Genetic taxonomic studies have suggested that the 8 currently accepted species, including the 2 marine mammal-associated species, represent a single species. Nevertheless, recent studies show that traditional species, and the marine mammals-associated species, can be differentiated by outer membrane genes polymorphism, insertion sequences and whole-chromosome preparations. Human brucellosis has been described associated to B. melitensis, B. abortus, B. suis and B. canis, among the traditional species. Human cases associated to the newer marine mammals-associated species have also been reported. Though B. abortus has the broadest geographical distribution, most human cases are now caused by B. melitensis, which usually produces the most severe disease. Microbiological procedures for Brucella detection and identification have been controversial for years. Blood, and eventually bone marrow, are usually the specimens for diagnosis of human brucellosis. Conventional blood cultures did not yield satisfactory results, and this led to the development of the classic biphasic blood cultures technique proposed by GSK2118436 Ruiz-Castan˜eda. Now, both lysescentrifugation methods and continuous monitoring blood cultures devices are able to detect Brucella with a good sensitivity. Early suspicion that an isolate might be a Brucella is important, both for clinical and epidemiological reasons, because of the hazard of laboratory-acquired brucellosis, and for the early detection of a hypothetical bioterrorist attack. Early suspicion may be currently established based on Gram staining, but final identification requires colonies growth on agar plates and performing biochemical or serological tests on these colonies. For all those reasons, the availability of methods that allow a rapid and reliable Brucella identification both from agar plates and directly from the blood culture bottles, once this is reported as positive by the continuous-monitoring blood culture systems, would be extremely useful. Direct detection methods based on PCR have been described, but these methods are expensive, can be affected by PCR inhibitors present in blood, and do not give any information about the viability of the microorganisms. Thus, they have not reached a wide diffusion by now. MALDI-TOF MS is an important and increasingly available tool in clinical microbiology laboratories, because it allows a rapid and accurate identification of bacteria. This explains the reliability at genus level and the low reliability at species level. Otherwise, the high similarity between all type strains is not surprising, since genetic taxonomic studies suggest that the 6 currently accepted species represent a single species.