A histidine-containing agar medium has been devised for quantitative detection of histamine-producing bacteria that are alleged to be associated with scombroid fish poisoning outbreaks. The responsible bacteria produce a marked pH change in the agar, with attendant color change of pH indicator adjacent to the colonies, thus facilitating their recognition. Proteus morganii and Klebsiella pneumoniae were the two most common histidine-decarboxylating species isolated from scombroid fish and mahi mahi.

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Cured meat products are subject to a type of bacterial spoilage in which the cured meat pigment is oxidized to a greenish or faded color. The microorganisms responsible for this effect appear to be a fairly restricted group of catalasenegative, salt-tolerant microorganisms that are capable of growing at low temperatures, and are able to oxidize certain substrates in the meat product with the accumulation of hydrogen peroxide. The most common organism isolated in this laboratory that is associated with this type of spoilage has been a heterofermentative Lactobacillum described by Niven, Castelani, and Alanson (1949). On the basis of detailed physiological and serological studies, this organism appeared to be a hitherto undescribed species. The cultures were reported to grow rather poorly in a wide variety of laboratory media. In view of the economic importance of this organism and its apparently unusual nutritive requirements, an investigation of its nutrition has been undertaken.

Sodium nitrite is known to be responsible for the production of the desirable heat-stable pink color in cured meats. It has also been used as an inhibitor of