Distribution of Legionella longbeachae and other legionellae in Japanese potting soils

Abstract

The distribution of Legionella longbeachae and Legionella spp. in Japanese potting soils was examined. Thirty samples were collected: 13 were composted wood products, 11 were potting mixes (containing composted wood products, sand, mineral fertilizer, and manure), 2 were peatmoss, 3 were peatmoss-sand mixes (containing peatmoss and sand), and 1 was a sample of hydroponic clay balls. A suspension of each sample was made in sterile distilled water and acidified, and 100 microl was plated on buffered charcoal yeast extract alpha (BCYEalpha) agar containing modified wadowsky yee (MWY) supplement and pimaricin (direct method). In parallel, each suspension was incubated at 33 degrees C for several months to allow for amebic enrichment, if present; the suspensions were then plated onto culture media as described above (enrichment method). A total of 46 strains of legionellae were isolated from 22 of the 24 samples (13 composted wood products, 11 potting mixes). L. longbeachae was isolated from 9 samples. The most predominant species of legionellae in potting soils was Legionella bozemanii, which was isolated from 13 samples. Legionella spp. and L. micdadei were isolated from 8 and 7 samples each. Compared with findings in potting soils in Australia (26/45; 58%), Japanese potting soils had an only 8.3% (2/24) isolation rate for L. longbeachae by the direct method. The components of composted wood products were broadleaves such as oak and Japanese oak, in contrast to the pine and eucalypt used in Australia, which may account for the different isolation rates. However, the amebic enrichment method was useful in increasing the recovery of legionellae in potting soils. Legionellae were not isolated from the peatmoss samples, a result identical to findings in surveys of similar material in Europe.