Assessing the activity of microbicides against bacterial spores: knowledge and pitfalls

Review of techniques for the in-situ sterilization of soil contaminated with Bacillus anthracis spores or other pathogens

This review summarizes the literature on efficacy of techniques to sterilize soil. Soil may need to be sterilized if contaminated with pathogens such as Bacillus anthracis. Sterilizing soil in-situ minimizes spread of the bio-contaminant. Soil is difficult to sterilize, with efficacy generally diminishing with depth. Methyl bromide, formaldehyde, and glutaraldehyde are the only soil treatment options that have been demonstrated at full-scale to effectively inactivate Bacillus spores. Soil sterilization modalities with high efficacy at bench-scale include wet and dry heat, metam sodium, chlorine dioxide gas, and activated sodium persulfate. Simple oxidants such as chlorine bleach are ineffective in sterilizing soil.

Enhancement of microbicidal efficacy of chemical disinfectants when combined with ultrasound technology

AIMS

This study investigated the antimicrobial efficacy of ultrasound technology (US) in combination with two different disinfectants (Disinfectant A and Disinfectant B), containing peracetic acid (PAA) and quaternary ammonium compounds (QACs), respectively, against two sporigenic pathogens, Aspergillus brasiliensis and Bacillus subtilis.

METHODS AND RESULTS

The microbicidal activity of the coupled treatment was compared with the use of the disinfectants alone, and the efficacy of the disinfection strategies was evaluated by the log reduction of the population of the microorganism inoculated onto stainless-steel surface. The combination treatment resulted in a log reduction of 5.40 and 3.88 (Disinfectant A + US) against A. brasiliensis and B. subtilis, at 850 and 500 ppm PAA, compared to 265 and 122 (Disinfectant A only). For Disinfectant B, in combination with US, showed a logarithmic reduction of 5.04 and 4.79 against A. brasiliensis and B. subtilis at 078% v v-1 and 392% v v-1 QACs, respectively, vs. 1.58 and 1.64 (Disinfectant B only). Moreover, no colonies or not statistically significant growth was observed within the US bath containing the disinfectant.

CONCLUSIONS

The antimicrobial efficacy of the two disinfectants was greatly enhanced when used in combination with US, and this also makes it possible to avoid the overuse of chemicals for disinfection.

The potential to manage releases of Bacillus anthracis using bioretention and a high flow media filter: Results of simulated runoff testing with tracer spores Bacillus globigii

The threat of bioterrorism has spurred research on the decontamination and containment of different agents. Anthrax [causative agent Bacillus anthracis (Ba)] is a disease that can lead to severe infections within human and animals, particularly when inhaled. This research investigated the use of spore-contaminated simulated runoff events into stormwater control measures (SCMs), which are designed to retain and improve the quality of runoff and may have the potential to filter and contain the spores. In this study, the effectiveness of a bioretention cell (BRC) and high flow media filter (HFMF) in Huron, Ohio, were evaluated for removal of Bacillus globigii (Bg) spores (a harmless cognate of Ba). Three 4-8 mm simulated runoff events were created for each SCM using a fire hydrant and Bg spores were injected into the runoff upstream of the SCM inlets. The BRC significantly (p < 0.001) outperformed the HFMF in reducing Bg concentrations and loads, with an average load reduction of 1.9 log (∼99% reduction) compared to 0.4 (∼60% reduction), respectively. A probable critical design factor leading to these differences was the infiltration rate of the media and subsequent retention time within the filters, which was supported by similar disparities in suspended solids reductions. Differences in spore removal may also have been due to particle size distribution of the HFMF, which was more gravelly than the bioretention cell. At 3 and 6 months after the-simulated runoff tests, soil samples taken from both SCMs, yielding detectable Bg spores within the top 15 cm of media, with increased spore concentrations where ponding occurred for longer durations during the tests. This suggests that forebays and areas near inlets may be hotspots for spore cleanup in a real-world bioterrorism incident.

Disinfectants and antiseptics: mechanisms of action and resistance

Chemical biocides are used for the prevention and control of infection in health care, targeted home hygiene or controlling microbial contamination for various industrial processes including but not limited to food, water and petroleum. However, their use has substantially increased since the implementation of programmes to control outbreaks of methicillin-resistant Staphylococcus aureus, Clostridioides difficile and severe acute respiratory syndrome coronavirus 2. Biocides interact with multiple targets on the bacterial cells. The number of targets affected and the severity of damage will result in an irreversible bactericidal effect or a reversible bacteriostatic one. Most biocides primarily target the cytoplasmic membrane and enzymes, although the specific bactericidal mechanisms vary among different biocide chemistries. Inappropriate usage or low concentrations of a biocide may act as a stressor while not killing bacterial pathogens, potentially leading to antimicrobial resistance. Biocides can also promote the transfer of antimicrobial resistance genes. In this Review, we explore our current understanding of the mechanisms of action of biocides, the bacterial resistance mechanisms encompassing both intrinsic and acquired resistance and the influence of bacterial biofilms on resistance. We also consider the impact of bacteria that survive biocide exposure in environmental and clinical contexts.

Revisiting Oral Antiseptics, Microorganism Targets and Effectiveness

A good oral health status is mostly dependent on good oral hygiene habits, which knowingly impacts systemic health. Although controversial, chemical oral antiseptics can be useful in adjunct use to mechanical dental plaque control techniques in the prevention and management of local and overall health and well-being. This review aims to revisit, gather and update evidence-based clinical indications for the use of the most popular oral antiseptics, considering different types, microorganism targets and effectiveness in order to establish updated clinical recommendations.

Impact of benzalkonium chloride, benzethonium chloride and chloroxylenol on bacterial antimicrobial resistance

This review examined 3655 articles on benzalkonium chloride (BKC), benzethonium chloride (BZT) and chloroxylenol (CHO) aiming to understand their impact on antimicrobial resistance. Following the application of inclusion/exclusion criteria, only 230 articles were retained for analysis; 212 concerned BKC, with only 18 for CHO and BZT. Seventy-eight percent of studies used MIC to measure BKC efficacy. Very few studies defined the term 'resistance' and 85% of studies defined 'resistance' as <10-fold increase (40% as low as 2-fold) in MIC. Only a few in vitro studies reported on formulated products and when they did, products performed better. In vitro studies looking at the impact of BKC exposure on bacterial resistance used either a stepwise training protocol or exposure to constant BKC concentrations. In these, BKC exposure resulted in elevated MIC or/and MBC, often associated with efflux, and at time, a change in antibiotic susceptibility profile. The clinical relevance of these findings was, however, neither reported nor addressed. Of note, several studies reported that bacterial strains with an elevated MIC or MBC remained susceptible to the in-use BKC concentration. BKC exposure was shown to reduce bacterial diversity in complex microbial microcosms, although the clinical significance of such a change has not been established. The impact of BKC exposure on the dissemination of resistant genes (notably efflux) remains speculative, although it manifests that clinical, veterinary and food isolates with elevated BKC MIC carried multiple efflux pump genes. The correlation between BKC usage and gene carriage, maintenance and dissemination has also not been established. The lack of clinical interpretation and significance in these studies does not allow to establish with certainty the role of BKC on AMR in practice. The limited literature and BZT and CHO do not allow to conclude that these will impact negatively on emerging bacterial resistance in practice.

Bacillus cereus sensu lato biofilm formation and its ecological importance

Biofilm formation is a ubiquitous process of bacterial communities that enables them to survive and persist in various environmental niches. The Bacillus cereus group includes phenotypically diversified species that are widely distributed in the environment. Often, B. cereus is considered a soil inhabitant, but it is also commonly isolated from plant roots, nematodes, and food products. Biofilms differ in their architecture and developmental processes, reflecting adaptations to specific niches. Importantly, some B. cereus strains are foodborne pathogens responsible for two types of gastrointestinal diseases, diarrhea and emesis, caused by distinct toxins. Thus, the persistency of biofilms is of particular concern for the food industry, and understanding the underlying mechanisms of biofilm formation contributes to cleaning procedures. This review focuses on the genetic background underpinning the regulation of biofilm development, as well as the matrix components associated with biofilms. We also reflect on the correlation between biofilm formation and the development of highly resistant spores. Finally, advances in our understanding of the ecological importance and evolution of biofilm formation in the B. cereus group are discussed.

Prevalence and Antimicrobial Resistance of Paeniclostridium sordellii in Hospital Settings

(1) Background: The purpose of this study was to determine the prevalence of clostridia strains in a hospital environment in Algeria and to evaluate their antimicrobial susceptibility to antibiotics and biocides. (2) Methods: Five hundred surface samples were collected from surfaces in the intensive care unit and surgical wards in the University Hospital of Tlemcen, Algeria. Bacterial identification was carried out using MALDI-TOF-MS, and then the minimum inhibitory concentrations (MICs) of various antimicrobial agents were determined by the E-test method. P. sordellii toxins were searched by enzymatic and PCR assays. Seven products intended for daily disinfection in the hospitals were tested against Clostridium spp. spore collections. (3) Results: Among 100 isolates, 90 P. sordellii were identified, and all strains were devoid of lethal and hemorrhagic toxin genes. Beta-lactam, linezolid, vancomycin, tigecycline, rifampicin, and chloramphenicol all proved effective against isolated strains. Among all strains tested, the spores of P. sordellii exhibited remarkable resistance to the tested biocides compared to other Clostridium species. The (chlorine-based 0.6%, 30 min), (glutaraldehyde solution 2.5%, 30 min), and (hydrogen peroxide/peracetic acid 3%, 15 min) products achieved the required reduction in spores. (4) Conclusions: Our hospital’s current cleaning and disinfection methods need to be optimized to effectively remove spores from caregivers’ hands, equipment, and surfaces.

Effectiveness of calcium hypochlorite, quaternary ammonium compounds, and sodium hypochlorite in eliminating vegetative cells and spores of Bacillus anthracis surrogate

BACKGROUND

The spore-forming bacterium Bacillus anthracis causes anthrax, an often-fatal infection in animals. Therefore, a rapid and reliable strategy to decontaminate areas, humans, and livestock from B. anthracis is very critical.

OBJECTIVES

The aim of this study was performed to evaluate the efficacy of sodium hypochlorite, calcium hypochlorite, and quaternary ammonium compound (QAC) sanitizers, which are commonly used in the food industry, to inhibit spores and vegetative cells of B. anthracis surrogate.

METHODS

We evaluated the efficacy of sodium hypochlorite, calcium hypochlorite, and a QAC in inhibiting vegetative cells and spores of a B. anthracis surrogate. We treated a 0.1-mL vegetative cell culture or spore solution with 10 mL sanitizer. The samples were serially diluted and cultured.

RESULTS

We found that 50 ppm sodium hypochlorite (pH 7), 1 ppm calcium hypochlorite, and 1 ppm QAC completely eliminated the cells in vegetative state. Exposure to 3,000 ppm sodium hypochlorite (pH 7) and 300 ppm calcium hypochlorite significantly eliminated the bacterial spores; however, 50,000 ppm QAC could not eliminate all spores.

CONCLUSIONS

Calcium hypochlorite and QAC showed better performance than sodium hypochlorite in completely eliminating vegetative cells of B. anthracis surrogate. QAC was ineffective against spores of the B. anthracis surrogate. Among the three commercial disinfectants tested, calcium hypochlorite most effectively eliminated both B. anthracis vegetative cells and spores.

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.

Opportunities for the application of real-time bacterial cell analysis using flow cytometry for the advancement of sterilization microbiology

Medical devices provide critical care and diagnostic applications through patient contact. Sterility assurance level (SAL) may be defined as the probability of a single viable micro-organism occurring on an item after a sterilization process. Sterilization microbiology often relies upon using an overkill validation method where a 12-log reduction in recalcitrant bacterial endospore population occurs during the process that exploits conventional laboratory-based culture media for enumeration. This timely review explores key assumptions underpinning use of conventional culture-based methods in sterilization microbiology. Consideration is given to how such methods may limit the ability to fully appreciate the inactivation kinetics of a sterilization process such as vaporized hydrogen peroxide (VH2O2) sterilization, and consequently design efficient sterilization processes. Specific use of the real-time flow cytometry (FCM) is described by way of elucidating the practical relevance of these limitation factors with implications and opportunities for the sterilization industry discussed. Application of FCM to address these culture-based limitation factors will inform real-time kinetic inactivation modelling and unlock potential to embrace emerging opportunities for pharma, medical device and sterilization industries including potentially disruptive applications that may involve reduced usage of sterilant.

Terminal sterilization of medical devices using vaporized hydrogen peroxide: a review of current methods and emerging opportunities

Medical devices are an important and growing aspect of healthcare provision and are increasing in complexity to meet established and emerging patient needs. Terminal sterilization plays a vital role in the provision of safe medical devices. While terminal sterilization technologies for medical devices include multiple radiation options, ethylene oxide remains the predominant nonthermal gaseous option, sterilizing c. 50% of all manufactured devices. Vaporized hydrogen peroxide (abbreviated VH2O2 by the International Organization for Standardization) is currently deployed for clinical sterilization applications, where its performance characteristics appear aligned to requirements, constituting a viable alternative low-temperature process for terminal processing of medical devices. However, VH2O2 has operational limitations that create technical challenges for industrial-scale adoption. This timely review provides a succinct overview of VH2O2 in gaseous sterilization and addresses its applicability for terminal sterilization of medical devices. It also describes underappreciated factors such as the occurrence of nonlinear microbial inactivation kinetic plots that may dictate a need to develop a new standard approach to validate VH2O2 for terminal sterilization of medical devices.

Review of Decontamination Techniques for the Inactivation of Bacillus anthracis and Other Spore-Forming Bacteria Associated with Building or Outdoor Materials

Since the intentional release of Bacillus anthracis spores through the U.S. Postal Service in the fall of 2001, research and development related to decontamination for this biological agent have increased substantially. This review synthesizes the advances made relative to B. anthracis spore decontamination science and technology since approximately 2002, referencing the open scientific literature and publicly available, well-documented scientific reports. In the process of conducting this review, scientific knowledge gaps have also been identified. This review focuses primarily on techniques that are commercially available and that could potentially be used in the large-scale decontamination of buildings and other structures, as well as outdoor environments. Since 2002, the body of scientific data related to decontamination and microbial sterilization has grown substantially, especially in terms of quantifying decontamination efficacy as a function of several factors. Specifically, progress has been made in understanding how decontaminant chemistry, the materials the microorganisms are associated with, environmental factors, and microbiological methods quantitatively impact spore inactivation. While advancement has been made in the past 15 years to further the state of the science in the inactivation of bacterial spores in a decontamination scenario, further research is warranted to close the scientific gaps that remain.

Efficiency of Different Disinfectants on Bacillus cereus Sensu Stricto Biofilms on Stainless-Steel Surfaces in Contact With Milk

The species of the Bacillus cereus group have the ability to adhere to and form biofilms on solid surfaces, including stainless steel, a material widely used in food industries. Biofilms allow for recontamination during food processing, and the "clean-in-place" (CIP) system is largely used by industries to control them. This study thus proposes to evaluate the efficacy of peracetic acid and sodium hypochlorite against biofilms induced on stainless-steel surfaces. The SAMN07414939 isolate (BioProject PRJNA390851), a recognized biofilm producer, was selected for biofilm induction on AISI 304 stainless steel. Biofilm induction was performed and classified into three categories: TCP (Tindalized, Contaminated, and Pasteurized milk), TCS (Tindalized milk Contaminated with Spores), and TCV (Tindalized milk Contaminated with Vegetative cells). Subsequently, the coupons were sanitized simulating a CIP procedure, on a pilot scale, using alkaline and acid solutions followed by disinfectants (peracetic acid and sodium hypochlorite). Microorganism adhesion on the surfaces reached 6.3 × 105 to 3.1 × 107 CFU/cm-2. Results did not show significant differences (p > 0.05) for surface adhesion between the three tested categories (TCP, TCS, and TCV) or (p > 0.05) between the two disinfectants (peracetic acid and sodium hypochlorite). Microbial populations adhered to the stainless-steel coupons are equally reduced after treatment with peracetic acid and sodium hypochlorite, with no differences in the control of B. cereus s.s. biofilms on AISI 304 stainless-steel surfaces.

Application of High Pressure with Homogenization, Temperature, Carbon Dioxide, and Cold Plasma for the Inactivation of Bacterial Spores: A Review

Formation of highly resistant spores is a concern for the safety of low-acid foods as they are a perfect vehicle for food spoilage and/or human infection. For spore inactivation, the strategy usually applied in the food industry is the intensification of traditional preservation methods to sterilization levels, which is often accompanied by decreases of nutritional and sensory properties. In order to overcome these unwanted side effects in food products, novel and emerging sterilization technologies are being developed, such as pressure-assisted thermal sterilization, high-pressure carbon dioxide, high-pressure homogenization, and cold plasma. In this review, the application of these emergent technologies is discussed, in order to understand the effects on bacterial spores and their inactivation and thus ensure food safety of low-acid foods. In general, the application of these novel technologies for inactivating spores is showing promising results. However, it is important to note that each technique has specific features that can be more suitable for a particular type of product. Thus, the most appropriate sterilization method for each product (and target microorganisms) should be assessed and carefully selected.

Evaluating the Sporicidal Activity of Disinfectants against Clostridium difficile and Bacillus amyloliquefaciens Spores by Using the Improved Methods Based on ASTM E2197-11

Spore-forming pathogenic bacteria, such as Clostridium difficile, are associated with nosocomial infection, leading to the increased use of sporicidal disinfectants, which impacts socioeconomic costs. However, C. difficile can be prevented using microorganisms such as Bacillus amyloliquefaciens, a prophylactic agent that has been proven to be effective against it in recent tests or it can be controlled by sporicidal disinfectants. These disinfectants against spores should be evaluated according to a known and recommended standard. Unfortunately, some newly manufactured disinfectants like Bioxy products have not yet been tested. ASTM E2197-11 is a standard test that uses stainless steel disks (1 cm in diameter) as carriers, and the performance of the test formulation is calculated by comparing the number of viable test organisms to that on the control carriers. Surface tests are preferable for evaluating disinfectants with sporicidal effects on hard surfaces. This study applies improved methods, based on the ASTM E2197-11 standard, for evaluating and comparing the sporicidal efficacies of several disinfectants against spores of C. difficile and B. amyloliquefaciens, which are used as the test organisms. With the improved method, all spores were recovered through vortexing and membrane filtration. The results show that chlorine-based products are effective in 5 min and Bioxy products at 5% w/v are effective in 10 min. Although Bioxy products may take longer to prove their effectiveness, their non-harmful effects to hospital surfaces and people have been well established in the literature.

Microbiological interactions with cold plasma

There is a diverse range of microbiological challenges facing the food, healthcare and clinical sectors. The increasing and pervasive resistance to broad-spectrum antibiotics and health-related concerns with many biocidal agents drives research for novel and complementary antimicrobial approaches. Biofilms display increased mechanical and antimicrobial stability and are the subject of extensive research. Cold plasmas (CP) have rapidly evolved as a technology for microbial decontamination, wound healing and cancer treatment, owing to the chemical and bio-active radicals generated known collectively as reactive oxygen and nitrogen species. This review outlines the basics of CP technology and discusses the interactions with a range of microbiological targets. Advances in mechanistic insights are presented and applications to food and clinical issues are discussed. The possibility of tailoring CP to control specific microbiological challenges is apparent. This review focuses on microbiological issues in relation to food- and healthcare-associated human infections, the role of CP in their elimination and the current status of plasma mechanisms of action.