Thermal Death Point: I. Spores of Clostridium Tetani

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Abstract
Effective temp. for destruction of spores in physiologic saline are 105[degree], 100[degree] and 95[degree] C. At 105[degree], the time was 5-10 min.; at 100[degree], 10-25 min.; at 95[degree], 25-60 min. At 95[degree], 3 strains resisted the 60-min. heating. Effective temp. for dry spores heated in absence of moisture, with the 6 strains studied, were 140[degree], 135[degree], 130[degree], and 125[degree]. At 140[degree], the time was 5-15 min.; at 135[degree], 5-25 min.; at 125[degree], 20-40 min. Dried spores heated under moist conditions showed no increased resistance, the effective temp. being 105[degree], 100[degree], and 95[degree]. In many of the strains, drying decreased thermal resistance. Drying the spores on sand decreased the number viable, and also tended to decrease their resistance when heated under moist conditions. Spores suspended in Clark and Lubs'' buffer solutions showed best resistance at pH 7. Above and below this point there was a graded falling off in thermal death time. Acid reactions were more toxic than alkaline. Spores suspended in 1% peptone solution of graded CH showed best resistance at approximately pH 7. Increasing amounts of organic matter (peptone) tended to increase the thermal death time when the suspending solution was at pH 7; at pH 10 and 5, the effect did not occur. Spores suspended in a solution of NaCl showed greatest resistance to heat at a salt concentration of 2%. 2 factors were involved in killing the spores: (1) temp.; and (2) temp. plus the variants studied. In some instances a given temp. was sufficiently high to be effective irrespective of the vari-able, and no effect of the variable was seen at this temp. in the time interval during which it was studied. At a lower temp. the effects of the variable factor were demonstrated.

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