Streptococci Flashcards
T/F: Streptococci are obligate anaerobes
FALSE - All strep are FACULATIVE ANAEROBES
All Streptococci are GM ___ cocci in ______ (arrangement).
Gm + in CHAINS
Streptococci are catalase ______
Negative
Group A Streptococci are also referred to as:
Streptococcus Pyogenes
Group A strep are classified as ____-Hemolytic, which means:
Beta hemolytic, means that they completely lyse red cells or produce a large clear zone on blood agar
the beta hemolytic streptococci are classified into groups A - O based on _________ _____________. *Bonus, which one is an ‘exception’.
They are classified based on complex carbs of the cell wall that act as antigen. Group D is an exception because it is NOT Beta hemolytic. Remember, Group A = Strep Pyogenes
Group A strep a further subdivided based on what feature?
They are divided based on immunological analysis of their M PROTEIN, of which there are 90+ serotypes.
M Protein appears on the surface of the bacteria.
Group A strep are transmitted by __________ and a (small/large) inoculum is required to infect
Respiratory droplets; a large inoculum is required. 5-10% of ppl carry strep pyogenes in nasopharynx
What are streptolysins and what do they do?
These are hemolytic enzymes that cause the beta hemolysis of Group A Strep
Streptolysin O:
an Oxygen-labile streptolysin that can induce anti-streptolysin-O antibody titers; these titers can be used in diagnosis
Streptolysin S:
A poorly antigenic streptolysin that is stable in oxygen
Streptokinase:
An enzyme that triggers blood proteolysis that DESTROYS FIBRIN CLOTS
What 2 factors contribute to Strep pyogenes ANTIPHAGOCYTIC activity?
- Hyaluronic acid capsule - without this they would not be pathogenic!
- M Proteins - more M protein = less phagocytosis. Also, Ab against an M protein = immunity to that strain.
What are SpeA SpeB and SpeC, and what two clinical presentations are they responsible for
These are proteases produced by Strep Pyogenes. They are also considered EXOTOXINs which can act as SUPERANTIGENS.
They cause:
1. The rash of Scarlet Fever
2. Streptococcal Toxic Shock Syndrome
5 invasive syndromes caused by strep pyogenes are:
- Puerperal fever - infected uterus at birth, now uncommon
- Acute pharyngitis/tonsilitis - fever, h/a, chills…treat soon to prevent rhematic fever
- Impetigo - superficial skin infection, infected via lesion
- Erysipelas - severe Cellulitis of dermis + underlying tissue
- Necrotizing Fasciitis - highly invasive strain produces a rapidly progressing destructive infection.
Rheumatic fever might occur _____ week(s) after an untreated strep infection; Acute glomerulonephritis might occur ___ week(s) later
Rheumatic fever - 2-3 weeks after strep throat
Glomerulo - 1 week after skin isolate infections
T/F: Penicillin resistance is never a problem with Streptococcus Pyogenes
TRUE! All Strep pyogenes are penicillin sensitive!!!
T/F: Group A strep are sensitive to bacitracin
TRUE. Strep pyogenes are Bacitracin sensitive!
T/F: Group B strep have Beta hemolysin
TRUE, but it is known to have a smaller zone of hemolysis than Group A
T/F: Group B strep are sensitive to Bacitracin
FALSE. Group B strep are resistant to bacitracin
What group of streptococci (A-O) does Strep. Agalactiae belong to ?
Group B
Group B strep can be part of the ______ or _______ normal flora
Vaginal or Colonic
Two patterns of Group B strep infection:
- Early onset - infection of bay @ birth from vaginal canal -> septicaemia, meningitis, pneumonia, death
- Late onset disease - infant to infant spread, has lower mortality
Why a re neonattes more susceptible to group B strep @ birth>
Lack of maternal Ab
Treatment for Group B strep infection:
PENICILLIN
Group D streptococci are also called:
Entercoccus
You have a streptococcus that can grow in 6.5% NaCl, what species is it likely to be?
Enterococcus faecalis or faecium; enterococci are the only strep that can grow in that conc.
Treatment for enterococcus:
Because they are resistant to so many antibiotics, VANCOMYCIN is best; however many strains are becoming resistant to Vancomycin.
What clinical syndromes are caused by entereococci
UTI, wound infection, sepsis. Especially in ELDERLY
Viridans Strep are ____ hemolytic
ALPHA
The species Strep Mutans and Strep sanguis are what from what family
Viridans (alpha hemolytic strep)
Viridans strep are normal inhabitants of:
mouth, nose, pharynx
Alpha-hemolytic streptococci are a frequent cause of what syndrome?
INFECTIVE ENNDOCARDITIS -> even minor oral trauma from chewing can produce a transient bacteremia -> cocci in blood may adhere to lesion on endocardium, typically a valve, to form a VEGETATION
You see a GM + lancet shaped diplococci on a culture; what species is it likely to be?
Streptococcus Pneumoniae (Pneumococcus)
the QUELLLING reaction can be useful to identify the capsule of what bacterial species
Neisseria
Pneumococcus produces what protease that aids in its pathogenicity?
an IgA protease, which degrades the IgA on the respiratory epithelium, reducing the chances of opsonization and phagocytosis.
T/F: pneumococcal pneumonia is the most common form of bacterial pneumonia
TRUE; it has a 5-20% fatality rate even when treated. bacteremia in 10-20% of cases
How to treat strep pneumoniae:
SENSITIVITY TESTING REQUIRED; unlike strep pyogenes, multiple antibiotic resistance is frequent in this species.
What vaccines are available for pneumococcus, and who gets each one?
- Polysaccharide (23 serotype) - used for 65+ or as young as 2 if at risk for disease. This is a T CELL INDEPENDENT VACCINE (poor booster response)
- Conjugated (13 serotype) - for peds, is conjugated to Diptheria => causes a T CELL IMMUNE RESPONSE. can prevent pneumococcal meningitis
Listeria Monocytogenes is a gm ___ ____, ____-hemolytic, and non/motile.
Listeria is a GM + ROD that is MOTILE.
There is a risk of _____ contamination by Listeria Monocytogenes because
Food conmination common because it can grow at low temps
Listera is commonly found in _____ and _____.
It is often transmitted ____ to human.
Soil and Water
animal to human txn. (Dairy, meat)
Describe the pathogenesis of listeria in 4 basic steps:
- Invades mononuclear phagocytes
- grown intracellularly
- moves between host cells via actin filament propulsion
- escape from phagosome by secretion of cytolysin, listeriolysin O
Clinical syndromes of L. Monocytogenes include:
Adult infection w/ meningitis, septicemia, and gastroenteritis
20% fatality rate
Prevent L. monocytogenes infection by:
avioding raw milk and unprocessed cheese, especially in IMMUNOCOMPRIMISED.
Drink pasturized milk
Anthrax Bacillus is a GM ___ _____
GM + rod
Anthrax bacillus is A/Anaerobic and can/cant form spores
IS AEROBIC and Spore forming
Typical anthrax transmission is:
ANIMAL TO ANIMAL.
Humans are an accidental rare exception
Name 3 pathways to human transmission (from animal) for anthrax bacillus
- Cutaneus
- inhalation
- Intestional
The pathogenicity of anthrax is due to what 3 factors
2 exotoxins and 1 protein:
- Protective antigen
- Edema Factor
- Lethal Factor
Function of anthrax’s ‘protective antigen’
facilitates entry of exotoxins into host. Ab against this protein would be protective
Function of anthrax’s ‘edema factor’
Adenylate cyclase that enters host cells and is activated by calmodulin
Function of anthrax’s ‘lethal factor’
disrupts signal transduction for cell division
clinical syndrome of Cutaneus anthrax
caused by contaminatin for skin by spores. Lesions produce black scab (eschar). untreated may lead to bacteremia.
LEAST SERIOUS PRESENTATION
Clinical syndrome of inhaled anthrax
Caused by inhaled spores. Happens in 3rd world to wool-sorters. Inhaled spores are phagocytsed by Macrophage -> spores germinate in regional lymph nodes -> MEDIASTINAL LYMPH NODE ENLARGEMENT. RAPIDLY FATAL if untreated.
Anthrax prevention
Crude vaccine with B. Anthracis proteins for at risk populations.
Treatment for anthrax poisoning
Ciprofloxacin, tetracycline, penicillin
