A 55-year-old man presented to the emergency department with complaints of a painful abscess on his inner right thigh that had been present for about 1 week. The patient was morbidly obese, with a significant medical history, including type 2 diabetes, hypertension, asthma, and previous abscesses. His glucose levels had been relatively well controlled, but his hypertension was poorly controlled, likely due to medication noncompliance. A physical examination revealed a 4- by 5-cm abscess in the inner thigh that extended up to the inguinal crease. The area was fluctuant and tender, with overlying skin that was moist and gray but with little erythema or drainage. An incision and drainage procedure was done in the emergency department, which recovered a large amount of purulent material that was submitted for aerobic culture. Therapy with intravenous vancomycin was begun, and the patient was admitted to the hospital. Two sets of blood cultures taken at admission were sterile. The serum creatinine level was mildly elevated (1.23 mg/dl), and a urinalysis revealed hazy urine with white blood cells (WBCs) (48 cells/high-power field [HPF]), a small amount of leukocyte esterase, a mucus level of 3+, elevated protein (100-mg/dl) and glucose (200-mg/dl) levels, and a small amount of blood. A midstream urine culture incubated at 35°C in ambient air grew <10,000 CFU/ml and was not worked up further.
A Gram stain of the abscess pus showed many Gram-positive cocci, many Gram-negative coccobacilli, and many polymorphonuclear leukocytes (PMNs). Anaerobic cultures were not performed. Aerobic cultures grew level 3+ pinpoint gray colonies on blood agar after 24 h of incubation in 5% CO2. There was scant growth on chocolate agar and no growth on MacConkey agar. The Gram stain revealed a pleomorphic Gram-positive organism with frequent coccoid forms as well as small rod-shaped forms. Plates were reincubated in an attempt to obtain better growth but were essentially unchanged after 72 h of incubation. The Gram stain at this time showed diphtheroid-like Gram-positive rods with some branching (Fig. 1). Tests for pyrrolidonyl arylamidase (PYR) and leucine aminopeptidase (LAP) gave positive reactions. The results for catalase and bile esculin tests were negative. Identification was attempted using the RapID ANA II system (Thermo Fisher Scientific, Remel Products, Lenexa, KS) and the ERIC electronic code compendium, which gave an identification of Actinomyces odontolyticus (biocode 073671), with >99.9% probability, no identification overlap, and a bioscore of 1/126, with acceptable biofrequency, but only an “adequate” confidence level, indicating that contraindicated tests had resulted in some deviation from the expected base pattern. No other organisms were recovered.
FIG 1.
Gram stain from pinpoint colonies growing on blood agar after 72 h of incubation. Magnification, ×1,000 (oil).
(For answer and discussion, see page 3709–3710 in this issue [doi:10.1128/JCM.02429-13].)