A synthetic furanone potentiates the effect of disinfectants on Salmonella in biofilm

Evaluation of Biofilm Cultivation Models for Efficacy Testing of Disinfectants against Salmonella Typhimurium Biofilms

Within the European Union, Salmonella is frequently reported in food and feed products. A major route of transmission is upon contact with contaminated surfaces. In nature, bacteria such as Salmonella are often encountered in biofilms, where they are protected against antibiotics and disinfectants. Therefore, the removal and inactivation of biofilms is essential to ensure hygienic conditions. Currently, recommendations for disinfectant usage are based on results of efficacy testing against planktonic bacteria. There are no biofilm-specific standards for the efficacy testing of disinfectants against Salmonella. Here, we assessed three models for disinfectant efficacy testing on Salmonella Typhimurium biofilms. Achievable bacterial counts per biofilm, repeatability, and intra-laboratory reproducibility were analyzed. Biofilms of two Salmonella strains were grown on different surfaces and treated with glutaraldehyde or peracetic acid. Disinfectant efficacy was compared with results for planktonic Salmonella. All methods resulted in highly repeatable cell numbers per biofilm, with one assay showing variations of less than 1 log10 CFU in all experiments for both strains tested. Disinfectant concentrations required to inactivate biofilms were higher compared to planktonic cells. Differences were found between the biofilm methods regarding maximal achievable cell numbers, repeatability, and intra-laboratory reproducibility of results, which may be used to identify the most appropriate method in relation to application context. Developing a standardized protocol for testing disinfectant efficacy on biofilms will help identify conditions that are effective against biofilms.

Furanone and phytol influence metabolic phenotypes regulated by acyl-homoserine lactone in Salmonella

Salmonella is an important foodborne pathogen, and it is unable to produce the quorum sensing signaling molecules called acyl-homoserine lactones (AHLs). However, it synthesizes the SdiA protein, detecting AHL molecules, also known as autoinducer-1 (AI-1), in the external environment. Exogenous AHLs can regulate specific genes related to virulence and stress response in Salmonella. Thus, interfering with quorum sensing can be a strategy to reduce virulence and help elucidate the cell-to-cell communication role in the pathogens' response to extracellular signals. This study aimed to evaluate the influence of the quorum sensing inhibitors furanone and phytol on phenotypes regulated by N-dodecanoyl homoserine lactone (C12-HSL) in Salmonella enterica serovar Enteritidis. The furanone C30 at 50 nM and phytol at 2 mM canceled the alterations promoted by C12-HSL on glucose consumption and the levels of free cellular thiol in Salmonella Enteritidis PT4 578 under anaerobic conditions. In silico analysis suggests that these compounds can bind to the SdiA protein of Salmonella Enteritidis and accommodate in the AHL binding pocket. Thus, furanone C30 and phytol act as antagonists of AI-1 and are likely inhibitors of the quorum sensing mechanism mediated by AHL in Salmonella.

Mechanisms of Inhibition of Quorum Sensing as an Alternative for the Control of E. coli and Salmonella

Quorum sensing (QS) is a process of cell–cell communication for bacteria such as E. coli and Salmonella that cause foodborne diseases, with the production, release, and detection of autoinducer (AI) molecules that participate in the regulation of virulence genes. All of these proteins are useful in coordinating collective behavior, the expression of virulence factors, and the pathogenicity of Gram-negative bacteria. In this work, we review the natural or synthetic inhibitor molecules of QS that inactivate the autoinducer and block QS regulatory proteins in E. coli and Salmonella. Furthermore, we describe mechanisms of QS inhibitors (QSIs) that act as competitive inhibitors, being a useful tool for preventing virulence gene expression through the downregulation of AI-2 production pathways and the disruption of signal uptake. In addition, we showed that QSIs have negative regulatory activity of genes related to bacterial biofilm formation on clinical artifacts, which confirms the therapeutic potential of QSIs in the control of infectious pathogens. Finally, we discuss resistance to QSIs, the design of next-generation QSIs, and how these molecules can be leveraged to provide a new antivirulence therapy to combat diseases caused by E. coli or Salmonella.

The Effect of Antimicrobial Resistance Plasmids Carrying blaCMY-2 on Biofilm Formation by Escherichia coli from the Broiler Production Chain

Extended-spectrum cephalosporin-resistant Escherichia coli (ESCR E. coli) with plasmids carrying the bla_CMY-2 resistance gene have been isolated from the Norwegian broiler production chain through the Norwegian monitoring program for antimicrobial resistance in animals, food and feed, NORM-VET. The aim of the present study was to investigate the biofilm forming abilities of these strains, and in particular to see whether these might be influenced by the carriage of bla_CMY-2 plasmids. The ESCR E. coli from the broiler production chain displayed relatively low biofilm forming abilities in the crystal violet biofilm assay as compared to quinolone-resistant E. coli (QREC) from the same population (mean ± SD = 0.686 ± 0.686 vs. 1.439 ± 0.933, respectively). Acquisition of two different bla_CMY-2 plasmids by QREC strains reduced their biofilm production in microtiter plates, but not their biofilm production on Congo Red agar plates. Furthermore, motility was reduced, but not planktonic growth. We hypothesize that genes carried by these plasmids may have caused the observed reduction in biofilm formation, possibly mediated through changes in flagellar expression or function. Furthermore, this may help explain the different biofilm forming abilities observed between ESCR E. coli and QREC. The results also indicate that the risk of biofilm reservoirs of antimicrobial resistant E. coli on in the broiler production is lower for ESCR E. coli than for QREC.

The Effect of Disinfectants on Quinolone Resistant E. coli (QREC) in Biofilm

The aim of disinfection is to reduce the number of microorganisms on surfaces which is a challenge due to biofilms. In the present study, six quinolone resistant Escherichia coli (QREC) strains with three different biofilm matrix compositions were included to assess the log₁₀ colony forming units (CFU) reduction effect of three disinfectants at various exposure times on biofilm of different ages and morphotypes. Biofilm was formed on stainless steel coupons for two and five days before transferred to tubes with Virocid 0, 25%, VirkonS 1%, and TP990 1% and left for various exposure times. The biofilms were scraped off and serial dilutions were spread on blood agar plates where colony forming units (CFU) were counted. A mean log₁₀ CFU reduction ≥4 was seen on two-day-old biofilm with VirkonS and Virocid (30 min) but not on five-day old biofilm. TP990 did not display sufficient effect under the conditions tested. The bactericidal effect was inferior to that reported on planktonic bacteria. The findings of this study should be considered when establishing both disinfectant routines and standard susceptibility tests, which further should accommodate E. coli biofilms and not only Pseudomonas as is the case today.

Efficacy of Synthetic Furanones on Listeria monocytogenes Biofilm Formation

Furanones are analogues of acylated homoserine lactones with proven antifouling activity in both Gram-positive and Gram-negative bacteria though the interference of various quorum sensing pathways. In an attempt to find new strategies to prevent and control Listeria monocytogenes biofilm formation on stainless steel (SS) surfaces, different concentrations of six synthetic furanones were applied on biofilms formed by strains isolated from food, environmental, and clinical sources grown onto AISI 316 SS coupons. Among the furanones tested, (Z-)-4-Bromo-5-(bromomethylene)-2(5H)-furanone and 3,4-Dichloro-2(5H)-furanone significantly (p < 0.05) reduced the adhesion capacity (>1 log CFU cm-2) in 24 h treated biofilms. Moreover, individually conducted experiments demonstrated that (Z-)-4-Bromo-5-(bromomethylene)-2(5H)-furanone was able to not only significantly (p < 0.05) prevent L. monocytogenes adhesion but also to reduce the growth rate of planktonic cells up to 48 h in a dose-dependent manner. LIVE/DEAD staining followed by epifluorescence microscopy visualisation confirmed these results show an alteration of the structure of the biofilm in furanone-treated samples. Additionally, it was demonstrated that 20 µmol L-1 of 3,4-Dichloro-2(5H)-furanone dosed at 0, 24 and 96 h was able to maintain a lower level of adhered cells (>1 log CFU cm-2; p < 0.05). Since furanones do not pose a selective pressure on bacteria, these results represent an appealing novel strategy for the prevention of L. monocytogenes biofilm grown onto SS.

Susceptibility of Salmonella Biofilm and Planktonic Bacteria to Common Disinfectant Agents Used in Poultry Processing

Poultry contaminated with Salmonella enterica subsp. enterica are a major cause of zoonotic foodborne gastroenteritis. Salmonella Heidelberg is a common serotype of Salmonella that has been implicated as a foodborne pathogen associated with the consumption of improperly prepared chicken. To better understand the effectiveness of common antimicrobial disinfectants (i.e., peroxyacetic acid [PAA], acidified hypochlorite [aCH], and cetylpyridinium chloride [CPC]), environmental isolates of nontyphoidal Salmonella were exposed to these agents under temperature, concentration, and contact time conditions consistent with poultry processing. Under simulated processing conditions (i.e., chiller tank and dipping stations), the bacteriostatic and bactericidal effects of each disinfectant were assessed against biofilm and planktonic cultures of each organism in a disinfectant challenge. Log reductions, planktonic MICs, and mean biofilm eradication concentrations were computed. The biofilms of each Salmonella isolate were more resistant to the disinfectants than were their planktonic counterparts. Although PAA was bacteriostatic and bactericidal against the biofilm and planktonic Salmonella isolates tested at concentrations up to 64 times the concentrations commonly used in a chiller tank during poultry processing, aCH was ineffective against the same isolates under identical conditions. At the simulated 8-s dipping station, CPC was bacteriostatic against all seven and bactericidal against six of the seven Salmonella isolates in their biofilm forms at concentrations within the regulatory range. These results indicate that at the current contact times and concentrations, aCH and PAA are not effective against these Salmonella isolates in their biofilm state. The use of CPC should be considered as a tool for controlling Salmonella biofilms in poultry processing environments.

Intra- and inter-species interactions within biofilms of important foodborne bacterial pathogens

A community-based sessile life style is the normal mode of growth and survival for many bacterial species. Under such conditions, cell-to-cell interactions are inevitable and ultimately lead to the establishment of dense, complex and highly structured biofilm populations encapsulated in a self-produced extracellular matrix and capable of coordinated and collective behavior. Remarkably, in food processing environments, a variety of different bacteria may attach to surfaces, survive, grow, and form biofilms. Salmonella enterica, Listeria monocytogenes, Escherichia coli, and Staphylococcus aureus are important bacterial pathogens commonly implicated in outbreaks of foodborne diseases, while all are known to be able to create biofilms on both abiotic and biotic surfaces. Particularly challenging is the attempt to understand the complexity of inter-bacterial interactions that can be encountered in such unwanted consortia, such as competitive and cooperative ones, together with their impact on the final outcome of these communities (e.g., maturation, physiology, antimicrobial resistance, virulence, dispersal). In this review, up-to-date data on both the intra- and inter-species interactions encountered in biofilms of these pathogens are presented. A better understanding of these interactions, both at molecular and biophysical levels, could lead to novel intervention strategies for controlling pathogenic biofilm formation in food processing environments and thus improve food safety.

Quorum sensing signalling and biofilm formation of brewery-derived bacteria, and inhibition of signalling by natural compounds

Bacteria use quorum sensing signalling in various functions, e.g. while forming biofilms, and inhibition of this signalling could be one way to control biofilm formation. The aim of this study was to evaluate the production of signalling molecules and its correlation with the biofilm formation capability of bacteria isolated from brewery filling process. A further aim was to study berry extracts and wood-derived terpenes for their possible quorum sensing inhibitory effects. Out of the twenty bacteria studied, five produced short-chain and five long-chain AHL (acyl homoserine lactone) signalling molecules when tested with the Chromobacterium violaceum CV026 reporter bacterium. Production of AI-2 (autoinducer-2) signalling molecules was detected from nine strains with the Vibrio harveyi BB170 bioassay. Over half of the strains produced biofilm in the microtitre plate assay, but the production of AHL and AI-2 signalling molecules and biofilm formation capability did not directly correlate with each other. Out of the 13 berry extracts and wood-derived terpenes screened, four compounds decreased AHL signalling without effect on growth. These were betulin, raspberry extract and two cloudberry extracts. The effect of these compounds on biofilm formation of the selected six bacterial strains varied. The phenolic extract of freeze-dried cloudberry fruit caused a statistically significant reduction of biofilm formation of Obesumbacterium proteus strain. Further experiments should aim at identifying the active compounds and revealing whether quorum sensing inhibition causes structural changes in the biofilms formed.

inhibitory effects of citral, cinnamaldehyde, and tea polyphenols on mixed biofilm formation by foodborne Staphylococcus aureus and Salmonella enteritidis

Biofilms are significant hazards in the food industry. In this study, we investigated the effects of food additive such as citral, cinnamaldehyde, and tea polyphenols on mixed biofilm formation by foodborne Staphylococcus aureus and Salmonella serotype Enteritidis. The adhesion rates of mixed strains in sub-MIC of additives were determined by a microtiter plate assay and bacterial communication signal autoinducer 2 (AI-2) production via a bioluminescence reporter Vibrio harveyi BB170. The structure of mixed biofilm was analyzed using scanning electron microscopy. The effect of the disinfectants hydrogen peroxide, sodium hypochlorite, and peracetic acid was tested on the mixed biofilm. Our results demonstrated that citral, cinnamaldehyde, and tea polyphenols were able to significantly inhibit mixed biofilm formation, while citral could reduce the synthesis of AI-2. Conversely, we observed a significant increase in AI-2 mediated by cinnamaldehyde. Tea polyphenols at lower concentrations induced AI-2 synthesis; however, AI-2 synthesis was significantly inhibited at higher concentrations (300 m g/ml). Food additives inhibited the adhesion of mixed bacteria on stainless steel chips and increased the sensitivity of the mixed biofilm to disinfectants. In conclusion, citral, cinnamaldehyde, and tea polyphenols had strong inhibitory effects on mixed biofilm formation and also enhanced the effect of disinfectant on mixed biofilm formation. This study provides a scientific basis for the application of natural food additives to control biofilm formation of foodborne bacteria.

Thiophenone and furanone in control of Escherichia coli O103:H2 virulence

Escherichia coli are a mutual and foodborne pathogen, causing severe intestinal infections typically characterized by diarrhoea and vomiting. Biofilms are often a common source of pathogenic and nonpathogenic bacteria. Quorum sensing is a phenomenon where bacteria communicate and initiate the regulation of several virulence factors and biofilm formation. Thus, quorum sensing has been a new target in the fight against bacterial biofilms. In this study, we investigated the effect of two quorum-sensing inhibitors for preventing in vitro biofilm formation in wild-type E. coli O103:H2. Furanone F202 originates from the red algae Delisea pulchra, and thiophenone TF101 is a sulphur analogue of furanone. We also investigated the effect of thiophenone and furanone on virulence factors controlled by quorum sensing. Both TF101 and F202 interfered with biofilm formation, although TF101 was more effective. TF101 reduced motility presumably by interfering with flagella production, visualized by microscopic techniques. The expressions of flhd, which are involved in flagella synthesis, were affected by thiophenone. This is the first study exploring the effect of thiophenone on E. coli biofilm formation and virulence factors.

Synthetic brominated furanone F202 prevents biofilm formation by potentially human pathogenic Escherichia coli O103:H2 and Salmonella ser. Agona on abiotic surfaces

AIMS

Investigate the use of a synthetic brominated furanone (F202) against the establishment of biofilm by Salmonella ser. Agona and E. coli O103:H2 under temperature conditions relevant for the food and feed industry as well as under temperature conditions optimum for growth.

METHODS AND RESULTS

Effect of F202 on biofilm formation by Salmonella ser. Agona and E. coli O103:H2 was evaluated using a microtiter plate assay and confocal microscopy. Effect of F202 on bacterial motility was investigated using swimming and swarming assays. Influence on flagellar synthesis by F202 was examined by flagellar staining. Results showed that F202 inhibited biofilm formation without being bactericidal. F202 was found to affect both swimming and swarming motility without, however, affecting the expression of flagella.

CONCLUSIONS

F202 showed its potential as a biofilm inhibitor of Salmonella ser. Agona and E. coli O103:H2 under temperature conditions relevant for the feed and food industry as well as temperatures optimum for growth. One potential mode of action of F202 was found to be by targeting flagellar function.

SIGNIFICANCE AND IMPACT OF THE STUDY

The present study gives valuable new knowledge to the potential use of furanones as a tool in biofilm management in the food and feed industry.

Commonly used disinfectants fail to eradicate Salmonella enterica biofilms from food contact surface materials

Salmonellosis is the second most common cause of food-borne illness worldwide. Contamination of surfaces in food processing environments may result in biofilm formation with a risk of food contamination. Effective decontamination of biofilm-contaminated surfaces is challenging. Using the CDC biofilm reactor, the activities of sodium hypochlorite, sodium hydroxide, and benzalkonium chloride were examined against an early (48-h) and relatively mature (168-h) Salmonella biofilm. All 3 agents result in reduction in viable counts of Salmonella; however, only sodium hydroxide resulted in eradication of the early biofilm. None of the agents achieved eradication of mature biofilm, even at the 90-min contact time. Studies of activity of chemical disinfection against biofilm should include assessment of activity against mature biofilm. The difficulty of eradication of established Salmonella biofilm serves to emphasize the priority of preventing access of Salmonella to postcook areas of food production facilities.

Biofilm building capacity of Salmonella enterica strains from the poultry farm environment

The Biofilm (BF) building capacity of different serotypes of Salmonella enterica derived from the poultry farm environment was investigated. Starting point for the investigation was the question if farm-isolated Salmonella serotypes with high importance for poultry meat and egg production are capable of forming a BF under defined laboratory conditions. Several isolates from different stages of the production cycle were chosen and compared to laboratory grown strains of the same serotype. BF building capacity was analyzed in a 96-well format during a time period of 2 days. Pulse field gel electrophoresis was used to establish a relationship between different isolates. The BF building capacity of a monospecies BF was strongly dependent on the temperature used for incubation. Results indicated further that certain farm isolates were capable of forming BF under laboratory conditions, whereas laboratory grown strains were not. Considerable differences between different field serovars and within one serovar exist. In conclusion, the BF building capacity of poultry-derived isolates is a function of adaptation to their host environment. Thus, the control of BF as a reservoir for Salmonella in the farm environment is of crucial importance for the overall improvement of food safety. Mechanical and substance-based approaches for this control exist in several variations, but overall decontamination success is difficult to achieve and needs to be especially adapted to the farm environment.

Clonal diversity and biofilm-forming ability of methicillin-resistant Staphylococcus pseudintermedius

OBJECTIVES

The aim of this study was to investigate the clonal epidemiology of methicillin-resistant Staphylococcus pseudintermedius (MRSP) isolates from dogs in Norway and to evaluate the antimicrobial resistance patterns and determine the biofilm-forming abilities of the isolates.

METHODS

All MRSP index isolates from each MRSP-positive dog detected in Norway until June 2011 were included (n = 23). The MICs of antimicrobial agents were determined by the VetMIC™ microdilution method. The genetic relationship between the isolates was investigated by multilocus sequence typing (MLST) and PFGE. The isolates' abilities to form biofilm on polystyrene were studied.

RESULTS

The MRSP isolates investigated grouped into 11 different sequence types (STs); MRSP ST106 occurred most frequently. There were a relatively smaller number of isolates belonging to ST71, the largely predominant ST in Europe. Isolates belonging to ST71 had a significantly greater ability to produce biofilm compared with the other isolates, and especially compared with MRSP ST106.

CONCLUSIONS

A heterogeneous clonal distribution was observed among MRSP from dogs in Norway. As opposed to previous findings in Europe, MRSP clones other than ST71 have spread in Norway, such as MRSP ST106. The results also show that MRSP ST71 is possibly a good biofilm producer, and this may in turn be a contributing factor to the nosocomial character of MRSP ST71.

Enhancement of the antimicrobial performance of biocidal formulations used for the preservation of white mineral dispersions

Biocides play an important role in the preservation of white mineral dispersions (WMD). Due to the occurrence of biocide-resistant bacteria and technical limitations in the use of biocides, new preservation strategies are required-like the enhancement of biocides by non-biocidal compounds. The aim of this study was to evaluate the biocide enhancement performance of lithium against various biocide-resistant bacteria in WMD. Subsequently, the minimal enhancing concentration (MEC) of lithium and the bioavailability of lithium in respect to the mode of introduction into WMD were investigated. The antimicrobial performance of biocidal formulations comprising isothiazolinones and formaldehyde releasers or isothiazolinones and glutaraldehyde has been evaluated against the related resistant bacterial spectrum in the presence of lithium. The MEC of lithium ranged from 1,350 to 1,500 ppm (based on the liquid phase weight of a WMD with 75% solids) for formaldehyde releasers and glutaraldehyde-based biocidal formulations, respectively. The biocide enhancing property of lithium was independent of whether lithium was introduced into WMD via a lithium-neutralised dispersant, added during the calcium carbonate grinding step, or dosed into the final product. Lithium is a non-biocidal compound which has been discovered to be a potent and universal biocide enhancer. Lithium boosts the biocidal activity of various biocides and provides a novel technique to overcome biocide resistance in WMD. Such a biocide enhancer represents a breakthrough that offers a potential tool to revolutionise the consumption of biocidal agents in the WMD producing industry.