Mycobacterium shottsii

Mycobacterium shottsii is a slowly growing, non-pigmented mycobacteria isolated from striped bass (Morone saxatilis) during an epizootic of mycobacteriosis in the Chesapeake Bay. Growth characteristics, acid-fastness and results of 16S rRNA gene sequencing were consistent with those of the genus Mycobacterium. A unique profile of biochemical reactions was observed among the 21 isolates. A single cluster of eight peaks identified by analysis of mycolic acids (HPLC) resembled those of reference patterns but differed in peak elution times from profiles of reference species of the Mycobacterium tuberculosis complex. Etymology: shottsii; of Shotts, named after Emmett Shotts, an American fish bacteriologist.

Description
Microscopy
 * Gram positive, acid-fast coccobacilli that may form cell aggregates in culture. Spores and cell branching are not present.

Colony characteristics
 * Colonies on Middlebrook 7H10 agar are dysgonic, rough, non-pigmented and typically flat with an irregular margin, becoming umbonate upon ageing.
 * Smooth colonies with an entire margin are seen less frequently.

Physiology
 * Visible colonies from a dilute inoculum are observed after 4–6 weeks incubation at 23°C.
 * Little or no growth occurs at 30°C and none at 37°C or above.
 * Isolates do not grow on MacConkey agar or with 5% NaCl, are negative for arylsulfatase (14 days), b-galactosidase, nitrate reductase, pyrazinamidase (7 days), semiquantitative catalase, Tween 80 hydrolysis and Tween opacity and have variable reactions for acid phosphatase and catalase at 68°C.
 * The type strain is resistant to p-aminosalicylic acid and isoniazid but susceptible to ethambutol, ethionamide, kanamycin, rifampicin and streptomycin in disc susceptibility tests.

Differential characteristics
 * The 16S rRNA gene sequence is unique among species of Mycobacterium and is most similar to those of Mycobacterium ulcerans and Mycobacterium marinum.
 * Isolate M175T could be differentiated from other slowly growing, non-pigmented mycobacteria by its inability to grow at 37 °C, production of niacin and urease, absence of nitrate reductase and resistance to isoniazid, thiacetazone and thiophene-2-carboxylic hydrazide.

Pathogenesis

 * Pathogenic to the striped bass (Morone saxatilis).

Type Strain

 * First isolated from granulomatous lesions in splenic tissue from a striped bass (Morone saxatilis).
 * Strain M175 = ATCC 700981 = JCM 12657 = NCTC 13215