Bacteria misagglutination in legionella surveillance programmes.

Several pathologies of respiratory tract are referred to be related to bacteria belonging to Legionella genus1. This pathology mainly affects immunocompromized people as nosocomial or community patients. Surveillance programs are required for monitoring bacteria diffusion and optimization of periodic decontamination action. Detection of Legionella pneumophila in water is based on well-standardized cultural and morphological analysis indicated in national guidelines2. Species assignment is typically performed by rapid agglutination tests3, which can be realized in few minutes. They usually provide univocal results in discrimination and serogrouping of L. pneumophila versus L. species including L. longbeachae, L. bozemanii, L. dumofii, L. jordanis, L. micdadei and L. anisa. This test is based on recognition of lipopolysaccharide present on the outer membrane4,5. We report some evidences where phenotypic procedures failed. During surveillance programs6,7 some unclearly identified bacteria from different regions were isolated. They showed morphological and cultivation features of legionellaceae but species classification, performed by agglutination test, gave negative or equivocal results (Figure 1). In particular they provide an absent or ambiguous agglutination of latex particles as can be observed in the representative Figure 1 (panels 1 and 3) where, positive results were obtained from a clear formation of precipitates (Figure 1, panel 2), as suggested by manufacturing practices and described by Dennis8 and related references. In principle this kind of equivocal results have to be considered negative. Bacteria that showed these results were definitely identified by DNA sequencing.