Biocides Benzalkonium Chloride Research Articles

Differential Selection for Survival and for Growth in Adaptive Laboratory Evolution Experiments With Benzalkonium Chloride.

Biocides are used to control microorganisms across different applications, but emerging resistance may pose risks for those applications. Resistance to biocides has commonly been studied using adaptive laboratory evolution (ALE) experiments with growth at subinhibitory concentrations linked to serial subculturing. It has been shown recently that Escherichia coli adapts to repeated lethal stress imposed by the biocide benzalkonium chloride (BAC) by increased survival (i.e., tolerance) and not by evolving the ability to grow at increased concentrations (i.e., resistance). Here, we investigate the contributions of evolution for tolerance as opposed to resistance for the outcome of ALE experiments with E. coli exposed to BAC. We find that BAC concentrations close to the half maximal effective concentration (EC50, 4.36 μg mL-1) show initial killing (~40%) before the population resumes growth. This indicates that cells face a two-fold selection pressure: for increased survival and for increased growth. To disentangle the effects of both selection pressures, we conducted two ALE experiments: (i) one with initial killing and continued stress close to the EC50 during growth and (ii) another with initial killing and no stress during growth. Phenotypic characterization of adapted populations showed that growth at higher BAC concentrations was only selected for when BAC was present during growth. Whole genome sequencing revealed distinct differences in mutated genes across treatments. Treatments selecting for survival-only led to mutations in genes for metabolic regulation (cyaA) and cellular structure (flagella fliJ), while treatments selecting for growth and survival led to mutations in genes related to stress response (hslO and tufA). Our results demonstrate that serial subculture ALE experiments with an antimicrobial at subinhibitory concentrations can select for increased growth and survival. This finding has implications for the design of ALE experiments to assess resistance risks of antimicrobials in different scenarios such as disinfection, preservation, and environmental pollution.

Effect of combination of ultraviolet radiation and biocide on fungal-induced corrosion of high-strength 7075 aluminum alloy

The effect of ultraviolet (UV) radiation and biocide benzalkonium chloride (BKC) on fungal-induced corrosion of AA7075 induced by Aspergillus terreus (A. terreus) was deeply studied using analysis of biological activity, surface analysis, and electrochemical measurements. Results demonstrated that the planktonic and sessile spore concentrations decline by more than two orders of magnitude when UV radiation and BKC are combinedly used compared with the control. UV radiation can inhibit the biological activity of A. terreus and influence the stability of passive film of AA7075. Except for direct disinfection, the physical adsorption of BKC on the specimen can effectively inhibit the attachment of A. terreus. The combination of UV radiation and BKC can much more effectively inhibit the corrosion of AA, especially pitting corrosion, due to their synergistic effect. The combined application of UV radiation and BKC can be a good method to effectively inhibit fungal-induced corrosion.

Single Method for Determination of Biocides Benzalkonium Chloride, Chloroxylenol and Chlorhexidine Gluconate in Cosmetics, Hygiene and Health Care Products by Using High Performance Liquid Chromatography

Single Method for Determination of Biocides Benzalkonium Chloride, Chloroxylenol and Chlorhexidine Gluconate in Cosmetics, Hygiene and Health Care Products by Using High Performance Liquid Chromatography

Genomic analysis of Listeria monocytogenes CC7 associated with clinical infections and persistence in the food industry

Listeria monocytogenes clonal complex 7 (CC7), belonging to lineage II, is the most common subtype among clinical listeriosis isolates in Norway, and is also commonly found in Norwegian food industry and outdoor environments. In the present study, the relative prevalence of CCs among clinical isolates of L. monocytogenes in European countries during 2010–2015 was determined. Then, phylogenomic and comparative genomic analyses was performed for 115 Norwegian and 255 international reference genomes from various sources, to examine potential explanations underlying the high prevalence of CC7 among Norwegian listeriosis cases. Selected isolates were also compared using in vitro virulence assays.The results showed a high relative prevalence of CC7 in clinical isolates from Norway and the neighboring Nordic countries Sweden and Finland. In contrast to in most other European countries, lineage II dominated among clinical isolates in these countries. Phylogenetic analysis of the 370 CC7 isolates separated the genomes into four clades, with the majority of Norwegian isolates (69 %) clustered in one of these clades, estimated to have diverged from the other clades around year 1830. The Norwegian isolates within this clade were widely distributed in different habitats; several (poultry) meat processing factories, a salmon processing plant, in nature, farms, and slugs, and among human clinical isolates. In particular, one pervasive CC7 clone was found across three poultry processing plants and one salmon processing plant, and also included three clinical isolates.All analysed CC7 isolates harbored the same set of 72 genes involved in both general and specific stress responses. Divergence was observed for plasmid-encoded genes including genes conferring resistance against arsenic (Tn554-arsCBADR), cadmium (cadA1C1 and cadA2C2), and the biocide benzalkonium chloride (bcrABC). No significant difference in prevalence of these genes was seen between isolates from different habitats or sources. Virulence attributes were highly conserved among the CC7 isolates. In vitro virulence studies of five representative CC7 isolates revealed a virulence potential that, in general, was not significantly lower than that of the control strain EGDe, with isolate-dependent differences that could not be correlated with genetic determinants.The study shows that CC7 is widespread in Norway, and that a pervasive CC7 clone was present in food processing plants. The study highlights the importance of CC7 and lineage II strains in causing listeriosis and shows that more research is needed to understand the reasons behind geographical differences in CC prevalence.

Contribution of RND-Type Efflux Pumps in Reduced Susceptibility to Biocides in Acinetobacter baumannii.

Bacterial efflux pumps are among the key mechanisms of resistance against antibiotics and biocides. We investigated whether differential expression levels of the RND-type efflux pumps AdeABC and AdeIJK impacted the susceptibility to commonly used biocides in multidrug-resistant Acinetobacter baumannii. Susceptibility testing and time-kill assays of defined laboratory and clinical A. baumannii strains with different levels of efflux pump expression were performed after exposure to the biocides benzalkonium chloride, chlorhexidine digluconate, ethanol, glucoprotamin, octenidine dihydrochloride, and triclosan. While the impact of efflux pump expression on susceptibility to the biocides was limited, noticeable differences were found in kill curves, where AdeABC expression correlated with greater survival after exposure to benzalkonium chloride, chlorhexidine digluconate, glucoprotamin, and octenidine dihydrochloride. AdeABC expression levels did not impact kill kinetics with ethanol nor triclosan. In conclusion, these data indicate that the overexpression of the RND-type efflux pumps AdeABC and AdeIJK contributes to the survival of A. baumannii when exposed to residual concentrations of biocides.

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.

Development of Quality Control Ranges for Biocide Susceptibility Testing.

Every laboratory test needs validation by quality controls. For biocide susceptibility testing (BST), neither quality control (QC) strains nor QC ranges applicable to these strains are currently available. As QC strains, four well-defined laboratory reference strains (Staphylococcus aureus ATCC® 6538, Enterococcus hirae ATCC® 10541, Escherichia coli ATCC® 10536 and Pseudomonas aeruginosa ATCC® 15442), which have been used previously for biocide efficacy testing, were selected. In an interlaboratory trial with eleven participating laboratories, BST QC ranges should be developed for the aforementioned four strains and the four biocides benzalkonium chloride, chlorhexidine, octenidine and polyhexanide. The performance of three different lots of tryptic soy broth was explored using the broth microdilution method and the data were subsequently evaluated using the RangeFinder software. As a result, QC ranges were defined for all reference strain–biocide combinations, except for P. aeruginosa ATCC® 15442 with the two biocides chlorhexidine and polyhexanide. The development of the latter two QC ranges was not possible, due to the limited solubility of the biocides in the test range required for P. aeruginosa ATCC® 15442. The newly developed QC ranges comprise three to five dilution steps. The establishment of QC ranges will contribute to the validation of BST in the future.

Antimicrobial and Biocide Resistance among Canine and Feline Enterococcus faecalis, Enterococcus faecium, Escherichia coli, Pseudomonas aeruginosa, and Acinetobacter baumannii Isolates from Diagnostic Submissions.

A total of 215 isolates from infections of dogs and cats, including 49 Enterococcus faecalis, 37 Enterococcus faecium, 59 Escherichia coli, 56 Pseudomonas aeruginosa, and 14 Acinetobacter baumannii, were investigated for their susceptibility to 27 (Gram-positive bacteria) or 20 (Gram-negative bacteria) antimicrobial agents/combinations of antimicrobial agents by broth microdilution according to the recommendations of the Clinical and Laboratory Standards Institute. Moreover, all isolates were analysed for their susceptibility to the biocides benzalkonium chloride, chlorhexidine, polyhexanide, and octenidine by a recently published broth microdilution biocide susceptibility testing method. While the E. faecalis isolates did not show expanded resistances, considerable numbers of the E. faecium isolates were resistant to penicillins, macrolides, tetracyclines, and fluoroquinolones. Even a single vancomycin-resistant isolate that carried the vanA gene cluster was detected. Expanded multiresistance phenotypes were also detected among the E. coli isolates, including a single carbapenem-resistant, blaOXA-48-positive isolate. In addition, multiresistant A. baumannii isolates were detected. The minimal inhibitory concentrations of the biocides showed unimodal distributions but differed with respect to the biocide and the bacterial species investigated. Although there were no indications of a development of biocide resistance, some P. aeruginosa isolates exhibited benzalkonium MICs higher than the highest test concentration.

Antimicrobial and Biocide Resistance among Feline and Canine Staphylococcus aureus and Staphylococcus pseudintermedius Isolates from Diagnostic Submissions.

A total of 114 Staphylococcus isolates from various infections of companion animals, including 43 feline Staphylococcus aureus, 19 canine S. aureus, 11 feline Staphylococcus pseudintermedius and 41 canine S. pseudintermedius were investigated for (i) their susceptibility to 24 antimicrobial agents and three combinations of antimicrobial agents by broth microdilution following CLSI recommendations and (ii) the corresponding resistance genes. In addition, the isolates were tested for their susceptibility to the four biocides benzalkonium chloride, chlorhexidine, polyhexanide and octenidine by a recently developed biocide susceptibility testing protocol. Penicillin resistance via blaZ was the dominant resistance property in all four groups of isolates ranging between 76.7 and 90.9%. About one quarter of the isolates (25.4%) proved to be methicillin-resistant and carried the genes mecA or mecC. Macrolide resistance was the second most prevalent resistance property (27.2%) and all isolates harbored the resistance genes erm(A), erm(B), erm(C), erm(T) or msr(A), alone or in combinations. Fluoroquinolone resistance was detected in 21.1% of all isolates tested, whereas tetracycline resistance via tet(K) and/or tet(M) occurred in 19.3% of the isolates. Resistance to last resort antimicrobial agents in human medicine was seen only in single isolates, if at all. The minimal inhibitory concentrations (MICs) of the four biocides showed unimodal distributions and were very similar for the four groups of staphylococci. Because of the large number of (multi)resistant isolates, antimicrobial susceptibility testing of feline and canine S. aureus and S. pseudintermedius isolates is highly recommended before the start of an antimicrobial chemotherapy. Moreover, no hints towards the development of biocide resistance were detected.

Staphylococcus aureus from Minas Artisanal Cheeses: Biocide Tolerance, Antibiotic Resistance and Enterotoxin Genes

Staphylococcus aureus is a common contaminant in artisanal raw-milk cheeses. Tolerance of S. aureus to biocides is a threat to disinfection in the cheese production environment, while antibiotic resistance and enterotoxin production are additional health concerns. This study aimed to evaluate the tolerance of S. aureus isolated from Minas artisanal cheeses to the biocides benzalkonium chloride, hexadecylpyridinium chloride, cetrimide, triclosan, hexachlorophene, and chlorhexidine, and the simultaneous occurrence of genes coding for antibiotic resistance (mecA, aacA-aphD, and tetK), efflux pumps [qacA/B and smr (qacC/D)], and enterotoxins (sea, seb, sec, sed, see, seg, seh, sei, and sej). Among the tested isolates, 38.2% were resistant to at least one biocide, and 73.1% were positive for one or more antibiotic resistance gene. Most of the biocide-tolerant and antibiotic-resistant isolates harbored efflux pump genes, and were positive for at least one staphylococcal enterotoxin gene. The study highlights the need for correct hygiene monitoring programs to ensure the safety of these products.

Benzalkonium chloride antagonises aminoglycoside antibiotics and promotes evolution of resistance.

BackgroundBiocide disinfectants are essential tools in infection control, but their use can inadvertently contribute to emergence of antibiotic-resistant bacteria. In this study we systematically examine the effect of the biocide benzalkonium chloride, which is primarily used for surface disinfection but is also present as a preservative in many consumer products, on the activity of aminoglycoside antibiotics in Acinetobacter baumannii.MethodsThe effect of subinhibitory BAC on aminoglycoside treatment of A. baumannii ATCC17978 was investigated using time-to-kill assays, MIC determination, directed evolution experiments, fluctuation tests and labelled gentamicin accumulation assays. Further MIC determinations and directed evolution experiments were performed with additional Gram-negative ESKAPE pathogens.FindingsIn A. baumannii ATCC17978, BAC prevents gentamicin killing and drastically increases the frequency at which resistant mutants emerge, through reducing intracellular antibiotic accumulation. BAC also increases the MIC of multiple aminoglycoside antibiotics (kanamycin, tobramycin, streptomycin, gentamicin and amikacin). BAC promotes the emergence of mutants with reduced gentamicin susceptibility in other Gram-negative ESKAPE pathogens but does not always alter the MIC. These effects occur at BAC concentrations which are similar to residual levels in high-use environments, and just below the concentration range for BAC when used as a preservative in eye drops and ear drops.InterpretationOur results suggest that subinhibitory BAC has the potential to antagonise aminoglycoside activity and promote the emergence of bacterial mutants with reduced susceptibility. We suggest that the extremely widespread use of BAC in clinical and home settings and its long half-life mean there is potential for these interactions to occur in the environment, or in patients who use BAC-containing products while taking aminoglycosides to treat skin, eye or ear infections, although such co-exposure is likely to be rare. We suggest that biocide stewardship is needed to prevent the types of exposure that can contribute to antibiotic resistance.FundingThis work was funded by the National Health and Medical Research Council of Australia. The funders had no role in study design, interpretation or decision to publish.

Distinct expression profiles of regulatory RNAs in the response to biocides in Staphylococcus aureus and Enterococcus faecium

The aim of the study was to characterize the antimicrobial activity of clinically-relevant biocides (chlorhexidine digluconate, benzalkonium chloride, PVP-iodine and triclosan) and to determine the sRNA expression profiles under biocide exposure in two major bacterial opportunistic pathogens, Enterococcus faecium and Staphylococcus aureus. In vitro activities were evaluated against S. aureus HG003 and E. faecium Aus0004. We determined MIC, MBC, sub-inhibitory concentrations (SIC) and growth curves under SIC conditions. sRNA expression study under SIC exposure of biocides was performed by RT-qPCR on 3 sRNAs expressed in S. aureus (RNAIII, SprD and SprX) and the first 9 sRNAs identified as expressed in E. faecium. MICs were higher against E. faecium than for S. aureus. Growth curves under increasing biocide concentrations highlighted two types of bactericidal activity: “on/off” effect for chlorhexidine, benzalkonium chloride, PVP-iodine and a “concentration-dependent” activity for triclosan. Exposure to biocide SICs led to an alteration of several sRNA expression profiles, mostly repressed. The distinct biocide activity profiles must be evaluated with other compounds and bacterial species to enrich the prediction of resistance risks associated with biocide usage. Biocide exposure induces various sRNA-mediated responses in both S. aureus and E. faecium, and further investigations are needed to decipher sRNA-driven regulatory networks.

Extensively-drug-resistant Klebsiella pneumoniae ST307 outbreak strain from north-eastern Germany does not show increased tolerance to quaternary ammonium compounds and chlorhexidine

An outbreak of extensively-drug-resistant Klebsiella pneumoniae strain ST307 in a cluster of hospitals in north-east Germany gave rise to the assumption that the epidemiological success of the strain could be based on increased tolerance to biocides. The tolerance of the outbreak strain was compared with epidemiologically unrelated clinical isolates of K.pneumoniae, and reference strains of Pseudomonas aeruginosa (ATCC 15442) and Escherichia coli K12 (NCTC 10538). Tests were performed in a miniaturized assay based on European Standard EN 1040. The widely used biocides benzalkonium chloride (BAC) and didecyl dimethyl ammonium chloride (DDAC), their commercial formulation Descosept spezial (DS), and the antiseptic agent chlorhexidine digluconate (CHG) were selected as test substances. These biocides are used regularly in the hospitals involved in the outbreak. All biocides had a bactericidal effect against all tested strains in the quantitative suspension test within 5 min at typically used concentrations and dilutions. The effectiveness of BAC and DDAC alone and in combination, and CHG antisepsis were not impaired under tested conditions. The outbreak strain did not show significantly increased tolerance towards biocides regarding the antiseptic. Thus, the epidemiological success of the strain has to be ascribed to other causes, such as inadequate hand hygiene of visitors.

A simple cation exchange model to assess the competitive adsorption between the herbicide paraquat and the biocide benzalkonium chloride on montmorillonite

Since adsorption on clay minerals is one of the most popular water-pollutant removal method, it is important to consider the coexistence of several compounds that can affect pollutant retention. In this work, the competitive behaviour between cationic herbicide paraquat (PQ) and a benzalkonium chloride compound (BAC) on montmorillonite (MMT) was performed by adsorption experiments and analysed by a theoretical cation exchange model. Experimental studies included adsorption isotherms, XRD, FTIR and zeta potential (ζ). Binary systems (BAC + PQ) were performed at different initial concentrations ratio BAC/PQ = 0.1; 0.5; 1.0; 2.0 and 3.0. Results showed that at higher BAC initial concentration, the maximum adsorbed PQ amount decreases. X-Ray diffractograms showed that as the BAC/PQ ratio increases, the MMT basal spacing peak shifts to lower angles suggesting that the basal spacing is mainly controlled by the presence of BAC. Besides, the total adsorbed amount (adsorbed PQ plus adsorbed BAC) is closer to clay CEC value (0.91 mEq g−1), at this value ζ ≅ 0 mV suggesting that the adsorption occurs through a cation exchange mechanism. The theoretical model applied was originally developed to describe the exchange of simple cations on clay minerals, however it was effective in predicting the behaviour of larger cations such as PQ and BAC. In this scenario, thermodynamic parameters calculated through the model indicate that cation exchange process is spontaneous towards adsorbed BAC, suggesting that an adsorbed PQ cation is replaced by an equivalent amount of BAC cation (expressed in terms of electrical charge).

Biocidal Activity of Phyto-Derivative Products Used on Phototrophic Biofilms Growing on Stone Surfaces of the Domus Aurea in Rome (Italy)

Hypogean or enclosed monuments are important cultural heritage sites that can suffer biodegradation. Many of the stone walls of the prestigious Domus Aurea are overwhelmed by dense biofilms and so need intervention. Room 93 was chosen as a study site with the aim to test the efficacy of phyto-derivatives as new biocides. Laboratory studies were performed comparing the effects of liquorice leaf extract (Glycyrrhiza glabra L.), lavender essential oil (Lavandula angustifolia Mill.) and a combination of both. In situ studies were also performed to test the effect of liquorice. The results were compared with those of the commonly used synthetic biocide benzalkonium chloride. The effects on the biofilms were assessed by microscopy along with chlorophyll fluorescence analysis. The phototrophs in the biofilms were identified morphologically, while the heterotrophs were identified with culture analysis and 16S gene sequencing. Results showed that the mixed solution liquorice/lavender was the most effective in inhibiting the photosynthetic activities of biofilms in the laboratory tests; while, in situ, the effect of liquorice was particularly encouraging as an efficient and low-invasive biocide. The results demonstrate a high potential biocidal efficacy of the phyto-derivatives, but also highlight the need to develop an efficient application regime.

Impact of High-Hydrostatic Pressure Treatments Applied Singly or in Combination with Moderate Heat on the Microbial Load, Antimicrobial Resistance, and Bacterial Diversity of Guacamole.

Guacamole is an avocado sauce highly appreciated for its pleasant taste and nutritional value. The present study addressed the impact of high-hydrostatic pressure (HP) treatments on the product safety and bacterial diversity. Four HP treatments, 5 min each, were applied: (A) 450 megapascals (MPa) at 22 °C; (B) 450 MPa at 50 °C; (C) 600 MPa at 22 °C; (D) 600 MPa at 50 °C. Controls and treated samples were refrigerated stored for 50 days. The residual surviving fraction was lowest for the 600 MPa treatment at 50 °C. Bacterial growth on media supplemented with antibiotics (cefotaxime and imipenem) or the biocide benzalkonium chloride was detected only from control samples but not from HP-treated samples. High throughput sequencing analysis indicated that the bacterial diversity of control samples was dominated by members of Fam. Enterobacteriaceae, but it changed to a lactic acid microbiota during storage. HP-treated samples showed reduced relative abundances of Enterobacteriaceae and lactic acid bacteria and higher abundances of Pantoea, Ralstonia and Methylobacterium. Results from the study indicate that HP treatments of guacamole at 50 °C show higher microbial inactivation compared to 22 °C. However, all treatments reduced the levels of Enterobacteriaceae and penem-tolerant bacteria and provided product stability against acidification by lactic acid bacteria.

Degradation of non-oxidizing biocide benzalkonium chloride and bulk dissolved organic matter in reverse osmosis concentrate by UV/chlorine oxidation

Non-oxidizing biocide that is used to inhibit the microorganism growth on RO membrane, are observed to be high concentration and toxic in RO concentrate. The synergistic oxidation process (SOP) of UV/chlorine was investigated to simultaneously reduced the content (60.2 %) and toxicity (57.0 %) of a representative biocide dodecylbenzyldimethylammonium chloride (DDBAC) in real RO concentrate, with a UV fluence 1080 mJ/cm2 and chlorine dose 20 mg/L. Besides eliminating the DDBAC, UV/chlorine reduced the UVA254 and fluorescence of the dissolved organic matters (DOM). The oxidation mechanism was verified to be the radical electrophilic addition rather than the chlorine-electrophilic substitution through the decay of electron-donation moiety and UVA254. As results, high molecular weight fractions of DOM (>2k Da, 79.2 %) was cleaved into low molecular weight fractions (<0.4k Da, 18.4 %) and organic halide was formed. Parallel-factor analysis of the fluorescence components suggested that decomposition of the protein-like fluorophore is most likely to surrogate the biocide removal and organic halide formation compared to other fluorophore components and UVA254. Accordingly, a portable fluorescence probe with 400 nm excitation and 410–600 nm emission wavelengths was developed as an online surrogate for the DDBAC removal and organic halide formation.

Evaluation of a Newly Developed Vacuum Dried Microtiter Plate for Rapid Biocide Susceptibility Testing of Clinical Enterococcus Faecium Isolates.

We investigated the suitability of a newly developed biocide susceptibility test system based on microtiter plates containing vacuum dried biocides as a fast and reliable screening method. The evaluated substances included the cationic biocides benzalkonium chloride (BAC), chlorhexidine dihydrochloride (CHX), cetylpyridinium chloride, didecyldimethylammonium chloride, and octenidine dihydrochloride. Testing a selection of Escherichia coli and enterococci, the biocide microtiter plates provided results comparable to those obtained from broth microdilution according to ISO 20776-1. Broad MIC ranges allowed for testing gram-positive and gram-negative species with the same plate design. In the second part of our study, we applied the established method to analyze the susceptibility of 90 clinical Enterococcus faecium isolates from a German university hospital, as previous studies have indicated a link between reduced susceptibility to substances such as CHX and BAC and vancomycin resistance. We therefore determined MIC and minimum bactericidal concentrations (MBC) for 48 non-clonal vancomycin susceptible and 42 non-clonal vancomycin resistant isolates, but MIC95 and MBC95 were quite similar in both groups. Our easy to handle and ready to use test system enables the routine surveillance of bacterial tolerance towards disinfectants in hospitals. As a result, hygiene measures can be adapted and nosocomial infections controlled despite increasing prevalence of antibiotic-resistant bacteria.

Aesthetic Alteration of Marble Surfaces Caused by Biofilm Formation: Effects of Chemical Cleaning

Despite the massive presence of biofilms causing aesthetic alteration to the façade of the Monza Cathedral, our team in a previous work proved that the biocolonization was not a primary damaging factor if compared to chemical-physical deterioration due to the impact of air pollution. Nonetheless, the conservators tried to remove the sessile dwelling microorganisms to reduce discolouration. In this research, two nearby sculpted leaves made of Candoglia marble were selected to study the effects of a chemical treatment combining the biocides benzalkonium chloride, hydrogen peroxide and Algophase® and mechanical cleaning procedures. One leaf was cleaned with the biocides and mechanically, and the other was left untreated as control. The impact of the treatment was investigated after 1 month from the cleaning by digital microscopy, environmental scanning electron microscopy, confocal microscopy and molecular methods to determine the composition and the functional profiles of the bacterial communities. Despite the acceptable aesthetic results obtained, the overall cleaning treatment was only partially effective in removing the biofilm from the colonized surfaces and, therefore, not adequately suitable for the specific substrate. Furthermore, the cleaning process selected microorganisms potentially more resistant to biocides so that the efficacy of future re-treatment by antimicrobial agents could be negatively affected.

Biocide susceptibilities and biofilm-forming capacities of Acinetobacter baumannii clinical isolates from Malaysia.

Acinetobacter baumannii is a Gram-negative nosocomial pathogen that has the capacity to develop resistance to all classes of antimicrobial compounds. However, very little is known regarding its susceptibility to biocides (antiseptics and disinfectants) and capacity to form biofilms, particularly for Malaysian isolates. To determine the susceptibility of A. baumannii isolates to commonly-used biocides, investigate their biofilm-forming capacities and the prevalence of biocide resistance and biofilm-associated genes. . The minimum inhibitory concentration (MIC) values of 100 A. baumannii hospital isolates from Terengganu, Malaysia, towards the biocides benzalkonium chloride (BZK), benzethonium chloride (BZT) and chlorhexidine digluconate (CLX), were determined by broth microdilution. The isolates were also examined for their ability to form biofilms in 96-well microplates. The prevalence of biocide resistance genes qacA, qacE and qacDE1 and the biofilm-associated genes bap and abaI were determined by polymerase chain reaction (PCR). Majority of the A. baumannii isolates (43%) showed higher MIC values (> 50 µg/mL) for CLX than for BZK (5% for MIC > 50 µg/mL) and BZT (9% for MIC > 50 µg/mL). The qacDE1 gene was predominant (63%) followed by qacE (28%) whereas no isolate was found harbouring qacA. All isolates were positive for the bap and abaI genes although the biofilm-forming capacity varied among the isolates. The Terengganu A. baumannii isolates showed higher prevalence of qacDE1 compared to qacE although no correlation was found with the biocides' MIC values. No correlation was also observed between the isolates' biofilm-forming capacity and the MIC values for the biocides.