The Bubonic plague is caused by an infection with Yersinia pestis, and it is definitely the most famous manifestation of this infection. When infected with the plague, patients will present with a (typically singular) large lymphadenopathy or bubo, fevers, chills, myalgias. This infection is typically transmitted through a bite of a flea, and the natural reservoirs are typically rodents. Now that we have antibiotics, this infection is very easily treated with aminoglycosides.
Yersinia pestis can also cause pneumonic plague when the organism is inhaled. This will present with hemoptysis, fever, dyspnea, and pleuritic chest pain. This is the rarest form of yersiniosis, which is good because it’s nearly 100% fatal, even with treatment.
Yersinia enterocolitica is a more common manifestation of yersinosis, and causes abdominal pain, fever, and dysentery. Sometimes, the mesenteric lymph nodes will become swollen with granulomatous microabscesses which might cause a misdiagnosis of Crohn’s Disease. This infection can also sometimes be confused with appendicitis (pseudoappendicitis).
Y. enterocolitica is typically transmitted through food or water, particularly undercooked pork meat, raw milk products, from contact with fecal matter of animals and at daycares.
Reactive arthritis can also occur after the organism has been cleared, causing patients to present with uveitis, urethritis, and arthritis.
Yersinia spp. are encapsulated and their polysaccharide capsule is make mostly of Vw antigen and the F1 antigen. Their outer membrane is made of Yops proteins which interfere with signal transduction in WBCs. These bacteria also have a Type-III Secretion System. It has a particularly thin layer of peptidoglycan that causes it to form bipolar staining when Gram stained.
Bacteroides fragilis is a common normal flora agent of the gastrointestinal tract. It’s actually really helpful for us, as it can create Vitamin K, which is essential for many clotting factors to function. The problem is when it endogenously spreads to areas where it’s not supposed to go and causes infection. It can cause brain abscesses, peritoneal abscesses, and because it is anaerobic and produces a gas, it can be a cause of gas gangrene, or myonecrosis.
One thing that’s really cool is that when the immune system interacts with the unique capsular antigen of B. fragilis, it actually induces the body to form an abscess around the organism.
Nearly every strain of this organism is penicillin-resistant because it has beta-lactamases, so treatment with clindamycin or metronidazole is necessary.
A 71-year-old female presents with diarrhea for 8-days. Vital signs reveal a temperature of 103F. Past medical history is significant for Crohn’s disease, common variable immunodeficiency, and cyromegalovirus colitis. Laboratory values reveal a C-reactive protein level of 280 mg/L (normal <50 mg/L), but normal WBC numbers and percentages. Blood cultures revealed a Gram-negative anaerobic bacillus. It was identified as Bacteroides fragilis by growth on a 20% bile plate. Why is this organism typically a beneficial organism?
A. Reduce the risk of kidney stones
B. Helps digest diary products
C. Improves cholesterol in people with Type-2 diabetes mellitus
D. Produces Vitamin K
A. Oxalobacter formigenes can break down calcium oxalate which makes up some kidney stones. (this fact is not board relavent)
B. Streptococcus thermophilus produces the enzyme lactase which digests the sugar in milk and dairy products (this fact is not board relavent)
C. Bifidobacteria bifidum may help improve cholesterol in women and people with type-2 diabetes mellitus (this fact is not board relavent)
D. Bacteroides spp. are known to produce vitamin K and while they are typically only 1% of the normal flora of the gut, evidence suggest that when patients lose their normal flora (antibiotic use), they might suffer coagulopathies.
Therefore,
A 7-year-old female presented to the hospital in New Mexico with fever, emesis, a generalized tonic-clonic seizure, and fatigue for two days. Vital signs reveal a temperature of 107F. History is significantly for moving to a new house in the preceding three weeks where she played in the family’s new crawl space, and swept a dusty chicken coop that contained mouse droppings, and camping at a national forest campground where she found and buried a dead squirrel. Physical examination revealed intermittent delirium and visual hallucinations. She did not have any nuchal rigidity, headaches, and she had clear breath sounds. Insect bites were found on both lower limbs, with an extremely large, tender, left inguinal lymph node. The patient held her left leg in an externally rotated position due to pain and discomfort. She developed worsening tachycardia, tachypnea, and hypotension. Blood cultures revealed a Gram-negative, bipolar-staining bacillus. What is the most likely causative agent?
A. Pasteurella multocida
B. Hantavirus
C. Yersinia pestis
D. Bacteroides fragilis
First, diagnose the patient.
A young child is presenting in the southwestern US is presenting with signs of acute infection. There are no signs of meningitis, so the cerebral symptoms are most likely due to the high fever. The history lays out a bunch of opportuinties for insect bites and inhalations of nasty things. The presence of a large, tender, single swollen lymph node is the only clue to the diagnosis in this patient. The patient goes on to develop the classic signs of sepsis.
The organisms that are Gram-negative and exhibit bipolar staining are: Pasteurella multocida, Yersinia spp., Francisella tularensis, Burkholderia spp., Haemophilus ducreyi. The good news is that each of these organisms have vastly different clinical manifestations. The presence of the bubo in a patient in the southwest really points the finger to: Bubonic plague
A. Pasteurella multocida is a normal flora agent in many animals including dogs and cats. This will most likely present in a patient with a history of animal bite, and might present as a cellulitis, or soft tissue infection.
B. Hantavirus is an infection that can occur in the southwestern US, especially in patients with recent contact with rodent excrement as it’s typically transmitted by inhaling rodent urine. This will present with fever, dizziness, shortness of breath, etc consistent with a pulmonary infection. However, the blood cultures point toward a bacterial infection instead of viral.
C. Yersinia pestis is the cause of the bubonic plague. It can manifest in a few different clinical presentations, but the most common and famous version is the formation of the bubo, which is a single, massively swollen, painful lymph node which typically drains from the bite of the flea. Typically there are a few cases every year in the southwestern US. This organism is Gram-negative and stains with a bipolar staining. Even though saying a patient has the plague is scary sounding, it’s pretty susceptible to antibiotics (for now).
D. Bacteroides fragilis can cause sepsis in patients, but it is not associated with bipolar staining and more typically causes abscesses in patients post surgery or trauma.
This was a real case that I found a case report on, which was fascinating. They also detail the steps they took in informing the appropriate government agencies. Ultimately, the team was able to quickly determine the cause, and manage her care to e point of full recovery.
Therefore,
References:
https://www.ncbi.nlm.nih.gov/books/NBK499837/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5977175/
https://iai.asm.org/content/iai/3/1/59.full.pdf
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2176045/
https://jcm.asm.org/content/44/9/3465
https://www.cdc.gov/hantavirus/pdf/hps-fact-sheet.pdf
https://academic.oup.com/jpids/article/3/4/e38/909057
The Bradley Lab 