Role of dose concentration in biocide efficacy against Pseudomonas aeruginosa biofilms

Efficacy of Novel Quaternary Ammonium and Phosphonium Salts Differing in Cation Type and Alkyl Chain Length against Antibiotic-Resistant Staphylococcus aureus

Antibacterial resistance poses a critical public health threat, challenging the prevention and treatment of bacterial infections. The search for innovative antibacterial agents has spurred significant interest in quaternary heteronium salts (QHSs), such as quaternary ammonium and phosphonium compounds as potential candidates. In this study, a library of 49 structurally related QHSs was synthesized, varying the cation type and alkyl chain length. Their antibacterial activities against Staphylococcus aureus, including antibiotic-resistant strains, were evaluated by determining minimum inhibitory/bactericidal concentrations (MIC/MBC) ≤ 64 µg/mL. Structure-activity relationship analyses highlighted alkyl-triphenylphosphonium and alkyl-methylimidazolium salts as the most effective against S. aureus CECT 976. The length of the alkyl side chain significantly influenced the antibacterial activity, with optimal chain lengths observed between C10 and C14. Dose-response relationships were assessed for selected QHSs, showing dose-dependent antibacterial activity following a non-linear pattern. Survival curves indicated effective eradication of S. aureus CECT 976 by QHSs at low concentrations, particularly compounds 1e, 3e, and 5e. Moreover, in vitro human cellular data indicated that compounds 2e, 4e, and 5e showed favourable safety profiles at concentrations ≤ 2 µg/mL. These findings highlight the potential of these QHSs as effective agents against susceptible and resistant bacterial strains, providing valuable insights for the rational design of bioactive QHSs.

Food grade disinfectants based on hydrogen peroxide/peracetic acid and sodium hypochlorite interfere with the adhesion of Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Listeria monocytogenes to stainless steel of differing surface roughness

This study aimed to evaluate the potential of the bacterium Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Listeria monocytogenes to adhere to stainless steel discs with differing degrees of surface roughness (Ra = 25.20-961.90 nm). Stainless steel is a material commonly used in the food industry for processing equipment, which is regularly exposed to cleaning procedures. The investigation included the commercial disinfectants hydrogen peroxide/peracetic acid and sodium hypochlorite which were evaluated for their antibacterial and anti-adhesion activity. The adhesion was assessed by the standard plate count method, while the broth microdilution method CLSI M07-A10 was used to determine the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of the disinfectants. Based on the MIC values, both disinfectants exerted significant inhibitory effects with MIC values for hydrogen peroxide/peracetic acid and sodium hypochlorite of 250 µg ml-1 and 500 µg ml-1, respectively. Whereas the MBC values were equal to the MIC for all bacteria except for E. coli with values 2-fold higher than the MIC. Obtained results also revealed that all tested bacteria were able to adhere to stainless steel surfaces, although differences were found for strains and surface roughness. The lowest adhesion rate of each strain was recorded on the roughest stainless steel disc at a Ra of 961.90 nm. Further, at a concentration of 1 MIC, the disinfectant sodium hypochlorite reduced initial bacterial adhesion to stainless steel surfaces to a significantly greater extent than the disinfectant hydrogen peroxide/peracetic acid. These findings are consistent with the results obtained by Scanning Electron Microscopy (SEM) analysis, which indicates the great applicability of the tested disinfectants for the control of bacterial adhesion in the food industry.

Determining effects of nitrate, arginine, and ferrous on antibiotic recalcitrance of clinical strains of Pseudomonas aeruginosa in biofilm-inspired alginate encapsulates

BACKGROUND

Biofilms play a role in recalcitrance and treatability of bacterial infections, but majority of known antibiotic resistance mechanisms are biofilm-independent. Biofilms of Pseudomonas aeruginosa, especially in cystic fibrosis patients infected with the alginate producing strains in their lungs, are hard to treat. Changes in growth-related bacterial metabolism in biofilm affect their antibiotic recalcitrance which could be considered for new therapies designed based on these changes. In this study, effects of nitrate, arginine, and ferrous were investigated on antibiotic recalcitrance in alginate-encapsulated P. aeruginosa strains isolated from cystic fibrosis patients in the presence of amikacin, tobramycin, and ciprofloxacin. Also, expression of an efflux pump gene, mexY, was analyzed in selected strains in the presence of amikacin and ferrous.

METHODS

Clinical P. aeruginosa strains were isolated from cystic fibrosis patients and minimum inhibitory concentration of amikacin, tobramycin, and ciprofloxacin was determined against all the strains. For each antibiotic, a susceptible and a resistant or an intermediate-resistant strain were selected, encapsulated into alginate beads, and subjected to minimal biofilm eradication concentration (MBEC) test. After determining MBECs, sub-MBEC concentrations (antibiotics at concentrations one level below the determined MBEC) for each antibiotic were selected and used to study the effects of nitrate, arginine, and ferrous on antibiotic recalcitrance of encapsulated strains. Effects of ferrous and amikacin on expression of the efflux pump gene, mexY, was studied on amikacin sensitive and intermediate-resistant strains. One-way ANOVA and t test were used as the statistical tests.

RESULTS

According to the results, the supplements had a dose-related effect on decreasing the number of viable cells; maximal effect was noted with ferrous, as ferrous supplementation significantly increased biofilm susceptibility to both ciprofloxacin and amikacin in all strains, and to tobramycin in a resistant strain. Also, treating an amikacin-intermediate strain with amikacin increased the expression of mexY gene, which has a role in P. aeruginosa antibiotic recalcitrance, while treating the same strain with ferrous and amikacin significantly decreased the expression of mexY gene, which was a promising result.

CONCLUSIONS

Our results support the possibility of using ferrous and arginine as an adjuvant to enhance the efficacy of conventional antimicrobial therapy of P. aeruginosa infections.

Local Antibiotic Delivery Options in Prosthetic Joint Infection

Prosthetic Joint Infection (PJI) causes significant morbidity and mortality for patients globally. Delivery of antibiotics to the site of infection has potential to improve the treatment outcomes and enhance biofilm eradication. These antibiotics can be delivered using an intra-articular catheter or combined with a carrier substance to enhance pharmacokinetic properties. Carrier options include non-resorbable polymethylmethacrylate (PMMA) bone cement and resorbable calcium sulphate, hydroxyapatite, bioactive glass, and hydrogels. PMMA allows for creation of structural spacers used in multi-stage revision procedures, however it requires subsequent removal and antibiotic compatibility and the levels delivered are variable. Calcium sulphate is the most researched resorbable carrier in PJI, but is associated with wound leakage and hypercalcaemia, and clinical evidence for its effectiveness remains at the early stage. Hydrogels provide a versatile combability with antibiotics and adjustable elution profiles, but clinical usage is currently limited. Novel anti-biofilm therapies include bacteriophages which have been used successfully in small case series.

A Multi-Purpose Approach to the Mechanisms of Action of Two Biocides (Benzalkonium Chloride and Dibromonitrilopropionamide): Discussion of Pseudomonas fluorescens’ Viability and Death

Biocides are widely used in water treatment for microbiological control. The rise of antimicrobial resistance and the need to assure properly managed water systems require a better understanding of the mechanisms of action of biocides and of their impact on cell’s viability as a function of dosage concentrations. The present work addresses these two aspects regarding the biocides benzalkonium chloride (BAC) and dibromonitrilopropionamide (DBNPA)—two biocides commonly found in the water treatment industry. For that, the following parameters were studied: culturability, membrane integrity, metabolic activity, cellular energy, and the structure and morphology of cells. Also, to assess cell’s death, a reliable positive control, consisting of cells killed by autoclave (dead cells), was introduced. The results confirmed that BAC is a lytic biocide and DBNPA a moderate electrophilic one. Furthermore, the comparison between cells exposed to the biocides’ minimum bactericidal concentrations (MBCs) and autoclaved cells revealed that other viability parameters should be taken into consideration as “death indicators.” The present work also shows that only for the concentrations above the MBC the viability indicators reached values statistically similar to the ones observed for the autoclaved cells (considered to be definitively dead). Finally, the importance of considering the biocide mechanism of action in the definition of the viability parameter to use in the viable but non-culturable (VBNC) determination is discussed.

Legionella: A Promising Supplementary Indicator of Microbial Drinking Water Quality in Municipal Engineered Water Systems

Opportunistic pathogens (OPs) are natural inhabitants and the predominant disease causative biotic agents in municipal engineered water systems (EWSs). In EWSs, OPs occur at high frequencies and concentrations, cause drinking-water-related disease outbreaks, and are a major factor threatening public health. Therefore, the prevalence of OPs in EWSs represents microbial drinking water quality. Closely or routinely monitoring the dynamics of OPs in municipal EWSs is thus critical to ensuring drinking water quality and protecting public health. Monitoring the dynamics of conventional (fecal) indicators (e.g., total coliforms, fecal coliforms, and Escherichia coli) is the customary or even exclusive means of assessing microbial drinking water quality. However, those indicators infer only fecal contamination due to treatment (e.g., disinfection within water utilities) failure and EWS infrastructure issues (e.g., water main breaks and infiltration), whereas OPs are not contaminants in drinking water. In addition, those indicators appear in EWSs at low concentrations (often absent in well-maintained EWSs) and are uncorrelated with OPs. For instance, conventional indicators decay, while OPs regrow with increasing hydraulic residence time. As a result, conventional indicators are poor indicators of OPs (the major aspect of microbial drinking water quality) in EWSs. An additional or supplementary indicator that can well infer the prevalence of OPs in EWSs is highly needed. This systematic review argues that Legionella as a dominant OP-containing genus and natural inhabitant in EWSs is a promising candidate for such a supplementary indicator. Through comprehensively comparing the behavior (i.e., occurrence, growth and regrowth, spatiotemporal variations in concentrations, resistance to disinfectant residuals, and responses to physicochemical water quality parameters) of major OPs (e.g., Legionella especially L. pneumophila, Mycobacterium, and Pseudomonas especially P. aeruginosa), this review proves that Legionella is a promising supplementary indicator for the prevalence of OPs in EWSs while other OPs lack this indication feature. Legionella as a dominant natural inhabitant in EWSs occurs frequently, has a high concentration, and correlates with more microbial and physicochemical water quality parameters than other common OPs. Legionella and OPs in EWSs share multiple key features such as high disinfectant resistance, biofilm formation, proliferation within amoebae, and significant spatiotemporal variations in concentrations. Therefore, the presence and concentration of Legionella well indicate the presence and concentrations of OPs (especially L. pneumophila) and microbial drinking water quality in EWSs. In addition, Legionella concentration indicates the efficacies of disinfectant residuals in EWSs. Furthermore, with the development of modern Legionella quantification methods (especially quantitative polymerase chain reactions), monitoring Legionella in ESWs is becoming easier, more affordable, and less labor-intensive. Those features make Legionella a proper supplementary indicator for microbial drinking water quality (especially the prevalence of OPs) in EWSs. Water authorities may use Legionella and conventional indicators in combination to more comprehensively assess microbial drinking water quality in municipal EWSs. Future work should further explore the indication role of Legionella in EWSs and propose drinking water Legionella concentration limits that indicate serious public health effects and require enhanced treatment (e.g., booster disinfection).

'Secondary biofilms' could cause failure of peracetic acid high-level disinfection of endoscopes

INTRODUCTION

The reduced susceptibility of biofilms to disinfectants presents a challenge to the successful reprocessing of medical equipment. This study examined the effect of residual biomass remaining after previous disinfection with peracetic acid (PAA) on the tolerance of subsequent mature Pseudomonas aeruginosa biofilms to PAA. The effect of enzymatic degradation of specific components of the extracellular polymeric substance (EPS) of P. aeruginosa biofilm on the effectiveness of PAA disinfection was also evaluated.

METHODS

The susceptibility of biofilm grown on the biomass of PAA-killed biofilm to PAA was compared with the PAA susceptibility of biofilm grown in wells of a 24-well plate by evaluating their viability using the plate count assay. The effect of PAA on biofilm biomass was measured using crystal violet quantification of total biofilm biomass, while its effect on the polysaccharide and protein components of biofilm EPS was quantified using the phenol-sulphuric acid assay or Bradford assay, respectively. A confocal microscope was used to visualize the distribution of living and dead cells in biofilms grown on residual biofilm biomass.

FINDINGS

The presence of residual biomass from previously disinfected biofilms significantly enhanced the tolerance of subsequent biofilms. A 96-h-old 'secondary biofilm' formed on disinfected biomass survived PAA concentrations of 4000 ppm, which exceeds the concentrations used in practice for high-level disinfection.

CONCLUSION

These observations indicate that, under certain circumstances, recolonization of residual EPS can cause failure of disinfection of medical equipment such as endoscopes, and emphasizes the importance of cleaning endoscopes prior to disinfection.

Current and future perspectives for controlling Vibrio biofilms in the seafood industry: a comprehensive review

The contamination of seafood with Vibrio species can have severe repercussions in the seafood industry. Vibrio species can form mature biofilms and persist on the surface of several seafoods such as crabs, oysters, mussels, and shrimp, for extended duration. Several conventional approaches have been employed to inhibit the growth of planktonic cells and prevent the formation of Vibrio biofilms. Since Vibrio biofilms are mostly resistant to these control measures, novel alternative methods need to be urgently developed. In this review, we propose environmentally friendly approaches to suppress Vibrio biofilm formation using a hypothesized mechanism of action.

Suction Hoses of Dental Units as a Potential Source of Microbial Contamination

OBJECTIVES

Dental units are necessary tools for modern dentistry. Microbial contamination of dental units is thought to be the result of biofilm formation in various parts of the unit. We aimed to identify the total microbial count in the suction hose of dental units, and detect the presence of Pseudomonas aeruginosa.

METHODS

Random sampling of suction hoses of dental units in Birjand, Iran, was performed in dental clinics on the first (n = 115) and last (n = 115) working days of the week. Total viable counts of bacteria and detection of P. aeruginosa were performed on plate count agar and cetrimide agar, respectively. Plates were incubated at 37 °C for 48 hours.

RESULTS

None of the samples were free from bacterial contamination. P. aeruginosa was detected in 22.6% and 18.3% of samples taken on the first and last working days, respectively.

CONCLUSIONS

Suction hoses were heavily contaminated with bacteria, especially opportunistic pathogens, and current disinfection does not adequately control the contamination.

Activity of Hospital Disinfectants against Vegetative Cells and Spores of Clostridioides difficile Embedded in Biofilms

Clostridioides difficile spores can survive in the environment in either mono- or mixed-species biofilms. However, no previous studies have investigated chemical disinfection of C. difficile spores embedded in biofilms. Thus, the purpose of this study was to assess the in vitro effectiveness of hospital disinfectants against C. difficile spores embedded within biofilms. Five unique C. difficile strains embedded in three different biofilm types grown for 72 or 120 h were exposed to seven different hospital disinfectants. C. difficile abundance [as log(number of CFU/milliliter)] was calculated after manufacturer-determined contact times along with biofilm biomass and microscopy. The primary analysis compared differences between C. difficile vegetative cell and spore counts as well as amounts of biomass after exposure to disinfectants. C. difficile vegetative cells and spores were recovered from biofilms regardless of the type of biofilm growth or biofilm growth time. No disinfectant was able to completely eliminate C. difficile from the biofilms. Overall, Clorox, ortho-phthalaldehyde (OPA), and Virex were most effective at killing C. difficile spores regardless of biofilm age, ribotype, or wash conditions (whether biofilms are washed or unwashed) (P = 0.001, each). Clorox and OPA were also effective at killing total vegetative cell growth (P = 0.001, each), but Virex was found to be ineffective against vegetative cell growth in biofilms (P = 0.77). Clorox and Virex were most effective in reducing biomass, followed by Nixall, OPA, and Vital Oxide. No disinfectant was able to completely eliminate C. difficile embedded within biofilms although differences among disinfectants were noted. Future research will be required to determine methods to eradicate this persister reservoir.

Immobilization of an antimicrobial peptide on silicon surface with stable activity by click chemistry

We click an antimicrobial peptide onto a silicon substrate to protect it from enzymolysis using a polySBMA spacer.

Influence of Nutrient Availability and Quorum Sensing on the Formation of Metabolically Inactive Microcolonies Within Structurally Heterogeneous Bacterial Biofilms: An Individual-Based 3D Cellular Automata Model

The resistance of bacterial biofilms to antibiotic treatment has been attributed to the emergence of structurally heterogeneous microenvironments containing metabolically inactive cell populations. In this study, we use a three-dimensional individual-based cellular automata model to investigate the influence of nutrient availability and quorum sensing on microbial heterogeneity in growing biofilms. Mature biofilms exhibited at least three structurally distinct strata: a high-volume, homogeneous region sandwiched between two compact sections of high heterogeneity. Cell death occurred preferentially in layers in close proximity to the substratum, resulting in increased heterogeneity in this section of the biofilm; the thickness and heterogeneity of this lowermost layer increased with time, ultimately leading to sloughing. The model predicted the formation of metabolically dormant cellular microniches embedded within faster-growing cell clusters. Biofilms utilizing quorum sensing were more heterogeneous compared to their non-quorum sensing counterparts, and resisted sloughing, featuring a cell-devoid layer of EPS atop the substratum upon which the remainder of the biofilm developed. Overall, our study provides a computational framework to analyze metabolic diversity and heterogeneity of biofilm-associated microorganisms and may pave the way toward gaining further insights into the biophysical mechanisms of antibiotic resistance.

Gel-Entrapped Staphylococcus aureus Bacteria as Models of Biofilm Infection Exhibit Growth in Dense Aggregates, Oxygen Limitation, Antibiotic Tolerance, and Heterogeneous Gene Expression

An experimental model that mimicked the structure and characteristics of in vivo biofilm infections, such as those occurring in the lung or in dermal wounds where no biomaterial surface is present, was developed. In these infections, microbial biofilm forms as cell aggregates interspersed in a layer of mucus or host matrix material. This structure was modeled by filling glass capillary tubes with an agarose gel that had been seeded with Staphylococcus aureus bacteria and then incubating the gel biofilm in medium for up to 30 h. Confocal microscopy showed that the bacteria formed in discrete pockets distributed throughout the gel matrix. These aggregates enlarged over time and also developed a size gradient, with the clusters being larger near the nutrient- and oxygen-supplied interface and smaller at greater depths. Bacteria entrapped in gels for 24 h grew slowly (specific growth rate, 0.06 h(-1)) and were much less susceptible to oxacillin, minocycline, or ciprofloxacin than planktonic cells. Microelectrode measurements showed that the oxygen concentration decreased with depth into the gel biofilm, falling to values less than 3% of air saturation at depths of 500 μm. An anaerobiosis-responsive green fluorescent protein reporter gene for lactate dehydrogenase was induced in the region of the gel where the measured oxygen concentrations were low, confirming biologically relevant hypoxia. These results show that the gel biofilm model captures key features of biofilm infection in mucus or compromised tissue: formation of dense, distinct aggregates, reduced specific growth rates, local hypoxia, and antibiotic tolerance.

Praziquantel degradation in marine aquarium water

Praziquantel (PZQ) is a drug commonly utilized to treat both human schistosomiasis and some parasitic infections and infestations in animals. In the aquarium industry, PZQ can be administered in a "bath" to treat the presence of ectoparasites on both the gills and skin of fish and elasmobranchs. In order to fully treat an infestation, the bath treatment has to maintain therapeutic levels of PZQ over a period of days or weeks. It has long been assumed that, once administered, PZQ is stable in a marine environment throughout the treatment interval and must be mechanically removed, but no controlled experiments have been conducted to validate that claim. This study aimed to determine if PZQ would break down naturally within a marine aquarium below its 2 ppm therapeutic level during a typical 30-day treatment: and if so, does the presence of fish or the elimination of all living biological material impact the degradation of PZQ? Three 650 L marine aquarium systems, each containing 12 fish (French grunts: Haemulon flavolineatum), and three 650 L marine aquariums each containing no fish were treated with PZQ (2 ppm) and concentrations were measured daily for 30 days. After one round of treatment, the PZQ was no longer detectable in any system after 8 (±1) days. The subsequent two PZQ treatments yielded even faster PZQ breakdown (non-detectable after 2 days and 2 ± 1 day, respectively) with slight variations between systems. Linear mixed effects models of the data indicate that day and trial most impact PZQ degradation, while the presence of fish was not a factor in the best-fit models. In a completely sterilized marine system (0.5 L) PZQ concentration remained unchanged over 15 days, suggesting that PZQ may be stable in a marine system during this time period. The degradation observed in non-sterile marine systems in this study may be microbial in nature. This work should be taken into consideration when providing PZQ bath treatments to marine animals to ensure maximum drug administration.

Impact of growth temperature and surface type on the resistance of Pseudomonas aeruginosa and Staphylococcus aureus biofilms to disinfectants

Biofilm formation of Pseudomonas aeruginosa and Staphylococcus aureus on food-contact-surfaces represents a significant risk for the public health. In this context, the present study investigates the relationship between the environmental conditions of biofilm formation and the resistance to disinfectants. Therefore, a static biofilm reactor, called NEC-Biofilm System, was established in order to study the effect of growth temperature (20, 30 and 37°C), and of the surface type (stainless steel and polycarbonate), on biofilm resistance to disinfectants. These conditions were selected to mimic the biofilm formation on abiotic surfaces of food processing industries. The antibiofilm assays were performed on biofilms grown during 24 h. The results showed that the growth temperature influenced significantly the biofilm resistance to disinfectants. These data also revealed that the growth temperature has a significant effect on the biofilm structure of both bacteria. Furthermore, the increase of the biofilm growth temperature increased significantly the algD transcript level in sessile P. aeruginosa cells, whereas the icaA one was not affected in S. aureus cells. Overall, our findings show that the biofilm structure and matrix cannot fully explain the biofilm resistance to disinfectant agents. Nevertheless, it underlines the intimate link between environmental conditions, commonly met in food sectors, and the biofilm resistance to disinfectants.

Efflux as a glutaraldehyde resistance mechanism in Pseudomonas fluorescens and Pseudomonas aeruginosa biofilms

A major challenge in microbial biofilm control is biocide resistance. Phenotypic adaptations and physical protective effects have been historically thought to be the primary mechanisms for glutaraldehyde resistance in bacterial biofilms. Recent studies indicate the presence of genetic mechanisms for glutaraldehyde resistance, but very little is known about the contributory genetic factors. Here, we demonstrate that efflux pumps contribute to glutaraldehyde resistance in Pseudomonas fluorescens and Pseudomonas aeruginosa biofilms. The RNA-seq data show that efflux pumps and phosphonate degradation, lipid biosynthesis, and polyamine biosynthesis metabolic pathways were induced upon glutaraldehyde exposure. Furthermore, chemical inhibition of efflux pumps potentiates glutaraldehyde activity, suggesting that efflux activity contributes to glutaraldehyde resistance. Additionally, induction of known modulators of biofilm formation, including phosphonate degradation, lipid biosynthesis, and polyamine biosynthesis, may contribute to biofilm resistance and resilience. Fundamental understanding of the genetic mechanism of biocide resistance is critical for the optimization of biocide use and development of novel disinfection strategies. Our results reveal genetic components involved in glutaraldehyde resistance and a potential strategy for improved control of biofilms.

Is peracetic acid suitable for the cleaning step of reprocessing flexible endoscopes?

The bioburden (blood, protein, pathogens and biofilm) on flexible endoscopes after use is often high and its removal is essential to allow effective disinfection, especially in the case of peracetic acid-based disinfectants, which are easily inactivated by organic material. Cleaning processes using conventional cleaners remove a variable but often sufficient amount of the bioburden. Some formulations based on peracetic acid are recommended by manufacturers for the cleaning step. We performed a systematic literature search and reviewed the available evidence to clarify the suitability of peracetic acid-based formulations for cleaning flexible endoscopes. A total of 243 studies were evaluated. No studies have yet demonstrated that peracetic acid-based cleaners are as effective as conventional cleaners. Some peracetic acid-based formulations have demonstrated some biofilm-cleaning effects and no biofilm-fixation potential, while others have a limited cleaning effect and a clear biofilm-fixation potential. All published data demonstrated a limited blood cleaning effect and a substantial blood and nerve tissue fixation potential of peracetic acid. No evidence-based guidelines on reprocessing flexible endoscopes currently recommend using cleaners containing peracetic acid, but some guidelines clearly recommend not using them because of their fixation potential. Evidence from some outbreaks, especially those involving highly multidrug-resistant gram-negative pathogens, indicated that disinfection using peracetic acid may be insufficient if the preceding cleaning step is not performed adequately. Based on this review we conclude that peracetic acid-based formulations should not be used for cleaning flexible endoscopes.

P. aeruginosa SGNH hydrolase-like proteins AlgJ and AlgX have similar topology but separate and distinct roles in alginate acetylation

The O-acetylation of polysaccharides is a common modification used by pathogenic organisms to protect against external forces. Pseudomonas aeruginosa secretes the anionic, O-acetylated exopolysaccharide alginate during chronic infection in the lungs of cystic fibrosis patients to form the major constituent of a protective biofilm matrix. Four proteins have been implicated in the O-acetylation of alginate, AlgIJF and AlgX. To probe the biological function of AlgJ, we determined its structure to 1.83 Å resolution. AlgJ is a SGNH hydrolase-like protein, which while structurally similar to the N-terminal domain of AlgX exhibits a distinctly different electrostatic surface potential. Consistent with other SGNH hydrolases, we identified a conserved catalytic triad composed of D190, H192 and S288 and demonstrated that AlgJ exhibits acetylesterase activity in vitro. Residues in the AlgJ signature motifs were found to form an extensive network of interactions that are critical for O-acetylation of alginate in vivo. Using two different electrospray ionization mass spectrometry (ESI-MS) assays we compared the abilities of AlgJ and AlgX to bind and acetylate alginate. Binding studies using defined length polymannuronic acid revealed that AlgJ exhibits either weak or no detectable polymer binding while AlgX binds polymannuronic acid specifically in a length-dependent manner. Additionally, AlgX was capable of utilizing the surrogate acetyl-donor 4-nitrophenyl acetate to catalyze the O-acetylation of polymannuronic acid. Our results, combined with previously published in vivo data, suggest that the annotated O-acetyltransferases AlgJ and AlgX have separate and distinct roles in O-acetylation. Our refined model for alginate acetylation places AlgX as the terminal acetlytransferase and provides a rationale for the variability in the number of proteins required for polysaccharide O-acetylation.

Bacteria utilize many defense strategies to protect themselves against external forces. One mechanism used by the bacterium Pseudomonas aeruginosa is the production of the long sugar polymer alginate. The bacteria use this polymer to form a biofilm – a barrier to protect against antibiotics and the host immune response. During its biosynthesis alginate undergoes a chemical modification whereby acetate is added to the polymer. Acetylation of alginate is important as this modification makes the bacterial biofilm less susceptible to recognition and clearance by the host immune system. In this paper we present the atomic structure of AlgJ; one of four proteins required for O-acetylation of the polymer. AlgJ is structurally similar to AlgX, which we have shown previously is also required for alginate acetylation. To understand why both enzymes are required for O-acetylation we functionally characterized the proteins and found that although AlgJ exhibits acetylesterase activity – catalyzing the removal of acetyl groups from a surrogate substrate – it does not bind to short mannuornic acid polymers. In contrast, AlgX bound alginate in a length-dependent manner and was capable of transfering acetate from a surrogate substrate onto alginate. This has allowed us to not only understand how acetate is added to alginate, but increases our understanding of how acetate is added to other bacterial sugar polymers.

What should be considered in the treatment of bacterial infections by multi-drug therapies: a mathematical perspective?

Bacterial infections are a global health concern with high levels of mortality and morbidity associated. The resistance of pathogens to drugs is one leading cause of this problem, being common the administration of multiple drugs to improve the therapeutic effects. This review critically explores diverse aspects involved in the treatment of bacterial infections through multi-drug therapies, from a mathematical and within-host perspectives. Five recent models were selected and are reviewed. These models fall into the following question: which drugs to select, the respective dose, the administration period to effectively eradicate the infection in the shortest period of time and with reduced side effects? In this analysis, three groups of variables were considered: pharmacokinetics, pharmacodynamics and disturbance variables. To date, there is no model that fully answers to this issue for a living organism and it is questionable whether this would be possible for any case of infection.

Biofilm formation and persistence on abiotic surfaces in the context of food and medical environments

The biofilm formation on abiotic surfaces in food and medical sectors constitutes a great public health concerns. In fact, biofilms present a persistent source for pathogens, such as Pseudomonas aeruginosa and Staphylococcus aureus, which lead to severe infections such as foodborne and nosocomial infections. Such biofilms are also a source of material deterioration and failure. The environmental conditions, commonly met in food and medical area, seem also to enhance the biofilm formation and their resistance to disinfectant agents. In this regard, this review highlights the effect of environmental conditions on bacterial adhesion and biofilm formation on abiotic surfaces in the context of food and medical environment. It also describes the current and emergent strategies used to study the biofilm formation and its eradication. The mechanisms of biofilm resistance to commercialized disinfectants are also discussed, since this phenomenon remains unclear to date.

Biofilms of a Bacillus subtilis hospital isolate protect Staphylococcus aureus from biocide action

The development of a biofilm constitutes a survival strategy by providing bacteria a protective environment safe from stresses such as microbicide action and can thus lead to important health-care problems. In this study, biofilm resistance of a Bacillus subtilis strain (called hereafter ND_medical) recently isolated from endoscope washer-disinfectors to peracetic acid was investigated and its ability to protect the pathogen Staphylococcus aureus in mixed biofilms was evaluated. Biocide action within Bacillus subtilis biofilms was visualised in real time using a non-invasive 4D confocal imaging method. The resistance of single species and mixed biofilms to peracetic acid was quantified using standard plate counting methods and their architecture was explored using confocal imaging and electronic microscopy. The results showed that the ND_medical strain demonstrates the ability to make very large amount of biofilm together with hyper-resistance to the concentration of PAA used in many formulations (3500 ppm). Evidences strongly suggest that the enhanced resistance of the ND_medical strain was related to the specific three-dimensional structure of the biofilm and the large amount of the extracellular matrix produced which can hinder the penetration of peracetic acid. When grown in mixed biofilm with Staphylococcus aureus, the ND_medical strain demonstrated the ability to protect the pathogen from PAA action, thus enabling its persistence in the environment. This work points out the ability of bacteria to adapt to an extremely hostile environment, and the necessity of considering multi-organism ecosystems instead of single species model to decipher the mechanisms of biofilm resistance to antimicrobials agents.

Optimal control strategies for disinfection of bacterial populations with persister and susceptible dynamics

It is increasingly clear that bacteria manage to evade killing by antibiotics and antimicrobials in a variety of ways, including mutation, phenotypic variations, and formation of biofilms. With recent advances in understanding the dynamics of the tolerance mechanisms, there have been subsequent advances in understanding how to manipulate the bacterial environments to eradicate the bacteria. This study focuses on using mathematical techniques to find the optimal disinfection strategy to eliminate the bacteria while managing the load of antibiotic that is applied. In this model, the bacterial population is separated into those that are tolerant to the antibiotic and those that are susceptible to disinfection. There are transitions between the two populations whose rates depend on the chemical environment. Our results extend previous mathematical studies to include more realistic methods of applying the disinfectant. The goal is to provide experimentally testable predictions that have been lacking in previous mathematical studies. In particular, we provide the optimal disinfection protocol under a variety of assumptions within the model that can be used to validate or invalidate our simplifying assumptions and the experimental hypotheses that we used to develop the model. We find that constant dosing is not the optimal method for disinfection. Rather, cycling between application and withdrawal of the antibiotic yields the fastest killing of the bacteria.

Resistance of bacterial biofilms to disinfectants: a review

A biofilm can be defined as a community of microorganisms adhering to a surface and surrounded by a complex matrix of extrapolymeric substances. It is now generally accepted that the biofilm growth mode induces microbial resistance to disinfection that can lead to substantial economic and health concerns. Although the precise origin of such resistance remains unclear, different studies have shown that it is a multifactorial process involving the spatial organization of the biofilm. This review will discuss the mechanisms identified as playing a role in biofilm resistance to disinfectants, as well as novel anti-biofilm strategies that have recently been explored.

Dynamics of the action of biocides in Pseudomonas aeruginosa biofilms

The biocidal activity of peracetic acid (PAA) and benzalkonium chloride (BAC) on Pseudomonas aeruginosa biofilms was investigated by using a recently developed confocal laser scanning microscopy (CLSM) method that enables the direct and real-time visualization of cell inactivation within the structure. This technique is based on monitoring the loss of fluorescence that corresponds to the leakage of a fluorophore out of cells due to membrane permeabilization by the biocides. Although this approach has previously been used with success with various Gram-positive species, it is not directly applicable to the visualization of Gram-negative strains such as P. aeruginosa, particularly because of limitations regarding fluorescence staining. After adapting the staining procedure to P. aeruginosa, the action of PAA and BAC on the biofilm formed by strain ATCC 15442 was investigated. The results revealed specific inactivation patterns as a function of the mode of action of the biocides. While PAA treatment triggered a uniform loss of fluorescence in the structure, the action of BAC was first localized at the periphery of cell clusters and then gradually spread throughout the biofilm. Visualization of the action of BAC in biofilms formed by three clinical isolates then confirmed the presence of a delay in penetration, showing that diffusion-reaction limitations could provide a major explanation for the resistance of P. aeruginosa biofilms to this biocide. Biochemical analysis suggested a key role for extracellular matrix characteristics in these processes.

The effects of glutaraldehyde on the control of single and dual biofilms of Bacillus cereus and Pseudomonas fluorescens

Glutaraldehyde (GLUT) was evaluated for control of single and dual species biofilms of Bacillus cereus and Pseudomonas fluorescens on stainless steel surfaces using a chemostat system. The biofilms were characterized in terms of mass, cell density, total and matrix proteins and polysaccharides. The control action of GLUT was assessed in terms of inactivation and removal of biofilm. Post-biocide action was characterized 3, 7, 12, 24, 48 and 72 h after treatment. Tests with planktonic cells were also performed for comparison. The results demonstrated that in dual species biofilms the metabolic activity, cell density and the content of matrix proteins were higher than those of either single species. Planktonic B. cereus was more susceptible to GLUT than P. fluorescens. The biocide susceptibility of dual species planktonic cultures was an average of each single species. Planktonic cells were more susceptible to GLUT than their biofilm counterparts. Biofilm inactivation was similar for both of the single biofilms while dual biofilms were more resistant than single species biofilms. GLUT at 200 mg l(-1) caused low biofilm removal (<10%). Analysis of the post-biocide treatment data revealed the ability of biofilms to recover their activity over time. However, 12 h after biocide application, sloughing events were detected for both single and dual species biofilms, but were more marked for those formed by P. fluorescens (removal >40% of the total biofilm). The overall results suggest that GLUT exerts significant antimicrobial activity against planktonic bacteria and a partial and reversible activity against B. cereus and P. fluorescens single and dual species biofilms. The biocide had low antifouling effects when analysed immediately after treatment. However, GLUT had significant long-term effects on biofilm removal, inducing significant sloughing events (recovery in terms of mass 72 h after treatment for single biofilms and 42 h later for dual biofilms). In general, dual species biofilms demonstrated higher resistance and resilience to GLUT exposure than either of the single species biofilms. P. fluorescens biofilms were more susceptible to the biocide than B. cereus biofilms.

Electrochemical and microbiological characterization of paper mill biofilms

Biofilm samples collected from inside and outside the press and former sections of paper machines in a Northwestern Ontario paper mill for a period of 2 years were characterized microbiologically and electrochemically. Bacterial community profiling was done using polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) and selected bacterial isolates were identified using 16S rDNA analysis. The bacterial community showed the presence of Proteobacteria, Firmicutes, and Actinobacteria. Sphingomonas sp. was found to be the most common bacterial species, which showed the highest production of extracellular polymeric substances. Bacteria isolated from biofilms showed better adhesion properties than those from water samples. Cyclic voltammetry and electrochemical impedance spectroscopy studies showed that bacteria isolated from biofilms and feed water collected from inside the machine were more easily oxidized than those from outside, suggesting the need for a more rigorous biofilm abatement strategy for inside paper machines.

Neutral super-oxidised solutions are effective in killing P. aeruginosa biofilms

Bacteria growing in biofilms can become up to 1000-fold more resistant to antibiotics and biocides as compared to their planktonic counterparts. As a result of this increased resistance, biofilms and biofilm-related infections cannot be effectively treated with conventional antibiotic therapy. The goal of this study was to determine the efficacy of three neutral pH, super-oxidised solutions (nSOSs, OIS-80, OIS-125, OIS-200, Microcyn Technology) varying in oxychlorine concentration (80, 125 and 200 ppm) against P. aeruginosa grown planktonically and as biofilms. Exposure for 20 s of exponential phase cells to any of the three solutions was sufficient to reduce viability by more than five logs. However, only exposure for 10 min to OIS-125 and OIS-200 for 10 min was sufficient to eradicate stationary phase P. aeruginosa cells. The efficacy of nSOSs on P. aeruginosa biofilms, grown to maturity in continuous flow tube reactors, was determined upon treatment up to 60 min. Viability pre- and post-treatment was determined by CFU counts. The effect of these solutions on P. aeruginosa biofilms and biofilm architecture was further visualised by confocal scanning laser microscopy and quantitatively analysed by COMSTAT. Under these experimental conditions, only OIS-125 and OIS-200 achieved a >3-log reduction and biofilm disaggregation within 30 min of exposure. Because OIS-125 and OIS-200 enhance the disaggregation of biofilms, their use in the treatment of surface-related biofilm infections deserves further investigation.

Prokaryotic microbiota of recycled paper mills with low or zero effluent

The tendency in the paper industry is to close all water loops to save water. This leads to higher process temperatures and may increase the colloidal and dissolved material in the process circulation. Increase of nutrients in the water circuits may favor microbiological growth and fouling. In this paper the chemical and microbial compositions of water circuits and deposits were studied of two closed cycled paper/board mills, one mill totally closed (0 m(3) waste water t(-1)), and the other low discharging (about 4 m(3 )t(-1)). The zero discharge mill accumulated high amounts (>10 g C L(-1)) of organic carbon in the circulation waters, about 40% of which composed of volatile acids (lactic, acetic, propionic and butyric acid). Water contents of sulfate, chloride, sodium and calcium increased to >1 g L(-1) of each. q-PCR targeted on 16S rRNA genes indicated that the bacteria in water circuits were mainly viable cells. In both mills anaerobic growth (10(6)-10(8) CFU mL(-1)) equalled or exceeded aerobic growth, with odor problem but no actual slime problem. The major part (40%) of all identifiable bacterial sequences were closest but yet distant (<96%) to Enterococcus cecorum and in the 4 m(3 )t(-1) discharging mill also Bacillus thermoamylovorans and Bacillus coagulans. Slimes and deposits from the mills contained high amounts, > or =10(8) g(-1), of archaean, but only the genus Methanothrix was identifiable from the cloned sequences. The findings indicate that closing the water circuits strongly limited diversity of the microbiota but allowed efficient mineralization of the dissolved and suspended matter.

Two-fluid model of biofilm disinfection

We consider a dynamic model of biofilm disinfection in two dimensions. The biofilm is treated as a viscous fluid immersed in a fluid of less viscosity. The bulk fluid moves due to an imposed external parabolic flow. The motion of the fluid is coupled to the biofilm inducing motion of the biofilm. Both the biofilm and the bulk fluid are dominated by viscous forces, hence the Reynolds number is negligible and the appropriate equations are Stokes equations. The governing partial differential equations are recast as boundary integral equations using a version of the Lorenz reciprocal relationship. This allows for robust treatment of the simplified fluid/biofilm motion. The transport of nutrients and antimicrobials, which depends directly on the velocities of the fluid and biofilm, is also included. Disinfection of the bacteria is considered under the assumption that the biofilm growth is overwhelmed by disinfection.

Microbiologic profile of flexible endoscope disinfection in two Brazilian hospitals

BACKGROUND

[corrected] Endoscopes are routinely used in hospitals and clinics of the world and they can be potential sources of cross-infection when the decontamination process is unsuitable

AIM

The routines of flexible endoscope (bronchoscopes, esophagogastroduodenoscopes and colonoscopes) disinfection procedures used in two Brazilian university hospitals were evaluated during a 3-year period

METHODS

Aleatory samples from internal channels of endoscopes were collected after patient examination and after cleaning/disinfection procedures

RESULTS

A contamination >3 log10 was achieved in samples recovered from endoscopes after patient examination. These samples yielded gram-negative bacilli (n = 142: 56%), gram-positive cocci (n = 43: 17%), yeast cells (n = 43: 17%), and gram-positive bacilli (n = 26: 10%). Approximately, 72 out of 149 samples (48.32%) collected after undergoing the cleaning and disinfection procedures disclosed gram-negative bacilli (n = 55: 61%), gram-positive cocci (n = 21: 23%), gram-positive bacilli (n = 8: 9%) and yeast cells (n = 6: 7%). Esophagogastroduodenoscopes and colonoscopes were the most frequently contaminated devices. Pseudomonas aeruginosa, Klebsiella pneumoniae, Escherichia coli, Enterobacter spp, Serratia marcescens, Proteus mirabilis, Citrobacter freundii, Staphylococcus aureus, Staphylococcus coagulase negative, Micrococcus luteus, Candida albicans, C. tropicalis, C. glabrata, C. guilliermondii, Bacillus spp and Corynebacterium spp were predominantly identified

CONCLUSION

Inappropriate cleaning and low times of disinfection were respectively the major factors associated with the presence of microorganisms in colonoscopes and esophagogastroduodenoscopes. By analyzing the identified germs, hospital disinfection was considered of either intermediate or poor level. After this investigation, both university centers improved their previous protocols for disinfection and conditions for reprocessing endoscopes.

Incorporating toxin hypothesis into a mathematical model of persister formation and dynamics

Biofilms are well known for their extreme tolerance to antibiotics. Recent experimental evidence has indicated the existence of a small fraction of specialized persister cells may be responsible for this tolerance. Although persister cells seem to exist in planktonic bacterial populations, within a biofilm the additional protection offered by the polymeric matrix allows persister cells to evade elimination and serve as a source for re-population. Whether persister cells develop through interactions with toxin/antitoxin modules or are senescent bacteria is an open question. In this investigation we contrast results of the analysis of a mathematical model of the toxin/antitoxin hypothesis for bacteria in a chemostat with results incorporating the senescence hypothesis. We find that the persister fraction of the population as a function of washout rate provides a viable distinction between the two hypotheses. We also give simulation results that indicate that a strategy of alternating dose/withdrawal disinfection can be effective in clearing the entire persister and susceptible populations of bacteria. This strategy was considered previously in analysis of a generic model of persister formation. We find that extending the model of persister formation to include the toxin/antitoxin interactions in a chemostat does not alter the qualitative results that success of the dosing strategy depends on the withdrawal time. While this treatment is restricted to planktonic bacterial populations, it serves as a framework for including persister cells in a spatially dependent biofilm model.

Optimisation of the long-term efficacy of dental chair waterline disinfection by the identification and rectification of factors associated with waterline disinfection failure

Although many studies have highlighted the problem of biofilm growth in dental chair unit waterlines (DUWs), no long-term studies on the efficacy of DUW disinfection using a large number of dental chair units (DCUs) have been reported.

OBJECTIVES

To investigate the long-term (21 months) efficacy of the Planmeca Waterline Cleaning System (WCS) to maintain the quality of DUW output water below the American Dental Association (ADA) recommended standard of < or =200cfu/mL of aerobic heterotrophic bacteria using once weekly disinfection with the hydrogen peroxide-and silver ion-containing disinfectant Planosil.

METHODS

Microbiological quality of DUW output water was monitored by culture on R2A agar for 10 DCUs fitted with the WCS. The presence of biofilm in DUWs was examined by electron microscopy.

RESULTS

During the first 9 months a high prevalence (28/300 disinfection cycles; 9.3%) of intermittent DUW disinfection failure occurred in 8/10 DCUs due to operator omission to disinfect all DUWs (10/28 failed cycles), incorrect compressed air pressure failing to distribute the disinfectant properly (4/28 failed cycles) and physical blockage of disinfectant intake valves due to corrosion effects of Planosil (14/28 failed cycles). On rectification of these faults through engineering redesign and procedural changes, no further cases of intermittent DUW disinfection failure were observed. Independently of these factors, a rapid and consistent decline in efficacy of DUW disinfection occurred in 4/10 DCUs following the initial 9 months of once weekly disinfection. There was a highly significant difference (P<0.0001) in the prevalence of strongly catalase-positive Novosphingobium and Sphingomonas bacterial species (mean average prevalence of 37.1%) in DUW output water from these 4 DCUs compared to the other 6 DCUs and DCU supply water (prevalence <1%), which correlated with biofilm presence in the DUWs and indicated selective pressure for maintenance of these species by prolonged disinfectant usage. Planosil was reformulated to a more concentrated form (Planosil Forte) and when used once weekly was found to maintain bacterial density in output water below the ADA standard for all 10 DCUs.

CONCLUSIONS

A variety of factors can contribute to failure of DUW disinfection in the long-term, including human error, disinfectant corrosion of equipment and natural selection of naturally disinfectant-tolerant bacterial species.

A novel automated waterline cleaning system that facilitates effective and consistent control of microbial biofilm contamination of dental chair unit waterlines: A one-year study

Microbial contamination of dental chair unit (DCU) output water caused by biofilm growth in dental unit waterlines (DUWs) is a universal problem and a potentially significant source of cross-infection. The microbial quality of output water from a Planmeca Compact i DCU equipped with the novel Water Management System (WMS), an integrated and automated DUW cleaning system, was investigated over a 12-month period with the hydrogen peroxide- and silver ion-containing disinfectants Planosil and Planosil Forte. Four weeks after connection to the potable-water quality mains supply the density of aerobic heterotrophic bacteria, rose from the low levels consistently found in the supply water throughout this study (mean average 77 cfu/mL) to 15,400 cfu/mL. Disinfection of DUWs once weekly with Planosil for 10 weeks resulted in a dramatic reduction in bacterial density immediately following disinfection (mean average 26 cfu/mL). Bacterial density rose steadily between disinfections and by 7 days post-disinfection, water quality failed (mean average 384 cfu/mL) the American Dental Association DCU water quality standard of <or=200 cfu/mL. The DCU was then disinfected once weekly for 40 weeks with Planosil Forte. The average bacterial density immediately post-disinfection was 20 cfu/mL and 7 days post-disinfection was 113 cfu/mL. Electron microscopy showed that improved output water quality following disinfection with both disinfectants was associated with marked elimination of DUW biofilm, but deterioration of water quality following disinfection was associated with its regrowth. The most common bacterial species cultured from the mains water and the DCU output water were Microcococcus luteus and Sphingomonas spp., respectively, the latter of which are known opportunistic pathogens. The findings of this study show that the Planmeca Compact i DCU equipped with the easy to use and automated WMS, that requires minimal effort on the part of the operator, consistently provides output water that passes the ADA quality standard of <or=200 cfu/mL for up to 7 days following once-weekly disinfection with Planosil Forte.

Sensitivity of bacterial biofilms and planktonic cells to a new antimicrobial agent, Oxsil 320N

The effective concentrations of disinfectants were determined for planktonic bacteria using the norms EN 1040 and NF T 72-150. This concentration corresponds to biocide efficacy after 5 min of contact, followed by neutralization. However, micro-organisms often colonize a substratum and form microcolonies or biofilms where they are enclosed in exopolymer matrices. Biofilms are commonly resistant to a broad range of antimicrobial agents, and resistance mechanisms involve exopolymer matrices, changes in gene expression and metabolic alterations. Due to these different resistance mechanisms, it is difficult to select and titrate antimicrobial agents to be effective against biofilms. In this context, SODIFRA developed a new disinfectant, Oxsil 320N (French patent 94 15 193). Oxsil 320N is an association of three active principles: hydrogen peroxide, acetic acid/peracetic acid and silver. This biocide was tested on planktonic bacteria and on 24-h biofilms formed on AISI 304 stainless steel surfaces. The effective concentration of Oxsil 320N was also determined on biofilms using SODIFRA recommendations (without neutralization of the biocide). Data showed that the antimicrobial efficacy measured on planktonic bacteria is not a reliable indicator of performance when biofilm is present. When biofilms were exposed to Oxsil 320N, the concentration needed to achieve a 10(5)-fold decrease in concentration was 10 times higher than that for bacterial suspensions (0.313% Oxsil 320N). An effective concentration of Oxsil 320N of 3.13% was required.

Biofilm formation by Pseudoalteromonas ruthenica and its removal by chlorine

The distribution of a recently described marine bacterium, SBT 033 GenBank Accession No. AY723742), Pseudoalteromonas ruthenica, at the seawater intake point, outfall and mixing point of an atomic power plant is described, and its ability to form biofilm was investigated. The effectiveness of the antifouling biocide chlorine in the inactivation of planktonic as well as biofilm cells of P. ruthenica was studied in the laboratory. The results show that the planktonic cells were more readily inactivated than the cells enclosed in a biofilm matrix. Viable counting showed that P. ruthenica cells in biofilms were up to 10 times more resistant to chlorine than those in liquid suspension. Using confocal laser scanning microscopy it was shown that significant detachment of P. ruthenica biofilm developed on a glass substratum could be accomplished by treatment with a dose of 1 mg l-1 chlorine. Chlorine-induced detachment led to a significant reduction in biofilm thickness (up to 69%) and substratum coverage (up to 61%), after 5-min contact time. The results show that P. ruthenica has a remarkable ability to form biofilms but chlorine, a common biocide, can be used to effectively kill and detach these biofilms.

Bacterial contamination of dental chair units in a modern dental hospital caused by leakage from suction system hoses containing extensive biofilm

Within six months of opening of the new Dublin Dental Hospital in September 1998, areas of corrosion were observed on many of the baseplates of the hospital's 103 dental chair units (DCUs) at the site of attachment of the suction hoses. The corroded areas were heavily contaminated with Pseudomonas spp. and related genera posing a risk of cross-infection, particularly for immunocompromised patients. These species were used as marker organisms to investigate the source of the contamination. P. aeruginosa was the predominant species recovered from 41 selected DCU baseplates (61% prevalence), whereas P. putida (46% prevalence) and P. aeruginosa (43% prevalence) were predominant at the attachment ends of 37 selected high-volume suction hoses. Forty-one selected isolates of P. aeruginosa from 13 DCU baseplates, 16 high-volume suction hoses and 12 coarse filter housings (another suction system site) from 19 separate DCUs were serotyped to determine the similarity of isolates at each site. The majority of isolates (68.3%) belonged to serotype O:10, while the remainder belonged to serotypes O:6 (7.3%), O:11 (7.3%), O:14 (9.8%) and O:5/O:16 (7.3%). Of the isolates from DCU baseplates, additional isolates with the same serotype were recovered from other suction system sites in 10/13 (77%) cases. Isolates of only one serotype were recovered from each of the 19 DCUs investigated. Forty-one serotyped isolates were also subject to computer-assisted analysis of SpeI-generated DNA fingerprint profiles, and similarity coefficient (S(AB)s) values were calculated for each pairwise combination of isolate profiles. The data obtained showed that the isolates consisted of two distinct main populations, each containing separate clades corresponding to specific serotypes. Serotype O:6 (three isolates), O:11 (three isolates) and O:5/O:16 (three isolates) belonged to a single strain in each case. Serotypes O:14 (four isolates) and O:10 (28 isolates) belonged to two strains in each case. The two serotype O:10 strains, termed fingerprint groups I (four isolates from three DCUs) and II (24 isolates from 10 DCUs), were the most distantly related of all the strains identified. These findings demonstrated that the hospital DCUs had become colonized with a small number of P. aeruginosa strains, one of which (serotype O:10, fingerprint group II) predominated. These results also confirmed that DCU baseplate contamination was most likely to be due to leakage from suction system hoses at the baseplate attachment sites, probably due to loosening during use. Replacement hose connectors that firmly retained the suction hoses in the attachment sites so that they could not be loosened by movement of the suction hoses solved this problem, and eliminated further contamination of the DCU baseplates.

Effectiveness of sodium benzoate as a freshwater low toxicity antifoulant when dispersed in solution and entrapped in silicone coatings

The traditional solution for preventing organisms from attaching to submerged surfaces is to apply antifouling coatings or biocides. Based on the varied defence mechanisms exhibited by biofilms, the antifoulant needs to prevent bacterial attachment during the early stages of biofilm formation. The potential of benzoic acid and sodium benzoate (NaB) as antifoulants for deterring freshwater bacterial attachment was evaluated with the antifoulants dispersed in solution or entrapped in silicone coatings. Effectiveness was based on the decrease in microbial attachment, limited toxicity, and minimum alteration of the properties of the coatings. The optimal NaB concentration when dispersed in solution, 700 mg l-1, resulted in a biofilm surface coverage of only 3.34% after four weeks. The model silicone, Sylgard 184, demonstrated a better overall performance than the commercial coating, RTV11. Sylgard 184 containing sodium benzoate had 41-52% less biofilm in comparison to the control Sylgard 184, whereas both the control and NaB-entrapped RTV11 coatings had significant biofilm coverage.

In situ quantification of biocide efficacy using GFP transformed Aureobasidium pullulans

AIMS

To develop a real-time in situ method to quantify loss of viability of Aureobasidium pullulans PRAFS8 cells attached to plasticized polyvinyl chloride (pPVC) with incorporated biocides, and to use the method to compare biocide efficacy in situ.

METHODS AND RESULTS

A. pullulans PRAFS8, transformed with green fluorescent protein (GFP), was used to quantify the efficacy of a range of biocides incorporated into pPVC. Experimentally, it was found that a density of 1.53 x 10(6) yeast cells per cm(2) of pPVC was optimal as increasing the density of the yeast cells to 6.12 x 10(6) cm(-2) attached to pPVC containing the biocide 2-n-octyl-4-isothiazolin-3-one (OIT) decreased the rate of fluorescence loss. A strong positive correlation between fluorescence and viable yeast cell number was observed and fluorescence was used as a direct indicator of cell viability. The effectiveness of five commercial biocides, commonly incorporated into pPVC at their in-use concentrations, was tested against yeast cells attached to the pPVC surface. The loss of fluorescence and hence viability in situ was quantified using image analysis. The biocides N-(trichloromethylthio) phthalimide (NCMP), 10,10'-oxybisphenoxarsine (OBPA), OIT and 2,3,5,6-tetrachloro-4-(methylsulphonyl) pyridine (TCMP) caused complete loss of fluorescence within 30-50 h. In contrast the biocide dichloro-octyl-isothiazoline caused only 55 +/- 15% fluorescence loss after 50 h. Starvation of the yeast cells in suspension for 24 h prior to attachment reduced their initial sensitivity to OBPA, NCMP, OIT and TCMP by 15-20%, but eventually the fluorescence was also completely lost.

CONCLUSIONS

The use of A. pullulans expressing cytosolic GFP enables the in situ quantification of loss of viability when cells are attached to pPVC with incorporated biocides.

SIGNIFICANCE AND IMPACT OF THE STUDY

GFP fluorescence was used as a real-time indicator of cell viability and thus can be applied for direct quantification of the effectiveness of a broad range of biocides, incorporated into the polymer mass and used to protect a variety of plastics or other materials from microbial growth.

Eight Gram-negative bacteria are 10 000 times more sensitive to cationic detergents than to anionic detergents

In liquid culture, eight typical Gram-negative bacteria were ca. 10 000-fold more sensitive to cationic detergents than to the anionic detergent sodium dodecyl sulfate. Cetyltrimethylammonium bromide (CTAB) was inhibitory at concentrations ranging from 0.0006% to 0.01%. Four pseudomonads able to form biofilms were ca. 1000-fold more resistant to CTAB on Luria–Bertani agar plates than they were in liquid culture. A lasI mutant of Pseudomonas aerugi nosa was only able to tolerate 0.1% CTAB on Luria–Bertani agar plates but could tolerate 5% CTAB when supplemented with homoserine lactone containing culture supernatants.Key words: sodium dodecyl sulfate, cetyltrimethylammonium bromide, bacterial detergent resistance, homoserine lactones, Pseudomonas biofilms.

Colored moderately thermophilic bacteria in paper-machine biofilms

Biofilms cause several problems in papermaking. This report describes a microbiological survey of colored biofilms in six paper and board machines, including two case studies of outbreaks of colored slimes in which the causative bacteria were found. A total of 95 pink-, red-, orange- or yellow-pigmented strains were isolated. Nearly all (99%) of the strains grew at 52 degrees C, 72% grew at 56 degrees C, but only 30% grew at 28 degrees C, indicating that most of the strains were moderately thermophilic. Biofilm formation potential and biocide susceptibility of the strains were analyzed with a microtiter plate assay. In the presence of 5 ppm of methylene bisthiocyanate or 2,2-dibromo-3-nitrilopropionamide in paper-machine water, 55 strains formed biofims. Moreover, 39 strains increased biofilm production by 5-753% in the presence of biocide, suggesting that biocide concentrations inhibitory to planktonic but not to surface-attached cells may actually promote biofouling. The cells may have inactivated a portion of the biocides, as the cell density in this assay was high, corresponding to the highest cell densities occurring in the circulating waters. Four groups of colored bacteria that were isolated from several mills were identified. Pink-pigmented Deinococcus geothermalis and red-pigmented Meiothermus silvanus occurred as common primary biofilm-formers in paper machines. This report is the first description of the involvement of Meiothermus species in red-slime formation in the paper industry. The third group of bacteria (putative new species related to Roseomonas) contained strains that were not biofilm formers, but which were commonly found in slimes of neutral or alkaline machines. The fourth group contained red-pigmented biofilm-forming strains representing a novel genus of alpha- Proteobacteria related to Rhodobacter. Many colored paper-machine bacteria are species previously known from microbial mats of hot springs. Some characteristics of the bacterial groups are described here in order to facilitate their recognition in future cases of colored-slime outbreaks in the paper industry.