Clues to anaerobic infection include Polymicrobial results on Gram stain or culture Bacteria are seen on Gram stain, but aerobic cultures are sterile Gas in pus or infected tissues Foul odor of pus or infected tissues Necrotic infected tissues Site of infection near mucosa where anaerobic microflora normally reside Testing Specimens for anaerobic culture should be obtained by aspiration or biopsy from normally sterile sites.