The name has been applied to certain Gram-negative facultatively anaerobic organisms that are oxidase-positive, catalase-negative, indole-negative, nitrate-reducing, lysine decarboxylase-positive, non-fermentative, urease-negative, gelatinase-negative, casein hydrolysis-negative, and non-motile. During 2 yr, we have encountered no strict anaerobes with similar characteristics, but anaerobic biotypes may exist. The facultative strains require haemin for aerobic growth from small inocula, and may appear to be anaerobic if the haemin concentration in the medium is less than 5 μg per ml. Variants not requiring haemin occur. Growth is favoured by 0·005 per cent, cystine. The organisms are antigenically related, but strains may vary in the proportions of their different antigens. The G+C content is 57–58 per cent.

Four anaerobic organisms, tolerant of up to 1 per cent, oxygen and having certain superficial similarities to the facultative strains, were investigated. The organisms were oxidase-positive (with tetramethy1--phenylenediamine), catalase-negative, non-fermentative, urease-positive, gelatinase-positive (Frazier method), and able to hydrolyse casein. The G+C content was 28·0–29·7 per cent. In electron micrographs, the spreading strains showed multiple polar processes, but no flagella.

Agar-pitting (corroding) colonies are a striking feature of the facultative and the anaerobic organisms, but both may give non-pitting variants. The taxonomic status of the anaerobes requires further investigation.

The name has probably been applied by different workers to organisms that are genotypically widely dissimilar.


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