Neutrophils are key players in immune reactions and their migration into infected tissue is pivotal to confining a pathogen to a local site. They have enormous potentials to eventually kill engulfed microbes. Aflatoxin B1 (AFB1) is thought to be a potent immunotoxic. To investigate the effect of AFB1 on blood neutrophils bactericidal activity, the in vitro effect of the AFB1 on killing capacity of neutrophil against two worldwide superbugs in animals, Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli), was investigated. Healthy dairy cows (n=8) were used as a source of neutrophils. The isolated blood neutrophils were exposed with and without 0.5 ng/ml of AFB1 for 3 hours; their capacity to kill E. coli and S. aureus was then monitored by a bactericidal assay using sample cultivation, accordingly. Briefly, 100 l live bacteria (5107 / ml) were added to 500 l viable neutrophils (5106 / ml), or to 500 l of normal saline containing no neutrophils, incubated for 1 hour, and finally serially diluted. After dilution and plating out, they were mixed with a sterile loop in duplicate onto Columbia sheep blood agar (Biokar Diagnostic, Beauvois, France). The plates were incubated overnight at 37°C and colony counts were performed. Results from the bactericidal assay are expressed and compared as the percentage of killed E. coli and/or S. aureus (% killing). The % killing of E. coli and S. aureus by AFB1-treated neutrophils was significantly lower than those of non-treated ones. The killing activity of neutrophils against E. coli in AFB1-treated and non-treated groups was 48.7  3.6% and 69.5  3.9 %, and against S. aureus was 19.3 ± 2.5 % and 33.4 ± 3.7 %, respectively. The higher growth of E. coli and S. aureus in AFB1-treated neutrophils confirm the fact that the AFB1 is immunotoxic in dairy cows. Further studies are in progress in our laboratories to explain the mechanism of this immunotoxicity.

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