Gram Negative: Yersinia, Francisella, Brucella, & Pasteurella

Question 1

Which four characteristics do Yersinia, Francisella, Brucella, and Pasteurella all share?

Answer 1

• Gram negative bacilli
• zoonotic diseases (they are primarily diseases of animals)
• extremely virulent (some species only require 10 organisms to cause disease!) and can penetrate any body area they touch, leading to multiple disease presentations
• facultative intracellular organisms that survive phagocytosis, move to the regional lymph nodes, and then seed into the bloodstream and other organs
• note that Pasteurella only has the 1st 2 characteristics, not all 4

Question 2

How do we treat Yersinia? Francisella? Brucella? Pasteurella?

Answer 2

• treat all with aminoglycoside (gentamycin, streptomycin) and/or doxycycline

Question 3

What disease does Yersinia pestis cause? How does it infect humans? What are its major virulence factors?

Answer 3

• causes the bubonic plague (or the pneumonic plague if it infects the lungs)
• the bug is harbored in wild rats and gets transmitted to domestic rats and humans via fleas (the vector)
• resists phagocytosis with its F1 (fraction 1), V, and W virulence factors
• (picture a RAT riding in a Fuel Injected VW bug/FLEA away from macrophages)

Question 4

What type of staining pattern does Yersinia pestis have?

Answer 4

• a bipolar staining pattern where the ends get stained more than the central region of the organism

Question 5

How do patients with the bubonic plague present? In which patients should we suspect this disease in?

Answer 5

• (bubonic plague caused by Yersinia pestis)
• infected lymph nodes (usually inguinal) swell and become red, hot, and painful (note that lymph involvement is not present in 25% of cases)
• fever and headache develop
• hemorrhages under the skin cause a black-ish discoloration (the “black death”)
• death within a few days if left untreated (75% mortality rate)
• suspect in patients who have been camping in Arizona or in New Mexico

Question 6

What other major species of Yersinia is there?

Answer 6

• Yersinia enterocolitica (causes gastroenteritis via invasion of gut epithelium, lymph nodes, and bloodstream)

Question 7

What disease does Francisella tularensis cause? How does it infect humans? What are the major presentations of this disease?

Answer 7

• causes tularemia (essentially a less severe version of the bubonic plague)
• the bug is transmitted to humans by handling infected rabbits and/or by getting bitten by infected ticks and deerflies
• (picture FRANCIS the RABBIT in a field of TULips, with a TICK and DEERFLY on its ears)
• major presentations: ulceroglandular tularemia (skin) and pneumonic tularemia (lungs)
• other presentations: oculoglandular tularemia (eyes) and typhoidal tularemia (GIT)

Question 8

What is ulceroglandular tularemia? How does it compare to the bubonic plague?

Answer 8

• (1 of the 2 major disease presentations of tularemia via infection with Francisella tularensis)
• well-demarcated hole in the skin with a black base develops at the site of contact/bite
• fever and other systemic symptoms
• local lymph nodes swell, redden, and become painful
• nearly identical to the bubonic plague, but can be differentiated by the single well-demarcated skin lesion
• it is far less morbid than the bubonic plague (5% vs. 75%)

Question 9

What is pneumonic tularemia?

Answer 9

• (1 of the 2 major disease presentations of tularemia via infection with Francisella tularensis)
• results from hematogenous spread of the organism, can follow ulceroglandular tularemia, or can be from inhalation of aerosolized bacteria during the skinning/evisceration of rabbits

Question 10

What disease does Brucella cause? How does it infect humans? How does its incidence compare to Yersinia and Francisella?

Answer 10

• causes brucellosis
• infects humans via direct contact with infected animal meat (cows, goats, pigs, dogs), aborted cow placentas, or ingestion of infected milk products
• its incidence is greater than the other two diseases (bubonic plague and tularemia), but cattle immunizations and milk pasteurizing have made a HUGE impact

Question 11

What is brucellosis? What is it also known as? How does it compare to the bubonic plague? In which patients should we suspect this disease in?

Answer 11

• (brucellosis caused by Brucella)
• brucellosis is an even milder form of bubonic plague than tularemia, and lacks any skin ulceration
• the fever in brucellosis slowly rises during the day and falls at night (hence why it is AKA “the undulant fever”)
• the symptoms can last months to years, but the disease is rarely fatal
• suspect in patients involved in the meat-packing industry, veterinarians, farmers, or travelers (eating animal meat and drinking milk in other countries)

Question 12

What does Pasteurella multocida cause? Where is it found?

Answer 12

• (remember, this organism is NOT a facultative intracellular organism, but is zoonotic like the others)
• causes the most common wound infection following a cat/dog bite/scratch
• it is found in the mouths of cats
• it is because of this organism that we don’t close these wounds with sutures, as this provides a good environment for its growth