Peptostreptococcus is a genus of anaerobic, Gram-positive, non-spore forming bacteria. The cells are small, spherical, and can occur in short chains, in pairs or individually. They typically move using cilia. Peptostreptococcus are slow-growing bacteria with increasing resistance to antimicrobial drugs. Peptostreptococcus is a normal inhabitant of the healthy lower reproductive tract of women. Pathogenesis Peptostreptococcus species are commensal organisms in humans, living predominantly in the mouth, skin, gastrointestinal, vagina and urinary tracts, and are members of the gut microbiota. Under immunosuppressed or traumatic conditions these organisms can become pathogenic, as well as septicemic, harming their host. Peptostreptococcus can cause brain, liver, breast, and lung abscesses, as well as generalized necrotizing soft tissue infections. They participate in mixed anaerobic infections, a term which is used to describe infections that are caused by multiple bacteria that do not require or may even be harmed by oxygen. Peptostreptococcus species are susceptible to beta-lactam antibiotics. They are isolated with high frequency from all specimen sources. Anaerobic gram-positive cocci such as Peptostreptococcus are the second most frequently recovered anaerobes and account for approximately one quarter of anaerobic isolates found. Most often Anaerobic gram-positive cocci are usually recovered mixed in with other anaerobic or aerobic bacteria from various infections at different sites of the human body. This contributes to the difficulty of isolating Peptostreptococcus organisms. Infections Peptostreptococcus species that are found in clinical infections were once part of the genus formerly known as Peptococcus. Peptostreptococcus is the only genus among anaerobic gram-positive cocci that is encountered in clinical infections. As such, Peptostreptococcus species are viewed as being clinically significant anaerobic cocci. Other similar clinically significant anaerobic cocci include Veillonella species (gram-negative cocci), and microaerophilic streptococci (aerotolerant). Anaerobic gram-positive cocci include various clinically significant species of the genus Peptostreptococcus. The species of anaerobic gram-positive cocci isolated most commonly include Peptostreptococcus magnus, Peptostreptococcus asaccharolyticus, Peptostreptococcus anaerobius, Peptostreptococcus prevotii, and Peptostreptococcus micros. Anaerobic gram-positive cocci that produce large amounts of lactic acid during the process of carbohydrate fermentation were reclassified as Streptococcus parvulus and Streptococcus morbillorum from Peptococcus or Peptostreptococcus. Most of these organisms are anaerobic, but some are microaerophilic. Due to a large amount of new research done on the human microbe and more information on bacteria, many species of bacteria have been renamed and re-classified. Based on DNA homology and whole-cell polypeptide-pattern study findings supported by phenotypic characteristics, the DNA homology group of microaerobic streptococci that was