Module 11 Lecture

Brucella classification

• Domain: Bacteria

• Phylum: Proteobacteria

• Class: alpha proteobacteria

• Order: Rhizoiales

• Family: Brucellaceae

• Genus: Brucella

• Speices: all one species with multiple serovars - abortus (cow), melitensis (goats), canus (dog), suis (pig)

  • serovars are isolated from different mammals

• genome — 2 chromosomes, 3.3 megabases, 57% GC content, 3300 total genes

Brucella general characteristics

• gram-negative (does not stain very well)

  • appear either as a small coccobacillus or bacillus, <1 um

• nonmotile

• non spore former

• no capsule present

• facultative intracellular pathogens

  • like to live in cell of choice, usually phagocytic cells

  • responsible for most human disease B. suis and B. abortus

• colony morphology - small, smooth, convex, barely translucent, varies on serovar

  • can grow on BAP and on chocolate plate (it is picky - no growth on TSA or MAC)

• aerobe & capnophile (O2 @ 21% & best growth at high CO2)

• catalase positive

• oxidase positive

Brucella spp. virulence factors

• zoonose: animal to human transmission

• Type four secretion system (T4SS)

  • aids in intracellular survival

  • engulfed by phagocytic cell by phagosome or endosome

  • in normal conditions bacteria travels through cytosol and phagosome fuses with lysosome for bacterial degradation

  • instead, the phagosome fuses with the ER by T4SS; injects into the membrane and redirects to the ER not the lysosome

    • the bacteria is now in ER membrane, bacteria replicates & spreads

Brucella spp.

• Brucellosis is the disease caused; also called undulating fever or malta fever

  • contact with infected animals or consuming infected animal products

• three stages

  • acute — 1 to 2 months post infection; symptoms are flu-like & nonspecific

    • best chance to culture the bacteria with decent diagnosis

  • subchronic — within a year of infection; symptoms are undulating fever (normal temp in morning, increase during day, and falls at night) and joint pain

    • harder to culture bacteria

  • chronic — continuous undulating fever & joint pain, fatigue & general unwellness

    • harder to culture the bacteria | mortality is low (~2%)

• human to human transmission is rare

• brucellosis in other mammals

  • reproductive organs for cattle due to presence of four carbon molecule

    • cows & bison affected by B. abortus

    • in males, it can cause infertility

    • in females it can cause spontaneous miscarriage

    • epidemiology is low in US; about 100-200 cases per year

      • require vaccination of livestock

    • high in Mediterranean basin because they lack domestic animal health program

      • no requirement of vaccination for their livestock, infection spreads and thrives in population

      • if a visit to Med with unpasteurized cheese then chance of contracting Brucella increases the risk of disease

Lab ID Brucella spp.

• must take patient history for potential exposure or occupational hazard, consumption of unpasterized dairy or trip to Mediterranean

• specimen of blood sample, bone marrow, liver/spleen biopsy

  • plate on BAP or chocolate agar; small smooth translucent colonies with slight blue hue, non-hemolytic

  • gram-negative coccobacilli; oxidase positive; catalase positive

  • distinction from other fastidious gram-negative by growth on BAP

  • BL3 condition

    • aerosol transmission or inhalation; must use caution when ID

• treatment and prevention of Brucella

  • lots of antibiotics — daily intramuscular injection of streptomycin (14 days) + oral antibiotic of doxycycline (6-8 weeks)

    • 5-10% chance of relapse because this bacteria divides slowly and it requires a long course of antibiotics to kill them

  • vaccine — RB51 for livestock (live attenuated)

Biological warfare Brucella spp.

• B. suis used by US in 1954

  • put in arterially shells and bombs; intended to make the enemies really sick with flu like symptoms & wanted it to be non-lethal

  • pathogen has low ID 50 has 10-100 cells (enough to cause infection in 50% of those exposed)

    • aerosol transmission when bomb goes off

    • never used!

Pasteurella

• also a zoonotic disease

• classification

  • Domain: Bacteria

  • Phylum: Proteobacteira

  • Class: gamma proteobacteria

  • Family: Pasteurellacaea

  • Genus: Pasteurella

  • Species: 17 spp. (most clinically relevant is P. multocida)

  • genome — 2 chromosomes, 2 mega bases, 2000 total genes

Pasteurella general characteristics

• gram-negative bipolar staining (safety pin); large central vacuole

• nonmotile

• non spore forming

• facultative anaerobes (like 21% O2 but its not required)

• catalase positive

• oxidase positive

• growth on BAP

• colony morphology — medium, smooth, gray/white, non-hemolytic, capsule present

• reservoir: upper respiratory tract of mammals and birds (not in humans usually)

Pasteurella virulence factors

• hyaluronic acid capsule ~ evades recognition from immune system

• LPS - can cause endotoxic shock (if disseminated)

• outer membrane proteins for adhesion to host cell

  • Omp and pili

Pasteurella disease

• cutaneous infection

  • occurs by domestic pet bites because pathogen is carried in the mouth (80% carriage by cats)

  • localized infection, rash, inflammation, swelling, swollen lymph nodes

  • without antibiotic treatment, the infection can disseminate into bacteremia

• upper respiratory tract infections

• can cause systemic infection and meningitis

Pasteurella Lab ID

• specimen is wound aspirate or blood sample if dissemination or CSF if meningitis

• cultured on BAP or chocolate - does not grow on MAC due to its fastidious nature

  • colonies appear medium, smooth, white/tan, non-hemolytic and they may appear mucoid due to capsule presence

• catalase positive & oxidase positive

• with gram staining, gram-negative bacilli & bipolar staining

Pasteurella prevention and treatment

• antibiotic prescription of penicillin or tetracycline or doxycycline

• vaccines available for mammals (none for humans yet)