Mycobacterium palustre

Mycobacterium palustre is a slowly growing mycobacterium first isolated from an environmental source in Finland. It is potentially pathogenic, and has been isolated from human and veterinary clinical specimens. Etymology: palustre; living in swamps, referring to the isolation of most members of this novel species from peatland run-off water.

Description
Microscopy
 * Gram positive, acid-fast bacilli.

Colony characteristics
 * Colonies on Middlebrook 7H10 agar are smooth, yellow scotochromogenic at 36 °C and photochromogenic or scotochromogenic at 42 °C.

Physiology
 * Visible growth from a dilute inoculum requires 2 to 3 weeks.
 * Mature colony size is reached in 4 weeks at 36 °C.
 * Growth occurs at temperatures between 30 and 42 °C, 36 °C being regarded as the optimum temperature.
 * Growth at 45 °C is detected from a heavy inoculum on Middlebrook agar after 5 to 6 weeks.
 * The species yields positive results in urease, pyrazinamidase, acid phosphatase and Tween 80 hydrolysis tests and variable results in nitrate reduction and alkaline phosphatase tests.
 * Test results are negative for semi-quantitative catalase (45 mm foam), a-galactosidase and b-galactosidase.

Differential characteristics
 * Phylogenetic analysis, based on 16S rDNA sequences, places M. palustre among the slowly growing mycobacteria, being most closely related to M. kubicae.
 * An important characteristic of M. palustre is its confusing hybridization with the M. avium complex AccuProbe. However, if two simple conventional tests, urease and Tween 80 hydrolysis, are included in the species verifcation,M. palustre is easily separated even from yellow-pigmented isolates of the M. avium complex, M. xenopi and M. celatum.

Pathogenesis

 * One clinical isolate was regarded as an unquestionable inducer of mycobacterial lymphadenitis in an Italian child.
 * The broad range of growth temperatures of the isolates studied may indicate enhanced ability to colonize warm-blooded animals such as pigs.

Type Strain

 * First isolated from water from a stream in Finland.
 * Strain E846 = ATCC BAA-377 = DSM 44572.