Microbiology of raw milk in New Zealand

The results of this study demonstrate the occurrence of the non-spore-forming pathogens, Staphylococcus aureus, Escherichia coli (total count and O157:H7), Listeria, Campylobacter and Salmonella, in New Zealand's raw milk supply. Samples of raw milk were collected monthly within five major dairying regions over one year. Each month, samples from five randomly selected farm vats in each region were collected for analysis (297 samples in total). Methods based on plate count techniques were used to enumerate S. aureus and E. coli. Enrichment methods in combination with a modified most probable number detection method were used to monitor samples for the presence of E. coli O157:H7, Listeria, Campylobacter and Salmonella. Salmonella was not detected in this study, and Campylobacter was isolated once (0.34%). E. coli was present at <100 cfu/ml in 99% of samples and exceeded 10(3)cfu/ml in 0.7% of samples. E. coli O157:H7 was not detected whereas non-pathogenic E. coli O157 strains (i.e. lacking genes for stx1, stx2, eae and Hly A) were detected in 1% of samples. S. aureus was not detected (<1 cfu/ml) in 21% of samples; levels were >1 but <100 cfu/ml in 60% of samples and on one occasion (0.34%) S. aureus exceeded 10(4)cfu/ml. L. monocytogenes was isolated from 0.68% of samples and L. innocua was present in 4% of samples. The results demonstrate that raw milk sampled from farm vats in New Zealand, as in other countries, inevitably contains recognised pathogens and, hence, control by pasteurisation or an equivalent treatment of raw milk remains paramount. Even so, the prevalence of most of these pathogens was lower than those reported in many of the studies performed in other countries.     

HYGIENIC PARAMETERS, TOXINS AND PATHOGEN OCCURRENCE IN RAW MILK CHEESES

In total, 71 samples of retail raw milk cheeses produced or imported in Belgium and samples of Belgian farmhouse cheeses were examined for cotiforms, β-glucuronidase positive Escherichia coli, Escherichia coli O157 , Staphylococcus aureus, Salmonella spp. , Listeria spp. and Listeria monocytogenes. The presence of staphylococcal enterotoxins was investigated on samples with S. aureus counts higher than 10³ cfu/g. The incidence of coliforms, β-glucuronidase positive E. coli and S. aureus was higher in soft than in blue veined, semi-hard, hard and fresh cheeses. Four mold-ripened soft cheeses were positive for E. coli O157. One of the 4 cheeses was positive for verotoxin VT2. Staphylococcal enterotoxins were detected in 1 soft redsmear cheese, which was positive for L. monocytogenes. L. monocytogenes was also detected in one fresh cheese . Salmonella was not detected in any of the 71 raw milk cheeses.     

INHIBITION OF LISTERIA MONOCYTOGENES AND OTHER BACTERIA BY A PLANT ESSENTIAL OIL (DMC) IN SPANISH SOFT CHEESE

The inhibitory effects of a mixture of plant essential oils (DMC) were tested in culture media and Spanish soft cheese. The minimum inhibitory concentration (MIC) was determined in plate count agar and tryptose broth, with pH adjusted to 6.5, against Listeria monocytogenes, Listeria innocua, Staphylococcus aureus, Lactobacillus brevis, Micrococcus luteus, Salmonella cholerasuis, Escherichia coli O157:H7 , Enterobacter cloacae, Pseudomonas aeruginosa and Pseudomonas fluorescens. The mixture of essential oils inhibited all Gram-positive bacteria tested at 40 ppm, but higher concentrations were needed to inhibit Gram-negative bacteria, and no inhibitory effect was found against Ps. fluorescens. The effects of DMC against L. monocytogenes and E. coli O157:H7 were evaluated in Spanish soft cheese (Queso Fresco, pH=6.5) stored at 7C. DMC had a bacteriostatic effect against L. monocytogenes at concentrations of 2500 ppm but was ineffective to control the growth of E. coli O157:H7 .     

MICROBIOLOGICAL STUDY OF ARZÚA CHEESE (NW SPAIN) THROUGHOUT CHEESEMAKING AND RIPENING

Changes during production and ripening in the microbial flora of 11 batches of Arzúa, a soft cheese made from raw cow's milk, were investigated. The following microbial groups were counted on the surface and interior of the cheese: total viable count (TVC), lactic acid bacteria (LAB), halotolerant flora, enterococci, proteolytic enterococci, staphylococci, Staphylococcus aureus, Enterobacteriaceae, faecal coliforms, molds, yeasts, Listeria spp. and (in milk) Brucella spp. pH and water activity were also determined. TVC and LAB were, generally, more than 9 log (cfu/g). Enterococci counts increased gradually, reaching values in excess of 6 log units. Halotolerant flora and staphylococci remained practically constant throughout ripening, at 6–8 and 5–7 log units, respectively. Maximum Enterobacteriaceae and faecal coliform counts exceeded 7 and 6 log units, respectively. Brucella spp. were not detected in any of the milk samples. Listeria spp. were detected in four batches, and Listeria monocytogenes in two.     

PRESENCE OF LISTERIA IN MEXICAN CHEESES

The presence of Listeria was investigated in ripened cheeses (Chihuahua, Manchego) and fresh cheese (Panela) from street vendors and retail stores in Mexico City. Cheeses were tested for Listeria, pH, NaCl, moisture and fat. Listeria selective cold enrichment was used to recover Listeria from positive samples. Fresh cheese had the lowest pH and NaCl contents and the highest moisture Chihuahua and Manchego cheeses made with pasteurized milk were negative for Listeria. Panela cheese samples were the most contaminated. The presence of Listeria was 65% in fresh cheeses: Listeria murrayi 20% , Listeria inoccua 15% , Listeria grayi 15%, and Listeria monocytogenes 15%. L. monocytogenes serotypes 1/2a, 1/2b and 4b were isolated from positive samples.     

A BELGIAN SURVEY OF HYGIENE INDICATOR BACTERIA AND PATHOGENIC BACTERIA IN RAW MILK AND DIRECT MARKETING OF RAW MILK FARM PRODUCTS

To monitor the bacteriological quality of raw milk and raw milk farm products, 143 samples of raw farm milk and 100 samples of raw milk farm products, 64 butters, 9 yogurts, 16 cheeses, 7 ice creams and 4 fresh cheeses, produced in Belgium were examined for coliforms, β-glucuronidase positive Escherichia coli, verotoxin producing Escherichia coli O157 , Staphylococcus aureus, Salmonella spp. , Listeria spp. and Listeria monocytogenes. The results were compared with the threshold and maximum values of the EC directive 92/46/EC or the maximum values of the Belgian Order of Council from September 3, 2000. The presence of staphylococcal enterotoxins was investigated on samples with S. aureus counts higher than the legal threshold values mentioned in the EC directive or, if not regulated in the directive, higher than the maximum value mentioned in the Belgian Order of Council. The obtained results for the hygiene-indicators coliforms, β-glucuronidase positive E. coli and S. aureus in the raw milk samples were comparable with most other industrialized countries. Compared to a prevalence of 0.7% and 6.3% for, respectively , E. coli O157 and L. monocytogenes, no Salmonella was found in the 25 g raw milk farm samples. The isolated E. coli O157 strain was confirmed to be verotoxigenic; it was positive for VT2 , eaeA and hly A. In butter not only a prevalence of 18.7% for L. monocytogenes in 25 g was found but also the maximum values for the hygiene-indicators mentioned in the Belgian Order of Council were often exceeded. No significant difference was found between the count of hygiene-indicators and the presence of Listeria spp. as well in raw milk as in raw milk butter. The bacteriological quality of on-farm made raw milk butter suggest that suitable hygienic conditions are not always provided. One of the 7 ice cream samples contained L. monocytogenes in 25 g.     

Microbiological and compositional status of Turkish white cheese

Results of the chemical and microbiological examination of 38 Turkish white cheese samples are presented. On average, the cheese was characterized by a high moisture and salt content, 58.18 and 3.56%, respectively, and a pH of 4.68. Significant variation was found in these compositional factors, indicating the extreme diversity of manufacturing practices. Microbiological analysis revealed the presence of high numbers of coliforms, faecal coliforms and Escherichia coli, extremely high numbers of faecal streptococci, and a low level and incidence of Staphylococcus aureus, Salmonella and Clostridium perfringens were not isolated from the samples. There was no correlation between the levels of coliforms, faecal coliforms, E. coli and enterococci, suggesting that the enterococci count in Turkish white cheese may not be a good indicator of sanitary practices.     

Occurrence and Antimicrobial Susceptibility of Listeria monocytogenes Isolated from Brined White Cheese in Jordan

Listeria monocytogenes is a serious foodborne pathogen that has been isolated from different dairy food products. Several foodborne outbreaks of listeriosis have been associated with consumption of cheese. The aims of this study were to determine the occurrence of L. monocytogenes and Listeria spp. in brined white cheese (BWC) sold in Jordan, and to determine the susceptibility of isolated L. monocytogenes to antimicrobials. Three hundred and fifty samples of 5 different types of BWC (akkawi, boiled, halloumi, pasteurized, and shellal) were collected from a local market in Jordan. The ISO (11290-1) procedure was followed for isolation and identification of Listeria spp. from cheese samples and a polymerase chain reaction (PCR) technique was used for confirmation of L. monocytogenes isolates. The VITEK2 automated system was used for testing antimicrobial susceptibility of L. monocytogenes isolates. The overall prevalence of Listeria spp. in cheese sample was 27.1%. L. monocytogenes was isolated from 39 (11.1%) samples. Other isolated species were L. grayi (6.9%), L. innocua (2%), L. ivanovii (4%), L. seeligeri (2%), and L. welshimeri (0.3%). The pH values and salt concentrations of L. monocytogenes positive cheese samples ranged from 5.10 to 6.32 and 5.64 to 13.16, respectively. L. monocytogenes isolates were sensitive or intermediate susceptible to imipenem, gentamicin, linezolid, teicoplanin, vancomycin, fusidic acid, trimethoprim/sulfamethoxazole, benzylpenicillin, ciprofloxacin, erythromycin, tetracycline, and rifampicin, but resistant to fosfomycin, oxacillin, and clindamycin.     

High incidence of Listeria monocytogenes in European red smear cheese

The incidence of Listeria and Listeria monocytogenes in European red smear cheese was determined in order to assess whether the lack of recent outbreaks of listeriosis associated with cheese is due to improved hygenic conditions in the dairies. Out of European red-smear cheese samples of various types, 15.8% contained organisms of the genus Listeria, 6.4% of the samples were contaminated with L. monocytogenes, 10.6% with L. innocua, and 1.2% with L. seeligeri. Six cheese samples contained two or more Listeria species, including at least one L. monocytogenes isolate. The incidences of L. monocytogenes in cheeses from various countries were: Italy 17.4%, Germany 9.2%, Austria 10%, and France 3.3%. Listeria were found most frequently in soft and semi-soft cheese. Eight samples contained more than 100 L. monocytogenes cfu/cm2 cheese surface, 2 samples had counts above 10(4) cfu/cm2 cheese surface. Surprisingly, a higher incidence of L. monocytogenes was observed in cheeses made from pasteurized milk (8.0%) than in cheeses manufactured from raw milk (4.8%). Phage-typing of isolated Listeria strains clearly confirmed that (i) contaminations within dairy plants were persistent over a period of several weeks to months and (ii) that cross-contamination within the dairy plant is and important factor. Comparison of our data with past surveys seems to indicate that contamination of red smear soft cheese with L. monocytogenes has not decreased sufficiently over the past 15 years. It is therefore strongly recommended that these products are monitored carefully by cheese-making companies.     

The occurrence of Listeria species in milk and dairy products: a national survey in England and Wales

A total of 4172 samples of milk, cheese and other dairy products were examined over a 1-year period for the presence of Listeria species. Strains of Listeria were found most frequently in soft, ripened cows milk cheese; 63 out of 769 (8.2%) samples contained Listeria monocytogenes, 25 samples contained species other than L. monocytogenes, and 18 samples contained both L. monocytogenes and other Listeria spp. Eleven samples of pasteurized cows milk (1.1%) from four dairies contained L. monocytogenes, and other Listeria spp. were isolated from a further five samples. Goats and ewes milk and their products, yogurt, cream and ice cream also occasionally contained Listeria spp. Levels of Listeria were usually low, but 20 samples of cheese contained more than 1000 cfu/g. Most strains of L. monocytogenes belonged to serotype 1/2 (58%) or serotype 4b (33%).     

Comparison of media and sampling locations for isolation of Listeria monocytogenes in queso fresco cheese

Listeriosis associated with Hispanic-style soft cheese is an ongoing public health concern. Although rapid detection methods based on molecular and immunological technologies have been applied successfully for detecting Listeria monocytogenes in foods, obtaining isolates of the pathogen is a critical procedure for epidemiologic studies and regulatory analysis. Oxford agar, a medium recommended by the U.S. Food and Drug Administration Bacteriological Analytical Manual (BAM) to isolate L. monocytogenes from cheese, is unable to differentiate L. monocytogenes from other Listeria species. Hence, two selective isolation media, L. monocytogenes blood agar (LMBA) and Rapid 'L. mono agar (RLMA), were compared with Oxford agar for isolating L. monocytogenes from cheese. Queso fresco cheese was inoculated at 10(0) or 10(1) CFU/g with a five-strain mixture of L. monocytogenes or with the five-strain L. monocytogenes mixture and Listeria innocua. Cheese samples were stored at 21, 12, and 4 degrees C and Listeria counts were determined at 3, 7, and 10 days; 7, 10, 14, 21 days; and 2, 4, 8, and 12 weeks postinoculation, respectively. Surface and interior cheese samples as well as liquid exudate produced during storage were assayed individually to determine differences in Listeria contamination at different sampling locations. L. monocytogenes was more easily differentiated from L. innocua on RLMA than LMBA and Oxford agar. Similar L. monocytogenes counts (ca. 10(4) CFU/g) were obtained on the last sampling day on the surface and interior of cheese samples (P > 0.05) for all storage temperatures and both initial inoculation levels, but smaller cell numbers were detected in the exudate produced during storage. In addition, simultaneous inoculation of L. innocua with L. monocytogenes did not affect the final L. monocytogenes counts in the cheese. The amount of exudate released from the cheese and decrease of pH correlated with storage temperature. More exudate was produced and a greater decrease of pH occurred at 21 degrees C than at 12 or 4 degrees C. Our results indicate that RLMA is a suitable medium for isolating L. monocytogenes from queso fresco cheese. Higher counts of L. monocytogenes were obtained from surface and interior samples of cheese than from the exudate of the cheese during storage. In addition, pH may be a useful indicator of improperly stored queso fresco cheese.     

Rabbit meat as a source of bacterial foodborne pathogens

Even though worldwide production of rabbit meat is >1,000,000 tons, little information is available for rabbit meat microbiology. This study provides data on the prevalence of Salmonella, Escherichia coli O157:H7, Yersinia enterocolitica, Listeria spp., motile Aeromonas spp., and Staphylococcus aureus on rabbit meat. A total of 24 rabbit carcasses from two abattoirs and 27 rabbit meat packages from supermarket displays were examined. In addition to culturing methods, associated virulence genes were investigated by PCR in suspect isolates and samples. Neither Salmonella nor E. coli O157:H7 was detected. All samples were negative for virulence-associated invA, stx1, and stx2 genes. At one abattoir, two carcasses (3.9%) carried Y. enterocolitica yst-, and two were positive for the yst gene, although viable Y. enterocolitica cells were not recovered from these samples. Seven samples (13.7%) were contaminated with Listeria. Of them, three were positive for hly and iap genes (Listeria monocytogenes hly+ / iap+), two carried Listeria seeligeri, one carried Listeria ivanovii, and one carried Listeria innocua. For detectable motile Aeromonas spp. (average count, 1.77 +/- 0.62 log CFU/g), the contamination rate was 35.3%, although ca. 90% of the samples were positive for the aerA and/or hlyA genes. The majority of aeromonad isolates were Aeromonas hydrophila aerA+ / hlyA+. Aeromonas caviae, Aeromonas popoffii, Aeromonas schubertii, and the two biovars of Aeromonas veronii were also isolated. The prevalence of S. aureus contamination (average count, 1.37 +/- 0.79 log CFU/g) was 52.9%. Among 27 S. aureus isolates, two harbored genes for staphylococcal enterotoxin B (seb), and two harbored genes for staphylococcal enterotoxin C (sec). The remaining isolates were negative for sea, seb, sec, sed, and see.     

Low incidence of foodborne pathogens of concern in raw milk utilized for farmstead cheese production

Overall milk quality and prevalence of four target pathogens in raw milk destined for farmstead cheesemaking was examined. Raw milk samples were collected weekly from June to September 2006 from 11 farmstead cheese operations manufacturing raw milk cheese from cow's, goat's, and sheep's milk. Samples were screened for Listeria monocytogenes, Staphylococcus aureus, Salmonella, and Escherichia coli O157:H7 both quantitatively (direct plating) and qualitatively (PCR). Overall, 96.8% of samples had standard plate counts of < 100,000 CFU/ml, 42.7% of which were < 1,000 CFU/ml. Although no federal standards exist for coliforms in raw milk, 61% of samples tested conformed to pasteurized milk standards under the U.S. Pasteurized Milk Ordinance (PMO) at < 10 CFU/ml. All cow and sheep milk samples and 93.8% of goat milk samples were within the limits dictated by the PMO for somatic cell counts. Of the 11 farms, 8 (73%) produced samples that were positive for S. aureus, which was detected in 34.6% (46 of 133) of milk samples. L. monocytogenes was isolated from three milk samples (2.3%), two of which were from the same farm. E. coli O157:H7 was recovered from one sample of goat's milk for an overall incidence of 0.75%. Salmonella was not recovered from any of the 133 samples. The findings of this study suggest that most raw milk intended for farmstead cheesemaking is of high microbiological quality with a low incidence of pathogens. These data will help inform risk assessments associated with the microbiological safety of farmstead cheeses, particularly those manufactured from raw milk.     

Microbiological safety of sandwiches from hospitals and other health care establishments in the United Kingdom with a focus on Listeria monocytogenes and other Listeria species

In the United Kingdom between 1999 and 2004, there were four outbreaks of Listeria monocytogenes infection associated with sandwiches purchased from or provided in hospitals. Elderly or immunocompromised individuals and pregnant women are particularly vulnerable to infection; therefore, the focus of this study was on sandwiches served in health care establishments. Of 3,249 sandwich samples collected between April 2005 and March 2006, 3.3% were of unsatisfactory microbiological quality because of high levels of Enterobacteriaceae (2.0%; > or = 10(4) CFU/g for sandwiches not containing salad), Escherichia coli (0.8%; > or = 10(2) CFU/g), Staphylococcus aureus (0.6%; > or = 10(2) CFU/g), and/or Listeria spp. (0.1%; two samples with L. welshimeri at 1.8 x 10(2) and 7.4 x 10(3) CFU/g and one sample with L. seeligeri at 1.8 x 10(3) CFU/g). Overall, 7.6% of sandwiches were contaminated with Listeria spp. L. monocytogenes was detected in 2.7% (88) of samples: 87 samples at < 10 CFU/g and 1 sample at 20 CFU/g. More frequent contamination with Listeria spp. and L. monocytogenes was found in sandwiches collected from hospital cafeterias, shops, or wards and in sandwiches stored and/or displayed at temperatures higher than 8 degrees C. The presence of Listeria spp. and L. monocytogenes also was associated with sandwiches that (i) were supplied from outside the establishment, (ii) were prepacked, (iii) had a main sandwich filling of poultry meat, or (iv) contained salad ingredients, soft cheese, and/or mayonnaise. Control of L. monocytogenes in sandwich manufacturing and within health care establishments is essential to minimize the potential for consumption of this bacterium at levels hazardous to health. The findings from this study support the proposal that manufacturers supplying sandwiches to health care establishments should follow the British Sandwich Association recommended guidelines of complete absence of L. monocytogenes in sandwiches at the point of production.     

Occurrence of Listeria spp. in critical control points and the environment of Minas Frescal cheese processing

Critical control points (CCPs) associated with Minas Frescal cheese (a Brazilian soft white cheese, eaten fresh) processing in two dairy factories were determined using flow diagrams and microbiological tests for detection of Listeria monocytogenes and other species of Listeria. A total of 218 samples were collected along the production line and environment. The CCPs identified were reception of raw milk, pasteurization, coagulation and storage. Thirteen samples were positive for Listeria; 9 samples were Listeria innocua, 2 were Listeria grayi and 2 were L. monocytogenes. In factory A, Listeria was found in 50% of raw milk samples, 33.3% of curd samples, 16.7% of pasteurized milk samples, 16.7% of cheese samples and 25% of rubber pipes used to transport the whey. The microorganism was not obtained from environmental samples in this plant. In factory B, Listeria was found in one sample of raw milk (16.7%) and in three samples of environment (17.6%) and L. monocytogenes was obtained from raw milk (16.7%) and the floor of the cheese refrigeration room (14.3%). Two serotypes, 4b and 1/2a, were observed among the strains of L. monocytogenes isolated, both which are frequently involved in outbreaks of food-borne listeriosis and sporadic cases of the disease all over the world.     

Elimination of Listeria monocytogenes in soft and red smear cheeses by irradiation with low energy electrons

Soft and red smear cheeses are frequently contaminated by Listeria monocytogenes , sometimes at relatively high concentration (< 10⁵ CFUg^-1). This bacterium is radiosensitive (D₁₀ value of approximately 0.45 kGy) but irradiation of the whole cheese by X-rays induced off-flavours when the dose exceeded 1.0 kGy. Irradiation could be effective in eliminating L. monocytogenes only from lightly contaminated cheeses (> 10²CFU g^-1).
L. monocytogenes appears only in the rind (where the pH is greater than 6.3) and never grows in the core of the cheese. Under these conditions, a specific irradiation of the rind after ripening, with a low-energy electron beam at relatively high doses (up to 3.0 kGy), allows the total elimination of L. monocytogenes in heavily contaminated samples (10⁵-10⁶ CFU g^-1) without noticeable modifications of the organoleptic properties of the cheese.     

Microbial quality of shrimp products of export trade produced from aquacultured shrimp

Bacteriological quality of individually quick frozen (IQF) shrimp products produced from aquacultured tiger shrimp (Penaeus monodon) has been analysed in terms of aerobic plate count (APC), coliforms, Escherichia coli, coagulase-positive staphylococci, Salmonella, and Listeria monocytogenes. Eight hundred forty-six samples of raw, peeled, and deveined tail-on (RPTO), 928 samples of cooked, peeled, and deveined tail-on (CPTO), 295 samples of headless, undeveined shell-on (HLSO), and 141 samples of raw, peeled, and deveined tail-off (RPND) shrimps were analysed for the above bacteriological parameters. Salmonella was isolated in only one sample of raw, peeled tail-on. Serotyping of the strain revealed that it was S. typhimurium. While none of the cooked, peeled tail-on shrimp samples exceeded the aerobic plate count (APC) of 10(5) colony forming units per gram (cfu/g), 2.5% of raw, peeled, tail-on, 6.4% of raw, peeled tail-off, and 7.5% of headless shell-on shrimp samples exceeded that level. Coliforms were detected in all the products, though at a low level. Prevalence of coliforms was higher in headless shell-on (26%) shrimps followed by raw, peeled, and deveined tail-off (19%), raw, peeled tail-on (10%), and cooked, peeled tail-on (3.8%) shrimps. While none of the cooked, peeled tail-on shrimp samples were positive for coagulase-positive staphylococci and E. coli, 0.6-1.3% of the raw, peeled tail-on were positive for staphylococci and E. coli, respectively. Prevalence of staphylococci was highest in raw, peeled tail-off (5%) shrimps and the highest prevalence of E. coli (4.8%) was noticed in headless shell-on shrimps. L. monocytogenes was not detected in any of the cooked, peeled tail-on shrimps. Overall results revealed that the plant under investigation had exerted good process control in order to maintain superior bacteriological quality of their products.     

Microbial Assessment in School Foodservices and Recommendations for Food Safety Improvement

ABSTRACT:  This study evaluated microbial food safety in school foodservices. Five school foodservices were randomly selected, and samples from water, cooking utensils, tableware, foodservice surroundings, and linen were collected in summer and winter ( N = 420). Tap and drinking water samples were collected, samples of food contact surfaces were collected by swab-kit, and samples for foodservice workers' hands and gloves were prepared by glove juice method. Aerobic plate count (APC) and coliform bacterial populations were enumerated on plate count agar (PCA) and desoxycholate lactose agar, respectively. The presence of Escherichia coli , Salmonella , Listeria monocytogenes , and Staphylococcus aureus was also examined by biochemical identification tests. In addition, PCA agar for APCs and Baird-Parker agar for S . aureus were used to enumerate airborne microorganisms. Higher APCs (< 0 to 5.1 log CFU/mL) than acceptable level were generally observed in water samples, while low coliform counts were found in the samples. High APCs were enumerated in cooking utensils, foodservice workers, tableware, and foodservice surroundings, and coliforms were also found in the samples for both seasons. The presence of Salmonella was found from only 10% of plastic glove samples (summer), and the presence of L . monocytogenes was not observed in all samples. S . aureus was detected in some of water, cooking utensils, tableware, employees, and foodservice surroundings, and E . coli was observed in cooking utensils (10% to 20%; summer). No obvious airborne bacteria were detected. These results showed that sanitation practice in school foodservices should be improved, and the results may be useful in microbial assessment of school foodservices.     

Antimicrobial chitosan-lysozyme (CL) films and coatings for enhancing microbial safety of mozzarella cheese

ABSTRACT:  This study investigated the antimicrobial activities of chitosan-lysozyme (CL) composite films and coatings against tested microorganisms inoculated onto the surface of Mozzarella cheese. CL film-forming solutions (FFS) with a pH of 4.4 to 4.5 were prepared by incorporating 0% or 60% lysozyme (per dry weight of chitosan) into chitosan FFS with or without a pH adjustment to 5.2. Sliced cheese was subjected to 3 CL package applications: film, lamination on a multilayer coextruded film, and coating. Cheese was inoculated with Listeria monocytogenes , Escherichia coli , or Pseudomonas fluorescens at 10⁴ CFU/g, or with mold and yeast at 10² CFU/g. Inoculated cheese was individually vacuum packaged and stored at 10 °C for sampling at 1, 7, and 14 d for bacteria, and at 10, 20, and 30 d for fungi. Inoculated bacteria survived but failed to multiply in untreated cheese during storage. Treated cheese received 0.43‐ to 1.25‐, 0.40‐ to 1.40‐, and 0.32- to 1.35-log reductions in E . coli , P. fluorescens , and L . monocytogenes , respectively. Incorporation of 60% lysozyme in chitosan FFS showed greater antimicrobial effect than chitosan alone on P. fluorescens and L . monocytogenes . The pH adjustment only affected the antimicrobial activity on L . monocytogenes , with lower pH (unadjusted) showing greater antimicrobial effect than pH 5.2. Mold and yeast increased to 10⁵ CFU/g in untreated cheese after 30 d storage. Growth of mold was completely inhibited in cheese packaged with CL films, while 0.24‐ to 1.90‐ and 0.06‐ to 0.50-log reductions in mold populations were observed in cheese packaged with CL-laminated films and coatings, respectively. All CL packaging applications resulted in 0.01- to 0.64-log reduction in yeast populations.     

Effects of cetylpyridinium chloride, acidified sodium chlorite, and potassium sorbate on populations of Escherichia coli O157:H7, Listeria monocytogenes, and Staphylococcus aureus on fresh beef

The effects of selected food-grade antimicrobial agents at decreasing the number of pathogenic bacteria on fresh beef were determined. Beef cubes inoculated with Escherichia coli O157:H7, Listeria monocytogenes, or Staphylococcus aureus were sprayed with 0.5% cetylpyridinium chloride (CPC), 0.12% acidified sodium chlorite (ASC), 0.1% potassium sorbate (PS), or an equal mix of any two solutions. The beef samples were placed on absorbent tray pads sprayed with each single or mixed solution, wrapped with polyvinyl chloride film, heat sealed, and stored at 4 degrees C for 2 weeks. Surface sanitization using CPC, ASC, or an equal mix of these two agents effectively reduced microbial numbers on the beef during storage. At day 0, ASC and the CPC-ASC mix reduced the number of E. coli O157:H7 by 2.50 and 1.58 log CFU/cm2, respectively. CPC demonstrated a 3.25-log reduction of L. monocytogenes and a 4.70-log reduction of S. aureus at 14 days. The CPC-PS mix reduced E. coli O157:H7 numbers by 1.46, L. monocytogenes by 2.95, and S. aureus by 4.41 log CFU/cm2 at 14 days. PS alone and the mixed solutions, CPC-ASC, CPC-PS, or ASC-PS, were not as effective as ASC or CPC alone. To effectively reduce E. coli O157:H7, L. monocytogenes, or S. aureus numbers, higher (> 0.1%) concentrations of PS were necessary. Loss of redness and light color of beef surfaces consistently coincided with decreases in pH for ASC-treated beef samples.