Raw Food Samples Research Articles

Rapid detection of Escherichia coli O157:H7 by a fluorescent microsphere-based immunochromatographic assay and immunomagnetic separation

To ensure food safety and avoid infections by Escherichia coli O157:H7 (E. coli O157:H7), we developed a novel fluorescent microsphere (FM)-based immunochromatography assay (FM-ICA). FMs were conjugated to anti-E. coli O157:H7 monoclonal antibody (MAb) as an ICA probe, Immunomagnetic beads (IM-beads) were prepared by conjugating functionalized magnetic microspheres with the antibody for enrichment and separation of pathogenic bacteria from complex food matrices. Under selected conditions, a standard curve of FM-ICA measurement of E. coli O157:H7 was developed with a linear range from 3 × 105 to 6 × 107 colony-forming units (CFU)/mL in PBS buffer. The recoveries of intra- and inter assay ranged from 101.64% to 107.03% and 95.62%–110.2% respectively, with CV below 10%. The FM-ICA showed good sensitivity, accuracy and precision. When IM-beads separation plus FM-ICA (IMS-FICA) were used to assay raw food samples, sensitivity was 3 × 103 CFU/mL, a 33-fold improvement compared with FM-ICA only. Moreover, this method had high specificity for E. coli O157:H7 and can be used to assay E. coli O157:H7 in beef, milk and water samples. This assay can be completed within 2 h and has great potential for on-site quantitation of E. coli O157:H7 with simplicity, rapidity, sensitivity, and cost-effectiveness.

Detection of chromosomal and plasmid-mediated mechanisms of colistin resistance in Escherichia coli and Klebsiella pneumoniae from Indian food samples.

Numerous previous publications on the detection of bacterial isolates harbouring the mcr-1 gene from animals and humans strongly suggest an underlying route of transmission of colistin resistance via the food chain. The aim of this study was to investigate the presence of colistin-resistant (Col-R) bacteria in Indian food samples and to identify the underlying mechanisms conferring colistin resistance. Raw food material, including poultry meat, mutton meat, fish, fruit and vegetables, collected from food outlets in Chennai, India, were processed to identify Col-R bacteria using eosin methylene blue agar supplemented with colistin. Colistin minimum inhibitory concentrations (MICs) were determined by the broth microdilution method. PCR for the mcr-1 and mcr-3 genes was performed on Col-R Escherichia coli and Klebsiella pneumoniae isolates. Mutations in the mgrB gene were analysed in K. pneumoniae isolates. One representative mcr-1-positive E. coli was subjected to whole-genome sequencing. Of 110 food samples tested, 51 (46.4%) were positive for non-intrinsic Col-R Gram-negative bacteria. Three E. coli isolates were found to harbour mcr-1, whereas none were positive for mcr-3. Ten K. pneumoniae isolates had alterations in mgrB, with mutations in four and insertional inactivation in six. The presence of Col-R bacteria and the mcr-1 gene in raw food samples further complicates the antimicrobial resistance scenario in India. To the best of our knowledge, this is the first report in the global literature on mgrB mutation and its insertional inactivation conferring Col-R in K. pneumoniae from food samples.

Food safety knowledge and microbiological hygiene of households in selected areas of Kwa-Zulu Natal, South Africa.

This study was conducted to determine the level of food safety knowledge and practices during food handling and preparation at household level in selected areas in KwaZulu-Natal province of South Africa. Fifty households were selected to participate based on their monthly income, age and educational level. Samples of raw foods were randomly collected from the participating households for microbial analyses. Swabs from food contact surfaces were also collected and analyzed for the presence of pathogens. Difference in demographic data regarding food safety knowledge was tested using chi-square and microbial counts were statistically analyzed (P<0.05). Knowledge of proper cold storage temperature was found to be inadequate as over 70% of respondents had no idea of their cold storage temperatures. High risk of cross contamination was observed due to improper thawing, packaging of meat with other ready to eat foods and poor food contact material handling. Microbial analyses of raw food samples showed the presence of aerobic spore formers (1.08-1.89 log cfu/mL), anaerobic spore formers (0.29-1.83 log cfu/mL) and Staphylococcus aureus (3.31-3.96 log cfu/mL). Contact surfaces were also positive for Listeria monocytogenes, Salmonella spp and Escherichia coli. Food safety knowledge and proper food handling practices were found to be inadequate in the areas studied and urgent intervention is required to prevent fatal incidences of food borne illnesses.

Molecular typing of Staphylococcus aureus of different origins based on the polymorphism of the spa gene: characterization of a novel spa type.

The present study was conducted to determine the molecular diversity of Staphylococcus aureus strains isolated from human, bovine and food samples based on the polymorphism of the spa gene. A total of 208 S. aureus isolated from human, bovine raw milk and food samples were assessed using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and single locus sequence typing (SLST) methods, followed by determination of spa types using Ridom SpaServer. Altogether, 15 distinct RFLP patterns were recorded (I-XV). The highest heterogeneity was observed among S. aureus isolated from humans, whereas most of bovine and food S. aureus isolates indicated certain RFLP patterns. Although most of the isolates from patients showed RFLP pattern I, none of the S. aureus isolated from carriers had this spa pattern. Besides, the results of SLST led to the characterization of 16 spa types, and one of them was a novel spa type which has been registered in Ridom SpaServer for the first time and designated as type t16929. Determination of a high number of shared RFLP patterns between human and food S. aureus isolates indicated possible transmission of S. aureus and the source of food contamination. Thus, effective hygiene measures should be taken to break transmission routes. However, it seems that S. aureus isolated from patients, carriers and bovine should be considered in a different way, since some isolates had similar patterns, while the others showed their own specific pattern.

Assessment of heavy metals in raw food samples from open markets in two African cities

The present study was performed to assess the level of biologically potent metallic elements (Al, Cd, Cr, Cu, Hg, Mn, Pb and Zn), metalloid (As) and non-metal (Se) in different raw food from open markets in Kinshasa (Democratic Republic of Congo) and Johannesburg (South Africa). Hundred twenty different food samples comprising of cabbage, bean, beef and fish were collected, digested in the microwave system and analysed for trace metals using ICP-OES, ICP-MS and mercury analyser. The obtained results were used to evaluate the health risk of these elements via consumption of foods. The investigation revealed that the mean level of trace elements ranged Al: 1.62 ± 0.32 to 52.10 ± 3.45, As: 1.62 ± 0.32 to 5.33 ± 1.04, Cd: 0.16 ± 0.09 to 3.93 ± 0.12, Cr: 0.58 ± 0.24 to 17.29 ± 2.03, Cu: 0.69 ± 0.15 to 15.70 ± 1.67, Hg: 1.53 ± 0.1 to 2.94 ± 0.23, Mn: 5.34 ± 1.37 to 18.31 ± 3.45, Pb: 0.16 ± 0.09 to 4.14 ± 1.08, Se: 0.18 ± 0.08 to 1.41 ± 0.97, Zn: 5.47 ± 1.83 to 75.12 ± 5.67 mg kg−1. The average values of As, Cd, Cr, Cu, Hg, Mn, Pb, Se and Zn in raw foods collected from Johannesburg market were significantly higher (p < 0.05) than those from the Kinshasa market. While the highest Al contents (p < 0.05) were found in the food sold in Kinshasa open market. The levels of most studied metals in the raw foods were exceeding the recommended maximum acceptable limit proposed by the Joint FAO/WHO Expert Committee on Food. The combined Target Hazard Quotients (THQ) values for all samples from both markets were greater than 1 which indicates a potential health risk to the local consumer.

Phenotypic and genotypic characterization of antibiotic resistance of methicillin-resistant Staphylococcus aureus isolated from hospital food

BackgroundPathogenic biotypes of the Methicillin-resistant Staphylococcus aureus (MRSA) strains are considered to be one of the major cause of food-borne diseases in hospitals. The present investigation was done to study the pattern of antibiotic resistance and prevalence of antibiotic resistance genes of different biotypes of the MRSA strains isolated from various types of hospital food samples.MethodsFour-hundred and eighty-five raw and cooked hospital food samples were cultured and MRSA strains were identified using the oxacillin and cefoxitin disk diffusion tests and mecA-based PCR amplification. Isolated strains were subjected to biotyping and their antibiotic resistance patterns were analyzed using the disk diffusion and PCR methods.ResultsPrevalence of S. aureus and MRSA were 9.69 and 7.62%, respectively. Meat and chicken barbecues had the highest prevalence of MRSA. Prevalence of bovine, ovine, poultry and human-based biotypes in the MRSA strains were 8.10, 8.10, 32.43 and 48.64%, respectively. All of the MRSA strains recovered from soup, salad and rice samples were related to human-based biotypes. MRSA strains harbored the highest prevalence of resistance against penicillin (100%), ceftaroline (100%), tetracycline (100%), erythromycin (89.18%) and trimethoprim-sulfamethoxazole (83.78%). TetK (72.97%), ermA (72.97%), msrA (64.86%) and aacA-D (62.16%) were the most commonly detected antibiotic resistance genes.ConclusionsPattern of antibiotic resistance and also distribution of antibiotic resistance genes were related to the biotype of MRSA strains. Presence of multi-drug resistance and also simultaneous presence of several antibiotic resistance genes in some MRSA isolates showed an important public health issue Further researches are required to found additional epidemiological aspects of the MRSA strains in hospital food samples.

Residues of organochlorine pesticides in surface soil and raw foods from rural areas of the Republic of Tajikistan

The central Asian Republic of Tajikistan has been an area of extensive historical agricultural pesticide use as well as large scale burials of banned chlorinated insecticides. The current investigation was a four year study of legacy organochlorine pesticides in surface soil and raw foods in four rural areas of Tajikistan. Study areas included the pesticide burial sites of Konibodom and Vakhsh, and family farms of Garm and Chimbuloq villages. These areas were selected to represent a diversity of pesticide disposal histories and to allow assessment of local pesticide contamination in Tajikistan. Each site was visited multiple times and over 500 samples of surface soil and raw foods were collected and analyzed for twenty legacy organochlorine pesticides. Various local food products were sampled to represent the range of raw foods potentially containing residues of banned pesticides, including dairy products, meat, edible plant and cotton seed products. The pesticide analytes included DDTs (DDT, DDD, DDE), lindane isomers (α, β, γ, δ BHC), endosulfan isomers (endosulfan I, II, sulfate), other cyclodienes (aldrin, α and γ chlordanes, dieldrin, endrin, endrin aldehyde and ketone, heptachlor, heptachlor epoxide), and methoxychlor. Pesticide analytes were selected based on availability of commercial standards and known or suspected historical pesticide use and burial. Pesticide contamination was highest in soil and generally low in meat, dairy, and plant products. DDT was consistently the highest measured individual pesticide at each of the four sampling areas, along with BHC isomers and endosulfan II. Soil concentrations of pesticides were extremely heterogeneous at the Vakhsh and Konibodam disposal sites with many soil samples greater than 10 ppm. In contrast, samples from farms in Chimbuloq and Garm had low concentrations of pesticides. Pesticide contamination in raw foods was generally low, indicating minimal transfer from the pesticide sites into local food chains.

Assessment of organochlorine pesticide residues in raw food samples from open markets in two African cities

This study investigates the level of organochlorine pesticides in the raw food from open markets in Kinshasa, Democratic Republic of Congo (DRC), and Johannesburg, South Africa. It assesses the potential health risks associated with the organochlorine pesticide residues. The Quick, Easy, Cheap, Effective, Rugged, and Safe (QuEChERS) method has been developed for sample preparation. A total of 120 food samples (beans, cabbage, beef, and fish) were obtained from the open markets. The mean concentrations of organochlorine pesticides in raw foods collected from the Johannesburg market were significantly higher (p < 0.05) than those from the Kinshasa market. DDE recorded the highest mean concentration (253.58 ± 4.78 μg kg−1) in beef from Johannesburg, and α-BHC recorded the lowest mean concentration (38.54 ± 7.46 μg kg−1) in beans from Kinshasa. The investigation of health risk estimates revealed that the number of organochlorine pesticides exceeded the reference dose in the collected food samples.

Bioavailability of Fe and Zn in selected legumes, cereals, meat and milk products consumed in Fiji

The present study reports contents and the bioavailability of Fe and Zn from 25 selected raw and cooked food samples. The results showed highest variation of Fe content in raw food samples ranging from 2.19±0.04 to 0.93±0.03mg/100g in legumes. The raw black eye bean, cheese and fish showed high Zn content up to 8.85±0.01, 12.93±0.26 and 172.03±5.09mg/100g, respectively. Pulses and cereals showed high level of ionizable Fe. Zn bioavailability was quite low in cereals as compared to pulses; 4.02% in yellow split to 17.40% in Bengal gram. Zn bioavailability of 17.40% is in cheese. Fe bioavailability is high in cooked rice 160.60%, white bread 428.30% and milk powder 241.67% showing that Fe bioavailability increased after cooking whereas the lowest in fish 0.84%. The multivariate and cluster analysis categorized studied foods into two main groups.

An Advanced Visual Qualitative and EVA Green‐Based Quantitative Isothermal Amplification Method to Detect Listeria Monocytogenes

AbstractThe purpose of this study is to apply the visual qualitative (LFD‐LAMP) and advanced quantitative loop‐mediated isothermal amplification (EVA‐LAMP) methods to detect Listeria monocytogenes, which is an important pathogenic foodborne bacterium. This research designed a new set of primers to amplify the hlyA gene of L. monocytogenes. The LFD‐LAMP products were detected by lateral flow device (LFD) with the naked eyes, and the test results were consistent with agarose gel electrophoresis. Meanwhile, an advanced quantitative LAMP assay was established which depended on the EVA Green. The detection limit of the EVA‐LAMP method was 10 pg/μL, and a good linear relationship was obtained. The subsequent analysis of contaminated raw food samples showed that the primers were able to identify L. monocytogenes in food. The LFD‐LAMP and EVA‐LAMP reactions can be used as sensitive, rapid and simple methods for the detection of L. monocytogenes, especially on field detection.Practical ApplicationsThis work suggests a specific, sensitive, cost‐effective and nonpollution LAMP assay for the detection of Listeria monocytogenes. A new set of hlyA‐based primers was designed and successfully used to detect L. monocytogenes in raw food samples. Amplicon detection by visual LFD method proved to be as useful as the gel, but more convenient and clean. The LFD‐LAMP detection method in this study testifies as a significant advancement toward making LAMP a potential on‐site detection. Otherwise, in contrast to the traditional real‐time LAMP approach, this is a novel study to describe a real‐time quantitative LAMP assay based on EVA Green to detect L. monocytogenes in the fields of food safety.

Phenotypic and genotypic studies on Escherichia coli strains isolated from food products of animal origin

Foodstuffs of animal origin may present hazards, due to bacterial contamination. This study was conducted to determine Escherichia coli in some types of animal source foods (raw milk, raw beef meat and raw poultry meat). Bacteriological examination of total 246 raw food samples of animal origin, raw milk, (105); beef meat (31) and poultry meat (110) were collected from different localities in Ismailia City showed that 64/246 (26.01%) of samples were infected with E. coli. Serological identification of (10) E. colistrains revealed that they were belonged to O111 polyvalent 1; O44 polyvalent 2 (2 strains for each); O78 polyvalent 4; O146 polyvalent 2; O26 polyvalent 1; O119 polyvalent 1; O86 polyvalent 1 and O18 polyvalent 3 (1 strain for each). E. coli strains showed high susceptible rate to Ciprofloxacin (CIP), (100%) and high resistance (100%) to Ampicillin (AMP), Metronidazole (MTZ), Amoxicillin (AML), and Vancomycin (VAS). Four strains of the isolated E. coli were submitted to molecular studies for detection of the eaeA (protein intimin), iutA (encoding aerobactin) and iss (increased serum survival protein) genes, by using PCR technique.

Thin-layer chromatography/direct analysis in real time time-of-flight mass spectrometry and isotope dilution to analyze organophosphorus insecticides in fatty foods

To assess food safety emergencies caused by highly hazardous chemical-tainted foods, simultaneous analysis of organophosphorus insecticides in fatty foods such as precooked foods was conducted using thin-layer chromatography/direct analysis in real time time-of-flight mass spectrometry (TLC/DART-TOFMS) and isotope dilution technique. Polar (methamidophos and acephate) and nonpolar organophosphorus insecticides (fenitrothion, diazinon, and EPN) were studied. Experiments to ascertain chromatographic patterns using TLC/DART-TOFMS reveal that it was more useful than GC/MS or GC/MS/MS for the simultaneous analyses of polar and nonpolar pesticides, while obviating the addition of a protective agent for tailing effects of polar pesticides. Lower helium gas temperature (260°C) for DART-TOFMS was suitable for the simultaneous analysis of target pesticides. Linearities were achieved respectively at a lower standard concentration range (0.05–5μg) for diazinon and EPN and at a higher standard concentration range (2.5–25μg) for methamidophos, acephate, and fenitrothion. Their respective coefficients of determination were ≥0.9989 and ≥0.9959. A few higher repeatabilities (RSDs) for diazinon and EPN were found (>20%), although isotope dilution technique was used. Application to the HPTLC plate without an automatic TLC sampler might be inferred as a cause of their higher RSDs. Detection limits were estimated in the higher picogram range for diazinon and EPN, and in the lower nanogram range for methamidophos, acephate, and fenitrothion. Aside from methamidophos, recovery results (n=3) obtained using a highly insecticide-tainted fatty food (dumpling) and raw food (grapefruit) samples (10mg/kg) using TLC/DART-TOFMS with both complex and simpler cleanups were not as susceptible to matrix effects (95–121%; RSD, 1.3–14%) as those using GC/MS/MS (102–117%; RSD, 0.4–8.5%), although dumpling samples using GC/MS were remarkably susceptible to matrix effects. The coupled method of TLC with simpler cleanup and DART-TOFMS can be regarded as the same analytical tool as GC/MS/MS, which is useful to assess food safety emergencies caused by highly hazardous chemical-tainted foods.

Estimation of Resistant Starch Content of Selected Routinely Consumed Indian Food Preparations

Resistant Starch, an important component of the diet, shows the potential health benefits against lifestyle diseases and many other health conditions. Resistant Starch (RS) refers to the portion of starch and starch products that resist digestion as it passes through the gastrointestinal tract, gets fermented in the colon by colonic microflora and produces short chain fatty acids which directly or indirectly help in preventing and/or controlling many diseases.Since the main sources of RS in the Indian diet are starchy foods like varieties of cereals, cereal products, roots and tubers, raw and processed legumes etc.it becomes important to determine the RS content of typical traditional Indian starchy cereal and legume preparations.Therefore the aim of this research was to estimate the RS content of selected, routinely consumed Indian food preparations and to determine the change in RS content of cereal and pulse preparations on cooking and on storage. RS content was estimated for two varieties of rice and four rice preparations, whole and refined wheat flour and four preparations made using these flours, legumes like whole moong, Kabuli chhana, Chana flour and preparations made using them. Five of these preparations were also analyzed for their RS content after an overnight storage in the refrigerator, to understand the effect of storage on their RS content.Amount of RS was estimated using the procedure given by Parchure and Kulkarni. RS content in freshly cooked preparations was compared with RS content in equivalent amount of raw ingredients. RS content of freshly cooked preparations was also compared with RS in equivalent amount of cooked and stored samples. Comparison of means was done using paired t test. One-way ANOVA was also used to compare RS content of freshly cooked rice preparations, wheat preparations and legume preparations. P ≤ 0.05 was considered statistically significant.The RS content of raw food samples ranged from as low as 0.50g% in whole wheat flour to 27.67g% in Kolam rice. The two varieties of rice, Basmati and Kolam contained 20.22g% and 27.67g% RS respectively whereas Whole wheat flour and Refined wheat flour contained 0.50g% and 0.65g% RS respectively. The RS in raw legumes was 1.93g%, 1.98g% and 4.52g% in Kabuli Chana, Chana flour and Whole Moongrespectively.Among four freshly cooked rice preparations RS varied from 0.46g% in cooked Kolam to 0.78g% in Khichdi. Among four wheat preparations (freshly cooked) RS content varied from 0.47g% in Puri to 0.61g% (food as eaten) in paratha. Chapatti and Bhatura contained 0.49g% and 0.54g% RS (food as eaten) respectively.RS in legume preparations ranged from 0.09g% in freshly cooked Pithle to 2.38g% in cooked Chole. The RS values for germinated Moong, MoongUsal, and soaked Kabuli chana were 0.79g%, 0.87g% and 0.73g% (food as eaten) respectively.In case of rice preparations RS content was significantly lower in all the four freshly cooked rice products as compared to RS in equivalent amount of raw rice. All freshly cooked wheat products showed increase in RS content after cooking as compared to their corresponding raw equivalents. Except for Bhatura, in which the increase was not significant, in the rest of wheat preparations the increase was statistically significant. In case of processed or cooked legume preparations, except for chole, significantly lower RS was found in all preparations as compared to their raw equivalent quantities.In all the preparations that were subjected to storage, RS content increased after an overnight storage. A significant increase was seen in pressure cooked and stored Kolam Rice.Comparison among freshly cooked rice preparations showed that Khichdi contained significantly higher amount of RS as compared to other rice preparations, whereasamong freshly made wheat preparations, highest RS content was observed in Paratha. The RS value for Paratha was significantly higher than chapatti and puri. Among legume preparations Chhole had significantly higher RS content than moong usal or pithle. To conclude, the findings of this research show that Resistant Starch content of food preparation is influenced by many factors such as cooking method, processing technique, storage. Considering that Indians consume a vast variety of starchy preparations, further research in this direction is needed, to create a complete database of Resistant Starch content of Indian starchy preparations, that are made using different cooking and processing techniques and stored under varied conditions.

Antimicrobial Properties of 39 Essential Oils against Thirteen Food-borne Microorganisms; Efficacy and Environmental Hygiene of Prunus armeniaca in Raw Food Preservation under Cold Storage

Aim: The present study investigated the antimicrobial properties of 39 diversified essential plant oils (EOs). The most bioactive EO was selected and tested for its environmental hygiene efficacy in the preservation of stored raw food. Methods: The antimicrobial efficacy of 39 EOs was examined against 13 representative food-borne microorganisms. Minimal inhibitory concentration (MIC) of extracted apricot (Prunus armeniaca) seed EO was evaluated. Different concentrations of extracted oil were applied to four types of low-fat raw foods under cold dry storage. Results: The results of the microbial sensitivity assay showed considerable positive responses to only 23 out of 39 EOs. Pru. armeniaca exhibited the most significant antimicrobial efficacy. Different MIC values of extracted Pru. armeniaca oil were documented as a result of strain variability of representative food-borne microorganisms. Extracted apricot EO concentration delayed bacterial food spoilage at 1000 μgml-1 while fungal spoilage delayed at 2000 μgml-1. Total bacterial viable count (TVC) of raw food samples treated with 1000 μgml-1 oil decreased sharply when compared with TVC of samples not treated with oil. Fungal growth was completely inhibited in samples treated with 2000 μgml-1 oil. Statistical analysis showed a significant association between the minimal inhibitory concentrations (MIC) of Pru. armeniaca EO and the growth of the 13 representative food-borne microorganisms, it was mostly 500μgml-1. Conclusion: The achieved study results support using of Pru. armeniaca EO in controlling shelf-life of raw foods stored under dry cold conditions.

Food hygiene control in school canteens of La Spezia municipality: years 2003-2012

The school canteens are public catering services of great interest as they provide meals to a high number of consumers who are particularly susceptible to health risks, therefore surveillance and health control are very important to ensure food safety. To this purpose, a convention between the Istituto Zooprofilattico Sperimentale of Piemonte Liguria e Valle d’Aosta, and La Spezia municipality was established for the health control of school canteens. In this article we report the results of analysis performed on food and swab surfaces samples collected during the period 2003-2012 in 22 school canteens and 3 cooking centers. From a total of 1187 samples: 313 raw foods were analyzed for chemical and microbiological parameters to verify compliance with legislation, 71 food preparations were analyzed for bacteria indicators to assess the good manufacturing practices, and 803 surface swabs were tested for total mesophilic count (TMC), Salmonella spp. and Listeria spp. to control cleaning/disinfection conditions. The results show that only 1.3% of raw food samples did not respect the limits imposed by legislation, and 1.4% of food preparations was positive for pathogens. In environmental swabs, pathogenic microorganisms were never isolated and TMC exceeded the limits of acceptability in no more than 27% of cases. The most contaminated surfaces were those in contact with food and the equipment difficult to clean. The results demonstrate that potential hazards are kept to acceptable levels in school canteens and cooking centers investigated. In fact, during the period considered no foodborne diseases were reported among users. However, data obtained may be useful to better define control measures to be adopted to improve the hygienic level production in these structures and to prevent foodborne infections.

Occurrence and antimicrobial susceptibility of Listeria monocytogenes isolates from retail raw foods

The occurrence and counts of Listeria monocytogenes were investigated in a total of 526 retail raw food samples. All L. monocytogenes isolates were further analyzed by serotyping and antimicrobial susceptibility assays. The molecular basis of tetracycline resistance of each isolate and the genetic relatedness were determined. L. monocytogenes isolates were found in 12.4% (65/526) of the samples, with counts below 102 CFU/g. L. monocytogenes was most commonly isolated from pork (20%, 20/100), seafood (13.8%, 15/109), chicken (13.2%, 14/106), and beef (10.3%, 11/107). In addition, L. monocytogenes was also detected in 4.8% (5/104) of raw mutton samples. Four serogroups were identified among the 65 L. monocytogenes isolates, with serogroups 1/2a-3a (60%) and 4b-4d-4e (24.6%) being dominant. Most L. monocytogenes isolates were resistant to cefotaxime (54.6%), fosfomycin (51.5%), and clarithromycin (36.4%). Some isolates showed intermediate resistance to streptomycin (12.1%), norfloxacin (13.6%), ciprofloxacin (13.6%), and nitrofurantoin (9.1%). Multiple resistances were observed in 72.3% of isolates. Genetic relatedness analysis revealed that there were no prominent associations between specific food types, serotypes, antimicrobial susceptibility profiles and Pulsed-field gel electrophoresis (PFGE) patterns. In addition, these isolates were multiresistant and belonged to the epidemiologically important serotypes 1/2a and 4b, implying a potential public health risk.

Detection of viable but non-culturable Escherichia coli O157:H7 from vegetable samples using quantitative PCR with propidium monoazide and immunological assays

Quantitative differentiation of the live fraction of pathogens in raw food samples is highly critical from a public health risk perspective, as many studies have shown that under stress conditions major foodborne pathogens enter a viable but non-culturable (VBNC) state in which bacteria can remain for long periods of time and maintain the potential for virulence. The objective of this study was to evaluate the applicability of propidium monoazide (PMA) quantitative PCR (qPCR) and immunological methods for detection of Escherichia coli O157:H7 VBNC populations induced by low temperature on the surface of lettuce and spinach plants. The primer/probe set selected influenced the qPCR signal in mixtures with a defined ratio of viable and non-viable cells. The PMA qPCR used in a background of added dead pathogens and epiphytic bacteria gave a detection limit of 103 CFU/g leaf and a linear quantitative detection range of 5 log. During quantification of VBNC cells from lettuce and spinach samples there was a good correlation between the PMA qPCR results and viable counts detected by microscopy, showing that PMA qPCR gives an accurate indication of the VBNC population. However, the commercially available immunoassay methods used to detect Shiga-like toxin production and the O157 antibody in vegetable samples with no detectable culturable pathogen underestimated the number of samples contaminated with E. coli O157:H7 VBNC cells. Results indicate that PMA qPCR is a suitable technique for the detection and quantification of VBNC cells of foodborne pathogens in contaminated raw lettuce and spinach.

A loop-mediated isothermal amplification method targets the HisJ gene for the detection of foodborne Salmonella

A loop-mediated isothermal amplification (LAMP) assay was developed and validated for the specific detection of Salmonella in food. The four primers required for LAMP were designed using a conserved region in the histidine transport protein-coding region of Salmonella. Seventy-nine reference strains of 72 Salmonella serovars and 23 non-Salmonella strains were detected by LAMP. The detection limit of this assay is 16 CFU per reaction in pure culture, up to tenfold more sensitive than that of the PCR assay with the same target gene. When applied in raw food samples, a sample pretreatment protocol was performed that included a pre-enrichment step in 0.1 % buffered peptone water, followed by a selective enrichment in Rappaport–Vassiliadis medium. Using this method, 200 assorted food samples were investigated for Salmonella, including fresh pork, whole chickens, and green vegetables. The sensitivity of LAMP for the detection of Salmonella in food samples was 93.55 %, versus 87.10 % that tested positive using conventional PCR. The results from this study showed that the HisJ-based LAMP is an effective method for the detection of foodborne Salmonella.

Health benefits and omega-3-fatty acid content of selected indigenous foods in the Limpopo Province, South Africa

The article is based on a study that aimed at identifying indigenous foods in the Limpopo Province that are believed to have health benefits and to analyse the omega-3-fatty acid content of the selected identified foods. The objectives of this study were to identify the indigenous foods believed to have health benefits with possible functional properties, to determine the different ailments that these foods were used for, and to analyse the omega-3-fatty acid content of the identified indigenous foods. The study population consisted of 46 women whose ages were above 60 years old. The participants were recruited from four districts in the Limpopo Province namely Waterberg, Vhembe, Mopani and Sekhukhune. Focus group discussions were held, wherein an interview schedule was used to lead the discussions. The data was analysed using thematic analysis. The fresh raw food samples were collected and taken to the CSIR for chemical analysis of bioactive compounds. The results of the study revealed that some indigenous green leafy vegetables have a high content of omega-3-fatty acids per fatty acid content. Indigenous foods were taken for their functional properties. Food items like Mormodica balsamina were identified to treat and prevent hypertension and diabetes mellitus. The food item is known as Mokhutsega in Northern Sotho, Nkaka in Xitsonga and Tshibavhi in Tshivenda. Some of the food items that were mentioned to treat diseases were Amaranthus thurnbergii and Cajanus cajan for the prevention of constipation. Donkey milk was taken to treat whooping cough. Of the seven indigenous foods analysed, six of them were green leafy vegetables and one was a fruit. The samples were analysed for omega-3-fatty acid content. The green leafy vegetables were found to contain omega-3-fatty acids. Linolenic acid, which has 18 carbon chains and three double bonds, was found to be the most abundant omega-3-fatty acid found in plant foods. The omega-3-fatty acids are said to be a factor in HDL concentration, thereby confirming the lowering of coronary heart diseases by green leafy vegetables.

English

Sixteen foods borne bacteria were isolated from raw food samples including okro, carrot, spinach, pepper, tomato, onion and cooked food samples (rice, yam, beans, meat and plantain). The isolates were characterized and identified asBacillus brevis, Bacillus congulans, Bacillus polymyxa, Bacillus lentus, Bacillus megaterium, Bacillus subtilis, Acinetobacter spp., Citrobacter freundii,Klebsiella aerogenes, Streptococcus agalactiae, Alcaligenes spp.,Corynebacterium spp., Enterobacter aerogenes, Enterobacter spp. andStaphylococcus epidermidis. These isolates were screened on egg yolk agar for toxigenic properties and thirteen of the sixteen were positive for toxin production while three were negative. Six out of the thirteen toxigenic bacterial were selected for further work. These were; E. coli, K. aerogenes, C. freundii, B. polymyxa, S. epidermidis and E. aerogenes. The effect of pH, thermal treatment and chemical preservatives on the growth rate and toxin elaboration of E. coli, K. aerogenes, C. freundii, B. polymyxa, S. epidermidis and E. aerogenes was studied. It was observed that E. coli had no viable growth until 48 h of incubation, while the other five isolates had visible growth right from the 24 h of incubation. Also E. coli did not produce toxin until the 96th hour of incubation; K. aerogenesand E. aerogenes were able to produce toxin at 24 h of incubation, while C. freundii, B. polymyxa and S. epidermidis produced toxin at 48 h of incubation. Also, 44°C was not suitable for toxin production. pH 3 and 5 were less favorable for toxin production despite the fact that isolates were able to grow at different temperature and pH ranges. The isolate were more sensitive to sodium metabisulfite than benzoic acid. Also, E. coli and K. aerogenes were able to elaborate toxin in their dormant state with 750 mg of sodium metabisulfite. Key words: Toxin production, viable growth, raw food sample, cooked food sample, E. coli, K. aerogenes, C. freundii, B. polymyxa, S. epidermidis and E. aerogenes.