Growth in Acanthamoeba sp. and antibiotic susceptibility of Legionella micdadei isolated from hot spring water samples.

As part of an epidemiological study on legionellosis, we attempted to isolate Legionella spp. from hot spring water samples, and were able to isolate Legionella micdadei from 3 (5.5%) of 55 samples. All of these isolates were able to grow within Acanthamoeba sp., suggesting that the isolates will be pathogens. We also confirmed that the K-2 strain from hot spring water grew in guinea pig monocytes. Sensitivity tests using 10 drugs showed that the isolates were most sensitive to imipenem, with the MIC90 of 0.032 microg/ml, were least sensitive to minocycline, with the MIC90 of 4 microg/ml, and were not sensitive to low amounts of other drugs.