EFFECTS OF ABIOTIC FACTORS AND INTERACTION WITH Listeria monocytogenes ON THE GROWTH PARAMETERS OF Aspergillus flavus AF54

ASURMENDI, PAULA; PASCUAL, LILIANA; BARBERIS, LUCILA

Estancia Grande, San Luis

Otro; XXXII Reunión científica anual de la Sociedad de Biología de Cuyo; 2014

Sociedad de Biología de Cuyo

In the storage ecosystem of brewer's grains, microorganisms such as aflatoxigenicA. flavus and L. monocytogeneswere isolated. The interaction between them and with respect to environmental factors is important to theprediction of contamination risk of this food with these undesirable microorganisms. Furthermore, biotic factorssuch as the presence in the same habitat of different microorganisms can develop ecological interactions betweenthem that are positive, negative or indifferent for fungal growth. The aim of the present work was evaluate theeffect of L. monocytogenes in interaction with aW, pH and temperature on the lag phase, and growth rate of A.flavus. The strains A. flavus AF54, L. monocytogenes LM1 and L. monocytogenes LM6 were assayed at thisstudy. The basic medium used was brewer's grains meal medium, previously adjusted to different aW (0.95, 0.98and 0.995) and pH (5, 7 and 9). Through the pour plate method, 100 uL of L. monocytogenes suspension (108c.f.u. mL-1) was added. Then, plates were inoculated in the center with the fungal strain and incubated for 21 daysat 25 °C. The diameter of the colony was measured and growth parameters were calculated. In general, the presence of L. monocytogenes exhibited increased on lag phase and decreased on growth rate of AF54. The lowest aW (0.95) assayed showed the largest lag phase and lowest growth rate. The pH was less influential than aW infungal growth parameters. The highest time of lag phase was observed at 0.95aW, pH 9 and co-inoculated with LM1 (53 h) or with LM6 (52 h) and the lowest growth rate of AF54 was 8.2 mm day-1, at 0.95aW, pH 5 and coinoculated with LM1. In conclusion, the presence of L. monocytogenes and osmotic stress generally increased fungal lag phase and decreased fungal growth.