Prevalence,molecular characterization,and antimicrobial resistance profiles of Listeria monocytogenes,Salmonella enterica,and Escherichia coli O157:H7 on dairy cattle farms in Jordan

This study determined the prevalence, pulsed-field gel electrophoresis profiles, and antimicrobial resistance profile of Listeria monocytogenes, Salmonella enterica, and Escherichia coli O157:H7 isolates from dairy cattle farms in Jordan. Samples from bulk tank milk (n = 305), cattle feces (n = 610), and rectoanal mucosal swabs (n = 610) were collected from 61 dairy cattle farms. We confirmed 32 L. monocytogenes, 28 S. enterica, and 24 E. coli O157:H7 isolates from the samples. The farm-level prevalence (at least 1 positive sample per farm) of L. monocytogenes, S. enterica, and E. coli O157:H7 was 27.9, 19.7, and 23.0%, respectively. The prevalence of L. monocytogenes, S. enterica, and E. coli O157:H7 in bulk tank milk was 7.5, 1.6, and 3.3%, respectively. The prevalence of L. monocytogenes and S. enterica in fecal samples was 1.5 and 3.8%, respectively, and the prevalence of E. coli O157:H7 in rectoanal mucosal swabs was 2.3%. Based on disk diffusion testing, all L. monocytogenes, S. enterica, and E. coli O157:H7 isolates exhibited resistance to at least 1 antimicrobial class. Multidrug resistance (resistance to 3 or more classes of antimicrobials) was exhibited by 96.9% of L. monocytogenes, 91.7% of E. coli O157:H7, and 82.1% of S. enterica isolates. Moreover, 93.8, 79.2, and 57.1% of the L. monocytogenes, E. coli O157:H7, and S. enterica isolates, respectively, were resistant to 5 or more antimicrobial classes. More than 50% of L. monocytogenes isolates were resistant to ampicillin, clindamycin, penicillin, erythromycin, quinupristin–dalfopristin, streptomycin, teicoplanin, linezolid, vancomycin, kanamycin, and tetracycline. More than 50% of S. enterica and E. coli O157:H7 isolates were resistant to ampicillin, cephalothin, nalidixic acid, kanamycin, streptomycin, amoxicillin–clavulanic acid, and tetracycline. The prevalence of the studied pathogens this study was comparable to reports from other countries. The isolated pathogens exhibited a high degree of antimicrobial resistance, suggesting that the bacterial flora of dairy cattle in Jordan are under intense antimicrobial selection pressure. Additional research is required to determine the causes and drivers of resistance, and to develop approaches to mitigating antimicrobial resistance.     

The fate of Escherichia coli O157 : H7 in Myzithra,Anthotyros, and Manouri whey cheeses during storage at 2 and 12°C

Myzithra, Anthotyros and Manouri whey cheeses were inoculated the day after production withEscherichia coli O157 : H7 at concentrations of approx. 1·8×10⁶cfu g⁻¹, and stored at 2 and 12°C for 30 and 20 days, respectively. The pH of the whey cheeses decreased from an initial value of approx. 6·20 to 5·83 or 5·60 (Myzithra) 5·75 or 5·20 (Anthotyros) and 5·80 or 5·30 (Manouri) by the end of the corresponding storage periods at 2 and 12°C, respectively. Escherichia coli O157 : H7 populations in the whey cheeses at the end of the 12°C storage period, had grown with an increase of approx. 1·3 log₁₀cfu g⁻¹. E. coli O157 : H7 populations in whey cheeses at the end of the 2°C storage period did not grow and decreased, with an approx. 2·5 log₁₀cfu g⁻¹reduction. Results showed that E. coli O157 : H7 can grow at 12°C and survive at 2°C storage in Myzithra, Anthotyros and Manouri whey cheeses, and therefore post-manufacturing contamination with this pathogen must be avoided by employing hygienic control programmes such as HACCP.     

Recovery of heat-stressed E. coli O157:H7 from ground beef and survival of E. coli O157:H7 in refrigerated and frozen ground beef and in fermented sausage kept at 7°C and 22°C

A study was undertaken to obtain information on survival of Escherichia coli O157:H7 in ground beef subjected to heat treatment, refrigeration and freezing and on survival of E. coli O157:H7 in fermented sausage kept at 7°C and 22°C. For the challenge test, a mixture of E. coli O157:H7 strains (EH 321, EH 385, EH 302) was used and enumeration was performed on an isolation medium suitable for recovery of stressed organisms: modified Levine's eosin methylene blue agar (mEMB). Heat resistance of E. coli O157:H7 decreased after pre-incubation at a reduced temperature.Escherichia coli O157:H7 was more susceptible to heat inactivation after storage at 7°C and die-off was even more enhanced if cultures were frozen prior to heat inactivation. The enhanced reduction of the pathogen at 56°C after prior storage under refrigeration was confirmed in a test with inoculated ground beef.Escherichia coli O157:H7 was able to survive in ground beef at 7°C for 11 days and at −18°C for 35 days showing maximal one log reduction during the storage period. Thus, ground beef contaminated with E. coli O157:H7 will remain a hazard even if the ground beef is held at low or freezing temperatures. At both 7°C and 22°C, a gradual reduction of E. coli O157:H7 was noticed in fermented sausage over the 35 days storage period resulting in a 2 log decrease of the high inoculum (10⁶cfu 25 g⁻¹). For the low inoculum (10³cfu 25 g⁻¹) a 2·5 log reduction was obtained in 7 and 28 days storage at respectively 22 and 7°C. Application of good hygienic practices and implementation of HACCP in the beef industry are important tools in the control of E. coli O157:H7.     

Survival of Listeria monocytogenes introduced as a post-aging contaminant during storage of low-salt Cheddar cheese at 4, 10, and 21°C

Traditional aged Cheddar cheese does not support Listeria monocytogenes growth and, in fact, gradual inactivation of the organism occurs during storage due to intrinsic characteristics of Cheddar cheese, such as presence of starter cultures, salt content, and acidity. However, consuming high-salt (sodium) levels is a health concern and the dairy industry is responding by creating reduced-salt cheeses. The microbiological stability of low-salt cheese has not been well documented. This study examined the survival of L. monocytogenes in low-salt compared with regular-salt Cheddar cheese at 2 pH levels stored at 4, 10, and 21°C. Cheddar cheeses were formulated at 0.7% and 1.8% NaCl (wt/wt) with both low and high pH and aged for 10 wk, resulting in 4 treatments: 0.7% NaCl and pH 5.1 (low salt and low pH); 0.7% NaCl and pH 5.5 (low salt and high pH); 1.8% NaCl and pH 5.8 (standard salt and high pH); and 1.8% NaCl and pH 5.3 (standard salt and low pH). Each treatment was comminuted and inoculated with a 5-strain cocktail of L. monocytogenes at a target level of 3.5 log cfu/g, then divided and incubated at 4, 10, and 21°C. Survival or growth of L. monocytogenes was monitored for up to 90, 90, and 30 d, respectively. Listeria monocytogenes decreased by 0.14 to 1.48 log cfu/g in all treatments. At the end of incubation at a given temperature, no significant difference existed in L. monocytogenes survival between the low and standard salt treatments at either low or high pH. Listeria monocytogenes counts decreased gradually regardless of a continuous increase in pH (end pH of 5.3 to 6.9) of low-salt treatments at all study temperatures. This study demonstrated that post-aging inoculation of L. monocytogenes into low-salt (0.7%, wt/wt) Cheddar cheeses at an initial pH of 5.1 to 5.5 does not support growth at 4, 10, and 21°C up to 90, 90, and 30 d, respectively. As none of the treatments demonstrated more than a 1.5 log reduction in L. monocytogenes counts, the need for good sanitation practices to prevent post-manufacturing cross contamination remains.     

Activity of citrus essential oils against Escherichia coli O157:H7 and Salmonella spp. and effects on beef subprimal cuts under refrigeration

Abstract: Escherichia coli O157:H7 and Salmonella spp. are bacterial pathogens often associated with beef, and cause many cases of foodborne illness each year in the United States. During beef slaughter and processing, these bacteria may spread from the hide or intestines to the carcass. The objective of this research was to investigate the use of naturally occurring compounds citrus essential oils (CEOs) extracted from orange peel to reduce or eliminate these pathogens at the chilling stage of processing, or during fabrication. Brisket flats (used to simulate beef subprimals) were spot inoculated with approximately 6 log of surrogate generic E. coli cocktail (previously shown to be identical in growth and survival parameters to E. coli O157:H7 and Salmonella spp.). Following drying, CEOs were applied by spraying at concentrations of 3% and 6% to the surface of different pieces of meat. Treatments were applied using a custom built spray cabinet at 2.07 bar and applied at a rate of 3.79 L/min to replicate commercial practices. The CEOs significantly reduced (P < 0.05) the concentration of E. coli on the brisket flats in comparison to inoculated no spray or water sprayed controls over a period of 90 d, while causing an initial reduction of approximately 1.4 log units. Total aerobic bacteria and psychrotrophic counts were also reduced on uninoculated briskets following treatment. These results indicate that 3% cold‐pressed terpeneless Valencia orange oil could be used as an additional intervention against E. coli O157:H7 and Salmonella spp. at the refrigerated storage stage of processing. Practical Application: CEOs are natural compounds that have been designated as Generally Recognized as Safe (GRAS). They can be used to control Salmonella spp. and E. coli O157:H7 on beef carcasses at the chilling stage.     

Effects of nisin, EDTA and salts of organic acids on Listeria monocytogenes, Salmonella and native microflora on fresh vacuum packaged shrimps stored at 4 °C

Nisin (500 IU ml⁻¹), EDTA (0.02 M), potassium sorbate (PS) (3%, w/v), sodium benzoate (SB) (3%, w/v) or sodium diacetate (SD) (3%, w/v); alone or in combination were used to dip uninoculated shrimps and shrimps inoculated with Listeria monocytogenes or Salmonella (∼4.0–5.0 log CFU g⁻¹). Shrimps were then drip-dried, vacuum packaged and stored at 4 °C for 7 days. Untreated shrimps were used as a control. Numbers of L. monocytogenes, Salmonella and native background microflora were determined on uninoculated and inoculated shrimps on days 0, 3 and 7. Nisin–EDTA–PS and nisin–EDTA–SD significantly reduced (p < 0.05) L. monocytogenes numbers by 1.07–1.27 and 1.32–1.36 log CFU g⁻¹, respectively, on day 0 and 3. However, all treatments failed to significantly reduce (p > 0.05) Salmonella counts on shrimps throughout storage. On day 7, numbers of aerobic bacteria, psychrotrophic bacteria and Pseudomonas on combined nisin–EDTA–salt of organic acids treated shrimps were significantly lower (p < 0.05) by 4.40–4.60, 3.50–4.01, and 3.84–3.99 log CFU g⁻¹ respectively, as compared to the control. Dipping in organic acids solutions followed by vacuum packaging and chilled storage can help reduce L. monocytogenes and native microflora, but not Salmonella, on fresh shrimps.     

Metabolomes of the psychrotolerant bacterium Listeria monocytogenes 10403S grown at 37 °C and 8 °C

Listeria monocytogenes is a food-borne pathogen with the ability to grow at refrigeration temperatures. Knowledge of the mechanisms involved in low temperature growth is incomplete and here we report the results of a metabolomics investigation of this. The small molecule contents of L. monocytogenes 10403S grown at 37 °C and 8 °C were compared by gas chromatography/mass spectrometry (GC/MS). Over 500 peaks were detected in both 37 °C and 8 °C-grown cells, and 103 were identified. Of the identified metabolites, the concentrations of 56 metabolites were increased (P < 0.05), while the concentrations of 8 metabolites were decreased at low temperature. Metabolites increasing in concentration at 8 °C included amino acids, sugars, organic acids, urea cycle intermediates, polyamines, and different compatible solutes. A principal component analysis (PCA) was used to visualize and compare the matrix containing the data in 6 samples, and this clearly identified the 37 °C and 8 °C metabolomes as different. The results indicated that an increase in solute concentrations in the cytoplasm was associated with low temperature adaptation, which may be a response to chill stress with the effect of lowering the freezing point of intracellular water and decreasing ice crystal formation.     

Field study on the microbiological quality of pickles in brine and survival of Salmonella Typhimurium and Listeria monocytogenes during storage at 4 °C

The aim of this study was to assess the microbiological quality and the ability of Listeria monocytogenes and Salmonella enterica serovar Typhimurium strains to survive during storage at 4 °C of all available brand names of brined pickles and some in-bulk ones, in the district of Athens. None of the samples could be characterized as heavily contaminated. The microbial populations detected could be due to inadequacy of packaging, regarding the ones available in-bulk and improper thermal treatment in the case of the canned ones. Moreover, the ability of both pathogens to survive for 5 days at 4 °C, in some products, has been exhibited.     

Viability of Listeria monocytogenes on commercially-prepared hams surface treated with acidic calcium sulfate and lauric arginate and stored at 4°C

We demonstrated the effectiveness of delivering an antimicrobial purge/fluid into shrink-wrap bags immediately prior to introducing the product and vacuum sealing, namely the “Sprayed Lethality In Container” (SLIC™) intervention delivery method. The pathogen was Listeria monocytogenes, the antimicrobials were acidic calcium sulfate (ACS; calcium sulfate plus lactic acid; 1:1 or 1:2 in dH₂O) and lauric arginate (LAE; Ethyl-N-dodecanoyl-l-arginate hydrochloride; 5% or 10% in dH₂O), and the product was commercially prepared “table brown” ham (ca. 3 pounds each). Hams were surface inoculated with a five-strain cocktail of L. monocytogenes (ca. 7.0 log₁₀ CFU per ham), added to shrink-wrap bags that already contained ACS or LAE, vacuum-sealed, and stored at 4 °C for 24 h. Pathogen levels decreased by 1.2, 1.6, 2.4, and 3.1 log₁₀ CFU/ham and 0.7, 1.6, 2.2, and 2.6 log₁₀ CFU/ham in samples treated with 2, 4, 6, and 8 mL of a 1:1 and 1:2 solution of ACS, respectively. In samples treated with 2, 4, 6, and 8 mL of a 5% solution of LAE, pathogen levels decreased by 3.3, 6.5, 5.6, and 6.5 log₁₀ CFU/ham, whereas when treated with a 10% solution of LAE pathogen levels decreased ca. 6.5 log₁₀ CFU/ham for all application volumes tested. The efficacy of ACS and LAE were further evaluated in shelf-life studies wherein hams were surface inoculated with either ca. 3.0 or 7.0 log₁₀ CFU of L. monocytogenes, added to shrink-wrap bags that contained 0, 4, 6, or 8 mL of either a 1:2 solution of ACS or a 5% solution of LAE, vacuum-sealed, and stored at 4 °C for 60 days. For hams inoculated with 7.0 log₁₀ CFU, L. monocytogenes levels decreased by ca.1.2, 1.5, and 2.0 log₁₀ CFU/ham and 5.1, 5.4, and 5.5 log₁₀ CFU/ham within 24 h at 4 °C in samples treated with 4, 6, and 8 mL of a 1:2 solution of ACS and a 5% solution of LAE, respectively, compared to control hams that were not treated with either antimicrobial. Thereafter, pathogen levels remained relatively unchanged (±1.0 log₁₀ CFU/ham ) after 60 days at 4 °C in hams treated with 4, 6, and 8 mL of a 1:2 solution of ACS and increased by ca. 2.0–5.0 log₁₀ CFU/ham in samples treated with 4, 6, and 8 mL of a 5% solution of LAE. For hams inoculated with 3.0 log₁₀ CFU, L. monocytogenes levels decreased by 1.3, 1.9, and 1.8 log₁₀ CFU/ham within 24 h at 4 °C in samples treated with 4, 6, and 8 mL of a 1:2 solution of ACS, respectively, compared to control hams that were not treated. Likewise, levels of the pathogen were reduced to below the limit of detection (i.e., 1.48 log₁₀ CFU/ham) in the presence of 4, 6, and 8 mL of a 5% solution of LAE within 24 h at 4 °C. After 60 days at 4 °C, pathogen levels remained relatively unchanged (±0.3 log₁₀ CFU/ham) in hams treated with 4, 6, and 8 mL of a 1:2 solution of ACS. However, levels of L. monocytogenes increased by ca. 2.0 log₁₀ CFU/ham in samples treated with 4 and 6 mL of a 5% LAE solution within 60 days but remained below the detection limit on samples treated with 8 mL of this antimicrobial. These data confirmed that application via SLIC™ of both ACS and LAE, at the concentrations and volumes used in this study, appreciably reduced levels of L. monocytogenes on the surface of hams within 24 h at 4 °C and showed potential for controlling outgrowth of the pathogen over 60 days of refrigerated storage.     

Survival of Salmonella Typhimurium and Escherichia coli O157:H7 on blueberries and impacts on berry quality during 12 weeks of frozen storage after washing with combinations of sodium dodecyl sulfate and organic acids or hydrogen peroxide

Salmonella spp. and Escherichia coli are well tolerant of freezing. This study was to investigate survival of the foodborne pathogens during storage at −18 ± 2°C for 12 weeks on blueberries after washing with: 500 ppm acetic acid plus 5,000 ppm sodium dodecyl sulfate (SDS) (AA/SDS), 20 ppm peroxyacetic acid plus 5,000 ppm SDS (PPA/SDS), or 200 ppm hydrogen peroxide plus 5,000 ppm SDS (H₂O₂/SDS), when compared with findings from no wash, or wash with water, 80 ppm PPA or 200 ppm chlorinated water. Following a 60 s contact with one of the three new solutions, the treatments showed 3.3–3.9 log₁₀ CFU/g reductions in Salmonella Typhimurium and E. coli O157:H7 counts. After 2 weeks of frozen storage, 3.9–4.2 log₁₀ CFU/g reductions of Salmonella and E. coli were observed. After 12 weeks of frozen storage, Salmonella and E. coli survivors were below detection limits (0.39 log₁₀ CFU/g) in berries washed with new solutions. The frozen storage had a significant impact (p < .05) on microbial counts of both treated and nontreated blueberries. Although none of these washings decreased the total phenolic and anthocyanins contents and apparent quality at time 0, frozen storage caused significant damage on the texture of both treated and nontreated blueberries. Interestingly, no significant decrease in the total phenolic, anthocyanins content, and apparent quality was observed during the 12-week frozen storage. The counts of total bacteria, yeasts, and molds decreased throughout storage for treated and untreated berries. This demonstrates that the three wash solutions enhance the safety of frozen berries.     

The effect of calcinated calcium and chlorine treatments on Escherichia coli O157:H7 87-23 population reduction in radish sprouts

Abstract: The effect of calcinated calcium spray on Escherichia coli O157:H7 87–23 population reduction during radish sprout production was studied. Artificially inoculated radish seeds were soaked in sodium hypochlorite (NaOCl) solutions (200 and 20000 ppm), rinsed in distilled water, and sprayed with water or a calcinated calcium solution during sprouting. Microbial plate count was obtained at each step of the process and germination rate was determined after 72 h of sprouting. Scanning electron microscopy (SEM) was done on treated seeds and sprouts to locate which parts were populated by the E. coli cells. The results showed that the active compound in the calcinated calcium was calcium oxide. The treatment of 200 ppm NaOCl soaking followed by 0.04% calcinated calcium spray resulted in no microbial growth after a 72‐h sprouting, while maintaining a high germination rate. The 0.4% calcinated calcium spray significantly reduced the germination rate and is therefore not recommended. Soaking the seeds in a 20000 ppm chlorine solution achieved the highest E. coli count reduction (1.65 log CFU/g). However, the E. coli cells that survived the 20000 ppm chlorine soak grew to 6 log CFU/g sprouts after a 72‐h sprouting, significantly higher than the initial count on the seeds. The SEM microimages showed that the bacteria were mostly located in the roots of the radish sprouts and all across the seed surface. The E. coli O157:H7 87–23 cells appeared to be located in biofilms or embedded into the radish sprout tissues during sprouting. Practical Application: The seed sanitation treatment with 20000 ppm chlorine solution that is currently used by the sprout industry was once again found to be ineffective in eliminating inoculated pathogenic cells. More importantly, the remaining cells that have survived the chlorine wash would grow during sprouting to reach an alarmingly high cell concentration. The new observation of E. coli cells and sprout tissue interaction manifested as embedding of the cells in sprout tissues, if confirmed, will have a significant impact on the microbial safety intervention strategies used in the sprout industry. This research demonstrated the importance of eliminating all pathogens on the seeds before germination and sprouting.     

Acid resistance and verocytotoxin productivity of enterohemorrhagic Escherichia coli O157:H7 exposed to microwave

Abstract: We examined the acid resistance and verocytotoxin (VT) productivity of enterohemorrhagic Escherichia coli O157:H7 irradiated by microwave with a domestic microwave oven and a commercial microwave radiator equipped with a thermo‐regulator. When the cell suspension (5 mL) chilled at 0 °C was treated with a domestic microwave oven at weak power (2.45 GHz, 100 W) for 60 s, the living cell number was reduced by 2 orders (final temperature, about 65 °C). The surviving cells showed lower acid resistance and VT productivity than nonirradiated cells. To examine the nonthermal effect of microwave on acid resistance and VT productivity, the cells in Luria‐Bertani medium were intermittently irradiated to keep the culture temperature at 37 °C with the microwave radiator (2.45 GHz, 0.6 W/mL). The intermittent radiation slightly reduced the acid resistance, but clearly suppressed the VT productivity. Microwave oven is probably useful for reducing not only the living cell number but also the acid resistance and VT productivity of EHEC O157:H7.     

Effect of Eryngium caeruleum essential oil on microbial and sensory quality of minced fish and fate of Listeria monocytogenes during the storage at 4°C

The present study investigated in vitro antimicrobial activity of Eryngium caeruleum essential oil (EEO) against five foodborne pathogenic bacteria based on microdilution and disk diffusion methods. Moreover, its effects on specific spoilage microorganisms, inoculated Listeria monocytogenes, and its sensory changes in minced fish were evaluated during 12 days of storage at refrigeration temperature. The results showed that Staphylococcus aureus and Escherichia coli were the most sensitive and the most resistant bacteria with a minimum inhibitory concentration of 0.125 and 1 mg/ml, as well as inhibition zones of 15.66 and 11.66 mm, respectively. Regarding the antimicrobial effect of EEO on the microbial profile and inoculated L. monocytogenes, treating with 0.4% EEO caused a significant decrease in the studied microorganisms when compared to the control group (p < 0.05). In addition, considering the sensory evaluation, the best scores were observed for the samples treated with 0.2% and 0.4% EEO. However, none of the groups obtained acceptable scores until the final day of storage except for the color attribute. In general, sensory evaluation and its correlation with microbial counting indicated that the treatment with 0.4% EEO was able to preserve the microbial quality of the minced fish at refrigeration temperature without any undesirable sensory effects.     

Escherichia coli O157:H7动态生长反响应面方程的扩展

以反应响应面方程分析Escherichia coli动态生长数据,并建立数学模型描述培养温度、初始pH值以及NaCl浓度对大肠杆菌的需氧、厌氧生长的影响.主要探讨通过响应面方程找出环境因素(培养温度、初始pH值以及NaCl浓度)与Escherichia coli生长参数LPD和GT之间的关系,并建立数学模型.     

Survival of Salmonella serovars introduced as a post-aging contaminant during storage of low-salt Cheddar cheese at 4, 10, and 21 °C

The microbiological stability of low-salt cheese has not been well documented. This study examined the survival of Salmonella in low-salt compared to regular salt Cheddar cheese with 2 pH levels. Cheddar cheeses were formulated at 0.7% and 1.8% NaCl (wt/wt) with both low and high-pH and aged for 12 wk resulting in four treatments: 0.7% NaCl and pH 5.1 (low-salt and low-pH); 0.7% NaCl and pH 5.5 (low-salt and high-pH); 1.8% NaCl and pH 5.7 (standard-salt and high-pH); and 1.8% NaCl and pH 5.3 (standard-salt and low-pH). Each treatment was comminuted and inoculated with a 5-serovar cocktail of Salmonella at a target level of 4 log CFU/g, then divided and incubated at 4, 10 and 21 °C for up to 90, 90, and 30 d, respectively. Salmonella counts decreased by 2.8 to 3.9 log CFU/g in all treatments. In the initial period of survival study, standard-salt treatments exhibited significantly lower Salmonella counts compared to low-salt treatments. The pH levels did not exhibit obvious significant effect in the Salmonella survival in low-salt treatments. Salmonella counts declined gradually regardless of a continuous increase in pH (end pH of 5.3 to 5.9) of low-salt treatments at all study temperatures. Salmonella counts were reduced faster at 21 °C storage. Although there were significant reductions in Salmonella counts, the treatments demonstrated survival of Salmonella for up to 90 d when stored at 4 or 10 °C and for up to 30 d at 21 °C, the need for good sanitation practices to prevent postmanufacturing cross contamination remains. PRACTICAL APPLICATION: Low-salt aged Cheddar cheese could not support the growth of inoculated Salmonella and in fact gradual reduction in Salmonella count occurred during storage. Besides being nutritionally better, low or reduced salt Cheddar are safe as their full salt counterparts and that salt may only be a minor food safety hurdle regarding the post-aging contamination and growth of Salmonella. However, the treatments could not demonstrate complete destruction of Salmonella for up to 90 d when stored at 4 or 10 °C and for up to 30 d at 21 °C, the need for good sanitation practices to prevent postmanufacturing cross-contamination remains.     

Activity of smoke wood condensates against Aeromonas hydrophila and Listeria monocytogenes in vacuum-packaged,cold-smoked rainbow trout stored at 4 °C

The antimicrobial effect of four smoke wood condensates against the psychrotrophic pathogensListeria monocytogenes and Aeromonas hydrophila was tested in vacuum-packed cold-smoked rainbow trout (Oncorhynchus mykiss) stored at refrigeration temperature. Salted trout samples were surface inoculated with L. monocytogenes or A. hydrophila, cold smoked, vacuum packaged and stored at 4 °C for 21 days. At different times of storage, samples were taken and analysed for L. monocytogenes and A. hydrophila by quantitative and qualitative procedures. All smoke extracts showed activity against A. hydrophila. However, only smoke extracts L1 and L2 were effective against L. monocytogenes. Although these extracts caused a reduction in viable cell counts of L. monocytogenes below the detectable level by surface plating procedure, this organism was detected by qualitative analysis in most of the samples. Finally, extracts L1 and L2 also reduced total viable cell counts to undetectable levels.     

A detection method of Escherichia coli O157:H7 based on immunomagnetic separation and aptamers-gold nanoparticle probe quenching Rhodamine B’s fluorescence

Food Science and Biotechnology - This research aimed to detect Escherichia coli O157:H7 in milk based on immunomagnetic probe separation technology and quenching effect of gold nanoparticles to...     

Growth of Listeria monocytogenes as a function of dynamic environment at 10°C and accuracy of growth predictions with available models

A combination of a factorial design and two central composite designs was used to assess quantitatively the effects and interactions of water activity (1–0·95) and pH (5·6–9·5) variations on the growth of Listeria monocytogenes in a meat broth at 10°C. At inoculation or at the beginning of the exponential phase, the cells were exposed to the addition of NaCl and acetic acid or NaCl and NaOH. The effects of abrupt fluctuating conditions on the generation and lag times were analysed using turbidity measurements. The data indicated that the cells exposed to osmotic and acid or alkaline variable conditions from the time of inoculation were less affected than cells exposed at the beginning of the exponential phase. In this last case, a lag phase could be induced and the growth recovery was different from those expected in the new environment. Generation time values were estimated by three available predictive models which describe the effects of temperature, salt concentration and pH on L. monocytogenes growth to highlight the potential problems of variable conditions.