Bacteriological examination of inflamed epidermal cysts: A survey between 2008 and 2009 at a hospital in Southern Taiwan

Background Inflamed epidermal cysts are common clinical conditions, and they frequently form abscesses. We designed a study to delineate the bacteriology of inflamed epidermal cysts. Methods We enrolled 61 adult patients with inflamed epidermal cysts characterized by surface erythema, with or without tenderness, or localized abscess formation within the cyst cavity. Incision and drainage of the cysts were performed, and the contents were sent for aerobic and anaerobic bacterial culture. The locations of the cyst and culture results were recorded for statistical analysis. Results A total of 61 cysts and 122 cultures were obtained. The most common locations of the inflamed cysts were the face, neck, and scalp (34.4%), followed by the trunk (32.8%), then the buttocks, inguinal areas, perineum, and axillae (16.4%), and the extremities (16.4%). The culture results were positive in 88.5% of patients, and anaerobes were more frequently isolated than were aerobes. Pure aerobes represented 31.1% of the cultures; pure anaerobes, 36.1%, and combined aerobes and anaerobes, 21.3% (n = 13). The most common anaerobic organisms found were Propionibacterium spp (40.8%), followed by Peptostreptococcus spp (36.7%), Staphylococcus saccharolyticus (14.4%), Prevotella (4.1%), Bacteroides fragilis (2.0%), and Fusobacterium spp (2.0%). The most commonly isolated aerobes were Staphylococcus spp (40%), followed by Enterobacter spp (11.3%), Proteus mirabilis (8.5%), Citrobacter diversus (8.5%), Klebsiella pneumoniae (5.7%), Corynebacterium (5.7%), Morganella morganii (2.9%), Enterococcus faecalis (2.9%), group A ß-hemolytic streptococcus (2.9%), Pseudomonas aeruginosa (2.9%), and Providencia rettgeri (2.9%). Conclusions Both aerobic and anaerobic microorganisms were present in the inflamed epidermal cysts, although the anaerobic bacteria, specifically, Propionibacterium spp and Peptostreptococcus spp, were isolated slightly more frequently. Antibiotics directed against anaerobes may be considered in the treatment regimen for inflamed epidermal cysts.