Gram Structure of Cocci.

Abstract

It has been shown 1 that when B. anthracis is exposed, in aqueous suspension, to certain dyes (Gentian Violet, Acriviolet, etc.) its Gram reaction is reversed; and that this reversal is accompanied by diminution in size and loss of weight of the bacterial bodies, together with increase in weight of the supernatant fluid. The existence of an outer Gram-positive cortex and inner Gram-negative medulla seemed thus to be proven. Gram-positive cocci could not be similarly changed by exposure to these dyes and it was, therefore, assumed that the Gram reaction of cocci might rest on a different mechanism from that of B. anthracis.

Experimental study running over the last 18 months, has shown, however, that exactly the same result as that produced in B. anthracis by exposure to certain dyes, may be produced in certain of the cocci by exposure to a temperature of 52° Centigrade for a period of 10 hours or so. (Figs. 1 and 2.) Aqueous suspensions of many strains of Staphylococcus aureus when treated in this way become entirely Gram-negative. They also diminish in size, but the organisms are too small to measure accurately with a filar micrometer so that the amount of loss in diameter cannot be exactly stated. When centrifugated in Hopkins tubes, the organisms which have been exposed to 52° occupy less than half the space taken by the controls. They also lose about 50% in weight. This loss in weight is accompanied by a corresponding, though not an exactly identical, increase in the weight of the supernatant fluid.

The reaction does not occur in all strains of cocci. For example, the Gram reaction of M. freudenreichii is entirely unaffected by exposure to 52° C. On the other hand, the Staphylococcus aureus with which most of the experiments here reported were done—a virulent and typical organism isolated from a human being—behaved with great constancy in this respect after certain of the puzzling factors of inconstancy met with in the early experiments had been determined and taken into account.