Interaction of Aspergillus flavus and A. parasiticus with Salmonella spp. isolated from peanuts

Abstract

Although Aspergillus flavus and Aspergillus parasiticusare the main microorganisms of concern in peanuts, due toaflatoxin contamination, severalSalmonellaoutbreaks from this product have been reported over the last tendecades. Thus, it is important to understand the relationship between microorganisms to predict, manage andestimate the diversity in the peanut supply chain. The purpose of this study was to evaluate aflatoxin productionduring the co-cultivation ofAspergillussectionFlaviandSalmonellaboth isolated from peanuts. Three strains ofA.sectionFlavi:A.flavusproducing aflatoxin B,A.flavusnon-producing aflatoxin andA. parasiticusproducingaflatoxin B and G were co-cultivated with seven serotypes ofSalmonellaof which six were isolated from thepeanut supply chain (S. Muenster, S. Miami, S. Glostrup, S. Javiana, S. Oranienburg and S. Yoruba) and one wasS. Typhimurium ATCC 14028. First of all, eachSalmonellastrain was inoculated by pour plate (ca. 5 log cfu/mL)in PDA (potato dextrose agar). Then, each pre-cultured fungus was inoculated in the center of the petri dish. Theplates were incubated at 30 °C and the fungal colony diameter was measured once a day for 7 days. As a controleachAspergillusstrain was cultivated in the absence ofSalmonellaculture. All three strains ofAspergilluswithabsence ofSalmonella(control) reached the maximum colony diameter and their growth rate was influencedwhen co-cultivated (p< 0.05) with allSalmonellaserotypes tested. The maximum inhibition in the colonydiameter was 20% forA.flavusaflatoxin B producer andA. parasiticus, and 18% forA.flavusnon- aflatoxinproducer when cultivated withSalmonella. However, no significant difference (p< 0.05) in reduction of colonydiameter was observed among theSalmonellaserotypes. Aflatoxin production was determined previously, byusing the agar plug technique on thin layer chromatography (TLC). The production of aflatoxin G byA. para-siticusin co-cultivation withSalmonellawasnot observed. On the other hand,A.flavuspreserved their char-acteristics of aflatoxin B production. The quantification of aflatoxin reduction bySalmonellainteraction wasevaluated using HPLC method. There was a maximum reduction of aflatoxin production of 88.7% and 72.9% inA.flavusandA. parasiticus,respectively,when cultivated withSalmonella. These results indicate that someserotypes ofSalmonellamay interfere with aflatoxin production and fungal growth ofA.flavusandA. parasiticusin the peanut supply chain.