Survival of acid-adapted Salmonella typhimurium in fermented millet and acidified broth at different storage temperatures

Salmonella typhimurium KSN 533 was adapted to acid by exposure to lactic acid at pH 5.0 for 18 h. Subsequently, acid-adapted and non-adapted cells were challenged with lactic acid (pH 3.8) in Brain-heart infusion (BHI) at 4°C and 30°C. Acid-adapted and non-adapted cells were also inoculated into already fermented millet broth (pH 3.8) and at beginning of millet fermentation with Lactobacillus fermentum starter culture. Survival curves of acid-adapted and non-adapted cells at pH 3.8 were fitted with the Weibull distribution model. Acid-adapted cells were generally resistant to subsequent acid stress than non-adapted cells. Regardless of adaptation, cells were more sensitive to acid shock (pH 3.8) at 30°C than at 4°C storage. Whereas both acid-adapted and non-adapted S. typhimurium cells survived in appreciable numbers of 5.5 and 3.5 log cfu/ml respectively after 72 h storage at 4°C, no viable cells were detected for both acid-adapted and non-adapted cells after 12 an 9 h respectively at 30°C. Acid-adaptation induced protection against lethal acid and cross protection against cold stresses. Regardless of adaptation, viable population of Salmonella showed a slight increase during the early stages of millet fermentation. Similar inactivation rates were observed for both acid-adapted and non-adapted cells when inoculated at the beginning of fermentation. Thus acid adaptation does not appear to influence survival of S. typhimurium when inoculated at the beginning of the fermentation although acid-adapted cells survived better in already fermented millet. Keywords: acid-adaptation, millet fermentation, Salmonella, lethal acid challeng

Microbial Safety of Milk Production and Fermented Dairy Products in Africa

In Africa, milk production, processing and consumption are integral part of traditional food supply, with dairy products being a staple component of recommended healthy diets. This review provides an overview of the microbial safety characteristics of milk production and fermented dairy products in Africa. The object is to highlight the main microbial food safety hazards in the dairy chain and to propose appropriate preventive and control measures. Pathogens of public health concern including Mycobacterium bovis, Brucella abortus and Coxiella burnettii, which have largely been eradicated in many developed nations, still persist in the dairy chain in Africa. Factors such as the natural antimicrobial systems in milk and traditional processing technologies, including fermentation, heating and use of antimicrobial additives, that can potentially contribute to microbial safety of milk and dairy products in Africa will be discussed. Practical approaches to controlling safety hazards in the dairy chain in Africa have been proposed. Governmental regulatory bodies need to set the necessary national and regional safety standards, perform inspections and put measures in place to ensure that the standards are met, including strong enforcement programs within smallholder dairy chains. Dairy chain actors would require upgraded knowledge and training in preventive approaches such as good agricultural practices (GAP), hazard analysis and critical control points (HACCP) design and implementation and good hygienic practices (GHPs). Food safety education programs should be incorporated into school curricula, beginning at the basic school levels, to improve food safety cognition among students and promote life-long safe food handling behaviour

Prevalence and characteristics of <em>Listeria monocytogenes</em> isolates in raw milk, heated milk and Nunu, a spontaneously fermented milk beverage in Ghana

Listeria monocytogenes is a gram-positive food-borne pathogen that causes listeriosis in humans. Currently, there is little information on the prevalence of Listeria monocytogenes in raw milk and traditional yoghurt-like milk beverage, nunu, in Ghana. The purpose of this study was to investigate the prevalence of L. monocytogenes isolates in raw cow milk, boiled milk and nunu in Ghana, and to characterize these L. monocytogenes isolates according to their serogroups, virulence potentials and antibiotic susceptibility profiles. A total of 254 samples comprising 114 raw cow milk, 56 boiled milk and 84 nunu were collected from dairy farms and market vendors for detection of L. monocytogenes. The overall prevalence of L. monocytogenes in raw milk, boiled milk and nunu was 5.5% (14/254). Listeria monocytogenes was prevalent in raw cow milk (8.8%; 10/114) and nunu (13.1%; 11/84), while no Listeria spp. was not detected in boiled milk. A total of 62 L. monocytogenes isolates were analysed to belong to molecular serogroups 1/2a-3a (32/62, 51.6%), 1/2b-3b-7 (14/62, 22.6%), 4b-4d-4e (9/62, 14.5%) and 1/2c-3c (7/62, 11.3%). All 62 L. monocytogenes isolates harbored the virulence-associated genes inlA, inlB, inlC, inlJ, plcA, actA, hlyA, iap and prfA. All Listeria monocytogenes in the present study were generally susceptible to the tested antibiotics, except neomycin and tetracycline, for which phenotypic resistance was observed among isolates

Technological properties and probiotic potential of <i>Lactobacillus fermentum</i> strains isolated from West African fermented millet dough

BACKGROUND: Throughout Africa, food fermentations are still driven by indigenous microorganisms which influence the nutritional, organoleptic and safety of the final products. However, for improved safety, consistent quality and beneficial health effects, a trend has emerged which involves the isolation of indigenous strains from traditional fermented products to be used as functional starter cultures. These functional starter cultures possess inherent functional characteristics and can contribute to food quality and safety by offering one or more organoleptic, nutritional, technological or health advantage (probiotics). With the aim of selecting potential probiotic starter cultures, Lactobacillus fermentum strains isolated from fermented millet dough were investigated for technological properties and probiotic traits in-vitro. RESULTS: A total of 176 L. fermentum strains were assessed for technological properties including rate of acidification, exopolysaccharide production and amylase activity. Following this, 48 strains showing desirable technological properties were first screened for acid resistance. Sixteen acid resistant strains were assessed for additional probiotic properties including resistance to bile salts, bile salt hydrolysis, antimicrobial property, haemolysis and antibiotics resistance. L. fermentum strains clustered into 3 groups represented by 36 %, 47 % and 17 % as fast, medium and slow acidifiers respectively. About 8 %, 78 % and 14 % of the strains showed strong, weak and no exopolysaccharides production respectively. Amylase activity was generally weak or not detected. After exposure of 48 L. fermentum strains to pH 2.5 for 4 h, 16 strains were considered to be acid resistant. All 16 strains were resistant to bile salt. Four strains demonstrated bile salt hydrolysis. Antimicrobial activity was observed towards Listeria monocytogenes and Staphylococcus aureus but not E. coli and Salmonella enteritidis. Lactobacillus fermentum strains were generally susceptible to antibiotics except 6 strains which showed resistance towards streptomycin, gentamicin and kanamycin. CONCLUSION: In vitro determination of technological and probiotic properties have shown strain specific difference among L. fermentum strains isolated from fermented millet dough. Sixteen (16) L. fermentum strains have been shown to possess desirable technological and probiotic characteristics in vitro. These strains are therefore good candidates for further studies to elucidate their full potential and possible application as novel probiotic starter cultures

The use of lactic acid bacteria starter culture in the production of<em> Nunu</em>, a spontaneously fermented milk product in Ghana

Nunu, a spontaneously fermented yoghurt-like product, is produced and consumed in parts of West Africa. A total of 373 predominant lactic acid bacteria (LAB) previously isolated and identified from Nunu product were assessed in vitro for their technological properties (acidification, exopolysaccharides production, lipolysis, proteolysis and antimicrobial activities). Following the determination of technological properties, Lactobacillus fermentum 22-16, Lactobacillus plantarum 8-2, Lactobacillus helveticus 22-7, and Leuconostoc mesenteroides 14-11 were used as single and combined starter cultures for Nunu fermentation. Starter culture fermented Nunu samples were assessed for amino acids profile and rate of acidification and were subsequently evaluated for consumer acceptability. For acidification properties, 82%, 59%, 34%, and 20% of strains belonging to Lactobacillus helveticus, L. plantarum, L. fermentum, and Leu. mesenteriodes, respectively, demonstrated fast acidification properties. High proteolytic activity (>100 to 150 μg/mL) was observed for 50% Leu. mesenteroides, 40% L. fermentum, 41% L. helveticus, 27% L. plantarum, and 10% Ent. faecium species. In starter culture fermented Nunu samples, all amino acids determined were detected in Nunu fermented with single starters of L. plantarum and L. helveticus and combined starter of L. fermntum and L. helveticus. Consumer sensory analysis showed varying degrees of acceptability for Nunu fermented with the different starter cultures

Prevalence, virulence factor genes and antibiotic resistance of<em> Bacillus cereus sensu lato </em>isolated from dairy farms and traditional dairy products

BACKGROUND: B. cereus are of particular interest in food safety and public health because of their capacity to cause food spoilage and disease through the production of various toxins. The aim of this study was to determine the prevalence, virulence factor genes and antibiotic resistance profile of B. cereus sensu lato isolated from cattle grazing soils and dairy products in Ghana. A total of 114 samples made up of 25 soil collected from cattle grazing farm land, 30 raw milk, 28 nunu (yoghurt-like product) and 31 woagashie (West African soft cheese). Ninety-six B. cereus sensu lato isolates from 54 positive samples were screened by PCR for the presence of 8 enterotoxigenic genes (hblA, hblC, hblD, nheA, nheB, nheC, cytK and entFM), and one emetic gene (ces). Phenotypic resistance to 15 antibiotics were also determined for 96 B. cereus sensu lato isolates. RESULTS: About 72% (18 of 25 soil), 47% (14 of 30 raw milk), 35% (10 of 28 nunu) and 39% (12 of 31 woagashi) were positive for B. cereus sensu lato with mean counts (log(10) cfu/g) of 4.2 ± 1.8, 3.3 ± 2.0, 1.8 ± 1.4 and 2.6 ± 1.8 respectively. The distribution of enterotoxigenic genes revealed that 13% (12/96 isolates) harboured all three gene encoding for haemolytic enterotoxin HBL complex genes (hblA, hblC and hblD), 25% (24/96 isolates) possessed no HBL gene, whereas 63% (60/96 isolates) possessed at least one of the three HBL genes. All three genes encoding for non-haemolytic enterotoxin (nheA, nheB and nheC) were detected in 60% (57/96) isolates, 14% (13/96) harboured only one gene, 19% (18/96) whereas 8% possessed none of the NHE genes. The detection rates of cytk, entFM, and ces genes were 75, 67 and 9% respectively. Bacillus cereus s. l. isolates were generally resistant to β-lactam antibiotics such as ampicillin (98%), oxacillin (92%), penicillin (100%), amoxicillin (100%), and cefepime (100%) but susceptible to other antibiotics tested. CONCLUSIONS: Bacillus cereus s. l. is prevalent in soil, raw milk and dairy products in Ghana. However, loads are at levels considered to be safe for consumption. Various enterotoxin genes associated with virulence of B. cereus are widespread among the isolates

Prevalence and characteristics of Listeria species from selected African countries

Listeriosis, caused by Listeria spp., presents varying clinical manifestations among individuals, from moderate fecal infections such as diarrhea to severe infections such as septicemia, meningitis and abortion or newborn listeriosis in perinatal patients. In Africa, listeriosis is attributed to poor sanitation and cross-contamination in food processing environments, particularly ready to eat (RTE) foods including dairy products, leafy vegetables, fish and meat. Despite the global increase in reported cases and research on listeriosis, data from Africa remains scarce and this could lead to possible underestimation of the importance of listeriosis on the continent. This paper therefore presents a comprehensive overview of currently available reports on Listeria spp. in Africa with emphasis on molecular characteristics, antimicrobial susceptibility, and prevalence in food, animal and environmental samples. The majority of studies on Listeria spp. in Africa have so far focused on the prevalence and antibiotic susceptibility of L. monocytogenes isolated from RTE foods and raw meat but rarely from humans, animals, and the environment. The overall calculated average prevalence values from the available reports are 23.7 and 22.2% for Listeria spp. and L. monocytogenes, respectively. Listeria spp. isolated from different parts of Africa are generally sensitive to ciprofloxacin, but resistant to penicillin. The majority of these studies employed conventional culture and biochemical tests to characterize Listeria spp. However, the use of modern molecular techniques such as PCR and whole-genome sequencing is on the rise. Most of the studies employing molecular tools were carried out in South Africa and Nigeria, with the predominant strain reported in South Africa being ST6. In order to provide a better understanding of the importance of listeria in Africa, there is the need for extensive and coordinated studies using modern molecular-based techniques to characterize the various Listeria species, and to assess the disease epidemiology using the one health concept

Development and Validation of an RP-HPLC Method for the Quantitative Analysis of Triclosan in Human Urine

Triclosan (TCS), a synthesized chlorinated phenolic compound, is commonly utilized in consumable products as an antimicrobial agent. TCS has sparked widespread awareness because of its toxicity and possible negative effect on public health in recent years. In this study, a highly sensitive, fast, and cost-effective isocratic reversed-phase high-performance liquid chromatography (RP-HPLC) method coupled with solid-phase extraction for analysis of triclosan in human urine samples was developed. The method utilized methanol and water in a ratio of 90 : 10 as the mobile phase on a Phenomenex Luna 3 µm C18(2) 100 Å, 150 × 4.60 mm stationary phase, with a runtime of 5 minutes. The method showed good resolution of triclosan in the presence of the sample matrix. Validation of the method was performed according to the International Council for Harmonization of Technical Requirements for Pharmaceuticals for Human Use (ICH). Linearity was tested over a range of 0.00625 µg/mL to 6.4 µg/mL, as accuracy recorded a recovery of 89.25%, 91.0%, and 92.75%. Limits of detection (LOD) and quantification (LOQ) were obtained to be 0.0173 µg/mL and 0.0525 µg/mL, respectively. The method proved to be robust over a temperature range of 26°C, 30°C, and 35°C and a flow rate of 0.5 ml, 1.0 ml, and 1.5 ml. The developed method was employed to detect and quantify triclosan in 153 urine samples, comprising 60 samples from Ibadan, Nigeria, and 93 samples from Kumasi, Ghana. Triclosan was detected in a total of 52 samples with an average content of 0.054588 µg/ml. This method can therefore be used for the routine analysis of triclosan in urine samples