The Resistance of Dehydrated Pneumococci to Chemicals and Heat

Abstract

Type-I pneumococcus in the form of both virulent and avirulent (S and R) dissociants is susceptible, when grown in broth, to the usual disinfectants, heavy metals, dye stuffs, anhydrous solvents, phenol, and iodine; and to certain more or less specific substances, such as optochin and bile salts. In 2 instances it could be shown (HgCl2, optochin) that the S organism was more readily killed than the R form. When collected by centrifugalization and rapidly dried to constant weight over CaCl2, a large proportion of the cells are killed, surviving % depending on technique employed. Surviving pneumococci may continue to decrease in number, but some, at all events, survive for as yet undetermined periods[long dash]18 mos. at least. Desiccated but living pneumococci of forms R and S are not killed in absence of water, by alcoholic solutions of the substances described, except in the case of heavy metals (Ag salts, AgNO3). Dried S pneumococci, contrary to the findings in moist cultures, are more resistant to HgCl2 than R forms. The thermal death point of moist R pneumococci (56[degree]) is distinctly higher than that of moist S pneumococci. When the 2 dissociants are dried, they both resist heating to 115[degree] for 30 min. but are killed by 120[degree] and above.