natural childbirth, breast feeding, increased social exposure through sport, other outdoor activities, less time spent indoors, diet and appropriate antibiotic use, may help restore the microbiome and perhaps reduce risks of allergic disease. Preventive efforts must focus on early life. The term ‘hygiene hypothesis’ must be abandoned. Promotion of a risk assessment approach (targeted hygiene) provides a framework for maximising protection against pathogen exposure while allowing spread of essential microbes between family members. To build on these findings, we must change public, public health and professional perceptions about the microbiome and about hygiene. We need to restore public understanding of hygiene as a means to prevent infectious disease.

A unified framework for developing effective hygiene procedures for hands, environmental surfaces and laundry in healthcare, domestic, food handling and other settings

Hygiene procedures for hands, surfaces and fabrics are central to preventing spread of infection in settings including healthcare, food production, catering, agriculture, public settings, and home and everyday life. They are used in situations including hand hygiene, clinical procedures, decontamination of environmental surfaces, respiratory hygiene, food handling, laundry hygiene, toilet hygiene and so on. Although the principles are common to all, approaches currently used in different settings are inconsistent. A concern is the use of inconsistent terminology which is misleading, especially to people we need to communicate with such as the public or cleaning professionals. This paper reviews the data on current approaches, alongside new insights to developing hygiene procedures. Using this data, we propose a more scientifically-grounded framework for developing procedures that maximize protection against infection, based on consistent principles and terminology, and applicable across all settings. A key feature is use of test models which assess the state of surfaces after treatment rather than product performance alone. This allows procedures that rely on removal of microbes to be compared with those employing chemical or thermal inactivation. This makes it possible to ensure that a consistent "safety target level" is achieved regardless of the type of procedure used, and allows us deliver maximum health benefit whilst ensuring prudent usage of antimicrobial agents, detergents, water and energy.

Preventing infection in the home

F undamental to controlling infection transmission in the home is the need to recognise it as an environment where all human activities occur, including food hygiene, hand hygiene and hygiene related to care of vulnerable groups. In recent years the concept of a risk assessment/risk reduction approach to hygiene has successfully controlled microbial risks in food and other manufacturing environments.

To deliver hygiene policy with real health benefits it is now accepted that a risk-based approach must also be developed for the home. The first step, hazard characterisation, involves identifying sites and surfaces where pathogens most frequently occur, and whether they are likely to be present in numbers that represent an infectious dose. A risk assessment is then made by considering this information together with an assessment of the probability of human exposure to the hazard. Risk reduction is achieved by application of a suitable hygiene procedure at the appropriate time.

Developing and promoting hygiene in the home and community

The last two decades have seen infectious diseases (IDs) moving back up the health agenda. If the burden of ID is to be contained, the responsibility must be shared by the public. The International Scientific Forum on Home Hygiene (IFH) is working to raise awareness of the role of home hygiene, and promote understanding of hygiene practice. To develop a strategy for home hygiene, IFH has used the available scientific data to formulate a risk-based approach. This "targeted hygiene" approach maximises protection against infection, whilst minimising any impact on the environment from cleaning and disinfection products, minimising any risks associated antimicrobial resistance, and sustaining interaction with the microbial flora of the environment. IFH has developed a comprehensive range of materials which are being promoted through the IFH website and other channels. Analysis of website traffic indicates significant demand for home hygiene information including scientific material and information in "plain language".

[Prevention of infection through hygiene in the home and community. The need for a family-centred approach]

Over the past 20 years, infectious disease has moved back up the health agenda, prompting new emphasis on developing strategies for prevention and control, including reduction of spread of infection within the family at home and in their social and work lives outside the home. This paper reviews the various issues that have contributed to this trend. In response to the need for a science-based approach to home hygiene, the International Scientific Forum on Home Hygiene has developed an approach based on risk management which involves identifying the critical control points for preventing the spread of infectious diseases in the home. If we are to be successful in achieving behaviour change in the community, we need to develop a family-centred approach which ensures an understanding of infectious disease agents and their mechanism of spread.

Importance of disinfection as a means of prevention in our changing world hygiene and the home

Contrary to expectation, the risks of infection are growing rather than declining, even in everyday life. After all, who is able to make a distinction between cleanliness and hygiene? This situation is further compounded by the growing number of persons who are susceptible to infections. If one wants to combat infectious diseases in an economically feasible and consistent manner, public support must be sought. In turn, the public have a right to be informed in a proper and responsible manner. The difference between "dirt" and "contamination" must be highlighted once again.To create a forum for everyday hygiene, an international expert working group was set up (http://www.ifh-homehygiene.org). The hallmark of this group is its holistic view of hygiene in the family setting, something that is not true in the case of most public health sectors. Based on the latest study results, the International Forum for Hygiene (IFH) has coined a new motto "Selective Hygiene", and evaluates the causes of infection so as to be able to react in an appropriate manner. The aim cannot be routine, daily repetitive decontamination of all potentially dangerous microbes that are found in a normal household, but rather selective reaction to important transmission processes, i.e. hands and foodstuffs, kitchen, bathroom and toilet. The motto can be summarized as follows: "Do the right thing at the right time". This, however, calls for an understanding of the risks and of effective procedures for microbial reduction. Depending on the respective circumstances, hands can be washed with running water or by using a hand disinfectant. Even experts must learn that hygiene in the home must be evaluated differently from that of the hospital setting. The comparatively lower risk is offset by markedly less awareness of the risks involved. These risks can be significantly increased by any members of the household who are ill. Hence in some cases it is advisable to use disinfectants in the home too - even if it is claimed in certain quarters that we have become "too clean", and have thus lower immunity. Study data demonstrate that disinfectants have become indispensable in the household in the context of "selective hygiene strategies" so as to prevent infectious diseases.

Methicillin-resistant Staphylococcus aureus, Clostridium difficile, and extended-spectrum beta-lactamase-producing Escherichia coli in the community: assessing the problem and controlling the spread

Although health care-associated methicillin resistant staphylococcus aureus and clostridium difficile strains are primarily a risk to hospital patients, people are increasingly concerned about their potential to circulate in the community and the home. They are thus looking for support in order to understand the extent of the risk, and guidance on how to deal with situations where preventing infection from these species becomes their responsibility. A further concern are the community-acquired MRSA and C. difficile strains, and other antibiotic resistant strains circulating in the community such as the Extended-spectrum beta-lactamase (ESBL) Escherichia coli. In response to concerns about such organisms in the community, the International Scientific Forum on Home Hygiene has produced a report evaluating MRSA, C. difficile, and ESBL-producing E. coli from a community viewpoint. The report summarizes what is known about their prevalence in the community, their mode of transmission in the home, and the extent to which they represent a risk. It also includes "advice sheets" giving practical guidance on what to do when there is a risk of infection transmission in the home.

Too clean, or not too clean: the hygiene hypothesis and home hygiene

The 'hygiene hypothesis' as originally formulated by Strachan, proposes that a cause of the recent rapid rise in atopic disorders could be a lower incidence of infection in early childhood, transmitted by unhygienic contact with older siblings. Use of the term 'hygiene hypothesis' has led to several interpretations, some of which are not supported by a broader survey of the evidence. The increase in allergic disorders does not correlate with the decrease in infection with pathogenic organisms, nor can it be explained by changes in domestic hygiene. A consensus is beginning to develop round the view that more fundamental changes in lifestyle have led to decreased exposure to certain microbial or other species, such as helminths, that are important for the development of immunoregulatory mechanisms. Although this review concludes that the relationship of the hypothesis to hygiene practice is not proven, it lends strong support to initiatives seeking to improve hygiene practice. It would however be helpful if the hypothesis were renamed, e.g. as the 'microbial exposure' hypothesis, or 'microbial deprivation' hypothesis, as proposed for instance by Bjorksten. Avoiding the term 'hygiene' would help focus attention on determining the true impact of microbes on atopic diseases, while minimizing risks of discouraging good hygiene practice.

Contamination of chicken carcasses in Gauteng, South Africa, by Salmonella, Listeria monocytogenes and Campylobacter

The presence of the foodborne pathogens, Salmonella spp., Listeria monocytogenes and Campylobacter spp., on 99 fresh and frozen chicken carcasses sourced from various retailers in Gauteng, South Africa, was investigated. Using culture methods, 60.6% of the carcasses were found to be contaminated with one or more pathogens, with 19.2%, 19.2% and 32.3% of the carcasses being found to harbour Salmonella, L. monocytogenes and Campylobacter, respectively. The extent of contamination with one or more pathogens was not significantly different (p>0.1) between fresh or frozen samples or between samples from butcheries, supermarkets or street vendors. Significantly more (p<0.1) fresh carcasses from butcheries than from other outlets were contaminated with Salmonella, while more fresh carcasses from supermarkets were contaminated with Campylobacter. The proportion of carcasses with L. monocytogenes from all sources were similar. Polymerase chain reaction (PCR) results indicate an even higher extent of pathogen contamination, but the PCR techniques need to be further refined before they can be used routinely.

Effects of cleaning and disinfection in reducing the spread of Norovirus contamination via environmental surfaces

A reverse transcriptase polymerase chain reaction assay was used to study the transfer of Norovirus (NV) from contaminated faecal material via fingers and cloths to other hand-contact surfaces. The results showed that, where fingers come into contact with virus-contaminated material, NV is consistently transferred via the fingers to melamine surfaces and from there to other typical hand-contact surfaces, such as taps, door handles and telephone receivers. It was found that contaminated fingers could sequentially transfer virus to up to seven clean surfaces. The effectiveness of detergent- and disinfectant-based cleaning regimes typical of those that might be used to decontaminate faecally contaminated surfaces and reduce spread of NV was also compared. It was found that detergent-based cleaning with a cloth to produce a visibly clean surface consistently failed to eliminate NV contamination. Where there was faecal soiling, although a combined hypochlorite/detergent formulation at 5000 ppm of available chlorine produced a significant risk reduction, NV contamination could still be detected on up to 28% of surfaces. In order consistently to achieve good hygiene, it was necessary to wipe the surface clean using a cloth soaked in detergent before applying the combined hypochlorite/detergent. When detergent cleaning alone or combined hypochlorite/detergent treatment failed to eliminate NV contamination from the surface and the cleaning cloth was then used to wipe another surface, the virus was transferred to that surface and to the hands of the person handling the cloth. In contrast, were surfaces where contaminated with NV-infected faecal suspension diluted to 1 in 10 and 1 in 80, intended to simulate surfaces that have become contaminated after secondary transfer, treatment with a combined bleach/detergent formulation, without prior cleaning, was sufficient to decontaminate surfaces and prevent transfer.

The effects of cleaning and disinfection in reducing Salmonella contamination in a laboratory model kitchen

AIMS

To establish a laboratory model to compare the effectiveness of detergent-based disinfection procedures for reducing cross-contamination risks during handling of contaminated chicken.

METHODS AND RESULTS

During handling of chickens, artificially contaminated with Salmonella enteritidis PT4, the organism was widely spread to hands, cloths, and hand- and food-contact surfaces. Hygiene procedures were assessed on the basis of their ability to reduce the number of recoverable salmonellas to <1 CFU. Although detergent-based cleaning using a typical bowl-wash routine without rinsing produced some risk reduction (from 100 to 61.4% of contaminated surfaces), it was insufficient to consistently restore surfaces to a hygienic state. By combining detergent-based cleaning with a rinsing step or with hypochlorite at 500 ppm (of available chlorine) some further reduction in microbial risk was achieved, but was not considered satisfactory for food hygiene purposes. By contrast the risk reduction produced by hypochlorite at 5000 ppm was highly significant and was sufficient to reduce the number of contaminated surfaces to 2.9%.

CONCLUSIONS

A key step in achieving a hygienic state through detergent-based cleaning is rinsing but even this will not produce a 'hygienic' result for difficult surfaces such as the chopping board or the dishcloth. Disinfectant compounds should be considered in order to reduce the potential for foodborne cross infection within the home environment.

SIGNIFICANCE AND IMPACT OF THE STUDY

Although tests are available to determine the performance of disinfectants, there are no quantitative procedures available to compare the risk reduction achieved by disinfection with that produced by detergent-based procedures. This study describes a reproducible laboratory method which can be used to differentiate the effectiveness of different hygiene procedures for reducing cross-contamination risks during food handling.

Developing an effective policy for home hygiene: a risk-based approach

Evaluation of the infection potential in the home suggests that improved hygiene practice could significantly reduce the impact of infectious diseases. Fundamental to developing infection prevention policy for the home is the need to recognise that people live in an environment where all human activities occur, including food and water hygiene, hand hygiene, and hygiene related to care of vulnerable groups. In all these situations, reducing infection risks is based on the same underlying microbiological principles. In developing countries, disposal of human and animal excreta and other waste is often also the responsibility of the family and community. Adopting a holistic approach provides the opportunity for a rational approach to home hygiene based on risk assessment. The International Scientific Forum on Home Hygiene (IFH) believes that to deliver hygiene policy with real health benefits, a risk-based approach must be developed and promoted for the home. A risk-based approach starts from the principle that pathogens are introduced continually into homes on people, food and water, pets, insects and air. Inadequate disposal of human and animal excreta serves to increase this risk. Additionally, sites where stagnant water accumulates, such as sinks, toilets and cleaning cloths can support microbial growth and become a source of infection. By assessing the frequency occurrence of pathogens and potential pathogens on hands, hand and food contact surfaces, laundry, reservoir and reservoir/disseminator sites, together with the potential for transfer in the home, the exposure risk can be assessed.

Significance of biocide usage and antimicrobial resistance in domiciliary environments

Recent events have raised awareness of the need for effective hygiene in the home. Not least is the requirement to reduce antibiotic resistance by reducing the need for antibiotic prescribing. Current evidence suggests that improved hygiene in the domestic setting could have a significant impact. Recently, it has been suggested that widespread biocide usage, particularly in consumer products, may be a contributory factor in antibiotic resistance. In developing home hygiene policies, however, it is important that biocide use as an integral part of good hygiene practice is not discouraged in situations where there is real benefit. Although laboratory data indicate possible links, it is necessary to assess whether and to what extent biocide exposure could contribute to antibiotic resistance in clinical practice. The extent to which reduced susceptibility to biocides resulting from biocide exposure could compromise their 'in-use' effectiveness must also be considered. Equally, it is important that changes in susceptibility induced by biocide exposure are assessed relative to those induced by antibiotic exposure or the phenotypic changes induced by 'normal' environmental 'stresses'. It is proposed that to be effective, home hygiene policy should be based on the concept of risk assessment and risk prevention. Using this approach, critical risk situations are identified and appropriate hygiene procedures applied to reduce risks. This may involve either soap and water cleaning, or cleaning combined with a disinfection process. A 'targeted' hygiene approach not only provides the most effective means of preventing infectious disease, it also offers a means of addressing concerns about 'too much hygiene' and 'too many antibacterials' amongst a public who have lost confidence regarding appropriate hygiene for their home environment.

Home hygiene: a risk approach

The need to place "prevention through hygiene" at the core of strategies for infection prevention has been emphasised by recent events. Indications are that re-evaluation of current practice and the promotion of improved hygiene in the domestic setting could have a significant impact in reducing infectious disease. If the public are to play a part however they must be properly informed. Encouraging the concept of the home as a setting in which the whole range of activities occur, including food hygiene, personal hygiene and hygiene related to medical care, provides the opportunity for a rational approach to home hygiene based on risk assessment. In the home surfaces (including hand surfaces) and other sites play an important part in the transmission of infection, especially food-borne infections. From an assessment of the frequency of occurrence of pathogens and potential pathogens at reservoirs, disseminators and hand and food contact sites together with the potential for transfer within the home, the risks of exposure can be assessed. This can be used to develop a rational approach in which effective hygiene procedures involving cleaning and disinfection as appropriate are targeted at these sites to reduce risks of cross contamination. This approach is consistent with the view that good home hygiene is not about "getting rid of household germs" but about targeting hygiene measures appropriately to reduce exposure to germs and thereby prevent cross infection. In motivating change, education programmes must take account of concerns related to antimicrobial resistance, the environment and the "health" of the immune system.

Achieving hygiene in the domestic kitchen: the effectiveness of commonly used cleaning procedures

AIMS

To quantify the transmission of Salmonella and Campylobacter to hands, cloths, and hand- and food-contact surfaces during the preparation of raw poultry in domestic kitchens, and to examine the impact on numbers of these bacteria of detergent-based cleaning alone, or in conjunction with thorough rising.

METHODS AND RESULTS

Groups of volunteers prepared chickens for cooking. Surfaces were sampled either before cleaning or after cleaning using water and detergent with or without thorough rinsing. Although cleaning followed by rinsing consistently achieved decontamination of surfaces contaminated with Campylobacter, significant numbers of surfaces were still contaminated with low numbers of Salmonella. Where cloths contaminated with Salmonella were stored overnight, a reduction in the efficacy of detergent-based cleaning regimes was observed.

CONCLUSIONS

Rinsing is the critical step in ensuring that bacteria are removed from surfaces during cleaning, but this may still leave residual contamination. Growth of Salmonella occurs in some contaminated cloths during overnight storage; Salmonella on cloths stored overnight are also more difficult to remove by washing.

SIGNIFICANCE AND IMPACT OF THE STUDY

Rinsing, as part of the cleaning process, is a critical step in achieving hygiene in the kitchen. However, to achieve completely hygienic surfaces, the use of an antimicrobial agent may be necessary.

Significance of biocide usage and antimicrobial resistance in domiciliary environments

Recent events have raised awareness of the need for effective hygiene in the home. Not least is the requirement to reduce antibiotic resistance by reducing the need for antibiotic prescribing. Current evidence suggests that improved hygiene in the domestic setting could have a significant impact. Recently, it has been suggested that widespread biocide usage, particularly in consumer products, may be a contributory factor in antibiotic resistance. In developing home hygiene policies, however, it is important that biocide use as an integral part of good hygiene practice is not discouraged in situations where there is real benefit. Although laboratory data indicate possible links, it is necessary to assess whether and to what extent biocide exposure could contribute to antibiotic resistance in clinical practice. The extent to which reduced susceptibility to biocides resulting from biocide exposure could compromise their 'in-use' effectiveness must also be considered. Equally, it is important that changes in susceptibility induced by biocide exposure are assessed relative to those induced by antibiotic exposure or the phenotypic changes induced by 'normal' environmental 'stresses'. It is proposed that to be effective, home hygiene policy should be based on the concept of risk assessment and risk prevention. Using this approach, critical risk situations are identified and appropriate hygiene procedures applied to reduce risks. This may involve either soap and water cleaning, or cleaning combined with a disinfection process. A 'targeted' hygiene approach not only provides the most effective means of preventing infectious disease, it also offers a means of addressing concerns about 'too much hygiene' and 'too many antibacterials' amongst a public who have lost confidence regarding appropriate hygiene for their home environment.

Survival of Salmonella in bathrooms and toilets in domestic homes following salmonellosis

The survival and environmental spread of Salmonella bacteria from domestic toilets was examined in homes, where a family member had recently suffered an attack of salmonellosis. In four out of six households tested, Salmonella bacteria persisted in the biofilm material found under the recess of the toilet bowl rim which was difficult to remove with household toilet cleaners. In two homes Salmonella bacteria became incorporated into the scaly biofilm adhering to the toilet bowl surface below the water line. Salmonella enteritidis persisted in one toilet for 4 weeks after the diarrhoea had stopped, despite the use of cleaning fluids. Salmonellas were not isolated from normally dry areas such as, the toilet seat, the flush handle and door handle. Toilet seeding experiments were set up with Salmonella enteritidis PT4 to mimic environmental conditions associated with acute diarrhoea. Flushing the toilet resulted in contamination of the toilet seat and the toilet seat lid. In one out of three seedings, Salmonella bacteria were also isolated from an air sample taken immediately after flushing, indicating that airborne spread of the organism could contaminate surfaces in the bathroom. In the seeded toilet Salmonella bacteria were isolated from the biofilm in the toilet bowl below the waterline for up to 50 d after seeding, and also on one occasion from the bowl water. The results suggest that during diarrhoeal illness, there is considerable risk of spread of Salmonella infection to other family members via the environment, including contaminated hands and surfaces in the toilet area.

The effectiveness of hygiene procedures for prevention of cross-contamination from chicken carcases in the domestic kitchen

Thirteen sites in each of 60 domestic kitchens were examined for Salmonella and Campylobacter spp. following the preparation of a chicken for cooking and the application of different hygiene regimes. During food preparation bacteria became widely disseminated to hand and food contact surfaces. Where cleaning was carried out with detergent and hot water using a prescribed routine there was no significant decrease in the frequency of contaminated surfaces. Where hypochlorite was used in addition, a significant reduction in the number of contaminated sites was observed. The study suggests that there is a need to better understand and promote effective hygiene procedures for the domestic kitchen.

Flow cytometric analysis of chlorhexidine action

The mechanism by which chlorhexidine kills bacteria is still ill defined. We have investigated the action of chlorhexidine on Escherichia coli JM101/psb311 using a combination of flow cytometry and traditional methods. Chlorhexidine-induced uptake by E. coli cells of bis-(1,3-dibutylbarturic acid) trimethine oxonol and propidium iodide, which monitor membrane potential and membrane integrity respectively, was shown to be concentration dependent for the range 0.003-0.3 mmol-1. In addition, cells in log phase growth were more susceptible to 0.03 mmol-1 chlorhexidine than those in stationary phase. There was, however, no direct correlation between dye uptake and decline in colony forming units.

Antimicrobial effects of tea-tree oil and its major components on Staphylococcus aureus, Staph. epidermidis and Propionibacterium acnes

Major components of two tea-tree oil samples were identified using thin layer and gas-liquid chromatography (TLC and GLC). Using a TLC-bioautographic technique, the tea-tree oils, terpinen-4-ol, alpha-terpineol and alpha-pinene were found to be active against Staphylococcus aureus, Staph. epidermidis and Propionibacterium acnes whereas cineole was inactive against these organisms. The MIC values of the three active compounds increased in the order alpha-terpineol < terpinen-4-ol < alpha-pinene for all three micro-organisms. MIC values of the tea-tree oils and terpinen-4-ol were lower for P. acnes than for the two staphylococci. This study supports the use of tea-tree oil in the treatment of acne, and demonstrates that terpinen-4-ol is not the sole active constituent of the oil.

In-vitro evaluation of the antimicrobial activities of Enantia chlorantha Oliv. extractives

A bioactivity-directed fractionation of the root-and stem-barks of Enantia chlorantha resulted in the isolation of palmatine chloride 1 and jatrorrhizine chloride 2 as the major antimicrobial constituents. MIC determinations indicated that these compounds were superior to those of well established broad spectrum antibiotics against some of the organisms used.

Interaction of iodine with Bacillus subtilis spores and spore forms

Buffered solutions of iodine (pH 7.0) were effective against Bacillus subtilis spores, but concentrations and contact times for effective sporicidal action were relatively high. Concentrations of 500 to 1000 ppm available iodine with a contact time of 30-45 min were required to produce a 3-5 log reduction. Treatment of spores with agents which caused progressive extraction of coat protein and cortex hexosamine was associated with increased sensitivity to iodine. Treatment of spores with iodine produced extraction of spore coat protein which was potentiated in the presence of NaOH, but there was no evidence of breakdown of cortex hexosamines or release of dipicolinic acid, either from intact spores or spore protoplasts. Sporicidal concentrations of iodine stimulated the uptake of (32P) phosphate over an initial period of 30-40 min, but phosphate then leaked from the cells; 1000 ppm available iodine produced total loss within 60 min. Results of this investigation are consistent with previous findings which suggest that the resistance of spores to biocides is related to the barrier properties of the spore outer layers and that the sporicidal action of halogen-releasing agents is related to their ability to cause coat and cortex degradation, leading to rehydration of the spore protoplast and allowing diffusion to their site of action on the underlying protoplast.

An evaluation of the repeatability and reproducibility of a surface test for the activity of disinfectants

A collaborative study was carried out to determine the precision of a disinfectant surface test method which is currently under consideration for development as a harmonized European standard surface test. Results indicate that significant variation in microbicidal effect occurs both within and between test laboratories despite careful standardization of test conditions, but that the variability may be less than that associated with suspension tests. Indications are that much of this variability derives from random variations in the resistance of the test strains from day to day and, most particularly, from test period to test period both within as well as between laboratories. It is concluded that although the test may be sufficiently reliable to be used as a standard method, adequate replication must be specified to distinguish borderline pass from borderline fail concentrations.

The use of impedance for preservative efficacy testing of pharmaceuticals and cosmetic products

Impedance was investigated for its applicability to preservative efficacy testing of pharmaceuticals and cosmetics. A good correlation between impedance detection time (Td) and total colony counts (colony-forming units (cfu)) was obtained for untreated suspensions of Staphylococcus aureus, Candida albicans, Aspergillus niger and Pseudomonas aeruginosa in phosphate-buffered saline (PBS). A good correlation between Td and the number of cfu was also obtained for suspensions of test organisms treated for varying contact periods with selected concentrations of chlorhexidine, methyl paraben and phenoxyethanol in PBS, and methyl paraben in cetomacrogol cream, but these correlations were significantly different from those for untreated suspensions. It was found that for any given number of cfu the Td for preservative treated cells was extended. It is concluded that impedance represents a valid method for preservative efficacy testing of pharmaceuticals and cosmetics which could be used to achieve more comprehensive but economic screening of formulations against a wider range of preservative systems and concentrations than is the current approach where only a limited range of systems are tested because of the workload involved.

A study of the use of rapid methods for preservative efficacy testing of pharmaceuticals and cosmetics

Three rapid microbiological methods, impedance, the direct epifluorescence technique (DEFT-MEM) and ATP bioluminescence (ATP-B) were evaluated for their applicability to preservative efficacy testing (PET) of pharmaceuticals and cosmetics. A good correlation between rapid method response and total colony counts was obtained for untreated suspensions of Staphylococcus aureus, Pseudomonas aeruginosa and Candida albicans with all three methods but, for Aspergillus niger, with impedance only. For chlorhexidine-treated suspensions of Staph. Aureus and C. albicans, a good dose-response curve was obtained with impedance, but ATP-B and DEFT-MEM methods underestimated the kill by the order of 1-6 logs. From the results of this study it is concluded that impedance offers an alternative method to colony counting methods for PET but, at their present level of method development, neither DEFT-MEM nor ATP-B can be considered as satisfactory.

Evaluation of the repeatability and reproducibility of European suspension test methods for antimicrobial activity of disinfectants and antiseptics

A collaborative study to determine the precision of the 1987 Method of test for the antimicrobial activity of disinfectants in food hygiene is described. The repeatability and reproducibility of the test was found to vary according to the nature of the test organism, the type of disinfectant product and the skill of the operator. Results indicate that significant differences in microbicidal effect (ME values) occur within test laboratories between test periods as well as between laboratories, and that much of this variability derives from apparently random variations in the resistance of test strains from day to day and test period to test period. Indications are that although the test is sufficiently reliable to be used as a standard method, adequate test replication must be specified to distinguish borderline pass from borderline fail disinfectant concentrations. The implications of the results in relation to current work on the development of unified European test methods for disinfectants is discussed.

Interaction of Bacillus subtilis spores with sodium hypochlorite, sodium dichloroisocyanurate and chloramine-T

Solutions of chlorine-releasing agents (CRAs) show varying activity against Bacillus subtilis spores; sodium hypochlorite (NaOCl) shows higher activity than sodium dichloroisocyanurate (NaDCC) which is more active than chloramine-T. Investigations with coat- and cortex-extracted spores indicate that resistance to CRAs depends not only on the spore coat but also the cortex. Whereas extraction of alkali-soluble coat protein increased sensitivity to NaOCl and NaDCC, degradation of coat and cortex material was required to achieve significant activity with chloramine-T. NaOCl (in the presence and absence of NaOH) and NaDCC (in the presence of NaOH only) produced degradation of spore coat and cortex material which may be related to their rapid sporicidal action at low concentrations under these conditions. By contrast, chloramine-T produced no degradation of cortex peptidoglycan and was only effective against normal and alkali-treated spores at high concentrations, requiring extraction of peptidoglycan with urea/dithiothreitol/sodium lauryl sulphate (UDS) or UDS/lysozyme to achieve significant activity at low concentrations. Results suggest that the sporicidal action of CRAs is associated with spore coat and cortex degradation causing rehydration of the protoplast allowing diffusion to the site of action on the underlying protoplast.