Pseudo-outbreak of Actinomyces graevenitzii associated with bronchoscopy

Abstract

Outbreaks and pseudo-outbreaks of infection related to bronchoscopy typically involve Gram-negative bacteria, Mycobacterium species or Legionella species. We report an unusual bronchoscopy-related pseudo-outbreak due to Actinomyces graevenitzii. Extensive epidemiological and microbiological investigation failed to identify a common source. Strain typing revealed that the cluster was comprised of heterogeneous strains of A. graevenitzii. A change in laboratory procedures for Actinomyces cultures was coincident with the emergence of the pseudo-outbreak, and we determined that A. graevenitzii isolates more readily adopted a white, dry, molar tooth appearance on anaerobic colistin nalidixic acid (CNA) agar which likely facilitated its detection and identification in bronchoscopic specimens. This unusual pseudo-outbreak was related to frequent requests of bronchoscopists for Actinomyces cultures combined with a change in microbiology laboratory practices.

FIG 1

Results for DiversiLab RepPCR strain typing for selected Actinomyces graevenitzii isolates. DiversiLab (DL) rep-PCR strain typing was performed on available Actinomyces graevenitzii isolates. The dendrogram shows relatedness determined by Kullback-Leibler analysis grouped according to DL pattern. The vertical dashed line indicates a 96% similarity of the DL profiles. The case number corresponds to that listed in Table 1, and the month during which the culture was obtained is indicated.

FIG 2

Actinomyces culture orders and results for 2013. Laboratory records were reviewed for Actinomyces cultures ordered and those with positive results for calendar year 2013. The vertical dashed line indicates the month during which the laboratory plating protocol for Actinomyces cultures was changed. Prior to that month, anaerobic CDC blood agar was used, and afterwards reducible CNA agar was used.

FIG 3

Morphology of A. graevenitzii on anaerobic CDC and reducible CNA agars. The same A. graevenitzii isolate growing on anaerobic CNA (A) and anaerobic CDC blood agar (B) at 72 h is shown. The proportion of dry- or molar-tooth-appearing colonies for 10 different A. graevenitzii isolates on anaerobic CNA (▲) or anaerobic CDC blood agar (●) was assessed at the indicated time points. The proportion of dry or molar-tooth colonies was significantly greater for anaerobic CNA agar (P < 0.001) at all time points.