Breast abscess due to Trueperella bernardiae and Actinotignum sanguinis

Sir,

Trueperella bernardiae is a facultative anaerobic gram-positive coccobacillus which is part of the normal microbiota of human skin and the oropharynx. This microorganism has been reported in only few cases of human infection, especially in wound and prosthetic joint infections [1-3]. On the other hand, Actinotignum sanguinis is a small facultative anaerobic gram-positive rod which forms part of the normal urogenital flora. They grow slowly and especially under anaerobic or in atmosphere enriched with CO₂. Actinotignum species have been rarely associated with urinary tract infections [4] and bacteremia [5].

We report a rare case of breast abscess caused by these two pathogens. To our best knowledge, this is the first report of breast abscess caused by these two microorganisms together. Table 1 shows all published cases of T. bernardiae and/or A. sanguinis infections.

Table 1.

Cases with infection caused by Trueperella bernardiae and/or Actinotignum sanguinis.

Patient (year of publication) Author	Age (years)/sex	Microorganism	Localization of infection	Microbiological diagnosis
1 (1996) Ieven M	69/M	Actinomyces bernardiae	Urinary tract	Urine, perirenal abscess and necrotic tissue cultures Blood culture (+)
2 (1998) Adderson EE	19/F	Arcanobacterium bernardiae	Hip	Synovial fluid culture
3 (1998) Lepargneur JP	75/M	Arcanobacterium bernardiae	Urinary tract	Urine culture
4 (2009) Bemer P	63/M	Arcanobacterium bernardiae	Knee	Intraoperatory specimen
		Staphylococcus. aureus
5 (2009) Loïez C	78/M	Arcanobacterium bernardiae	Hip prosthesis	Intraoperatory specimen
6 (2010) Sirijatuphat R	60/M	Arcanobacterium bernardiae	Kidney	Perinephric drainage culture
			Pleura
7 (2010) Clarke TM	62/F	Arcanobacterium bernardiae	Skin abscess	Abscess and tissue cultures
		Morganella morganii
8 (2011) Weitzel T	72/F	Arcanobacterium bernardiae	Blood	Blood cultures (+)
9 (2013) Otto MP	78/F	Trueperella bernardiae	Wound	Ulcer culture
		Bacteroides fragilis		Blood cultures (+)
		Enterococcus avium
10 (2015) Parha E	68/F	Trueperella bernardiae	Brain	Abscess culture
		Peptoniphilus harei
11 (2015) Schneider UV	45/M	Trueperella bernardiae	Skin ulcers	Ulcer tissue culture
		Peptoniphilus lacrimalis
12 (2016) Rattes ALR	24/F	Trueperella bernardiae	Wound	Umbilical secretion culture
13 (2016) Gilarranz R	73/F	Trueperella bernardiae	Knee prosthesis	Synovial fluid
				Blood cultures (+)
14 (2016) VanGorder B	77/F	Trueperella bernardiae	Skin	Drainage abscess culture
15 (2017) Cobo F	69/F	Trueperella bernardiae	Wound	Wound secretion culture
16 (2017) Cobo F	70/F	Trueperella bernardiae	Inguinal granuloma	Wound secretion culture
		Escherichia coli
17 (2017) Pedersen H.	NR	Actinotignum sanguinis	Blood	Blood cultures (+)
18 (PR/2018) Calatrava E	39/F	Trueperella bernardiae	Breast abscess	Drainage abscess culture
		Actinotignum sanguinis

M: male; F: female; NR: not reported; PR: present report

A 39-year-old woman refers ten days history of pain and local swelling in her right breast. Her clinical history was unremarkable, and she was in treatment with cloxacillin (1g /8h) for seven days. The abscess was drained by puncture and the fluid obtained sent to the microbiology laboratory for culture. The sample was inoculated in blood agar (both aerobic and anaerobic) (BD Columbia Agar 5% Sheepblood^®, Becton Dickinson) chocolate agar (BD Choco Agar, Becton Dickinson), thioglycolate broth (BD™ Fluid Thioglycolate Medium, Becton Dickinson), Mannitol agar (BD Mannitol Salt, Becton Dickinson) and MacConkey (BD Mac Conkey II, Becton Dickinson).

Gram stain of the abscess showed gram positive bacilli, and on the second day of incubation two types of colonies grew on both aerobic and anaerobic blood agar and chocolate agar. They were identified with MALDI-TOF MS (Bruker Biotyper, Billerica, MA, USA) as Trueperella bernardiae (score 2,13) and Actinotignum sanguinis (score 2,22). The MIC of different antibiotics was carried out by the E-test method in Brucella agar supplemented with hemin, vitamin K1 and lacked sheep blood incubated at 37°C. As no specific clinical breakpoints have been established for T. bernardiae and A. sanguinis, we used the EUCAST PK/PD (non-species related) clinical breakpoints. T. bernardiae was susceptible to ciprofloxacin (0.5 mg/L), gentamicin (1.5 mg/L), imipenem (0.016 mg/L), linezolid (0.25 mg/L), penicillin (0.032 mg/L), rifampicin (<0.016 mg/L), tetracycline (0.094 mg/L), vancomycin (0.19 mg/L), and resistant to trimethoprim-sulfamethoxazole (>32 mg/L), clindamycin (1 mg/L) and erythromycin (1 mg/L). A. sanguinis was susceptible to ciprofloxacin (0.5 mg/L), gentamicin (<0.016 mg/L), linezolid (0.047 mg/L), penicillin (<0.016 mg/L), vancomycin (<0.016 mg/L), and resistant to trimethoprim/sulfamethoxazole (>32 mg/L), clindamycin (>256 mg/L) and erythromycin (>256 mg/L). Antimicrobial treatment was changed to amoxicillin-clavulanic (875/125 mg/8h) for 10 days, and at three months of follow-up the woman was asymptomatic.

The diagnosis of T. bernardiae and A. sanguinis is based on culture of an adequate sample. Identification using conventional laboratory methods could be difficult and when isolated in clinical samples these microorganisms are usually not identified, especially T. bernardiae due to it coryneform aspect. The recent introduction of mass spectrometry for routine analysis in the clinical laboratories may help in the final identification of these pathogens, and can help to know the true incidence of infections with these bacteria. For this reason it is highly recommended to use the MALDI-TOF method for identification.

Overall, drug resistance in T. bernardiae and A. sanguinis may be not considered still a problem. According to different studies, T. bernardiae was susceptible to all antimicrobials tested, except to ciprofloxacin [6, 7]. On the other hand, the genus Actinotignum has demonstrated high susceptibility to ß-lactams and vancomycin [5]. In other study, 12 isolates of Actinotignum spp. were susceptible to penicillin [8]. However, treatment of choice for these microorganisms has not been clearly established due to the scarcity of data and the absence of breakpoints for these bacteria. Further studies are necessary in order to establish the best therapeutic option.

In summary, it is still unknown the true clinical implications of T. bernardiae and A. sanguinis, but with the generalized use of MALDI-TOF in the majority of laboratories, the diagnosis of these pathogens implicated in human infections probably will increase. Microbiologists should be aware of these microorganisms especially if the new diagnostic techniques area applied.

FUNDING

None to declare

CONFLICT OF INTEREST

The authors declare that they have no conflicts of interest