Characterisation of significant Gram positive bacilli from soft tissue infections

SummaryIntroductionGram positive bacilli (GPB) isolated from soft tissue infections are often neglected or ignored due to their fastidious nature and the lack of reliable phenotypic identification methods. This study was done to characterise clinically significant aero-tolerant GPB isolated from surgically obtained samples in patients with soft tissue infections.MethodsForty-six GPB isolates collected during a 2 year study period were identified using partial 16s rRNA sequencing and API Coryne. Antibiotic susceptibility testing to penicillin, amoxycillin/clavulanate, moxifloxacin and erythromycin was performed on these isolates using Etest. Clinical data were gathered from patients’ medical records.ResultsThe most common isolates identified by 16s rRNA sequencing were Actinomyces species (n = 30, 65%) and Corynebacterium species (n = 9, 20%). The majority of the Actinomyces species infections were located below the waist, in particular the perianal region. There was poor agreement between API Coryne and genotypic identification, with only one-third of the isolates being correctly identified to species level. Actinomyces species were uniformly susceptible to penicillin and amoxicillin/clavulanate. Antibiotic susceptibilities were more varied for the other genera isolated.ConclusionActinomyces species comprised two-thirds of aerobically growing GPB isolates and may represent an under-reported cause of bacterial soft tissue infections. Penicillin and amoxycillin/clavulanate may be the empiric antibiotics of choice for Actinomyces species as all isolates were susceptible.