Identification of human staphylococcal and streptococcal species Flashcards
Where in out body is it sterile free (safe from microbes)
larynx, trachea, bronchi, and lungs
What body parts contain our normal flora
nose and pharynx
-pharynx contains bacteria often found in normal flora of the oral cavity such as staphylococci, Neisseria, and hemolytic species of streptococcus
Where is the first site where pathogenic bacteria invade and colonize
upper respiratory tract
-the environment such as pH, oxygen, and moisture can be quite diverse depending on location
-as a result nasal and throat cultures tend to contain varying bacteria species often contain streptococcus and staphylococcus
How do staphylococcus appear when stained?
-gram positive spheres grape like clusters
How do streptococcus appear when stained?
-gram positive sphere, grown in chains (when in broth)
What is the first test used to determine the difference between staph and strep
catalase test
positive = staph –> next is coagulase test –> grow on blood agar and MSA
negative = strep –> next is hemolysis –> (alpha) do optochin test (beta or gamma) do bacitracin
What similarities do S. aureus and S. epidermis share?
1.Both are halophiles
2. both have catalase enzymes
3. both are gram positive
4.both have grape like cluster arrangements
5. both are spheres
-both are found in nasopharynx and skin
What test can we use to distinguish between S, aureus and S. epidermidis
- coagulase test
- MSA media
- Blood agar media
coagulase
is an enzyme some pathogenic bacteria produce to induce blood cell clotting
-the blood clot serves as a refuge or hiding place for pathogens
coagulase test
- S. epidermidis and Aureus are placed in a tube of blood plasma
- S. Aureus produces coagulase, causing the plasma to thicken
- S. epidermidis does not produce coagulase, causing no change in the consistency of the plasma
S. Aureus and S. epidermidis on MSA plates
- samples obtained by nasal swabs are streaked on MSA plates
- The MSA plates will be incubated overnight at 37 C
- Mannitol fermenters will produce acid which will turn phenol red yellow
S.Aureus ferments mannitol
S. epidermidis does not ferment mannitol
S. Aureus and S. epidermidis on blood agar plate
- samples obtained by nasal swabs can be streaked on blood agar
- beta hemolytic bacteria (complete breakdown of RBC-clearing media around growth) (S. aureus)
- gamma hemolytic bacteria (no breakdown of RBC- no change in media) (S. epidermidis)
S. Aureus
-considered an opportunistic pathogen
-approx. 30% of the population carries S. aureus on their skin or in the upper respiratory tract
-leading cause of infective endocarditis
-also the leading cause of bacteremia
alpha hemolytic bacteria
-partial breakdown of RBC (green-brown color colonies and media)
- S. pneumoniae and S. viridans
Beta hemolytic bacteria
-complete breakdown of RBC (clearing growth around media)
- S. pyogenes and S. agalactiae
gamma hemolytic bacteria
- no breakdown of RBC (no change in media)
optochin test
-a disc containing a standard concentration of the antibiotic optochin is placed after the sample is streaked
-if there is a circular ring of growth (zone of inhibition) around the disc the bacteria is sensitive to the antibiotic
S. pneumonia is sensitive to optochin
S. viridans is resistant to optochin
Bacitracin test
-a disc containing a standard concentration of the antibiotic bacitracin is placed after the sample is streaked
-s. pyogenes is sensitive to bacitracin resulting in zone of inhibition
- s. agalactiae is resistant to bacitracin
How does bacitracin work
can inhibit the growth of bacteria by preventing the transport of NAG and NAM from cytoplasm to the site of cell wall synthesis. This weakens the cell wall resulting in death by osmotic pressure
S. pneumonia
-can be apart of residential microbiota in the sinus, nasal cavity, and upper respiratory tract
-when our immune system is compromised it can become an opportunistic pathogen, colonizing the air sacs of the lungs and causing pneumococcal pneumonia
S. pyogenes
- is a group A streptococcus species and a strict parasite
- typically infects the skin or pharynx and tends to cause diseases when out residential microbiota has been depleted
-mild infections cause pharyngitis whereas severe infections can cause scarlet fever or necrotizing fasciitis
dichotomist key
flow chart used to identify staph and strep
-a tool that consist of a series of choices that allow us to determine the identity of an unknown item
