Micro: Bacterial Infections of CNS Flashcards
Describe Neisseria meningitidis bacteriology
- Gram (-) diplococci, facultative intracellular
- Human restricted
- Encapsulated
- ~13 serotypes
- Oxidase +, catalase +
- Ferments glucose and maltose, NOT sucrose or lactose
- Grows on chocolate agar or Thayer Martin, NOT blood agar
Pathogenesis of Neisseria meningitidis
- Airborne droplets
- Colonizes nasopharynx
- Spread + colonization can be enhanced by concomitant URI
- Often resolves w/o symptoms, IgG-enhanced complement and neutrophils defend, leaving lifelong immunity to infecting strain
What are the 3 ways N. meningitidis can affect you?
- Enters bloodstream –> meningococcemia
- Colonizes joints –> septic arthritis
- Colonizes meninges –> meningitis, fatal if untreated
Virulence factors of Meningococci
- IgA protease - cleaves IgA, reduces defense of mucus membrane
- Polysaccharide capsule - resists phagocytosis
- Endotoxin LOS - causes fever, shock
Exam findings for N. meningitidis septic arthritis and meningitis
1/3 cases adult, 2/3 peds
Septic arthritis: joint pain –> draw joint fluid
Meningitis: Adults - fever, headache, stiff neck, coma
Kids: irritability, convulsions, lassitude, fever, abd discomfort/vomiting
Both: CSF tap + admit
Exam findings for N. meningitidis meningococcemia
Fever, hourly-spreading petechial skin rash –> draw blood + CSF, admit to ICU
- 5-15% develop Waterhouse Friderichen syndrome (fatal)
Waterhouse-Friderichen syndrome
- A fatal complication of meningococcemia
- High fever, shock, widespread purpura, DIC, thrombocytopenia, destruction of adrenal glands
Labs for septic arthritis, meningitis, and meningococcemia
Septic arthritis: gram stain and culture joint fluid on chocolate agar
Meningitis: CSF- increased PMNs, Gram stain and culture on chocolate agar. Gram (-) cocci in CSF sufficient for diagnosis. Alt latex agglutination test for capsule polysaccharide in CSF
Meningococcemia: blood - gram stain and culture on chocolate agar, test for DIC
How can you differentiate N. meningitidis from N. gonorrheae?
Only meningococci ferment maltose
- alt, IF
N. Meningitidis treatment
Penicillin G
Alt. Ceftriaxone, cefotaxime, cefuroxime, chloramphenicol
- Prescribing glucocorticosteroids for rash and arthritis is VERY BAD
Prevention of N. meningitidis
- close contacts of patient zero get prophylactic rifampin, ceftriaxone, or ciprofloxacin
- vaccines recommended: travelers, college, 11-12 y/os
Group B strep bacteriology
S. agalactiae
- encapsulated Gram + cocci
- B-hemolytic
- polysaccharide toxin virulence factor
- pilus-like attachment virulence factor
- serotype-specific Ab-mediated immunity
- Normal vag flora, transmits to bb before and during delivery
- Can also be normal flora in GI, upper respiratory tract
Besides neonates, what is another risk group for GBS?
Geriatrics w/ predispositions (diabetes, malignancy, CHF)
GBS exam
Patient presents with pain, fever, symptoms specific to site
Meningitis: spinal tap for Gram + cocci in pairs or small chains
Cellulitis/abscess: Gram stain, culture appropriate fluid. CT/MRI for deep abscess
ECG for endocarditis
GBS labs
CAMP test: CAMP factor secreted by GBS, enhances activity of B-hemolysin from S. aureus
Hippurase/Hippurate test: colorimetric test for hippurase, produced by GBS (and others)
GBS treatment
IV penicillin or amoxicillin
- vanc if allergic
- surgical intervention if necessary
Pneuomococcus Bacteriology
Strep pneumoniae
- Gram +, catalase (-), alpha hemolytic, facultative anaerobe
- Form diploccoci in chains on culture
- Pathogenic strains are encapsulated
- MCC of community acquired pneumonia, bacterial meningitis, bacteremia, otitis media. Causes lots of other shit too, kills many children worldwide
Pneumococcus Pathogenesis
- colonizes upper resp tract w/ adhesion virulence factors
- infections peak in Fall and Winter
- contained by innate immunity in healthy people, in kids or people with lung issues or immunosupression, bacteria spreads
- CAPSULE is major virulence factor, but also has: IgA protease, teichoic acid
What are the 2 types of pneumococcal disease?
- direct extension: sinuses, bronchi, eustachian tubes
- hematogenous spread: blood, joint fluid, peritoneum, CSF
- capsule protective against phagocytosis UNLESS anti-capsule IgG is present
- pathogenic strains all contain pneumolysin, some have hemolysin, neuraminidase, hyaluronidase
- infection raises STRONG INFLAMMATORY RESPONSE
Pneumococcus exam for diseases of direct extension
- sinusitis, otitis media, bronchitis, pneumonia
-pneumonia kills 10-20% - patient looks ill and anxious
- predispositions: asthma, COPD, chronic bronchitis, smoking/secondhand smoke
Radiology: adolescents and adults -> lobar consolidation
infants + little kids -> scattered consolidation, bronchopneumonia
Pneumococcus exam for hematogenous spread
-meningitis, septic arthritis, pericarditis, endocarditis, osteomyelitis
- bimodal distribution (under 5, older than 65) + immunosuppressed
Meningitis: mental status changes, lethargy, delirium, Brudzinski +, cranial nerve palsies, focal neuro defects
Labs for non-invasive, invasive pneumococcus
Non-invasive: can be treated based on exam, optional gram stain
Invasive: Gram stain and culture
- antibiotics sensitivity testing
- urine antigen testing useful in pneumonia in young kids who don’t produce enough sputum
Typical spinal tap findings in BACTERIAL MENINGITIS
- elevated opening pressure
- elevated WBC and neutrophils
- elevated protein
- decreased glucose
- highly elevated lactic acid
- Gram stain and culture + unless abx started >4 hrs prior to tap
Pneumococcus treatment (noninvasive)
Severe pneumonia: admit, vancomycin
If less than severe pneumonia: amocixillin or cephalosporin, fluoroquinolones or doxy for adults only. outpatient.
Pneumococcus treatment (invasive)
Admit, start abx, start cultures, do abx susceptibility tests on cultures
- initial abx are vancomycin + ceftriaxone or cefotaxime
- if tests come back resistant, add rifampin, meropenem, or chloramphenicol
- steroids can be used w/ caution in addition to abx, early in abx course
- cellulitis, septic arthritis -> surgery
Pneumococcus prevention
- Prevnar7 vaccine –> raises protective IgG against capsules of 7 serotypes most commonly caused invasive disease prior to 2000
- Prevnar13: added 6 newly problematic serotypes
