Effects Of Ecophysiological Factors And Their Interactions On Growth of Aspergillus fumigatus Strains Isolated From Animal Feeds

GABRIELA A. PENA; MARÍA F. LANDA; MARÍA D.P. MONGE; CARLOS A.R. ROSA; STELLA M. CHIACCHIERA; LILIA R. CAVAGLIERI

Mendoza

Congreso; International Society of Mycotoxicology; 2011

Aspergillus fumigatus, the most common cause of invasive aspergillosis in immunocompromised individuals, is a common fungus found in contaminated animal feed. This fungus is able to produce tremorgenic mycotoxins and to induce neurological syndromes in farm workers who have manipulated mouldy feed. One of the most abundantly metabolites produced by A. fumigatus is gliotoxin, a toxin with potent immunosuppressive, genotoxic, cytotoxic and apoptotic effects. The aim of this study was to evaluate the effects of water activity (aW), pH, temperature and oxygen tension and their interactions on (i) the lag phase prior to growth and (ii) growth rate of A. fumigatus strains. In this experiment two A. fumigatus strains gliotoxin producers were used, Af16 strain (reference number: RC2063) isolated from corn silage for dairy cattle and A89 strain (reference number: RC2108) isolated from brewer¡¯s grain destined for swine feed in Argentina. Brewer¡¯s grain extract agar (BGEA) was prepared at 3%. The aW of the basic medium was adjusted to 0.995, 0.98 and 0.93 with glycerol, the medium was autoclaved at 120 ¨¬C for 20 min. After that, the pH level of medium was adjusted to 5, 7 and 9 with addition of variable volumes of HCl or NaOH concentrate solutions. The plates were centrally needle-inoculated and incubated for 14 days at 18 and 25¡ÆC in normal oxygen tension, and 37¡ÆC under normal and reduced oxygen tension (5% C02, 0.4% O2). All treatments were repeated three times. Radial growth rates (mm/hours) were calculated as the slope of the linear regression obtained from plotting the colony radius of the replicates against time. The lag phase was obtained by extrapolation of this line to the x axis. It was observable when oxygen tension was normal, that at 37¡ÆC and 0.98 aW for all pH levels, there were the shortest lag phases (5.25 to 7.57 hours for A89 strain and 9.50 to 13.35 hours for Af16 strain) without statistics differences between strains (p¡Â 0.05). However, at 18¡ÆC, 0.93 aW and pH 5, 7 and 9, both strains showed the most extended lag phases (>336 hours). In other hand, the growth rate of the two strains decreased significantly as temperature and aW decreased (p¡Â 0.05). The optimum conditions for A. fumigatus growth were 37¡ÆC, 0.98 aW and pH 7 for A89 and Af16 strains while 18¡ÆC and 0.93 aW for all pH, completely inhibited growth of both strains (p¡Â 0.05). At low oxygen condition, lag phases were longer than in normal condition at 37¡ÆC and 0.98 aW for both strains; whereas the average growth rate was higher (p¡Â 0.05). The gliotoxin production showed a similar behaviour of growth rate. These results suggest that this fungus is able to growth under several incubation conditions, some of them prevalent in stored animal feeds. This fact represents a high risk of contamination to animals and farm workers handling improperly the stored animal feed.