Bacterial blood infections Flashcards by Jacob Thorn

Basic characteristics of Rickettsia

-Obligate intracellular bacteria

Aerobic gram (-) rods

LPS has weak endotoxin activity

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Bacteria responsible for Rock Mountain spotted fever

Rickettsia rickettsii

Rickettsia parkeri (particularly in western US)

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Rickettsia in the typhus group

Rickettsia prowazekii

Rickettsia typhi

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How do Rickettsia escape the phagosome

Using phospholipase

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Where do Rickettsia grow/replicate

In the cytoplasm/nucleus

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How are Rickettsia energy parasites?

THey have transporters that exchange ADP for host ATP

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What Rickettsia lyse their host cell?

Members of the typhus group

R. prowazekii and R. typhi

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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

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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

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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)

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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

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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

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How does the spotted fever group of Rickettsia exit the cell?

Utilizing actin polymerization

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How does the typhus group of Rickettsia exit the host cell?

By lysing the cell

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Where does the RMSF rash present?

Petechial rash on the extrimities (includes soles and palms)

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Resevoir Rickettsia prowazekii

Humans

Vector in US is flying squirrel fleas

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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)

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Organism responsible for epidemic typhus

Rickettsia prowazekii

More severe disease than Rickettsia typhi

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What cells does Ehrlichia infect?

Monocytes and tissue phagocytes (including spleen, liver, and lymph nodes)

Disrupts monocytes Fx and regulation of the inflammatory response

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Anaplasma vector and resevoir

Vector = Ixodes ticks

Resevoir = small mammals

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Erlichia vector and resevoir

Vector = Amblyomma americanum (Lone star tick)

Resevoir = white-tailed deer

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What type of host cells does Erlicihia ewingii and Anaplasma phagocytophilum infection?

They intracellularly infect granulocytes

Pathology is related to macrophage activation

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What type of bacterial morphology is characteristic of Borrelia

Gram (-) spirochetes

Extracellular frank pathogen

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Organism responsible for epidemic relapsing fever

Borrelia recurrentis - louse-borne

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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 ## Footnote 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 ## Footnote 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 ## Footnote 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 ## Footnote 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 ## Footnote *Borrelia recurrentis* is responsible for epidemic relapsing fever (the other relapsing fever, more severe disease)

Incubation of relapsing fever

## Footnote 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 ## Footnote 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 ## Footnote Typhoid fever caused by *Salmonella typhi*

C. *Ehrlichia chafeensis* ## Footnote In *Anaplasma* - morulea are present in neutrophils and other granulocytes