Fate of Salmonella typhimurium DT 104 during the Fermentation of ‘Siljo’, a Traditional Ethiopian Fermented Legume Condiment, and during Product Storage at Ambient and Refrigeration Temperatures

Summary The survival of Salmonella spp. in fermenting foods and their elimination during prolonged fermentation is documented. This prompted the study to evaluate the fate of Salmonella typhimurium DT 104 during the fermentation of ‘Siljo’, a traditional fermented legume condiment, and during the storage of the fermented product at ambient and cold temperatures. ‘Siljo‘ was made to ferment naturally and the count of lactic acid bacteria reached 9.9 log c.f.u./ml on day 5. The pH dropped from an initial value of 5.8–4.65 during this time. The lactic acid flora was dominated by Leuconostoc spp. At ambient temperature storage (18–22 °C), the product spoiled on day 16. The spoilage was caused by Bacillus spp. At refrigerated storage (4 °C), however, the count of Bacillus spp. was below detectable limits (<1 log c.f.u./ml) until the end of experiment on day 16. When Salmonella typhimurium DT 104 was inoculated into the fermenting gruel at low initial levels (2.8 log c.f.u./ml), the count decreased steadily and the test strain was not detected by enrichment on day 5. At higher initial inoculum level (5.5 log c.f.u./ml), complete elimination was observed on day 7. In a non-fermenting control gruel, count of the test strain increased by about 3 log units on day 7. In another experiment, the fermented product was inoculated with Salmonella typhimurium DT 104 at low or high inoculum levels and stored at ambient and refrigeration temperatures. Under ambient temperature storage, the test strain was not detectable by enrichment on days 3 and 6 at low and high initial inoculum levels, respectively. The count of the test strain did not decrease markedly under refrigerated storage. The results indicated that, at normal contamination levels in the kitchen environment, fermentation for five days would completely eliminate Salmonella typhimurium DT 104 from the fermenting gruel; ambient temperature storage of the product would completely eliminate the pathogen after three days; and its survival is markedly prolonged by cold storage.     

Control of foodborne pathogens during sufu fermentation and aging

Control of the foodborne pathogens Escherichia coli O157:H7, Salmonella typhimurium, Staphylococcus aureus, and Listeria monocytogenes during sufu fermentation was evaluated. Before fermentation, pathogens were inoculated onto tofu (substrate for sufu) at 5 log cfu/g or 3 log cfu/g, and starter culture (Actinomucor elegans) was inoculated at 3 log cfu/g. After 2 days of fermentation at 30 degrees C, the four pathogens reached 7 to 9 log cfu/g, and the mold count reached 6 to 7 log cfu/g. After fermentation, sufu samples were aged in a solution of 10% alcohol + 12% NaCl. After 1 month of aging, the total bacterial count was 6 to 7 log cfu/g, but all foodborne pathogens and mold were reduced to nondetectable levels. The total bacterial count decreased after aging for 2 months and 3 months, but the differences were not significant (P > 0.05) compared with the count after 1 month. Microorganism in experimental sufu from different aging periods and in commercial sufu were compared. A total of 270 isolates were purified and identified by the BBL Crystal Identification System. From the experimental sufu samples, 49 Bacillus spp. (20.4%), 167 Enterococcus spp. (69.6%), 6 Shewanella putrefaciens (2.4%), and 18 miscellaneous gram-negative bacilli (7.5%) were identified. From commercial sufu samples, 17 Bacillus spp. (56.7%), 2 Enterococcus durans (6.7%), 5 miscellaneous gram-negative bacilli (16.7%), 5 Corynbacterium aquaticum (16.7%), and 1 Shewanella putrefaciens (3.3%) were obtained. Although the longer aging period did not significantly decrease the total bacterial count, it may help in the development of sufu flavor. This study showed that sufu fermentation and aging can control common foodborne pathogens, so sufu is a safe product even though its preparation does not include pasteurization.     

利用X-Neu5Ac为底物测定唾液酸酶活性在诊断细菌性阴道病的价值

目的利用5溴-4氯-3吲哚乙酰基神经氨酸盐（X-Neu5Ac）为底物测定阴道唾液酸酶活性诊断细菌性阴道病（bacterial vaginosis,BV）的价值.方法健康妇女30例,临床Amsel法诊断为BV的患者45例,共计75例进行了阴道分泌物分析和检测,并与唾液酸酶活性法诊断作了对比研究.取阴道分泌物作为标本分别进行唾液酸酶活性和阴道菌群定量分析,检测细菌包括乳酸杆菌、类杆菌、肠杆菌、葡萄球菌、肠球菌和阴道加德纳菌.唾液酸酶活性测定利用的底物为X-Neu5Ac,特异活性用其产物 ——甲氧基苯酚的纳摩尔数来表示.结果阴道液唾液酸酶活性测定诊断细菌性阴道病的敏感性、特异性、阳性预期值和阴性预期值分别为88.9%、90%、93%和84.3%.唾液酸酶法在检测细菌性阴道病上和传统的Amsel法比较,差异无显著性（P＞0.05）.唾液酸酶阳性组Gv活菌数（6.96 log CFU/g）明显高于唾液酸酶阴性组（2.05 log CFU/g）（P＜0.01）.唾液酸酶阳性组产H2O2阴道乳杆菌（LB＋）活菌数（4.26 Log CFU/g）明显低于唾液酸酶阴性组（8.66 Log CFU/g）（P＜0.01）.唾液酸酶阳性组与唾液酸酶阴性组两组的阴道液中需氧菌活菌数差异无显著性（P＞0.05）,主要包括金黄色葡萄球菌、肠球菌和肠杆菌.结论利用X-Neu5Ac作为唾液酸酶的底物测定唾液酸酶活性的方法是诊断细菌性阴道病的有效检测方法.阴道内唾液酸酶活性增强,厌氧菌数量增加,LB＋数量减少,提示BV发生恶化.     

Control of Foodborne Pathogens during Sufu Fermentation and Aging

ABSTRACT:?

Referee: Dr. Catharina Y. W. Ang, National Center Toxicology Research, HFT-230, FDA, 3900 NCTR Road, Jefferson, AR 72079

Control of the foodborne pathogens Escherichia coli O157:H7, Salmonella typhimurium, Staphylococcus aureus, and Listeria monocytogenes during sufu fermentation was evaluated. Before fermentation, pathogens were inoculated onto tofu (substrate for sufu) at 5 log cfu/g or 3 log cfu/g, and starter culture (Actinomucor elegans) was inoculated at 3 log cfu/g. After 2 days of fermentation at 30°C, the four pathogens reached 7 to 9 log cfu/g, and the mold count reached 6 to 7 log cfu/g. After fermentation, sufu samples were aged in a solution of 10% alcohol + 12% NaCl. After 1 month of aging, the total bacterial count was 6 to 7 log cfu/g, but all foodborne pathogens and mold were reduced to nondetectable levels. The total bacterial count decreased after aging for 2 months and 3 months, but the differences were not significant (P>0.05) compared with the count after 1 month. Microorganism in experimental sufu from different aging periods and in commercial sufu were compared. A total of 270 isolates were purified and identified by the BBL Crystal Identification System. From the experimental sufu samples, 49 Bacillus spp. (20.4%), 167 Enterococcus spp. (69.6%), 6 Shewanella putrefaciens (2.4%), and 18 miscellaneous Gram-negative bacilli (7.5%) were identified. From commercial sufu samples, 17 Bacillus. spp. (56.7%), 2 Enterococcus durans (6.7%), 5 miscellaneous Gram-negative bacilli (16.7%), 5 Corynbacterium aquaticum (16.7%), and 1 Shewanella putrefaciens (3.3%) were obtained. Although the longer aging period did not significantly decrease the total bacterial count, it may help in the development of sufu flavor. This study showed that sufu fermentation and aging can control common foodborne pathogens, so sufu is a safe product even though its preparation does not include pasteurization.     

Control of microbiological quality and shelf-life of catfish (Clarias gariepinus) by chemical preservatives and smoking

Fresh catfish ( Clarias gariepinus ) were subjected to different concentrations of sodium benzoate or potassium sorbate and smoked traditionally before evaluation for microbiological, chemical and organoleptic characteristics during ambient tropical storage. Unsmoked fish samples showed diverse microflora ( Enterobacter, Escherichia, Serratia, Bacillus, Staphylococcus, Streptococcus, Penicillium, Aspergillus and Achlya genera) while smoked samples were dominated by Gram-positive bacterial flora ( Bacillus, Staphylococcus and Streptococcus ) and spoilage moulds ( Penicillium verrucosum, Aspergillus flavus and Achlya spp.). Significant reduction in microbial population occurred in most samples following smoking with samples subjected to 0.4% (w/v) potassium sorbate showing the lowest microbial load and maximum shelf-stability. However, marked microbial increase occurred after day 4 of storage in control and benzoate-treated samples. Changes in pH were marginal but decreased after day 12 of storage. Moisture content decreased sharply after smoking and remained low after day 4 of storage. Overall, potassium sorbate treatment (0.4% w/v) was most effective in controlling microbial quality and extended the shelf-life of the samples by 8 d.     

Quantification of thermophilic <Emphasis Type="Italic">Campylobacter</Emphasis> spp. in broilers during meat processing

Campylobacter spp. is a common cause of gastrointestinal illness. Since animal products, especially poultry meat, are an important source of human outbreaks of campylobacteriosis, tracing back to processing and initial production is of great interest. Samples were collected at a German poultry slaughterhouse for the estimation of the prevalence of Campylobacter at different processing steps. Quantification of Campylobacter in each of the samples was also performed. Out of 99 samples examined, 51 (51.5%) were positive for Campylobacter, with bacterial counts ranging from log(10) 6.5 cfu sample(-1) for carcasses to log 3.6 cfu ml(-1) for scalding water. The Campylobacter isolates (n = 51) were subtyped by pulsed-field gel electrophoresis using SmaI and KpnI restriction enzymes. Molecular typing showed a multitude of strains with different molecular patterns. Strains found in cloacal swabs before processing could also be isolated from carcasses at different processing steps.     

Microbial challenges of poultry meat production

Food safety and shelf-life are both important microbial concerns in relation to broiler meat production. Focus is mainly placed on the absence or control of potentially pathogenic microbes such as Salmonella spp. and Campylobacter spp. but, from the commercial point of view, other spoilage bacteria also play a role as potential threats. Regarding food safety, the primary target should be the production of pathogen-free live animals, thus allowing slaughter plants to keep the processing line free of those microorganisms.Consumers believe that quality of foods from organic production is superior to foods from conventional production. The aim of the present study was to evaluate and compare the bacterial quality of chicken meat from organic and conventional production on the basis of traditional meat quality criteria. Fresh free grazing broiler carcasses were purchased directly from rural households (n = 80) and fresh retail chicken parts from conventional broiler carcasses from the local supermarkets in the region of Epirus (Poultry Producers Association. Arta) (n = 200).The samples were microbiologically tested for the presence of bacteria such as: Salmonella spp., Listeria monocytogenes, Staphylococcus aureus, Enterobacteriaceae, Escherichia coli, Campylobacter spp., and C. perfringens. Total count of aerobic mesophilic bacteria was also determined. Bacteriological tests were performed by means of standard methods of isolation and identification of individual species of bacteria according to ISO requirements. API-tests (bioMerieux) and Vitek 2 Identification System (bioMerieux) were used for biochemical determination. High levels of microbial contamination and occurrence of pathogenic bacteria at then fresh free grazing broiler carcasses reflect the poor hygienic quality of the slaughter conditions in the rural households.     

改良PCA培养基检测鸡肉胴体中的污染细菌

通过添加鸡肉浸液改良经典PCA培养基获得模拟鸡肉营养条件的近自然的CEA培养基,用于检测鸡肉中对营养要求苛刻的污染细菌。根据添加不同浓度的新鲜鸡肉浸液所获得菌落总数的变化获得最佳添加浓度,并利用生化特性及16SrRNA序列对仅生长于CEA培养基的细菌进行了鉴定。在CEA培养基上获得的细菌数量和多样性都显著高于PCA培养基(P0.05),且分离到3株无法在PCA培养基上生长的细菌,经鉴定其与Enterococcus faecalis、Rothia mucllaginosa,Staphylococcus saprophyticus subsp.saprophyticus的相似性分别为99%、96%、99%。E.faecalis因产生生物胺而被认为是肉品中的腐败菌,后两者则均是条件致病菌株,他们的存在对鸡肉产品的安全可能造成隐患。该方法中的近自然培养法能提高对微生物数量和种类的检测灵敏度,特别适于对营养要求苛刻的污染细菌的检出。     

Carnobacterium divergens - a dominating bacterium of pork meat juice

Nonspoiled food that nevertheless contains bacterial pathogens constitutes a much more serious health problem than spoiled food, as the consumer is not warned beforehand. However, data on the diversity of bacterial species in meat juice are rare. To study the bacterial load of fresh pork from ten different distributors, we applied a combination of the conventional culture-based and molecular methods for detecting and quantifying the microbial spectrum of fresh pork meat juice samples. Altogether, we identified 23 bacterial species of ten different families analyzed by 16S rRNA gene sequencing. The majority of isolates were belonging to the typical spoilage bacterial population of lactic acid bacteria (LAB), Enterococcaceae, and Pseudomonadaceae. Several additional isolates were identified as Staphylococcus spp. and Bacillus spp. originating from human and animal skin and other environmental niches including plants, soil, and water. Carnobacterium divergens, a LAB contributing to the spoilage of raw meat even at refrigeration temperature, was the most frequently isolated species in our study (5/10) with a bacterial load of 10(3) - 10(7) CFU mL(-1). In several of the analyzed pork meat juice samples, two bacterial faecal indicators, Serratia grimesii and Serratia proteamaculans, were identified together with another opportunistic food-borne pathogen, Staphylococcus equorum. Our data reveal a high bacterial load of fresh pork meat supporting the potential health risk of meat juice for the end consumer even under refrigerated conditions.     

Effects of lactoferrin supplementation on ileal and total tract nutrient digestibility, gastrointestinal microbial populations, and immune characteristics of ileal cannulated, healthy, adult dogs

Orally supplemented lactoferrin derived from bovine milk is purported to have beneficial effects on gut health of animals. Bovine lactoferrin (0, 60, or 120 mg/d) was fed to ileal cannulated, adult dogs in a replicated 3 x 3 Latin square design with 14 d periods. Control dogs tended (p = 0.06) to have higher fecal DM concentrations compared with dogs supplemented with 120 mg/d lactoferrin (34.5 vs. 32.9%). Fecal scores ranged from 3.0 - 3.3, suggesting that feces of all dogs was near the desired consistency, with dogs supplemented with 120 mg/d lactoferrin tending (p = 0.08) to have higher fecal scores. Ileal azoreductase activity tended (p < 0.10) to be higher in dogs supplemented with 60 or 120 mg/d lactoferrin (609 vs. 592 nmol/h per g ileal DM, respectively) as compared with unsupplemented dogs (272 nmol/h per g ileal DM). The following bacterial groups were measured: bifidobacteria, Campylobacter spp., Clostridium spp., eubacteria, Escherichia coli, Lactobacillus spp., Staphylococcus spp., and Streptococcus spp. Fecal streptococci concentrations were lower (p < 0.05) for dogs receiving 60 mg/d lactoferrin (8.60 log10 cfu/g fecal DM) as compared with unsupplemented dogs (9.19 log10 cfu/g fecal DM) or dogs receiving 120mg lactoferrin/d (9.43 log10 cfu/g fecal DM). Dogs supplemented with 120mg/d lactoferrin tended (p = 0.08) to have higher fecal indole concentrations as compared to unsupplemented dogs (1.80 vs. 1.46 micromol/g fecal DM). Because most bacterial groups measured were unaffected, it appears that lactoferrin did not exhibit prebiotic activity, and based on the data collected, lactoferrin also did not appear to have major effects on indices of health in the dog.     

Microbiological Contamination of Reindeer Carcass During Slaughter

Microbiological counts for 10 different sampling sites of 28 reindeer carcasses were studied in 3 reindeer slaughterhouses in Finland. On each carcass the hindshank, round, abdomen, flank, brisket, foreleg, shoulder, neck, foreback and back were sampled immediately after slaughter, using a nondestructive swabbing method. The overall mean bacterial count for 10 sampling sites of reindeer carcasses was 1.51 ± 0.51 log10 cfu/cm2. Statistically significant differences were detected between sampling sites. The back part of the reindeer carcass, i.e. hindshank, round, back and foreback, seemed to be relatively clean. The most contaminated parts were the foreleg, brisket and abdomen (2.05–2.95 log10 cfu/cm2); these could be used for monitoring the hygiene of the reindeer carcass after slaughter. Differences between the 3 slaughterhouses were detected for some sampling sites, which may be due to differences in slaughter techniques and hygiene.     

Interaction of live and dead Escherichia coli O157:H7 and fluorescent microspheres with lettuce tissue suggests bacterial processes do not mediate adherence

AIMS: The goal of this study was to determine whether any specific bacterial processes (biochemical or genetic) or cell surface moieties were required for the interaction between Escherichia coli O157:H7 and lettuce plant tissue. METHODS AND RESULTS: Escherichia coli O157:H7 and Fluospheres (fluorescent polystyrene microspheres) were used in experiments to investigate interactions with lettuce. Fluospheres were used as they are a non-biological material, of similar size and shape to a bacterial cell, but lack bacterial cell surface moieties and the ability to respond genetically. Live and glutaraldehyde-killed E. coli O157:H7 attached at levels of c. 5.8 log(10) cells per cm(2) following immersion of lettuce pieces into a suspension containing c. 8 log(10) CFU ml(-1). In a separate experiment, numbers of bacteria or Fluospheres associated with lettuce decreased by c. 1.5 log cm(-2) following a 1-min wash. Exposure times of 1 min, 1 h, or 6 h had little effect on the level of attachment for Fluospheres, and live or killed cells of E. coli O157:H7 to lettuce tissue. SIGNIFICANCE: These results indicate that bacterial processes and cell surface moieties are not required for the initial interaction of E. coli O157:H7 to lettuce plant tissue.     

Chitosan inactivates spoilage yeasts but enhances survival of Escherichia coli O157:H7 in apple juice

AIMS: To develop new measures for controlling both spoilage and pathogenic micro-organisms in unpasteurized apple juice using chitosan. METHODS AND RESULTS: Micro-organisms were isolated and identified from apple juice treated or untreated with chitosan using enrichment, selective media, microscopy, substrate assimilation patterns and ribosomal DNA profiling. Chitosan (0.05-0.1%) delayed spoilage by yeasts at 25 degrees C for up to 12 days but the effect was species specific: Kloeckera apiculata and Metschnikowia pulcherrima were inactivated but Saccharomyces cerevisiae and Pichia spp. multiplied slowly. In challenge experiments at 25 degrees C, total yeast counts were 3-5 log CFU ml(-1) lower in chitosan-treated juices than in the controls for 4 days but the survival of Escherichia coli O157:H7 was extended from 1 to 2 days; at 4 degrees C, chitosan reduced the yeast counts by 2-3 log CFU ml(-1) for up to 10 days but survival of the pathogen was prolonged from 3 to 5 days. The survival of Salmonella enterica serovar Typhimurium was unaffected by chitosan at either temperature. CONCLUSIONS: The addition of chitosan to apple juice delayed spoilage by yeasts but enhanced the survival of E. coli O157:H7. SIGNIFICANCE AND IMPACT OF THE STUDY: The results suggest that the use of chitosan in the treatment of fruit juices may potentially lead to an increased risk of food poisoning from E. coli O157:H7.     

Effect of temperature on the microbial flora of herring fillets stored in air or carbon dioxide

The microbial development on fillets of herring from the Baltic Sea was studied at temperatures from 0-15 C in air or 100% carbon dioxide (96-100% CO2). The shelf-life of the fillets , defined as the time for the 'total aerobic count' to reach 1 X 10(7) c.f.u./g increased with decreased temperature from 1 d at 15 degrees C to 7 d at 0 degrees C (air). The corresponding values in CO2 were 3 d and 33 d, respectively. The initial flora of the herring fillets was dominated by Alteromonas putrefaciens and Pseudomonas spp. and so was the spoilage flora after storage in air (together 62-95% of the flora: all temperatures). Alteromonas putrefaciens predominated slightly at 2 degrees C to 15 degrees C, while Pseudomonas spp. dominated at 0 degrees C. The Pseudomonas flora was mainly split between Ps. fragi , Ps. fluorescens and a heterogenous group of unidentified Pseudomonas spp. The proportions were not influenced by temperature. In 100% CO2 at the time of spoilage the flora consisted of a significant number of Lactobacillus spp. Below 4 C the domination was almost complete while at 10 degrees C and 15 degrees C. Enterobacteriaceae, Vibrionaceae and Alt. putrefaciens was also found. It was concluded that the microbiological shelf-life of herring fillets is improved by refrigeration storage in 100% CO2 but for good results the temperature should not exceed 2 degrees C.     

Use of an electronic nose system for diagnoses of urinary tract infections

The use of volatile production patterns produced by bacterial contaminants in urine samples were examined using electronic nose technology. In two experiments 25 and 45 samples from patients were analysed for specific bacterial contaminants using agar culture techniques and the major UTI bacterial species identified. These samples were also analysed by incubation in a volatile generation test tube system for 4-5 h. The volatile production patterns were then analysed using an electronic nose system with 14 conducting polymer sensors. In the first experiment analysis of the data using a neural network (NN) enabled identification of all but one of the samples correctly when compared to the culture information. Four groups could be distinguished, i.e. normal urine, Escherichia coli infected, Proteus spp. and Staphylococcus spp. In the second experiment it was again possible to use NN systems to examine the volatile production patterns and identify 18 of 19 unknown UTI cases. Only one normal patient sample was mis-identified as an E. coli infected sample. Discriminant function analysis also differentiated between normal urine samples, that infected with E. coli and with Staphylococcus spp. This study has shown the potential for early detection of microbial contaminants in urine samples using electronic nose technology for the first time. These findings will have implications for the development of rapid systems for use in clinical practice.     

Observations on the Microbiology of Cooked Chicken Carcasses

S ummary . The residual microbial flora and the flora developing during storage at 1–3° and at 16°, of chicken carcasses cooked in a circulating moist air oven operated at 85°, have been studied. All parts of the carcasses reached and maintained 85° for at least 50 min, and the residual flora consisted largely of spore forming bacteria. The predominant residual species were Bacillus subtilis and Clostridium bifermentans. Non-sporing bacteria were not detected after cooking nor after storage at 1–3° for up to 7 days. Storage at 16° for 3 days markedly increased the number of non-sporing organisms although off-odours typical of spoilage were not apparent until at least 10 days. Staphylococcus aureus and Salmonella spp. were not detected after cooking and storage and Cl. welchii was rarely isolated. It is concluded that poultry cooked by this method present a minimal risk of food-borne infection or intoxication by these organisms if contamination after cooking is avoided, the carcasses are cooled rapidly to c , 3° and stored at this temperature or frozen.     

Growth at sub-zero temperatures of black spot fungi from meat

Glycerol can prevent both freezing and desiccation of micro-organisms growing at sub-zero temperatures. On media containing glycerol, at concentrations readily tolerated by the organisms at ambient temperatures, three species of fungi isolated from black spot spoilt meat failed to grow at temperatures much below -5°C. This would, therefore, seem to be the minimum possible growth temperature of these organisms. Although the fungi could grow on frozen media, their rates of growth were such that, on frozen meat, several months would be required for colonies to become barely visible. It therefore seems that significant black spot spoilage will only develop on frozen meat if it is held at temperatures within 2–3° below the freezing point for prolonged periods, or if the meat surface reaches higher temperatures with surface drying inhibiting bacterial growth. There has been little study during the last 50 years of mould spoilage of meat, although it is still of importance in the international trade in frozen meats. Because moulds grow relatively slowly, they only spoil meat if the storage conditions prevent bacterial growth, but there are few firm data on the time and temperature requirements for visible mould growth to develop in the absence of bacterial spoilage. Such data are necessary if the causes of particular outbreaks of fungal spoilage are to be assessed correctly.     

Bacteriological quality of skin-moisturizing creams and lotions distributed in a tropical developing country

AIMS: To evaluate the bacteriological quality of skin moisturizing products in the South-west part of Nigeria and study factors predisposing their bacterial contamination under tropical conditions. METHODS AND RESULTS: Viable counts for bacteria exceeded 10(3) cfu ml(-1) or cfu g(-1) in 8 (16.3%) commercially available creams and lotions at time of purchase. Escherichia coli (8), Pseudomonas spp. (7), Staphylococcus spp. (9) and Bacillus spp. (6) were the most commonly recovered bacteria. Following use by volunteers, the proportion of E. coli and other Gram-negative organisms recovered increased. Organic matter, particularly in the absence of preservatives, enhanced survival and growth of bacteria in creams stored under ambient tropical conditions during challenge experiments. CONCLUSIONS: Contaminated products are relatively uncommon but some products present a potential health hazard because they are unable to suppress the growth of organisms of likely faecal origin during use. SIGNIFICANCE AND IMPACT OF THE STUDY: Quality assurance during manufacture, pack size, preservative evaluation, organic matter and water content were identified as factors to be considered during the development of creams and lotions for use in tropical developing countries.     

Effect of packaging conditions on the growth of micro-organisms and the quality characteristics of fresh mushrooms (Agaricus bisporus) stored at inadequate temperatures

Mushrooms were packed in two polymeric films (perforated and non-perforated PVC) and stored at 17 degrees C and 25 degrees C. The carbon dioxide and oxygen content inside the packages, aerobic mesophiles, Pseudomonas spp., faecal coliforms, Escherichia coli, anaerobic spores and major sensory factors (colour, texture, development stage and presence of moulds) were determined. The non-perforated packages had the highest contents of CO2 (6-7%), the lowest contents of O2 (0.013-0.17%) and the most desirable quality parameters (texture, development stage and absence of moulds). Pseudomonas spp. counts were around 1 logarithmic unit lower in mushrooms packaged in non-perforated film as the O2 concentrations were lower than in perforated film. The mushrooms themselves were inoculated with an enterotoxin A-producing strain of Staphylococcus aureus, packaged in overwrapped trays and stored at 17 and 25 degrees C. Staphylococcus aureus did not grow in the samples stored at 17 degrees C. Only slight growth was observed in mushrooms packaged with non-perforated film after 1 day at 25 degrees C. No enterotoxin was detected in any package. Faecal coliform counts were <2 log cfu g(-1). Escherichia coli was not isolated in any of the samples. At 25 degrees C, counts of anaerobic spores of around 2 log cfu g(-1) were detected in those mushrooms packaged in non-perforated film.     

Detection and characterization of a bacteriocin produced by Lactococcus lactis subsp. cremoris R isolated from radish

Bacteria isolated from radish were identified as Lactococcus lactis subsp. cremoris R and their bacteriocin was designated lactococcin R. Lactococcin R was sensitive to some proteolytic enzymes (proteinase-K, pronase-E, proteases, pepsin, α-chymotrypsin) but was resistant to trypsin, papain, catalase, lysozyme and lipase, organic solvents, or heating at 90 °C for 15, 30 and 60 min, or 121 °C for 15 min. Lactococcin R remained active after storage at −20 and −70 °C for 3 months and after exposure to a pH of 2–9. The molecular weight of lactococcin R was about 2·5 kDa. Lactococcin R was active against many food-borne pathogenic and food spoilage bacteria such as Clostridium, Staphylococcus, Listeria, Bacillus, Micrococcus, Enterococcus, Lactobacillus, Leuconostoc, Streptococcus and Pediococcus spp., but was not active against any Gram-negative bacteria. Lactococcin R was produced during log phase and reached a maximum activity (1600 AU ml⁻¹) at early stationary phase. The highest lactococcin R production was obtained in MRS broth with 0·5% glucose, at 6·5–7·0 initial pH values, 30 °C temperature and 18–24-h incubation times. Lactococcin R adsorbed maximally to its heat-killed producing cells at pH 6–7 (95%). Crude lactococcin R at 1280 AU ml⁻¹ was bactericidal, reducing colony counts of Listeria monocytogenes by 99·98% in 3 h. Lactococcin R should be useful as a biopreservative to prevent growth of food-borne pathogenic and food spoilage bacteria in ready-to-eat, dairy, meat, poultry and other food products. Lactococcin R differs from nisin in having a lower molecular weight, 2·5 kDa vs 3·4 kDa, and in being sensitive to pepsin and α-chymotrypsin to which nisin is resistant.