Brucella melitensis : A nasty bug with hidden credentials for virulence

Abstract

On September 23, 1905, a cargo carrying 60 goats from Malta arrived in New York. The herd was kept in quarantine because of several deaths that occurred during the journey. Crewmen, an agent from the U.S. Bureau of Animal Industry, which was responsible for the shipment, and a woman who drank milk that “escaped” from the quarantine station displayed the characteristic symptoms of “Mediterranean fever.” Lieutenant Colonel David Bruce, a physician of the Royal Army, who discovered “Micrococcus melitensis ” in 1887 in infected British soldiers residing in Malta, had forewarned the U.S. sanitary authorities about the risk of “Mediterranean fever” by importing goats from Malta. In November 1906, after isolation of “M. melitensis,” the goats were destroyed. Almost 100 years after this episode, the genome sequence of Brucella melitensis (renamed after David Bruce) has been resolved by DelVecchio et al. (1), bringing new light to the understanding of the biology of this pathogen. The disease, known as brucellosis, is found in all continents, affecting mainly low-income countries; in addition, it constitutes a contemporary concern because Brucella strains are potential agents of biological warfare. The six recognized Brucella species, named according to their host preference, affect economically important livestock, and several undesignated strains infect marine mammals. Abortion is the main outcome of the infection in pregnant animals, resulting from complex, not well understood interactions between the placental tissues, the intracellular brucellae, and the fetus. Brucella invades professional and nonprofessional phagocytes and replicates within compartments resembling the endoplasmic reticulum after evading fusion with lysosomes (2). The brucellae are exceedingly well adapted to this niche (see Fig. 1, which is published as supporting information on the PNAS web site, www.pnas.org) and do not survive for protracted periods of time outside the host. Their textbook description, “facultative intracellular parasites,” does …