Journal of Infectious Diseases & Therapy
Open Access

Pilonidal disease is a relatively common condition affecting an estimated 26 per 100,000 patients and with a spectrum of presentations [1]. It may vary from an acute presentation associated with an abscess to chronically inflamed sinuses with persistent drainage. Although several theories exist on the cause of pilonidal sinus it has become accepted that the condition is acquired and is associated with loose hairs which may act as a foreign body and ultimately form pits with or without secondary infection [2,3]. Commonly identified bacteria in pilonidal disease are mainly anaerobic but also aerobic or facultative anaerobic organisms are found. These organisms are mainly Bacteroides spp., Escherichia coli, Proteus spp., and Pseudomonas spp. [4]. Interestingly, Staphylococcus spp., are not commonly found in these abscesses [5]. In this report we describe a case of a pilonidal sinus infection caused by Actinotignum schaalii (formerly Actinobaculum schaalii) and review our cases and the literature relating to skin and soft tissue infections with this organism.

A 19 year old male student presented to our institute’s emergency department with a left superior buttock abscess within the natal cleft that had been increasing in size over the past 4 months, painful on lying down and unresponsive to two courses of oral antibiotics (unknown) given by his GP. He had no systemic features of infection otherwise. The patient had no relevant medical history and was not known to have inflammatory bowel disease nor did he have a family history of such. He was a non-smoker and non-drinker. Examination showed a fluctuant mass at the ‘6 o’clock’ area with numerous pustules around discharging pus. A large palpable collection over the left superior buttock extended from the abscess. Per rectum examination was tender at the ‘6’oclock’ point of purulent discharge. The patient was diagnosed with complex pilonidal abscess with other differentials being hidradenitis suppurativa, perianal abscess and perianal fistula.

Magnetic resonance imaging was carried out to rule out anorectal fistulae. MRI pelvis (Figure 1) showed a perianal fistula at the 6 o'clock position that appeared to communicate with both left and right sided subcutaneous inflammatory changes with small subcutaneous abscesses noted measuring 17 × 7 mm. Several small collections were noted bilaterally, slightly larger on the left. The patient underwent an examination under anesthetic, incision and drainage of the pilonidal sinus with operative findings of purulent fluid expressed from three sinus openings (two sinus openings over the left superior buttock and one sinus opening over the right superior buttock) with four sinus openings over the midline lower back and natal cleft. All sinuses communicated via an extensive superficial cavity system lined with granulation tissue. Operative swab microscopy revealed a large number of polymorphs but no organisms were seen on gram stain. Culture grew mixed anaerobes on day 2 (gram positive bacilli, gram positive cocci and gram negative bacilli) but there was no growth in CO₂. On day 3 of culture it was noted that the Horse blood agar plate incubated in CO₂ had moderate amount of pure growth of A. schaalii. This organism was identified using MALDI-TOF (Bruker Biotyper 3.1 database version 4.0.0.1, Bruker Daltonik Bremen, Germany). There are no formal guidelines for susceptibility testing or interpretation of MIC results for this organism: antimicrobial susceptibility testing was performed using direct colony suspension of 0.5 McFarland inoculated onto Meuller-Hinton Sheep Blood agar (Thermo Fisher Scientific, Australia). Etest gradient strips (bioMérieux, Marcy l’Etoile, France) were placed onto the media and incubated in 5% CO₂ at 35-37°C for 24 h. MIC results are shown in Table 1. The abscess responded well to surgical treatment along with empiric treatment of a single dose of intravenous ceftriaxone 1 g and intravenous metronidazole 500 mg given post-operatively. The patient represented 2 months later with a recurrent pilonidal sinus. Incision and drainage was re-performed with wound culture revealing Staphylococcus aureus sensitive to flucloxacillin.  He had an uneventful recovery with nil recurrence.

Table 1: Antimicrobial susceptibility results of A. schaalii isolate.

Figure 1: MRI image (axial) showing location and size of pilonidal abscess.

A broad search strategy was undertaken given the limited publications on Actinotignum schaalii using MEDLINE (from January 1946 to December 2017) and EMBASE (from January 1980-December 2017). The search was carried out using keywords: Actinotignum, Actinotignum schaalii, Actinobaculum, and Actinobaculum schaalii, and was limited to humans and English articles. There were 96 articles found in the search. The authors reviewed all of these articles and excluded those that were not related to abscesses, skin infections or soft tissue infections. There were 33 cases of A. schaalii related abscesses, skin or soft tissue infections. Two of these cases were pilonidal sinuses infections. There are two previous published cases of A. schaalii pilonidal sinus infection.

Laboratory information system review

Monash Health is a large tertiary referral health network which services over 2000 beds from five hospitals in Victoria, Australia. The MALDI-TOF MS was introduced into routine laboratory work in February 2014. We searched the Laboratory Information System in the Microbiology Laboratory for non-urine specimens including the word “Actinobaculum” or “Actinotignum” from February 2014 until July 2017.

Actinotignum schaalii is a bacterium, first described in 1997, belonging to the genus that includes Actinotignum urinale, Actinotignum massiliense, Actinotignum sanguinis and Actinotignum suis [6-8]. It is likely part of the normal flora in the skin, genital and urinary tract region and is a difficult to culture Gram-positive bacillus that is a facultative anaerobe, non-motile, catalase negative bacterium that is increasingly recognized as a human pathogen [7-11]. Previously it had been difficult to identify and regularly dismissed as a contaminant or potentially overgrown by other organisms due to its slow growth [12,13]. However, with PCR techniques it appears that A. schaalii is much more common than thought. One study showed the prevalence of A. schaalii in urine was 16% and in those older than 60 years the prevalence increased to 22% by PCR [13]. Despite being a well-recognised uropathogen the number of cases of abscesses and skin or soft tissue infections attributed to this organism is limited.

  In our literature review we have found 43 cases (including our institutional cases, Table 2) of A. schaalii abscesses, skin and soft tissue infections. The average age of patients with infection with A. schaalii is 39 years old with a slight predilection towards females 0.85:1 (M: F) [6,7,10,12,14-19]. This contrasts with it affecting mainly the elderly population >65 years old as an uropathogen [13,14]. Location of infection is mainly in the groin region (10/43), breast (8/43) or perineum (8/43) three of these cases (including our case) were pilonidal abscesses. This data is summarized in Table 2 below. This is consistent with the knowledge that A. schaalii is part of the normal flora in the skin, genital and urinary tract region [13]. In these 3 cases of pilonidal abscesses all were surgically drained with two cases having additional antibiotic treatment. One case of pilonidal abscess had a good outcome, one case was unknown, and our case had recurrence albeit with a different organism. It is hard to draw conclusions on whether A. schaalii pilonidal abscesses have better or worse outcomes than those with other organisms due to the small sample size. It is also known that pilonidal abscesses have high recurrence rates with a long-term study of mean follow-up 14.8 years citing a 22% long-term recurrence rate, thus whether the recurrence was due to the inherent nature of the disease is also a factor to consider [20]. Our institutional data (Table 3) also showed a sizeable proportion (5/12) of breast abscesses. Of these, 3 were managed with aspiration and antibiotics with good outcome. The remaining 2 were treated with either antibiotics only or with surgical intervention plus antibiotics due to necrotizing fasciitis. Generally, the management of breast abscesses can be incision and drainage, aspiration (± repeated) and/or antibiotics with oral antibiotics often trialed prior to incision or aspiration techniques [21-24]. Our institution methods are in line with current accepted practices with no strong evidence to suggest a particular technique is better than another [25]. In the limited number of patients in this subgroup of breast infections good outcomes were seen in all which may suggest that A. schaalii breast abscesses should be treated like any other breast abscess.

Table 2: Cases of Actinotignum schaalii Abscess, skin and soft tissue infection.

Review of the 43 cases shows A. schaalii generally to be associated with simple collections that can be treated mostly without complications. Occasionally, severe infection such as Fournier’s gangrene/necrotising fasciitis can be a result of this organism. Whether this is due to the combined pathogenicity of other organisms it can co-exist with needs to be further investigated. Generally, it has a good response to treatment which in this review was surgical, antibiotics, a combination of both, or in one case local povidone iodine. 29/43 cases had favourable outcomes, 2/43 had recurrences and the remainder had unknown outcomes. It appears that collections/ skin or soft tissue infections with A. schaalii appear to be very true table with no serious morbidity reported in the literature [6,7,10,12,14-19].

Although there are no formal guidelines for susceptibility testing for A. schaalii, the literature suggests that this organism usually appears susceptible to amoxicillin, ceftriaxone and vancomycin in vitro but resistant to ciprofloxacin, metronidazole & cotrimoxazole.  With regards to antibiotic choice, 9 cases describe resistance with ciprofloxacin found to be ineffective in 5/9 cases, followed by 4/9 cases of metronidazole, 2/9 cases clindamycin and 2/9 cases trimethoprim. Therefore, for empiric treatment a penicillin is preferred otherwise ceftriaxone is also another effective choice [12,13,16,21,22]. As A. schaalii is a facultative anaerobe with potential resistance to metronidazole there may be lack of treatment efficacy if metronidazole is given alone. We suggest it is important to have prolonged anaerobic cultures for microbiological investigation of pilonidal sinus infections, MALDI-TOF to help with accurate identification of bacteria especially in metronidazole unresponsive cases and to also consider an A. schaalii infection. There are no established guidelines with regards to length of duration of antibiotic treatment for A. schaalii infections. With regards to pilonidal abscess current guidelines recommend a limited role for antibiotics unless there is underlying immunosuppression, systemic illness or significant cellulitis [2,23]. It is important to note that while studies and guidelines support antibiotics in limited settings, whether these guidelines also apply to A. schaalii infected pilonidal sinuses is yet uncertain.  This may not be completely unreasonable in infections with Actinomyces spp. as they potentially be prolonged infections or have multiple recurrences [16].

A. schaalii is becoming increasingly recognized due to better methods of identifying this organism. This study shows that this organism is not only limited to being an uropathogen. Despite this, there are not many reported cases of A. schaalii infections in skin, soft tissue and as abscesses. More research is required to elucidate the virulence of this organism, and whether this is a result of co-infection with other organisms or due to its own pathogenicity.

We acknowledge the patient for willingness to collaborate and Leanne Tilson (Microbiology) for her assistance with microbiological testing. This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.