Actinobaculum schaalii: a new cause of mastitis

Abstract number: R2214

Agudo S., Domingo D., Navarro J.L., Arenal N., López-Brea M.

Objective:Actinobaculum sp. is a Gram-positive rod closely related to the genus Actinomyces. A new species, Actinobaculum schaalii was first discovered in 1997 and has been related to urinary tract infections. We report one case of A. schaalii isolate found in a breast abscess.

Methods: The drainage obtained was immediately sent to the Microbiological Department. The specimen was cultured in Columbia agar with 5% sheep blood, chocolate agar and Brucella blood agar incubated in aerobic, microaerophilic and anaerobic environments, respectively. The strain was characterised by using the Rapid ID32A systems (bioMérieux, France) in according to manufacter's instructions. For definite confirmation, isolate was referred to a reference laboratory for PCR of the bacterial 16S RNA gene sequencing. Minimum inhibitory concentrations (MICs) to penicillin, amoxycillin and clavulanic, clyndamycin, erythromycin and linezolid, were determined by E-test on Mueller Hinton sheep blood agar in anaerobic conditions.

Results: A 32 year-old woman presented inflammation in the right breast. An initial diagnosis of a breast abscess was made and needle aspiration was attempted. Four months later, she developed a new abscess in the same place. The abscess was drained and the pus was sent for bacteriological culture. The sample was processed by standard protocols, but bacteriological investigations were negative. The patient was treated with ceftidoren. After two months, a breast magnetic resonance imaging was performed to control the evolution and the abscess was observed one more time. It was required other drainage procedure, the sample was immediately sent to the Microbiological Department. After 48 h anaerobic incubation, colonies <1 mm in diameter, grey, convex and weakly-haemolytic were obtained. The Api Rapid ID32 identified the microorganism as Actinomyces meyeri with the code 0521473705. The result of the definite confirmation by PCR was A. schaalii. According to the Clinical and Laboratory Standards Institute criteria for Streptococcus spp., the isolate was susceptible to all antibiotics tested.

Conclusion: This is the first case of A. schaalii isolate found in a breast abscess. These organisms could be missed in routine cultures due to the anaerobic and slow growth. It is recommended that the identification of A. schaalii be done by performing Rapid ID32A test system and 16S rRNA gene sequencing, at least until the manufacters' databases have been updated.