The Retrospective on Atypical Brucella Species Leads to Novel Definitions

Abstract

The genus Brucella currently comprises twelve species of facultative intracellular bacteria with variable zoonotic potential. Six of them have been considered as classical, causing brucellosis in terrestrial mammalian hosts, with two species originated from marine mammals. In the past fifteen years, field research as well as improved pathogen detection and typing have allowed the identification of four new species, namely Brucella microti, Brucella inopinata, Brucella papionis, Brucella vulpis, and of numerous strains, isolated from a wide range of hosts, including for the first time cold-blooded animals. While their genome sequences are still highly similar to those of classical strains, some of them are characterized by atypical phenotypes such as higher growth rate, increased resistance to acid stress, motility, and lethality in the murine infection model. In our review, we provide an overview of state-of-the-art knowledge about these novel Brucella sp., with emphasis on their phylogenetic positions in the genus, their metabolic characteristics, acid stress resistance mechanisms, and their behavior in well-established in cellulo and in vivo infection models. Comparison of phylogenetic classification and phenotypical properties between classical and novel Brucella species and strains finally lead us to propose a more adapted terminology, distinguishing between core and non-core, and typical versus atypical brucellae, respectively.

Activation of mucosal immunity as a novel therapeutic strategy for combating brucellosis

“…The study of different Brucella species may assist in learning Brucella ’s pathogenesis and tenets of host protection. The discovery of B. microti in voles ( Scholz et al, 2008 ) and later in other host species ( Occhialini et al, 2022 ), extends the genus diversity, whereby B. microti shares metabolic traits, conserved VirB type IV secretion system, and early granuloma formation with other Brucella pathogens of livestock ( Scholz et al, 2008 ; Hanna et al, 2011 ; Jiménez de Bagüés et al, 2011 ; Occhialini et al, 2022 ). Brucella microti offers another model to study brucellosis since it can be lethal in mice and actively proliferates in murine macrophages.…”

Brucella abortus in Kazakhstan, population structure and comparison with worldwide genetic diversity

“…may be transmitted to humans resulting in a severe disease requiring a specific and long-term antibiotic treatment with significant burden to public health systems ( Franc et al, 2018 ). The genus Brucella currently contains 12 validly published species ( Olsen and Palmer, 2014 ; Whatmore and Foster, 2021 ; Occhialini et al, 2022 ). Brucella melitensis , Brucella abortus , B. suis , B. ovis , B. neotomae, and B. canis are often referred to as “classical” Brucella species in the literature.…”

Minimum Core Genome Sequence Typing of Brucella From China

“…9,10 The Brucella host range will likely continue expanding, because Brucella-like strains from frogs were newly identified, which may expand the natural host of Brucella to amphibians. 11 The commercially and clinically most relevant Brucella species include B. melitensis, B. suis and B. abortus, and they can all infect humans and result in serious clinical symptoms. Brucellosis in China was first reported in 1905.…”

“…inopinata strains BO1 T and BO2 9,10 . The Brucella host range will likely continue expanding, because Brucella -like strains from frogs were newly identified, which may expand the natural host of Brucella to amphibians 11 . The commercially and clinically most relevant Brucella species include B .…”