Mycobacterium pinnipedii

Mycobacterium pinnipedii is a member of the Mycobacterium tuberculosis complex which primarily infects seals. It is a slowly growing Mycobacterium.

A comparison of Mycobacterium tuberculosis complex isolates from seals (pinnipeds) in Australia, Argentina, Uruguay, Great Britain and New Zealand was undertaken to determine their relationships to each other and their taxonomic position within the complex.

Isolates from 30 cases of tuberculosis in six species of pinniped and seven related isolates were compared to representative and standard strains of the M. tuberculosis complex. The seal isolates could be distinguished from other members of the M. tuberculosis complex, including the recently defined ‘Mycobacterium canettii’ and ‘Mycobacterium caprae’, on the basis of host preference and phenotypic and genetic tests. Pinnipeds appear to be the natural host for this ‘seal bacillus’, although the organism is also pathogenic in guinea pigs, rabbits, humans, Brazilian tapir (Tapirus terrestris) and, possibly, cattle. Infection caused by the seal bacillus is predominantly associated with granulomatous lesions in the peripheral lymph nodes, lungs, pleura, spleen and peritoneum. Cases of disseminated disease have been found. As with other members of the Mycobacterium tuberculosis complex, aerosols are the most likely route of transmission.

Etymology: pinnipedii, of a pinniped, referring to the host animal from which the organism was first isolated.

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Description

• Acid/alcohol-fast, non-spore-forming, non-motile bacilli

with loose cord formation.

• Growth is generally enhanced by sodium pyruvate and usually occurs within 3–6 weeks of incubation on egg-based media at 36–37C. *Colonies are dysgonic, rough, flat and non-photochromogenic.
• Isolates are negative for nitrate reduction and generally negative for niacin accumulation; some isolates demonstrate low to medium reactions for niacin.

Molecular differentiation

• All isolates share the same 16S rRNA sequence with all members of the Mycobacterium tuberculosis complex.
• All isolates contain the sequences IS6110, IS1081, mpb70 and mtp40, yet fail to produce detectable MPB70 antigen.
• The pncA gene contains CAC (His) at codon 57 and the oxyR gene shows G at nt 285, similar to M. tuberculosis, M. microti and M. africanum.
• The seal isolate spoligotypes form a cluster that is clearly different from those of all other members of the M. tuberculosis complex.
• The isolates are susceptible to isoniazid, rifampicin, streptomycin, ethambutol and paraminosalicylic acid.

Pathogenesis

• Isolates can be recovered from the lung and associated lymph nodes of tuberculous pinnipeds, and occasionally from mesenteric lymph nodes and organs such as the liver.
• Pathogenic in guinea pigs and rabbits; the apparent incidental infection of a human, bovine and tapir indicates that they may have a wide host range.

Type Strain

• The type strain is 6482T (=ATCC BAA-688T= NCTC 13288T)

References

• COUSINS (D.V.), BASTIDA (R.), CATALDI (A.), QUSE (V.), REDROBE (S.), DOW (S.), DUIGNAN (P.), MURRAY (A.), DUPONT (C.), AHMED (N.), COLLINS (D.M.), BUTLER (W.R.), DAWSON (D.), RODRÍGUEZ (D.), LOUREIRO (J.), ROMANO (M.I.), ALITO (A.), ZUMARRAGA (M.) and BERNARDELLI (A.): Tuberculosis in seals caused by a novel member of the Mycobacterium tuberculosis complex: Mycobacterium pinnipedii sp. nov. Int. J. Syst. Evol. Microbiol., 2003, 53, 1305-1314.