Brucella

A genus of Gram-negative intracellular pathogens causing brucellosis, the most common bacterial zoonosis worldwide. Brucella species depend on nickel-activated urease for gastrointestinal survival during the initial phase of infection, and urease immunization has been shown to protect against Brucella challenge — providing direct evidence that Ni-dependent enzymes are viable vaccine targets.

Nickel-Dependent Virulence

Ni-Urease -- Gateway to Infection

  • Urease is essential for survival during gastrointestinal passage and initial intestinal colonization [1].
  • Brucella is typically acquired through ingestion of contaminated dairy products or direct contact with infected animals. The oral route demands acid resistance during gastric transit.
  • Urease-generated ammonia and bicarbonate buffer the acidic microenvironment of the stomach, enabling bacteria to reach the intestinal mucosa intact.
  • Once past the GI barrier, Brucella establishes intracellular infection in macrophages, where it resides in a modified phagosome.

Urease as Vaccine Target

  • Immunization with urease protects against Brucella infection — one of the clearest demonstrations that a Ni-dependent virulence factor can serve as a protective antigen [1].
  • This validates urease as a targetable vulnerability, paralleling the HspA vaccine candidate approach for helicobacter pylori.
  • The finding has broader implications: any pathogen whose colonization depends on urease-mediated acid survival could be targeted with urease-based immunization strategies.

Iron Acquisition

  • Brucella species produce siderophores (brucebactin) for iron scavenging within the macrophage phagosome [1].
  • Iron acquisition is critical for intracellular survival and replication, complementing the nickel-dependent acid survival that enables initial colonization [1].

Clinical Significance

  • Brucellosis: causes undulant fever, arthritis, endocarditis, neurobrucellosis. Over 500,000 new human cases annually worldwide [1].
  • Zoonotic reservoir: cattle (B. abortus), goats/sheep (B. melitensis), swine (B. suis), dogs (B. canis) [1].
  • Intracellular persistence: survives within macrophages by preventing phagosome-lysosome fusion, creating chronic and relapsing infections [1].
  • Occupational and food-borne: pasteurization of dairy products is the primary prevention strategy; absence of pasteurization in endemic regions drives ongoing transmission.
  • Treatment requires prolonged combination antibiotic therapy (doxycycline + streptomycin/rifampin), and relapse rates remain significant.

The Nickel-Vaccine Connection

Brucella illustrates a clean narrative: a pathogen that must traverse the stomach to establish infection, depends on Ni-urease for that transit, and can be blocked by targeting that enzyme immunologically. This makes the nickel-urease axis both a virulence determinant and a therapeutic vulnerability.

Connections

References (1)

  1. . maier 2019 nickel microbial pathogenesis

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