Pulmonary actinomycosis is relatively rare. The common pathogens in humans mainly include: actinomyces israeli, actinomyces naeslundii,actinomyces odontolyticus, actinomyces viscosus,actinomyces meyeri, and actinomyces gerencseriae[10]. Actinomyces graevenitzii cultured in this case is a newly recognized pathogen that was first isolated from 4 clinical human specimens in 1997 by Ramos et al[11]. Kentaro Nagaoka etal described a case of multiple lung abscesses caused by actinomyces graevenitzii that resembled pulmonary coccidioidomycosis and progressed rapidly[7]. A case of disseminated infection with both actinomyces graevenitzii and tuberculosis had been reported by Andreas Tietz et al[4]. However, little is known about the clinical features and pathogenesis of this bacterium. Co-infection of actinomyces graevenitzii with other pathogens is rare. To our knowledge, the present case presented as a lung abscess with cavitary lesions is the first of pulmonary actinomycosis caused by actinomyces graevenitzii, actinomyces odontolyticus and multiple other pathogens including aspergillus, klebsiella pneumoniae, pseudomonas aeruginosa, streptococcus constellations and candida albican.
The diagnosis of pulmonary actinomycosis is quite challenging. Several reports found that 25–49% of pulmonary actinomycosis were initially suspected of lung malignancy[12]. With the development of metagenomic next generation sequencing (mNGS) technology, the detection rate of actinomyces has been increasing, but whether it is a pathogenic bacterium should be carefully considered. One case report showed that lung adenocarcinoma mimiced lung actinomycosis by mNGS[3]. Therefore, pulmonary actinomycosis co-existing with lung cancer should be highly concerned. A histopathological diagnosis is of great importance to prevent misdiagnosis. In our case CT-guide percutaneous lung biopsy was performed. Histopathologic findings including chronic suppurative inflammation, sulfur granules and radiating filamentous colonies consistent with actinomyces. It should be noted that sulfur granules, long regarded as a histological hallmark of actinomycosis, are very strongly suggestive of the diagnosis. However, they are not entirely specific to actinomycosis, since these granules can also be found in nocardiosis, botryomycosis, aspergillosis, and coccidioidomycosis[7]. The diagnosis requires a combination of medical history, risk factors, pathological and biochemical parameters.
The treatment is prolonged antibiotic therapy, with adjuvant surgery in severe cases. A massive dose of penicillin is the first choice of treatment. However the treatment recommendation is based on a single actinomyces infection.In the present case treatment with ceftriaxone for one month in early time was non-effective. The reason maybe the co-infection or poor antibiotic sensitivity. It was reported that most of the infections induced by actinomyces meyeri and actinomyces graevenitzii were poly-microbial co-infection. Reduced oxygen tension and inhibition of phagocytes induced by bacterial infections might enhance the pathogenicity of actinomyces species[4]. That is the reason why the reported case progressed quickly. One report showed that actinomyces graevenitzii isolates were resistant to ceftriaxone and piperacillin-tazobactam, and all isolates were susceptible to penicillin and amoxicillin[4]. For pulmonary co-infection, a early and combined antibiotic therapy is the most reasonable strategy. In this case, we used voriconazole according to GM test although only candida albican was cultured. Although the therapeutic effect was ideal, it remained to be considered whether actinomycosis leaded to a false positive BALF GM test.
In conclusion, this case highlights the potential association of actinomycosis with other polymicrobial co-infection as well as the importance of early recognition of opportunistic infection to ensure a favourable outcome.