Microbiology Flashcards by Karin Golob

What is an infection of the brain parenchyma called?

Encephalitis

Brain Abscess

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What is an infection of the meninges called?

meningitis

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What is an infection of the spinal cord tissue called?

myelitis

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What is the definition of meningitis?

Meningitis is an inflammation of meninges with exudative response in CSF

Infectious agents that can cause meningitis include:

bacteria

viruses

fungi

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What is the #1 cause of meningitis in the US? Out of the US?

USA: Streptococcus pneumoniae

Other: Haemophilus Influenzae Type b

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What are conditions that predispose patients to bacterial meningitis?

Age: very young or very old
Immunocompromised state
basal skull fracture
head trauma, post neurosurgery
cerebrospinal fluid shunt

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What are key steps in the development of bacterial meningitis?

Hematogenous delivery of bacteria to subarachnoid space
Host immune response
Edema
Increased intracranial pressure
Decreased cerebral blood flow
Damage, seizures, herniation

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What are the clincal presentations of bacterial meningitis?

Headache

Fever

Meningismus - Irritated meninges (i.e. stiff neck)

Altered sensorium

Kernig’s sign

Brudzinski’s sign

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What is Kernig’s sign?

positive when the thigh is bent at the hip and knee at 90 degree angles, and subsequent extension in the knee is painful (leading to resistance)

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What is Brudzinski’s neck sign?

appearance of involuntary lifting of the legs when lifting a patient’s head, while lying down

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What diagnostic laboratory tests suggest bacterial meningitis?

CSF findings:

WBC count >= 1000/mm3

Cell differential: Mostly PMNs

Protein: Mild to marked elevation

CSF-to-serum glucose ratio: Normal to marked decrease

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What are characteristics of Neisseria?

Gram (-) cocci in pairs

Oxidase +
(have cytochrome C oxidase)

Aerobic

Can multiply in microaerophilic conditions

Cultured on chocolate agar

Sugar reactions are completed to determine species

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What are key virulence factors of Neisseria meningitidis?

Capsule

Antiphagocytic: interfere with complement deposition and prevent C3b-mediated uptake

12 serogroups: Groups B and C most commonly meningitis in US

Lipooligosaccharide (LOS)

antibodies directed against capsular polysaccharide are bactericidal in the presence of complement

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What is Lipooligosaccharide (LOS)?

toxic properties of N. meningitidis that is made up of an inner and outer saccharide layer and Lipid A

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How does Neisseria meningitidis present clinically?

Asymptomatic pharyngeal carriers
Meningococcemia: meningococci in blood

May occur with or without:

*- Petechiae and/or purpura**
Waterhouse-Friderichsen syndrome
*- Meningitis**
Chronic recurring meningococcal disease

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What is Waterhouse-Friderichsen syndrome?

Present in Neisseria meningitidis infection, caused by LOS, presents with:

Shock

Disseminated Intravascular Coagulation (DIC)

bilateral destruction of adrenal glands

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What vaccinations are used against Neisseria meningitidis?

Tetravalent conjugate vaccine called MCV4:

contains capsular polysaccharide from A, C, Y, and W135

each conjugated to diphtheria toxoid

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Why is group B neisseria meningitidis not included in the vaccine if it is one of most common causes of meningitis?

Vaccines against B don’t work b/c of molecular mimicry

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What is the most common cause of neonatal meningitis?

Group B streptococci

“B” is for Baby

E. Coli

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What are characteristics of Group B strep?

Gram (+) cocci

Catalase (-)

beta hemolyti

bacitracin insensitive

Group B-specific cell wall antigen

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How is neonatal Group B strep infections prevented?

Prophylactic penicillin G i.v. during labor (ampicillin alternative) to women at risk of delivering a baby with group B strep infection (i.e. Group B strep in vaginal flora)

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What are properties of Listeria monocytogenes?

Gm (+) rod

Aerobic

Grows at cold temperatures

widely distributed in nature

Typically a food-borne pathogen

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What are the virulence factors of L. monocytogenes?

Facultative intracellular pathogen

Produces Listerolysin (LLO)

After bacteria escapes phagosome, organism multiplies in cytoplasm and moves within cell by mechanism that involves host actin polymerization

Bacteria spread directly from cell to cell without re-entering extracellular space

What is listerolysin?

Toxin produced by L. monocytogenes that promotes release of the bacteria from phagosomes into the cytoplasm

responsible for teh hemolytic phenotype of L. monocytogenes on blood agar plates

What are the major causes of bacterial meningitis in newborns?

**Group B strep** E. coli Listeria monocytogenes

What are the major causes of bacterial meningitis in infants?

Neisseria meningitidis Haemophilus influenzae Streptococcus pneumoniae

What are the major causes of bacterial meningitis in children and teens?

N. meningitidis S. pneumoniae

What are the major causes of bacterial meningitis in adults?

S. pneumoniae N. meningitidis Mycobacteria

What are clinical manifestations of **viral** meningitis?

- Pathophysiologic - Fever, **vomiting**, **headache**, **nuchal rigidity**, and **photophobia** - WBCs: **2-2000/mm3** - Protein: **near normal** - Gram stain: nothing - Culture: negative (Note: bacterial meningitis does not regularly include the vomiting)

What are diagnostic measures of viral meningitis?

**CSF IgM titers** and **PCR techniques** - Presence of pathogen-specific IgG in CSF at levels similar or higher than serum

What are clinical manifestations of viral encephalitis?

Fever Headache alterations in conciousness confusion seizures paralysis changes in sensation or vision

What are examples of viruses that can lead to encephalitis (direct infection with killing of neural cells)?

**Herpes (HSV):** can cause hemorrhagic necrosis w/inflammation and neuronophagia **Poliovirus****:** specific destruction of motor neurons in spinal cord and brainstem **Rabies:** infect and destroy neurons

What are characteristics of Picornaviruses?

- Icosahedral symmetry (2, 3, 5 fold sym.) - non enveloped ssRNA (+) sense RNA is infectious (example: poliovirus)

How is poliovirus spread?

- through sewage contaminated water - virus is very stable

What are characteristics of poliovirus?

- a **picornavirus** - **3 serotypes (1, 2, and 3)** but no common antigen - Humans are only susceptible hosts

Name two paramyxovirus systemic infections

Measels Mumps

What are the three paramyxovirus encephalities?

acute disseminated encephalomyelitis (ADEM) measles inclusion body encephalitis (MIBE) subacute sclerosing panencephalitis (SSPE)

What are Koplick's spots?

a prodromic viral enanthem of measles manifesting two days before the measles rash itself

What are the characteristics of a paramyxovirus?

Negative sense RNA Enveloped

What are the characteristics of the rabies virus?

Rhabdovirus Bullet shaped (think werewolf silver bullet) Enveloped Negative sense ssRNA Neronal infection

Three steps to rabies treatment are:

Wash bite area Inject rabies immunoglobin Vaccinate (killed vaccine)

Pathologically what is used to diagnose a rabies infected brain (postmordem)

Negri bodies: eosinopholic cytoplasmic inclusion bodies DFA staining

What are the arboviruses and which families cause encephalitis?

**Ar**thropod vector**bo**rne viruses Show seasonality (summer) Flavavirus Togavirus (alphavirus) Bunyavirus

What types of encephalitis do flavavirus cause?

West Nile St. Louis Japanese

What are the flavaviruses and what are their symptoms and how are they diagnosed?

West Nile, St. Louis, Japanese Sudden onset Most subclinical Mild: Fever, malaise, nausea and vomiting, headache Severe: fever, weakness, widely distributed rash Neurological: myelytis, ataxia, seizures, optic neuritis, altered metal status ELISA for IgM in serum or CSF

What are the Togaviruses, what are their symptoms and how are they diagnosed?

WEE, VEE, EEE Flu-like symptoms that progress to encephalitis 3-10 days post infection. Generally resolves w/o sequelae.

What demographic is at the highest risk for West Nile Virus infection?

Old people who garden or spend a lot of time outside.

What are the bunyaviruses that cause encephalitis? Who are the most likely victims?

LaCrosse Virus Most common cause of pediatric arbovirus encephalitis in the US.

What herpes viruses cause encephalitis and in what age groups?

HSV-1 (adults) HSV-2 (infants) CMV (infants and immunesuppresed)

What is the worst kind of viral encephalitis and what are it's symptoms?

HSV 30-70% fatality rate Sx include: hallucinations, seizures, personality changes and aphasia

What drugs do you use to treat HSV encephalitis?

Acyclovir Gancyclovir

What causes Progressive Multifocal Leukoencephalopathy?

Reactivation of a polyomavirus in the immunosuppressed JC virus

What is the pathophysiology of Progressive Multifocal Leukoencephalopathy?

Widespread foci of demyelination in the brain. Leisions are round and become larger and more confluent with time. The subcortical white matter is affected first then the underlying white matter.

In what species did transmissible spongeform encephalopathies evolve?

Sheep

What are the three forms of transmissible spongiform encephalopathies in humans?

Kuru (canibalism) Creutzfeld-Jacob Familial Neurogenic Syndromes

What are the familial neurogenic syndromes and what causes them?

PrP gene mutations Gerstmann-Straussler-Scheinker Syndrome Familial Fatal Insomnia Atypical Dementia Spastic Paraparesis with Dementia

What causes Merkel Cell Cancer?

Merkle Cell Polyoma virus