A Hospital-Associated Outbreak of Legionnaires' Disease Caused by Legionella pneumophila Serogroup 1 Is Characterized by Stable Genetic Fingerprinting but Variable Monoclonal Antibody Patterns

Abstract

An outbreak of 18 pneumonia cases caused by Legionella pneumophila serogroup 1 occurred at a Swedish university hospital 1996 to 1999. Eight clinical isolates obtained by culture from the respiratory tract were compared to 20 environmental isolates from the hospital and to 21 epidemiologically unrelated isolates in Sweden, mostly from patients, by using pulsed-field gel electrophoresis (PFGE), amplified fragment length polymorphism analysis (AFLP), and monoclonal antibody (MAb) typing. All patients and most environmental isolates from the outbreak hospital belonged to the same genotypic cluster in both PFGE and AFLP. This genotype was distinctly different from other strains, including a cluster from a second hospital in a different part of the country. The MAb subtype of the outbreak clone was Knoxville except for three isolates that were Oxford. A variation in the MAb reactivity pattern was also found in a second genotypic cluster. These changes in the MAb reactivity pattern were due to the absence or presence of the lag-1 gene coding for an Oacetyltransferase that is responsible for expression of the lipopolysaccharide epitope recognized by MAb 3/1 of the Dresden Panel. In all MAb 3/1-positive strains, the lag-1 gene was present on a genetic element that was bordered by a direct repeat that showed a high degree of sequence homology. Due to this homology, the lag-1 gene region seemed to be an unstable element in the chromosome. MAb patterns are thus a valuable adjunct to genotyping methods in defining subgroups inside a genotypic cluster of L. pneumophila sg 1.

Sequence-based and monoclonal antibody typing of Legionella pneumophila isolated from patients in Portugal during 1987-2008

“…On the other hand, identical STs were found among strains reactive with different MAbs (see Table). These two facts support the idea that it is valuable to add genotyping methods to MAb typing when defining profiles within a phenotypic subgroup [7,9].…”

“…The combination of a genotypic method with monoclonal antibody (MAb) typing has been described as a useful approach for epidemiological typing of L. pneumophila isolates [7][8][9][10]. MAbs of the Dresden panel allow subdividing the serogroup 1 of L. pneumophila as having, or not having, the epitope recognised by the MAb 3/1.…”

Comparison of Three Molecular Methods Used for Subtyping of Legionella pneumophila Strains Isolated during an Epidemic of Legionellosis in Rome

“…However, the efficiencies of the various typing methods vary, and not all typing methods are standardized (14,26,27). The need for extensive comparison among the different molecular typing methods is widely recognized (3,7). By exploiting the need for molecular characterization of isolates from a recent epidemic of L. pneumophila serogroup 1 infection to establish the source of infection, in the present study we have compared three molecular typing methods.…”

“…As serotyping is insufficient as a means of ascertaining the actual source of contamination (3,15), the genetic relatedness between human and environmental strains was determined both by comparison of the genomic profiles by pulse-field gel electrophoresis (PFGE) and amplified fragment length polymorphism analysis (AFLP) analysis and by comparison of the nucleotide sequences of five genes by sequence-based typing (SBT). Data from the epidemic-related isolates were also compared to data from unrelated strains.…”

Variable genetic element typing: a quick method for epidemiological subtyping of Legionella pneumophila

“…Some of them were indistinguishable by MAb subgrouping and SBT thus proving a transmission from the environmental source to the patient. Sets C and H differed in both markers, whereas sets K, L, and M were indistinguishable by genetic typing but expressed a different monoclonal subtype which is related to the deletion of the lag -1 gene [5] (Table 1).…”