8_Gram Positives iI Flashcards
What are the 3 key diseases caused by S. pneumoniae?
-
acute bacterial pneumonia
- part of normal nasopharyngeal flora (5-40%)
- major causative agent of pneumonia in the aged and immunocompromised patients
- Sxs: fever, cough with sputum, dull chest
-
otitis media
- middle ear infection
-
meningitis
- most common cause of meningitis
- Sxs: fever, neck pain, headache
What is the Lancefield grouping of S. penumoniae?
NONE! It’s a non-Lancefield pathogen
What is the S. pneumoniae vaccine?
(structure and serotypes)
- Pneumovax
- Structure is a polysaccharide capsule w/ multiple serotypes
- Capsular serotypes: some strains are more virulence than others
- Original vaccine was targeted against the 6 most virulent serotypes
multivalent vaccine:
define
- multivalence means it is directed against multiple serotypes;
- antigenic portion of the polysaccharide from each of the multiple serotypes is attached to a carrier so the vaccine can be directed against multiple serotypes
of the serotypes in the Streptococcus pneumoniae vaccine, which serotype is most virulent?
serotype 4 is more virulent than serotype 19A
Is S. pneumoniae competent?
What does this allow it to do?
- S. pneumoniae is naturally competent
- can take up DNA by transformation and –> incorporate the new DNA by RecA-mediated homologous recombination.
how are more virulent strains of S. pneumoniae able to escape a vaccine?
- Natural competence allows more virulent strains (such as serotype 4) –> to pick up the capsule from less virulent strains (such as serotype 19A).
- This allows them to escape the vaccine.
Why do we need 13- and 23-valent vaccines to combat the S. penumoniae bacteria?
- Because of natural competence and the ability of more virulent strains to pick up the capsule from less virulent strains
- Need the 13 and 23 valent vaccines to cover additional serotypes. (Pneumovax13 and Pneumovax23)
S. pneumoniae:
distinguishing features
- Gram-positive, lancet-shaped diplococci
- Catalase negative
- Quellung rxn (capsular swelling) – positive
GBS (Group B Streptococcus);
Streptotoccus agalactiae
location, frequency, transmission, sxs
- found in normal vaginal flora: 10-30% of women
- transmitted
- birth or by carrier or by contaminated materials
- newborns are sensitive due to underdeveloped normal flora
- Sxs may not develop until the infant goes home
- Therefore, pregnant women are screened and treated w/ Abx prior to birth
Diseases caused by Group B Streptoccocus, and sxs
(Streptococcus agalactiae)
- Neonatal Meningitis
- sxs: fever, lethargy, poor feeding, seizures
- can be cultured from CSF after lumbar puncture
- Neonatal Pneumonia
•cyanosis, tachypnea (rapid respiration), respiratory distress
- Post-partum Endometritis
Group B Streptococci (S. agalactiae):
distinguishing features
- Gram-positive cocci in short chains
- Found in CSF
- Systemic can be found in blood sample
- CAMP test positive
- CAMP factor enhances hemolysis caused by S. aureus hemolysins
What is the CAMP Test Positive?
- identify group B βeta-hemolytic streptococci (Streptococcus agalactiae) based on their formation of a substance (CAMP factor) that enlarges the area of hemolysis formed by the β-hemolysin elaborated from Staphylococcus aureus.
Which 2 genera are Group D Enterococci found in?
Group D Enterococci is a diverse group containing bacteria from 2 different genera:
- Enterococcus and
- Streptococcus
Enterococci:
location, diseases it can cause, and 2 examples
- Location: GI tract normal flora; nosocomial pathogens (aka found in the hospital and are Abx-resistant)
- Can cause:
- septicemia
- UTI
- endocarditis
- Ex. E. faecium, and E. faecalis
How are commensal bacteria converted to pathogens?
Virulence factors that are acquired from mobile genetic elements (plasmids, transposons, and PAIs- pathogenicity island) –> can convert the commensals to pathogens
What can result from antibiotic resistance?
Can lead to:
- multi-drug resistant strains (MDR)
- vancomycin resistance enterococci (VRE)
Enterococci (Group D):
distinguishing factors
- Enterococci
- Gram-positive cocci that often occur in singles, pairs (diplococci) or short chains
- Catalase negative
- PYR positive (Pyrrolidonyl Arylamidase (PYR) test)
- Grows in bile salts and 6.5% NaCl
Corynebacterium diphtheriae:
distinguishing factors
(shape, location, transmission)
- Gram-positive club-shaped rod
- does not disseminate but forms pseudomembrane in the back of the throat, including:
- fibrin
- leukocytes
- necrotic epithelial cells
- bacteria
Diphtheria toxin
(structure, function, and targets of the)
- Produced by C. Diphtheriae
- Structure
- AB toxin
- B subunit protective factor
- A subunit is ADP ribosylates Elongation Factor 2 (EF2) of the ribosome, inhibiting protein synthesis and killing the cell
- Targets
- heart cells –> arrhythmia, myocarditis
- nerve cells –> peripheral and cranial palsy
Listeria monocytogenes:
distinguishing factors
(structure, location, diseases caused)
- Gram-positice rod
- Grows intracellularly;
- Tx by:
- food borne illness (milk, soft cheeses, butter, and deli meats)
- spreads into blood stream –> to CNS
- Can cause:
- meningitis in fetus if mother ingests it (even if mother is asymptomatic)
- can cause meningitis is immunosuppressed patientsa and sometimes pregnant women
Define and describe the unique mechanism for:
spreading L. monocytogenes between eukaryotic cells
- “Host Cell Actin Polymerization”
- Process
- Internalin (surface protein found on L. monoctogenes) allows invasion
- Listeria lysin O (LLO) allows escape into the cytoplasm,
- then the bacteria polymerize host actin to move between eukaryotic cells
Spirochetes:
distinguishing characteristics
- Gram-negative bacteria
- too thin to see by light microscopy
- uses dark-field microscopy is commonly used.
Endoflagella:
define
- structure
- special flagella of the spirochetes;
- wound around their tiny cork-screw shape;
- these endoflagella together form what is called an axial filament
- location
- sits between outer membrane and peptidoglycan layer
what are the 3 genera that are pathogenic for man?
- Treponema (Syphilis)
- Borrelia (Relapsing fever and Lyme disease)
- Leptospira (Leptospirosis)
- Which bacteria causes Syphilis?
- How is it transmitted?
- Does the outer membrane have LPS?
- Treponema pallidum
- Usually sexually transmitted; causes a chronic illness
- The Treponema pallidum does NOT HAVE LPS in its outer membrane
sequential stages of:
Syphilus
- Inoculation by sexual contact
-
Primary syphilis
- chancre, which is a sore on the surface of the tongue - infectious
-
Secondary syphilis
- rash and mucocutaneous lesions - infectious
-
Latent syphilis
- no symptoms; relapses to secondary syphilis
-
Tertiary syphilis
- invasion into cardiac or nerve cells (brain)
Describe the step:
Primary Syphilis
- long incubation –>
- to a lesion that starts as a painless papule and forms an ulcer (chancre)
- contagious throughout entire period
Describe the step:
Secondary syphilis
- mucocutaneous lesions and rash
- very contagious
- 2-8 wks after primary chancre
- (the primary and secondary stages may overlap)
Describe the step:
Latent Syphilus
- asymptomatic
- can cycle back to secondary syphilis (relapse) until there are enough antibodies to prevent more relapses
- relapses becomes less severe with time
Describe the step:
Tertiary syphilis
- Affects the nervous and cardiovascular disease, most commonly
- Due to growth of spirochetes in the brain or heart disease
- occurs in untreated patients
CC: Congenital Syphilis
(effects, and sxs)
- Treponema pallidum passes the placenta to the fetus causing death or skeletal system defects
- Newborns will have mucosal patches which are infectious
What are the laboratory tests for Treponema pallidum?
- Diagnosed by darkfield microscopy, or
- fluorescent microscopy or by serology (especially in secondary syphilis)
Tx and prevention of syphilis
- Treatment: penicillin (usually)
- alternatives are tetracycline, doxycycline, and azithromycin
- Prevention:
- safe sex practices; all whoa re infected and their sexual contacts should be treated
Borrelia burgdorferi:
shape, seen with
- large spirochete; (lrgst in size of pathogenic spirochetes)
- can be seen w/ light microscope
- stained w/ Gram stain, Giemsa, or Wright stain
Which bacteria causes Lyme disease?
How is it transmitted? Sxs
- Borrelia burdorferi causes Lyme disease
- transmitted by the Deer tick (most common tick-transmitted disease)
- variety of sxs, affecting multiple body systems
describe the lifecycle of the Ixodes tick
- Deer tick (Ixodes scapularis) takes 2 years to mature
- 1st year - nymphs feeding on small mammals
- 2nd year - adults and feed on deer.
- In both cases the tick becomes infected with Borrelia burgdorferi when it feeds on small mammals (esp. white footed mice).
- Infected nymphs or adults can infect a person but it is usually a nymph (primary route).
First stage, Second stage, and Late stage of
Lyme disease
- First stage:
- nymphs are small ticks; people don’t usually remember being bitten
- develops bulls-eye rash (erythema migrans) at bite site
- sxs: fever, headache, myalgia, joint pain
- Second stage:
- days - months later; patient develops neurologic or cardiac abnormalities
- Late stage:
- arthritis in 2/3 untreated patients
Diagnosis and tratment for:
Lyme’s disease
Diagnosis
- usually based on hx and clinical observations
- Abx titers to B. bergdorferi can be confirmed by immunofluorescent assay or ELISA
- positive results can be confirmed by Western blot
Treatment
- Abx should be initiated as soon as possible
- Doxycycline and amoxicillin for tx
Prevention
- prevention is focused on preventing tick bites (clothing, insect repellents)
- check for ticks and remove immediately
