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The occurrence of Metabacterium polyspora in guinea pig feces and a microscopic study of its endospores
Fecal material from 39 guinea pigs was collected and microscopically surveyed for the presence of Metabacterium polyspora, a large, Gram-positive bacterium uniquely forming many endospores. It was found in the feces of 9 of 11 adult female guinea pigs, 5 of 14 adult males, and 3 of 14 infants. The abundance was high in pregnant sows near the time of delivery. The persistence in newborn infants depended on continued contact with feces containing Metabacterium. Mechanical enrichments of M. polyspora were prepared from fecal suspensions by filtration to remove coarse plant debris followed by centrifugation to eliminate smaller bacteria. M. polyspora sporangia measured from 10 - 25 pm in length by 5 pm in width and enveloped 2 - 8 endospores. Individual endospores measured 8 pm by 2 Jlm. Scanning electron micrographs of sporangia displayed a relatively smooth cell surface. In some cases the outer envelope was folded and snugly contoured the endospores. Subpolar appendages were commonly present at one end of the sporangia; they measured about 60 nm in width and up to 720 nm in length. The spores were brightly refractile in phasecontrast illumination and retained Wirtz-Conklin's spore stain. They could not be resolved in Sacks and Alderton's aqueous polymer two-phase system. Germination depended on nutrients, was activated by ethanol, and was decreased by heating at 80°C for 30 minutes. M. polyspora failed to grow on a variety of media under aerobic and anaerobic conditions. The common occurrence of M. polyspora within the indigenous microflora of guinea pigs and current knowledge justifies that Metabacterium Chatton and Perard 1913 be described and be placed as a genus of uncertain affiliation with the endospore-forming rods and cocci in future editions of Bergey's Manual of Determinative Bacteriology.