TABLE 5.

Toxicity to boar spermatozoa of methanol extracts prepared from boiled rice inoculated with different Bacillus strains 4 days earlier

Inoculum	EC50 of methanol extracts of inoculum culture (μg ml−1)a	Concn of various parameters equivalent to EC50b
		B. cereus contamination (CFU ml of rice−1)c	Methanol extracts from inoculated rice (μg of dry solids ml−1)c	Contaminated riced
B. cereus F-5881	0.072	106–107	38	7.5 (3)
B. cereus 4810/72	0.026	106–107	30	7.5 (3)
B. mycoides ATCC 6462T	>68	>108–109	>650	>150 (60)
B. cereus ATCC 14579T	17	>108–109	>523	>150 (60)

^aBacteria were cultivated on tryptic soy agar for 10 days at 28°C, and 500 mg (wet weight) of cells was extracted with methanol. The evaporation residue of the methanol extract was dissolved in DMSO. Extended boar semen was exposed to serial dilutions (in DMSO) of the extract, and sperm motility was measured after 1 and 2 days of exposure. 

^bEC₅₀, endpoint dilution of methanol-extracted solids (dry weight) per milliliter of extended boar semen causing >50% decrease in sperm motility. The average difference between assays of duplicate samples was 20% with semen of different boars. 

^cAliquots of boiled rice (60 g; two parallel experiments) were inoculated with the Bacillus strains (10⁵ to 10⁶ CFU g⁻¹). After 4 days at room temperature, the rice was extracted with 1 volume of methanol. The evaporated residue of the methanol extract was serially diluted in DMSO, and the motility of boar spermatozoa was measured after 1 and 2 days of exposure. A blank assay was performed with diluent (DMSO) only. 

^dValues are in milliliters; values in parentheses are equivalent amounts, in grams.