Direct adhesion force measurements between E. coli and human uroepithelial cells in cranberry juice cocktail

Scope: Atomic force microscopy (AFM) was used to directly measure the nanoscale adhesion forces between P‐fimbriated Escherichia coli (E. coli) and human uroepithelial cells exposed to cranberry juice, in order to reveal the molecular mechanisms by which cranberry juice cocktail (CJC) affects bacterial adhesion. Methods and results: Bacterial cell probes were created by attaching P‐fimbriated E. coli HB101pDC1 or non‐fimbriated E. coli HB101 to AFM tips, and the cellular probes were used to directly measure the adhesion forces between E. coli and uroepithelial cells in solutions containing: 0, 2.5, 5, 10, and 27 wt% CJC. Macroscale attachment of E. coli to uroepithelial cells was measured and correlated to nanoscale adhesion force measurements. The adhesion forces between E. coli HB101pDC1 and uroepithelial cells were dose‐dependent, and decreased from 9.32±2.37 nN in the absence of CJC to 0.75±0.19 nN in 27 wt% CJC. Adhesion forces between E. coli HB101 and uroepithelial cells were low in buffer (0.74±0.18 nN), and did not change significantly in CJC (0.78±0.18 nN in 27 wt% CJC; P=0.794). Conclusion: Our study shows that CJC significantly decreases nanoscale adhesion forces between P‐fimbriated E. coli and uroepithelial cells.     

Cranberry derived proanthocyanidins can prevent pathogen invasion of kidney epithelial cells

The in vitro effectivity of cranberry derived proanthocyanidins (PACs) for the mitigation of kidney cell infection by selected uro- and entero-pathogens is examined with an adhesion/invasion assay and confocal microscopy. This study demonstrates that PACs effectively reduce invasion of canine kidney cells by pathogenic bacteria: Escherichia coli CFT073 and O157:H7, Enterococcus faecalis 29212, and Pseudomonas aeruginosa 10145. These effects demonstrate the potential for cranberry derived PACs as a useful tool in the prevention of kidney infection.     

Effect of juice processing on cranberry antibacterial properties

The effects of the industrial juice process on the ability of neutralized cranberry samples and extracts (polar, apolar and anthocyanins) to inhibit the growth of Enterococcus faecium resistant to vancomycin (ERV), Escherichia coli O157:H7 EDL 933, E. coli ATCC 25922, Listeria monocytogenes HPB 2812, Pseudomonas aeruginosa ATCC 15442, Salmonella Typhimurium SL1344 and Staphylococcus aureus ATCC 29213 were investigated. The juice process appeared to have a general enhancing effect on the antibacterial properties of cranberry polar and anthocyanin extracts. The lowest minimum inhibitory concentrations (MICs) (1.80–7.0 μg phenol/well) were obtained when S. aureus, S. Typhimurium, and ERV were exposed to the juice concentrate. The growth of P. aeruginosa, L. monocytogenes, E. coli ATCC, and E. coli O157:H7 was not inhibited by the juice concentrate, but did show sensitivity (maximal tolerated concentrations of 0.007–0.4 μg phenol/well). The lowest MICs (22.6–90.5 μg phenol/well) for P. aeruginosa, S. aureus, S. Typhimurium, and ERV were observed when they were exposed to the cranberry anthocyanin extract obtained from cranberry pomace. The results also showed a negative effect of the juice process on the antibacterial properties of the cranberry apolar extracts: the one obtained from frozen cranberries was most efficient against P. aeruginosa, S. aureus, L. monocytogenes and S. Typhimirium (MIC of 45.50 μg phenol/well). The tested bacteria showed the greatest resistance toward the cranberry extracts obtained from the mash and the macerated and depectinized mash.     

COLOUR REACTION SCREENING OF CLONES WITH DIACETYL AND ACETOIN REDUCTASE ACTIVITIES

A genomic library of the chromosomal DNA of a brewing strain (Saccharomyces carlsbergensis) has been made in a Escherichia coli HB101 strain as host. A coloured test allowing one to isolate recombined clones possessing diacetyl (DR) and acetoin (AR) reductase activities is described. This test allowed one to detect 3 Escherichia coli clones having both activities (DR and AR) from among 3000 E. coli strains constituting the genomic library of Saccharomyces carlsbergensis in E. coli.     

Assessment of bacterial biofilm on stainless steel by hyperspectral fluorescence imaging

Hyperspectral fluorescence imaging techniques were investigated for detection of two genera of microbial biofilms on stainless steel material which is commonly used to manufacture food processing equipment. Stainless steel coupons were deposited in nonpathogenic E. coli O157:H7 and Salmonella cultures, prepared using M9 minimal medium with casamino acids (M9C), for 6 days at 37 °C. Hyperspectral fluorescence emission images of the biofilm formations on the stainless coupons were acquired from 416 to 700 nm with the use of ultraviolet-A (320–400 nm) excitation. In general, emission peaks for both bacteria were observed in the blue region at approximately 480 nm and thus provided the highest contrast between the biofilms and background stainless steel coupons. A simple thresholding of the 480 nm image showed significantly larger biofilm regions for E. coli O157:H7 than for Salmonella. Viable cell counts suggested that Salmonella formed significantly higher density biofilm regions than E. coli O157:H7 in M9C medium. On the basis of principal component analysis (PCA) of the hyperspectral fluorescence images, the second principal component image exhibited the most distinguishable morphological differences for the concentrated biofilm formations between E. coli and Salmonella. E. coli formed granular aggregates of biofilms above the medium on stainless steel while Salmonella formed dense biofilm in the medium-air interface region (pellicle). This investigation demonstrated the feasibility of implementing fluorescence imaging techniques to rapidly screen large surface areas of food processing equipment for bacterial contamination. Company and product names are used for clarity and do not imply any endorsement by USDA to the exclusion of other comparable products.     

Biofilm formation by Escherichia coli in hypertonic sucrose media

High osmotic environments produced by NaCl or sucrose have been used as reliable and traditional methods of food preservation. We tested, Escherichia coli as an indicator of food-contaminating bacterium, to determine if it can form biofilm in a hyperosmotic environment. E. coli K-12 IAM1264 did not form biofilm in LB broth that contained 1 M NaCl. However, the bacterium formed biofilm in LB broth that contained 1 M sucrose, although the planktonic growth was greatly suppressed. The biofilm, formed on solid surfaces, such as titer-plate well walls and glass slides, solely around the air–liquid interface. Both biofilm forming cells and planktonic cells in the hypertonic medium adopted a characteristic, fat and filamentous morphology with no FtsZ rings, which are a prerequisite for septum formation. Biofilm forming cells were found to be alive based on propidium iodide staining. The presence of 1 M sucrose in the food environment is not sufficient to prevent biofilm formation by E. coli.     

Biofilm Formation Characteristics of Pseudomonas lundensis Isolated from Meat

Biofilms formations of spoilage and pathogenic bacteria on food or food contact surfaces have attracted increasing attention. These events may lead to a higher risk of food spoilage and foodborne disease transmission. While Pseudomonas lundensis is one of the most important bacteria that cause spoilage in chilled meat, its capability for biofilm formation has been seldom reported. Here, we investigated biofilm formation characteristics of P. lundensis mainly by using crystal violet staining, and confocal laser scanning microscopy (CLSM). The swarming and swimming motility, biofilm formation in different temperatures (30, 10, and 4 °C) and the protease activity of the target strain were also assessed. The results showed that P. lundensis showed a typical surface‐associated motility and was quite capable of forming biofilms in different temperatures (30, 10, and 4 °C). The strain began to adhere to the contact surfaces and form biofilms early in the 4 to 6 h. The biofilms began to be formed in massive amounts after 12 h at 30 °C, and the extracellular polysaccharides increased as the biofilm structure developed. Compared with at 30 °C, more biofilms were formed at 4 and 10 °C even by a low bacterial density. The protease activity in the biofilm was significantly correlated with the biofilm formation. Moreover, the protease activity in biofilm was significantly higher than that of the corresponding planktonic cultures after cultured 12 h at 30 °C.     

Susceptibility of Escherichia coli O157 to chitosan‐arginine in beef liquid purge is affected by bacterial cell growth phase

Here, we evaluated the impact of bacterial growth stage on the effect of chitosan‐arginine (Ch‐arg) on Escherichia coli O157:H7 cell numbers and metabolic activity within contaminated beef juice held at room temperature. Using a lux‐marked metabolic reporter strain of E. coli O157:H7, the results showed that Ch‐arg was most bioactive against cells in the lag phase and exponential phase. In comparison, there was a reduced, although still significant, inhibitory effect of Ch‐arg on the viability and metabolic activity of E. coli O157 held in stationary phase. Ch‐arg reduced, but did not eliminate E. coli O157 growth in the meat juice over 48 h. Based on the evidence presented here and elsewhere, we conclude that Ch‐arg can limit the growth and activity of food spoilage bacteria; however, it cannot completely eliminate bacterial contaminants originally present. Ch‐arg should therefore be viewed as a potentially protective measure rather than a biocidal agent that completely eliminates the risk of pathogen transfer in the food chain.     

Cranberry cocktail juice, cranberry concentrates, and proanthocyanidins reduce reovirus infectivity titers in African green monkey kidney epithelial cell cultures

Studies were performed to investigate the effect of several cranberry and grape juice extracts on the inhibition of reovirus infectivity following cell culture inoculation. Infectivity testing was performed utilizing cranberry juice extracts NutriCran-100 and NutriCran-90. At 5% extract concentrations, titers were reduced by ca. 50%. Cranberry cocktail juice caused an infectivity loss of ca. 10%. We ascribe these data to higher concentrations of proanthocyanidins (PACs) in the cranberry extracts. Further testing was performed utilizing purified high and low molecular weight cranberry PAC fractions (CB HMW and CB LMW, respectively), a cranberry flavonol glycoside (CB EToAc), cranberry anthocyanins (CB CA), and a grape PAC extract. Reovirus titers were reduced to undetectable levels at PAC concentrations < or =0.2%. CB CA had no effect on the inhibition of infectivity titers. Loss of infectivity titers was in the order: GP PAC>CB HMW>CB LMW>CB EToAc. Probe homogenization of CB HMW enhanced the extract to efficacy levels equal to that of grape PAC. Reovirus dsRNA segments were undetectable 96-h postcranberry cocktail juice pretreatment of MA-104 cell cultures. This study indicates an inhibition of reovirus infectivity titers by cranberry or grape juices or their purified PAC extracts. Viral inhibition probably occurs at the host cell surface.     

Inactivation of Escherichia coli in orange juice using ozone

This research investigated the efficacy of gaseous ozone for the inactivation of Escherichia coli ATCC 25922 and NCTC 12900 strains in orange juice. Orange juice inoculated with E. coli (10⁶ CFU mL^− 1) as a challenge microorganism was treated with ozone at 75–78 µg mL^− 1 for different time periods (0–18 min). The efficacy of ozone for inactivation of both strains of E. coli was evaluated as a function of different juice types: model orange juice, fresh unfiltered juice, juice without pulp, and juice filtered through 500 µm or 1 mm sieves. Fast inactivation rates for total reduction of E. coli were achieved in model orange juice (60 s) and in juice with low pulp content (6 min). However, in unfiltered juice inactivation was achieved after 15–18 min. This indicated that juice organic matter interferes with antibacterial activity of gaseous ozone. The effect of prior acid (pH 5.0) exposure of E. coli strains on the inactivation efficacy of ozone treatment was also investigated. There was a strain effect observed, where prior acid exposure resulted in higher inactivation times in some cases by comparison with the control cells. However, the overarching influence on inactivation efficacy of ozone was related to the pulp content. Generally, the applied gaseous ozone treatment of orange juice resulted in a population reduction of 5 log cycles.

Industrial relevance

To facilitate the preservation of unstable nutrients many juice processors have investigated alternatives to thermal pasteurisation, including un-pasteurised short shelf life juices with high retail value. This trend has continued within the European Union. However within the US recent regulations by the FDA have required processors to achieve a 5-log reduction in the numbers of the most resistant pathogens in their finished products. Pathogenic E. coli may survive in acid environments such as fruit juices for long periods. This study demonstrates that the use of ozone as a non-thermal technology is effective for inactivation of E. coli and acid exposed E. coli in orange juice. Information on the design of the ozone treatment for inactivation of E. coli which results into safe juice products is also among the main outputs of this work. Ozone auto-decomposition makes this technology safe for fruit juice processing.     

Inactivation of Escherichia coli O157:H7 on stainless steel upon exposure to Paenibacillus polymyxa biofilms

We investigated the potential use of biofilm formed by a competitive-exclusion (CE) microorganism to inactivate Escherichia coli O157:H7 on a stainless steel surface. Five microorganisms showing inhibitory activities against E. coli O157:H7 were isolated from vegetable seeds and sprouts. The microorganism with the greatest antimicrobial activity was identified as Paenibacillus polymyxa (strain T5). In tryptic soy broth (TSB), strain T5 reached a higher population at 25 °C than at 12 or 37 °C without losing inhibitory activity against E. coli O157:H7. When P. polymyxa (6 log CFU/mL) was co-cultured with E. coli O157:H7 (2, 3, 4, or 5 log CFU/mL) in TSB at 25 °C, the number of E. coli O157:H7 decreased significantly within 24 h. P. polymyxa formed a biofilm on stainless steel coupons (SSCs) in TSB at 25 °C within 24 h, and cells in biofilms, compared to attached cells without biofilm formation, showed significantly increased resistance to a dry environment (43% relative humidity [RH]). With the exception of an inoculum of 4 log CFU/coupon at 100% RH, upon exposure to biofilm formed by P. polymyxa on SSCs, populations of E. coli O157:H7 (2, 4, or 6 log CFU/coupon) were significantly reduced within 48 h. Most notably, when E. coli O157:H7 at 2 log CFU/coupon was applied to SSCs on which P. polymyxa biofilm had formed, it was inactivated within 1 h, regardless of RH. These results will be useful when developing strategies using biofilms produced by competitive exclusion microorganisms to inactivate foodborne pathogens in food processing environments.     

Genomic and phenotypic characterization of Escherichia coli isolates recovered from the uterus of puerperal dairy cows

The role of Escherichia coli in the pathogenesis of the puerperal uterine infection of the cow is largely unknown. It is proposed that E. coli favors the persistence of Arcanobacterium pyogenes and gram-negative bacteria that are pivotal to the establishment of the infection. Here, we report the genomic and phenotypic characteristics of 72 E. coli isolates recovered from the uterus of dairy cows with normal puerperium (n = 12; 35 isolates) or clinical metritis (n = 18; 37 isolates), in an attempt to identify characteristics that are related to the establishment of uterine infection. We evaluated DNA fingerprints generated by repetitive element sequence-based PCR, phylogenetic grouping, the presence of 15 virulence factor genes, in vitro biofilm formation and its relationship to curli fimbriae expression, and cellulose production. We found a wide genetic diversity (40 clonal types), including types common to normal puerperium and clinical metritis cows (n = 6), as well as types specific to normal puerperium (n = 14) or clinical metritis (n = 20) cows. Isolates were assigned to phylogenetic groups B1 (58%), A (31%), and D (11%). Only 4 virulence factor genes were detected (hlyE, hlyA, iuc, and eaeA). In vitro biofilm formation was significantly affected by culture medium and incubation temperature. Curli fimbriae expression and cellulose production, although related to biofilm formation, were not required for it. None of the evaluated E. coli characteristics were significantly related to the establishment of the uterine infection. In conclusion, data presented in this paper indicate that E. coli isolates recovered from the uterus of puerperal cows present a wide genetic diversity, do not belong to a known pathogenic group, and have a low potential of virulence and persistence. This corroborates the putative role of the bacterium in the pathogenesis of the puerperal uterine infection of the cow.     

Radio frequency electric fields processing of orange juice

The non-thermal process of radio frequency electric fields (RFEF) has been shown to inactivate bacteria in apple juice at moderately low temperatures, but has yet to be extended to inactivate bacteria in orange juice. An 80 kW RFEF pasteurizer was used to process pulp-free orange juice at flow rates of 1.0 and 1.4 l/min. Escherichia coli K12 in orange juice was exposed to electric field strengths of 15 and 20 kV/cm at frequencies of 21, 30, and 40 kHz. Ascorbic acid (Vitamin C) content and color of the juice before and after treatment were analyzed. Electrical energy costs were calculated using the measured voltage and current. An energy balance was performed using the inlet and outlet temperatures. Processing at an outlet temperature of 65 °C reduced the population of E. coli by 3.3 log relative to the control. Increasing the treatment time and temperature and decreasing the frequency enhanced the level of inactivation. Varying the electric field strength over the range of conditions used had no effect on the inactivation. No loss in ascorbic acid or enzymatic browning was observed due to RFEF processing. The electrical energy determined using the voltage and current was 180 J/ml. This was in good agreement with the energy calculated using the temperature data. The electrical cost was $0.0026/l of orange juice. The results provided the first evidence that the RFEF process inactivates bacteria in orange juice at moderately low temperatures.

Industrial relevance

The RFEF process has been shown to inactivate E. coli in apple juice at moderately low temperatures, but has yet to be extended to inactivate bacteria in orange juice. An RFEF pilot plant pasteurizer was used to process orange juice at rates of up to 1.4 l/min. RFEF processing reduced the population of E. coli by 99.3% at 60 °C and a hold time of 3 s, whereas conventional heating at the same conditions had no effect on the E. coli. This work demonstrated that the non-thermal RFEF process can be extended to inactivate bacteria in orange juice.     

Reduction of Escherichia coli O157:H7 in Biofilms Using Bacteriophage BPECO 19

Biofilm formation is a growing concern in the food industry. Escherichia coli O157:H7 is one of the most important foodborne pathogens that can persists in food and food‐related environments and subsequently produce biofilms. The efficacy of bacteriophage BPECO 19 was evaluated against three E. coli O157:H7 strains in biofilms. Biofilms of the three E. coli O157:H7 strains were grown on abiotic (stainless steel, rubber, and minimum biofilm eradication concentration [MBEC^TM] device) and biotic (lettuce) surfaces at different temperatures. The effectiveness of bacteriophage BPECO 19 in reducing preformed biofilms on these surfaces was further evaluated by treating the surfaces with a phage suspension (10⁸ PFU/mL) for 2 h. The results indicated that the phage treatment significantly reduced (P  < 0.05) the number of adhered cells in all the surfaces. Following phage treatment, the viability of adhered cells was reduced by ≥3 log CFU/cm², 2.4 log CFU/cm², and 3.1 log CFU/peg in biofilms grown on stainless steel, rubber, and the MBEC^TM device, respectively. Likewise, the phage treatment reduced cell viability by ≥2 log CFU/cm² in biofilms grown on lettuce. Overall, these results suggested that bacteriophages such as BPECO 19 could be effective in reducing the viability of biofilm‐adhered cells.     

In vitro probiotic evaluation of potential antioxidant lactic acid bacteria isolated from idli batter fermented with Piper betle leaves

Lactic acid bacteria isolated from food sources can be introduced as probiotics because of their health‐promoting and nonpathogenic characteristics. Eight lactic acid bacteria from idli batter fermented with Piper betle leaves were selected to screen the antioxidant potential and biofilm‐forming ability. Five isolates exhibited good antioxidant potential and biofilm formation and showed antagonistic activity against the pathogenic biofilm‐forming Staphylococcus aureus. Further, in vitro probiotic properties of five isolates exhibited excellent acid tolerance, bile tolerance, simulated gastrointestinal juice tolerance, auto‐aggregation and co‐aggregation and hydrophobicity and showed resistance to antibiotics such as ciprofloxacin, nalidixic acid, norfloxacin and colistin. Isolates also showed positive bile salt hydrolase activity, cholesterol assimilation, β‐galactosidase production and mucin binding ability. The isolate KJBB10 exhibited good adhesion and pathogen exclusion percentage with human colon cancer cells (HCT‐15 and HT‐29). Hence, the isolates KJBB10, KJBB56 and KJBC06 can be used as beneficial probiotic starter cultures for the formulation of functional foods.     

The effects of acid adaptation on Escherichia coli inactivation using power ultrasound

Inactivation of Escherichia coli in liquids was carried out using power ultrasound. Parameters examined included amplitude levels (0.4 µm, 7.5 µm, 37.5 µm), treatment time, cell condition (non-adapted cells, acid adapted cells), liquid media (TSB, model orange juice and model apple juice) and E. coli strain (ATCC 25922, NCTC 12900). The efficacy of ultrasound treatment was found to be a function of amplitude level, treatment time and media (p < 0.05). The kinetics of inactivation followed zero order kinetics (R > 0.95), with the highest inactivation achieved using an amplitude of 37.5 µm. The D-values of E. coli 25922 at all amplitudes in model orange juice were not significantly different than in TSB media. However, at 0.4 µm and 37.5 µm amplitude D-values of E. coli 12900 were significantly different in model orange juice compared to TSB media. When efficacy of ultrasound was assessed in model apple juice and phosphate buffered saline treatment times were significantly reduced by comparison with TSB. Inactivation of E. coli was found to be influenced by strain, prior acid adaptation and suspension liquid, but the effect was negated at the higher amplitude levels.

Industrial relevance

To facilitate the preservation of unstable nutrients many juice processors have investigated alternatives to thermal pasteurisation, including un-pasteurised short shelf life juices with high retail value. This trend has continued within the European Union. However within the US recent regulations by the FDA have required processors to achieve a 5-log reduction in the numbers of the most resistant pathogens in their finished products. This rule comes after a rise in the number of food borne illness outbreaks and consumer illnesses associated with consumption of untreated juice products. Pathogenic E. coli may survive in acid environments such as fruit juices for long periods. Ultrasound has been identified as one possible non-thermal technology to meet the required microbial log reduction. However it is important to determine if conditions such as acid adaptation and pathogen strain influence ultrasound efficacy, if the technology is to be adopted by industry.     

Attachment and biofilm formation by Escherichia coli O157:H7 on stainless steel as influenced by exopolysaccharide production, nutrient availability, and temperature

The influence of exopolysaccharide (EPS) production, nutrient availability, and temperature on attachment and biofilm formation by Escherichia coli O157:H7 strains ATCC 43895 (wild type) and 43895-EPS (extensive EPS-producing mutant) on stainless steel coupons (SSCs) was investigated. Cells grown on heated lettuce juice agar and modified tryptic soy agar were suspended in phosphate-buffered saline (PBS). SSCs were immersed in the cell suspension (10(9) CFU/ml) at 4 degrees C for 24 h. Biofilm formation by cells attached to SSCs as affected by immersing in 10% tryptic soy broth (TSB), lettuce juice broth (LJB), and minimal salts broth (MSB) at 12 and 22 degrees C was studied. A significantly lower number of strain 43895-EPS cells, compared to strain ATCC 43895 cells, attached to SSCs during a 24-h incubation (4 degrees C) period in PBS suspension. Neither strain formed a biofilm on SSCs subsequently immersed in 10% TSB or LJB, but both strains formed biofilms in MSB. Populations of attached cells and planktonic cells of strain ATCC 43895 gradually decreased during incubation for 6 days in LJB at 22 degrees C, but populations of strain 43895-EPS remained constant for 6 days at 22 degrees C, indicating that the EPS-producing mutant, compared to the wild-type strain, has a higher tolerance to the low-nutrient environment presented by LJB. It is concluded that EPS production by E. coli O157:H7 inhibits attachment to SSCs and that reduced nutrient availability enhances biofilm formation. Biofilms formed under conditions favorable for EPS production may protect E. coli O157:H7 against sanitizers used to decontaminate lettuce and produce processing environments. Studies are under way to test this hypothesis.     

Kojic acid and tea polyphenols inactivate Escherichia coli O157:H7 in vitro and on salmon fillets by inflicting damage on cell membrane and binding to genomic DNA

The development of effective natural antibacterial agents is important due to the insecurity of synthetic antimicrobial agents and consumer preferences. In this study, kojic acid (KA) and tea polyphenols (TP) were found to exhibit synergistic inhibitory effect against Escherichia coli O157:H7 with a fractional inhibitory concentration index of 0.25. KA combined with TP at 25% of their minimum inhibitory concentrations (MICs) completely inactivated E. coli O157:H7 within 4 h. Subsequently, propidium iodide uptake tests, genomic DNA interaction analysis, molecular docking, field emission scanning electron microscopy and biofilm formation assay were conducted to understand the synergistic antibacterial mechanism of KA-TP. The results demonstrated that KA-TP attacked the cell membrane cooperatively, thus disturbing membrane integrity and cell structure, and KA could bind to the genomic DNA to affect the biofilm formation of E. coli O157:H7. Moreover, the contamination of E. coli O157:H7 on raw salmon fillets was eliminated to varying degrees after soaking treatments with KA and/or TP for 30 min. The depuration effect was further enhanced when KA combined with TP, and more than 2-log reduction of E. coli O157:H7 was obtained under the treatment of KA-TP at 2 MIC, suggesting that KA-TP may serve as a natural compound disinfectant for ready-to-eat aquatic products.     

Ultraviolet Treatment of Orange Juice to Inactivate <Emphasis Type="Italic">E. coli</Emphasis> O157:H7 as Affected by Native Microflora

The effect of yeast concentration on ultraviolet (UV) inactivation of five strains of Escherichia coli O157:H7 from different sources, inoculated both individually and simultaneously in orange juice, was analyzed and mathematically modeled. The presence of yeast cells in orange juice decreases the performance of UV radiation on E. coli inactivation. UV absorption coefficients in the juice increased with increasing yeast concentration, and higher UV doses were necessary to inactivate bacterial strains. UV intensities of I = 3.00 ± 0.3 mW/cm² and exposure times (t) between 0 and 10 min were applied; radiation doses (energy, E = I × t) ranging between 0 and 2 J/cm² were measured using a UV digital radiometer. All the tested individual strains showed higher resistance to the treatment when UV radiation was applied at 4 °C in comparison to 20 °C. UV inactivation of E. coli O157:H7 individual strain was satisfactory fitted with a first order kinetic model. A linear relationship was found between UV absorptivities and D values (radiation doses required to decrease microbial population by 90%) for each strain. The dose required to reach 5-log reduction for the most unfavorable conditions that is the most UV resistant strain, and maximum background yeast concentration was 2.19 J/cm² at 4 °C (corresponding to 11 min of UV treatment) and 2.09 J/cm² at 20 °C (corresponding to 10.55 min of UV treatment). When a cocktail of strains was inoculated in orange juice, the logistic equation was the best model that fits the experimental results due to the deviation from the log-linear kinetics. The UV resistance between strain cocktail and single strain were mathematically compared. Slopes of the decline curves for strain cocktail at high UV doses were lower than the slopes of the log-linear equation calculated for the individual strains, even for the most resistant one. Therefore, microbial inactivation tests using a cocktail of strains are particularly important to determine the performance of the UV inactivation treatment.     

Production of biofilm and quorum sensing by Escherichia coli O157:H7 and its transfer from contact surfaces to meat,poultry, ready-to-eat deli,and produce products

Multistate outbreaks of Escherichia coli O157:H7 infections through consumption of contaminated foods including produce products have brought a great safety concern. The objectives of this study were to determine the effect of biofilm and quorum sensing production on the attachment of E. coli O157:H7 on food contact surfaces and to evaluate the transfer of the pathogen from the food contact to various food products. E. coli O157:H7 produced maximum levels of AI-2 signals in 12 h of incubation in tested meat, poultry, and produce broths and subsequently formed strong biofilm in 24 h of incubation. In general, E. coli O157:H7 formed stronger biofilm on stainless steel than glass. Furthermore, E. coli O157:H7 that had attached on the surface of stainless steel was able to transfer to meat, poultry, ready-to-eat deli, and produce products. Strong attachment of the transferred pathogen on produce products (cantaloupe, lettuce, carrot, and spinach) was detected (>10³ CFU/cm²) even after washing these products with water. Our findings suggest that biofilm formation by E. coli O157:H7 on food contact surfaces can be a concern for efficient control of the pathogen particularly in produce products that require no heating or cooking prior to consumption.