Reply to Agger and Kowalski

To the Editor—We read with interest the article " Actinomyces in Chronic Gran-ulomatous Disease: An Emerging and Un-anticipated Pathogen " by Reichenbach et al [1]. However, we do not believe this series of patients with chronic granulo-matous disease (CGD) and Actinomyces infection demonstrates compelling evidence to dismiss the traditionally recognized risk factor of microbial catalase as the most important virulence factor in patients with CGD unless phenotypic-negative catalase results from the species isolated in this series are made available. Actinomyces infection in patients with CGD should not necessarily be considered as supporting evidence for a different mechanism of virulence, because Ac-tinomyces species are not universally cat-alase negative, as was suggested in the article [1]. It is notable that, of the 8 Actinomyces isolates identified to the species level, 7 were identified as Actinomyces naeslundii (6 specimens had positive culture results, and 1 specimen had positive serological test results). The genospecies type 2 of A. naeslundii is catalase-positive in ∼55% of isolates, and 30% of all geno-species isolates of A. naeslundii were cat-alase positive in one dental study [2]. Occasionally , other Actinomyces species can be catalase positive, as well [3]. In a recent review of 92 clinically significant strains of Actinomyces species identified by 16S ri-bosomal DNA analysis, no isolates were identified as A. naeslundii, which highlighted the infrequency of this organism as a cause of clinically significant disease in patients without CGD [4]. Without this essential biochemical data, the conclusion that the " susceptibility of patients with CGD to infection with cat-alase-negative Actinomyces species confirms that catalase production is neither necessary nor sufficient for microbial vir-ulence in CGD " is not supported by this article [1, pp 1708–1709]. Rather, catalase positivity, which is frequently found in A. naeslundii, may still explain most of these infections. In conclusion, this series may not significantly depart from the traditional association of catalase-positive microbial infections and CGD. Although cat-alase-negative infections in patients with CGD have been described, the frequency of such infections, compared with those due to catalase-producing organisms, and the importance of alternative mechanisms require further investigation.bic and facultative gram-positive bacilli. In: Koneman's color atlas and textbook of diagnostic microbiology. Genotypic diversity of clinical Actinomyces species: phenotype , source, and disease correlation among genospecies. To the Editor—We appreciate the comments of Drs Agger and Kowalski, which echo the traditional assumption that microbial catalase production is the " most important virulence factor in …