Document Type : Review


1 Department of Microbiology and Virology, School of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran

2 Antimicrobial Resistance Research Center, Mashhad University of Medical Sciences, Mashhad

3 Microbiology Research Center Ghaem Medical Center, Mashhad University of Medical Sciences (MUMS), Mashhad, Iran


Today, human bloodstream infections (BSIs) are recognized as a major cause of morbidity and mortality worldwide. The bacteria, responsible for bacteremia, are usually identified in diagnostic clinical laboratories, using blood cultures. True bacteremia is defined as a positive blood culture (>15 CFU/mL), with signs and symptoms of infection (e.g., fever and chills). A wide range of bacteria can cause true bacteremia and some bacterial isolates from BSIs may be responsible for contamination. Gram-positive bacilli, such as Bacillus species, and coryneform bacteria are suspected sources of contamination in blood cultures. However, in certain patients, such as immunocompromised patients and intravenous drug users, gram-positive bacilli can act as a true pathogen. Therefore, it is important to know when gram positive bacilli act as a true pathogen and when they act as contamination. So, the rapidly diagnosis of true pathogens and appropriate treatment play a very important role in controlling infection with these bacteria. Effective measures are especially important in patients with an underlying disease or an immunocompromised status. In this article, we reviewed the literature on common Gram-positive rod-shaped bacteria, which were isolated from blood cultures and were suspected to be true pathogens or contaminants.