Effects of Phage Concentration, Bacterial Density, and Temperature on Phage Control of Beef Spoilage

Retail beef steaks, inoculated with graded amounts of a Pseudomonas spp. and homologous phage, were subjected to a range of retail case temperatures to assess the significance of any interactive effects upon retail case life. The potential of phage to increase the case life of beef was unaffected by temperature within the range 1–10°C but was significantly influenced by the interactive effects of initial bacterial density and phage concentration. A maximum increase in the retail case life of beef, from 3.4 to 6.4 days, required initial bacterial densities of 4.6 × 10³ CFU/cm² and phage concentration of 9.7 × 10⁷ PFU/ cm².     

Efficacy of bacteriophage LISTEXP100 combined with chemical antimicrobials in reducing Listeria monocytogenes in cooked turkey and roast beef

The aim of this study was to verify the effectiveness of the commercially available anti-Listeria phage preparation LISTEX^™P100 in reducing Listeria monocytogenes on ready-to-eat (RTE) roast beef and cooked turkey in the presence or absence of the chemical antimicrobials potassium lactate (PL) and sodium diacetate (SD). Sliced RTE meat cores at 4 and 10 °C were inoculated with cold-adapted L. monocytogenes to result in a surface contamination level of 10³ CFU/cm². LISTEX^TMP100 was applied at 10⁷ PFU/cm² and samples taken at regular time intervals during the RTE product's shelf life to enumerate viable L. monocytogenes. LISTEX^™P100 was effective during incubation at 4 °C with initial reductions of L. monocytogenes of 2.1 log₁₀ CFU/cm² and 1.7 log₁₀ CFU/cm², respectively, for cooked turkey and roast beef without chemical antimicrobials (there was no significant difference to the initial L. monocytogenes reductions in the presence of LISTEX^TMP100 for cooked turkey containing PL and roast beef containing SD-PL). In the samples containing no chemical antimicrobials, the presence of phage resulted in lower L. monocytogenes numbers, relative to the untreated control, of about 2 log CFU/cm² over a 28-day storage period at 4 °C. An initial L. monocytogenes cell reduction of 1.5 log₁₀ CFU/cm² and 1.7 log₁₀ CFU/cm², respectively, for cooked turkey and roast beef containing no chemical antimicrobials was achieved by the phage at 10 °C (abusive temperature). At this temperature, the L. monocytogenes cell numbers of samples treated with LISTEX™ P100 remained below those of the untreated control only during the first 14 days of the experiment for roast beef samples with and without antimicrobials. On day 28, the L. monocytogenes numbers on samples containing chemical antimicrobials and treated with LISTEX^TMP100 stored at 4 and 10 °C were 4.5 log₁₀ CFU/cm² and 7.5 log₁₀ CFU/cm², respectively, for cooked turkey, and 1.2 log₁₀ CFU/cm² and 7.2 log₁₀ CFU/cm², respectively, for roast beef. In both cooked turkey samples with and without chemical antimicrobials stored at 10 °C, the phage-treated samples had significantly lower numbers of L. monocytogenes when compared to the untreated controls throughout the 28-day storage period (P < 0.0001). For roast beef and cooked turkey containing chemical antimicrobials treated with LISTEX^TMP100 and stored at 4 °C, no more than a 2 log CFU/cm² increase of L. monocytogenes was observed throughout the stated shelf life of the product. This study shows that LISTEX^™P100 causes an initial reduction of L. monocytogenes numbers and can serve as an additional hurdle to enhance the safety of RTE meats when used in combination with chemical antimicrobials.     

Practical application of bacteriophage in food manufacturing facilities for the control of Listeria sp.

Listeria monocytogenes is a foodborne pathogen with the ability to persist and form biofilm matrices in processing environments of food manufacturing facilities. Bacteriophages are bacterial viruses with host specific lethality. Published research on the application of phage to control Listeria sp. in manufacturing environments is limited. In this study, we have assessed the capacity of bacteriophage P100 (Listex™) to reduce incidence of Listeria sp. in the ready-to-eat (RTE) environment of refrigerated (4°C) and ambient (20°C) temperature facilities using two different application strategies. A moderate application applied as a single treatment every 24 hr over three days (2 × 10⁷ PFU/ml) and an intensified application applied once every 6 hr over a 24 hr period (1 × 10⁸ PFU/ml). Environmental nonfood contact surface (NFCS) samples were collected and analyzed for the presence of Listeria sp. before and after treatment. When the moderate treatment protocol was applied the incidence of positives decreased from 51.3 to 17.5% in the 4°C environment and from 67.5 to 23.1% in the 20°C production area. For the intensified phage treatment method, the initial positive rate in the 4°C environment ranged from 5 to 47.5%, with an overall 43% reduction in Listeria sp. In the 20°C facility, initial environmental Listeria sp. ranged from 15 to 50%, with an overall reduction of 32% after treatment with phage P100. Data indicate the application of Listeria specific phage P100 in RTE food production environments by either the moderate or intensified application method can reduce incidence and be considered an additional intervention strategy for controlling this pathogen on NFCS.     

The probiotic,Leuconostoc mesenteroides,inhibits Listeria monocytogenes biofilm formation

Listeria monocytogenes biofilm formation renders these cells highly resistant to current sanitation methods, and probiotics may be a promising approach to the efficient inhibition of Listeria biofilms. In the present study, three Leuconostoc mesenteroides strains of lactic acid bacteria isolated from kimchi were shown to be effective probiotics for inhibiting Listeria biofilm formation. Biofilms of two L. monocytogenes serotypes, 1/2a (ATCC15313) and 4b (ATCC19115), in dual-species culture with each probiotic strain were decreased by more than 40-fold as compared with single-species Listeria biofilms; for instance, a reduction from 5.4 × 10⁶ colony forming units (CFU)/cm² L. monocytogenes ATCC19115 in single-species biofilms to 1.1 × 10⁵ CFU/cm² in dual-species biofilms. Most likely, one of the Leuconostoc strains, L. mesenteroides W51, led to the highest Listeria biofilm inhibition without affecting the growth of L. monocytogenes. The cell-free supernatant from the L. mesenteroides W51 culture containing large protein molecules (>30 kDa) also inhibited Listeria biofilms. These data indicate that Leuconostoc probiotics can be used to repress L. monocytogenes biofilm contamination on surfaces at food processing facilities.     

Microbiological quality of fresh fruit and vegetable products in Catalonia (Spain) using normalised plate‐counting methods and real time polymerase chain reaction (QPCR)

BACKGROUND: Commercially available fruits and raw and ready‐to‐eat vegetables (n = 445) were examined for aerobic, coliform, and yeast and mould counts using normalised methods. Listeria spp., Listeria monocytogenes and Salmonella spp. were detected by real time polymerase chain reaction (QPCR) after enrichment. RESULTS: Aerobic plate counts ranged from < 10 to > 10⁹ colony‐forming units (CFU) g^?1, with the lowest and highest counts recorded for fruits and sprouts respectively. The highest incidence level of coliforms was found in ready‐to‐eat vegetables, with up to 65.7% of samples containing from 5 to 9 log₁₀CFU g^?1. Yeasts and moulds showed their highest incidence level between 5 and 6 log₁₀ CFU g^?1, with an overall range from < 2 to 9 log₁₀ CFU g^?1. Salmonella spp., Listeria spp. and L. monocytogenes were detected in 0.67, 2.7 and 0.9% respectively of the total samples examined. CONCLUSION: The samples analysed can be gathered into two main groups, one showing low microbial counts (fruits) and a second group (raw whole leaves and roots and packed ready‐to‐eat vegetables) with higher microbial contamination. Although incidence levels of pathogenic bacteria reported here are in the lower range of those reported elsewhere, positive detections highlight the importance of good hygienic measures throughout the whole food chain. Copyright © 2007 Society of Chemical Industry     

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.     

Inactivation of Escherichia coli O157:H7 and Listeria monocytogenes inoculated on raw salmon fillets by pulsed UV-light treatment

The efficacy of pulsed UV‐light to inactivate of Escherichia coli O157:H7 and Listeria monocytogenes Scott A on salmon fillets was investigated in this study by evaluating the effects of treatment times and distance from the UV strobe. The sterilization system generated 5.6 J cm^?2 per pulse at the lamp surface for an input voltage of 3800 V and three pulses per second. Skin or muscle side inoculated salmon fillet (8 cm × 1.5 cm) in a Petri dish was placed on shelf at three different distances from the UV strobe; 3, 5, and 8 cm. At each distance, the pulsed UV‐light treatment was performed for 15, 30, 45, and 60 s. For E. coli O157:H7, maximum log₁₀ reduction was 1.09 log₁₀ CFU g^?1 on muscle side at 8 cm for 60‐s treatment, whereas 0.86 log₁₀ CFU g^?1 reduction on skin at 5 cm for 30‐s treatment. For L. monocytogenes Scott A, maximum reduction was 1.02 log₁₀ CFU g^?1 at 8 cm for 60‐s treatment on skin side, whereas 0.74 log₁₀ CFU g^?1 reduction on muscle at 8 cm for 60‐s treatment. The fillet's surface temperature increased up to 100degrC within 60‐s treatment time. Therefore, some fish samples were overheated after 30 and 45 s at 3‐ and 5‐cm distances from light source, respectively, which resulted in visual colour and quality changes. Overall, this study demonstrated that about one log reduction (c. 90%) of E. coli O157:H7 or L. monocytogenes could be achieved at 60‐s treatment at 8 cm distance without affecting the quality.     

Effectiveness of bacteriophage JN01 incorporated in gelatin film with protocatechuic acid on biocontrol of Escherichia coli O157:H7 in beef

A new gelatin-protocatechuic acid (PCA) film with Escherichia coli O157:H7 phage JN01 was developed and characterised. After incorporated with JN01, swelling value, water vapour permeability, water solubility and elongation at break of gelatin-PCA film were not significantly different. The addition of JN01 increased b value and transparency of film, while it decreased L value, a value and tensile strength of film. Moreover, the gelatin-PCA-JN01 film presented antioxidant activity of 60.07%. Furthermore, JN01 could be steadily released from gelatin-JN01 and gelatin-PCA-JN01 films in aqueous solution, and their release rates were 7.56% and 0.12% after 11 h, respectively. The microstructure analysis showed that JN01 particles were clustered and uniformly distributed in film, and the aggregation would be attenuated in the presence of PCA. Meanwhile, E. coli O157:H7 counts were 1.13 log₁₀CFU mL⁻¹ and 0.45 log₁₀CFU mL⁻¹ lower in gelatin-JN01 and gelatin-PCA-JN01 films compared with pure gelatin film in vitro at 4 °C for 24 h, respectively. After stored at 4 °C for 7 days, Escherichia coli O157:H7 counts were 1.00 log₁₀CFU g⁻¹ and 0.80 log₁₀CFU g⁻¹ lower in beef packed with these two gelatin films, compared with beef without gelatin film, respectively. In conclusion, the developed gelatin-PCA-JN01 film has potential application in food preservation.     

Microbiological Decontamination of Poultry Feed—Evaluation of Steam Conditioners

The microbial decontamination of chicken feed, obtained from a commercial pellet mill, was evaluated using a direct-fired steam conditioner (DFSC; APC System^™). The standard plate count of the feeds before (mash) and after (pellets) conditioning ranged from 65×10⁴ to 83×10⁵ colony forming units (CFU) g⁻¹ and from 91×10¹ to 92×10³ CFU g⁻¹, respectively. The incidence of Escherichia coli , Salmonella and Listeria in the feeds before conditioning was 61·7, 8·3 and 27·1%, respectively. Following conditioning these levels were reduced to 1·7, 1·7 and 0%, respectively. Species of Listeria and Salmonella identified included L monocytogenes , L innocua and S agona , S ohio , S heidelberg , S senftenberg , S tallahasse and S braenderup , respectively. Compared with a conventional, indirect-fired boiler-generated-steam conditioner (IFSC) the direct-fired steam conditioner proved superior in regards to pathogen decontamination; no E coli , Salmonella or Listeria were recovered from mash lots positive for these microorganisms. However, with the IFSC system, both E coli and L monocytogens were recovered at levels of 11·1 and 5·6%, respectively.     

A Combination of Chemical and Ultrasonication Treatments to Reduce Campylobacter jejuni on Raw Poultry

Cost-effective and acceptable decontamination technologies that can be readily applied to the broiler-processing industry have been proposed as a strategy to reduce pathogenic organisms on carcasses and improve food safety. The objective of this study was to determine the potential of combining chemical and ultrasonication processes to reduce Campylobacter, total viable counts (TVCs) and total Enterobacteriaceae counts (TECs) on broiler carcasses. Drumsticks were inoculated with Campylobacter jejuni and immersed in 12 % (w/v) trisodium phosphate (TSP), 2 % (w/v) citric acid (CA) or 5 % (w/v) capric acid sodium salt (CP) solutions for 1 min, while ultrasonication was performed at 40, 60 or 80 kHz. In addition, chemicals were administered in sequential combination (TSP?+?CA, TSP?+?CP or CA?+?CP) while ultrasonication was performed at the frequencies mentioned. The sequential treatment of TSP and CP with ultrasonication at 80 kHz achieved the greatest reductions for C. jejuni (4.5–4.6 log₁₀ colony forming units (CFU)/cm²) and TVC (1.9 log₁₀ CFU/cm²). Enterobacteriaceae were susceptible to the sequential application of CA and CP and ultrasonication at 80 kHz (2 log₁₀ CFU/cm²). This study demonstrated that combining chemical decontaminants with ultrasonication can significantly (p?相似文献   

Efficacy of neutral electrolyzed water for sanitization of cutting boards used in the preparation of foods

The effectiveness of neutral electrolyzed water (NEW) to sanitize cutting boards used for food preparation was investigated. Cutting boards made of hardwood and bamboo were inoculated with Escherichia coli K12 and Listeria innocua, dried for 1 h, washed, rinsed and sanitized with NEW, sodium hypochlorite (NaClO) solution, or tap water (control). After each washing protocol, surviving bacterial populations were determined. Results showed that both NEW and NaClO sanitizing solutions produced similar levels of bacterial reductions. In manual washing, the population reductions by NEW and NaClO were 3.4 and 3.6 log₁₀ CFU/100 cm² for E. coli, and 4.1 and 3.9 log₁₀ CFU/100 cm² for L. innocua, respectively. In the automatic washing, the reductions by NEW and NaClO were 4.0 and 4.0 log₁₀ CFU/100 cm² for E. coli, and 4.2 and 3.6 log₁₀ CFU/100 cm² for L. innocua, respectively. No significant differences (P > 0.05) were observed in surviving bacteria counts when comparing board material types.     

Reduction of Listeria monocytogenes in cold‐smoked salmon by bacteriophage P100, nisin and lauric arginate,singly or in combinations

Three GRAS antimicrobials including, lauric arginate (LAE), bacteriophage P100 (phage P100) and bacteriocin nisin, were evaluated either singly or in combinations for the reduction of initial load of Listeria monocytogenes in cold‐smoked salmon (CSS). The stability of phage P100 in the presence of LAE (200 ppm) and nisin (500 ppm) or at 10× and 100× of these concentrations was determined at 4 °C or 30 °C for 24 h in a broth model. Phage P100 was found to be highly stable in the presence of these antimicrobial agents as plaque‐forming units (PFU) did not vary between control and antimicrobial‐treated phage. The survival of L. monocytogenes in the presence of phage P100, nisin and LAE showed remarkable reduction within 24 h both at 4 °C or 30 °C in broth. Treatment of CSS containing 3.5 log CFU cm^?2 L. monocytogenes with phage P100 (10⁸ PFU mL^?1), nisin (500 ppm) and LAE (200 ppm) showed strong listericidal action and reduced the L. monocytogenes by 2–3 log CFU cm^?2 after 24 h. Among the combined treatments, phage P100 + LAE or nisin + LAE exhibited the most listericidal action in which L. monocytogenes cells were reduced to undetectable level within 24 h in CSS.     

Grape seed extract for foodborne virus reduction on produce

Grape seed extract (GSE) is reported to have antibacterial properties with few current studies on antiviral activity. Recently, we reported the effects of GSE against foodborne viral surrogates in vitro. This study evaluated the application of GSE (commercial Gravinol-S) against hepatitis A virus (HAV) and human norovirus surrogates, feline calicivirus (FCV-F9) and murine norovirus (MNV-1), on model produce. Washed and air-dried lettuce (3 × 3 cm²) and jalapeno peppers (25–30 g) were inoculated with FCV-F9, MNV-1, or HAV at high (∼7 log₁₀ PFU/ml) or low (∼5 log₁₀ PFU/ml) titers, and treated with 0.25, 0.5, 1 mg/ml GSE or water for 30 s to 5 min. Treatments were stopped/diluted with cell-culture media containing 10% heat-inactivated fetal bovine serum and evaluated using plaque assays. At high titers, FCV-F9 was reduced by 2.33, 2.58, and 2.71 log₁₀ PFU on lettuce; and 2.20, 2.74, and 3.05 log₁₀ PFU on peppers after 1 min using 0.25, 0.50, and 1 mg/ml GSE, respectively. Low FCV-F9 titers could not be detected after 1 min at all three GSE concentrations. Low titer MNV-1 was reduced by 0.2–0.3 log₁₀ PFU on lettuce and 0.8 log₁₀ PFU on peppers, without reduction of high titer. GSE at 0.25–1 mg/ml after 1 min caused 0.7–1.1 and 1–1.3 log₁₀ PFU reduction for high and low HAV titers, respectively on both commodities. Instrumental color analysis showed no significant differences between treated and untreated produce. GSE shows potential for foodborne viral reduction on produce as part of hurdle technologies.     

In-milk inactivation of Escherichia coli O157:H7 by the environmental lytic bacteriophage ECPS-6

Shiga toxin-producing Escherichia coli is a common foodborne pathogen which transmission includes dairy products. In the search for novel biocontrol methods, bacteriophages have become important candidates for the eradication of foodborne pathogens. The aim of this study was to evaluate the bacteriophage-mediated reduction of E. coli O157:H7 in raw and filtered milk. Laboratory-scale tests showed that the bacteriophage ECPS-6 efficiently adsorbed to E. coli O157: H7 cells. Furthermore, ECPS-6 remained stable when heated at 70°C for 20 min and in a wide pH range from 3.0 to 11.0. The trials on contaminated milk were performed using filtered and unfiltered raw milk contaminated with 1 × 10⁵ CFU × ml⁻¹ of E. coli O157: H7. Bacteriophage was added at multiplicity of infection (MOI) 5 and 50. The ECPS-6 reached the highest lytic activity at MOI = 5 (25°C) which resulted in 4.74 Log₁₀ CFU × ml⁻¹ and 7.3 Log₁₀ CFU × ml⁻¹ reduction after 10 days for both tested strains, respectively. Under refrigerated conditions (4°C) the quantity of E. coli decreased to 1.5 Log₁₀ CFU × ml⁻¹ and 3.04 Log₁₀ CFU × ml⁻¹ for these strains, respectively. Usage of MOI = 50 for the treatment unfiltered milk led to the reduction of E. coli O157:H7 A-2 below the detection limit after 6 hr.     

Effect of spraying on chemical properties and bactericidal efficacy of electrolysed oxidizing water

A three‐factor, three‐by‐three‐by‐two‐level factorial designs were used for studying the effects of air pressure, sprayer orifice size and electrostatic charge of a spray gun on pH, oxidation‐reduction potential (ORP), electric conductivity and residual chlorine of electrolysed oxidizing (EO) waters with either low (9 mg L^?1) or high concentration (88 mg L^?1) of chlorine. Results indicated that a smaller orifice produced higher reduction in ORP and chlorine concentration than larger orifices. Electrostatic charge, in general, did not cause a significant reduction in chlorine concentration. High air pressure spray retained more chlorine and gave a higher ORP than low air pressure. EO water with high initial chlorine concentration achieved at least a 3–4 log₁₀ CFU mL^?1 reduction in Listeria monocytogenes populations when sprayed with the spray gun, while spraying with a commercial backpack sprayer or a poly‐tank sprayer eliminated Listeria population (9.4 log₁₀ CFU mL^?1 reductions) completely. These results demonstrated that although spraying reduced the chlorine in EO water by 20–97%, application of EO water through spraying has potential for reducing bacteria in food‐processing operations.     

Microbiological Properties of Pork Cheek Meat as Affected by Acetic Acid and Temperature

Our objective was to determine the effect of acetic acid (AA) and temperature in inhibiting Salmonella typhimurium, aerobic plate counts (APCs) and total coliforms on pork cheek meat. Compared with initial APCs of control cheeks, a reduction in log₁₀ CFU/cm² APC by more than 78.6% was found in all samples that were treated with 20 and 40° acetic acid (P < 0.05). Additionally, total coliforms for acidtreated cheeks were lower for both AA treatments (P < 0.05). Cheeks (n = 10/treatment) were also sprayed in a commercial pork slaughter facility carcass wash with 2% AA (25°) and compared to control (non-treated) cheeks. The incidence of Salmonella decreased by 67% for acid-treated cheeks (P < 0.05). A significant decrease in APCs and coliforms occurred for the acid-treated cheeks (P < 0.05).     

INACTIVATION OF ESCHERICHIA COLI O157:H7 ON INOCULATED ALFALFA SEEDS WITH OZONATED WATER UNDER PRESSURE1

Alfalfa seeds inoculated with Escherichia coli O157:H7 (～10⁵ CFU/g) were subjected to low hydrostatic pressure. Seeds immersed in ozonated water at 4C were held at 8 and 12‐psi ozone pressure for 2, 4, 8, 16, 32, and 64 min. Alternatively, seeds were continuously sparged with ozone for up to 64 min and then held at 12 psi for 5 min. Controls consisted of sparging and pressurization with air. Thirty‐two minute treatments of continuous ozone sparging followed by pressurization of seeds at 12 psi for 5 min were repeated with the addition of four surfactants (Tween 20, Tween 80, SPAN 20, and SPAN 80) in the treatment water. Enumeration of E. coli O157:H7 on treated, untreated, and control seeds was done on tryptic soy agar supplemented with 50 μg/mL of nalidixic acid. The reduction in population of E. coli O157:H7 on seeds treated with the 8 and 12 psi hydrostatic pressure in ozonated water ranged from 0.74 ?1.56 log₁₀ CFU/g and 0.72 – 1.62 log₁₀ CFU/g, respectively. Control treatments carried out with air pressurization of seeds resulted in maximum population reductions of 1.55 log₁₀ and 1.83 log₁₀ CFU/g for 8 and 12 psi, respectively. For seeds treated with continuous ozone sparging (2 – 64 min) followed by pressurization at 12 psi for 5 min, the highest reduction was 2.03 log₁₀ CFU/g. Reductions were, however, not significantly different (P > 0.05) from control treatment (with air) which reduced the populations by 0.57 – 2.19 log₁₀ CFU/g. The presence of surfactants during continuous sparging of water followed by pressurization at 12 psi was not beneficial. None of the treatments adversely affected the germination of the seeds.     

Efficacy of Neutral Electrolyzed Water,Quaternary Ammonium and Lactic Acid‐Based Solutions in Controlling Microbial Contamination of Food Cutting Boards Using a Manual Spraying Technique

Bactericidal activity of neutral electrolyzed water (NEW), quaternary ammonium (QUAT), and lactic acid‐based solutions was investigated using a manual spraying technique against Salmonella Typhimurium, Escherichia coli O157:H7, Campylobacter jejuni, Listeria monocytogenes and Staphylococcus aureus that were inoculated onto the surface of scarred polypropylene and wooden food cutting boards. Antimicrobial activity was also examined when using cutting boards in preparation of raw chopped beef, chicken tenders or salmon fillets. Viable counts of survivors were determined as log₁₀ CFU/100 cm² within 0 (untreated control), 1, 3, and 5 min of treatment at ambient temperature. Within the first minute of treatment, NEW and QUAT solutions caused more than 3 log₁₀ bacterial reductions on polypropylene surfaces whereas less than 3 log₁₀ reductions were achieved on wooden surfaces. After 5 min of treatment, more than 5 log₁₀ reductions were achieved for all bacterial strains inoculated onto polypropylene surfaces. Using NEW and QUAT solutions within 5 min reduced Gram‐negative bacteria by 4.58 to 4.85 log₁₀ compared to more than 5 log₁₀ reductions in Gram‐positive bacteria inoculated onto wooden surfaces. Lactic acid treatment was significantly less effective (P < 0.05) compared to NEW and QUAT treatments. A decline in antimicrobial effectiveness was observed (0.5 to <2 log₁₀ reductions were achieved within the first minute) when both cutting board types were used to prepare raw chopped beef, chicken tenders or salmon fillets.     

Influence of gamma irradiation on growth and survival of Escherichia coli O157:H7 and quality of cig kofte, a traditional raw meat product

Cig kofte is a traditional Turkish food containing raw ground meat. Samples inoculated with Escherichia coli O157:H7 were irradiated at 0.5–6 kGy with a ⁶⁰Co source and stored at 4 and 25 °C. Total aerobic mesophilic count decreased with increasing irradiation doses, D₁₀ value was 0.83 kGy. Escherichia coli O157:H7 count decreased from 5.1 log₁₀ CFU g^?1 to an undetectable level (<1 log₁₀ CFU g^?1) after 1‐day storage at 4 °C following irradiation at 2 kGy, D₁₀‐value was 0.29 kGy. Irradiation doses up to 2 kGy did not affect sensory quality after 1 day. There was colour loss in samples irradiated at 2 kGy or above and stored for longer periods. Storage of the irradiated products at abused temperature must be avoided for safety assurance. Irradiation at 2 kGy has a great potential for extending the shelf‐life of cig kofte and assuring safety by decreasing the number of E. coli O157:H7 and other bacteria, but further studies with suitable package designs are needed to decrease quality degradation during extended storage.     

Quantification of Plesiomonas shigelloides in Pure Culture and Clams by Competitive PCR

A quantitative assay for Plesiomonas shigelloides in pure culture and clams based on the competitive polymerase chain reaction was developed. This is the first report for quantitative detection of P. shigelloides by competitive PCR. Forward (PS-F), reverse (PS23RV3), and hybrid primers were designed, and the specificity of the forward and reverse primer for P. shigelloides was proven. An internal standard DNA sequence was synthesized by PCR, with the hybrid primer as the forward primers and PS23RV3 as the reverse primer. A single concentration (0.588 pg/PCR) of internal standard (IS) was used for competitive PCR. The lowest level of detection of P. shigelloides was 80 CFU per PCR in pure culture, 240 CFU/g of clam tissue without enrichment, and 40 CFU/g of clam tissue after 7 hrs. nonselective enrichment at 37°C. There was a linear relationship between the log of the ratio of the relative fluorescent intensities of amplified target DNA bands to the internal standard DNA bands (IS) and the log of the CFU within a certain range in pure cultures and in clam tissue either with or without enrichment. The linear range with cells from a pure culture was the DNA derived from 8.0 × 10¹ to 8.0 × 10⁴ CFU per PCR while with clam tissue, the linear range was the DNA derived from 2.4 × 10² to 2.4 × 10⁵ CFU/g of tissue (1.2 × 10¹ to 1.2 × 10⁴ CFU per PCR) without enrichment, and 4.0 × 10¹ to 1.2 × 10⁴ CFU/g of clam tissue with enrichment, respectively.