Effects of spray volume, type of surface tissue and inoculum level on the survival of Escherichia coli on beef sprayed with 5% lactic acid

Membrane, fat and cut muscle surfaces of beef were inoculated with Escherichia coli at numbers about 4, 1 or −1 log cfu/cm². The inoculated meat was sprayed with water or 5% lactic acid at volumes of 0.5, 0.1 or 0.02 ml/cm². Spraying with water reduced the numbers of E. coli on membrane surfaces by up to 1 log unit, but had little effect on the numbers of E. coli on fat or cut muscle surfaces. Spraying with 5% lactic acid reduced the highest numbers of E. coli on membrane surfaces by up to 4 log units; but those numbers on fat or cut muscle surfaces were reduced by ≤1.5 log unit, and the reductions declined with decreasing volumes of 5% lactic acid. With inocula of 1 log cfu/cm², spraying lactic acid in any volume reduced the numbers of E. coli on membrane or fat surfaces by about 1 log unit, and the numbers on cut muscle surfaces by between 0.8 and 0.2 log unit. E. coli were detected in enrichment cultures of samples from all surfaces inoculated with E. coli at −1 log cfu/cm² and sprayed with 5% lactic acid at 0.5 ml/cm². The findings indicate that spraying relatively heavily contaminated cuts or trimmings with 5% lactic acid at ≥0.1 ml/cm² can be expected to reduce numbers of E. coli and, presumably, associated pathogens by between 0.5 and 1 log unit. However, such a treatment is likely to be at best marginally effective for reduce the numbers of these organisms on lightly contaminated product.     

Role of cellulose in protecting Shiga toxin producing Escherichia coli against oxidative and acidic stress

This study assessed the role of cellulose in protecting Shiga toxin-producing Escherichia coli (STEC) against environmental stress. Cellulose producing STEC strain 19B (O5:H-) and 49B (O103:H2) as well as their cellulose deficient derivates (19D and 49D) were subjected to oxidative (10, 20 and 30 mM H₂O₂) and acidic (pH 3.0, 3.5 and 4.5) stress. Approximately 4.25, 2.46 or 1.74 log CFU ml⁻¹ of the 19B cells survived a 2.5-h treatment with 10, 20 and 30 mM H₂O₂, respectively, while none of the 19D cells (8.02 logs) survived the same treatments. The population of 49D decreased from 7.70 to <0.60 log CFU ml⁻¹, whereas that of 49B decreased from 7.70 to 2.47 log CFU ml⁻¹ by a 2-h treatment with 30 mM H₂O₂. Approximately 2.63 log CFU ml⁻¹ of the 19B cells survived at pH 3.0 for 1 h and 4.75 log CFU ml⁻¹ of the 49B cells survived at pH 3.0 for 1.5 h, but the 19D and 49D cells did not survive these treatments. Results indicated that cellulose protected the selected STEC strains against oxidative treatments with 10-30 mM of H₂O₂ and acidic treatments at pH 3.0-3.5.     

Mechanism of the combined anti-bacterial effect of green tea extract and NaCl against Staphylococcus aureus and Escherichia coli O157:H7

The mechanism of the combined anti-bacterial effect of green tea extract (GTE) and NaCl against Staphylococcus aureus NBRC 13276 and Escherichia coli O157:H7 was investigated. After treatment for 1 h, GTE was more effective against S. aureus than E. coli O157:H7, and combined GTE/NaCl treatment caused greater cellular damage in S. aureus NBRC 13276, where it was bactericidal, than E. coli O157:H7. Compared to treatment with 1.0 mg/mL GTE, which had no effect on the survival rate of E. coli O157:H7 after 48 h, treatment with 4% NaCl alone caused greater cellular damage. Moreover, bacteria pretreated with NaCl showed delayed growth in the presence of GTE. It is therefore likely that susceptibility of E. coli O157:H7 to GTE was increased by exposure to NaCl. E. coli O157:H7 pretreated with GTE and NaCl did not multiply in the presence of GTE. Visualization of the catechin components of GTE-treated bacteria using an electron microscope and SDS-PAGE analysis of cell proteins showed that GTE attached to proteins on the surface of the bacteria to form high-molecular weight complexes, suggesting the possibility that GTE inhibits the uptake and secretion of substrates and inhibits enzyme activity. Notably, after the GTE treatment for 1 h, both bacterial strains suffered injury but recovered by cultivation in rich medium. The damage and aggregation of proteins caused by GTE treatment were repaired upon treatment with LP diluent.     

Comparison of intense pulsed light- and ultraviolet (UVC)-induced cell damage in Listeria monocytogenes and Escherichia coli O157:H7

The purpose of this study was to compare the degree of microbial inactivation and cell damage induced by intense pulsed light (IPL) and short-wavelength ultraviolet (UVC) in Listeria monocytogenes and Escherichia coli O157:H7. The viability of the food-borne pathogens treated with IPL and UVC (254 nm) decreased exponentially with treatment time. Particularly dramatic reductions in L. monocytogenes and E. coli O157:H7 were observed for IPL treatments at energy densities of 376 and 455 W/m², with an approximately 7-log reduction for a treatment time of 60-180 s. Also, a 4-log reduction of L. monocytogenes and a 5-log reduction of E. coli O157:H7 were achieved with UVC irradiation for 1200 s. The types and amounts of IPL- and UVC-induced DNA damage in both microorganisms were determined and compared. DNAs from cells irradiated with either IPL or UVC accumulated double-strand breaks (DSBs), single-strand breaks, and cyclobutane pyrimidine dimers, and with a similar pattern; however, more DSBs were detected following UVC than following IPL in both types of microorganism. Transmission electron microscopy observations of IPL- and UVC-induced cell damage clearly indicate that bacterial cell structures were destroyed by IPL treatment but not by UVC treatment.     

Antibiotic resistance in Campylobacter jejuni and Campylobacter coli isolated from food in Poland

This study presents the results of investigations on the susceptibility of Campylobacter spp. strains isolated from chicken meat and giblets to fluorochinolones (ciprofloxacin), macrolides (erythromycin), tetracyclines (tetracycline) and aminoglycosides (gentamicin) andV an analysis of the molecular mechanisms of resistance to the selected antibiotics.Between January 2008 and December 2009 a total of 218 samples of chicken meat and giblets from retail trade in Poland were examined. Campylobacter bacteria were found in 143 samples, that is in 65.6% of the total number embraced by the study. Campylobacter coli was the most ubiquitous - its presence was determined in 108 samples out of 143 (75.5%), whereas Campylobacter jejuni was found in 35 of the contaminated samples (24.5%).The results obtained point to the high percentage (97.9%) of Campylobacter isolates resistant to ciprofloxacin. 92 strains (64.3%) were resistant to tetracycline, 14 (9.1%) to erythromycin and only 9 (6.3%) to gentamicin. Moreover, ten out of the 143 resistant Campylobacter strains (7.0%) were found to be resistant to at least three unrelated antibiotics.     

Fate of Listeria monocytogenes and Escherichia coli O157:H7 in the presence of natural background microbiota on conventional and organic lettuce

Foodborne illnesses due to the consumption of contaminated raw vegetables is a continuing food safety concern. The limited efficacy of chlorine products to disinfect in fresh-cut industries, has led to study other methods or strategies to improve the safety of processed fresh-cut products. It has been reported that the presence of competing microorganisms on the surfaces of fresh produce can contribute to the reduction of pathogens. The aim of this study was to evaluate the interactions between the natural background microbiota of shredded conventional and organic lettuce and Listeria monocytogenes and Escherichia coli O157:H7. The effect of different initial load of background microbiota (‘low’, ‘medium’ and ‘high’) was tested for its ability to reduce L. monocytogenes and E. coli O157:H7 populations on shredded lettuce during storage at 10 ± 1 °C for 8 days. After the different pre-conditioning steps in order to obtain different initial loads of microbiota, in general, we observed that varying its size had no effect on L. monocytogenes and E. coli O157:H7 survival/growth during the storage period. Only differences on the survival/growth of L. monocytogenes and E. coli O157:H7 inoculated onto organic and conventional lettuce, respectively at the end of storage period at 10 °C were found. These results highlight the necessity for corrective measures to avoid contamination of fresh-cut vegetables with foodborne pathogens.     

The occurrence of Campylobacter spp. in Estonian broiler chicken production in 2002–2007

The aim of the present study was to monitor the occurrence of Campylobacter spp. in broiler chicken production in Estonia from 2002 to 2007. Campylobacter spp. was isolated in 163 (12.3%) of 1320 broiler chicken meat samples form 2002 to 2007 and in 115 (6.3%) of 1819 cecal samples in 2005–2007. Campylobacter jejuni was the most commonly isolated species (98.2%), followed by Campylobacter coli (1.4%) and Campylobacter lari (0.4%). The seasonal peak of Campylobacter contamination was from July to September. Our findings showed that Campylobacter contamination at all levels of broiler chicken production in Estonia was low.     

Efficacy of pulsed electric fields for the inactivation of indicator microorganisms and foodborne pathogens in liquids and raw chicken

This study investigated the ability of pulsed electric fields (PEF) to inactivate a range of microorganisms in liquid media and on raw chicken meat. The susceptibilities of ten Campylobacter isolates (seven Campylobacter jejuni isolates and three Campylobacter coli isolates), Escherichia coli (ATCC 25922) and Salmonella Enteritidis (ATCC 13076) to PEF in liquid media were investigated. All Campylobacter isolates tested in liquid were susceptible to PEF treatment (65 kV/cm, 5 μs, 500 Hz) with reductions of between 4.33 and 7.22 log₁₀ CFU/mL observed for the longest treatment (30 s). Significant differences in susceptibility were observed between Campylobacter isolates subjected to equivalent PEF treatments ranging from 2.41 to 5.19 log₁₀ CFU/mL. Campylobacter isolates processed in liquid media were found to be more sensitive to PEF than E. coli and S. Enteritidis (P < 0.05). The application of PEF (3.75 and 15 kV/cm, 10 μs, 5 Hz) to inoculated samples of raw chicken did not result in any significant reductions in total viable counts, Enterobacteriaceae, C. jejuni, E. coli or S. Enteritidis. Therefore, under the conditions used in this study, PEF technology may not be suitable as a food safety intervention measure for the control of microbial contaminants on broilers during processing although it may have potential to reduce contamination of process water (e.g. scald or spin chill water).     

Quantitative detection of viable foodborne E. coli O157:H7, Listeria monocytogenes and Salmonella in fresh-cut vegetables combining propidium monoazide and real-time PCR

The increase of foodborne outbreaks associated with fresh vegetables has highlighted the importance of developing rapid and specific methods for the detection and quantification of foodborne pathogens. In this sense, real-time PCR (qPCR) fulfills these requirements although it may detect dead cells. Recently, a potential strategy to specifically detect viable cells has been proposed relying on the use of DNA binding molecules as sample pretreatment previous to the qPCR. In this study propidium monoazide (PMA) and reagent D, combined with qPCR, were evaluated for the detection and quantification of viable Escherichia coli O157:H7, Salmonella and Listeria monocytogenes. Initially, the optimal concentration of both reagents was determined for discrimination between viable and dead bacteria in cell suspensions. Although both reagents showed similar reductions for the three pathogens, reagent D was toxic to L. monocytogenes and Salmonella and therefore only PMA was used to evaluate the applicability of this technique on food samples. A final concentration of 50 μM PMA was assayed in artificially inoculated spinach and mixed salad. PMA-qPCR signal was negative for all dead cell concentrations tested except for mixed salad inoculated with L. monocytogenes at the highest concentration. These results demonstrate that PMA-qPCR is a suitable technique for the detection and quantification of viable pathogens in fresh-cut vegetables at the levels normally found in vegetable samples.     

Inactivation of Escherichia coli O157:H7 and spoilage yeasts in germicidal UV-C-irradiated and heat-treated clear apple juice

The decimal reduction times (D) of individual and composited Escherichia coli O157:H7 or spoilage yeasts in UV-C irradiated and heated (55 °C) clear apple juices (pH 3.68, 12.5 °Brix) were determined. Spoilage yeasts (D = 6.38-11.04 min) were found to be generally more UV-C resistant than E. coli O157:H7 (D = 0.5-2.76 min), while the opposite was observed in terms of thermal resistance (E. coli D=0.9-4.43 min; yeast D = 0.03-6.10 min). All spoilage yeast proliferated in the untreated juice (25 °C) while all E. coli strains were inactivated. Except for E. coli O157:H7 in UV-C irradiated apple juice, the composited inocula of both pathogenic and spoilage test organisms were less tolerant than the identified most resistant strain or species. The results of this study may be used in identifying appropriate target organisms, as well as the modes of inoculation, in challenge studies and eventually in the establishment and validation of process lethalities for apple juices and similar commodities.     

Prediction of Escherichia coli O157:H7 adhesion and potential to form biofilm under experimental conditions

Escherichia coli O:157:H7 adhesion and potential to form biofilm on three different surfaces commonly used in the food industry was evaluated using probabilistic models; the surfaces tested were stainless steel 304 (SS304), poly(vinyl chloride) film covered with thick cloth (PVC1) and poly(vinyl chloride) film covered with thin cloth (PVC2). Using a Central Composite Rotational Design (CCRD), the effect of contact time (0 h, 7 h, 24 h, 41 h and 48 h) and temperature (12 °C, 17 °C, 28 °C, 39 °C and 44 °C) on the probability of achieving a particular adherent cell count (Log₁₀ CFU cm⁻²) was determined. By analyzing response surface plots and their corresponding contour plots and by determining quadratic equations for each surface, experimental values were shown to be significant in accordance with predicted values in all cases. The adjusted determination coefficient (R_adj²) was 90.5%, 97.2% and 98.9% for SS304, PVC1 and PVC2, respectively, and the level of significance was P ≤ 0.001. The bias factor (B_f) and accuracy factor (A_f) both approached 1.0 for the three surfaces evaluated. The model equations for predicting optimum response values were verified effectively by a validation data set for all surfaces evaluated. Therefore, an RSM provides a useful and accurate method for predicting E. coli O157:H7 adhesion and potential to form biofilm on SS304, PVC1 and PVC2 and could be considered to be a standard way to ensure food safety with respect to E. coli O157:H7 contamination through adhesion and biofilm formation.     

Seasonal prevalence of Vibrio species in retail shrimps with an emphasis on Vibrio parahaemolyticus

Seasonal prevalence of Vibrio species in shrimp samples from retail outlets in the South-western part of Iran was studied. A total of 300 samples were analyzed (75 samples in each season). Special attention was paid to the prevalence of total and pathogenic Vibrio parahaemolyticus. All the TCBS isolates were first identified to the genus level with PCR and then identified to the species level using a battery of biochemical reactions and tests. To investigate the pathogenicity of the isolated V. parahaemolyticus, multiplex PCR (tl, tdh and trh genes) was performed. Vibrios were detected during the whole investigation period, depending on the sampling season. They were detected in 18.6% of the winter samples, 64% of the spring samples, 70.6% of the summer samples and 41.3% of the autumn samples. Vibrio calviensis and Vibrio alginolyticus were dominant in samples of different seasons, with the average prevalence of 18.6% and 17.6%, respectively. V. parahaemolyticus was found in 4.0% of the winter samples, 13.3% of the spring samples, 18.6% of the summer samples and 8% of the autumn samples. During the period of this study, two tdh-positive strains were isolated, while no trh-positive V. parahaemolyticus strain was detected in samples of different seasons.     

Resistances to UV-C irradiation of Salmonella Typhimurium and Staphylococcus aureus in wet and dried suspensions on surface with egg residues

To clarify the effects of food sediments on ultraviolet-C (254 nm) sanitation in food-related environments, we examined the resistance of pathogenic bacteria (Salmonella Typhimurium and Staphylococcus aureus) cells, in wet and dried suspensions adhered with 1.5-15% w/v egg albumen, 1.5-15% yolk or 3.0-30% whole egg solutions, against UV-C irradiation. Bacterial suspensions (0.1 ml of 8 log CFU/ml) were put on 47 mmφ glass dishes and dried at room temperature (20-24 °C) for 180 min in a bio safety cabinet with ventilation. Viable S. Typhimurium and S. aureus cells in distilled water decreased during the drying period from 7.2 to 3.2 and from 8.0 to 6.5 log CFU/dish, respectively,. On the other hand, the bacteria cells were protected from drying by egg compounds, even by the lowest concentration. The UV-C treatment (0.16 mW/cm² for 10 min) showed a clear bactericidal effect in the absence of egg compounds. However, the bactericidal effect was inhibited by 15% yolk and 30% whole egg. Results in this study suggested that the small food sediment protect bacteria on the surfaces from dryness and UV-C irradiation and it might introduce cross contamination.     

Anti-listeria activity of Pediococcus pentosaceus BCC 3772 and application as starter culture for Nham, a traditional fermented pork sausage

Lactic acid bacteria forming bacteriocin active against Listeria monocytogenes were screened for potential use in controlling growth of L. monocytogenes in Nham, a Thai traditional fermented pork sausage. Based on the spot-on-lawn assay, Pediococcus pentosaceus BCC 3772 was found to produce the highest anti-listeria activity. Through a series of chromatographic techniques, Edman N-terminal sequencing and mass spectrometry, this anti-listeria compound showed a complete homology to pediocin PA-1/AcH. Inoculation of P. pentosaceus BCC 3772 in Nham caused a significant decrease of 3.2 log in population of spiked L. monocytogenes within 18-24 h of fermentation, in comparison with the initial count with no significant changes in sensory properties and consumer acceptability on the overall characteristics of the final fermented Nham products. These results indicate that the P. pentosaceus BCC 3772 should be useful as a functional starter culture for control of L. monocytogenes without compromising the unique quality of Nham.     

Characterization of a novel bacteriocin produced by Lactobacillus sakei LSJ618 isolated from traditional Chinese fermented radish

A novel bacteriocin, sakacin LSJ618, produced by the strain Lactobacillus sakei LSJ618 isolated from traditional Chinese fermented radish, was studied. L. sakei LSJ618 was identified by both phenotypical and physiological tests combined with 16S rDNA sequence analysis. Sakacin LSJ618 is sensitive to hydrolytic enzymes including lipase, is stable between pH 2-8, and is heat resistant (30 min at 121 °C). Sakacin LSJ618 exhibits inhibitory activity against food-spoiling bacteria and food-borne pathogens, including the Gram-positive Listeria monocytogenes, Staphylococcus aureus, Sarcina sp., Micrococcus luteus, and the Gram-negative Proteus sp. and Escherichia coli, but not against most of the lactic acid bacteria tested. Maximal production of bacteriocin was reached in the late stationary phase, and inhibitory activity declined within 26 h. The mode of action of sakacin LSJ618 was determined to be bactericidal, as evidenced by its action upon Micrococcus tetragenus. After partial purification by ammonium sulfate precipitation and Sephadex G-25 chromatography, the molecular weight of sakacin LSJ618 was determined to be 5.2 kDa by Tricine-SDS-PAGE. The identified properties of sakacin LSJ618 indicate that it is a novel bacteriocin with potential application as a biopreservative in the food industry.     

Real-time PCR with internal amplification control for the detection of Cronobacter spp. (Enterobacter sakazakii) in food samples

Cronobacter spp. (Enterobacter sakazakii) is an opportunistic pathogen and is linked with life-threatening infections in neonates. The organism has been isolated from a wide variety of foods and environments. In this study, a Taqman real-time PCR assay incorporating an internal amplification control (IAC) was developed and evaluated for specific detection of Cronobacter spp. in foods. Previously reported macromolecular synthesis (MMS) operon sequence was selected for specificity, and 67 bacterial strains, including four strains of Cronobacter spp., were evaluated. All Cronobacter strains were successfully identified, however no cross-reactivity was observed with non-Cronobacter strains. Detection limit of the assay in pure culture and formula infant without enrichment was 1.2 × 10³ CFU/ml (1.2 × 10¹ CFU/assay). After 24 h enrichment in broth, as few as 10⁰ CFU/ml or g of Cronobacter could be detected in artificially contaminated food samples (infant formula, sterilized milk and chicken meat). The detection limit of the real-time PCR assay however remained unaffected in the presence of 10⁸ CFU/ml Salmonella typhimurium in another analysis. A total of 92 food samples were analyzed for the presence of Cronobacter, out of which two pork samples were found as positive by real-time PCR, whereas only one was detected by the ISO standard method. The adjusted real-time PCR assay can be adopted to rapidly detect Cronobacter spp. in food samples with high specificity and sensitivity, and can prevent false negative results by using the IAC.     

Identification of the wedge clam Donax trunculus by a simple PCR technique

The wedge clam Donax trunculus is an important bivalve commercial species in Portugal which can be easily mistaken with other three morphologically similar species (Donax semistriatus, Donax vittatus and Donax variegatus) that have a lower market price. This may lead fish sellers to make false claims about the authenticity of their products in order to get higher profits. To overcome this problem it is important to develop analytical techniques that can be used to test the authenticity of the species that is being sold. In this study we present two DNA extraction methodologies and a simple PCR method for the accurate identification of D. trunculus based on the amplification of the nuclear marker 5S rDNA. The PCR amplification results showed that this method is reliable to differentiate D. trunculus and D. variegatus from the remaining Donax species, since fragments of D. trunculus were about 275-300bp while D. variegatus were about ∼450 bp a little lower molecular weight than DNA fragments of the other two species (∼500 bp).     

Pesticide residues in Brassica vegetables and exposure assessment of consumers

The presence of pesticide residues in Brassica vegetables (365 samples) produced in north-eastern Poland (2006-2009) was determined and their health risks assessed. The analytical procedure was developed to examine of 130 pesticides of different chemical classes (chloroorganic, phosphoroorganic, carbamates, strobilurines, neonicotinoids, amides, pyrimidines, benzimidazoles, imidazoles and triazoles) in broccoli, Brussels sprouts, cauliflower, head and Chinese cabbage. Pesticides were extracted using matrix solid phase dispersion (MSPD) and analyzed by gas chromatography (GC) with dual detection system: electron capture (ECD) and nitrogen-phosphorus (NPD). Linearity (R² ≥ 0.997) was good over the concentration range from 2.5 to 0.001 mg/kg for all the pesticides, and instrumental detection limits ranged from 0.001 to 0.01 mg/kg. Mean recoveries for vegetables spiked at three fortification levels (0.001-2.5 mg/kg) ranged from 70.07 to 118.90%. Relative standard deviations ranged from 0.15 to 8.58%, except: dicofol, pyridaben (acaricides), dichloran (fungicide), isofenphos, triasophos (insecticides) where mean recoveries were above 120% (122.2-127%) and also dichlofluanid, tecnazene (fungicides), dichlobenil (herbicide), endosulfan-sulfate, phorate, phosmet (insecticides) with mean recoveries below 70% (42.83-69.1%). The method used to monitor pesticide residues in vegetables. Fifteen different pesticides (insecticides mainly) were detected in 118 samples (32%), while multiple pesticides (more than one pesticide residue) in about 4% samples. Chlorpyrifos and cypermethrin were the most commonly detected pesticides. Chlorpyrifos was present in 27.4% items and ranged from 0.005 to 1.51 mg/kg, while cypermethrin were detected in 3.3% samples and ranged from 0.02 to 0.19 mg/kg. Thirty-three (9%) samples exceeded the maximum residue levels (MRLs). The dietary intake of residues of some pesticides can pose acute hazards. Data obtained were then used for estimating the potential health risks associated with the exposures to these pesticides. The estimated daily intakes (EDIs) ranged from 0.005% of the ADI (acceptable daily intake) for fenhexamid to 4.454% of the ADI for diazinon. Combine cumulative exposure for chlorpyrifos detected on Brassica were 0.777% of ADI. The results show that occurrence of pesticide residues in Brassica vegetables from this region could not be considered a serious public health problem. Nevertheless, an investigation into continuous monitoring and tighter regulation of pesticide residues in vegetables is recommended.     

Inactivation of Listeria innocua in brined white cheese by a combination of nisin and heat

The objective of this study was to investigate the effect of nisin alone and in combination with heat (63 °C/5 min) on the inactivation of Listeria innocua in white cheese. Nisin was added at different concentrations (500, 1000, and 1500 IU ml⁻¹) to pasteurized milk before curd formation. The curd was soaked for 24 h in 10% solution of brine containing ca 10⁶ CFU ml⁻¹ of a cocktail mixture of three strains of L. innocua. Part of the nisin treated samples were heat treated at 63 °C/5 min. Total mesophilic count (TMC), L. innocua survivors and changes in the pH of white cheese were monitored each 2 d for a period of 12 d of storage at 4 or 10 °C. Nisin at 500 IU ml⁻¹ did not diminish TMC in white cheese compared to the control. The combination of heat and nisin (1000 or 1500 IU ml⁻¹) exhibited a bacteriostatic effect on TMC throughout the storage period at 4 or 10 °C. Nisin at 500 IU ml⁻¹ had a marginal inhibitory activity against L. innocua. However, nisin at 1000 and 1500 IU ml⁻¹l resulted in a more than 2 log₁₀ reduction in L. innocua count and the effect was more prominent at 10 °C. In comparison, the combination of nisin (1000 or1500 IU ml⁻¹) and heat treatment exhibited a synergistic inhibitory activity against L. innocua, where a complete elimination of the organism was accrued after 6 and 8 d of storage at 10 and 4 °C. Therefore, nisin and heat combination could be used as a prudent hurdle to preclude the growth of Listeria in white cheese, especially under the condition of abused refrigeration conditions.