streptococci Flashcards
(40 cards)
-Streptococci represent a diverse group of gram — organisms
- many normally colonise — membrane
1- prodominent component of ——
2- many of —- virulence
3- However may also invade normally sterile body sites, causing significant —-
- positive
- mucosal
- respiratory, gastrointestinal
and genital tract - low
- disease
streptococci : basic lab features:
1- they are gram – shaped — can either be: —- tr —-
2- Optimal growth media
supplemented with —-
- may cause —- on blood agar
3- catalase is —
4- most are —–
- positive
-cocci - can be chains either long or short or pair ( diplococci )
- blood
- haemolytic ( destruction of rbc )
- negative
- facultative anaerobes
(Some are strict (obligate) anaerobes)
classification of systems:
1- based of their actions on —–
2- based on — contained in their cell wall
3- —- classification based on emm gene ( codes for m protein )
- blood containing agar ( haemolytic )
- antigen ( lance field classification )
- molecular ( new)
true or false:
Some clinically important streptococci often referred to by both Lancefield group and haemolysis patter
true
streptococci:
—- : Reduce Hb and cause a greenish discolouration of blood agar
—- : Lyse blood cells & cause complete clearing of blood agar in the vicinity of their growth
—- : no change in blood agar
- alpha haemolytic
- beta haemolytic
- gamma haemolytic
lancefield classification is a — system of grouping streptococci based on specific —- present in their cell wall
groups — of most clinical siginifance
basis of tests:
- serological
- antigen
- A-G
- antibody/anitgen reaction , positive if angulation is detected
clinically important streptococci :
- Strep. pyogenes (Group A, beta-haemolytic)
- Strep. agalactiae (Group B, beta haemolytic)
- Other beta-haemolytic streptococci
- alpha-haemolytic streptococci
-“viridans” streptococci
- Strep. pneumoniae (pneumococcus) - Enterococci (Group D, beta or non-haemolytic)
- Peptostreptococcus (anaerobic or non-haemolytic)
-STREPTOCOCCUS PYOGENES are group — and — haemolytic streptococci
- commonly colonise — of children and young adults ( colonisation is —- , influenced by —- and competition from other — in orpharynx)
- among the — prevalent pf human bacterial pathogen
- major cause of:
- A
- beta
- propharnyx
- transients
- immunity
- organics
- most
- bacterial pharyngitis
( in Irish epidemiology the invasive group A strep is notifiable disease )
GROUP A, beta HAEMOLYTIC STREPTOCOCCI: VIRULENCE MECHANISMS
- virulence factors include
1- — components :
—- : resists pahogystocis
—- : peptidoglycan can activate alternative complement system
2- — proteins :
->80 types, mediate attachment to cells, anti-phagocytic
- Major virulence factors – some types associated with greater severity of disease
-the M-like proteins bind —-
3- —- :
* Streptolysin O/S
exotoxins
– ASOT titre
* Hyaluronidase
– Tissue destruction,
allowing spread of
infection
* Leucocidin
* Haemolysins
* Streptokinase
4- —— erthyrogenic exotoxins
- responsible for fever and rash
- protent activators of — ( toxic shock syndrome )
- activate of — to increase secretion of —-
- produced by — and —
- structural
- capsule
- cell wall
- m protein
- IgG/igM
- cytolysins
- pyrogenic
- immune system
- T cells
- pro inflammatory cytokines
- antigen presenting cells and t lymphocytes
( check slide 13 for summary )
clinical infections include :
1- suppuartive infection as:
2- post infectious immune mediated complication as:
- supportive :
1. Pharyngitis
2. Scarlet fever
3. Erysipelas, cellulitis, necrotising fasciitis
4. Toxic shock syndrome, bloodstream infection - post - infectious :
– Rheumatic fever* - May later develop rheumatic heart disease
– Glomerulonephritis
- STREPTOCOCCAL PHARYNGITIS:
1- One of the most common bacterial infections of —-
2- occasionally due to group —-or —
3- spread: —- and its facilitated by —
4- incubation period:
5- history:
- childhood
- c or g
- Person-to-person via droplets (saliva ornasal secretions)
- Facilitated by overcrowding
- 2-4 days
- sore throat , headaches , fever , nausea , vomiting especially in children
( on examination: - Redness, oedema,
lymphoid hyperplasia - Enlarged tonsils with
exudate, enlarged
tender lymph nodes - Fever
lab findings: - positive throat culture
- immunological
(antibody) response
(anti-streptolysin O
titre, ASOT)
Hyperaemic, enlarged tonsils
with exudate
complication of STREPTOCOCCAL PHARYNGITIS:
1- suppurative complication:
2- non suppurative (immunoligcal sequele) :
- main reason for antibiotic treatment is to —-
- suppurative:
– Quinsy – peritonsillar abscess
– Otitis media
– Acute mastoiditis - non- suppurative :
– Acute glomerulonephritis
– Acute rheumatic fever - to prevent rheumatic fever
Delayed-type skin reactivity to pyrogenic toxin produced by the
organism —–
—– may also occur following impetigo
- scarletina ( from scarlet fever )
- pharungitis + fever
- Impetigo
- Erysipelas
- Cellulitis
- Necrotising fasciitis
are all under —-
skin and soft tissue infection
other serious infection include;
1- streptococcal toxic shock sydrnom which causes inflammation in — followed by —-
- causes production of —
- progresses —-
2- —- infection and mortality reaches —
- soft tissue inflammation
- followed by pain fever , chills , multi organ failure
- pyrogenic exotoxin
- rapidly
- blood stream
- 40%
complication : RHEUMATIC
FEVER & GLOMERULONEPHRITIS
Post-streptococcal auto-immune complications
* Affect a minority of people who have group A streptococcal infection
* Immune reaction: Development of antibodies to some fraction of the organism
– In rheumatic fever: the antibodies cross-react with cardiac tissue → immune complex deposition on the heart
– In post-streptococcal glomerulonephritis: immune
complexes are deposited on the glomerular basement
membrane
– Molecular mimicry
acute rheunaric fever is associated w — but not —-
- occurs —- weeks later
- symomts include:
-with recover , affected heart valves become —–
- —- required if undergoing procedure
that may put patient at risk of endocarditis
- Diagnosis is based on the ——
- streptococcal pharyngitis
- streptococcal skin infections
- 203 weeks
- joint pain , fever , carditis , may also get neurological involvement (Syndenham’s chorea)
- thickened and deformed
- Antibiotic prophylaxis
- jones criteria
acute glomerulonephritis is associated w —- and sometimes with —-
- causes:
- —-
- majority of young patients recover —- but may lead to:
-streptococcal pharyngitis
-streptococcal skin infections
- oedema , puffy face , swollen extremities due to sodium and water retention
- hypertension w albumin and blood in urine
- competly may lead to:
* However, may lead to permanent renal damage
* May warrant lifelong dialysis or renal transplantation
* Or may be fatal
STREPTOCOCCUS AGALACTIAE:
- in group —
- – haemolytic streptococci
- colonises the — and —
- —– % women intermittent carry S. agalactiae in vagina
- may be carried in —-
- important cause of neonatal sepsis:
- b
- b
- lower gi and gu tract
- 10-40%
- throat
- Neonatal colonization usually occurs via the mother’s
genital tract - Risk factors:
- Maternal colonisation
- Premature delivery / Premature rupture of membranes
- Prolonged labour
- Low birth rate
- Intra-partum fever
GROUP B -HAEMOLYTIC STREPTOCOCCI:
VIRULENCE MECHANISMS
1- —- polysacride:
- different — based on capsular polysaccharides
2- types —– most commonly associated w colonisation and disease
3- —-
4- —
5 — proteins as–
- capsule
- serotypes
- la, III, v
- haemolysins
- hyalurindase
- surface proteins - adhesins
other b-haemolytic streptococci :
- can cause similar disses as — but without —- complications
1- group c streptococci :
2- group g streptocci :
- group a
- immunilogical
- group c:
- Puerperal fever
- Tonsillitis
- Wound sepsis
- group g:
- Upper respiratory tract infections
- Endocarditis
A.“viridans” streptococci
B. Streptococcus pneumoniae
(‘pneumococcus’)
are both under —-
alpha-HAEMOLYTIC STREPTOCOCCI
viridian streptococci:
1- are found in —
2- most lack — exception for s.bovis in group d
3- clinical infection includes several associations with —- and —
- and its invasive disease often related to breech in —
- — and —- are the commonest viridian strep has — and infective —-
4- —- for dental caries
5- — purulent infections as brain and liver abscesses
5- — linked to colon cancer and infective endocarditis
- Oropharynx, GIT & GU
tract - lance field antigens
- associated w dental caries and endocarditis
- mussel surfaces
- strep sangus and strep mitis
-tooth biofilm - infective endocaditis
- strep mutans
- strep. angiosus ( milleri )
- strep bovis
-s peneumiua is type of — haemolytic and gram – in the shape of – in chains or dipoloccocci
- carried in — by :
1—– of healthy adults
2- —- of healthy children
- it has a —- of more than 90 serotypes and – available against some serotypes
- variety of clincial infections
-alpha
- +ve
-cocci
- nasopharynx
- 5-10%
-20-40%
- vaccines
(info: Gram-positive diplococci, i.e.
Pneumococcus
(Humphreys, Willatts & Vincent)
CHEKC SLIDE 32 SOOO IMPORTANT )
