The genus Brevibacterium (phylum, Actinobac-teria) are described as non-motile, non-sporing, non-acid-fast, irregular-shaped organisms that belong to the "coryneform" group. Like other coryneform bacteria, Brevibacterium sp. are Gram positive rods, but both their staining pattern and shape can vary, depending on the age and condition of the cells. They also are high G+C organisms (60 to 67 mol%). Brevibac-terium are strictly aerobic, catalase-positive mesophiles, with an optimum growth temperatures between 20°C and 35°C. Most species are salt-tolerant (>10%) and able to grow over a wide pH range.There are currently eighteen recognized species; the phylogeny of twelve representative species is shown in Figure 2-8.

Several are of medical importance and have been considered as opportunistic pathogens. One species, Brevibacterium linens, is important in fermented foods, mainly because it is involved in the manufacture of bacterial, surface-ripened cheeses, such as Limburger and Muenster. In these products, B. linens produces a yellow-orange-red pigment on the cheese surface that gives these cheeses their characteristic appearance. Their ability to hydrolyze pro teins and metabolize amino acids, especially the sulfur-containing amino acids, also contributes to cheese ripening and flavor development in a variety of cheeses.

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