Streptococcus Flashcards
What are the general characteristics of the Streptococcus genus?
What tests would you run to detemin species level?
- gram positive cocci in pairs or chains
- facultative and capnophilic (like CO2)
- Fastidious species – complex nutritional needs
- Species level tests
- Serology (Lancefield A-W)
- Hemolysis
- Biochemical/physiological properties
Where are colonies of S. pyogenes found?
What diseases are caused by S. pyogene?
- Colonies
- asymptomatic URT and transient skin colonization
- person to person spread by respiratory droplets
- crowded facilities
- Diseases
- Superficiel
- pharyngitis (5-5 yr olds)– winer
- lasts 1-4 days (comp. = rheumatic fever/glomerulonephritis)
- pyoderma (2-5 yr olds)– summer
- erysipelas (St. Anthony’s fire)
- pharyngitis (5-5 yr olds)– winer
- Deep Tissue
- cellulitis
- necrotizing fasciitis
- Toxin mediated
- TSS
- Scarlet fever
- Immunological
- rheumatic fever (+RF/AGN) in resource poor countries
- glomerulonephritis
- Superficiel
What are two important aspects of S. pyogenes cell wall?
- Hyalluronic acid capsule
- antiphagocytic (prevents being recognized by immune system)
- M protein
- binds to plasma fibrinogen – prevents complement activation adn opsonization
- neutralized by M-protein antibody
- only for that specific serotype
What disease is present in the image?
What is the likely bacterial cause?
How could you distinguish between viral or bacterial cause?
Pharyngitis (Strep Throat)
S. pyogenes
- if viral, would also expect conjunctivitis
- severe bacterial: swollen pharyngeal mucosa w/ exudate
- peritonsillar or retropharyngeal abscesses
What disease is shown in the image provide? What is the likely bacterial cause?
Red/furred tongue
Rash initially on upper chest, spreads to extremities
disappears in 5-7 days follwed by desquamation
- Scarlet Fever
- S. pyogenes
- caused by 3 toxins: streptococcal pyrogenic exotoxins A, B, C
- –> spread through blood and localize on skin
What disease is shown in the image provided?
What are the likely bacterial causes?
Usually present on face or legs– introduced from minor trauma (scratch)
Progression is from vesicles –> pustules –> rupture & crust over
not painful and patients don’t feel ill
Streptococcal impetigo/pyoderma
S. pyogenes and S. aureus (major b/c antibiotic resistance)
What disease is indicated in the image shown?
Infection involving skin and subcutaneous tissue
What is often the cause of this disease?
cellulitis
due to traumatic/surgical wound, insect bite
often no entry site is apparent
S. pyogenes
What disease is indicated in the image shown?
Ususally on the malar areas of the face– “butterfly rash” bright & red appearance of the skin
Erysipelas
severe form of cellulitis
S. pyogenes
What disease is shown in the image provided?
Starts like cellulitis –> bulleas, gangrene & systemic signs
obstructed blood supply along fascial planes
What is the treatment?
Necrotizing fasciitis (hemolytic streptococcal gangrene)
S. pyogenes (60% cases)
requires extensive debridement and antibiotic treatment
What disease is characterized by fever, malaise, HT and multiple organ failure?
What bacteria is probably responsible for this disease?
Streptococcal Toxic Shock Syndrome:
can also cause pharyngitis (rare), cellulitis (some), NF (always)
streptococal pyrogenic exotoxins = super-antigens
How could you differentiate between cellulitis and erysipelas?
Erysipelas often presents on the face
Also, erysipelas usually has a clear boundary between diseased skin and non-diseased skin that is not present in cellulitis
What disease is characterized by inflammatory changes in the heart, joints, S/C tissue 1-3 weeks after pharyngitis
What bacterial is likely responsible?
What protein is the cause of this specific reaction?
What are the 4 human proteins targeted by this disease?
Acute rheumatic fever (ARF) & rheumatic heart disease (RHD)
Streptococcal pyogenes (rich in M proteins)
M protein antibodies cross-react w/ host tissue proteins
Targets: myosin, tropomyosin, laminin, and keratin
What disease is characterized by acute inflammation, hypertension, hematuria and proteinuria seen after pharyngitis or skin infections?
What bacteria is likely responsible?
What is the physiologic cause of this disease?
Acute glomerulonephritis (AGN)
Streptococcal pyogenes
Ag-Ab complexes on glomerular basement membrane
glomerular capillaries are filled with monocytes adn PMNs
How can you identify Streptococcal pyogenes?
Hemolytic?
Gram stain shape?
catalase?
A disc?
PYR test?
growth requirement?
- beta-hemolytic,
- gram positive (purple) chains of cocci
- catalase negative
- bacitracin (A disc) sensitive
- Positive PYR test (turns disk pink) (only streptococci that is positive)
- requires enriched medium (blood/serum)
What are the following test results for Streptococcus agalactiae?
catalase?
hemolysis?
gram stain shape?
group?
A disk (bacitracin)?
CAMP test?
Hydrolysis of bile esculin?
Hydrolysis of sodium hippurate?
location?
- catalase (-)
- beta-hemolysis
- gram positive in cocci chains
- group B
- A disk (bacitracin) resistant
- CAMP test (positive)- causes synergistic hemolysis with S. aureus
- Hydrolysis of bile esculin (negative)
- Hydrolysis of sodium hippurate (positive)
- location
- native to female urogenital tract & rectum
- babies acquire from mother or babies in nursery
Why is it dangerous for a pregnant woman to have genital colonization of S. agalacitae?
- genital coonization increases risk of premature birth
- premature infants are at greater risk of disease
- Since newborns do not have anticapsular antibodies, they are at risk for contracting a more serious disease
- major cause neonatal meningitis
Aside from pregnant women, what population is most susceptible to infections caused by S. agalactia?
What types of diseases does it cause?
immunocompromised
bacteremia, pneumonia, bone,skin & soft tissue infections
What bacteria is often responsible for UTI during and after pregnancy as well as chorioamnionitis and puerperal sepsis (serious septicemia after childbirth)?
S. agalactiae
What bacteria is responsile for bacteremia, pneumonia and meningitis in newblorns?
How is it acquired?
Why are they particularly susceptible?
S. agalactiae
major cause of neonatal meningitis
acquired by aspiration of infected amniotic fluid
they have few alveolar macrophages, poor neutrophils chemotaxis and phagocytosis
What steps can be taken to prevent S. agalctiae diseases?
- screen anogenital at 35-37 weeks pregnancy
- chemoprophylaxis culture for positive cases
- for women w/ history childbirth & GBS disease
- chemoprophylaxis regardless
What are th 5 groups of viridan Streptococci? Why are they named viridan?
Where are they located?
- Mitis (includes S. peumoniae)
- Anginosus
- Salivarius
- Mutans
- Bovis
they are called viridans b/c they produces a green pigment on blood agar (alpha-hemolysis)
Found in oral cavity/URT
Which bacteria group are the most common cause of sub-acute endocarditis?
Viridan Streptococci
Important: S. mitis, S. mutans, S. salivarius, S. sanguis
How can you identify Streptococcal pneumoniae?
Gram stain?
catalase?
Bile soluble?
Growth requirement?
Response to CO2?
hemolysis?
Quellung reactin?
P disk (optochin?)
location?
- Sample
- pneumonia (sputum/blood)
- meningitis (CSF)
- OM (aspirate)
- urine (pneumonia/meningitis)
- gram positive coccus diplococci
- catalase (-)
- Yes, bile soluble (lysed)
- Requries blood/serum
- often capsulated, growth enhanced by CO2
- alpha-hemolysis on blood agar
- Quellung reaction (+) appear swollen
- P disk sensitive
- Location
- colonized nasopharynx (5-10% adult) (20-40% children)
- URT to midle ear, sinuses, meninges, lungs & blood
Which proteins are particularly important for Streptococcal pneumoniae pathology?
- IgA protease
- pneumolysin (Ply)
- kills ciliated epithelial cells & phagocytic cells
- helps in penetration through epithelium
- lysis causes edema, hemorrhage, bacterial growth
