Factors associated with the serological prevalence of Salmonella enterica in Greek finishing swineherds.

Blood samples were taken from 50 finishing pigs at 90-105 kg in each of 59 randomly selected farrow-to-finish herds. The sera were tested for antibodies to Salmonella enterica by the Danish mix-ELISA. Samples with an optical density of > 10% were considered to be positive. Associations between the odds of seropositivity of pigs and possible risk factors were evaluated in multivariable logistic regression models. The results of the analysis indicated that pigs fed non-pelleted dry or wet ration had 11 (P = 0.0004) or 9 (P = 0.02) times, respectively, lower odds of seropositivity than those fed pelleted ration. The risk of seropositivity was 4 (P = 0.0006) times higher in pigs fed a combination of chlortetracycline, procaine penicillin and sulphamethazine during fattening than in those fed an approved growth promotor or a probiotic.

Seroprevalence and antibiotic sensitivity of serotypes of Salmonella enterica in Greek pig herds.

Blood samples were taken from 50 pigs in each of 59 farrow-to-finish production herds and from 40 pigs in each of four of five registered multiplying herds. Samples of feed and faeces were also collected from 17 of the production herds and from the four multiplying herds. The sera were tested for antibodies to Salmonella enterica by the Danish mix-ELISA, and the organisms were isolated, serotyped and sensitivity tested by standard techniques. The average within-herd seroprevalence was 3.4 per cent and at least one pig tested seropositive in 21 of the 59 herds. In the multiplying herds, only a single seroreactor was detected. Salmonellae were isolated from only five of 95 feed samples, from two of the 17 herds sampled, Salmonella tennessee in four of five samples from one herd and an untypable strain in one of five samples from another. Four infected faecal samples were detected in four herds; they harboured Salmonella typhimurium, Salmonella bredeney or Salmonella london. No salmonellae were isolated from the samples of feed and faeces taken from the multiplying herds. The S london and S typhimurium had a low sensitivity to streptomycin, kanamycin and neomycin, and the S typhimurium also had low sensitivity to amoxycillin, ticarcillin, piperacillin, amoxycillin + clavulanic acid, cefalotin and cefoperazone. The other isolates were sensitive to all the antimicrobial agents tested.

Prediction of Listeria spp. growth as affected by various levels of chemicals, pH, temperature and storage time in a model broth.

The effects of concentration of NaCl (0.5 to 12.5%), methyl paraben (0.0 to 0.2%), sodium propionate (0.3%), sodium benzoate (0.1%), potassium sorbate (0.3%), pH (> 5.9) temperature (4 to 30 degrees C), storage time (up to 58 d) and inoculum (> 10(5) to > 10(-2) per ml) on the log10 probability percentage of one cell of Listeria spp. to initiate growth in a broth system were evaluated in a factorial design study. At pH 5.96 and temperature ranging from 4 to 30 degrees C the concentrations of sodium propionate, potassium sorbate, and sodium benzoate examined allowed growth of L. monocytogenes with lag phases at 4 degrees C of 18, 27 and 21 days, respectively. For 0.1 and 0.2% methyl paraben growth of all Listeria spp. was initiated at 8 degrees C and 30 degrees C, respectively. At pH 6, concentration of 12% NaCl supported the growth of L. monocytogenes at 8 to 30 degrees C, whereas 12.5% inhibited all Listeria species. Four regression equations were derived relating probability of growth initiation to temperature, concentrations of NaCl and preservatives storage time, and Listeria species specific effects. From these equations, the number of cells needed for growth initiation can be calculated. The impact of this type of quantitative study and its possible application on the development of microbial standards for foods is discussed.

Temperature distribution and prevalence of Listeria spp. in domestic, retail and industrial refrigerators in Greece.

The present paper examined the presence of Listeria spp. in the environment of domestic, retail and industrial refrigerators. From 136 household refrigerators, 136 surface samples were taken from the walls or shelves, and 125 from cheese compartments. Only two refrigerators harboured L. monocytogenes. From 228 food store refrigerators, 335 samples were taken. Of these, 118 were in in contact with cheeses, 69 with sausages, 21 with cheese and sausages, 20 with miscellaneous products and 107 from refrigerator handles. Listeria spp. and L. monocytogenes were found in 3.1% and 1.7%, of the samples respectively. Listeria spp. was not detected in any of the nine dairy plant refrigerators examined. Listeria monocytogenes and L. innocua were found in 4.5 and 36.4%, respectively, of the 22 refrigerators inside meat processing plants, with only one of 22 refrigerators handles being positive for L. monocytogenes. Temperature distribution in the refrigerators was also investigated. Fifty five per cent of the 136 domestic and 32% of the 228 retail store refrigerators had temperatures of greater than or equal to 9 degrees C. The range of refrigeration temperatures of the industrial refrigerators was 0-2 degrees C for meat plants and 2-7 degrees C for dairy plants. No correlation of any kind could be established between the prevalence of Listeria spp. and the temperature of the various refrigerators due to the low number of positive samples.

Potential growth and control of Escherichia coli O157:H7 in soft hispanic type cheese.

This study examined growth and control of two enterohemorrhagic Escherichia coli serotype O157:H7 strains in a soft Hispanic type cheese (Queso Fresco). Cheese was made in the laboratory using a commercial procedure and after inoculation it was stored under vacuum at temperatures ranging from 8 to 30 degrees C. The minimum temperature that allowed growth of E. coli in the unmodified normal cheese (pH 6.6) was 10 degrees C. No growth of either strains was observed during a 2 month storage period at 8 degrees C. Accumulated data from the growth studies were used for development of models relating square root of 1/LT (LT = lag time) and specific growth rate, to temperature. The effect of selected antimicrobials (potassium sorbate, sodium benzoate, and sodium lactate) added to milk or cheese on the growth and survival of these pathogens at various storage temperatures was also evaluated. Addition of sodium benzoate (0.3%) to cheese (pH 6.6) or addition of potassium sorbate (0.3%) to cheese (pH 6) made from milk acidified to pH 5.9 with propionic acid, had a significant impact on delaying or preventing growth of the pathogens.

Potential growth and control of Salmonella in Hispanic type soft cheese.

This study evaluated the growth and control of Salmonella serotypes in a soft Hispanic type cheese (Queso Fresco). Cheese was made in the laboratory using a commercial procedure and after inoculation it was stored under vacuum at temperatures ranging from 6 to 30 degrees C. The minimum temperature that allowed growth of Salmonella was 8 degrees C. Accumulated data from the growth studies were used for the development of models relating the square root of 1/LT (LT = lag time) and specific growth rate to temperature. The effect of selected antimicrobials (potassium sorbate, sodium benzoate and sodium lactate) on the growth and survival of Salmonella in milk and in cheese at various storage temperatures was also examined. Addition of sodium benzoate (0.3%) to cheese (pH 6.6) or addition of potassium sorbate (0.3%) to cheese (pH 6.0) made from milk, which was acidified to pH 5.9 with propionic acid, had a significant impact on delaying or preventing growth of the pathogen.

Modeling lag phase of nonproteolytic Clostridium botulinum toxigenesis in cooked turkey and chicken breast as affected by temperature, sodium lactate, sodium chloride and spore inoculum.

The length of the lag phase (LP) of toxigenesis in commercially cooked turkey meat stored under vacuum was determined as affected by 0, 1.2, 2 and 3% sodium lactate (L), 0, 1 and 2% NaCl (S), spore (pool of nonproteolytic B and E strains: B2, B17, B197, B706, E211, E250, E KA-2 and E Beluga) inoculum (I) of 10(-2) to 10(4), storage temperature (T) of 4, 8, 12, 16, 20 and 30 degrees C and their interactions. The time from inoculation to the detection of first toxic sample was defined as LP. Using regression analysis the following model predictive of LP of C. botulinum toxigenesis in the cooked turkey breast was derived: Log(1/LP) = -2.2877 -0.1235(S) -0.2174(L) +0.4391(square root of T) +0.0204(square root of T) (I). The model explained 94.5% of the variation in results, in which square root of T was the most influential factor (65%), followed by L (21.2%), interaction of I and square root of T (4.9%) and S (3.4%). The model predicted LPs longer than those observed in 28.3% of the comparisons, but only in 1% of the comparisons when the lower limit of the 90% confidence interval of LP was used. Similar trends on the effect of L on C. botulinum were observed in an inoculated chicken meat study. This study demonstrated quantitatively that increasing L and S concentrations and lowering of T had a beneficial effect on delaying toxigenesis.

Disease determinants of sporadic salmonellosis in four northern California counties. A case-control study of older children and adults.

A population-based, case-control study of sporadic salmonellosis was conducted in 1988 and 1989 in four northern California counties. The study included 120 patients and 265 control subjects. Conditional logistic regression analysis (adjusted for age) revealed that patients were more likely to consume undercooked chicken prior to the onset of disease (odds ratio [OR], 23.57; 95% confidence interval [CI], 2.89 to 192.30). Elevated associations were also found with recent travel to foreign countries (OR, 9.69; 95% CI, 3.18 to 29.56), diabetes (OR, 6.29; 95% CI, 1.56 to 25.34), hormonal replacement therapy (principally conjugated estrogen) in older women (OR, 4.20; 95% CI, 1.82 to 9.71), and antibiotic therapy prior to illness (OR, 1.96; 95% CI, 0.86 to 4.37). The problems of studying self-selected cases that may lead to alternative explanations for these findings are also discussed.

Growth and toxigenesis of C. botulinum type E in fishes packaged under modified atmospheres.

Modified atmosphere packaging of fresh fish is used to market high quality products in some European countries. The potential risk of C. botulinum growth in these extended shelf-life foods is still a concern; especially since toxigenesis may precede organoleptic spoilage. This paper will present toxigenic data from rockfish, salmon and sole muscle tissues which were inoculated with a pool of non-proteolytic C. botulinum type E at seven levels (10(-2)-10(4) spores/sample), and stored under vacuum and 100% CO2, at incubation temperatures between 30 and 4 degrees C, for up to 60 days. Factorial experimental design allowed predictive formulae to be developed able to describe the lag time prior to C. botulinum toxigenesis and the probability of one spore to initiate toxigenesis based upon the storage conditions. Accurate characterization of the microbial ecology of C. botulinum in modified atmosphere-packaged fish, will support safe exploitation of these packaging systems in the market place, and identify critical control points for potential product or process abuses.

Present state of knowledge on staphylococcal intoxication.

Globally, staphylococcal intoxication remains a very common food poisoning. In this review, emphasis is being placed on epidemiological aspects of the problem and the effect of food environment on the survival and growth of staphylococci and production of enterotoxins. The high prevalence of staphylococci in raw foods of animal origin requires effective processing for safety. Man remains a major reservoir for post-process recontamination. The effect of the intrinsic characteristics of foods (pH, water activity, Eh, preservatives competing microbial flora, natural food) and extrinsic parameters of processing and storage (temperature, freezing, irradiation, dehydration, packaging, humidity) on staphylococcal survival, growth and enterotoxin production has been evaluated extensively. While staphylococci can be destroyed easily the enterotoxins can survive practically all food processing. While extreme levels of intrinsic variables can control enterotoxin production, yet the environment of most foods is conductive to staphylococcal growth. Rapid food cooling, refrigeration and consumer, food handler and processor education remain the key to staphylococcal food poisoning prevention.

Campylobacter jejuni Infection on Poultry Farms and its Effect on Poultry Meat Contamination during Slaughtering.

In 1984, we monitored 4 ranches with a total of 24 houses (15,000-20,000 birds/house) for 3 consecutive generations (January-August). On epidemiologic grounds, infection of birds did not originate at the hatcheries or the central water and feed. Considering all lots of birds, the infection rate increased from 2.3% by the 10th day to 9.5, 29.7, 47.9, 65.7, 78.6 and 81.8% by the 20th, 30th, 40th, 45th, 50th day and at slaughter times, respectively. Transmission from one generation of chickens to the next via the old litter is suspected, but not proven microbiologically. A 5-log reduction of Campylobacter jejuni was shown in experimentally inoculated litters stored at 17 and 30°C for 6 d and 8°C for 11 d. The houses remained empty for 9-29 d before being filled with new chicks. Carrier flocks contaminated the slaughterhouse equipment to such an extent that negative flocks processed afterwards resulted in contaminated meat. Lack of effective sanitation at the end of the day contributed to the contamination of meat from Campylobacter -free birds processed the next day. Feather picker drip water was positive 94% of the sampling times at levels of log10 3.4 (1.0-4.7). Scalding temperatures did not affect the level of contamination in the finished products (P>0.2). An ELISA based on heat-stable antigens was adapted for the detection of circulating antibodies. Of 56 broilers aged 50 to 68 d, only 2 (3.5%) 68 d old with log10 5.4 C. jejuni /g of feces were considered as positive. Birds considered negative harbored C jejuni in their ceca at levels of log10 2.0 to 5.4/g of feces. Five out of 6 (83%) 18 month-old hens were considered as positive. Yet, none of these birds were found carrying C. jejuni in their feathers or ceca.

Preliminary Observations on the Occurrence of Campylobacter jejuni at Four California Chicken Ranches.

During a 3-month period from April to July, 1983, three Campylobacter jejuni survey studies were done at four chicken ranches in Northern California. In Survey 1, 29 of 200 (14.5%) total cloacal swab and dropping samples collected from the 20 occupied houses on the four ranches were positive for C. jejuni . Positive samples were from two of the four ranches. On one of these ranches, both occupied houses were positive. However, on the other ranch, only one of six houses was positive. Follow- up feed, water, litter and dropping samples were collected from three houses on this latter ranch during Survey 2. Again, positive samples were from only one house with 26 of 30 (86.7%) droppings positive for C. jejuni and 3 of 20 (15%) water samples positive. No feed or litter samples were positive. During Survey 3, cloacal swabs or bird dropping samples were collected from two houses on each of three ranches at approximately weekly intervals from the time of arrival of new flocks of chickens. All six houses ultimately became positive. The first positive samples were collected from one house when chickens in that house were 12 d old. This house had contained C. jejuni -positive chickens during Survey 1, had old litter, and had not been very thoroughly cleaned and disinfected. First positive samples in each of the other five houses were collected when chickens were between 40 and 46 d old. Two of these houses had previously been positive for C. jejuni but had old litter replaced with new and had been thoroughly cleaned and disinfected. The three other houses had been negative for C. jejuni during Survey 1. Two of these houses had new litter and had been well cleaned. The other house contained old litter and had not been well cleaned. When each house became positive, virtually all samples from that house were positive within a week indicating that C. jejuni likely spreads rapidly among birds in the house.

Use of enzyme linked immunosorbent assay (ELISA) in the quantitation of Clostridium perfringens type A enterotoxin and antienterotoxin antibodies.

ELISA procedure for quantitation of enterotoxin of Clostridium perfringens type A was worked out. It was possible to detect as little as 0.0022 microgramme of enterotoxin. When applied to quantitate the enterotoxin in laboratory contaminated faeces and cooked minced beef, ELISA detected as little as 0.024 microgramme of enterotoxin. ELISA procedure for determination of titre of antibodies to enterotoxin was also developed using hyperimmunised rabbit and sheep sera. It was possible to use this procedure in sero-survey.

Prevalence of Campylobacter jejuni in chicken wings.

Campylobacter jejuni was found in 82.9% of 94 chicken wing packages analyzed on the day of arrival at supermarkets and in 15.5% of 45 packages obtained from the supermarket shelves a few days later. The number of bacterial cells ranged from 10(2) to 10(3.9) per wing. The prevalence of C. jejuni in the wings varied with the brand, the day of sampling, and the age of the product.

Prevalence of Campylobacter jejuni in two California chicken processing plants.

Two federally inspected California chicken processing plants participated in Campylobacter jejuni prevalence studies. Twelve sampling sites were included in each of four groups. Groups were based on bird age, scald water temperature, and plant sampled. Scald water temperatures of 60 degrees C (140 degrees F) did not contribute to a lower prevalence of C. jejuni in edible parts, as did temperatures of 53 degrees C (127 degrees F) and 49 degrees C (120 degrees F). The feather picker and chilling tank were areas of major cross-contamination. C. jejuni was isolated from 68% of the ready-for-market products. The organism was recovered from 60 to 100% of the ceca in the four groups, and some numbers in the fecal material exceeded 10(6)/g. The level of C. jejuni in intestinal tracts seemed to correlate with the presence of the organism in the edible parts.

Prevalence of Campylobacter jejuni at Different Sampling Sites in Two California Turkey Processing Plants.

A prevalence survey for Campylobaeter jejuni from 12 sites was made in two turkey processing plants. Both plants are federally inspected but differ in the age of birds slaughtered (18 and 24 wk for plant A and B, respectively) and scald water temperatures (2.5 min at 60°C and 3 min at 57.2°C for plants A and B, respectively). A total of 594 samples were taken during the period May to July 1982. Isolation rates for individual sites and plant A and B, respectively, were as follows: feathers 23.3 and 3.3%, scald water overflow 5.7 and 5.6%, feather picker drip water 66.7 and 94.4%, recycled water for cleaning gutters 77.8 and 77.8%, ceca 86.7 and 93.3%, final carcass wash water 61.1 and 27.8%, neck skin before chiller 36.7 and 10%, chiller water overflow 0 and 44.4%, neck skin after chiller, hearts, livers, wings and mechanically deboned meat 0 and 0%. These isolation rates were based on detection levels of > 10 cells/ml or g for all water samples, skin and deboned meat, > 100 cells/g for feathers, heart, liver or wing and > 1000 cells/g for fecal samples. Mean cell counts per gram of feces were log10 5, with a range of log10 3.4 to log10 6.8. The defeathering equipment contributed significantly to cross-contamination. Use of chlorinated water in the chillers at 14 to 18 ppm levels may be responsible for the absence of C. jejuni in the edible turkey parts.

Production of italian dry salami: effect of starter culture and chemical acidulation on staphylococcal growth in salami under commercial manufacturing conditions.

The effect of starter culture and chemical acidulation on the growth and enterotoxigenesis of Staphylococcus aureus strain S-6 in Italian dry salami under commercial manufacturing conditions was studied. The experimental design included two levels of S. aureus (10 and 10/g), three levels of starter culture (0, 10, and 10/g), three levels of initial pH (pH(0)) (6.1, 5.5, and 4.8), two manufacturing plants, and three replications. S. aureus growth in the salami was affected significantly (P < 0.005) by pH(0), initial levels of S. aureus (staph(0)) and lactic acid bacteria (LAB(0)), day of fermentation, and by the interactions of pH(0) x day, pH(0) x LAB(0), LAB(0) x staph(0), pH(0) x staph(0), and pH(0) x location of fermentation. In general, the lower the pH(0) and the higher the LAB(0), the greater the inhibition of S. aureus. The LAB levels during the fermentation were affected significantly (P < 0.005) by pH(0), LAB(0), day of fermentation, location, LAB(0) x pH(0), and LAB(0) x day. Derived regression equations related level of S. aureus and LAB at any day of fermentation to a number of microbiological and chemical variables. Close similarity of observed and predicted levels of S. aureus and LAB growth demonstrated the usefulness of the experimental approach in evaluating the safety of a process. No detectable enterotoxin or thermonuclease was found at any stage of processing even when S. aureus reached levels of 10/g of salami.

Production of Italian Dry Salami. I. Initiation of Staphylococcal Growth in Salami Under Commercial Manufacturing Conditions.

Three strains of Staphylococcus aureus (S-6, 137 and 472) were inoculated, in duplicate, into Italian-style dry salami made with finished product as starter and processed under commercial manufacturing conditions. Five levels of S. aureus ranging from 2.2 × 102 - 1.8 × 107 cells/g were used. A fourth strain (264) was inoculated at a level of 105 cells/g. All strains of S. aureus grew at every level of inoculation, but the amount of growth was dependent on inoculum size. Strains S-6 and 472 increased in number by 1.2 - 2.9 logs (mean 2.14) at inoculum levels of 2.3 × 102 - 2.5 × 103 cells/g, and by 2.1 - 3.2 logs (mean 2.66) at inoculum levels of 3.7 × 104 - 6.6 × 105 cells/g. Strain 137 was very sensitive to salami environment and only increased by 0.47 - 1.86 logs (mean 1.23) even at the greatest inoculum level. Strain 264 increased in numbers by 1.5 logs in the presence of 5 × 105 inoculated lactobacilli/g and by 2.5 logs in the presence of 6 × 104 naturally occurring lactic acid bacteria. Staphylococci occurring naturally in salami mix were unable to grow to levels greater than 2 × 104 cells at any time during processing of experimental sausages. Thermonuclease was detected only in salamis inoculated with strains S-6 and 472 at initial levels of greater than 3.7 × 104 cells/g and only when growth reached levels greater than 107 cells/g. No enterotoxin was detected in any of the inoculated samples. Development of regression equations allowed description of the growth of inoculated S. aureus in the salami during manufacturing as affected by a number of variables.