Bacterial blood infections Flashcards
Basic characteristics of Rickettsia
-Obligate intracellular bacteria
Aerobic gram (-) rods
LPS has weak endotoxin activity
Bacteria responsible for Rock Mountain spotted fever
Rickettsia rickettsii
Rickettsia parkeri (particularly in western US)
Rickettsia in the typhus group
Rickettsia prowazekii
Rickettsia typhi
How do Rickettsia escape the phagosome
Using phospholipase
Where do Rickettsia grow/replicate
In the cytoplasm/nucleus
How are Rickettsia energy parasites?
THey have transporters that exchange ADP for host ATP
What Rickettsia lyse their host cell?
Members of the typhus group
R. prowazekii and R. typhi
What leads to reduced platelet count and increased coagulation time in Pt’s infected with Rickettsia?
Rickettsia induced oxidative damage to endothelium and vascular smooth muscle leads to platelet adherence
Platelets ares pulled out of circulation - leads to reduced count and increased coagulation time
What causes microthrombi in Pt’s w/ Rickettsia infection?
Damaged endothelial cells w/ their adherent platelets can be released into circulation - causing blockages in vasculature
Rickettsia rickettsii
Rocky mountain spotted fever
Vector: hard ticks
Dermacentor andersoni (wood tick) in Rocky Mountain states
Dermacentor variabilis (dog tick) in SE US and West Coast
Incubation - ~7 days (range: 2-14 days)
Rash in rocky mountain spotted fever
Usually begins as a maculopapular rash that progress to a petechial rash
Develops 2-5 days after exposure in 90% of cases
Initially seen on extremities and spreads to trunk
What is indicative of a poor prognosis in Rocky Mountain Spotted fever?
Absent or late developing rash
Death in 20-40% w/o Tx or misDx
How does the spotted fever group of Rickettsia exit the cell?
Utilizing actin polymerization
How does the typhus group of Rickettsia exit the host cell?
By lysing the cell
Where does the RMSF rash present?
Petechial rash on the extrimities (includes soles and palms)
Resevoir Rickettsia prowazekii
Humans
Vector in US is flying squirrel fleas
Rash presentation w/ Rickettsia typhi and Rickettsia prowazekii
Rickettsia Prowazekii - rash presents initially (rash only in ~50% of cases) on chest/Abdomen before spreading to extrimities (oppositie w/ Rickettsia that causes RMSF)
Organism responsible for epidemic typhus
Rickettsia prowazekii
More severe disease than Rickettsia typhi
What cells does Ehrlichia infect?
Monocytes and tissue phagocytes (including spleen, liver, and lymph nodes)
Disrupts monocytes Fx and regulation of the inflammatory response
Anaplasma vector and resevoir
Vector = Ixodes ticks
Resevoir = small mammals
Erlichia vector and resevoir
Vector = Amblyomma americanum (Lone star tick)
Resevoir = white-tailed deer
What type of host cells does Erlicihia ewingii and Anaplasma phagocytophilum infection?
They intracellularly infect granulocytes
Pathology is related to macrophage activation
What type of bacterial morphology is characteristic of Borrelia
Gram (-) spirochetes
Extracellular frank pathogen
Organism responsible for epidemic relapsing fever
Borrelia recurrentis - louse-borne
Organism responsible for endemic relapsing fever
Many species of tick-borne Borrelia
Virulence factors of Borrelia
Eschar - seen in soft-body tick bite spreading endemic Borrelia
Jarish-Herxheimer Rx’n
Shock-like sxs after initiation of Abx therapy for spirochete infection (killing intracellular bacteria in RBCs causing them to lyse and release inflammatory molecules)
Bartonella characteristics
Gram (-), short, aerobic rods
Fastidious requirements
What Pt’s are prone to bacillary angiomatosis by Bartonella henselae?
HIV Pt’s
Tx w/ azithromycin in immunocompromised Pt’s
What causes Yersinia pestis to upregulate virulence factors upon entering its definitive host?
Increased temperature from flea to human
What type of bacterial capsule does Yersinia pestis have?
Protein capsule - F1 antigen
Resists phagocytosis by macrophages
When does a Yersinia infected Pt become contagious?
When the bacteria spreads to the lungs (Pneumonic plague)
Yersinia pestis (characteristic gram-negative with a bipolar, or “safety pin” appearance, with Gram/Giemsa stain)
Tx for Yersinia pestis
Aminoglycosides (streptomycin/gentamicin)
Salmonella typhi
Gram (-) rod
Encapsulated w/ Vi antigen
Resistant to bile salts
Low infectious dose <1000 bacteria
Salmonella typhi virulence and pathenogenesis
Abx to Tx typhoid fever
Ceftriaxone
Azithromycin
Salmonella typhi has high levels of Abx resistance and must test to determine its presence
Cipro used to be first-line Tx, but is becoming less effective
Only spirochete disease dx’d by microscopic demonstration of spirochetes in peripheral blood?
Endemic relapsing fever (Borrelia infection)
Which of the following bacteria cause an infection that spreads from an initial papule to the regional lymph node causing significant lymphadenopathy in immunocompetent patients following a cat bite?
Bartonella henselae
Which of the following bacteria are transmitted by body lice? (Select all correct answers)
Rickettsia prowazekii
Borrelia recurrentis
Which of the following structures provides spirochetes with their characteristic motility?
Periplasmic flagella
A 13-year-old migrant from Somalia, presents at a hospital in Italy with a high fever, headache, and general malaise. He notes that he first experienced these symptoms a few weeks ago while living in a refugee camp in Libya. He states that he has a high fever for a few days and then it goes away for a few days before returning again. A blood smear was negative for Plasmodium spp., but a Giemsa-stained blood smear was positive for many helical bacteria. Which of the following virulence determinants contribute to the clinical presentation caused by this pathogen?
Antigenic variation
Relapsing fever = Borrelia infection
Borrelia recurrentis is spread by what vector?
Body lice
Epidemic relapsing fever
Stain to ID Borrelia
Giemsa and Wright stain
What vector transmits the pathogen responisble for endemic relapsing fever?
Soft-bodied ticks (quickly feed ~20 min)
Transmits Borrelia hermsii (and other Borrelia sp. responsible for endemic relapsing fever)
What Borrelia infection occurs most commonly in the US?
Endemic relapsing fever
Borrelia recurrentis is responsible for epidemic relapsing fever (the other relapsing fever, more severe disease)
Incubation of relapsing fever
Borrelia = infectious organism
Vector for Rikettsia prowlezecki
Body lice
Epidemic typhus
On July 30, a 54-year-old man became ill with fever, headache, arthralgia, myalgia, and nausea while vacationing at the Wild Horse Island, Montana. Two days later he visited the emergency room of a local hospital, but a diagnosis was not made. Over the next several days he improved, and on August 6, he and his family began driving back to their home in Seattle, Washington. During the trip, he experienced another febrile episode. That evening, he was taken to the emergency room of a Seattle hospital where he was diagnosed with relapsing fever. Which of the following was likely the source of his infection?
Relapsing fever caused by Borrelia and transmitted by a soft-bodied tick
Soft-bodied ticks located in the western US
Distrubition, vector, and resevoir of Yersinia pestis in US
Vector = rodent fleas
Resevoir = prairie dogs (gophers) in US and rodents
Yersinia pestis - pre-inflammatory vs. inflammatory stages
Virulence factors of Yersinia pestis
-Plasminogen activator protease
-Type III secretion
-Lipid A modification
-Protein capsule
-Environmental sensing and regulation of virulence
Clinical presentations of Yersinia pestis
B. Disruption of protein synthesis by binding to the 30S ribosomal subunit
MOA of aminoglycosides (i.e. gentamicin)
Highest burden of typhoid fever is endemic to?
India Subcontinent
China
SE Asia
Africa
Virulence of Salmonella typhi
Pathogenesis of Salmonella typhi
Rose spots are characteristic of what type of bacterial infection?
Salmonella typhi - rose spots (groups of blanching papules on abdomen and sometimes posterior neck)
C. Ingestion of contaminated food
Typhoid fever caused by Salmonella typhi
C. Ehrlichia chafeensis
In Anaplasma - morulea are present in neutrophils and other granulocytes
