Removal of Listeria monocytogenes, Staphylococcus aureus and Escherichia coli O157:H7 biofilms on stainless steel using scallop shell powder

Biofilms on steel surfaces containing Listeria monocytogenes, Staphylococcus aureus and Escherichia coli O157:H7 continue to threaten dairy and meat processors. In this study, the ability of scallop shell powder (SSP) to remove biofilms formed by these three pathogens on stainless steel plates was examined. Whey powder solution (WPS) and bench wash water (BWW) provided by dairy and meat factories, respectively, were inoculated with L. monocytogenes, S. aureus or E. coli O157:H7 (9 log₁₀ CFU/ml). Stainless steel plates (10 cm²) were placed in the inoculated fluids and incubated at 20 °C at 48 h to form biofilms. After drying and washing in sterile water, the plates were treated with 0.0, 0.25, or 0.50% (w/v) SSP slurries for 1, 5, or 10 min and then quantitatively examined for the three pathogens. Both 0.25 and 0.50% SSP reduced L. monocytogenes on the plates by 4 log CFU/cm² with a 1 min exposure to 0.50% SSP decreasing S. aureus by 5 logs CFU/cm². After 1 min in 0.25 and 0.50% SSP, E. coli O157:H7 populations in WPS and BWW biofilms decreased 4 and 6 log CFU/cm² and 3 and 5 log CFU/cm², respectively. Increasing the concentration of SSP led to significantly increased efficacy against the tested pathogens (P < 0.05). In conclusion, this study showed that SSP slurries could significantly reduce the numbers of L. monocytogenes, S. aureus and E. coli O157:H7 in biofilms on stainless steel surfaces.     

Microbiological contamination of sheep carcases in Finland by excision and swabbing sampling

The aims of this study were to provide data on the microbiological contamination of sheep carcases slaughtered in Finland, and to compare excision and swabbing methods for microbiological sampling of sheep carcases. The results were also compared to the requirements laid down in Regulation (EC) No 2073/2005. A number of 50 sheep carcases were sampled both by excision and by swabbing with gauze at four slaughterhouses. The samples were analysed for total viable counts (TVC's), Enterobacteriaceae, and Escherichia coli. The same carcases were also sampled for Salmonella spp. by swabbing. The mean levels of TVC's and Enterobacteriaceae, and the results for Salmonella spp. were in line with the requirements laid down in Regulation (EC) No 2073/2005. The mean levels of TVC's for samples by excision and by swabbing were 3.77 log CFU/cm² and 3.16 log CFU/cm², respectively. Enterobacteriaceae were recovered from 72% and 76% of the carcases, and E. coli from 48% and 61% by excision and swabbing, respectively. No carcases were found positive for Salmonella spp. The mean levels of TVC's, Enterobacteriaceae and E. coli were significantly higher for the samples by excision than for the samples by swabbing. When the relationship between the sampling methods were analysed, the results for excision samples and swabbing samples were related for the TVC's, and there was a significant correlation between the sampling methods for Enterobacteriaceae. The results suggest that swabbing by gauze can be used as an alternative sampling method to excision. In addition, a significant correlation was seen between the results for Enterobacteriaceae and E. coli for the samples collected by swabbing, suggesting that E. coli can be used as an indicator bacterium instead for Enterobaceteriaceae for sampling of sheep carcases by swabbing.     

Distribution of microflora on cattle hides and its transmission to meat via direct contact

In the study, total numbers and distribution of hide microflora, as well as its transferability to meat via direct contact, were investigated. Average total viable counts of bacteria (TVC) and Enterobacteriaceae counts (EC) on 40 bovine hides (cattle from three geographic regions; slaughtered at single abattoir) were 6.7 and 4.3 log cfu/cm², respectively. All hides contained generic Escherichia coli (GEC) but Salmonella spp. was not isolated from any bovine hide examined. Distal leg (metacarpus) and brisket areas were contaminated significantly heavier, in terms of TVC (6.9 and 7.1 log cfu/cm², respectively), EC (4.5 and 4.3 log cfu/cm², respectively) and GEC (occurrence 75% and 65%, respectively), than rump, flank and neck areas. No statistically significant differences in TVC, EC and GEC between the top layer and the lower layer (closer to skin) of the hide hair on visually clean hides were found. Only a small proportion (between 0.5 and 0.00002%) of total microflora (TVC) of hide was transmitted onto meat via direct contact under applied contact conditions (0.5–2 kg for 2 s; stationary or “sliding” contact). Nevertheless, the associated meat safety risks are assessed as significant, due to both high microbial loads existing on hide and high frequency of the hide-origin carcass cross contamination occurring in practice.     

Validation studies on an online monitoring system for reducing faecal and microbial contamination on beef carcasses

The objective of this research was to establish the reduction in the incidence of carcass faecal contamination and microbial counts that could be achieved in a beef slaughter plant using a novel information technology based online monitoring system. On 18 separate visits over the course of 6 months, every carcass (approximately 500 per day) was examined at the final inspection stand for visible faecal contamination. Each incidence was attributed to dehiding or evisceration operations. On each visit, 10 carcasses were swabbed at the trimming stand, at the hock, rump, anus, brisket and flank to determine total viable counts (TVC), Escherichia coli counts (ECC), total enteric counts (TEC) and total coliform counts (TCC). Over the course of this study, faecal contamination rates for dehiding and evisceration were reduced from 54.2% to 28.2% and from 32.5% to 13.7%, respectively. TVC remained constant at approximately 3.0 log₁₀ cfu cm⁻² while ECC, TEC and TCC decreased by 0.56 log₁₀ cfu cm⁻², 0.83 log₁₀ cfu cm⁻² and 0.9 log₁₀ cfu cm⁻², respectively. Online monitoring is therefore an effective means of reducing the incidence of bovine carcass faecal and enteric counts.     

Prevalence and quantification of Campylobacter contamination on raw chicken carcasses for retail sale in China

The quantitative contamination load of Campylobacter on raw chicken carcasses at retail outlets in seven provinces and cities of China was determined. A total of 1587 carcasses over 12 consecutive months were sampled. The overall Campylobacter contamination rate was 45.1% and 19.8% of contaminated carcasses was higher in the load than 3.0 log₁₀CFU/g. The median load was 2.1 log₁₀CFU/g with 1.4 log₁₀CFU/g as the 25th percentile and 2.9 log₁₀CFU/g as the 75th percentile, respectively. Using logistic regression, it observed the significant provincial and monthly variations in prevalence, freshly slaughtered chicken carcasses (63.1%) were found to be 2.3 times higher compared to chilled carcasses (32.9%), while no statistical significance was observed in prevalence among chicken carcasses that had various packaging solution (P = 0.370) nor from different market types (P = 0.680) suggesting that possible cross-contamination had occurred during processing and transportation. The present study found that 52.1%, 59.9%, 2.9%, 8.8% and 8.3% of carcasses were contaminated with C. jejuni, C. coli, C. lari, C. fetus, and C. upsaliensis, respectively. A higher proportion of C. coli (45.4%) than C. jejuni (39.5%) were cultured from the contaminated carcasses and this finding was suggestive of a high degree of cross-contamination occurred not just among poultry products, but also with pork products before/at retail points in China. This study provided quantitative data suitable for a risk assessment model designed to evaluate useful intervention methods to facilitate a reduction in the risk of campylobacteriosis arising from the consumption of contaminated domestically produced chicken meat in China.     

The incidence of significant foodborne pathogens in domestic refrigerators

The interior surfaces of household refrigerators are at risk of becoming contaminated with foodborne pathogens, increasing the risks of cross-contamination to other food items, including higher risk ready-to-eat foods. This study determined the incidence of a number of significant foodborne pathogens, and the general hygienic status (as estimated by total viable counts (TVCs), and total coliform counts (TCCs)) on the interior surfaces of domestic refrigerators (n = 342). Campylobacter spp., Salmonella spp. and Escherichia coli O157:H7 were not recovered from any refrigerators, but Staphylococcus aureus was recovered from 6.4%, Listeria monocytogenes and E. coli from 1.2% and Yersinia enterocolitica from 0.6% of examined refrigerators. As the recovered species can survive and grow under refrigeration or conditions of mild temperature abuse, such pathogens may transfer to (and develop to clinically significant numbers in) food in domestic fridges. Such risks are of particular concern in relation to “ready-to-eat” foods, which will not receive further bactericidal treatments (cooking) before consumption. The study estimated TVCs ranging from 2.91 log₁₀ cfu/cm² to 8.78 log₁₀ cfu/cm² and TTCs ranging from 0.045 log₁₀ cfu/cm² to 5.96 log₁₀ cfu/cm² indicating very poor standards of consumer refrigerator management and hygiene, and posing risks to consumer health. The study findings highlight the importance of adequate temperature control and thorough, regular cleaning of domestic refrigerators to ensure food safety, and of effective cooking as the last link in the domestic food service chain.     

The efficacy of disinfectant misting in the lairage of a pig abattoir to reduce Salmonella and Enterobacteriaceae on pigs prior to slaughter

Water misting/showers are used in abattoir lairages to improve meat quality, and to cool and calm pigs after transport and during hot weather. One novel approach, which has not been investigated to date, is to add a disinfectant to the misting water as a means of topically reducing Salmonella on pigs prior to slaughter, thereby potentially controlling this organism in the abattoir. The objective of this study was therefore to evaluate misting with water or with Virkon^® S (an approved disinfectant for use in the presence of animals), for their ability to topically reduce Salmonella on high seroprevalence pig herds before stunning and to reduce Enterobacteriaceae.Three experimental groups were investigated: control group (i.e., no misting); water group (misting with cold, 15–17 °C, water, herein referred to as water); and a disinfectant group (misting with 0.5% Virkon^® S). As pigs entered the abattoir, each animal was swabbed along its back before being allocated to its experimental group. Each group was randomly assigned to one of 3 lairage pens that were separated by non-trial pens. After 30 min of misting with water or disinfectant, pigs were moved to the stunning area, where each pig was again swabbed, as above. Swabs were analyzed for the presence of Salmonella and enumeration of Enterobacteriaceae.Before misting, Salmonella prevalence on the pigs was 79.0%, 72.1% and 83.6% for the control, water and disinfectant groups, respectively. After misting, Salmonella prevalence increased to 94.3% in the water group; whereas for the disinfectant group, the prevalence increased marginally to 85.9%. No change in Salmonella prevalence was detected for the control group. In line with the Salmonella results, no significant differences were observed in Enterobacteriaceae counts in the control group at either time point (4.37 and 5.01 log₁₀ CFU/cm², respectively) or in the disinfectant group before and after misting (4.02 and 4.26 log₁₀ CFU/cm², respectively). However, a 2.3 log₁₀ CFU/cm² increase in Enterobacteriaceae was recorded for the water group after misting as compared to before misting (p < 0.05).Since misting with water alone increased topical Salmonella contamination on pigs before slaughter, a risk assessment based on known Salmonella data, meat quality and welfare is recommended to determine whether its use is justifiable. On the other hand, the findings from this study suggest that misting with Virkon^® S at 0.5% could have a role in topical antisepsis of pigs contaminated with Salmonella prior to slaughter and as such this warrants further investigation.     

Microbiological evaluation of fresh-cut organic vegetables produced in Zambia

This study was undertaken to assess the microbiological quality of fresh-cut organic vegetables produced in Zambia. Fresh-cut organic mixed vegetables and green beans produced in Zambia were analysed for aerobic plate counts, coliforms, Enterobacteriaceae, Escherichia coli, Bacillus cereus, Clostridium perfringens, Listeria monocytogenes, Salmonella spp., Staphylococcus aureus, and yeast and mould counts. The study included 160 samples for most of the parameters. The vegetables were grown on farms meant primarily for the export market. The vegetables were treated/washed with 150 μg ml⁻¹ chlorine solution at the processing plant prior to sampling. The aerobic plate count ranged between 3 log₁₀ and 9.7 log₁₀ CFU/g, with the highest count recorded for green beans. The largest grouping (26.1%) of vegetable samples fell between 3 and 4 log₁₀ CFU/g. Coliform counts were between 1.0 log₁₀ and 7.7 log₁₀ CFU/g. The highest incidence level was 31.4% for total coliform counts between 3 log₁₀ and 4 log₁₀ CFU/g. E. coli was only detected on mixed vegetables in the range of 0.6 log₁₀ to 3 log₁₀ CFU/g, while Enterobacteriaceae counts ranged between 1.6 log₁₀ and 9.8 log₁₀ CFU/g with the highest counts being found on green beans. The highest incidence level was of 25.8% for counts within the same range as the aerobic plate counts. Yeast and mould counts showed the highest incidence level between 5 log₁₀ and 6 log₁₀ CFU/g with an overall range between 1.5 log₁₀ and 5.6 log₁₀ CFU/g. L. monocytogenes, Salmonella spp. and S. aureus were detected in 20%, 23.1% and 83.9% of samples, respectively . C. perfringens and B. cereus were not detected in any of the samples analysed.     

Quantification and variability of Escherichia coli and Staphylococcus aureus cross-contamination during serving and consumption of cooked thick porridge in Lungwena rural households, Malawi

The study investigated bacterial transfer to cooked thick porridge via ladles and hands during serving in 29 households in Lungwena, rural Malawi. Household stored water used for hand and ladle washing, was contaminated with Escherichia coli and Staphylococcus. aureus from hands of members of the household or from contaminated ladles used in food preparation. The results showed that hands became contaminated with E. coli and S. aureus cells in the range 0.6–3.7 and 2.2–4.3 log₁₀ CFU/cm², respectively, following washing with the contaminated water. Ladles became contaminated with 0.9–3.2 log₁₀ CFU/cm² of E. coli cells whereas contamination with S. aureus on ladles ranged between 1.9 and 4.6 log₁₀ CFU/cm². Bacterial transfer from hands to food ranged from <1 to 3.6 log₁₀ CFU/g for E. coli and 2.1 to 4.2 log₁₀ CFU/g for S. aureus. Ladle surfaces transferred from 1.3 to 3.1 and from 1.2 to 4.3 log₁₀ CFU/g of E. coli and S. aureus, respectively, on to the food. Contamination of food by hands was significantly (p < 0.05) higher than that of ladles and transfer of S. aureus was significantly (p < 0.05) higher than that of E. coli. The amount of bacteria transferred to the recipient depended on the wash water type and bacteria type. The study has demonstrated that although the traditional cooking of thick porridge inactivates S. aureus and E. coli, the porridge can be contaminated with bacteria during consumption using hands and serving on to a plate with wooden ladles.     

Effects of UV-C on physicochemical quality attributes and Salmonella enteritidis inactivation in liquid egg products

The perspectives of UV-C radiation as a non-thermal treatment for liquid egg products were evaluated from the point of view of the effects on egg quality attributes and the decontamination efficiency against the main egg contaminant Salmonella enterica subsp. enterica Ser. Enteritidis. UV-C treated egg fractions (egg yolk, egg white and whole egg) were analyzed for changes in pH, color, temperature-dependent viscosity and TBARS index, and were inoculated with S. enteritidis (ATCC 13076). Contrary to heat treatments, UV-C was not affecting viscosity and pH. Browning due to Maillard was perceptible in egg yolk and whole egg at low UV-C doses, but the corresponding browning indexes were always lower than in heat pasteurized egg fractions. Major changes were only due to lipid oxidation. TBARS values at the highest UV-C doses were larger than in pasteurized egg yolk and whole egg; under dynamic conditions and 0.61 J cm^?2, results were not significantly different to natural untreated samples. And UV-C was effective to inactivate S. enteritidis. In egg white, a load reduction up to 5.3 log₁₀ was achieved under dynamic conditions (9.22 J cm^?2, 39 min), while 3.3 log₁₀ and 3.8 log₁₀ reductions were recorded in egg yolk and whole egg. Static treatments were less efficient, but still, load reductions between 1.7 and 2.8 log₁₀ were obtained. At 3.94 mW cm^?2, time necessary to achieve a 4D reduction of Salmonella cells was estimated to be around 7.4 min in egg white.     

Potential of Escherichia coli as a surrogate indicator for postchill broiler carcasses with high Campylobacter counts

Surrogating Campylobacter contamination level in broiler carcasses with other bacterial indicators, used to evaluate the hygienic status of the slaughterline operations, might be stimulation to the broiler meat industry to improve control of Campylobacter during slaughter. Theoretically, Escherichia coli might have some practical merits as a potential indicator for carcasses contaminated with Campylobacter. This study investigates the correlation between the counts of E. coli and Campylobacter in 231 postchill broiler carcasses. The impact of setting a process hygiene target based on E. coli counts on reducing the frequency of carcasses contaminated with Campylobacter at level of ≥3 log₁₀ CFU/g was also investigated. Almost half (48.9% (46/94)) of the carcasses with enumerable Campylobacter (≥1 log₁₀ CFU/g) had E. coli counts between 3 and 4 log₁₀ CFU/g. In addition, 54.8% (17/31) of the carcasses contaminated with Campylobacter of ≥3 log₁₀ CFU/g were correlated with E. coli count range of ≥3 & <4 log₁₀ CFU/g. A theoretical scenario assuming that hygiene and processing measures could allow achieving a target for E. coli that not exceeding 3 log₁₀ CFU/g showed a parallel impact on Campylobacter contamination in broiler carcasses. In such scenario, the overall number of Campylobacter-positive carcasses could be dropped from 40.6% to 12.5%; in addition, 80.6% (25/31) of the carcasses contaminated with Campylobacter of ≥3 log₁₀ CFU/g could be eliminated. Findings from this study reveal that a hygiene target based on E. coli count could be used as an indirect sanitary tool for reducing the level of Campylobacter contamination in postchill broiler carcasses.     

Use of chemical treatments applied alone and in combination to reduce Campylobacter on raw poultry

Research focussing on the use of chemicals to decontaminate poultry carcasses to reduce pathogenic and spoilage organisms has increased in recent years. The objective of this study was to evaluate the efficacy of 12% (w/v) trisodium phosphate (TSP), 2% (w/v) citric acid (CA) and 5% (w/v) capric acid sodium salt (CP) in reducing Campylobacter, total viable counts and total Enterobacteriaceae counts on poultry. These chemicals were also used in various combinations (TSP + CA, TSP + CP and CA + CP) to determine if sequential treatments would enhance microbial reductions. TSP (1.9–2.3 log₁₀ cfu cm²) and CP (2.2–2.4 log₁₀ cfu cm²) gave the largest Campylobacter jejuni reductions while TSP was the most effective at reducing TVC (0.9 log₁₀ cfu cm²) and TEC (0.9 log₁₀ cfu cm²). TSP + CP was the most effective combination treatment (2.9 log₁₀ cfu cm²) for reducing C. jejuni counts and was significantly (P < 0.05) greater than any of the single chemical treatments, with the exception of CP treatment against strain 1146 (2.4 log₁₀ cfu cm²). The TVC and TEC populations proved more resistant to combination treatments as only TSP + CP showed a significantly (p < 0.05) enhanced reductive efficacy in comparison to single CP treatment. This study provides further data on the efficacy of a number of potential chemicals used alone and in combination for the decontamination of raw poultry.     

Antimicrobial action and effects on beef quality attributes of a gaseous ozone treatment at refrigeration temperatures

The effects of gaseous ozone treatment at refrigeration temperatures, on microbial counts (total aerobic mesophilic heterotrophic microorganisms and inoculated Escherichia coli) in culture media and in beef samples were analyzed. The influence of ozone on beef quality properties such as surface color and rancidity was measured.The effect of gaseous ozone (154 × 10^?6 kg m^?3) in culture media inoculated with E. coli after 3- or 24-h treatment at 0° and 4 °C caused a total inactivation of this microorganism.For beef samples treated with the same gaseous ozone concentration, the highest microbial inhibition was observed at 0 °C and after 24-h exposure, producing a decrease of 0.7 and 2.0 log₁₀ cycles in E. coli and total aerobic mesophilic heterotrophic microorganism counts respectively; however, both the surface color and lipid oxidation of these beef samples were unacceptable. Shorter exposure times (3 h) to the tested ozone concentration at both temperatures (0–4 °C), reduced 0.5 log₁₀ cycles the counts of total aerobic mesophilic heterotrophic microorganisms and 0.6–1.0 log₁₀ cycles the counts of E. coli, without changing the color or producing rancidity in beef.     

Antimicrobial efficacy of vacuum impregnation washing with malic acid applied to whole paprika,carrots, king oyster mushrooms and muskmelons

Antimicrobial effect of vacuum impregnation (VI) applied to organic acid washing against Salmonella Typhimurium, Escherichia coli O157:H7 and Listeria monocytogenes on paprika fruit, carrots, king oyster mushrooms and muskmelons was investigated. Samples were treated with intermittent VI with 21.3 kPa and compared with dipping washing in 2% malic acid. The initial sample pathogen levels were approximately 10⁵–10⁷ CFU/cm². Enumerations of the three pathogens on paprika and carrots treated with VI washing were reduced to below the detection limit (= 1 log₁₀ CFU/cm²) after 3–5 min and 15–20 min, respectively. For each time point where populations of the three pathogens were reduced to below the detection limit by VI treatment, populations of 1.2–1.9 log CFU/cm² and 2.5 to 2.8 log CFU/cm² survived on paprika and carrots, respectively, when subjected to dipping treatment. After 20 min of dipping treatment, surviving populations of the three pathogens ranged from 3.5 to 4.1 and 3.3 to 4.4 log CFU/cm² on king oyster mushrooms and muskmelons, respectively. After 20 min of VI treatment, surviving populations of the three pathogens ranged from 3.0 to 3.6 log and 3.1 to 4.1 log CFU/cm², respectively, on king oyster mushrooms and muskmelons. Additionally, there were no significant (P ≥ 0.05) differences in pathogen reductions between dipping and VI treatment for both king oyster mushrooms and muskmelons. King oyster mushrooms (R_a = 6.02 ± 1.65 μm) and muskmelons (R_a = 11.43 ± 1.68 μm) had relatively large roughness values compared to those of paprika (R_a = 0.60 ± 0.10 μm) and carrots (R_a = 2.51 ± 0.50 μm). Scanning electron photomicrographs showed many deep protected sites in king oyster mushrooms and muskmelons with many microbes located deep in these sites following VI treatment. Instrumental color, texture and titratable acidity values of paprika and carrots subjected to VI washing treatment with 2% malic acid for 5 and 20 min were not significantly (P ≥ 0.05) different from those of untreated control samples during 7 day storage.     

Quantitative estimation of Campylobacter cross-contamination in carcasses and chicken products at an abattoir

This study aimed to investigate Campylobacter contamination in carcasses and chicken products derived from a Campylobacter-negative flock when the flock is slaughtered immediately after a Campylobacter-positive flock. The first 2 flocks slaughtered on 10 different dates were investigated at an abattoir. Eighteen of the 20 flocks tested were positive for Campylobacter. A Campylobacter-negative flock was slaughtered immediately after a Campylobacter-positive flock on only 1 of the 10 slaughter dates. In this case, Campylobacter was detected in the carcasses and chicken products originating from the Campylobacter-negative flock, and all the flaA genotypes of these isolates were identical to those present in the caecal contents, carcasses, and chicken products from the Campylobacter-positive flock. The Campylobacter concentrations in the products originating from the Campylobacter-negative flock were: close to the enumeration limit (1.7 log₁₀ cfu/carcass) in the carcass samples; and below the enumeration limit (2.0 log₁₀ cfu/g) in the liver samples. The mean Campylobacter concentrations in the carcasses and liver products originating from the 18 Campylobacter-positive flocks were 3.8 log₁₀ cfu/carcass and 2.6 log₁₀ cfu/g, respectively. While 91% (246/270) of chicken products originating from Campylobacter-positive flocks were positive for Campylobacter, chicken products originating from the remaining Campylobacter-negative flock were free from Campylobacter cross-contamination by slaughter prior to a Campylobacter-positive flock. These results prove that slaughtering Campylobacter-negative flocks does not introduce Campylobacter into the abattoirs and indicate that although carcasses and chicken products originating from the Campylobacter-negative flock were cross-contaminated with Campylobacter from the Campylobacter-positive flock slaughtered immediately before, the Campylobacter contamination levels were lower than those in carcasses and chicken products from Campylobacter-positive flocks. Based on these findings, the reduction of Campylobacter prevalence in broiler flocks should be taken as an effective control measure for preventing introduction of Campylobacter into abattoirs and consequently for reducing Campylobacter prevalence in chicken products in addition to the good hygienic practice at abattoirs and logistic slaughter.     

Microbiological quality and safety of minimally processed vegetables marketed in Campinas,SP – Brazil,as assessed by traditional and alternative methods

In this study, a total of 172 samples of minimally processed vegetables (MPV) were collected from supermarkets in the city of Campinas, Brazil. The MPV were analyzed using traditional and/or alternative methods for total aerobic mesophilic bacteria, total coliforms, Escherichia coli, coagulase positive staphylococci, Salmonella and Listeria monocytogenes. All the MPV analyzed presented populations of aerobic mesophilic microorganisms and total coliforms were >4 log₁₀ CFU/g and 1.0–3.4 log₁₀ CFU/g, respectively. E. coli was enumerated in only 10 samples out of 172 collected, while none of the 172 samples of MPV presented contamination by coagulase positive Staphylococcus (<10¹ CFU/g). Among the four methods used for detection of Salmonella in MPV (Vidas, 1,2 Test, Reveal, and Traditional), when Reveal was used a total of 29 positive samples were reported. For L. monocytogenes, the four methods tested (Vidas, Vip, Reveal, and traditional) performed similarly. The presence of Salmonella and L. monocytogenes in MPV was confirmed in one (watercress) and two samples (watercress and escarole), respectively. In conclusion, it has been observed that the microbiological quality of MPV commercialized in Campinas is generally satisfactory. Besides, the choice of microbiological method should be based not only on resource and time issues, but also on parameters such as sensitivity and specificity for the specific foods under analysis.     

Radio frequency heating of comminuted meats - considerations in relation to microbial challenge studies

Bacillus cereus and Clostridium perfringens vegetative cell and spore cocktails in maximum recovery diluent (MRD) were inoculated into pork luncheon meat to challenge a previously developed radio frequency (RF) cooking protocol. After RF cooking and cooling microbial enumeration results showed a reduction in B. cereus vegetative cell and spores of 5.4 and 1.8 log₁₀ cfu g⁻¹, respectively while the corresponding reduction for C. perfringens vegetative cells and spores were 6.8 and 4.1 log₁₀ cfu g⁻¹, respectively. However, post cooking temperatures within the product were lower than anticipated. Subsequent analysis of product thermal and dielectric properties indicated that MRD addition and compositional variations within meat ingredients altered thermal and dielectric properties which in turn contributed to reduced and less uniform temperatures. The study shows that for RF microbial challenge studies, adjustment of product formulation prior to MRD addition is critical to ensure a similar composition to the normal product and a true picture of microbial inactivation.     

Development of a real-time PCR procedure for quantification of viable Escherichia coli in populations of E. coli exposed to lactic acid,and the acid tolerance of verotoxigenic E. coli (VTEC) from cattle hides

The aims of this study were to develop a real-time PCR procedure for determining the effects on Escherichia coli of treatment for decontaminating beef carcasses with lactic acid solution, and determining if there were differences in the acid tolerance of E. coli generally and verotoxigenic E. coli (VTEC). Suspensions of E. coli were incubated with 4% lactic acid at pH 3.6. The numbers of surviving E. coli at different incubation times were determined from plate counts and from quantification by real-time PCR of the uidA gene in DNA preparations. The numbers of viable E. coli progressively declined, by about 4 log units during incubation for 6 h. The mean cycle threshold (Ct) values for uidA in DNA from samples collected at different times and treated or not treated with propidium monoazide (PMA) before DNA extraction were similar. Treatment with 1% sodium deoxycholate (SD) before PMA treatment resulted in an increase of >6 Ct when the reduction in viable cell number was around 1 log. When E. coli incubated with 4% lactic acid solutions of pH 2.4, 2.8, 3.2 or 3.6 were resuscitated in half strength brain heart infusion (BHI) for 2 h before treatments with SD and PMA, the slope of the plot relating Ct values to the numbers of viable E. coli was 1.85 Ct log cfu⁻¹ with the correlation coefficient (R²) being 0.80. The findings indicate that while the membranes of E. coli inactivated by 4% lactic acid were largely impermeable to PMA, the membranes of both dead and injured cells were rendered permeable to PMA by treatment with 1% SD. Resuscitation in BHI restored the membrane barrier properties of the injured cells. Treatment with lactic acid resulted in increases in Ct values of 4.1, 3.7, 2.5 and 1.5 for the uidA, stx₁, stx₂ and eae genes, respectively; and the increases in Ct values for the latter two genes were significantly different (p < 0.05) from that for the uidA gene. This indicates that VTEC carrying stx₂ and/or eae were more acid resistant than other E. coli. Thus, caution should be exercised when using generic E. coli as an indicator for VTEC for assessment of the antimicrobial efficacy of organic acid decontaminating treatments at abattoirs.     

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.