Advantages of culture mediums containing small percentages of agar

Abstract

It is true that semisolid mediums have been suggested from time to time. Rosenthal1 and Klie2 experimented with concentrations of gelatin as low as 2.5%. The luxuriant growth obtained probably as a result of diffusion of the inhibiting metabolic products and the extension through the soft jelly of the colonies of motile bacteria caused gelatin to be preferred by many workers and resulted in its being given up with reluctance, in favor of the more convenient agar. Hiss3 and later Hesse4 found that 0^ agar permitted flagellated bacteria to travel through it and suggested this medium as a means for differentiating between the motile typhoid bacillus and the nonmotile colon bacillus. Jackson and Melia5 working with the Hesse medium found that about 0.4%. of dried agar was the equivalent of the 0.5% recommended by those who had not taken into consideration the moisture content of thread agar. North6 found that semisolid mediums were more suitable for preserving stock cultures, doubtless for the reason that unlike solid mediums they did not hold the concentrated products of growth in direct co' ntact with the bacteria. The gelatin-agar medium, attributed by North to Guarnari, contains but 0.3% of agar. Lignieres 7 has more recently made the claim that a semisolid medium containing but 0.25% of agar is superior to broth or solid mediums for the cultivation of anaerobic bacteria. That there are advantages in still lower percentages than have heretofore been employed has been revealed in the work reported in the following. The extreme simplicity of such a procedure has caused me to feel that it could not be new to any one but myself, and I nave sought diligently to find references to previous work along the same line, but so far unsuccessfully.