Streptococci Flashcards
What are some general characteristics of streptococci ?
- gram + cocci (single, pairs, and chains)
- occurs in pairs and chains microscopically
- facultative anaerobes
- catalase (-)
- normal flora of the skin, mucous membrane, mouth, pharynx and urogenital
- hemolytic reactions
What is alpha hemolysis ?
partial lysis of RBC
- greenish discoloration to agar
What is beta hemolysis ?
complete lysis of RBC
- clearing of the agar around colonies
What is gamma hemolysis ?
no lysis of RBC
- no change of the agar around the colonies
Which hemolysis have the biggest impact on human health ?
alpha & beta
What infections are caused by streptococcus pyogenes ?
- strep throat
- tonsilitis
- erysipelas (contagious skin infection)
- impetigo (around nose, mouth, extremities)
- septicemia (systemic infection in the blood)
- pneumonia (respiratory)
- necrotizing fasciitis (flesh eating bacteria)
What is the function of streptolysin O in strep. pyogenes ?
- SLO exotoxin (rare)
- oxygen labile (will destroy/inhibit O2)
- only will perform beta hemolysis in anaerobic conditions
What is the function of streptolysin S in strep. pyogenes ?
- SLS exotoxin (common)
- oxygen stable
- hemolysis occurs under aerobic or anaerobic conditions
What is the function of erythrogenic toxin in strep. pyogenes ?
rash of scarlet fever
- toxin is absorbed and carried by the blood
What is the function of streptokinase/fibrinolysin in strep. pyogenes ?
- breakdown of fibers
- helps organism to spread
What is the function of hyaluronidase in strep. pyogenes ?
breaks down hyaluronic acid which binds connective fibers
What is the function of exotoxins in strep. pyogenes ?
fever and shock
What is the strep bacteria that is a Group A streptococci ?
streptococcus pyogenes
- sensitive to bacitracin (won’t grow in it’s presence)
What is the significance of having post-streptococcal diseases ?
happen after having Strep A infection
- not the infection that causes the disease but it’s the antigen (antigen-antibody reaction)
- your immune system recognizes the antigen as Strep A (when it isn’t) and your body will start to attack the heart valves and glomerulus of the kidney because the antigen of group A resembles this
What are the 2 post-streptococcal diseases ?
- Rheumatic fever: 10-14 days after (joint issues, myocarditis) caused by the system attacking the heart valves
- Glomerulonephritis: caused by attack to glomerulus of the kidney (headache, increased BP, low grade fever, weight gain, facial/periorbital edema)
What is impetigo ?
one of the most common skin infections among kids
- staph aureus or strep pyogenes
- blisters or sores on face, neck, hands, and diaper area
What are some symptoms of scarlet fever ?
rash & tongue may have whitish coating and appear swollen
- reverse strawberry appearance
What are some morphology of Strep. pyogenes ?
- beta hemolytic
- Lancefield group A
- bacitracin sensitive (can’t grow in presence of antibiotic bacitracin)
What are some characteristics of Strep. agalactiae (group B strep) (GBS) ?
- normal flora especially in urogenital and oral cavity
- generally harmless and most don’t even know they have it
- about 25% found in pregnant women
- bacitracin& SXT resistant
What happens if a pregnant person has GBS (group B strep) ?
if tested (+) then they are given IV antibiotics during labor to kill the bacteria
- can’t be done before because it grows back quickly
What infections are caused by group B strep ?
- meningitis and/or septicemia in newborns
- infections in post-partum women
- female urogenital tract
- wound and skin infections
What is some morphology of group B strep ?
- beta hemolytic
- Lancefield Group B
- CAMP test (+)
What is the group B streptococci ?
streptococci agalactiae
What is Lancefield grouping ?
method of grouping catalase-negative & coagulase-negative bacteria based on carb composition of bacterial antigens found on their cell walls
What is the CAMP test ?
test to identify group B beta-streptococci based on their formation of a substance (CAMP factor) that enlarges the area of hemolysis formed by beta hemolysin from staph. aureus
- read at 24 hr mark
- make sure aureus and agalactiae don’t touch
- make a line of staph. aureus and do strep. agalactiae perpendicular to it
Is strep group A CAMP + or - ?
-
Is strep group B CAMP + or - ?
+
What are some general characteristics of Group D strep and enterococcus ?
- hemolytic reaction (can be alpha, beta, or gamma)
- gamma most isolated
- normal intestinal flora
- bile esculin +
What infections are caused by group D strep and enterococcus ?
- wounds
- endocarditis
- urinary tract infections
how can you differentiate enterococcus from streptococci ?
can tolerate wide range of temps (10-45) and high NaCl concentrations
How do you know if a species is a Vancomycin Resistant Enterococcus (VRE) ?
can grow in the vancomycin agar
- more common in nosocomial or hospital acquired infections
What are some characteristics of enterococcus ?
- 90% gamma hemolytic
- susceptibility to penicillin low (typically resistant)
- identify using: bile esculin +, 6.5% salt+ (growth occurs)
What is the bile esculin test ?
seeing if the species hydrolyze esculin to products that react with ferric citrate in the bile esculin agar medium to produce insoluble iron salts which results in the blackening of the medium
- if it turn black then (+)
- enterococci are bile esculin +
What are the group D streptococcus ?
- strep. bovis
- strep. equinus
- susceptible to penicillin (will work)
- Identification: bile esculin +, 6.5% NaCl (-) won’t grow in salt broth
What are the alpha hemolytic streptococcus ?
- pneumoniae
- viridans
What are the beta hemolytic streptococcus ?
- pyogenes
- agalactiae
What are the gamma hemolytic streptococcus ?
enterococcus
- E. faecalis
- E. faecium
What are the general characteristics of streptococcus pneumoniae
- gram (+) cocci in pairs (diplococci), slightly enlongated (lancet-shaped)
- common oropharyngeal (mouth and pharynx) flora
- need increased CO2 for better growth
- alpha hemolytic
- optochin sensitive
What are infections caused by strep. pneumoniae ?
- common cause of community acquired pneumonia
- meningitis
- septicemia
- pericarditis
- pleuritis
- otitis media
- sinusitis
How do we identify strep. pneumoniae ?
- alpha hemolysis
- lysed by bile salts (rarely used test)
- serological (latex coated beads-look for agglutination)
- optochin sensitive
What are some general characteristics of strep viridans ?
- normal flora of urogenital, mouth, nose, pharynx, skin
- not normally pathogenic (under certain circumstances)
- Ex.) bacterial endocarditis, streptococcus mutans (dental caries)
What is the clinically significant strep pyogenes infection ?
strep throat
What bacteria cause impetigo ?
Staph aureus or strep pyogenes
- common skin infection among kids (blisters/sores on face, neck, hands, diaper areas)
How do we differentiate between enterococcus and strep group D with a 6.5% NaCl (salt) test ?
- enterococcus can tolerate high salt concentrations while strep D can’t
