Glutamate Decarboxylase-Dependent Acid Resistance in Brucella spp.: Distribution and Contribution to Fitness under Extremely Acidic Conditions

Abstract

f Brucella is an expanding genus of major zoonotic pathogens, including at least 10 genetically very close species occupying a wide range of niches from soil to wildlife, livestock, and humans. Recently, we have shown that in the new species Brucella microti, the glutamate decarboxylase (Gad)-dependent system (GAD system) contributes to survival at a pH of 2.5 and also to infection in mice by the oral route. In order to study the functionality of the GAD system in the genus Brucella, 47 isolates, representative of all known species and strains of this genus, and 16 strains of the closest neighbor genus, Ochrobactrum, were studied using microbiological, biochemical, and genetic approaches. In agreement with the genome sequences, the GAD system of classical species was not functional, unlike that of most strains of Brucella ceti, Brucella pinnipedialis, and newly described species (B. microti, Brucella inopinata BO1, B. inopinata-like BO2, and Brucella sp. isolated from bullfrogs). In the presence of glutamate, these species were more acid resistant in vitro than classical terrestrial brucellae. Expression in trans of the gad locus from representative Brucella species in the Escherichia coli MG1655 mutant strain lacking the GAD system restored the acid-resistant phenotype. The highly conserved GAD system of the newly described or atypical Brucella species may play an important role in their adaptation to acidic external and host environments. Furthermore, the GAD phenotype was shown to be a useful diagnostic tool to distinguish these latter Brucella strains from Ochrobactrum and from classical terrestrial pathogenic Brucella species, which are GAD negative. Brucellae are the etiologic agents of brucellosis, the most widespread bacterial zoonosis, infecting livestock and humans (human incidence, 500,000/year). The disease is endemic in the Mediterranean, in Near East and Middle East countries, and in Latin America (1, 2). These pathogens are classified as different species on the basis of specific phenotypic traits and their natural hosts (3): Brucella melitensis (isolated from goats and sheep), Brucella abortus (cattle and bison), Brucella suis (pigs and wild boar), and Brucella canis (dogs). Transmitted to humans via the mucosal, cutaneous, respiratory or, most frequently, oral route, these species may induce undulant fever (Malta fever) and a wide range of clinical manifestations, including encephalitis and endocarditis. With a few exceptions, Brucella species isolated from marine mammals (Brucella pinnipedialis and Brucella ceti) have not been described as human pathogens. Two other species are nonpathogenic for humans: Brucella ovis (sheep) and Brucella neotomae (desert woodrat) (3). Being known for 20 years or longer, these eight species are considered "classical". More recently, three "new" species/strains were identified: B. microti from common vole, red fox, and also soil (4-7) and Brucella inopinata BO1 and B. inopinata-like BO2 from patients with a breast implant infection (8, 9) and a chronic destructiv...

The role of ‘atypical’Brucellain amphibians: are we facing novel emerging pathogens?

“…One special feature of the newly described or ‘atypical’ Brucella is a functional glutamate decarboxylase‐dependent system that favours both survival at low pH thereby facilitating oral infection and a useful distinguishing marker to classical brucellae and closely related genera (Damiano et al . ). Nevertheless, apart from provisional classifications, further heterogeneities with respect to variant lipopolysaccharides (LPS), phage lysis, serum agglutination and dye sensitivities are observed (Whatmore et al .…”

“…With respect to their 16S rRNA and recA genes, almost all 'classical' species and also B. microti share identical gene sequences, whereas B. inopinata, B. papionis and B. vulpis show a few differences of two to three nucleotides . One special feature of the newly described or 'atypical' Brucella is a functional glutamate decarboxylase-dependent system that favours both survival at low pH thereby facilitating oral infection and a useful distinguishing marker to classical brucellae and closely related genera (Damiano et al 2015). Nevertheless, apart from provisional classifications, further heterogeneities with respect to variant lipopolysaccharides (LPS), phage lysis, serum agglutination and dye sensitivities are observed (Whatmore et al 2014).…”

Integrating metabolic and evolutionary engineering for enhanced propionic acid production under cross stress: a multi-omics perspective

“…In this study, the expression of ADI and CK were not detected in RNA-seq and metabolome analysis, but the proteins were detected in the proteome. Moreover, the glutamate decarboxylase (GAD) pathway, which can consume H + [35], did not show significant differential expression in the mutant I, II, and III, respectively. Therefore, the trajectory of change of ADI and GAD remained consistent, whereby mutant II showed more positive regulation of ADI and GAD, while mutant I was more positive in the regulation of CK.…”

Lethality of Brucella microti in a murine model of infection depends on the wbkE gene involved in O-polysaccharide synthesis

“…In the last decade, new species of Brucella, such as Brucella microti, Brucella inopinata and isolates from Australian rodents and amphibians, have been described [2]. These strains are metabolically more active, acidresistant and fast-growing when compared to the wellknown classical, human-pathogenic Brucella species, which include Brucella abortus, Brucella melitensis, Brucella suis and Brucella canis [2][3][4][5][6][7]. Their isolation from hitherto unknown wildlife hosts and the environment raised the question whether Brucella may be transmitted from these reservoirs to livestock and humans living in officially brucellosis-free areas of the world.…”