Chitosan molecular weights affect anthracnose incidence and elicitation of defence-related enzymes in avocado (Persea americana) cultivar 'Fuerte'.

Anthracnose decay is one of the major causes of postharvest losses of avocados (Persea americana), during marketing. Currently, Prochloraz® fungicide is used to control anthracnose at postharvest stage which poses threat to consumer safety. Therefore, this study evaluated the effects of high and low molecular weight chitosan on the control of avocado anthracnose and fruit defence mechanism. In curative inoculation, avocados '(Fuerte') were inoculated via the wounds with C. gloeosporioides spore suspension (20 µL, 1 × 106 spores mL-1). Thereafter coated with different concentrations (0.5%, 1% and 1.5%) of low (LMWC) and high molecular weight (HMWC) chitosan and fruits were held at 25 °C for 5 days. The % anthracnose incidence in avocado fruits was recorded on day 5. During preventative inoculation, wounded fruits were dipped in different concentrations of LMWC or HMWC solutions, and subsequently inoculated with C. gloeosporioides suspension. Preventatively inoculated fruits were stored for 28 days at 6.5 °C, 85% RH and thereafter for 5 days at 25 °C and 75% RH to simulated market shelf condition. The % anthracnose incidence was recorded on day 5. Fruit treated with Prochloraz® and water were included as controls for both curative and preventative infected fruits. Promising chitosan coatings with the lowest anthracnose incidence and the controls were investigated for skin epicatechin content, defence-related genes; phenylalanine ammonia lyase (PAL), lipoxygenase (LOX), fatty acid elongase (avael) and desaturase (avfad 12-3), chalcone synthase (CHS) and flavonol synthase (FLS) using RT- qPCR method. The zeta potential of selected chitosan coatings was done following standard procedures. Percentage of anthracnose incidence were lowest in 1.5% LMWC (18%, 3 mm) compared to Prochloraz® (23%, 5 mm) and the untreated fruit (90%, 24 mm). The 1.5% LMWC had the highest up-regulation of PAL, avfael, avfad 12-3, CHS, FLS genes and down-regulation of LOX gene with concomitant increase in epicatechin content (340 mg kg-1) relative to other chitosan treatments, untreated and Prochloraz® treated fruits. The superior positive zeta potential of LMWC 1.5% coating corroborates its effectiveness in controlling avocado anthracnose than HMWC 1.5%. It is possible that the interaction between the positively charged chitosan amino group (-NH3+) and the negatively charged microbial cell membrane is responsible for the enhanced antifungal activity. In late season naturally infected fruits dipped in 1.5% LMWC, anthracnose incidence dropped to 28% while Prochloraz® treated fruits showed anthracnose incidence of 82% on day 8 at the market shelf. LMWC 1.5% can replace the currently used Prochloraz®.

Behaviour of Aspergillus parasiticus in aflatoxin production as influenced by storage parameters using response surface methodology approach.

Aspergillus parasiticus is a pre-harvest and postharvest pathogen that is known to produce aflatoxin; however, it is less studied compared to A. flavus. Inappropriate storage conditions are a cause of food spoilage and growth of mycotoxigenic fungi especially in low moisture foods thus constituting hazards to health. Hence, this study investigated the behaviour of A. parasiticus on aflatoxin production in inoculated wheat flour as influenced by storage conditions using the response surface methodology. Twenty experimental runs consisting of independent variables (incubation temperature (A), time (B) and (C) moisture content) and responses (aflatoxin concentrations, i.e., AFB1, AFB2, AFG1, AFG2 and AFTOT) were developed. A central composite face-centered design was used with lower and upper limits: A (25-35 °C), B (7-15 days) and C (15-25%), while the non-inoculated wheat flour served as the negative control. Aflatoxin production was determined using High Performance Liquid Chromatography (HPLC) according to standard procedures. Numerical and graphical process variables were optimized, adequate models were predicted and optimal point prediction for aflatoxin concentration was determined. AFG1 concentrations ranged from 1.10 to 360.06 µg/g, AFG2 (0.91-446.94 µg/g), AFB2 (7.95-488.77 µg/g), AFB1 (17.21-20,666.6 µg/g) and AFTOT (15.91-21,851.09 µg/g). Aflatoxin concentration increased with increase in 'B' and 'A' but decreased with prolonged increase in 'B'. AFB1 concentrations in A. parasiticus inoculated wheat flour increased at prolonged 'B' and 'A' at constant moisture (12.09%). A reduced cubic model was significantly adequate to describe the relationship between process variables and responses (AFG1 and AFG2), cubic model (AFB1 and AFTOT) and a transformed square root cubic model for AFG2 concentrations (p ≤ 0.05). 'A' influenced AFG1 production more than 'C' while 'C' and 'A' had no significant effect on AFG2 production. Process variables 'AB' influenced AFB2 concentrations more than 'C' while 'A' had a more significant effect on the AFTOT production than 'B' (p ≤ 0.05). The predicted (R2) and adjusted coefficient of regression (adj R2) were in reasonable agreement. After optimal point prediction and validation, minimum aflatoxin concentration ≤ 0 µg/g could be achieved at the predicted conditions (A = 30.42 °C, B = 10.58 days and C = 14.49%) except in AFG2 (3.33 µg/g).

Genome Sequence of Campylobacter fetus subsp. venerealis NW_ED23, Isolated from Bovine Sheath Wash.

Campylobacter fetus subsp. venerealis is the causative agent of bovine genital campylobacteriosis, which is mostly characterized by reproduction problems. The strain reported in this study was isolated from bull sheath wash in South Africa.

Biofilm Production Potential of Salmonella Serovars Isolated from Chickens in North West Province, South Africa.

Bacterial biofilms have recently gained considerable interest in the food production and medical industries due to their ability to resist destruction by disinfectants and other antimicrobials. Biofilms are extracellular polymer matrices that may enhance the survival of pathogens even when exposed to environmental stress. The effect of incubation temperatures (25°C, 37°C, and 40°C) and Salmonella serotype on biofilm-forming potentials was evaluated. Previously typed Salmonella serotypes (55) isolated from the gut of chickens were accessed for biofilms formation using a standard assay. Salmonella Typhimurium ATCC 14028TM and Salmonella Enteritidis ATCC 13076TM (positive controls), Escherichia coli (internal control) and un-inoculated Luria Bertani (LB) broth (negative control) were used. The isolates formed no biofilm (11.86-13.56%), weak (11.86-45.76%), moderate (18.64-20.34%), strong biofilms (23.73-54.24%) across the various temperatures investigated. Serotypes, Salmonella Heidelberg and Salmonella Weltevreden were the strongest biofilm formers at temperatures (25°C, 37°C, and 40°C, respectively). The potential of a large proportion (80%) of Salmonella serotypes to form biofilms increased with increasing incubation temperatures but decreased at 40°C. Findings indicate that average temperature favours biofilm formation by Salmonella serotypes. However, the influence of incubation temperature on biofilm formation was greater when compared to serotype. A positive correlation exists between Salmonella biofilm formed at 25°C, 37°C and 40°C (p ≥ 0.01). The ability of Salmonella species to form biofilms at 25°C and 37°C suggests that these serotypes may present severe challenges to food-processing and hospital facilities.

Occurrence, Genetic Diversities And Antibiotic Resistance Profiles Of Salmonella Serovars Isolated From Chickens.

PURPOSE: Contamination with Salmonella on food products and poultry in particular has been linked to foodborne infections and/or death in humans. This study investigated the occurrence, genetic diversities and antibiotic resistance profiles of Salmonella strains isolated from chickens. PATIENTS AND METHODS: Twenty each duplicate faecal swab samples were collected from five different poultry pens of broilers, layers and indigenous chickens in the North-West Province, South Africa. Isolates identities were confirmed through amplification and sequence analysis of 16S rRNA and the invA gene fragments after which phylogenetic tree was constructed. Salmonella enteritidis (ATCC:13076TM), Salmonella Typhimurium (ATCC:14028TM) and E. coli (ATCC:259622TM) were used as positive and negative controls, respectively. The serotypes of Salmonella isolates were determined. Antibiotic-resistant profiles of the isolates against eleven antimicrobial agents were determined. RESULTS: Eighty-four (84%) of representative isolates possessed the invA genes. The percent occurrence and diversity of Salmonella subspecies in chickens were 1.81-30.9% and was highest in Salmonella enterica subsp. enterica. Notably, the following serotypes Salmonella bongori (10.09%), Salmonella Pullorum (1.81%), Salmonella Typhimurium (12.72%), Salmonella Weltevreden, Salmonella Chingola, Salmonella Houten and Salmonella Bareily (1.81%). Isolates (96.6%) displayed multidrug resistance profiles and the identification of isolates with more than nine antibiotic resistance was a cause for concern. CONCLUSION: This study indicates that isolates had pre-exposure histories to the antibiotics tested and may pose severe threats to food security and public health.

Polyphasic Assessment of Aflatoxin Production Potential in Selected Aspergilli.

This study investigated the aflatoxin production potentials of selected fungi using a polyphasic approach. Internally transcribed spacer region of the fungi was amplified using the polymerase chain reaction. Forty-five Aspergillus strains were further assessed for aflatoxin production using the conventional methods such as growth on yeast extract sucrose, ß-cyclodextrin neutral red desiccated coconut agar (ß-CNRDCA); expression of the aflatoxin regulatory genes and the use of both thin-layer chromatography (TLC) and high-performance liquid chromatography (HPLC). A large proportion (82.22%) of the isolates harbored the Nor-1 gene while 55.56%, 68.89%, and 80% possessed the ver-1, omt-A, and aflR genes, respectively. All 100% the isolates harbored the aflJ gene. Twenty-three isolates were positive for aflatoxin production based on the yeast extract sucrose medium (YES) test; ammonium vapor test (51%), yellow pigment production (75.5%), and ß-CNRDCA tests; and blue/green fluorescence (57.7%). Based on TLC detection 42.2% produced aflatoxins while in the HPLC, total aflatoxin (AFTOT) production concentrations ranged from 6.77-71,453 µg/g. Detectable aflatoxin B1 (AFB1) concentrations obtained from the HPLC ranged between 3.76 and 70,288 µg/g; 6.77 and 242.50 µg/g for aflatoxin B2 (AFB2); 1.87 and 745.30 µg/g for aflatoxin G1 (AFG1); and 1.67 and 768.52 µg/g for aflatoxin G2 (AFG2). AFTOT contamination levels were higher than European Union tolerable limits (4 µg/kg). The regression coefficient was one (R2 = 1) while significant differences exist in the aflatoxin concentrations of Aspergillus (p ≤ 0.05). This study reports the potentials of Aspergillus oryzae previously known as a non-aflatoxin producer to produce AFG1, AFG2, AFB1, and AFB2 toxins. Aspergillus species in feedlots of animals reared for food are capable of producing aflatoxins which could pose hazards to health.