Enhanced primary isolation of Legionella pneumophila from clinical specimens by low-pH treatment

During the 12-month study period, 919 clinical specimens were submitted to the laboratory for culture of Legionella pneumophila. All specimens were plated onto nonselective and semiselective media both directly and after treatment with a KCl-HCl solution, pH 2.2. Of the 51 specimens (5.5%) positive for L. pneumophila and Legionella-like organisms, 20 were recovered by acid pretreatment only, 5 were recovered by direct plating only, and 26 were recovered by both acid pretreatment and direct inoculation. These data demonstrated that acid pretreatment substantially improved the recovery of L. pneumophila and Legionella-like organisms from the clinical specimens examined.