Prevalence of enterotoxigenic Staphylococcus aureus in fishery products and fish processing factory workers

Of the 168 fishery products and 87 samples from fish processing factory workers analyzed, 21 (17%) and 54 (62%) were found positive for enterotoxigenic Staphylococcus aureus, respectively. Among the products, incidence was high in frozen peeled un-deveined (PUD) prawns and frozen fish cutlets (33% each) compared to frozen peeled and deveined (PD) prawns and frozen squids (25% and 20%, respectively). 21 out of 51 strains (41%) isolated from products and in 15 out of 54 strains from processing workers (28%) were found to be enterotoxigenic. The enterotoxin type Staphylococcal enterotoxin C (SEC) (57%) was predominated followed by Staphylococcal enterotoxin A (SEA) (43%) in products and Staphylococcal enterotoxin B (SEB) (40%), Staphylococcal enterotoxin C (SEC) (40%) and Staphylococcal enterotoxin A (SEA) (20%) in workers.     

Survival of Listeria monocytogenes inoculated in retail soymilk products

The consumption of soymilk products has been growing; because these foods contain proteins and isoflavone, and lack of lactose and cholesterol. The survival and growth of Listeria monocytogenes in the soymilk products were investigated by inoculating Listeria monocytogenes into various retail soymilk products which claimed to improve or fortify the functional properties. The results show that the refrigeration cannot successfully prevent the growth of Listeria monocytogenes in soymilk products. The addition of fiber content and higher viscosity in soymilk may significantly inhibit the growth of L. monocytogenes at 4–7 °C; however, this phenomenon was not observed when the incubation temperature was elevated to 22 °C. The change of pH value and TTS (total soluble solids) in soymilk products owing to L. monocytogenes, especially those with rich fiber content, might be negligible for the public. Thus the possible contamination of L. monocytogenes to soymilk products should be of crucial concern.     

Microbiological quality of fresh vegetables and fruits sold in Singapore

The aim of this study was to characterise the microbiological quality of selected common fresh vegetables and fruits commercially sold in Singapore in order to provide insight into any potential health hazards associated with consumption of these commodities. A total of 125 samples, collected from major supermarkets and local markets, were tested for aerobic mesophilic and psychrotrophic bacterial counts. One hundred samples were analysed for enumeration of yeasts and moulds, enumeration of coliforms and detection of Escherichia coli O157:H7 and Salmonella spp. Aerobic mesophilic counts ranged from 1.6 to 9.1 log cfu/g, with the lowest and the highest counts recorded for orange and bean sprouts, respectively. The highest level of coliforms was found in bean sprouts and fresh-cut salad, with 50% of samples containing more than 5 log cfu/g. Like coliform counts, the highest counts of yeasts and moulds were obtained in bean sprouts and fresh-cut salads. Fresh-cut salads also had the highest mean psychrotrophic plate count of 4.9 log cfu/g. Although no E. coli O157:H7 or Salmonella spp. was detected in the fruits and vegetables analysed in this study, high bacterial counts, especially in bean sprouts and fresh-cut salad, imply that effective control measures should be implemented to improve the microbiological quality of fresh produce sold in Singapore.     

Evaluation of growth and transfer of Staphylococcus aureus from poultry meat to surfaces of stainless steel and polyethylene and their disinfection

The growth of Staphylococcus aureus inoculated onto poultry meat was investigated under different incubation periods and temperature patterns. Transfer of this microorganism to surface materials and their disinfection was also evaluated. The evaluation of transfer was carried out by placing the contaminated meat cubes on stainless steel and polyethylene surfaces for 10 s and 10 min each, and the surfaces were disinfected with 0.5% chlorhexidine digluconate (CHXdG) for 1 and 10 min each. After 24 h, there was a significant increase of the bacteria count at 20 °C, but not at temperatures between 7 and 15 °C. Significant counts of S. aureus were transferred after a few seconds of contact of the cubes with both materials, and significant differences of transferred cell counts were not detected among the surface materials or durations of contact. The CHXdG solution was able to inactivate all the transferred cells after 10 min of exposure; however, the same result was not observed with 1-min exposure. The time of contact and the type of surface material did not influence the quantity of the transferred cells. The 0.5% CHXdG solution was effective for the disinfection of the contaminated surfaces without previous cleaning.     

Microbiological quality and safety of minimally processed fruits in the marketplace of southern Portugal

The availability of fresh-cut fruit (FCF) in the marketplace has been increasing in Portugal, although reports of its microbial quality are not known. Due to the growing concerns of these commodities over their microbial safety, the objectives of this work were to study the microbiological quality and prevalence of Salmonella and Listeria monocytogenes on fresh-cut fruits sold in southern Portugal. A study to examine the changes in pH and microbial counts, before and after the expiration dates, was also made. A total of 160 samples was purchased in the local grocery stores between September 2011 and August 2014, before their sell-by date. These samples were assayed for aerobic mesophilic (AM) and psychrotrophic (AP) microorganisms, yeasts and molds (YM), lactic-acid bacteria (LAB), coliforms (TC), Escherichia coli and coagulase positive staphylococci as well as L. monocytogenes and Salmonella. The microbiological counts ranged from 3.0-9.2 lg cfu/g (AM); 2.2–10.7 lg cfu/g (AP); 2.3–10.4 lg cfu/g (YM); 1.9–9.0 lg cfu/g (LAB) and less than 1–9.1 lg cfu/g (TC). The melons and watermelon presented the highest levels of the microbial quality parameters studied. However, no E. coli, staphylococci, Salmonella and L. monocytogenes were detected in any of the samples. After the sell-by date, an increase of the AM, AP, LAB and YM values was observed in all fruits. Conversely, the differences found in TC counts before and after the best-before date had no statistical significance. A decrease in pH was observed in all fruits except pineapple whose pH slightly increased after 14 days of storage. The results highlight the importance of preventing contamination and cross contamination, selecting adequate decontamination technologies and maintaining a strict temperature control during processing, distribution and selling of FCF.     

Acquisition of pulsed electric fields resistance in Staphylococcus aureus after exposure to heat and alkaline shocks

Staphylococcus aureus cells were exposed to acid (4.5) and alkaline (9.5) pH, hydrogen peroxide (50 μM), sodium chloride (10%), heat (45 °C) and to a cold shock (4 °C) for 2 h and then treated by pulsed electric fields (PEF). Exposing S. aureus cells to acidic, oxidative, hyperosmotic or cold shock conditions resulted in no protection to PEF. By contrast, heat and alkaline shocks increased the resistance of S. aureus cells to PEF, regardless the electric field strength applied, the pH and a_w of the treatment medium and the strain and growth phase investigated. A ΔsigB deletion mutant was also able to develop these cross-resistance responses demonstrating that the σ^B factor is not necessary for the acquisition of resistance to PEF after exposure to heat and alkaline shocks. When cells were recovered in selective medium (with NaCl added) alkaline-shocked, but not heat-shocked cells, also showed higher PEF resistance than control cells. This investigation contributes to increase the knowledge on the factors determining bacterial PEF resistance and may help in the design of new preservation methods involving PEF.     

Open-refrigerated retail display case temperature profile and its impact on product quality and microbiota of stored baby spinach

Maintaining proper storage temperature is critical for ensuring the quality and safety of fresh-cut products. The US Food and Drug Administration Food Code recommend that packaged fresh-cut leafy green vegetables be kept no warmer than 5 °C at all times to ensure food safety. Substantial temperature variations, however, within the widely used open refrigerated display cases used in retail stores are known to present the technical challenge of complying with this federal guidance for industry. This study determined the extent of the spatial and temporal temperature variations within two commercial open-refrigerated display cases under different operating conditions, and their impact on the quality and microbial growth of packaged baby spinach products. The packaged products were received within 2 d of commercial processing and temperature data loggers were placed inside-and-outside of each bag. All bags were immediately loaded in the display cases and the overall visual quality, tissue electrolyte leakage, total aerobic mesophilic bacteria and psychrotrophic bacteria were evaluated for each bag. Results from this study showed that the temperature variation in the cases was dependent on spatial location, thermostat setting, and defrost cycle interval and duration of defrost. The largest temperature differentials were found for samples located in the front and back rows of the display cases. Samples located in the front rows had the highest temperature due to heat penetration from the surrounding ambient environment, while those in the back were damaged as temperatures fell below freezing. These products received low quality scores and had higher tissue electrolyte leakage. In order to reduce the large temperature variations in the display cases, insulating foam boards were installed which significantly (P < 0.05) decreased the temperature variation by 3.5 °C and enabled samples in the front rows of the cases to remain less than 5 °C as recommended by the FDA. These results suggest that the quality and safety of packaged ready-to-eat spinach at retail will benefit from improvements in open refrigerated case design or the utilization of insulation, doors or curtains.     

Prevalence of molecular markers for Salmonella and Shiga toxigenic Escherichia coli (STEC) in whole-muscle beef cuts sold at retail markets in Costa Rica

The present study sought to determine the prevalence of molecular markers for Salmonella and Shiga toxigenic Escherichia coli (STEC) serogroups O26, O45, O103, O111, O121, O145, and O157 in whole-muscle beef cuts sold at retail in urban and semi-rural areas of Costa Rica. A total of 279 (171 urban, 108 semi-rural) samples were purchased from 93 butcher shops between August of 2012 and August of 2013 and tested for the presence of molecular markers characteristic of Salmonella and STEC using the DuPont Qualicon BAX^® System. The overall prevalence of Salmonella and STEC markers was 3.6% (10/279) and 4.7% (13/279), respectively. Salmonella markers were more frequently found in semi-rural (6.5%; 7/108) than in urban (1.8%; 3/171) areas. Similarly, STEC markers were more commonly detected in semi-rural (7.4%; 8/108) than in urban (2.9%; 5/171) areas. A marginal association was found between Salmonella markers and sampling location (P = 0.0496), whereas the presence of STEC markers and sampling location were considered independent (P = 0.1416). Among the 13 positive samples for STEC, 38 O-antigen gene fragments were amplified, with serogroups O45 and O121 being the predominant (28.9 and 21.1%, respectively). Markers for somatic antigens O111 and O157 were not detected in any of the samples. The present investigation is the first of its kind in Central America and shows that both Salmonella and STEC may be commonly present in whole-muscle raw beef cuts sold at retail markets in Costa Rica. Consequently, consumers may be directly at risk of foodborne illness due if meat products are not adequately cooked and handled in food service or domestic settings. Future work should emphasize continuous monitoring of the presence of these and other zoonotic pathogens in meat and meat products and on the implementation and validation of adequate food safety controls along the farm-to-table continuum.     

Prevalence and trends of bacterial contamination in fresh fruits and vegetables sold at retail in Canada

In recent years, fresh fruits and vegetables have been linked to numerous foodborne illness outbreaks in different regions of the world, including in Canada. In light of rising concerns over the microbial safety of these commodities, the Canadian Food Inspection Agency conducted retail surveys to obtain information on the occurrence of bacterial pathogens in a wide range of produce available in the Canadian marketplace (local vs. imported, organic vs. conventional). Samples (n = 31,329) were collected across Canada over four years (2009–2013) and consisted of leafy vegetables (n = 12,073), leafy herbs (n = 6032), green onions (n = 3381), cantaloupes (n = 3230), tomatoes (n = 4837) and berries (n = 1776). These samples were analysed in ISO 17025-accredited laboratories for various bacterial pathogens (Salmonella, Escherichia coli O157, Shigella, Campylobacter and Listeria monocytogenes), as well as for generic E. coli, an indicator of fecal contamination. The Wilson confidence interval was used to determine the prevalence of the different micro-organisms in the commodities investigated. Control charts and seasonal indices, statistical tools adapted here to explore the large amount of data collected for each commodity, were used to identify potential adverse events or trends in bacterial contamination. The prevalence of bacterial contamination observed during this study in the six commodities examined was generally very low, with prevalence intervals ranging from [0, 0.08%] in tomatoes to [0.79, 1.30%] in leafy herbs. Most of the samples that were reported as “positive for bacterial contamination” had elevated (>100 CFU or MPN/g) levels of generic E. coli, but did not have detectable levels of the bacterial pathogens investigated. Of the samples that did have detectable levels of bacterial pathogens, the only bacteria that were both detected and isolated were Salmonella and L. monocytogenes. Despite the overall low prevalence of contamination seen in most produce, a notable seasonal trend was observed in the leafy vegetable group, where higher bacterial contamination rates were confirmed in the summer in organic as opposed to conventional products. These findings provide valuable baseline information that can support food safety decisions, and confirm that the vast majority of fresh fruits and vegetables available on the Canadian market are safe in terms of bacteriological hazards.     

Microbiological quality of tomatoes and peppers produced under the good agricultural practices protocol AGRO 2-1 & 2-2 in Crete, Greece

The efficiency of the good agricultural practices (GAP) protocol AGRO 2-1 & 2-2, in advancing microbiological-quality of tomatoes and peppers, was studied in greenhouses at Ierapetra, Crete, Greece. The 240 tested vegetables-samples, produced under AGRO 2-1 & 2-2, showed satisfactory quality: Listeria monocytogenes absent per 25 g; Escherichia coli < 20 Colony Forming Units per gram (CFU/g); total coliforms 4.37–4.68 log CFU/g; aerobic plate counts 5.78–5.92 log CFU/g. Based on actual results and practices evaluation, we conclude that AGRO 2-1 & 2-2 can reduce microbial hazards for consumers and furthermore can establish practices in compliance to basic Euro-Retailer-Produce GAP (EUREPGAP) requirements.     

Increasing the microbial inactivation of Staphylococcus aureus in sauces by a combination of enterocin AS-48 and 2-nitropropanol, and mild heat treatments

Staphylococcus aureus was challenged with the cyclic bacteriocin AS-48 in four commercial sauces singly and in combination with sublethal heat treatments (50-60 °C, for 5 min) and with 2-nitro-1-propanol (2NPOH). Heating at 60 °C in combination with AS-48 (25 μg/ml) reduced initial counts (4.1-4.5 log CFU/ml) below detection limit (1.0 log CFU/ml), while a combined treatment at 55 °C inhibited proliferation of staphylococci in sauces for 24 h at 22 °C. In BHI broth, enterocin AS-48 (0-15 μg/ml) acted synergistically with 2NPOH (0-220 mM), reducing the concentrations of both antimicrobials required for inactivation of S. aureus. In sauces, enterocin AS-48 (25 μg/ml) plus 2NPOH (25 mM) reduced initial cell concentrations (4.1-5.0 log CFU/ml) below detectable levels within 8-24 h, depending on the sauce. The combinations of enterocin AS-48 and 2NPOH or sublethal heat are interesting for testing as part of hurdle technology aimed at reducing the risks for proliferation of S. aureus in sauces.     

Occurrence of pathogenic bacteria in raw milk, cultured pasteurised milk and naturally soured milk produced at small-scale dairies in Zimbabwe

The presence of selected pathogenic bacteria in raw milk (RM), cultured pasteurised milk (CPM), and naturally soured raw milk (NSRM) sold at three small-scale dairies in Zimbabwe was determined. Mean levels of Escherichia coli in RM, CPM and NSRM were 4.5, 7.1 and 7.8 log₁₀ CFU ml⁻¹, respectively. Enterotoxigenic E. coli (ETEC), producing heat-stable enterotoxin (ST1) was found in 16 of the samples. Presumptive Staphylococcus aureus was identified in 7 of 12 RM, 15 of 27 CPM and 20 of 21 NSRM samples at mean levels of 5.2, 7.3 and 7.8 log₁₀ CFU ml⁻¹, respectively. Klebsiella pneumonia spp., Enterobacter cloacae, Proteus mirabilis, Hafnia alvei, Citrobacter spp., Serratia marcescens and Aeromonas hydrophilia were found in 27 samples. The high number of S. aureus, E. coli, identification of ETEC-ST1 and the other pathogenic microorganisms found in pasteurised and unpasteurised milk products represent a health hazard to the consumers and emphasises the need for improved hygiene practice at all levels in the dairy.     

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.     

Prevalence and quantification of Salmonella contamination in raw chicken carcasses at the retail in China

The quantitative contamination load of Salmonella in raw chicken carcasses at the retail level in six provinces and cities of China was determined within 1595 carcasses over 12 consecutive months. The overall Salmonella contamination rate was 41.6% and the median load of those contaminated was 4.6 MPN/100 g with 1.8 MPN/100 g as the 25th percentile and 18.0 MPN/100 g as the 75th percentile. There were significant variations in prevalence among carcasses sampled either in different provinces or sampling months. Carcasses collected in August had not only the highest prevalence of contamination (55.8%), but also the highest median (14.0 MPN/100 g) and 75th percentile load (120.0 MPN/100 g) values compared to January with lowest prevalence (26.5%), median (1.5 MPN/100 g) and 75th percentile load (7.6 MPN/100 g). The chilled (55.1%) stored carcasses was significantly higher in prevalence than those frozen (33.5%) and those freshly slaughtered (28.3%), those unpackaged (45.1%) was more likely to be contaminated with Salmonella than those packaged (37.4%). The present study revealed the widely prevalent Salmonella contamination among retail carcasses, indicating a strong potential of the cross-contamination occurred before and/or at the retail level. The study also provided quantitative data for a risk assessment evaluating potential intervention methods to reduce the risk of salmonellosis by consuming chicken meat of Chinese origin.     

Development and application of a centrifugation-plating method to study the biodiversity of Bacillus species in rice products

A centrifugation-plating method was developed, using amylase and Tween 80 pre-treatment, for detection and enumeration of Bacillus spp. in rice products. The high sensitivity of this method improved detection of a variety of Bacillus species in rice products compared to the spread-plate method. Bacillus spp. were detected in 33 out of 35 raw rice samples with the centrifugation-plating method, but only 13 samples using the spread-plating method, even though 1 mL of a 10⁻¹ sample dilution was used, to increase sensitivity of the method. Known toxigenic or potentially toxigenic species (Bacillus cereus/Bacillus thuringiensis, Bacillus subtilis, Bacillus licheniformis, and Bacillus pumilus) were those most frequently found in both raw and cooked rice.     

Changes in the microbiological and physicochemical quality of high-pressure-treated oysters (Crassostrea gigas) during chilled storage

Changes in the physicochemical and microbiological quality of oysters HP-treated at 260, 400 or 600 MPa for 5 min and stored at 2 °C on ice for 31 days were investigated. Microbial counts after HP treatment showed that the bacterial load was initially reduced at all pressures to levels below the detection limit. HP-treated oysters showed significantly increased pH and lightness (P < 0.05) relative to untreated oysters; during storage, pH changed little in the pressurised oysters but decreased slightly in untreated oysters. Little changes in colour were observed during storage at 2 °C on ice, compared to untreated oysters, which showed increased b-values (stronger yellow colour). From tests of mechanical properties, HP-treated oysters showed significantly increased cutting strength (P < 0.05) with increasing treatment pressure compared to controls throughout storage. However, HP increased lipid oxidation, the rate of which was dependent on the pressure applied. This study confirmed that HP processing can inactivate microorganisms and delay microbial growth in chilled stored oysters, but also affects their quality attributes.     

Mineralogical and Geochemical Studies of Oil Shale Deposits in the Cretaceous/Paleogene succession at Quseir Area,Egypt

Cretaceous/Paleogene succession in Quseir area represents one of the most important economic sedimentary rocks, which contain phosphate and oil shale beds. Oil shale samples selected from nine mines around Quseir area were subjected to mineralogical, petrographical and geochemical analyses. As raveled by X-ray diffraction analysis, the oil shale samples are composed of calcite, quartz, dolomite, smectite, kaolinite, gypsum and pyrite. The petrographical investigation of the studied oil shales indicates the dominance of two microfacies: calcareous foraminiferal claystone and Calci-mudstone. The EDX results of oil shale samples show that the pyrite found as framboidal-disseminated particles in smectite. The high ratio of the sulfur and organic carbon contents in the selected mines indicate highly reducing environment. Five mines (El-Nakheil, Abu Tundub, Abu Tundub Bahree, El Beida and Hammadat) are markedly rich in organic content and can be considered as good to excellent source rock.