Biofilm-producing abilities of Salmonella strains isolated from Turkey

Antimicrobial Peptides: A Promising Alternative to Conventional Antimicrobials for Combating Polymicrobial Biofilms

Polymicrobial biofilms adhere to surfaces and enhance pathogen resistance to conventional treatments, significantly contributing to chronic infections in the respiratory tract, oral cavity, chronic wounds, and on medical devices. This review examines antimicrobial peptides (AMPs) as a promising alternative to traditional antibiotics for treating biofilm-associated infections. AMPs, which can be produced as part of the innate immune response or synthesized therapeutically, have broad-spectrum antimicrobial activity, often disrupting microbial cell membranes and causing cell death. Many specifically target negatively charged bacterial membranes, unlike host cell membranes. Research shows AMPs effectively inhibit and disrupt polymicrobial biofilms and can enhance conventional antibiotics' efficacy. Preclinical and clinical research is advancing, with animal studies and clinical trials showing promise against multidrug-resistant bacteria and fungi. Numerous patents indicate increasing interest in AMPs. However, challenges such as peptide stability, potential cytotoxicity, and high production costs must be addressed. Ongoing research focuses on optimizing AMP structures, enhancing stability, and developing cost-effective production methods. In summary, AMPs offer a novel approach to combating biofilm-associated infections, with their unique mechanisms and synergistic potential with existing antibiotics positioning them as promising candidates for future treatments.

Intestinal biofilms: pathophysiological relevance, host defense, and therapeutic opportunities

SUMMARYThe human intestinal tract harbors a profound variety of microorganisms that live in symbiosis with the host and each other. It is a complex and highly dynamic environment whose homeostasis directly relates to human health. Dysbiosis of the gut microbiota and polymicrobial biofilms have been associated with gastrointestinal diseases, including irritable bowel syndrome, inflammatory bowel diseases, and colorectal cancers. This review covers the molecular composition and organization of intestinal biofilms, mechanistic aspects of biofilm signaling networks for bacterial communication and behavior, and synergistic effects in polymicrobial biofilms. It further describes the clinical relevance and diseases associated with gut biofilms, the role of biofilms in antimicrobial resistance, and the intestinal host defense system and therapeutic strategies counteracting biofilms. Taken together, this review summarizes the latest knowledge and research on intestinal biofilms and their role in gut disorders and provides directions toward the development of biofilm-specific treatments.

Pan-Genome-Wide Association Study reveals a key role of the salmochelin receptor IroN in the biofilm formation of Salmonella Typhimurium and its monophasic variant 4,[5],12:i:

Salmonella enterica subsp. enterica serovar Typhimurium variant 4,[5],12:i:- (so called S. 4,[5],12:i:-) has rapidly become one of the most prevalent serovars in humans in Europe, with clinical cases associated with foodborne from pork products. The mechanisms, genetic basis and biofilms relevance by which S. 4,[5],12:i:- maintains and spreads its presence in pigs remain unclear. In this study, we examined the genetic basis of biofilm production in 78 strains of S. 4,[5],12:i:- (n = 57) and S. Typhimurium (n = 21), from human gastroenteritis, food products and asymptomatic pigs. The former showed a lower Specific Biofilm Formation index (SBF) and distant phylogenetic clades, suggesting that the ability to form biofilms is not a crucial adaptation for the S. 4,[5],12:i:- emerging success in pigs. However, using a pan-Genome-Wide Association Study (pan-GWAS) we identified genetic determinants of biofilm formation, revealing 167 common orthologous groups and genes associated with the SBF. The analysis of annotated sequences highlighted specific genetic deletions in three chromosomal regions of S. 4,[5],12:i:- correlating with SBF values: i) the complete fimbrial operon stbABCDE widely recognized as the most critical factor involved in Salmonella adherence; ii) the hxlA, hlxB, and pgiA genes, which expression in S. Typhimurium is induced in the tonsils during swine infection, and iii) the entire iroA locus related to the characteristic deletion of the second-phase flagellar genomic region in S. 4,[5],12:i:-. Consequently, we further investigated the role of the iro-genes on biofilm by constructing S. Typhimurium deletion mutants in iroBCDE and iroN. While iroBCDE showed no significant impact, iroN clearly contributed to S. Typhimurium biofilm formation. In conclusion, the pan-GWAS approach allowed us to uncover complex interactions between genetic and phenotypic factors influencing biofilm formation in S. 4,[5],12:i:- and S. Typhimurium.

High Biofilm-Forming Multidrug-Resistant Salmonella Infantis Strains from the Poultry Production Chain

The ability of Salmonella species to adhere to surfaces and form biofilms, leading to persistent environmental reservoirs, might represent a direct link between environmental contamination and food processing contamination. The purpose of this study was to investigate the biofilm-forming ability of 80 multidrug-resistant (MDR) and extended-spectrum beta-lactamase (ESBL) producing Salmonella enterica serovar Infantis strains isolated from the broiler food chain production through whole genome sequencing (WGS), PCR, and morphotype association assays. Biofilm formation was quantified by testing the strains at two different temperatures, using 96-well polystyrene plates. The rough and dry colony (rdar) morphotype was assessed visually on Congo red agar (CRA) plates. Based on our results, all tested S. Infantis strains produced biofilm at 22 °C with an rdar morphotype, while at 37 °C, all the isolates tested negative, except one positive. Most isolates (58.75%) exhibited strong biofilm production, while 36.25% showed moderate production. Only 5 out of 80 (6.25%) were weak biofilm producers. WGS analysis showed the presence of the fim cluster (fimADF) and the csg cluster (csgBAC and csgDEFG), also described in S. Typhimurium, which are responsible for fimbriae production. PCR demonstrated the presence of csgD, csgB, and fimA in all 80 S. Infantis strains. To our knowledge, this is the first study comparing the effects of two different temperatures on the biofilm formation capacity of ESBL producing S. Infantis from the broiler production chain. This study highlights that the initial biofilm components, such as curli and cellulose, are specifically expressed at lower temperatures. It is important to emphasize that within the broiler farm, the environmental temperature ranges between 18-22 °C, which is the optimum temperature for in vitro biofilm formation by Salmonella spp. This temperature range facilitates the expression of biofilm-associated genes, contributing to the persistence of S. Infantis in the environment. This complicates biosecurity measures and makes disinfection protocols on the farm and in the production chain more difficult, posing serious public health concerns.

Phenotypic Characteristics That May Contribute to Persistence of Salmonella Strains in the Pistachio Supply Chain

Salmonella enterica subsp. enterica strain diversity in California pistachios is limited; some strains have persisted in the pistachio supply chain for ≥10 years. Representative isolates of six persistent strains and three sporadic strains isolated from California pistachios were selected to evaluate copper resistance, growth in pistachio hull slurry, biofilm formation, desiccation tolerance, and survival during subsequent storage. The presence of a copper homeostasis and silver-resistance island sequence in three of the persistent strains was associated with an increase in tolerance to CuSO4 from 7.5 mM to 15 mM under anaerobic but not aerobic conditions; all isolates were resistant to ≥120 mM Cu-EDTA under both anerobic and aerobic conditions. When inoculated into pistachio hull slurry at 2.75 ± 0.04 log CFU/mL and incubated at 30 °C, the populations of Salmonella Enteritidis strain A (sporadic) increased to significantly lower levels than the other strains at 16, 20, 24, and 28 h but not at 40 and 48 h. Maximum populations of 8.70-8.85 log CFU/mL were observed for all strains at ≥40 h of incubation. All nine Salmonella strains produced weak to strong biofilms after 4 days at 25 °C; seven strains, including two sporadic strains, produced moderate biofilms, and Salmonella Liverpool strain A (persistent) produced a strong biofilm. The rdar+ and rdar- morphotypes were observed in both persistent and sporadic Salmonella strains. Population declines of 5.03 log were observed for Salmonella Enteritidis strain A within 18 h of drying on filter paper whereas reductions of 0.50-1.25 log were observed for the other eight Salmonella strains. Population reductions (3.98-5.12 log) of these eight strains were not significantly different after storage at 25 ± 1 °C and 35% relative humidity for 50 days. The phenotypic characteristics evaluated here do not independently account for the persistence of a small number of Salmonella strains associated with the California pistachio production chain.

Glyoxylate cycle maintains the metabolic homeostasis of Pseudomonas aeruginosa in viable but nonculturable state induced by chlorine stress

Bacteria enter a viable but non-culturable (VBNC) state with low metabolic activity to cope with environmental stress (e.g., chlorine disinfection). Elucidating the mechanism and key pathway of VBNC bacteria maintaining low metabolic competence is of great significance to realize their effective control and reduce their environmental and health risks. This study discovered that the glyoxylate cycle is a key metabolic pathway for VBNC bacteria, but not for culturable bacteria. And blocking the glyoxylate cycle pathway inhibited the reactivation and led to the death of VBNC bacteria. The main mechanisms involved the breakdown of material and energy metabolism and the antioxidant system. Gas chromatography-tandem mass spectrometry analysis showed that blocking the glyoxylate cycle led to a disruption of carbohydrate metabolism and fatty acid catabolism in VBNC bacteria. As a result, the energy metabolism system of VBNC bacteria collapsed and the abundance of energy metabolites (ATP, NAD⁺ and NADP⁺) decreased significantly. Moreover, the decrease in the level of quorum sensing signaling molecules (quinolinone and N-Butanoyl-D-homoserine lactone) inhibited the synthesis of extracellular polymeric substances (EPSs) and biofilm formation. And the downregulation of glycerophospholipid metabolic competence increased the permeability of cell membranes, leading to the entry of large amounts of hypochlorous acid (HClO) into the bacteria. In addition, the down-regulation of nucleotide metabolism, glutathione metabolism, and the reduction of antioxidant enzyme content resulted in the inability to scavenge reactive oxygen species (ROS) generated by chlorine stress. The large production of ROS and the reduction of antioxidants together led to the breakdown of the antioxidant system of VBNC bacteria. In short, the glyoxylate cycle is the key metabolism pathway of VBNC bacteria for stress resistance and maintaining cellular metabolic balance, and targeting the glyoxylate cycle represents an attractive strategy for developing new and efficient disinfection methods for the control of VBNC bacteria.

Antimicrobial and Antibiofilm Effect of Commonly Used Disinfectants on Salmonella Infantis Isolates

Salmonella enterica subsp. enterica serovar Infantis is the most prevalent serovar in broilers and broiler meat in the European Union. The aim of our study was to test the biofilm formation and antimicrobial effect of disinfectants on genetically characterized S. Infantis isolates from poultry, food, and humans. For the biofilm formation under various temperature conditions (8 °C, 20 °C, and 28 °C) and incubation times (72 h and 168 h), the crystal violet staining method was used. The evaluation of the in vitro antimicrobial effect of Ecocid^® S, ethanol, and hydrogen peroxide was determined using the broth microdilution method. The antibiofilm effect of subinhibitory concentration (1/8 MIC) of disinfectants was then tested on S. Infantis 323/19 strain that had the highest biofilm formation potential. Our results showed that the biofilm formation was strain-specific; however, it was higher at 20 °C and prolonged incubation time. Moreover, strains carrying a pESI plasmid showed higher biofilm formation potential. The antibiofilm potential of disinfectants on S. Infantis 323/19 strain at 20 °C was effective after a shorter incubation time. As shown in our study, more effective precautionary measures should be implemented to ensure biofilm prevention and removal in order to control the S. Infantis occurrence.

Structural variations on Salmonella biofilm by exposition to river water

Biofilm formation, as adapting strategies, is the result of stressful conditions that Salmonella faces in hostile environments like surface water. We evaluated river water effect on Salmonella biofilm formation ability in terms of physical, morphological characteristics and chemical composition. A new morphotype SPAM (soft, pink and mucoid) was detected in Oranienburg strains S-76 and S-347 (environmental and clinical isolate). Oranienburg serotypes showed very marked behavior in adherence, pellicle liquid-air and resistance, being Oranienburg S-76 the strongest biofilm producer. All strains when exposed to river water presented an overlapping mucoid layer in the morphotype and increased their motility except Oranienburg S-347. The most motile was Typhimurium (control) and the least Infantis S-304 (clinical isolate). Mannose, glucose, galactose and ribose were the main biofilm sugar components; type and concentration of sugar suggest a morphotype/serotype dependent pattern. Strong morphotypes expressed in this study may be an effective protective strategy for Salmonella in hostile environments.

Effects of environmental conditions (temperature, pH, and glucose) on biofilm formation of Salmonella enterica serotype Kentucky and virulence gene expression

Salmonella is a foodborne pathogen and an emerging zoonotic bacterial threat in the food industry. The aim of this study was to evaluate the biofilm formation by a cocktail culture of 3 wild isolates of Salmonella enterica serotype Kentucky on plastic (PLA), silicon rubber (SR), and chicken skin surfaces under various temperatures (4, 10, 25, 37, and 42°C) and pH values (4.0, 5.0, 6.0, 7.0, and 8.0). Then, at the optimum temperature and pH, the effects of supplementation with glucose (0, 0.025, 0.05, and 0.4% w/v) on biofilm formation were assessed on each of the surfaces. The results indicated that higher temperatures (25 to 42°C) and pH values (7.0 and 8.0) led to more robust biofilm formation than lower temperatures (4 and 10°C) and lower pH levels (4.0 to 6.0). Moreover, biofilm formation was induced by 0.025% glucose during incubation at the optimum temperature (37°C) and pH (7.0) but inhibited by 0.4% glucose. Consistent with this finding, virulence related gene (rpoS, rpoH, hilA, and avrA) expression was increased at 0.025% glucose and significantly reduced at 0.4% glucose. This results also confirmed by field emission scanning electron microscope, confocal laser scanning microscopy, and autoinducer-2 determination. This study concluded that optimum environmental conditions (temperature 37°C, pH 7.0, and 0.25% glucose) exhibited strong biofilm formation on food and food contract surfaces as well as increased the virulence gene expression levels, indicating that these environmental conditions might be threating conditions for food safety.

Biofilm Formation by Salmonella enterica Strains

Biofilm formation by five different Salmonella enterica strains was assessed qualitatively and quantitatively under different incubation conditions. The strains exhibited different adherence abilities to test tubes. The isolates revealed Red Dry and Rough (RDAR) and Brown Dry and Rough (BDAR) morphotypes when cultured on Congo Red Agar (CRA). The pellicles formed by the tested strains ranged from strong to fragile when incubated in LB without NaCl at 27 °C. Smooth and White (SAW) morphotype on CRA and very weak pellicles were observed when the bacterial strains were incubated at 37 °C. The effect of temperature and media on biofilm formation by the tested strains was significant. Among the five Salmonella isolates, S. enteritidis TM 6 and S. enteritidis TM 68 formed strong biofilms when incubated in LB without NaCl at 27 °C for 24 h and consequently selected to be analysed under scanning electron microscope (SEM). Scanning electron micrographs revealed that S. enteritidis TM 6 formed more complex colonies when compared to those formed by S. enteritidis TM 68. As far as we know, this is the first study that provides quantitative and qualitative data for 5 Salmonella enterica isolates in different media mimicking four different nutritional conditions at two different temperatures after 24 and 48 h. The strains included two serovars S. bredeney and S. anatum, which are rarely accounted for. Additionally, the studies that described S. enteritidis biofilms under SEM are extremely limited, which makes it among the first comprehensive studies that screened for S. enteritidis biofilms.

Rugose Morphotype in Salmonella Typhimurium and Salmonella Heidelberg Induced by Sequential Exposure to Subinhibitory Sodium Hypochlorite Aids in Biofilm Tolerance to Lethal Sodium Hypochlorite on Polystyrene and Stainless Steel Surfaces

Salmonella biofilms act as a continuous source for cross-contamination in the food processing environments. In this study, a stable rugose morphotype of Salmonella was first induced by sequential exposure to subinhibitory concentrations (SICs) of sodium hypochlorite (NaOCl) (ranging from 50 to 300 ppm over 18-day period) in tryptic soy broth. Then, rugose and smooth morphotypes of Salmonella Typhimurium ATCC 14028 and Salmonella Heidelberg ATCC 8326 were characterized for biofilm forming abilities on polystyrene and stainless steel surfaces. Rugose morphotype of both ATCC 14028 and ATCC 8326 exhibited higher Exopolysaccharide (EPS) formation than smooth morphotype (p ≤ 0.05). Also, the SICs of NaOCl (200 or 300 ppm in broth model) increased the biofilm formation ability of rugose morphotype of ATCC 8326 (p ≤ 0.05) but decreased that of ATCC 14028. The 2-day-old Salmonella biofilms were treated with biocidal concentrations of 50, 100, or 200 ppm NaOCl (pH 6.15) in water for 5, 10, or 20 min at room temperature. The biofilm reduction in CFU/cm2 for the rugose was lower than the smooth morphotype on both surfaces (p ≤ 0.05) by lethal NaOCl in water. Scanning electron micrographs on both polystyrene and stainless steel surfaces demonstrated that the rugose morphotype produced a denser biofilm than the smooth morphotype. Transmission electron micrographs revealed the cell wall roughness in rugose morphotype, which may help in tolerance to NaOCl. The gene expression data indicate that the expression of biofilm regulator (csgD), curli (csgA, csgB, and csgC), and cellulose (bcsE) was significantly increased in rugose morphotype when induced by sequential exposure of NaOCl SICs. These findings reveal that the rugose morphotype of S. Typhimurium and S. Heidelberg produced significantly denser biofilm on food contact surfaces, which also increased with sequential exposure to SICs of NaOCl in the case of S. Heidelberg, and these biofilms were more tolerant to biocidal NaOCl concentrations commonly used in the food processing plants.

Understanding Antimicrobial Resistance (AMR) Profiles of Salmonella Biofilm and Planktonic Bacteria Challenged with Disinfectants Commonly Used During Poultry Processing

Foodborne pathogens such as Salmonella that survive cleaning and disinfection during poultry processing are a public health concern because pathogens that survive disinfectants have greater potential to exhibit resistance to antibiotics and disinfectants after their initial disinfectant challenge. While the mechanisms conferring antimicrobial resistance (AMR) after exposure to disinfectants is complex, understanding the effects of disinfectants on Salmonella in both their planktonic and biofilm states is becoming increasingly important, as AMR and disinfectant tolerant bacteria are becoming more prevalent in the food chain. This review examines the modes of action of various types of disinfectants commonly used during poultry processing (quaternary ammonium, organic acids, chlorine, alkaline detergents) and the mechanisms that may confer tolerance to disinfectants and cross-protection to antibiotics. The goal of this review article is to characterize the AMR profiles of Salmonella in both their planktonic and biofilm state that have been challenged with hexadecylpyridinium chloride (HDP), peracetic acid (PAA), sodium hypochlorite (SHY) and trisodium phosphate (TSP) in order to understand the risk of these disinfectants inducing AMR in surviving bacteria that may enter the food chain.

Investigation of the effect of different environmental conditions on biofilm structure of Salmonella enterica serotype Virchow via FTIR spectroscopy

This study aims to describe the content of polymeric matrix components under different incubation temperatures and pH levels. Optimal biofilm production of 15 S. Virchow isolates occurred following the incubation in LB^-NaCl for 72 h, at pH 6.6 and 20 °C. The expression of csgA, csgD, adrA and bcsA genes at 20 °C, 25 °C and 30 °C in S. Virchow DMC18 was analyzed, and it was discovered that the maximum production of cellulose and curli fimbriae occurred at 20 °C. The physical characteristics of pellicle structure of S. Virchow DMC18 was determined as rigid at 20 °C, while becoming fragile at higher temperatures. FTIR analyses confirmed the obtained molecular findings. The intensities of the 16 different peaks originating from carbohydrate, protein, and nucleic acid in the spectra of biofilm samples significantly diminished (p < 0.05) with the increasing temperature. The highest intensities of lipids and carbohydrates were observed at 20 °C indicating the changes in cell surface properties.

Natural freeze-thaw cycles may increase the risk associated with Salmonella contamination in surface and groundwater environments

Groundwater contamination by bacteria poses a serious threat to our drinking water supplies. In cold climate regions, microorganisms introduced to upper soil layers by spreading of animal manure are subject to low temperatures and multiple cycles of freezing and thawing at the beginning of winter and during spring melt. We investigated the influence of temperature fluctuations around the freezing point, known as freeze-thaw (FT), on the inactivation rates, growth, and biofilm formation of a manure-isolated strain of Salmonella typhimurium. Moreover, the effects of FT on the transport characteristics of S. typhimurium in quartz sand were monitored in model porewater solutions of two different ionic strengths (IS: 10 and 100 mM KCl) and two different humic acid (HA) concentrations (1 and 5 mg/L). Increasing numbers of FT cycles were found to decrease the deposition of S. typhimurium onto quartz sand and increase the percentage of detached cells in sand-packed column experiments. Based on the calculated bacterial attachment efficiencies, the predicted minimum setback distances between the location of water supply wells and manure spreading activities are higher when the effects of FT are taken into consideration. While FT treatment significantly affected cell viability (in the presence of HA), most cells were in a viable but non-culturable (VBNC) state with compromised ability to form biofilm. This investigation demonstrates the effects of spring temperature variations in upper soil layers on S. typhimurium properties and the potential increased risk of bacterial contamination in representative aquifer environments in cold climate regions.

Multipurpose efficacy of the lyophilized cell-free supernatant of Salmonella bongori isolated from the freshwater fish, Devario aequipinnatus: toxicity against microbial pathogens and mosquito vectors

Presently, the discovery of effective drugs and pesticides from eco-friendly biological sources is an important challenge in the field of life sciences. The present research was aimed for standardizing an innovative approach in the evaluation of the biological potentiality of the metabolites of fish-associated bacteria. We have identified 17 skin-associated bacteria from the freshwater fish, giant danio, Devario aquipinnatus. They were screened through biofilm forming and extracellular enzyme producing ability. The results of preliminary antibacterial evaluation of the bacterial supernatants underlined the importance of three potential strains (BH8, BH10 and BH11) for further applied research. Hence, such strains were subsequently subjected to a novel extraction procedure to overcome the difficulties found in polar solvents mixed with the supernatant. The lyophilized cell-free supernatant (LCFS) of 3 isolates were individually extracted by using methanol. During the testing of LCFS's methanolic extract (LCFS-ME) of 3 isolates, only the extract of BH11-strain exhibited potent inhibitory activity against the pathogenic bacteria and fungi. Furthermore, the larvicidal and mosquitocidal assays on the filariasis vector, Culex quinquefasciatus also showed its potent toxicity on both the adults and developmental instars of mosquito. Through molecular and phylogenetic analyses, the BH11 strain was identified as Salmonella bongori (KR350635). The present finding emphasized that the S. bongori could be an important novel source of effective antimicrobials and mosquitocidal agents.

Salmonella and Campylobacter biofilm formation: a comparative assessment from farm to fork

It takes several steps to bring food from the farm to the fork (dining table), and contamination with food-borne pathogens can occur at any point in the process. Campylobacter spp. and Salmonella spp. are the main microorganisms responsible for foodborne disease in the EU. These two pathogens are able to persist throughout the food supply chain thanks to their ability to form biofilms. Owing to the high prevalence of Salmonella and especially of Campylobacter in the food supply chain and the huge efforts of food authorities to reduce these levels, it is of great importance to fully understand their mechanisms of persistence. Diverse studies have evaluated the biofilm-forming capacity of foodborne pathogens isolated at different steps of food production. Nonetheless, the principal obstacle of these studies is to reproduce the real conditions that microorganisms encounter in the food supply chain. While there are a wide number of Salmonella biofilm studies, information on Campylobacter biofilms is still limited. A comparison between the two microorganisms could help to develop new research in the field of Campylobacter biofilms. Therefore, this review evaluates relevant work in the field of Salmonella and Campylobacter biofilms and the applicability of the data obtained from these studies to real working conditions. © 2018 Society of Chemical Industry.

Salmonella enterica growth and biofilm formation in flesh and peel cantaloupe extracts on four food-contact surfaces

Salmonella enterica is responsible for the highest number of foodborne disease outbreaks pertaining to cantaloupe industry. The objective of this study was to examine the growth and biofilm formation by outbreak strains of S. enterica ser. Poona (S. Poona), S. enterica ser. Stanley (S. Stanley) and S. enterica ser. Montevideo (S. Montevideo) on different food-contact processing surfaces in cantaloupe flesh and peel extracts at 22 °C and 10 °C. The generation time of all S. enterica strains tested was shorter in the high concentration (50 mg/ml) of cantaloupe extract and high temperature. In 50 mg/ml of cantaloupe flesh or peel extract, the populations of S. enterica were increased by 5 log CFU/ml in 24 h at 22 °C and 1 log CFU/ml in 72 h at 10 °C. In 2 mg/ml of cantaloupe flesh or peel extracts, the populations of S. enterica were increased by 3.5 log CFU/ml in 56 h at 22 °C, but there were no changes in 72 h at 10 °C. The biofilm production of S. enterica was greater at 50 mg/ml of cantaloupe extract and 22 °C, but no major differences (P ≥ 0.05) were found among the strains tested. In 50 mg/ml cantaloupe extract, S. enterica produced 5-6 log CFU/cm² biofilm in 4-7 d at 22 °C and approximately 3.5-4 log CFU/cm² in 7 d at 10 °C. In 2 mg/ml of cantaloupe extract, S. enterica produced 4-4.5 log CFU/cm² biofilms in 4-7 d at 22 °C and 3 log CFU/cm² in 7 d at 10 °C. Biofilm formation by S. Poona (01A4754) was lowest on buna-n rubber compared to stainless steel, polyethylene and polyurethane surfaces under the majority of conditions tested. Overall, these findings show that S. enterica strains can grow rapidly and form biofilms on different cantaloupe processing surfaces in the presence of low concentrations of cantaloupe flesh or peel extracts.

Integrated combined effects of temperature, pH and sodium chloride concentration on biofilm formation by Salmonella enterica ser. Enteritidis and Typhimurium under low nutrient food-related conditions

Salmonella enterica is a major foodborne bacterial pathogen. This forms biofilms on surfaces and persists, depending on the strain and the environment. The integrative interaction of temperature (T; 13-39 °C), pH (5-8) and sodium chloride (NaCl) concentration (0.5-8.5%) on biofilm formation by two S. enterica strains (ser. Enteritidis and Typhimurium) was here evaluated under low nutrient conditions. This was achieved using response surface methodology to model the combined effect of each factor on the response, through mathematical quadratic fitting of the outcomes of a sequence of designed experiments. These last were executed by incubating stainless steel coupons carrying sessile bacteria, for 24 h, in 1:10 diluted tryptone soya broth, under 15 different combinations of three independent factors (T, pH and NaCl). For each strain, a second order polynomial model, describing the relationship between biofilm formation (log CFU/cm²) and the factors (T, pH and NaCl), was developed using least square regression analysis. Both derived models predicted the combined influences of these factors on biofilm formation, with agreement between predictions and experimental observations (R² ≥ 0.96, P ≤ 0.0001). For both strains, the increase of NaCl content restricted their sessile growth, while under low salinity conditions (NaCl < 4%) biofilm formation was favored as pH increased, regardless of T. Interestingly, under low salt content, and depending on the strain, biofilm formation was either favored or hindered by increasing T. Thus, 34.5 and 13 °C were the T predicted to maximize biofilm formation by strains Enteritidis and Typhimurium, respectively, something which was also experimentally verified. To sum, these models can predict the interactive influences of crucial food-related factors on biofilm growth of a significant foodborne pathogen towards the efforts to limit its persistence in food industry.

Effect of Temperature and Gamma Radiation on Salmonella Hadar Biofilm Production on Different Food Contact Surfaces

Salmonella is a pathogen transmitted by foods and it is one of the most important target bacteria in food irradiation studies. Few works were carried out on the effectiveness of gamma radiation against biofilms formed by this bacterium. Salmonella can form a biofilm on different material surfaces. The physicochemical properties of surfaces and environmental factors influence the adhesion of this pathogen. The present study investigated the effect of gamma radiation (1 and 2 kGy) and temperature (28°C and 37°C) on the development of Salmonella Hadar biofilm on polyvinyl chloride (PVC), glass, cellophane paper (CELLO), and polystyrene (POLY). The obtained results indicated that biofilm production is surface and temperature dependent. In addition, biofilm formation decreased significantly after gamma irradiation at either 1 or 2 kGy doses. However, the agfD and adrA genes expression did not demonstrate significant decrease. This work highlighted that gamma radiation treatment could reduce the biofilm formation of Salmonella enterica serovar Hadar on different food contact surfaces.

Biofilm formation by Salmonella enterica serovar 1,4,[5],12:i:- Portuguese isolates: a phenotypic, genotypic, and socio-geographic analysis

Biofilm-forming ability is well established as an important virulence factor. However, there are no studies available regarding biofilm formation of Salmonella Typhimurium 1,4,[5],12:i:-, the new pandemic serovar in Europe. To address this problem, biofilm expression by Salmonella 1,4,[5],12:i:- was evaluated using 133 isolates from clinical, environmental and animal origins, collected in Portugal from 2006 to 2011. Biofilm detection was performed by phenotypic and genotypic methods, such growth characterization in agar and broth medium, optical density determination by microtiter assays and direct observation by fluorescent in situ hybridization. Biofilm-related genes adrA, csgD and gcpA were detected by PCR. A socio-geographic characterization of strains as biofilm producers was also performed. Results showed that biofilm formation in monophasic Salmonella is widely distributed in Portuguese isolates and could be one of the reasons for its dissemination in this country. Biofilm expression varies between locations, showing that isolates from some regions like Lisboa or Ponta Delgada have an increased ability to persist in the environment due to an enhanced biofilm production. Biofilm formation also varies between risk groups, with a higher prevalence in isolates from salmonellosis infections in women. Therefore, the analysis of the socio-geographic distribution of biofilm-forming bacteria should be considered for the establishment of more adequate regulatory measures or therapeutics regimens, especially important due to the continuous increase of infections caused by antimicrobial resistant microorganisms.