Molecular Comparison of Isolates from a Recurring Outbreak of Legionnaires' Disease Spanning 22 Years

Abstract

During outbreak investigations molecular analytical methods are necessary to discriminate among clinical isolates and to establish a link with environmental isolates. In addition to monoclonal antibodies used as an initial subtyping method, other methods employed have been pulse-field gel electrophoresis, amplified fragment length polymorphosim (AFLP), arbitrarily primed PCR, multilocus variable-number tandem repeat, and sequence-based typing (SBT). In the present study, the authors used SBT to study the relationships among clinical and environmental isolates of Legionella pneumophila isolated from the same hotel during a 22-year period. Water samples were collected from the hotel and cultured using standard procedures for the recovery of Legionella isolates from environmental sources. To determine the discriminatory power of the SBT procedure, eight isolates that share the same monoclonal antibody (MAb) subtype were included. These isolates represent four enzyme types based on previous studies using multilocus enzyme electrophoresis (MLEE). All isolates were tested with a panel of MAbs to determine their subtype. Isolates were compared by AFLP. Patient isolates and representative environmental isolates from both outbreaks were analyzed by a sequence-based typing scheme.