Microbiology-Bacterial Meningitis Flashcards
What clinical signs will many patients with bacterial meningitis typically demonstrate?
Sudden onset of fever, headache and stiff neck. Kernig’s and Brudzinski’s signs: pain with the movements shown below. Altered mental status may also be a symptom.
What are the major causes of bacterial meningitis in the US?
1) Strep pneumoniae 2) Group B strep (in babies) 3) Neisseria 4) H. Influenze 5) Listeria
Why have rates of bacterial meningitis decreased recently in the US?
Development of the polyvalent conjugate strep pneumoniae vaccine that can be given to kids. The capsule is the primary virulence factor of strep pneumoniae is its capsule and the vaccine helps the body to make antibodies that will opsinize the bacteria for phagocytosis.
What demographics are most susceptible to bacterial meningitis?
Age (young and old), immunocompromised, basal skull fracture, head trauma, CSF shunts
What are the general steps in development of bacterial meningitis?
Hematogenous delivery of bacteria to subarachnoid space -> PMN infiltrate -> Edema -> Increased intracranial pressure -> Decreased cerebral blood flow -> Brain damage, seizures, herniation
What does normal CSF look like?
< 20 WBCs per mm3 in newborns
What does CSF look like in a patient with bacterial meningitis?
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You are working at the university health clinic during an outbreak of bacterial meningitis at the dorms. What lab characteristics of the offending bacteria would you expect to see in these patients?
In young people, the most common cause of bacterial meningitis is Neisseria. It is a gram-negative cocci in pairs, oxidase positive.
What are the main virulence factors of N. meningitidis?
Its capsule interferes with complement deposition and phagocytitic uptake. It also has IgA proteases.
What are the most common serogroups of N. meningitidis that cause infection in the US?
Types B and C. Type B does not have a vaccine because our body won’t make antibodies against it because it is similar to our normal flora E. Coli capsule.
What characteristic of N. meningitidis causes most tissue damage?
LOS (like LPS but shorter)
What is the most common source of infection of N. meningitidis?
The asymptomatic carrier in close quarters with other people (military barracks and dorms)
What is the clinical spectrum of meningococcemia (N. meningitidis in the blood)?
Petchiae/purpura, Waterhouse-Friderichsen syndrome (shock, DIC, destruction of adrenal glands), Meningitis and Chronic recurring meningococcal disease.
What genetic predisposition causes chronic recurring meningococcal disease?
People with deficiencies in the terminal parts of complement, this prevents lysis of the infecting bacteria
What N. meningitidis serotype causes epidemics in less developed nations and younger children?
Serogroup A
Where does L. monocytogenes like to grow? What would it look like in the lab?
Cold food reservoirs. In the lab it is gram + rod, catalase positive, beta hemolytic.
What factors contribute to listeria’s virulence?
LLO. It promotes release of bacteria from phagosomes into the cytoplasm. Listeria also moves from cell to cell without ever leaving the cell.
