The mechanism of serum fastness

Abstract

Soon after the discovery of the agglutinins it was observed that some strains of a given microorganism were not agglutinated by a specific immune serum. Such non-agglutinable strains are said to be serum fast. The mechanism of serum fastness is not well understood. Ehrlich's explanation of this phenomenon on the basis of suppressed receptors does enable us to visualize the condition, but a suppression of receptors is probably far from what actually takes place.

In our studies 1 on pellicle formation it has been shown that pellicle forming bacteria are rich in acetone-ether soluble substances. Bacteria which ordinarily do not grow in pellicle were caused to do so by growing them in broth to which had been added glycerine or carbohydrates which they did not ferment. By growing the staphylococcus on glycerine broth for a few generations it began to grow in a pellicle, and finally formed as definite a pellicle as the tubercle bacillus, or other pellicle forming organisms.

The acetone-ether soluble substances of staphylococci grown in this way increased from 7.9 per cent. to 39.9 per cent.

It was concluded that pellicle formation was due to the increased amounts of acetone-ether soluble substances by virtue of which the bacteria resist wetting, and are thus supported on the surface of the medium by surface tension.

The present study concerns the effect of wetting on the agglutination reaction.

A laboratory strain of the staphylococcus aureus was grown in parallel cultures on ordinary broth and three per cent. glycerin broth respectively. Rabblits were immunized with killed cultures of the staphylococcus grown on ordinary broth. In the interest of brevity the strain grown in ordinary broth will be referred to as the “lean” strain and that grown in glycerine broth as the “fat” strain.