Sheep Milk Symbiotic Ice Cream: Effect of Inulin and Apple Fiber on the Survival of Five Probiotic Bacterial Strains during Simulated In Vitro Digestion Conditions

We conducted a study to determine the survival of bacterial cells under in vitro digestion. For this purpose, ice cream mixes were prepared: control, with 4% inulin, 2.5% inulin and 1.5% apple fiber and 4% apple fiber. Each inoculum (pH = 4.60 ± 0.05), containing 9 log cfu g^-1 bacteria, at 5% (w/w) was added to the ice cream mixes (Lacticaseibacilluscasei 431, Lactobacillus acidophilus LA-5, Lacticaseibacillus paracasei L-26, Lacticaseibacillusrhamnosus, Bifidobacterium animalis ssp. lactis BB-12) and fermentation was carried out to pH 4.60 ± 0.05. The in vitro digestion method simulated the stages of digestion that occur in the mouth, stomach and small intestine under optimal controlled conditions (pH value, time and temperature). At each stage of digestion, the survival rate of probiotic bacteria was determined using the plate-deep method. As expected, in the oral stage, there was no significant reduction in the viability of the probiotic bacteria in any ice cream group compared to their content before digestion. In the stomach stage, Bifidobacterium animalis ssp. lactis BB-12 strain had the highest viable counts (8.48 log cfu g^-1) among the control samples. Furthermore, a 4% addition of inulin to ice cream with Bifidobacterium BB-12 increased gastric juice tolerance and limited strain reduction by only 16.7% compared to the number of bacterial cells before digestion. Regarding ice cream samples with Bifidobacterium BB-12, replacing part of the inulin with apple fiber resulted in increased survival at the stomach stage and a low reduction in the bacterial population of only 15.6% compared to samples before digestion. At the stomach stage, the positive effect of the addition of inulin and apple fiber was also demonstrated for ice cream samples with Lacticaseibacilluscasei 431 (9.47 log cfu g^-1), Lactobacillus acidophilus LA-5 (8.06 log cfu g^-1) and Lacticaseibacillus paracasei L-26 (5.79 log cfu g^-1). This study showed the highest sensitivity to simulated gastric stress for ice cream samples with Lacticaseibacillusrhamnosus (4.54 log cfu g^-1). Our study confirmed that the 4% addition of inulin to ice cream increases the survival rate of L. casei and Bifidobacterium BB-12 in simulated intestinal juice with bile by 0.87 and 2.26 log cfu g^-1, respectively. The highest viable count in the small intestine stage was observed in ice cream with L. acidophilus. The addition of inulin increased the survival of L. rhamnosus by 10.8% and Bifidobacterium BB-12 by about 22% under conditions of simulated in vitro digestion compared to their control samples. The survival rates of L. casei and L. paracasei were also highly affected by the 4% addition of apple fiber, where the increase under gastrointestinal passage conditions was determined to range from 7.86-11.26% compared to their control counterparts. In comparison, the lowest survival rate was found in the control ice cream with L. rhamnosus (47.40%). In our study at the intestinal stage, only five ice cream groups: a sample with 4% inulin and L. acidophilus, a control sample with Bifidobacterium BB12, a sample with 2.5% inulin and 1.5% apple fiber with Bifidobacterium BB12, a control sample with L. rhamnosus, a sample with 4% fiber and L. rhamnosus reported bacterial cell counts below 6 log cfu g^-1 but higher than 5 log cfu g^-1. However, in the remaining ice cream groups, viable counts of bacterial cells ranged from 6.11 to 8.88 log cfu g^-1, ensuring a therapeutic effect. Studies have clearly indicated that sheep milk ice cream could provide a suitable matrix for the delivery of probiotics and prebiotics and contribute to intestinal homeostasis. The obtained results have an applicative character and may play an essential role in developing new functional sheep milk ice cream.

Prevalence and antimicrobial resistance of Shiga toxin-producing Escherichia coli in milk and dairy products in Egypt

Food contaminated with Shiga toxin-producing Escherichia coli (STEC) represents a hazardous public health problem worldwide. Therefore, the present study was performed to elucidate the virulent and antimicrobial resistance characteristics of STEC isolated from milk and dairy products marketed in Egypt. A total of 125 samples (raw market milk, bulk tank milk, Kareish cheese, white soft cheese, and small scale-produced ice cream, 25 each) were collected for determination the prevalence and antimicrobial resistance profiling of STEC. Thirty-six STEC isolates were recovered from milk and dairy products. Serological analysis illustrated that three isolates were E. coli O157:H7 and 33 isolates belonged to different serotypes. Molecular examination indicated that all isolates harboured stx1 and/or stx2 genes, 14 isolates expressed eaeA gene and 3 isolates possessed rfbE gene. Antimicrobial resistance profiling of the isolates was both phenotypically and genetically examined. Interestingly, 31 out of 36 (86.11%) isolates were multidrug-resistant and harboured the extended-spectrum β-lactamase encoding genes, namely, bla_CTX-M-15, bla_SHV-12 and bla_CTX-M-14. Moreover, 12 isolates (33.33%) harboured plasmid-mediated quinolone resistant gene, qnrS. The overall conclusion of the current investigation indicated insufficient hygienic measures adopted during milking, handling, and processing leading to development of pathogenic and multidrug-resistant STEC.

Application of an Environmental Phage-Based Assay (Sample6 Detect HT/L) for the Detection of Listeria spp. in Ice Cream

Background: Dairy products are common sources of Listeria outbreaks, and early detection of the pathogen is critical to prevent outbreaks of illnesses and financial losses for dairy producers. Objective: This study aimed to evaluate Sample6 Detect HT/L for effective detection of Listeria monocytogenes and L. innocua in ice cream. Methods: Performance of the Sample6 DETECT HT/L was compared with U.S. Food and Drug Administration (FDA) Bacteriological Analytical Manual (BAM) Chapter 10 method for detection of Listeria spp. in ice cream using an unpaired study design. Results: R2-enriched samples tested with Sample6 Detect HT/L performed as well as the reference method at all time points tested from 15 to 24 h. R2 is a proprietary blend for use with the test kit that helps with early detection. All the dPOD_C values (Sample6 Detect HT/L presumptive and confirmed results) equaled zero, indicating 100% concordance between the methods. Both Sample6 Detect HT/L and FDA BAM results showed low dPOD_C values, with confidence intervals indicating no significant differences between Sample6 Detect HT/L and reference method results. Conclusions: Sample6 Detect HT/L is suitable to detect Listeria spp. in ice cream, even with a 12 h enrichment. Sample6 Detect HT/L demonstrated equivalent detection of L. monocytogenes and L. innocua from R2-enriched samples as expected with 15 and 18 h enrichment when compared with the 24 h FDA BAM method for L. monocytogenes. Highlights: These results indicate that Sample6 Detect HT/L, primarily developed for environmental samples, can be used to detect Listeria spp. in ice cream with less incubation time, resulting in faster detection.

Rapid Detection of Listeria in Ice Cream in 13 Hours Using the Roka Listeria Detection Assay

Background: Listeria contamination is a major concern in the ice cream industry; therefore, early and accurate detection is vital. Current detection methods require about a 24 h enrichment period for detection. Objective: Enhance the early detection of Listeria in ice cream using the highly sensitive isothermal ribosomal RNA-based Roka/Atlas Listeria Detection Assay. Methods: The R2 Medium was developed for Listeria enrichment by Molecular Epidemiology, Inc. (Seattle, WA). Comparative growth curve studies were performed on the new R2 Medium for Listeria and the currently validated media for the Roka Listeria Detection Assay. Subsequently, a method comparison between the Roka Listeria Detection Assay and the U.S. Food and Drug Administration's (FDA) Bacteriological Analytical Manual (BAM) Chapter 10 reference method on ice cream was carried out. Results: The R2 Medium supports the growth of L. monocytogenes better than Buffered Listeria Enrichment Broth, Demi-Fraser broth, and Modified University of Vermont Broth, as indicated by the faster growth rate of the organism. When used as an enrichment medium in a method comparison study of ice cream, the results showed that R2 Medium-enriched samples tested with the Roka Listeria Detection Assay gave an equivalent performance compared with the 24 h FDA-BAM reference method at 10 and 18 h post-enrichment for Listeria. Conclusions: The results from this study indicate that the new R2 Medium and the highly sensitive Roka Listeria Detection Assay allowed for the rapid detection of Listeria species in ice cream in 13 h. Highlights: The Roka Listeria Detection Assay, in conjunction with a new media formulation (R2 Medium), allowed for the early detection of Listeria in ice cream and may be applied in other food matrixes and environmental samples.

Infectious Dose of Listeria monocytogenes in Outbreak Linked to Ice Cream, United States, 2015

Listeriosis can occur in susceptible populations when products with low-level contamination are distributed widely.

The relationship between the number of ingested Listeria monocytogenes cells in food and the likelihood of developing listeriosis is not well understood. Data from an outbreak of listeriosis linked to milkshakes made from ice cream produced in 1 factory showed that contaminated products were distributed widely to the public without any reported cases, except for 4 cases of severe illness in persons who were highly susceptible. The ingestion of high doses of L. monocytogenes by these patients infected through milkshakes was unlikely if possible additional contamination associated with the preparation of the milkshake is ruled out. This outbreak illustrated that the vast majority of the population did not become ill after ingesting a low level of L. monocytogenes but raises the question of listeriosis cases in highly susceptible persons after distribution of low-level contaminated products that did not support the growth of this pathogen.

Assessing the genome level diversity of Listeria monocytogenes from contaminated ice cream and environmental samples linked to a listeriosis outbreak in the United States

A listeriosis outbreak in the United States implicated contaminated ice cream produced by one company, which operated 3 facilities. We performed single nucleotide polymorphism (SNP)-based whole genome sequencing (WGS) analysis on Listeria monocytogenes from food, environmental and clinical sources, identifying two clusters and a single branch, belonging to PCR serogroup IIb and genetic lineage I. WGS Cluster I, representing one outbreak strain, contained 82 food and environmental isolates from Facility I and 4 clinical isolates. These isolates differed by up to 29 SNPs, exhibited 9 pulsed-field gel electrophoresis (PFGE) profiles and multilocus sequence typing (MLST) sequence type (ST) 5 of clonal complex 5 (CC5). WGS Cluster II contained 51 food and environmental isolates from Facility II, 4 food isolates from Facility I and 5 clinical isolates. Among them the isolates from Facility II and clinical isolates formed a clade and represented another outbreak strain. Isolates in this clade differed by up to 29 SNPs, exhibited 3 PFGE profiles and ST5. The only isolate collected from Facility III belonged to singleton ST489, which was in a single branch separate from Clusters I and II, and was not associated with the outbreak. WGS analyses clustered together outbreak-associated isolates exhibiting multiple PFGE profiles, while differentiating them from epidemiologically unrelated isolates that exhibited outbreak PFGE profiles. The complete genome of a Cluster I isolate allowed the identification and analyses of putative prophages, revealing that Cluster I isolates differed by the gain or loss of three putative prophages, causing the banding pattern differences among all 3 AscI-PFGE profiles observed in Cluster I isolates. WGS data suggested that certain ice cream varieties and/or production lines might have contamination sources unique to them. The SNP-based analysis was able to distinguish CC5 as a group from non-CC5 isolates and differentiate among CC5 isolates from different outbreaks/incidents.

In vitro gastrointestinal resistance of Lactobacillus acidophilus La-5 and Bifidobacterium animalis Bb-12 in soy and/or milk-based synbiotic apple ice creams

The viability and resistance to simulated gastrointestinal (GI) conditions of Lactobacillus acidophilus La-5 and Bifidobacterium animalis Bb-12 in synbiotic ice creams, in which milk was replaced by soy extract and/or whey protein isolate (WPI) with inulin, were investigated. The ice creams were showed to be satisfactory vehicles for La-5 and Bb-12 (populations around 7.5logCFU/g), even after the whole storage period (84days/-18°C). In all formulations, the propidium monoazide qPCR (PMA-qPCR) analysis demonstrated that probiotics could resist the in vitro GI assay, with significant survival levels, achieving survival rates exceeding 50%. Additionally, scanning electron microscopy images evidenced cells with morphological differences, suggesting physiological changes in response to the induced stress during the in vitro assay. Although all formulations provided resistance to the probiotic strains under GI stress, the variation found in probiotic survival suggests that GI tolerance is indeed affected by the choice of the food matrix.

Effect of Chocobar Ice Cream Containing Bifidobacterium on Salivary Streptococcus mutans and Lactobacilli: A Randomised Controlled Trial

PURPOSE

To examine the effect of chocobar ice cream containing bifidobacteria on salivary mutans streptococci and lactobacilli.

MATERIALS AND METHODS

A double-blind, randomised controlled trial was conducted with 30 subjects (18 to 22 years of age) divided into 2 groups, test (chocobar ice cream with probiotics) and control (chocobar ice cream without probiotics). The subjects were instructed to eat the allotted chocobar ice cream once daily for 18 days. Saliva samples collected at intervals were cultured on Mitis Salivarius agar and Rogosa agar and examined for salivary mutans streptococci and lactobacilli, respectively. The Mann-Whitney U-test, Friedman and Wilcoxon signed-rank tests were used for statistical analysis.

RESULTS

Postingestion in the test group, a statistically significant reduction (p < 0.05) of salivary mutans streptococci was recorded, but a non-significant trend was seen for lactobacilli. Significant differences were was also observed between follow-ups.

CONCLUSION

Short-term daily ingestion of ice cream containing probiotic bifidobacteria may reduce salivary levels of mutans streptococci in young adults.

When ice cream was poisonous: adulteration, ptomaines, and bacteriology in the United States, 1850-1910

With the increasing popularity of ice cream in the nineteenth century, the incidence of foodborne illness attributed to this dessert exploded. Struggling to understand the causes of the mysterious and sometimes lethal ailment called "ice cream poisoning," Victorian doctors and scientists advanced theories including toxic vanilla, galvanism in ice cream freezers, and extreme indigestion. In the late 1880s Victor C. Vaughan's argument that ice cream poisoning could be attributed to the ptomaine "tyrotoxicon" received widespread acceptance. To date historians have neglected the role played by the ptomaine theory of food poisoning in shaping the evolution of both scientific thinking and public health in the late nineteenth century. The case of ice cream poisoning illustrates the emergence, impact, and decline of the ptomaine idea.

Salivary mutans streptococci and lactobacilli modulations in young children on consumption of probiotic ice-cream containing Bifidobacterium lactis Bb12 and Lactobacillus acidophilus La5

OBJECTIVES

To compare the levels of mutans streptococci and lactobacilli in saliva of school children, before and after consumption of probiotic and control ice-cream.

MATERIALS AND METHODS

A double-blind, cross-over, placebo-controlled trial was carried out in forty, 12-14 year-old children, with no clinically detectable caries. The selected children were randomized equally into two groups I and II. Following an initial run-in period of 1 week, children in group I and II were given ice-creams 'A' and 'B', respectively, for 10 days. Being a cross-over study, the ice-creams were interchanged in the two groups after a 2-week wash-out period. Saliva samples at baseline and follow-up were assessed using Dentocult SM and Dentocult LB kits.

RESULTS

On statistical evaluation, it was seen that probiotic ice-cream brought about a statistically significant reduction (p-value = 0.003) in salivary mutans streptococci levels with no significant effect on lactobacilli levels.

CONCLUSION

In conclusion, probiotic ice-cream containing Bifidobacterium lactis Bb-12 ATCC27536 and Lactobacillus acidophilus La-5 can reduce the levels of certain caries-associated micro-organisms in saliva.

Centers for Disease Control and Prevention (CDC). Notes from the field: Yersinia enterocolitica infections associated with pasteurized milk --- southwestern Pennsylvania, March-August, 2011

On July 22, 2011, a pediatric infectious disease physician reported a culture-confirmed case of Yersinia enterocolitica infection to the Allegheny County Health Department (ACHD), Pennsylvania. Two additional cases in Allegheny County with onset around the same time were identified by Pennsylvania's version of the National Electronic Disease Surveillance System aberration detection algorithm, which routinely evaluates disease reports, searching for unusual events. During March-August for the 3-year period 2008-2010, three cases of Y. enterocolitica infection had been reported in Allegheny County and a total of five in southwestern Pennsylvania. Subsequent review of the surveillance data identified 16 culture-confirmed patients with symptom onset during March 24-August 5, 2011. Patients were aged 1-75 years (median: 26.5 years). Seven patients (44%) were hospitalized; three were admitted to an intensive care unit.

Effect of food models and low-temperature storage on the adhesion of Lactobacillus rhamnosus GG to Caco-2 cells

This study evaluated the effects of fat and sugar levels on the surface properties of Lactobacillus rhamnosus GG during storage in food model systems, simulating yogurt and ice cream, and related them with the ability of the bacterial cells to adhere to Caco-2 cells. Freeze-dried L. rhamnosus GG cells were added to the model food systems and stored for 7 days. The bacterial cells were analyzed for cell viability, hydrophobicity, ζ potential, and their ability to adhere to Caco-2 cells. The results indicated that the food type and its composition affected the surface and adhesion properties of the bacterial cells during storage, with yogurt being a better delivery vehicle than ice cream in terms of bacterial adhesion to Caco-2 cells. The most important factor influencing bacterial adhesion was the storage time rather than the levels of fats and sugars, indicating that conformational changes were taking place on the surface of the bacterial cells during storage.

[Diarrhoea and fever in chemotherapy patients due to listeriosis]

We present two patients with colorectal carcinoma who were admitted with fever and diarrhoea during treatment with chemotherapy. Blood cultures taken from both patients revealed an infection with Listeria monocytogenes. A contaminated ice cream was probably the source of infection in one patient. The other patient died of the listeriosis. Patients with diminished cellular immunity are at risk of invasive listeriosis. Listeriosis has a high mortality rate in this group of patients. Intravenous penicillin or ampicillin for 4 to 6 weeks is the first choice of antibiotic treatment. These antibiotics can be combined with an aminoglycoside or trimethoprim-sulfamethoxazole for a synergistic effect. To prevent invasive listeriosis we recommend strict dietary advice to all patients with diminished cellular immunity.

Occurrence of psychrotolerant Bacillus cereus group strains in ice creams

The occurrences of Bacillus cereus group strains in 40 ice cream samples were investigated. Among 109 isolated B. cereus group strains confirmed by 16S rDNA sequence analysis only 50 were identified as B. cereus and one as B. thuringiensis by using FDA (U.S. Food and Drug Administration) standard, indicating the two identification standards were highly inconsistent. Furthermore, the psychrotolerant growth properties and the occurrence of specific psychrotolerant genes of the isolates were also studied. Both psychrotolerant 16S rDNA fragments and enterotoxic genes could be detected among mesophilic and psychrotolerant strains. No relationship among psychrotolerance, presence of psychrotolerant 16S rDNA fragments and enterotoxic genes were found and the specific cspA fragment was only detected in a small fraction (9.5%) of the psychrotolerant isolates. One psychrotolerant isolate Bw2-1 was identified as B. weihenstephanensis, but no clear distinguishing characteristics between B. weihenstephanensis and psychrotolerant B. cereus were found. These results might be of importance for gaining further understanding of the growth properties of B. weihenstephanensis and psychrotolerant B. cereus as well as their contribution to food poisoning.

Coliform and Escherichia coli contamination of desserts served in public restaurants from Guadalajara, Mexico, and Houston, Texas

Bacterial enteropathogens acquired from contaminated food are the principal causes of travelers' diarrhea (TD). We evaluated desserts obtained from popular restaurants in the tourist city of Guadalajara, Mexico, and Houston, Texas, to determine coliform and Escherichia coli contamination levels and presence of diarrheagenic E. coli known to be important in TD. Contamination for all organisms was seen for desserts served in Guadalajara restaurants. Desserts should be considered as potentially risky foods for development of TD among international visitors to developing regions of the world.

[Tracing to the source of staphylococcus aureus isolates from ice cream]

OBJECTIVE

To investigate the contamination of Staphylococcus aureus isolates in ice cream by phenotypic typing and molecular typing.

METHODS

The Staphylococcus aureus isolates were separated from ice cream, filler, cutter, salves and material. The separated isolates were characterized by drug-resistance, staphylococcal enterotoxin (SEA-E), SE (A-E, G-J) genes and pulsed-field gel electrophoresis (PFGE) types.

RESULT

Two Staphylococcus aureus isolates were separated, one from ice cream, another from cutter. Their characteristics of drug-resistance, staphylococcal enterotoxin (SEA-E), SE (A-E,G-J) genes and PFGE type were the same.

CONCLUSION

The two Staphylococcus aureus isolates were the same clone. The contaminated Staphylococcus aureus isolates could be traced to the contaminated cutters.

Epidemiology and risk factors of brucellosis in Alexandria governorate

This study aimed to describe the trend and to identify possible risk factors for brucellosis in Alexandria in northern Egypt. We enrolled 72 confirmed cases of brucellosis and 144 age-matched controls in this study. Participants were interviewed at home using a structured questionnaire. Working with animals, breeding goats and eating ice cream bought from street vendors were significantly associated (P < 0.05) with brucellosis by univariate and multivariate analysis. Contact with infected animals and their products was the most important method of transmission.

Isolation of Salmonella typhimurium from outbreak-associated cake mix

During May and June of 2005, 26 persons in several states were infected by a single strain (isolates indistinguishable by pulsed-field gel electrophoresis) of Salmonella enterica serotype Typhimurium after eating cake batter ice cream. The cake mix used to prepare the cake batter in the ice cream was implicated by epidemiologic investigation as the source of Salmonella contamination. Initial tests did not detect Salmonella in cake mix collected during the outbreak investigation. The objective of this study was to evaluate different procedures to isolate Salmonella from the implicated cake mix, cake, and ice cream. All outbreak-associated food samples (14 samples) were collected during the outbreak investigation by health departments of several of the states involved. Different combinations of Salmonella isolation procedures, including sample size, preenrichment broth, enrichment broth, enrichment temperature, and isolation medium, were used. Salmonella Typhimurium was isolated from two cake mix samples; the food isolates were indistinguishable from the outbreak pattern by pulsed-field gel electrophoresis subtyping. Universal preenrichment broth was substantially better than was lactose broth for preenrichment, and tetrathionate broth was better than was Rappaport-Vassiliadis broth for isolating Salmonella from the two positive cake mix samples. Although more typical Salmonella colonies were observed on plates from enrichment cultures grown at 35 degrees C, more confirmed Salmonella isolates were obtained from plates of enrichment cultures grown at 42 degrees C. Brilliant green agar, xylose lysine tergitol 4 agar, xylose lysine desoxycholate agar, Hektoen enteric agar, and bismuth sulfite agar plates were equally effective in isolating Salmonella from cake mix. The best combination of preenrichment-enrichment conditions for isolating the outbreak strain of Salmonella was preenrichment of cake mix samples in universal preenrichment broth at 35 degrees C for 24 h, followed by enrichment in tetrathionate broth at 42 degrees C for 24 h.

[Staphylococcus aureus in food determined by polymerase chain reaction]

OBJECTIVE

To establish a rapid polymerase chain reaction (PCR)method for detection of staphylococcus aureus in milk, ice cream and meat.

METHODS

Two pairs of oligonucleotide primers were designed with thermo nuclease gene nuc and surfaced-associated fibrinogen-binding protein gene ClfA to detect staphylococcus aureus. Fifty-two staphylococcus aureus and thirty-one non staphylococcus aureus were amplified by PCR to verify the specificity. Various numbers of bacteria were added into milk, ice cream and meat. After enrichment, DNA extracted in different time was amplified by PCR to verify detection limit.

RESULTS

Each primer pair allows specific detection. The limit of detection was 10 cfu/g (ml) in three kinds of food. Whole procedure of detection could be finished in 24 hours.

CONCLUSION

A rapid, sensitive and specific PCR method can be applied detecting staphylococcus aureus in milk, ice cream and meat.

Viability of human-derived probiotic lactobacilli in ice cream produced with sucrose and aspartame

A mixture of human-derived probiotic strains of Lactobacillus acidophilus, L. agilis and L. rhamnosus was used as a probiotic culture in ice cream manufacture. Viability and survival of these probiotic cultures were investigated in two different ice cream formulations. Ice cream with sucrose and ice cream with aspartame were prepared and each of these was divided into two subgroups: one with direct addition of the probiotic culture and one with milk fermented by the same probiotic culture. Ice cream samples were stored at -20 degrees C for 6 months and the survival rate of cultures were determined monthly. Probiotic cultures underwent tests for resistance to bile salts, antibiotics, acidic conditions; they were found to be highly resistant to such challenges. Chemical analysis of ice cream samples, such as determination of acidity, pH and solid matter, was also performed. The probiotic cultures remained unchanged in ice cream stored for up to 6 months regardless of the sweeteners used. Using probiotic cultures in ice cream mixes did not alter the characteristics of the product.

Detection and enumeration of Salmonella enteritidis in homemade ice cream associated with an outbreak: comparison of conventional and real-time PCR methods

Salmonellosis caused by Salmonella Enteritidis (SE) is a significant cause of foodborne illnesses in the United States. Consumption of undercooked eggs and egg-containing products has been the primary risk factor for the disease. The importance of the bacterial enumeration technique has been enormously stressed because of the quantitative risk analysis of SE in shell eggs. Traditional enumeration methods mainly depend on slow and tedious most-probable-number (MPN) methods. Therefore, specific, sensitive, and rapid methods for SE quantitation are needed to collect sufficient data for risk assessment and food safety policy development. We previously developed a real-time quantitative PCR assay for the direct detection and enumeration of SE and, in this study, applied it to naturally contaminated ice cream samples with and without enrichment. The detection limit of the real-time PCR assay was determined with artificially inoculated ice cream. When applied to the direct detection and quantification of SE in ice cream, the real-time PCR assay was as sensitive as the conventional plate count method in frequency of detection. However, populations of SE derived from real-time quantitative PCR were approximately 1 log higher than provided by MPN and CFU values obtained by conventional culture methods. The detection and enumeration of SE in naturally contaminated ice cream can be completed in 3 h by this real-time PCR method, whereas the cultural enrichment method requires 5 to 7 days. A commercial immunoassay for the specific detection of SE was also included in the study. The real-time PCR assay proved to be a valuable tool that may be useful to the food industry in monitoring its processes to improve product quality and safety.

Modeling and Optimization of Biopolymer (Polyhydroxyalkanoates) Production From Ice Cream Residue by Novel Statistical Experimental Design

Polyhydroxyalkanoates (PHAs) are thermoplastic polyesters synthesized by Ralstonia eutropha and other bacteria as a form of intracellular carbon and energy storage and are accumulated as lipid inclusions in the cytoplasm of these bacteria. The modeling and optimization of PHA production by fermentation from industrial waste (ice cream residue) was studied by employing statistical experimental design methods. A series of iterative experimental designs was used to find optimal factor conditions (medium components and fermentation process time) in the order of fractional factorial design, path of steepest ascent, and full factorial augmented with axial design (rotational central composite design). An optimal range characterized by lipid (15 mg/mL) and % lipid (88%) values was found and further investigated to verify the optimal conditions for PHA production from ice cream (56.68 mL of ice cream or 56.68% ice cream in water [v/v], 5.03 mL of buffer, 1 mL of mineral salts solution, 100 muL of trace element solution, 100 mL of seed culture, and 213.76 h of fermentation time).

Evaluation of the VIDAS Listeria (LIS) immunoassay for the detection of Listeria in foods using demi-Fraser and Fraser enrichment broths, as modification of AOAC Official Method 999.06 (AOAC Official Method 2004.06)

A multilaboratory study was conducted to compare the VIDAS LIS immunoassay with the standard cultural methods for the detection of Listeria in foods using an enrichment modification of AOAC Official Method 999.06. The modified enrichment protocol was implemented to harmonize the VIDAS LIS assay with the VIDAS LMO2 assay. Five food types--brie cheese, vanilla ice cream, frozen green beans, frozen raw tilapia fish, and cooked roast beef--at 3 inoculation levels, were analyzed by each method. A total of 15 laboratories representing government and industry participated. In this study, 1206 test portions were tested, of which 1170 were used in the statistical analysis. There were 433 positive by the VIDAS LIS assay and 396 positive by the standard culture methods. A Chi-square analysis of each of the 5 food types, at the 3 inoculation levels tested, was performed. The resulting average Chi square analysis, 0.42, indicated that, overall, there are no statistical differences between the VIDAS LIS assay and the standard methods at the 5% level of significance.

3M Petrifilm Staph Express Count plate method for the enumeration of Staphylococcus aureus in selected dairy foods: collaborative study

The 3M Petrifilm Staph Express Count plate method was compared with AOAC Official Method 975.55 for the enumeration of Staphylococcus aureus in selected foods. Five foods--ice cream, raw milk, yogurt, whey powder, and cheese--were analyzed for S. aureus by 12 collaborating laboratories. For each food tested, the collaborators received 8 blind test samples consisting of a control sample, a low inoculation level, a medium inoculation level, and a medium inoculation level with background flora, each in duplicate. The mean log10 counts for the methods were comparable for all 5 foods. The repeatability and reproducibility variances of the 24 h Petrifilm Staph Express Count plate method were similar to those of the 72 h standard method.

Quantitative risk assessment of Listeria monocytogenes in ready-to-eat foods: the FAO/WHO approach

Quantitative microbiological risk assessment is a very new and unique scientific approach able to link, for the first time, data from food (in the farm-to-fork continuum) and the various data on human disease to provide a clear estimation of the impact of contaminated food on human public health. The Food and Agriculture Organization of the United Nations (FAO) and the World Health Organization (WHO) have recently launched risk assessment studies of a number of pathogen-food commodity combinations (Salmonella in eggs and in broiler chickens, Listeria monocytogenes in ready-to-eat foods, Campylobacter in broiler chickens, Vibrio in seafood) to be used to lower the risk associated with these food-borne diseases and ensure fair practices in the international trade of food. The FAO/WHO Listeria risk assessment was undertaken in part to determine how previously developed risk assessments done at the national level could be adapted or expanded to address concerns related to L. monocytogenes in ready-to-eat foods at an international level. In addition, after initiation of the risk assessment, the risk assessors were asked by the Codex Committee on Food to consider three specific questions related to ready-to-eat foods in general, which are: (1). estimate the risk for consumers in different susceptible populations groups (elderly, infants, pregnant women and immunocompromised patients) relative to the general population; (2). estimate the risk for L. monocytogenes in foods that support growth and foods that do not support growth under specific storage and shelf-life conditions; (3). estimate the risk from L. monocytogenes in food when the number of organisms ranges from absence in 25 g to 1000 colonies forming units per gram or milliliter, or does not exceed specified levels at the point of consumption. To achieve these goals, new dose-response relationships and exposure assessments for ready-to-eat foods were developed. Preliminary data indicate that eliminating the higher dose levels at the time of consumption has a large impact on the number of predicted cases.

[Street-vendor foods: quality of ice creams, sherbets and sorbets sold in the urban agglomeration of Antananarivo]

A survey of selling conditions and bacteriological examinations of ice-cream was carried-out in Antananarivo from June 1996 to May 1997. The way of investigation by vendors and of bacteriological examinations were widely described. Sellers had classic features of a street-vended food vendor: uneducated, no having professional training and mishandling foodstuffs. 202 samples of ice-cream were collected. The contamination prevalence rate was of 95% +/- 3.7%. Salmonella typhimurium was isolated from one sample. Immediate and rigourous measures ought to be put into effect by authorities to right this alarming situation.

Cleaning frequency and the microbial load in ice-cream

This study investigates the efficacy of a 62 h cleaning frequency in the manufacturing of ice-cream. Various product and product contact surfaces were sampled progressively throughout the time period between cleaning cycles, and analyzed for microbial growth. The coliform and standard plate counts (SPC) of these samples did not vary significantly over time after 0, 24, 48, or 62 h from Cleaning in Place (CiP). Data for product contact surfaces were significant for the SPC representing sample locations. Some of the variables in cleaning practices had significant influence on microbial loads. An increase in the number of flavors manufactured caused a decrease in SPC within the 24 h interval, but by the 48 h interval the SPC increased. More washouts within the first 24 h interval were favorable, as indicated by decreased SPC. The more frequently the liquefier was sanitized within the 62 h interval, the lower the SPC. This study indicates that food safety was not compromised and safety practices were effectively implemented throughout the process.

[Occurrence of beta-lactamase types ESBL and AmpC among gram-negative rods isolated from food]

The aim of the study was to isolate extended spectrum beta-laktamases (ESBL) and chromosomal beta-laktamases AmpC producing strains from food products. A total of 739 Gram-negative bacteria were tested with double disc diffusion method using cefotaxim, ceftasidim and amoxycillin with clavulanic acid. One strain producing ESBL and belonging to Stenotrophomonas maltophilia was detected from the ice cream (0.14% of all strains). From different food products a total of 14 microorganisms (1.9%) having AmpC enzymes have been isolated. They belonged to Enterobacter spp, Hafnia spp, Morganella spp, Citrobacter, Acinetobacter, and Cedecea. Appearance of strains producing beta-laktamases ESBL and AmpC among microorganism isolated from food make it necessary to monitor enzymes activity during routine microbiological control of foods.

Dry rehydratable film method for rapid enumeration of coliforms in foods (3M Petrifilm Rapid Coliform Count plate): collaborative study

A rehydratable dry-film plating method for coliforms in foods, the 3M Petrifilm Rapid Coliform Count plate method, was compared with the U.S. Food and Drug Administration's Bacteriological Analytical Manual method for nondairy foods and the American Public Health Association's Standard Methods for the Examination of Dairy Products (SMEDP) method for dairy foods. Six food types, vanilla ice cream, cheddar cheese, fresh refrigerated uncooked pasta, wheat flour, prepared frozen macaroni and cheese, and frozen hash browns, were analyzed for coliforms by 11 collaborating laboratories. For each food product tested, the collaborators received 8 blind samples consisting of a control sample and 3 levels of inoculated sample, each in duplicate. The mean log counts for the methods were comparable. The repeatability and reproducibility variances of the Petrifilm Rapid Coliform Count method at 14 and 24 h were not significantly different from those of the standard methods.

Multicenter study of street foods in 13 towns on four continents by the food and environmental hygiene study group of the international network of pasteur and associated institutes

An international multicenter study of ready-to-eat foods, sandwiches, and ice creams or sorbets sold in the streets and their vendors was carried out to assess the microbiological quality of these foods and to identify characteristics of the vendors possibly associated with pathogens. Thirteen towns in Africa, America, Asia, and Oceania were involved in the study. A single protocol was used in all 13 centers: representative sampling was by random selection of vendors and a sample of foods bought from each of these vendors at a time and date selected at random. Microbiological analyses were carried out using standardized Association Française de Normalisation methods, and the use of a standardized questionnaire to collect data concerning the characteristics of the vendors. Fifteen surveys were carried out, with 3,003 food samples from 1,268 vendors. The proportion of unsatisfactory food samples was between 12.7 and 82.9% for ice creams and sorbets and between 11.3 and 92% for sandwiches. For ice creams and sorbets, the sale of a large number of units (>80 per day) increased the risk of unsatisfactory food by a factor of 2.8 (95% confidence interval [CI]: 1.5 to 5.1), lack of training in food hygiene by 6.6 (95% CI: 1.1 to 50). and by a factor of 2.8 (95% CI: 1.4 to 5.4) for mobile vendors. These risk factors were not identified for sandwiches, this difference may be due to the presence of a cooking step in their preparation. These results show that the poor microbiological quality of these street foods constitutes a potential hazard to public health, that the extent of this hazard varies between the cities studied, and that vendors' health education in food safety is a crucial factor in the prevention of foodborne infections.

Natural exopolysaccharides enhance survival of lactic acid bacteria in frozen dairy desserts

Viable lactic acid-producing bacteria in frozen dairy desserts can be a source of beta-galactosidase for persons who absorb lactose insufficiently. However, freezing kills many of the cells, causing loss of enzymatic activity. Cultures selected for high beta-galactosidase activities and high survival rates in the presence of bile were examined for survivability during freezing in reduced-fat ice cream. Encapsulated S. thermophilus strains survived better than their nonencapsulated mutants in reduced-fat ice cream after freezing and frozen storage at -29 degrees C for 16 d (28 vs. 19%). However, a small nonencapsulated strain of Lactobacillus delbrueckii sp. bulgaricus survived better than the large encapsulated strain in reduced-fat ice cream. Factors that improved survival of encapsulated S. thermophilus 1068 in ice cream were 1) harvest of cells in the late-log phase of growth at 37 degrees C rather than at 40, 42.5, or 45 degrees C; 2) overrun at 50% rather than 100%; and 3) storage at -17 degrees C rather than -23 or -29 degrees C. Survival of strain ST1068 was unaffected by 1) neutralization of acid during growth or 2) substitution of nitrogen for air in building overrun.

Characterization and growth of Bacillus spp. in heat-treated cream with and without nisin

AIMS

To study the germination and growth of both inoculated and naturally occurring Bacillus strains in heat-treated cream with and without nisin.

METHODS AND RESULTS

In heat-treated cream (90 degrees C for 15 min) stored at 8 degrees C, growth was dominated by naturally occurring Bacillus strains such as Bacillus pumilus and B. licheniformis. Only six of the 52 isolated strains were B. cereus/thuringiensis. All of the B. cereus strains, but none of the other strains, produced enterotoxin when tested with the TECRA and reverse passive latex agglutination kits. Bacterial growth during storage of the cream at 8 or 10 degrees C was completely inhibited by low concentrations of nisin.

CONCLUSION

The high number of Bacillus strains surviving the heat treatment represent a risk for heat-treated food that contains cream. The safety of the cream, for instance in "ready-to-eat" products, can be improved by the addition of low concentrations of nisin.

SIGNIFICANCE AND IMPACT OF THE STUDY

Spores of several Bacillus species may survive heat treatment of cream, but low concentration of nisin with inhibit germination and growth.

Low-dose irradiation as a measure to improve microbial quality of ice cream

The present study was undertaken to investigate the efficacy of low-dose irradiation to improve the microbial safety of ice cream. Initially three different flavors (vanilla, strawberry and chocolate) of ice cream were exposed, at -72 degrees C, to doses of 1, 2, 5, 10 and 30 kGy to gamma-radiation. Irradiation at 1 kGy resulted in reduction of microbial population by one log cycle, thus meeting the requirement limits prescribed by Bureau of Indian Standards. Pathogens such as Listeria monocytogenes 036, Yersinia enterocoliticta 5692 and Escherichia coli O157:H19, respectively, showed the D10 values 0.38, 0.15 and 0.2 kGy in ice cream at -72 degrees C suggesting the efficacy of low doses (1 kGy) in eliminating them. Sensory evaluation studies of ice cream irradiated at 1, 2, 3 and 5 kGy by a 15 member panel demonstrated that doses higher than 2 kGy irradiation induced off-odour and an aftertaste was evident in vanilla ice cream. A radiation dose of 1 kGy was sufficient to eliminate the natural number of pathogens present in the ice cream. No statistically significant differences were observed in the sensory attributes of all the three flavours of ice cream either unirradiated or exposed to 1 kGy (P < 0.05).

Prevalence and molecular characterization of Aeromonas spp. in ready-to-eat foods in Italy

A survey was carried out in Italy to ascertain the prevalence of Aeromonas spp. in ready-to-eat foods (vegetables, cheeses, meat products, and ice creams) and the level of molecular heterogeneity of the isolates found by macrorestriction analysis of genomic DNA with pulsed-field gel electrophoresis (PFGE). In total, 46 (14.4%) of the 320 food samples examined were found positive for Aeromonas spp. The highest percentages of isolation were discovered in vegetables, particularly lettuce (45.0%), endive (40.0%), and rucola (20.0%). Ricotta was the only cheese type analyzed that showed a high frequency of isolation (45.0%). Among meat products, salami and raw ham (25.0% of samples positive) and, to a lesser extent, baloney (5.0%) were found positive for Aeromonas spp. Aeromonas hydrophila was the most common isolate from foods of animal origin, whereas Aeromonas caviae was the dominant species in vegetables. No motile aeromonads were found in ice cream samples. Aeromonas isolates showed a high level of genetic heterogeneity, because 24 PFGE patterns were identified among 27 A. hydrophila strains and 20 PFGE patterns were found in 23 A. caviae isolates. In conclusion, consumers of ready-to-eat foods in Italy are regularly exposed to many genetically distinct strains of A. hydrophila and A. caviae without evident signs of malaise, and therefore, few of these strains, if any, are likely to be pathogenic.

Persistent Listeria monocytogenes strains show enhanced adherence to food contact surface after short contact times

Adherence of 3 persistent and 14 nonpersistent Listeria monocytogenes strains to stainless steel surfaces after short and long contact times was investigated. L. monocytogenes strains were obtained from poultry plants and an ice cream plant throughout several years. Adherence tests were performed in tryptic soy broth at 25 degrees C for 1, 2, and 72 h. Test surfaces were rinsed after the contact time, and attached cells were stained with acridine orange and enumerated with an epifluorescence microscope. The persistent poultry plant strains showed adherence 2- to 11-fold higher than the nonpersistent strains following 1- and 2-h contact times. The adherence of the persistent ice cream plant strain after 1- and 2-h contact times was higher than most of the nonpersistent strains. Seven of 12 nonpersistent ice cream strains showed an adherence of less than half that of the persistent strain. After 72 h, the differences in adherence were not as marked, since half the nonpersistent strains had reached adherence levels comparable with the persistent strains. In fact, three nonpersistent strains showed even higher adherence than the persistent strains. Thus, results of this study reveal that persistent L. monocytogenes strains show enhanced adherence at short contact times, promoting their survival in food processing facilities and possibly having an effect on initiation of persistent plant contamination.

Evaluation of the bacteriological quality of ice cream sold at San Jose, Costa Rica

The presence of total and fecal coliforms, E. coli, Listeria sp and Salmonella sp. was evaluated in 65 samples of both commercial and homemade ice cream. 37.1% of homemade ice cream and 20% of commercial ice cream did not fulfill the international standard for total coliforms. At the same time 82.9% of home made samples and 56.7% of commercial ones presented fecal coliforms. E. coli was found in 51.4% of home made samples and 26.7% of commercial ones. Sixteen Listeria sp. isolates were obtained, 50% corresponded to Listeria monocytogenes and 50% to L. innocua. The overall presence of L. monocytogenes in ice cream samples was of 12.3% and it was isolated in all cases, from homemade ice cream samples. Salmonella was not isolated from the samples analyzed. Although the results obtained show an important improvement in the quality of ice cream, compared with a previous work done also in Costa Rica, further efforts shall be done, in order to offer safe products to consumers.

Equivalence of assurance Gold Enzyme Immunoassay for visual or instrumental detection of motile and nonmotile Salmonella in all foods to AOAC culture method: collaborative study

Six foods representative of a wide variety of processed, dried powder processed, and raw food types were analyzed by the Assurance Gold Salmonella Enzyme Immunoassay (EIA) and AOAC INTERNATIONAL culture method. Paired samples of each food type were simultaneously analyzed; one sample by the Assurance method and one by the AOAC culture method. The results for Assurance method were read visually and instrumentally with a microplate reader. A total of 24 laboratories representing federal government agencies and private industry, in the United States and Canada, participated in this collaborative study. Food types were inoculated with species of Salmonella with the exception of raw ground chicken, which was naturally contaminated. No statistical differences (p < 0.05) were observed between Assurance Gold Salmonella EIA with either visual or instrumental interpretation and the AOAC culture method for any inoculation level of any food type or naturally contaminated food. The Assurance visual and instrumental options of reading sample reactions produced the same results for 1277 of the 1296 sample and controls analyzed.

Equivalence of Visual Immunoprecipitate Assay (VIP) for Salmonella for the detection of motile and nonmotile Salmonella in all foods to AOAC culture method: collaborative study

Six foods representative of a wide variety of processed, dried powder processed, and raw food types were analyzed by the Visual Immunoprecipitate Assay (VIP) for Salmonella and AOAC INTERNATIONAL culture method. Paired samples of each food type were simultaneously analyzed; one sample by the VIP method and one by the AOAC culture method. A total of 24 laboratories representing federal government agencies and private industry, in the United States and Canada, participated in this collaborative study. Food types were inoculated with species of Salmonella with the exception of raw ground chicken, which was naturally contaminated. No statistical differences (p < 0.05) were observed between VIP for Salmonella interpretation and the AOAC culture method for any inoculation level of any food type or naturally contaminated food. The method was adopted Official First Action status by AOAC INTERNATIONAL.

[Epidemiologic study and cost analysis of an Slamonella enteritidis epidemic]

Salmonellosis is one of the most common forms of foodborne infection. An outbreak of gastroenteritidis associated with a wedding party was investigated, even to value the costs falling on individuals, the health services and society as a whole. One hundred and fifty nine wedding guests were interviewed by phone. Multivariate analysis was used to assess which food were significantly associated with infection. One hundred and thirteen cases were identified; ten stool samples were culture positive for Salmonella enteritidis. Handmade ice-cream and babà (a typical Italian pastry) were significantly associated with infection. The cost of a case was estimated to be between US $ 74 (for non hospitalised patients) and US $ 1,896 (for hospitalised patients). The outbreak was caused by a strain of Salmonella enteritidis and the vehicle of infection were unpasteurised eggs used to prepare the ice-cream. The economic impact of this outbreak was considerable and mainly due to the hospitalisation.

Immobilization with metal hydroxides as a means to concentrate food-borne bacteria for detection by cultural and molecular methods

The application of nucleic acid amplification methods to the detection of food-borne pathogens could be facilitated by concentrating the organisms from the food matrix before detection. This study evaluated the utility of metal hydroxide immobilization for the concentration of bacterial cells from dairy foods prior to detection by cultural and molecular methods. Using reconstituted nonfat dry milk (NFDM) as a model, two food-borne pathogens (Listeria monocytogenes and Salmonella enterica serovar Enteritidis) were concentrated from 25-ml samples by the sequential steps of clarification and high-speed centrifugation (designated primary concentration) and immobilization with zirconium hydroxide and low-speed centrifugation (designated secondary concentration). Sample volume reduction after immobilization with zirconium hydroxide was 50-fold, with total bacterial recoveries ranging from 78 to 96% of input for serovar Enteritidis and 65 to 96% of input for L. monocytogenes. Immobilized bacteria remained viable and could be enumerated by standard cultural procedures. When followed by RNA extraction and subsequent detection by reverse transcription (RT)-PCR, detection limits of 10(1) to 10(2) CFU/25 ml of reconstituted NFDM were achieved for both organisms. The bacterial-immobilization step was relatively nonspecific, resulting in recovery of >50% of the input cells when evaluated on a panel of representative bacterial strains of significance to foods. The method could be adapted to more complex dairy products, such as whole milk and ice cream, for which bacterial recoveries after immobilization ranged from 64 to >100%, with subsequent RT-PCR detection limits of >/=10(2) CFU/ml for whole milk and >/=10(1) CFU for ice cream for both serovar Enteritidis and L. monocytogenes. The bacterial-immobilization method is easy, rapid, and inexpensive and may have applications for the concentration of a wide variety of food-borne bacteria prior to detection by both conventional and alternative methods.

Probiotic culture survival and implications in fermented frozen yogurt characteristics

Low-fat ice cream mix was fermented with probiotic-supplemented and traditional starter culture systems and evaluated for culture survival, composition, and sensory characteristics of frozen product. Fermentations were stopped when the titratable acidity reached 0.15% greater than the initial titratable acidity (end point 1) or when the pH reached 5.6 (end point 2). Mix was frozen and stored for 11 wk at -20 degrees C. The traditional yogurt culture system contained the strains Streptococcus salivarius ssp. thermophilus and Lactobacillus delbrueckii ssp. bulgaricus. The probiotic-supplemented system contained the traditional cultures as well as Bifidobacterium longum and Lactobacillus acidophilus. We compared recovery of Bifodobacterium by three methods, a repair-detection system with roll-tubes and plates on modified bifid glucose medium and plates with maltose + galactose reinforced clostridial medium. Culture bacteria in both systems did not decrease in the yogurt during frozen storage. The roll-tube method with modified bifid glucose agar and repair detection system provided at least one-half log10 cfu/ml higher recovery of B. longum compared with recoveries using modified bifid glucose agar or maltose + galactose reinforced clostridial agar on petri plates. No change in concentrations of lactose or protein for products fermented with either culture system occurred during storage. Acid flavor was more intense when product was fermented to pH 5.6, but yogurt flavor was not intensified. The presence of probiotic bacteria in the supplemented system seemed to cause no differences in protein and lactose concentration and sensory characteristics.

[Microbiological quality of street-vendor ice cream in Dakar]

During a multicenter study initiated by the International Network of Pasteur Institutes and Associated Institutes, microbiological quality of street-vended ice creams in Dakar was evaluated. 313 samples of ice creams from 170 street-vendors were collected and tested for common foodborne pathogens and indicator organisms. Results showed that microbiological quality of 45% of tested samples was unsatisfactory because of large populations of aerobic mesophilic organisms (36.7%), thermotolerant coliforms bacteria (21.4%) and sometimes E. coli. (10.6%). Strict pathogens as Salmonella, Shigella and Vibrio cholerae were not found. An investigation conducted among vendors showed a lack of education and training; these vendors need information about food preparation and storage practices that reduce microbiological contamination of foods.

Resistance to antibiotics, metals, hydrophobicity and klebocinogeny of Klebsiella pneumoniae isolated from foods

Milk samples and milk products (69 in toto) were screened for the presence of Klebsiella pneumoniae (52%), and maximum isolations (77%) were from ice cream samples (13). The isolates were hydrophobic, non-haemolytic and possessed both mannose resistant (MR) and mannose sensitive (MS) pili or only MR pili when tested with human or sheep blood, respectively. All isolates were resistant to one metal at least whereas about 98% exhibited resistance to two or more metal ions. The resistance frequency of 93%, 90% and 66.7% was observed against silver (20 micrograms/ml), cadmium (20 micrograms/ml) and mercuric ions (20 micrograms/ml), respectively. Multiple drug resistance (MDR) was observed in 10% of the isolates only. A direct correlation between the metal ion and antibiotic resistance was found in MDR strains. The klebocin typeability of 53% and 61% was observed with 153-158 and 153-156, U-5 and U-6 groups, respectively. The most common typing patterns involved strains 424 (21%) and 442 (31.8%). Only 61% of the isolates showed enterotoxigenicity by the coagglutination test.

[Pathogenic gene analysis of Listeria isolated from foods]

In 1996-1997, Listeria in foods from 12 provinces of China were detected by using the national standard examination method GB 4789.30-94 (routine traditional methods). Twenty four strains Listeria monocytogenes and 141 strains Listeria were identified by biochemical procedures and animal toxicity experiment. Polymerase Chain Reaction(PCR) was used to amplify two specific DNA fragments(719 bp and 446 bp) of listeriolysin O and internalin genes with two pairs of primer--Hly1-2 and Inl1-2, respectively. The experiment results showed that 57 strains contained only internalin, 27 strains contained both internalin and listeriolysin O from the pathogenic genes of isolated strains.

Characterization of Listeria monocytogenes from an ice cream plant by serotyping and pulsed-field gel electrophoresis

One dominating strain of serotype 1/2b was found when serotyping and pulsed-field gel electrophoresis (PFGE) patterns were used for the characterization of 41 Listeria monocytogenes isolates originating from an ice cream plant. Samples were taken from the production environment, equipment and ice cream during the years 1990-1997. Serotyping divided the isolates into two serovars, 1/2b and 4b. Three rare-cutting enzymes (ApaI, AscI and SmaI) were used in the creation of PFGE patterns. AscI resulted in the best restriction enzyme digestion patterns (REDPs) for visual comparison. Eight different AscI REDPs were obtained, whereas ApaI produced six and SmaI seven banding patterns. When one-band differences are taken into account, 12 different PFGE types were distinguished based on information obtained with all three enzymes. The dominant PFGE type was found to have persisted in the ice cream plant for seven years. Improved and precisely targeted cleaning and disinfection practices combined with structural changes making for easier cleaning of the packaging machine, resulted in eradication of L. monocytogenes from this plant.

Consequences in Georgia of a nationwide outbreak of Salmonella infections: what you don't know might hurt you

OBJECTIVES

This study assessed the impact in Georgia of a nationwide salmonellosis outbreak caused by ice cream products and the effectiveness of the subsequent warning against eating the implicated products.

METHODS

A telephone survey of 250 randomly selected Georgia customers of the ice cream producer was conducted 13 to 17 days after the warning.

RESULTS

Respondents from 179 households representing 628 persons were interviewed. The median date of first hearing the warning was 5 days after it was issued, and 16 respondents (9%) had not heard it. Among those who had heard the warning, 42 (26%) did not initially believe the products were unsafe. In 22 (31%) of the 72 households that had the implicated ice cream when the respondent heard the warning, someone subsequently ate the ice cream. Diarrhea was reported in 26% (121/463) of persons who had eaten the products but in only 5% (8/152) who had not (odds ratio [controlling for household clustering] = 3.8; 95% confidence interval = 2.0, 7.5). We estimate this outbreak caused 11,000 cases of diarrhea in Georgia, 1760 (16%) with exposure after the warning.

CONCLUSIONS

A large outbreak occurred in Georgia, much of which might have been prevented by a more timely and convincing warning.