Cultivation and visualization of mycobacteria on molecular filter membranes.

The molecular filter membrane (MF) was developed for the recovery of small numbers of bacterial contminants in water and air (Goets, 1953a,b; McKee et al., 1953). A number of pathogenic bacteria, including the tubercle bacillus, were grown on these filters by Orlando and Bolduan (1953). These membranes are worthy of further study in the cultivation of mycobacteria. The possible advantages of the membrane should include recovery of every tubercle bacillus in a large volume of liquid such as urine or spinal fluid, accelerated detection of growth, and the feasibility of washing residual antibiotics out of clinical inocula without loss of bacilli. The filters could be used also for morphological and biochemical studies of intact colonies. Orlando and Bolduan (1953, personal communication) grew Mycobacterium tuberculosis on the filters over Lowenstein-Jensen egg medium, and we have repeated their work and extended it to include subcultures of a number of other mycobacterial species and strains. In this paper we shall stress visualization of growth with special reference to the use of a neutral red stain and its significance in the characterization of growth as well as to oblique lighting for early detection of colonies.