Immunologic diagnosis of Legionnaires' disease: cross-reactions with anaerobic and microaerophilic organisms and infections caused by them

J Infect Dis. 1980 May;141(5):652-5. doi: 10.1093/infdis/141.5.652.


The hundred twenty-four isolates of anaerobic and microaerophilis organisms were examined with a polyvalent direct immunofluorescent antibody (DFA) reagent directed against Legionella pneumophila, serogroups (SG) I-IV. Three of 53 isolates of Bacteroides fragilis cross-reated with the SG I component of the reagent. Rabbit antisera to three SG I strains of L. pneumophila cross-reacted with these three B. fragilis isolates, and cross-reactivity was not due to preexisting rabbit antibodies; antisera to a fourth SG I strain did not cross-react with these isolates. Indirect fluorescent antibody (IFA) examinations of convalescent-phase sera from eight of 41 patients with B. fragilis group infections showed titers of greater than or equal to 1:128 or a fourfold or greater seroconversion against L. pneumophila, SG I. All eight patients had bacteremia due to B. fragilis, but five B. fragilis isolates available from these patients were DFA-negative. Thus, false-positive reactions may result from DFA as well as IFA examinations of sera from patients with B. fragilis infections.

MeSH terms

  • Aerobiosis
  • Anaerobiosis
  • Animals
  • Antibodies, Bacterial
  • Antibody Specificity
  • Bacteroides Infections / diagnosis
  • Bacteroides fragilis / immunology
  • Cross Reactions*
  • False Positive Reactions
  • Fluorescent Antibody Technique
  • Humans
  • Legionnaires' Disease / diagnosis*
  • Rabbits


  • Antibodies, Bacterial