Cocci Flashcards
What are the 3 groups of cocci?
- Streptococcus (gram +)
- Staphlococcus (gram +)
- Neisseria (gram -)
Explain the gram staining procedure
- smear and fix sample onto glass slide
- stain with crystal violet (gram + will hold onto to this dye)
- treat with iodine to permanently lock crystal violet stain
- wash and decolorize with alcohol
- counter stain with safranin (gram - will stain safranin)
List the 5 species of Streptococcus
- Group A strep
- Group B strep
- Streptococcus pneumoniae (pneumococci)
- Viridians Streptococci
- Enterococci
List the 3 species of Staphylococcus
- Staph. aureus
- staph. epidermis
- staph. saprophyticus
List the 2 species of Neisseria
- Neisseria Meningitidis
2. Neisseria Gonorrhea
First step in differentiating the cocci
Gram staining will divide the 3 genuses into 2 groups: 1) gram positive -staph and strep; and 2) gram neg -neisseria
How to differentiate strep from staph?
Do a catalase test. Strep will test negative while Staph will test positive because Staph has catalase.
Which species of strep are alpha-hemolytic? What does alpha-hemolytic mean?
alpha-hemolytic means that the bacteria can partially lyse RBCs. Strep. pneumoniae and Viridians strep are part of this group.
How to differentiate btw the alpha-hemolytic strep?
Strep. pneumoniae will be sensitive to bile/optochin while viridians strep will be resistant to bile/optochin.
What species of strep are beta-hemolytic? What does it mean to be beta-hemolytic?
Bacteria that are beta-hemolytic can completely lyse RBCs showing up clear on agar plates. The two species that are beta-hemolytic are Group A and Group B strep.
How to differentiate btw the beta-hemolytic strep?
Group A is sensitive to bacitracin while Group B is not sensitive to bacitracin
There are also gamma-hemolytic strep. What does being gamma-hemolytic mean?
These bacteria cannot lyse RBCs and will appear red on blood agar plate b/c no change.
What is lancefield-typing used for?
Lancefield typing is a serotype method using antiserums to detect different streptococci
What are some of the virulence factors of Group A strep?
Group A strep is catalase neg, beta-hemolytic, bacitracins sensitive gram positive cocci.
Two structural virulence factors: M protein, Pili
Lots of toxins: streptokinase (break down blood clot), streptodornase (break down DNA), hyaluronidase (break down tissues), pyrogenic toxin (fever inducing), erythrogenic toxin (skin rash)
Can Group A strep spread to other sites?
Yes, because of streptokinase, it can break down blood clots and hyaluronidase, it can break down tissues.
What is the link between scarlet fever and Group A strep?
Group A strep has erythrogenic toxin that can cause scarlet fever, but this toxin is carried on bacteriophage that may not be passed along. it is rare of group A to cause scarlet fever, but it can.
What are the 2 reservoirs of Group A strep?
- carriers (in throat and skin all the time)
2. infected person
How is Group A strep transmitted?
Group A strep is transmitted via direct contact to susceptible people
Which abx is always effective against group A strep?
bacitracin b/c Group A strep is sensitive to it, but bacitracin is pretty toxic so penicillin is given in place of it
During recovery after group A strep infection (sore throat or skin infection), people can present with 3 post-streptococcal conditions.
- post-streptococcal glomeronephritis (pain, blood and protein urine)
- Rheumatic Fever (fever, arthritis, endocarditis)
- Sydenham’s Chorea in children (obsessive compulsive d/o/neurological symptoms)
What are two ways to diagnose group A strep infection in patients?
- swab-culture (gram staining and check for bacitracin sensitivity) -accurate but slow
- Rapid office tests with Antibody assays -fast but less sensitive = lots of false positives.
What is a suitable test to confirm a diagnosis of post-strep glomerulonephritis?
Blood test for IgM antibody to Group A streptococci
What is the CAMP test for?
The CAMP test can confirm Group B strep diagnosis. A positive test will see synergistic hemolysis of Group B strep and staph. aureus
What is the major virulence factor of Group B strep?
capsule
What is another name of Group B strep?
Group B strep is also known as streptococcus agalactiae.
How is Group B strep transmitted?
Group B strep can be found in women’s genital tract and can be transmitted to neonates
What are CDC recommendations on Group B strep and pregnant women?
Group B strep can be passed on from mom’s genital tract to neonates, and can cause fatal meningitis. Hence, the CDC recommends that women at 35 weeks of pregnancy should get tested for Group B strep. Also women with previous baby with group B infection or with unknown fever or with membrane rupture lasting 18 hours be offered prophylaxis penicillin.
What are some main diagnostic similarities and differences btw Group A and Group B strep?
Similarities -gram positive cocci, part of strep genus, catalase negative, beta-hemolytic
Differences -Group A is sensitive and Group B isn’t sensitive to bacitracin; Also Group A will have negative CAMP test while Group B will have synergistic hemolysis with staph aureus. Group A is associated with post-strep conditions while Group B is not pathogenic unless in neonates and can cause fatal meningitis.
What is the major virulence factor of streptococcus pneumoniae?
Streptococcus pneumoniae is an alpha-hemolytic, bile sensitive gram positive cocci. Its major virulence factor is the capsule.
There are vaccines for which species of cocci?
Streptococcus pneumoniae and neisseria meningitis
What is the Quellung rxn? List the 6 microbes that will have a positive Quellung reaction.
The Quellung reaction is a biochemical reaction in which antibodies bind to the bacterial capsule of Streptococcus pneumoniae, Klebsiella pneumoniae, Neisseria meningitidis, Haemophilus influenzae, Escherichia coli, and Salmonella. The antibody reaction allows these species to be visualized under a microscope. If the reaction is positive, the capsule becomes opaque and appears to enlarge.
Streptococcus pneumoniae reservoir
people
Explain pathogenesis of streptococcus pneumoniae
if innate immunity (mucus/cilia) is affected will make people more susceptible to getting it. Also, other causes include smoking, virus, allergy, drugs, heart failure and mechanical obstruction can cause disease.
How to treat streptococcus pneumonia?
1) offer vaccine to elderly/susceptible groups
2) identify and treat UNDERLYING cause
3) Abx sensitivity test b/c some are resistant to penicillin
Viridians Streptococcus reservoir and virulence factors
mouth
sugar-metabolizing enzymes
Pathogenesis of viridians strep.
Viridian strep will create high molecular weight sugars which will form dental plaque. Can lead to cavities and can also lead to bacteremia, resulting in endocarditis
Staphlococcus will test positive for catalase. Then, how to differentiate btw the 3 species?
Staph aureus will also test positive for coagulase, which can cause blood clotting. Staph epidermis and staph saprophyticus will test negative for coagulase
What are some of the virulence factors of staph aureus
Structural: protein A, capsule, coagulase
Toxins: DNAse, enterotoxin, exfoliation, leukocidin, toxic shock syndrome toxin
Which cocci have multi-drug resistance?
Staphlococcus aureus
S. epidermis is a huge problem in which population
huge problems in people with catheters and have IV lines. Also, found in infected piercings
What’s the best way to prevent infection with staphylococcus epidermis?
replacing IVs and catheters. Most hospitals have time limits for these.
Staphlococcus saprophyticus is linked to causing
UTIs
A microorganism is found to be a gram positive coccus, growing in clumps, catalase positive, salt resistent and coagulase positive.
Staphlococcus aureus
A microorganism is found to be a gram positive coccus, catalase negative, alpha hemolytic and found in mouth and resistant to bile.
viridians streptococcus
The catalase positive, coagulase negative gram positive cocci can further be differentiated by
Staphylococcus epidermis is sensitive to novobiocin while staphylococcus saprophyticus is resistant to novobiocin
How to differentiate gram negative cocci?
Using a chocolate agar (blood agar heated up), add maltose: neisseria meningitidis will ferment while neisseria gonorrhea will not.
What are the main virulence factors of neisseria meningitidis?
structural - capsule
toxin - LPS
What are virulence factors of neisseria gonnorhea?
structure - pili
toxin -LOS
Neisseria Meningitidis reservoir, transmission, prevention and treatment
reservoirs: carriers and respiratory
transmission: droplets
prevention: vaccine
treatment: penicillin
Neisseria Gonorrhea reservoir, transmission, prevention, and treatment
reservoirs: genital tract, chronic infection
transmission: sexual contact, birth
prevention: behavioral, neonatal eye drops
treatment: NOT penicillin b/c often resistant
