Practical 1

Frage	Antworten
Why is mannitol salt agar used to select for normal skin flora?	Because the high salt agar inhibits bacterial growth.
What is mannitol salt agar used for? Which microbe.	Staphylococci aureus
After you have observed a Gram-positive coccus, you need additional information before performing a coagulase test. What is this additional information?	Before performing a coagulase test you must perform a catalase. If positive you would do a coagulase test.
If a bacteria is gram positive, catalase positive and co-agulase positive. What is it?	S. aureus
If a bacteria is gram positive, catalase positive and produces acid from mannose. What is it?	S. epidemidis
If a bacteria is gram positive, catalase positive and produces no acid from frutose. What is it?	S. saprophyticus
List three identifying characteristics of S. aureus.	1. Gram positive 2. Catalase positive 3 Coagulase positive 4. Cocci shaped
List 4 factors that protect the skin from infection.	1. Keratinised layer repels water and promotes skin dryness 2. Salt production from sweat glands inhibits microbial growth 3. sebum produced by sebaceous glands 4. Normal Microflora
What is coagulase? How is it related to pathogenicity of Staphylococci?	Coagulase is a type of protein enzmye that acts as a mechanism for clotting within the blood by activating prothrombin. Staphylococci aureus uses coagulase within the blood to produce fibrinogen/coagulase clots that protect the bacteria from phagocytosis as they hide within these clots. Macropharges cannot reach the bacteria.
When doing a skin culture, why is the swab first moistened with saline?	Helps bacteria from sample to adhere to swab.
What test can differentiate the three major species of Staphylococcus? List 4.	1. Colony Pigment 3. Coagulase 4. Microbact Staph 12s 5. DNase test
How could you distinguish S. epidermidis from S. saprophyticus in the Micrococcaceae identification Key?	S. epidemidis produces acid from mannose S. saprophyticus does not produce acid from mannose, mannitol or fructose.
Why are staphylococcal infections frequent among hospital patients? 3 reasons.	1. Staphylococci are commonly found on the skin of nurses, doctors and visitors and easily introduced into patients. 2. Hospitalised patients are more prone to infections as they are immunocompromised. 3. Intravenous therapy dramatically increases as microbes can colonise venous line in the vein resulting in infection.
What is Vogel Johnson Agar and what is it used for? Species Example Samples Composition	Pathogenic Staphylococci S. aureus Samples: Food wounds and skin Composed of: tellurite
What is the catalase test?	Test that decides if the microorganism produces the enzyme catalse. Catalse breaks down hydrogen peroxide in to molecular O2 and H2O. Oxygen bubbles indicate a positive result.
What is the coagulase test for? What microbe tests positive?	Identifies coagulase positive microbes. S. aureus is differentiated by this test.
List 5 identifying characteristics of S. epidermidis	1. Coagulase negative 2. Catalase positive 3. Cocci shaped 4. Mannitol negative 5. Mannose positive (produces acid)
List 6 identify characteristics of S. saprophyticus	1. Gram positive 2. Catalase positive 3. Coagulase negative 4. Cocci shaped 5. Manitol Negative 6. Fructose Negitive
List 4 tests that distinguish major species of Staphylococci	1.Microbact 12s 2. DNase test 3. Colony Pigment test 4. Coagulase test
What is the DNase test and what is a positive result.	It is the Deoxyribonuclease test. Indicates if a microbe uses Dnase as it's carbon source. A positive result displays clearing around the growth/colony sites.
What is the colony pigment test? How does it work?	It's purpose is to identify a microbial colony by colour and morphology. Carotenoid pigments are orange to yellow. Beta-galactosidase has a colour change from green to plum after the addition of fast blue reagent.
What is the Staphlyococci Staph 12s kit do? How does it do it?	Works by identifying the 22 clinically significant species of Staph. Works by sugar utilisation and and colormetric enzyme detection. Contains 12 tests that undergo colour metric change indicating a positive result. These changes occur via pH indicators and enzyme detection substrates.
Why is blood agar a differential media for Streptococci?	Because Steptococci undergoes RBC haemolysis on blood agar plates. Haemolysis types can be used for identification.
Is gram staining results of significant importance for identification of microorganisms from the throat.	Yes, although streptoccoci is common other bacteria such as Neisseria can also be found. Gram stain allows for separation of these species. Gram staining also allows the morphology of bacteria to be observed and there for identified.
A gram-positive cocci has been found that cannot be identified as Staph or Strep. What enzyme test will quickly differentiate between these two bacteria?	Catalase test. Staphylococci = positive and Streptococci= negative
What type of haemolysis is produced by S. pneumoniae?	Alpha
What type of haemolysis is produced by S. pyogenes?	Beta
How do you determine is a sore throat is caused by S. pyogenes or S. pneumoniae?	1. Complete a haemolysis test on blood agar (pnuemoniae = alpha; pyogenes = beta) 2. Bacitracin test 3. Optchin test (positive = S. pnuemoniae)
List the names of 4 types of diseases caused by S. pyrogenes.	1. Scarlet fever 2. Acute pharyngitis 3. Strepticoccal toxic shock syndrome 4. Impetigo
How would you differentiate between alpha and beta haemolysis?	Alpha haemolysis is caused by S. progenes and is complete haemolysis with a claen colony edge. Beta haemolysis is caused by S. pneumoniae and is partial haemolysis. Methmoglobin is produced resulting in a cloudy green zone surrounding the colony.
What does the Optichin test illustrate?	Alpha Haemolysis to differentiate S. pneumoniae and S. pyogenes. A positive result for S. pnuemoniae is considered when the zone of inhibition exceeds 14mm (6mm disk).
What are the 3 types of haemolysis and what are their patterns?	1. Alpha = partial haemolysis (methmoglobin production = green colony edge) 2. Beta = complete haemolysis 3. Gamma = no haemolysis
Which streptococci are considered most commonly pathogenic?	Beta haemolysis= S. pyogenes
What are the 4 main microflora in the throat/upper respiratory tract?	1. Staphylococci 2. Streptococci 3. Neisseria 3. Haemaphilus
Why is infection rare in the upper respiratory tract?	Because of microbial antagonism.
What species causes acute pharyngitis?	Streptococci species (specifically S. pyogenes)
What is the bacitracin Test?	Used to identify beta-haemolytic streptococci, S. pyogenes from other Strep. Any zone of inhibition is regarded positive for beta-haemolyitic Strep.

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