A Clinical Case of Postoperative Subgaleal Abscess Caused by Actinomyces odontolyticus

1. Introduction

Actinomyces odontolyticus is a Gram-positive, facultatively anaerobic bacterium of the genus Actinomyces. It is a normal inhabitant of the mucous membranes of the oral cavity, upper respiratory tract and gastrointestinal tract of humans. However, when the barrier function of the body is compromised, this microorganism can become pathogenic, causing various infectious processes, including abscesses, bacteremia and soft tissue infections [1,2].

Infections associated with A.odontolyticus are relatively rare. They include liver abscesses, empyemas and inflammatory diseases of the cervicofacial region. These infections most commonly develop after surgery, trauma, or in the setting of a patient's compromised immune response [2].

Diagnosis of infections caused by A. odontolyticus is difficult because clinical manifestations are nonspecific and the bacterium grows slowly on standard nutrient media. Long-term culturing, mass spectrometry (MALDI-TOF) and molecular genetic studies are recommended for accurate identification of the pathogen [3].

The present clinical case demonstrates the development of a soft tissue infection of a postoperative wound caused by A.odontolyticus, which emphasizes the importance of including this microorganism in the differential diagnosis in inflammatory processes in surgical patients.

2. Case Presentation

A 55-year-old female patient was admitted to the emergency room of the Karaganda Medical University Clinic in Karaganda, Kazakhstan, with complaints of intense stabbing pains in the right side of the abdomen, primarily in the right iliac region, dry mouth, and a temperature rise to 37.5°C. The pain began three days before admission, initially in the abdominal area without a clear localization, and then it moved to the right iliac region. The patient has no history of surgical interventions or chronic diseases.

Upon examination, the patient showed tenderness on palpation in the right iliac region, with positive signs of Sitkovsky, Rovsing, and Bartomé-Michelson. Laboratory tests revealed an elevated level of C-reactive protein (6 mg/L, reference range <5 mg/L), while the white blood cell count was within normal limits. A computed tomography (CT) scan of the abdominal organs showed signs of acute appendicitis (Figure 1 and Figure 2). The patient underwent surgery – an open appendectomy through an oblique incision according to Volkovich-Dyakonov. Intraoperatively, the diagnosis of acute phlegmonous appendicitis was confirmed.

In the early postoperative period, the patient had a persistent elevated body temperature of 37.5°C–38.0°C, localized tenderness at the site of the surgical wound, but no local hyperemia. Leukocytosis was observed (11.2×10⁹/L, reference range from 4 to 9×10⁹/L) with an increase in neutrophils (neutrophils - 78%, reference range from 35% to 70%, band neutrophils - 4%, reference range from 1% to 5%). Despite antibacterial therapy (Cef III, 1.0 gram intramuscularly twice daily), no clinical improvement was observed, raising suspicion of a subgaleal abscess of the postoperative wound (Figure 3). On the 6th day after surgery, the patient underwent wound revision under local anesthesia with 0.5% Novocain solution (30 ml). During the procedure, a collection of pus under the aponeurosis of the external oblique abdominal muscle was diagnosed, and the abscess cavity was drained (Figure 4). A sample for microbiological analysis was collected and sent to the research laboratory of the Karaganda Medical University.

The material was cultured on blood agar according to standard microbiological procedures. After incubation, colonies were found that, based on morphological characteristics, were consistent with the Actinomyces genus, with a colony-forming unit (CFU) count of 10^5. MALDI-TOF mass spectrometry was used for precise microorganism identification, which confirmed the presence of Actinomyces odontolyticus (Figure 5). Antibiotic susceptibility testing was also conducted, allowing for the selection of an effective antibacterial treatment. A. odontolyticus showed sensitivity to penicillin, amoxicillin, cefoxitin, ceftriaxone, imipenem, fusidic acid, tetracycline, levofloxacin, and linezolid, but was resistant to clindamycin and azithromycin.

In accordance with the results of sensitivity testing to antibacterial drugs, the patient was prescribed ceftriaxone in a dose of 1.0 g intramuscularly 2 times a day, daily dressings with antiseptic solutions. On the background of the treatment positive dynamics was noted: the main complaints regressed, body temperature normalized. In the control analyses the level of leukocytes was 7×109/l. The postoperative wound was cleared of purulent discharge, edema and hyperemia regressed, the postoperative wound was tightened by secondary tension, with active growth of granulation tissue. The patient was discharged in satisfactory condition. Bacteriologic culture was repeatedly taken from the area of the postoperative wound, as a result of which A. odontolyticus was not identified, indicating a positive effect of treatment and complete elimination of this pathogen.

3. Discussion

Abdominal actinomycosis is a rare disease caused by facultatively anaerobic, Gram-positive bacilli of the genus Actinomyces, which normally inhabit the oral cavity, nasopharynx, gastrointestinal tract, skin, and genitourinary tract [3]. However, these microorganisms can become pathogenic when the barrier function of mucous membranes is compromised, for example, due to surgical interventions. Abdominal actinomycosis usually develops after invasive procedures or due to abdominal infection such as appendicitis [4]. In some cases of actinomycosis affecting the abdomen, Actinomyces can cause pericarditis or liver damage, with A. odontolyticus being found in liver abscesses [5].

In our case, the patient developed actinomycosis after appendectomy, manifested by a subgaleal abscess in the right iliac region. It should be noted that this disease is predominantly diagnosed in immunocompromised patients.

Screening of the material obtained from the postoperative abscess revealed the presence of colonies morphologically corresponding to representatives of the genus Actinomyces. The diagnosis was confirmed using MALDI-TOF mass spectrometry, which made it possible to accurately identify Actinomyces odontolyticus. Traditional biochemical tests for the identification of suspected Actinomyces species can be applied to most of them, but often there is an indifferent growth in test media, which leads to false negative results and low reproducibility [6]. In this regard, given the limited accuracy of conventional biochemical methods, alternative methods with high accuracy, such as MALDI-TOF mass spectrometry, which is widely used in clinical laboratories, have been increasingly used recently [7]. In one comparative study, MALDI-TOF correctly identified 97% of 32 strains to the species level, while a commercially available biochemical kit achieved only 33% success [8].

Positive dynamics was observed against the background of antibacterial therapy with ceftriaxone: the patient's clinical condition improved. It should be noted that sensitivity testing of anaerobic bacteria is rarely performed in clinical microbiological laboratories. However, this is often not a particular problem for Actinomyces species, since they usually do not show resistance to beta-lactam drugs, and being gram-positive, they are also sensitive to vancomycin [9].

Thus, actinomycosis remains a significant diagnostic problem in clinical practice. In this case, bacterial translocation on the background of acute phlegmonous appendicitis probably caused the formation of a subgaleal abscess caused by A. odontolyticus.

4. Conclusions

This case is the first example of abdominal actinomycosis caused by A. odontolyticus reported in the Republic of Kazakhstan. He emphasizes the critical importance of early laboratory diagnosis of microorganisms and their spectrum of antibiotic sensitivity for the appointment of timely and effective treatment. The use of modern diagnostic methods, such as MALDI-TOF mass spectrometry, makes it possible to identify pathogens and conduct effective therapy.