Solveig Langsrud

Does the Wide Use of Quaternary Ammonium Compounds Enhance the Selection and Spread of Antimicrobial Resistance and Thus Threaten Our Health

Quaternary ammonium compounds (QACs) are widely used biocides that possess antimicrobial effect against a broad range of microorganisms. These compounds are used for numerous industrial purposes, water treatment, antifungal treatment in horticulture, as well as in pharmaceutical and everyday consumer products as preserving agents, foam boosters, and detergents. Resistance toward QACs is widespread among a diverse range of microorganisms and is facilitated by several mechanisms such as modifications in the membrane composition, expression of stress response and repair systems, or expression of efflux pump genes. Development of resistance in both pathogenic and nonpathogenic bacteria has been related to application in human medicine and the food industry. QACs in cosmetic products will inevitably come into intimate contact with the skin or mucosal linings in the mouth and thus are likely to add to the selection pressure toward more QAC-resistant microorganisms among the skin or mouth flora. There is increasing evidence of coresistance and cross-resistance between QACs and a range of other clinically important antibiotics and disinfectants. Use of QACs may have driven the fixation and spread of certain resistance cassette collectors (class 1 integrons), currently responsible for a major part of antimicrobial resistance in gram-negative bacteria. More indiscriminate use of QACs such as in cosmetic products may drive the selection of further new genetic elements that will aid in the persistence and spread of antimicrobial resistance and thus in limiting our treatment options for microbial infections.

Occurrence of and a possible mechanism for resistance to a quaternary ammonium compound in Listeria monocytogenes.

In a study of 200 Listeria monocytogenes isolates, 10% were determined to be resistant to benzalkonium chloride (BC). Serial subcultivation of initially BC sensitive (BC(S)) and BC resistant (BC(R)) isolates in sublethal concentrations of BC resulted in enhanced and approximately equal resistance of all strains to the compound. Fifty per cent of the BC(R) isolates showed resistance to ethidium bromide (EB) as well. A proton motive force (pmf)-dependent efflux of EB was demonstrated in BC(R) isolates, and in originally sensitive strains adapted to grow in BC. This efflux was not found in BC(S) strains. The result indicate that BC can induce a broad resistance mechanism based on a pmf-driven efflux pump. There was no indication that this type of resistance was related to resistance to antibiotics.

Biofilm Formation and the Presence of the Intercellular Adhesion Locus ica among Staphylococci from Food and Food Processing Environments

ABSTRACT In clinical staphylococci, the presence of the ica genes and biofilm formation are considered important for virulence. Biofilm formation may also be of importance for survival and virulence in food-related staphylococci. In the present work, staphylococci from the food industry were found to differ greatly in their abilities to form biofilms on polystyrene. A total of 7 and 21 of 144 food-related strains were found to be strong and weak biofilm formers, respectively. Glucose and sodium chloride stimulated biofilm formation. The biofilm-forming strains belonged to nine different coagulase-negative species of Staphylococcus. The icaA gene of the intercellular adhesion locus was detected by Southern blotting and hybridization in 38 of 67 food-related strains tested. The presence of icaA was positively correlated with strong biofilm formation. The icaA gene was partly sequenced for 22 food-related strains from nine different species of Staphylococcus, and their icaA genes were found to have DNA similarities to previously sequenced icaA genes of 69 to 100%. Northern blot analysis indicated that the expression of the ica genes was higher in strong biofilm formers than that seen with strains not forming biofilms. Biofilm formation on polystyrene was positively correlated with biofilm formation on stainless steel and with resistance to quaternary ammonium compounds, a group of disinfectants.

Biofilm forming abilities of Salmonella are correlated with persistence in fish meal- and feed factories

BackgroundFeed contaminated with Salmonella spp. constitutes a risk of Salmonella infections in animals, and subsequently in the consumers of animal products. Salmonella are occasionally isolated from the feed factory environment and some clones of Salmonella persist in the factory environment for several years. One hypothesis is that biofilm formation facilitates persistence by protecting bacteria against environmental stress, e.g. disinfection. The aim of this study was to investigate the biofilm forming potential of Salmonella strains from feed- and fishmeal factories. The study included 111 Salmonella strains isolated from Norwegian feed and fish meal factories in the period 1991–2006 of serovar Agona, serovar Montevideo, serovar Senftenberg and serovar Typhimurium.ResultsSignificant differences were found between serovars regarding the abilities to form biofilm on polystyrene (microtiter plate assay) and in the air-liquid interface of nutrient broth (pellicle assay). Strains of serovar Agona and serovar Montevideo were good biofilm producers. In Norwegian factories, clones of these serovars have been observed to persist for several years. Most serovar Senftenberg clones appear to persist for a shorter period, and strains of this serovar were medium biofilm producers in our test systems. Strains of the serovar Typhimurium were relatively poor biofilm producers. Salmonella ser. Typhimurium clones have not been observed to persist even though this serovar is resident in Norwegian wild life. When classifying strains according to persistence or presumed non-persistence, persistent strains produced more biofilm than presumed non-persisting strains.ConclusionThe results indicate a correlation between persistence and biofilm formation which suggests that biofilm forming ability may be an important factor for persistence of Salmonella in the factory environment.

Attachment and biofilm formation by foodborne bacteria in meat processing environments: Causes, implications, role of bacterial interactions and control by alternative novel methods

Attachment of potential spoilage and pathogenic bacteria to food contact surfaces and the subsequent biofilm formation represent serious challenges to the meat industry, since these may lead to cross-contamination of the products, resulting in lowered-shelf life and transmission of diseases. In meat processing environments, microorganisms are sometimes associated to surfaces in complex multispecies communities, while bacterial interactions have been shown to play a key role in cell attachment and detachment from biofilms, as well as in the resistance of biofilm community members against antimicrobial treatments. Disinfection of food contact surfaces in such environments is a challenging task, aggravated by the great antimicrobial resistance of biofilm associated bacteria. In recent years, several alternative novel methods, such as essential oils and bacteriophages, have been successfully tested as an alternative means for the disinfection of microbial-contaminated food contact surfaces. In this review, all these aspects of biofilm formation in meat processing environments are discussed from a microbial meat-quality and safety perspective.

Bacterial disinfectant resistance—a challenge for the food industry

Abstract The focus on hygiene in the food industry has resulted in an increasing use of chemical disinfection and it has been speculated that this will impose a selective pressure and contribute to the emergence of disinfectant-resistant microorganisms. The frequency of strains with a low-level resistance to quaternary ammonium compounds (QAC) is relatively high for Listeria monocytogenes (10%), Staphylococcus spp. (13%) and Pseudomonas spp. (30%) and lower for lactic acid bacteria (1.5%) and coliforms (1%) isolated from food and food processing industry. In general, bacteria isolated after disinfection are more resistant and represent a potential food safety or food spoilage problem. Adaptation to disinfectants may be accompanied by cross-resistance to related disinfectants. We have recently found a genetic linkage between resistance to QAC and antibiotics in food associated staphylococci, and there is a growing concern about cross-resistance between antibiotics and disinfectants. Disinfectant resistance can in most cases be prevented by effective cleaning and disinfection procedures. More effort should be made to avoid build-up of resistance in food production environments.

Bacterial resistance to disinfectants containing quaternary ammonium compounds

Abstract Quaternary ammonium compounds (QAC) are widely used as disinfectants in both medical and food environments. Microbial contaminants are, therefore, regularly exposed to their action and the isolation from clinical and food sources of resistant bacteria continues to be reported in many countries. Resistance to QAC in clinical strains of staphylococci is encoded by one of at least three resistance genes, designated qacA, qacB and qacC . Using hybridisation analysis, we have shown that these QAC resistance genes are also distributed among staphylococcal strains in the food industry. In addition, we have discovered two new resistance determinants in these food isolates, which are now being characterised and sequenced. Although the general level of resistance of pure cultures is low, the resistant strains have originally been isolated after exposure to the recommended user concentration of a commercial brand of QAC. We have also studied resistance to QAC in pseudomonads isolated from the food industry. Their level of resistance is much higher than that found in staphylococci. About 30% of the collected strains were able to grow in 200 μg·ml −1 benzalkonium chloride, the lowest recommended use concentration for this commonly used type of QAC.

Evaluation of efficacy of disinfectants against Salmonella from the feed industry

Aims:  To evaluate disinfectants against Salmonella under conditions relevant for the feed industry.

Intrinsic and acquired resistance to quaternary ammonium compounds in food‐related Pseudomonas spp.

Aims: To determine the sensitivity of a strain used for disinfectants testing (Pseudomonas aeruginosa ATCC 15442) and food‐associated isolates to benzalkonium chloride and didecyl dimethylammonium chloride (DDAC). To determine whether the increase in bacterial resistance after adaptation to DDAC can be associated with phenotypic changes. To test the activity of alternative disinfectants to eliminate resistant Pseudomonas spp.

Factors contributing to the survival of poultry associated Pseudomonas spp. exposed to a quaternary ammonium compound

Resistance to benzalkonium chloride (BC) among Pseudomonas spp. isolated from poultry carcasses was determined and strategies for elimination of resistant strains evaluated. This investigation showed that resistance was quite common, about 30% of the isolates being able to grow in 200 μg ml−1 BC. Pseudomonas fluorescens strains were generally less susceptible than strains of Ps. lundensis and Ps. fragi. An overnight incubation in medium containing 200 μg ml−1 BC was sufficient to reduce the susceptibility of two Pseudomonas strains to the lethal effect of BC significantly. Adding EDTA enhanced the lethal effect of BC, but the effect was reduced after growing cells in medium containing BC and EDTA. Growth in medium with a quaternary ammonium compound (QAC) rendered the cells more susceptible to chlorine, phenolics and alkylaminoacetate. These results indicate that alternating use of QACs with these compounds can be used to avoid build‐up of resistant strains. In addition, increased temperatures improved the lethal effect of BC and should be considered when planning disinfection routines.