Microbiology Flashcards
What is an infection of the brain parenchyma called?
Encephalitis
or
Brain Abscess
What is an infection of the meninges called?
meningitis
What is an infection of the spinal cord tissue called?
myelitis
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
What is the #1 cause of meningitis in the US? Out of the US?
USA: Streptococcus pneumoniae
Other: Haemophilus Influenzae Type b
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
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
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
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)
What is Brudzinski’s neck sign?
appearance of involuntary lifting of the legs when lifting a patient’s head, while lying down
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
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
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
What is Lipooligosaccharide (LOS)?
toxic properties of N. meningitidis that is made up of an inner and outer saccharide layer and Lipid A
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
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
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
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
What is the most common cause of neonatal meningitis?
Group B streptococci
“B” is for Baby
E. Coli
What are characteristics of Group B strep?
Gram (+) cocci
Catalase (-)
beta hemolyti
bacitracin insensitive
Group B-specific cell wall antigen
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)
What are properties of Listeria monocytogenes?
Gm (+) rod
Aerobic
Grows at cold temperatures
widely distributed in nature
Typically a food-borne pathogen
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?
Arthropod vectorborne 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
