Factors affecting survival of Shigatoxin-producing Escherichia coli on abiotic surfaces

Method to Study the Survival Abilities of Foodborne Bacterial Pathogens Under Food Processing Conditions

Properly using controllable atmospheric containers can facilitate investigations of the survival abilities and physiological states of key and emerging-foodborne pathogens under recreated applicable food processing environmental conditions. Notably, saturated salt solutions can efficiently control relative humidity in airtight containers. This chapter describes a practical experimental setup, with necessary prerequisites for exposing foodborne pathogens to simulated and relevant food processing environmental conditions. Subsequent analyses for studying cell physiology will also be suggested.

Effects of surface-attached durations, nutrients, and relative humidity on the resuspension of bacteria during human walking

Resuspension caused by human walking activities is an important source of indoor bioaerosols and has been associated with health effects such as allergies and asthma. However, it is unknown whether inhalation of resuspended bioaerosols is an important exposure pathway for airborne infection. Also, crucial factors influencing the resuspension of settled microbes have not been quantified. In this study, we experimentally investigated the resuspension of culturable bacteria from human-stepping on polyvinyl chloride (PVC) flooring under different conditions. We determined the bacterial resuspension emission factor (ER), a normalized resuspension parameter for the ratio of resuspended mass in the air to the mass of settled particles, for two common bacteria, Escherichia coli and Salmonella enterica. The investigation involved varying factors such as microbial surface-attached durations (0, 1, 2, and 3 days), the absence or presence of nutrients on flooring surfaces, and changes in relative humidity (RH) (35%, 65%, and 85%). The results showed that, in the absence of nutrients, the highest ER values for E. coli and S. enterica were 3.8 × 10-5 ± 5.2 × 10-6 and 5.3 × 10-5 ± 6.0 × 10-6, respectively, associated with surface-attached duration of 0 days. As the surface-attached duration increased from 0 to 3 days, ER values decreased by 92% and 84% for E. coli and S. enterica, respectively. In addition, we observed that ER values decreased with the increasing RH, which is consistent with particle adhesion theory. This research offers valuable insights into microbial resuspension during human walking activities and holds the potential for assisting in the assessment and estimation of risks related to human exposure to bioaerosols.

Relationship between Desiccation Tolerance and Biofilm Formation in Shiga Toxin-Producing Escherichia coli

Shiga toxin-producing Escherichia coli (STEC) is a major concern in the food industry and requires effective control measures to prevent foodborne illnesses. Previous studies have demonstrated increased difficulty in the control of biofilm-forming STEC. Desiccation, achieved through osmotic stress and water removal, has emerged as a potential antimicrobial hurdle. This study focused on 254 genetically diverse E. coli strains collected from cattle, carcass hides, hide-off carcasses, and processing equipment. Of these, 141 (55.51%) were STEC and 113 (44.48%) were generic E. coli. The biofilm-forming capabilities of these isolates were assessed, and their desiccation tolerance was investigated to understand the relationships between growth temperature, relative humidity (RH), and bacterial survival. Only 28% of the STEC isolates had the ability to form biofilms, compared to 60% of the generic E. coli. Stainless steel surfaces were exposed to different combinations of temperature (0 °C or 35 °C) and relative humidity (75% or 100%), and the bacterial attachment and survival rates were measured over 72 h and compared to controls. The results revealed that all the strains exposed to 75% relative humidity (RH) at any temperature had reduced growth (p < 0.001). In contrast, 35 °C and 100% RH supported bacterial proliferation, except for isolates forming the strongest biofilms. The ability of E. coli to form a biofilm did not impact growth reduction at 75% RH. Therefore, desiccation treatment at 75% RH at temperatures of 0 °C or 35 °C holds promise as a novel antimicrobial hurdle for the removal of biofilm-forming E. coli from challenging-to-clean surfaces and equipment within food processing facilities.

Formation and Transfer of Multi-Species Biofilms Containing E. coli O103:H2 on Food Contact Surfaces to Beef

Interactions of Shiga toxin–producing E. coli (STEC; O103:H2) with lactic acid bacteria (LAB) or spoilage bacteria (SP) multispecies biofilms on polyurethane (TPU) and stainless-steel (SS) were assessed at 10 and 25°C under wet and dry conditions after 6, 30, and 60 days of storage. One LAB T1: Carnobacterium piscicola + Lactobacillus bulgaricus, and two SP T2: Comamonas koreensis + Raoultella terrigena; T3: Pseudomonas aeruginosa + C. koreensis were assessed for their ability to form multispecies biofilms with O103:H2. O103:H2 single-species biofilms served as a control positive (T4). Coupons were stored dry (20–50% relative humidity; RH) or moist (60–90% RH) for up to 60 days, at which point O103:H2 transfer to beef and survival was evaluated. At 25°C, T3 decreased beef contamination with O103:H2 by 2.54 log₁₀ CFU/g (P < 0.001). Overall, at 25°C contamination of beef with O103:H2 decreased (P < 0.001) from 3.17 log₁₀ CFU/g on Day 6 to 0.62 log₁₀ CFU/g on Day 60. With 60 days dry biofilms on TPU, an antagonistic interaction was observed among O103:H2 and multispecies biofilm T1 and T3. E. coli O103:H2 was not recovered from T1 and T3 after 60 days but it was recovered (33%) from T2 and T4 dry biofilms. At 10°C, contamination of beef with O103:H2 decreased (P < 0.001) from 1.38 log₁₀ CFU/g after 6 days to 0.47 log₁₀ CFU/g after 60 days. At 10°C, recovery of O103:H2 from 60 days dry biofilms could only be detected after enrichment and was always higher for T2 than T4 biofilms. Regardless of temperature, the transfer of O103:H2 to beef from the biofilm on TPU was greater (P < 0.001) than SS. Moist biofilms also resulted in greater (P < 0.001) cell transfer to beef than dry biofilms at 10 and 25°C. Development of SP or LAB multispecies biofilms with O103:H2 can either increase or diminish the likelihood of beef contamination. Environmental conditions such as humidity, contact surface type, as well as biofilm aging all can influence the risk of beef being contaminated by STEC within multi-species biofilms attached to food contact surfaces.

Manual emptying of ventilated improved pit latrines and hygiene challenges - a baseline survey in a peri-urban community in KwaZulu-Natal, South Africa

The presence of Escherichia coli and Staphylococcus spp. was determined on the skin, personal protective equipment, the municipal vehicle, and various surfaces at ten households in a peri-urban community (KwaZulu-Natal, South Africa) before and after manual emptying of ventilated improved pit latrines. Surface samples (n = 14) were collected using sterile wet wipes, and target bacteria were detected using standard procedures. Additionally, E. coli was enumerated in soil samples from an area of open defecation (log₁₀ 3.7 MPN/g) and areas where geophagia occurred (log₁₀ 2.7 - log₁₀ 3.3 MPN/g), using a most probable number (MPN) method. The detection frequency for the target bacteria on household surfaces (e.g., the walkway between the pit latrine and the municipal vehicle) and on municipal workers' hands (which were frequently contaminated before pit emptying), occasionally increased after the pits were emptied, indicating that manual pit emptying might pose a potential health risk to workers and community members.

What is the relationship between indoor air quality parameters and airborne microorganisms in hospital environments? A systematic review and meta-analysis

Airborne microorganisms in hospitals have been associated with several hospital-acquired infections (HAIs), and various measures of indoor air quality (IAQ) parameters such as temperature, relative humidity, carbon dioxide (CO₂ ), particle mass concentration, and particle size have been linked to pathogen survival or mitigation of pathogen spread. To investigate whether there are quantitative relationships between the concentration of airborne microorganisms and the IAQ in the hospital environment. Web of Science, Scopus and PubMed databases were searched for studies reporting airborne microbial levels and any IAQ parameter(s) in hospital environments, from database inception to October 2020. Pooled effect estimates were determined via random-effects models. Seventeen of 654 studies were eligible for the meta-analysis. The concentration of airborne microbial measured as aerobic colony count (ACC) was significantly correlated with temperature (r = 0.25 [95% CI = 0.06-0.42], p = 0.01), CO₂ concentration (r = 0.53 [95% CI = 0.40-0.64], p ˂ 0.001), particle mass concentration (≤5 µg/m³ ; r = 0.40 [95% CI = 0.04-0.66], p = 0.03), and particle size (≤5 and ˃5 µm), (r = 0.51 [95% CI = 0.12-0.77], p = 0.01 and r = 0.55 [95% CI = 0.20-0.78], p = 0.003), respectively, while not being significantly correlated with relative humidity or particulate matter of size >5 µm. Conversely, airborne total fungi (TF) were not significantly correlated with temperature, relative humidity, or CO₂ level. However, there was a significant weak correlation between ACC and TF (r = 0.31 [95% CI = 0.07-0.52], p = 0.013). Although significant correlations exist between ACC and IAQ parameters, the relationship is not definitive; the IAQ parameters may affect the microorganisms but are not responsible for the presence of airborne microorganisms. Environmental parameters could be related to the generating source, survival, dispersion, and deposition rate of microorganisms. Future studies should record IAQ parameters and factors such as healthcare worker presence and the activities carried out such as cleaning, sanitizing, and disinfection protocols. Foot traffic would influence both the generation of microorganisms and their deposition rate onto surfaces in the hospital environment. These data would inform models to improve the understanding of the likely concentration of airborne microorganisms and provide an alternative approach for real-time monitoring of the healthcare environment.

Development of a rapid method for assessing the efficacy of antibacterial photocatalytic coatings

Visible-light activated photocatalytic coatings may represent an attractive antimicrobial solution in domains such as food, beverage, pharmaceutical, biomedical and wastewater remediation. However, testing methods to determine the antibacterial effects of photocatalytic coatings are limited and require specialist expertise. This paper describes the development of a method that enables rapid screening of coatings for photocatalytic-antibacterial activity. Relying on the ability of viable microorganisms to reduce the dye resazurin from a blue to a pink colour, the method relates the time taken to detect this colour change with number of viable microorganisms. The antibacterial activity of two photocatalytic materials (bismuth oxide and titanium dioxide) were screened against two pathogenic organisms (Escherichia coli and Klebsiella pneumoniae) that represent potential target microorganisms using traditional testing and enumeration techniques (BS ISO 27447:2009) and the novel rapid method. Bismuth oxide showed excellent antibacterial activity under ambient visible light against E. coli, but was less effective against K. pneumoniae. The rapid method showed excellent agreement with existing tests in terms of number of viable cells recovered. Due to advantages such as low cost, high throughput, and less reliance on microbiological expertise, this method is recommended for researchers seeking an inexpensive first-stage screen for putative photocatalytic-antibacterial coatings.

Tenacity of Enterococcus cecorum at different environmental conditions

AIMS

Our aim was to analyse the survival of Enterococcus cecorum (EC) at various temperatures, relative air humidities and on different substrates commonly existing in broiler houses.

METHODS AND RESULTS

A pathogenic EC isolate (EC14) was used to inoculate sterile litter, polyvinyl chloride (PVC) and dust samples. Incubation at 37, 25 or 15°C with either 32% relative humidity (RH) or 78% RH followed. At defined time points (0-4272 h post-inoculation), samples were examined in triplicate for the total viable count. Selected combinations were repeated for a non-pathogenic and two additional pathogenic EC strains. For EC14, the measured survival time ranged from 48 to 4272 h (178 days) depending on the substrate-humidity-temperature combination. The longevity was the highest on litter, followed by dust and then PVC. Lower temperatures facilitated its survival, lower relative air humidity favoured the survival only in combination with 25 or 15°C. All three pathogenic strains showed longer survival times (up to 432 h, 18 days) compared to the non-pathogenic EC strain (168 h, 7 days) under the same conditions.

CONCLUSIONS

Enterococcus cecorum demonstrates a high persistence in the environment especially at 15°C and 32% RH.

SIGNIFICANCE AND IMPACT OF THE STUDY

Hygiene management plans should consider the durability of EC and the risk of a carry-over to control consecutive EC outbreaks.

Transfer efficacy of Escherichia coli O157:H7 between surfaces of green mature tomatoes and common food processing materials

The objectives of this study were: a) to evaluate E. coli O157:H7 survival on green mature tomatoes and squares of common food processing materials – stainless steel, plastic (HDPE), and vinyl conveyor belt (PVC) – post-drying, stored at 25 ºC in the humidified environment for four days; b) to determine pathogen transfer rates (wet, 90 minutes, or 24-hours drying post-inoculation), from inoculated tomato surfaces to uninoculated steel, plastic, and vinyl conveyor belt squares and conversely. It was shown that E. coli O157:H7 did not survive well on the surface of tomatoes, resulting in a decline from 5.3 log10 CFU.mL-1 90 minutes post-drying to 1.4 log10 CFU.mL-1 on day 4. Similarly, the pathogen did not survive well on the surface of food processing squares, with numbers declining over 4 days from 4.04, 4.44, and 4.19 CFU.mL-1 of rinsate 90 minutes squares post-drying to 0.72, 0.50, 0.83  log10 CFU.mL-1, which is close to the detection limit, for the steel, vinyl belt, and plastic, respectively. Successful cross-contamination between tomatoes and food processing surfaces was achieved during wet transfer; while transfer after 90 minutes inoculum post-drying and 24 hours were less successful. This can be explained by both lack of liquid media with suspended bacteria for transfer and fast pathogen die-off after desiccation. Dry transfers, as shown by the percentage of “positive” for pathogen presence tomatoes and squares, as well as bacterial counts, were more successful from tomatoes to squares, but not conversely. Special concern raised vinyl conveyor belt, where the surface picked up the most pathogen cells from the surface of tomatoes, resulting in 100% positive during 90 minute-dry transfers, followed by plastic (66.7% positive) and steel (55.6% positive). To summarize, we presented data on the possibility of cross-contamination between mature green tomatoes and common food processing surfaces, which may be interesting for the processors for risk evaluation.

Bacterial community in commercial airliner cabins in China

Considering the amount of time that crew members and passengers spend on airliners and the potential health impact of pathogenic bacteria, it is important to understand the population of bacteria inside airliners and the factors affecting the bacterial concentration. This study recorded the species of airborne and cabin surface culturable bacteria inside various airliner. Seven flights ranging from 3 to 5 hours in duration on different types of airliner were chosen. Multiple species of bacteria in the air of the airliners, such as Brachybacterium paraconglomeratum, were identified by means of the 16S ribosomal RNA gene sequencing method, and most of the bacteria were Gram-positive. This study found that the bacterial concentration in the airliners decreases as the relative humidity increases. The decrease in the number of airborne bacteria may be the reason for the reduced occurrence of unwanted symptoms exhibited by passengers.

Influence of suspension liquid total solids on E. coli O157:H7 survival and transfer efficacy between green tomatoes and cardboard

The objectives of this study were: a) to determine E. coli O157:H7 survival on tomatoes and cardboard squares post-drying, stored at 25 ºC in humidified environment for four days, in buffered peptone water (BPW), and 0.1% diluted peptone (DP); b) to determine pathogen transfer rates (0, 1.5, or 24-hours drying post-inoculation), from inoculated tomato surfaces to uninoculated cardboard squares and conversely; and c) to evaluate SystemSure Plus ATP luminometer for recognizing contamination on visibly soiled (BPW) or visible clean (DP) cardboard. In tomato inoculation studies, E. coli O157:H7 survived better on the fruit when the inoculum was prepared using DP as compared to BPW. The 1.5-hours post drying counts of 5.34 and 5.76 log10 CFU.mL-1 in the rinsate substantially declined to 1.45 and 1.17 log10 CFU.mL-1 on day four, for DP and BPW, respectively. In cardboard inoculation studies, E. coli O157:H7 persisted for four days, with 1.5-hours post-drying counts and day four counts of 4.53 (DP) and 2.55 log10 CFU.mL-1 (BPW), contrary to 3.81 (DP) and 1.92 log10 CFU.mL-1 (BPW). Under the first impression, the slower die-off of E. coli O157:H7 on cardboard questions the possibility of reusing cardboard boxes due to the potential for cross-contamination. In wet transfer (0 hour drying) trials, both tomato-to-cardboard and cardboard-to-tomato yielded 100% positive transfers irrespective of diluent type. Dry transfer (1.5-hours drying interval post inoculation) from tomato-to-cardboard were 100% positive, but no positives were noted when inoculated, dried cardboard was contacted to tomatoes, irrespective of diluent. Results of transfers with BPW as the diluent showed 100% positive transfer from 24-hours dry tomatoes-to-cardboard, as inoculation spots on the tomatoes remained moist due to hygroscopic nature of solutes in BPW. Conversely, only a 40% positive transfer rate was observed under the same conditions with DP as diluent. No positive transfers were recorded from 24-hours dry cardboard-to-tomatoes, irrespective of diluent type. Though E. coli O157:H7 survived better on the surface of cardboard compared to the surface of tomatoes on day four, the dry transfers were more efficient from tomatoes-to-cardboard than conversely, possibly due to smooth and hydrophobic properties of the tomato, and rough and porous surface of the cardboard. ATP luciferase UltrasnapTM swab test showed 9/9 “pass” results for sterile liquid DP and BPW, while 9/9 “fail” results were observed with liquid peptone and BPW contaminated at ca. 9.0 log10 CFU.mL-1E. coli O157:H7. Cardboard squares treated and dried, with sterile DP, showed 8/9 “pass” ATP luciferase results, and 1/9 “warning”, while cardboard squares with contaminated DP showed 9/9 “fail” result. Cardboard squares treated and dried, with sterile BPW, showed 7/9 “pass” ATP luciferase results, and 2/9 “warning”, while cardboard squares with contaminated BPW showed 9/9 “fail” result. Luminometer can simplify detection of microbial load, as well as organic residues, helping to check cardboard boxes for cleanness.

Method to Study the Survival Abilities of Foodborne Bacterial Pathogens Under Food Processing Conditions

The proper use of controllable atmospheric containers can facilitate investigations related to the survival abilities, and physiological states of key and emerging foodborne pathogens under recreated applicable food processing environmental conditions. Of particular note, the use of saturated salt solutions can efficiently control relative humidity in airtight containers. This chapter describes a practical experimental setup, with necessary prerequisites for exposing foodborne pathogens to simulated and relevant food processing environmental conditions. Subsequent analyses for studying cell physiology will also be suggested.

Influence of temperature, humidity, and diluent type on survival of Salmonella spp. on the surface of raw tomatoes

Tomatoes are an important commodity, placing fourth among most popular vegetables in the U.S. However, fresh tomatoes lack a final pathogen elimination step and have been implicated in Salmonella-related outbreaks. The purpose of the study was to evaluate survival of Salmonella post-drying in three diluents on the surface of green mature tomatoes at 12 °C or 25 °C. Additionally, low and high air relative humidity influence was evaluated at 25 °C on pathogen survival. A five Salmonella rifampin-resistant strain cocktail was double-washed in buffered peptone water (BPW) and resuspended in 0.1% peptone, BPW, or fresh tomato serum. Inoculum (0.1 mL) was allowed to dry on the surface of tomatoes. For study I, tomatoes were placed in 12 °C and 25 °C incubators with no humidity control and sampled on days 0, 1, 3, and 5. For study II, tomatoes were sampled on days 0, 1 (biosafety hood storage) and on day 5 after storage in two 25 oC incubators (low and high relative humidity). Salmonella was recovered from tomatoes (20 mL BPW) and plated (TSA-rif80, 37 °C, 48 hours). Post-drying Salmonella counts (ca. 4.5 – 5.0 log10 CFU.mL-1) remained at 4.03 and 4.40 log10 CFU.mL-1 in serum after 5 days of storage at 12 °C and 25 °C, respectively. Conversely, corresponding counts in BPW and peptone were lower at ca. 1.4 to 1.8 and 2.2 to 2.8 log units at 12 °C and 25 °C, respectively. At low humidity, post-drying Salmonella counts showed highest decline for peptone (final 1.98 log10 CFU.mL-1) compared to BPW (3.79 log10 CFU.mL-1) and tomato serum (4.75 log10 CFU.mL-1) on day 5. Counts declined rapidly to 0.03, 0.56, and 0.44 log10 CFU.mL-1 for peptone, BPW, and tomato serum, respectively, at high humidity on day 5. To summarize, it was shown that increased solutes have protective effect on Salmonella in desiccated conditions, while high humidity storage causes accelerated death of stationary culture within five days storage period.

Microorganisms @ materials surfaces in aircraft: Potential risks for public health? - A systematic review

BACKGROUND

Civil air travel is increasingly recognized as an important potential source for the rapid spread of infectious diseases that were geographically confined in the past, creating international epidemics with great health and socio-economic impact.

OBJECTIVE

The objective of this systematic review is to elucidate the correlations of materials surfaces (composition, structure, properties) and microbial dependences on them in aircraft.

METHODS

The review was prepared according to PRISMA guidelines. Based on a systematic search for studies published before 30 June 2018 in English, we selected and reviewed the contamination, tenacity, and transmission of microorganisms related to specific surfaces within the aircraft cabin. We also reviewed the chemical composition and properties of these surface materials applied within aircraft.

RESULTS

From a total of 828 records 15 articles were included for further analysis in this systematic review, indicating that the aircraft interior surfaces in seat areas (tray tables, armrests, seat covers) and lavatories (door knob handles, toilet flush buttons) are generally colonized by various types of potentially hazardous microorganisms.

CONCLUSIONS

The interior surfaces in seat and lavatory areas could pose higher health risks by causing infections due to their relatively high microbial contamination compared with other interior surfaces. The classification, chemical composition, surface structures and physicochemical properties of materials surfaces have a varied effect on the adhesion, colonization, tenacity and potential transmission of microorganisms within the aircraft cabin. Strategies are proposed for the interruption of surface-related infection chains in the aircraft field.

Survival and transfer efficacy of mixed strain Salmonella enterica ser. Typhimurium from beef burgers to abiotic surfaces and determination of individual strain contribution

The aim of the study was to evaluate the survival and transfer efficacy of 3 Salmonella Typhimurium strains from beef burgers to abiotic surfaces and determine the individual strain distribution. S. Typhimurium population on beef burgers during incubation remained constant at initial levels of contamination approximately 3 and 5 log CFU/g. Additionally, the survival of pathogens on soiled HDPE surfaces was significant during incubation at both initial inocula, while ca 1.5 log CFU/cm² reduction was observed at 168h. The log transformed transfer rate (log₁₀Tr) was -1.86±0.23 and -1.75±0.40 for high and low inoculum. The level of initial contamination did not have any statistical important impact on bacterial transfer (P>0.05). In addition, the results regarding the strain contribution revealed rather random individual proportion of each strain, recovered from HDPE, SS surfaces and beef burgers. However, the dominance of each strain was strongly dependent on surface at low inoculum and time in case of high inoculum. This observed strain variability during survival and transfer of S. Typhimurium might be of great importance in order to understand and consequently limit the possibility of cross contamination during food processing in a common household.

Strategies for recovering of planktonic and sessile cells of Escherichia coli O157:H7 from freshwater environment

The experiments were performed with Escherichia coli O157:H7 EDL 933 in freshwater microcosms at 12 °C. At 35, 45, and 70 days, samples were taken and filtered through 0.45 μm membrane filters. The following alternatives were tested to evaluate the recovery percentage of injured cells: (1) selective media CHROMagar(™)O157 and chromID(™)O157:H7 agar, at 37 °C for 24 h; (2) tryptic soy agar supplemented with yeast extract (TSAE), incubated at 25 °C for 2 or 4 h, then transferred to CHROMagar(™)O157 or chromID(™)O157:H7 agar at 37 °C (TSAE2h-CHROM, TSAE4h-CHROM and TSAE2h-ID, TSAE4h-ID); (3) thin agar layer (TAL) method, TSAE was overlaid on CHROMagar(™)O157 or chromID(™)O157:H7 agar (TALCHROM and TALID, respectively) and incubated at 37 °C for 24 h; and (4) TALCHROM at 25 °C for 4 h, then continued up to complete 24 h at 37 °C (TALCHROM4h). Furthermore, the recovery of E. coli O157:H7 cells adhering to glass coverslips were evaluated to mimic biofilm conditions. The recovery percentages obtained from each alternative were calculated relative to TSAE counts. After 70 days, TSAE4h-CHROM and TALCHROM4h showed the highest recovery percentage (>90 %) from water microcosms. Despite the improved recovery of cell adhering to glass surfaces, the percentages obtained with TSAE4h-CHROM were low. Further studies for the recovery of biofilm-forming E. coli O157:H7 are required. Pre-incubation on TSAE at 25 °C for 4 h, combined with CHROMagar(™)O157, or by thin agar layer method (TALCHROM) enhanced significantly the recovery of viable cells of E. coli O157:H7 after prolonged stay in water microcosms.

The response of foodborne pathogens to osmotic and desiccation stresses in the food chain

In combination with other strategies, hyperosmolarity and desiccation are frequently used by the food processing industry as a means to prevent bacterial proliferation, and particularly that of foodborne pathogens, in food products. However, it is increasingly observed that bacteria, including human pathogens, encode mechanisms to survive and withstand these stresses. This review provides an overview of the mechanisms employed by Salmonella spp., Shiga toxin producing E. coli, Cronobacter spp., Listeria monocytogenes and Campylobacter spp. to tolerate osmotic and desiccation stresses and identifies gaps in knowledge which need to be addressed to ensure the safety of low water activity and desiccated food products.

Dustborne and airborne Gram-positive and Gram-negative bacteria in high versus low ERMI homes

The study aimed at investigating Gram-positive and Gram-negative bacteria in moldy and non-moldy homes, as defined by the home's Environmental Relative Moldiness Index (ERMI) value. The ERMI values were determined from floor dust samples in 2010 and 2011 and homes were classified into low (<5) and high (>5) ERMI groups based on the average ERMI values as well as 2011 ERMI values. Dust and air samples were collected from the homes in 2011 and all samples were analyzed for Gram-positive and Gram-negative bacteria using QPCR assays, endotoxin by the LAL assay, and N-acetyl-muramic acid using HPLC. In addition, air samples were analyzed for culturable bacteria. When average ERMI values were considered, the concentration and load of Gram-positive bacteria determined with QPCR in house dust, but not air, were significantly greater in high ERMI homes than in low ERMI homes. Furthermore, the concentration of endotoxin, but not muramic acid, in the dust was significantly greater in high ERMI than in low ERMI homes. In contrast, when ERMI values of 2011 were considered, Gram-negative bacteria determined with QPCR in air, endotoxin in air, and muramic acid in dust were significantly greater in high ERMI homes. The results suggest that both short-term and long-term mold contamination in homes could be linked with the bacterial concentrations in house dust, however, only the current mold status was associated with bacterial concentrations in air. Although correlations were found between endotoxin and Gram-negative bacteria as well as between muramic acid and Gram-positive bacteria in the entire data set, diverging associations were observed between the different measures of bacteria and the home moldiness. It is likely that concentrations of cells obtained by QPCR and concentrations of cell wall components are not equivalent and represent too broad categories to understand the bacterial composition and sources of the home microbiota.

Behavior of different Shiga toxin-producing Escherichia coli serotypes in various experimentally contaminated raw-milk cheeses

Shiga toxin-producing Escherichia coli (STEC) is an important cause of food-borne illness. The public health implication of the presence of STEC in dairy products remains unclear. Knowledge of STEC behavior in cheeses would help to evaluate the human health risk. The aim of our study was to observe the growth and survival of experimentally inoculated STEC strains in raw-milk cheeses manufactured and ripened according to five technological schemes: blue-type cheese, uncooked pressed cheese with long ripening and with short ripening steps, cooked cheese, and lactic cheese. Cheeses were contaminated with different STEC serotypes (O157:H7, O26:H11, O103:H2, and O145:H28) at the milk preparation stage. STEC growth and survival were monitored on selective media during the entire manufacturing process. STEC grew (2 to 3 log(10) CFU · g(-1)) in blue-type cheese and the two uncooked pressed cheeses during the first 24 h of cheese making. Then, STEC levels progressively decreased in cheeses that were ripened for more than 6 months. In cooked cheese and in lactic cheese with a long acidic coagulation step (pH < 4.5), STEC did not grow. Their levels decreased after the cooking step in the cooked cheese and after the coagulation step in the lactic cheese, but STEC was still detectable at the end of ripening and storage. A serotype effect was found: in all cheeses studied, serotype O157:H7 grew less strongly and was less persistent than the others serotypes. This study improves knowledge of the behavior of different STEC serotypes in various raw-milk cheeses.

Heterogeneity in resistance to food-related stresses and biofilm formation ability among verocytotoxigenic Escherichia coli strains

This study assessed the resistance of ten verocytotoxigenic Escherichia coli (VTEC) isolates of commonly encountered serogroups/-types and two non-pathogenic E. coli strains to various food-related stresses (acid, alkaline, heat and high hydrostatic pressure treatments) and their biofilm formation ability. In addition, the global changes in the cellular composition in response to the exposure to these adverse environments were monitored by Fourier Transform Infrared (FT-IR) spectroscopy for two of the strains. Large inter-strain variations in stress resistance were observed. The most tolerant strains belonged to serogroup O157 which included both the O157:H7 type strain EDL933 and a representative isolate of the sorbitol fermenting O157:H- VTEC clone (strain MF3582). Strain C-600, a non-pathogenic laboratory strain, was sensitive to multiple stresses. Although wide variation in biofilm-forming ability was observed among VTEC isolates, no consistent relationships between biofilm-forming ability and capacity to withstand stress exposures were found. Analysis of the allelic status of the rpoS gene, involved in the general stress response of stationary-phase cells, allowed detection of loss-of-function mutations for two strains, E218/02 and MF2411, both of them showing as common features a high sensitivity to alkaline and heat treatments and a poor ability to form mature biofilms. Evidences found in this study confirm rpoS as a highly mutable gene in nature, and suggest its relevance not only for the mount of an active stress response but also for the establishment of mature biofilm communities. Our findings contribute to increase the knowledge on the resistance of VTEC to environmental stresses commonly encountered in the food chain, which can lead to improved strategies for preventing VTEC infections.

Surface behaviour of S. Typhimurium, S. Derby, S. Brandenburg and S. Infantis

Cross-contamination due to Salmonella on the surface of processing equipment greatly contributes to contamination of pork products. Therefore, a clear understanding of surface and survival behaviour of relevant Salmonella serovars in pork processing environments is needed to develop better strategies for Salmonella control. Within this study the biofilm forming behaviour of S. Typhimurium, S. Derby, S. Brandenburg and S. Infantis isolates was analysed using the crystal violet assay. This assay, commonly used to analyse total biofilm formation, revealed variation in biofilm forming capacity between and within serovars. This has not been shown before for S. Derby, S. Brandenburg and S. Infantis. From each serovar, isolates with different biofilm forming capacity were selected to analyse biofilm formation on stainless steel. This revealed no significant differences between biofilm formation on polystyrene compared to stainless steel. Furthermore a relation was observed between biofilm forming capacity of an isolate and survival on stainless steel surfaces. On such surfaces, biofilms showed greater and longer survival than planktonic cells, and they were less susceptible to peracetic acid disinfection treatments. However, the latter effect was marginal and only observed in the presence of organic material, which drastically decreased the activity of peracetic acid. With the obtained results a hierarchical cluster was also performed to identify differences and similarities between the four different serovars. This indicated that the surface behaviour of S. Typhimurium was more comparable to S. Infantis than to S. Derby or S. Brandenburg.

High stability of Stx2 phage in food and under food-processing conditions

Bacteriophages (phages) carrying Shiga toxin genes constitute a major virulence attribute in enterohemorrhagic Escherichia coli (EHEC). Several EHEC outbreaks have been linked to food. The survival of such strains in different foods has received much attention, while the fate of the mobile Shiga toxin-converting phages (Stx phages) has been less studied. We have investigated the stability of an Stx phage in several food products and examined how storage, food processing, and disinfection influence the infectivity of phage particles. The study involved a recombinant Stx phage (Δstx::cat) of an E. coli O103:H25 strain from a Norwegian outbreak in 2006. Temperature, matrix, and time were factors of major importance for the stability of phage particles. Phages stored at cooling temperatures (4°C) showed a dramatic reduction in stability compared to those stored at room temperature. The importance of the matrix was evident at higher temperatures (60°C). Phages in ground beef were below the detection level when heated to 60°C for more than 10 min, while phages in broth exposed to the same heating conditions showed a 5-log-higher stability. The phages tolerated desiccation poorly but were infective for a substantial period of time in solutions. Under moist conditions, they also had a high ability to tolerate exposure to several disinfectants. In a dry-fermented sausage model, phages were shown to infect E. coli in situ. The results show that Stx phage particles can maintain their infectivity in foods and under food-processing conditions.

Streptococcus pneumoniae is desiccation tolerant and infectious upon rehydration

Streptococcus pneumoniae (pneumococcus) is a frequent colonizer of the nasopharynx and one of the leading causative agents of otitis media, pneumonia, and meningitis. The current literature asserts that S. pneumoniae is transmitted person to person via respiratory droplets; however, environmental surfaces (fomites) have been linked to the spread of other respiratory pathogens. Desiccation tolerance has been to shown to be essential for long-term survival on dry surfaces. This study investigated the survival and infectivity of S. pneumoniae following desiccation under ambient conditions. We recovered viable bacteria after all desiccation periods tested, ranging from 1 h to 4 weeks. Experiments conducted under nutrient limitation indicate that desiccation is a condition separate from starvation. Desiccation of an acapsular mutant and 15 different clinical isolates shows that S. pneumoniae desiccation tolerance is independent of the polysaccharide capsule and is a species-wide phenomenon, respectively. Experiments demonstrating that nondesiccated and desiccated S. pneumoniae strains colonize the nasopharynx at comparable levels, combined with their ability to survive long-term desiccation, suggest that fomites may serve as alternate sources of pneumococcal infection.

Even with the advent of multivalent capsular polysaccharide conjugate vaccines, S. pneumoniae continues to be a major cause of morbidity and mortality worldwide. Every year, there are approximately 7 million cases of pneumococcus-based otitis media in the United States alone, while pneumococcal invasive diseases are responsible for more than 1 million deaths globally. It is believed that the human upper respiratory tract is the sole niche of S. pneumoniae and, thus, that spread occurs via close contact with an infected individual. In this study, we characterized the desiccation tolerance of S. pneumoniae and found that it can survive for many weeks postdehydration and retain infectivity. Our results suggest that desiccation tolerance is an inherent trait of this genetically variable species and that fomites may be a source of transmission.

Micro ecosystems from feed industry surfaces: a survival and biofilm study of Salmonella versus host resident flora strains

BACKGROUND

The presence of Salmonella enterica serovars in feed ingredients, products and processing facilities is a well recognized problem worldwide. In Norwegian feed factories, strict control measures are implemented to avoid establishment and spreading of Salmonella throughout the processing chain. There is limited knowledge on the presence and survival of the resident microflora in feed production plants. Information on interactions between Salmonella and other bacteria in feed production plants and how they affect survival and biofilm formation of Salmonella is also limited. The aim of this study was to identify resident microbiota found in feed production environments, and to compare the survival of resident flora strains and Salmonella to stress factors typically found in feed processing environments. Moreover, the role of dominant resident flora strains in the biofilm development of Salmonella was determined.

RESULTS

Surface microflora characterization from two feed productions plants, by means of 16 S rDNA sequencing, revealed a wide diversity of bacteria. Survival, disinfection and biofilm formation experiments were conducted on selected dominant resident flora strains and Salmonella. Results showed higher survival properties by resident flora isolates for desiccation, and disinfection compared to Salmonella isolates. Dual-species biofilms favored Salmonella growth compared to Salmonella in mono-species biofilms, with biovolume increases of 2.8-fold and 3.2-fold in the presence of Staphylococcus and Pseudomonas, respectively.

CONCLUSIONS

These results offer an overview of the microflora composition found in feed industry processing environments, their survival under relevant stresses and their potential effect on biofilm formation in the presence of Salmonella. Eliminating the establishment of resident flora isolates in feed industry surfaces is therefore of interest for impeding conditions for Salmonella colonization and growth on feed industry surfaces. In-depth investigations are still needed to determine whether resident flora has a definite role in the persistence of Salmonella in feed processing environments.

Enhanced surface colonization by Escherichia coli O157:H7 in biofilms formed by an Acinetobacter calcoaceticus isolate from meat-processing environments

A meat factory commensal bacterium, Acinetobacter calcoaceticus, affected the spatial distribution of Escherichia coli O157:H7 surface colonization. The biovolume of E. coli O157:H7 was 400-fold higher (1.2 x 10(6) microm(3)) in a dynamic cocultured biofilm than in a monoculture (3.0 x 10(3) microm(3)), and E. coli O157:H7 colonized spaces between A. calcoaceticus cell clusters.