Gram Positive Cocci Flashcards
1
Q
What three genera make up 90-99% of GPC clinical isolates?
A
Staphylococcus
Streptococcus
Enterococcus
2
Q
Which genera of GPC are catalase positive?
A
Staphylococci and Micrococci
3
Q
Which genera of GPC are catalase negative?
A
Streptococci
4
Q
What test is conducted to distinguish between Micrococci and Staphylococci?
A
Modified oxidase test
5
Q
Which genera of catalase positive GPC is Oxidase negative?
A
Staphylococci
6
Q
Which genera of catalase positive GPC is Oxidase positive?
A
Micrococci
7
Q
What secondary test can we perform to determine Staphylococci species?
A
Coagulase testing
8
Q
Which species of Staphylococci is coagulase positive?
A
Staphylococcus aureus
9
Q
What secondary testing do we perform to determine the species of Coagulase Negative Staphylococci?
A
Novobiocin testing
10
Q
Which species of Staphylococci is Novobiocin resistent?
A
Staphylococcus saprophyticus
11
Q
Which species of Staphylococci is Novobiocin sensitive?
A
Staphylococcus epidermidis
12
Q
Are GPC usually Oxidase pos or neg?
A
Negative
13
Q
Are GPC usually catalase pos or neg?
A
Positive
14
Q
When viewing a clinical smear how are GPC usually arranged?
A
- clusters
- single cells
- pairs (diplococci)
- tetrads
15
Q
How many species/subspecies of Staphylococci are there?
A
57
16
Q
Name the usual characteristics of Staphylococci sp.
A
- non-motile
- non-spore forming
- most are facultative
- attack sugars fermentatively
17
Q
How do we divide the staphylococci species?
A
Into coagulase pos or neg species
18
Q
What is the most virulent and clinically significant pathogen among the Staphylococci?
A
Staphylococcus aureus
19
Q
On a culture plate, what colour is Staphylococcus aureus likely to be?
A
yellow
20
Q
True or false: Staphylococcus aureus is both slide and tube coagulase positive.
A
true
21
Q
Staphylococcus aureus is NF when not in an environment where it is overtly pathogenic. Name the areas on the human body where it is normally found
A
- anterior nares (nostrils)
- nasopharynx
- perineal area
- skin
- various mucosal surfaces
22
Q
In a hospital environment what percentage of people are carriers of Staphylococcus aureus?
A
60-70%
23
Q
What organism (genus and species) is considered a significant cause of nosocomial infections?
A
Staphylococcus aureus
24
Q
What is MRSA?
A
Methicillin Resistant Staphylococcus aureus.
25
What are some infections Staphylococcus aureus causes?
- Wound infections
- Bacteraemia/endocarditis/pericarditis
- Meningitis
- Pulmonary infections
- Osteomyelitis and septic arthritis
- Food poisoning
- Scalded skin syndrome
- Toxic shock syndrome
26
What virulence factor in Staphylococcus aureus causes food poisoning?
heat stable enterotoxins
27
Name the virulence factors S. aureus contains.
1. Capsular polysaccharides
2. Protein A
3. Enzymes
4. Haemolysins (not on BA)
5. Toxins
28
What enzymes can S. aureus produce?
- Catalase
- Coagulase
- Fibrinolysins
- Hyaluronidase
- Lipases
- Nuclease
- Beta-lactamases
29
What type of toxins does S. aureus produce?
- Epidermolytic toxins
| - Enterotoxins
30
What organism (genus and species) is the most common coagulase negative staphylococci (CoNS)?
Staphylococcus epidermidis 50-80%
31
What organism (genus and species) makes up 90% of all skin flora??
Staphylococcus epidermidis
32
True or false: Almost all truly significant infections with S. epidermidis are of nosocomial origin.
True
33
What does S. epidermidis produce on artificial surfaces (i.e. shunts, catheters, metal plates etc) that helps it to survive and become resistant to therapy and the immune response (i.e. phagocytosis)
Biofilm
34
What does S. epidermidis readily acquire from other bacteria?
resistance to antibiotics
35
When do we consider S. epidermidis to be clinically relevant for reporting?
- Purity of growth is substantial (+++)
- quantity of growth (+++)
- Site of the infection (i.e. sterile site such as blood culture, or wound infection oozing puss)
- Clinical Hx (i.e. recent hospital admission/surgery)
36
Is Staphylococcus epidermidis haemolytic on Blood Agar?
not usually
37
On a culture plate, what colour is the colony growth of S. epidermidis?
Grey to white colonies
38
Where is Staphylococcus saprophyticus usually found?
In the GIT
39
What organism is the most commonly associated with community acquired UTI's?
Staphylococcus saprophyticus
40
What organism is the most common cause of cystitis (after E. coli), urethritis in men and prostatitis (elderly men)?
Staphylococcus saprophyticus
41
On a culture plate, what colour is the colony growth of S. saprophyticus?
usually very bright white glossy colonies
42
What are the virulence factors of S. saprophyticus?
- adherence to epithelial cells
- urease production
- produces slime layer in the presence of urine and urease (very sticky in urinary system)
43
What organism has a virulence factor of adherence specificity to uroepithelial, urethral and periurethral cells?
Staphylococcus saprophyticus
44
What two primary test results (systematics) would indicate that you should consider an isolate as belonging to the genus Staphylococcus?
Catalase pos and modified oxidase neg
45
What is the difference between plasma and serum?
Plasma is the fluid in blood that contains clotting factor (fibrinogen) while serum does not.
46
List 4 virulence factors. How does each virulence factor for S. aureus act to assist in its ability to cause infection?
- Protein A - confuses the binding orientation of Fc portion of the antibody allowing the organism to avoid phagocytosis.
- Beta - lactamases - confers resistance against penicillin, ampicillin, and other beta lactam antibiotics
- Haemolysins - lyses RBC to release nutrients therefore allowing the organism to benefit form the lysed nutrients.
- Toxins - Epidermolytic toxins cause scalded skin syndrome and enterotoxins can cause food poisoning or toxic shock syndrome.
47
Explain the theory behind the oxidase test
Detects the presence of the enzyme cytochrome c (enzymes that are involved in the electron transport chain) via a reagent that when oxidised produces a dark violet purple colour indicating the presence of the enzyme which confirms a positive result for oxidase. This helps to differentiate GN bacteria.
48
What type of infections is S. epidermidis normally associated with and why?
nosocomial infections
49
What is coagulase?
An enzyme which reacts with fibrinogen causing coagulation.
50
What are the two forms of test for coagulase?
- Bound Coagulase (cell wall) via slide coagulase test
| - Free coagulase (secreted) detected by the tube coagulase test.
51
What type of plasma causes false positives with the coagulase test?
citrated plasma (blood collected in citrate tube instead of edta)
52
What is the rapid test for coagulase?
Slide coagulase (also called "clumping factor")
53
What should all negative test results for coagulase be checked by? Why?
tube method since strains deficient in clumping factor may produce free coagulase.
54
What is the scientific name for Group A Streptococcus?
Streptococcus pyogenes (beta haemolytic)
55
What is the scientific name for Group B Streptococcus?
Streptococcus agalactiae (beta haemolytic)
56
What antibiotic is the drug of choice used to treat suspected streptococcal pharyngitis?
Penicillin or erythromycin if the infection does not resolve on its own
57
What is the likely identity of an unknown organism that is a GPC, catalase negative and was Hippurate positive?
Streptococcus agalactiae
58
What is the likely identity of an unknown organism that is a GPC, catalase negative and sensitive to Bacitracin?
Streptococcus pyogenes
59
How could you easily differentiate between S. pneumoniae and a member of the viridians streptococci?
Bile solubility test.
| S. pneumonia is bile soluble whereas Viridians streptococci is not.
60
Which species is resistant to vancomycin?
Enterococcus faecium
61
Where is Group B Strep. most likely to be found as NF?
URT - Throat
62
What is the principle difference in colony morphology between Group A & B strep?
Group A has large zones of Beta haemolysis on BA
| Group B has small zones of Beta Haemolysis on BA
63
What systemic infection are the viridians streptococci usually associated with?
Endocarditis/septicaemia
64
What is the advantage of using the bile solubility test over the optochin test when using these to ID S. pneumoniae?
Bile solubility is a rapid (10 min) test which gets results faster in order to report to the doctor in a timely fashion so they can treat the patient faster.
65
What are the main identifying features of S. pneumoniae? (Primary and secondary test results)
- Two colony types (Mucoid is S - form, rough is draughtsman R - form)
- Alpha haemolytic (narrow) zones on BA
- Fastiduous (requires BA or CHOC)
- GP diplococci in a lancet shape
- Optochin sensitive
- Bile soluble
66
What immunological property is thought to play an important role in conferring protection against pneumococcal infection?
Humoral Immunity
67
What 3 groups of people would most likely be affected by pneumococcal infection?
- very young
- elderly
- immunocompromised
68
List four virulence factors of Group A Streptococcus and give an example of how/why each acts to confer pathogenicity?
- M Proteins assist with resisting phagocytosis and adherence to epithelial cells.
- Haemolysins O and S are toxic to host cells
- Streptococcal Pyogenic Exotoxins cause toxic shock syndrome and hypotension.
- Hyaluronic acid capsule - mucoid isolates evade phagocytosis due to being antigenic invisible, also assist with bacteria adhering to host tissue.
69
List four virulence factors of Group A Streptococcus and give an example of how/why each acts to confer pathogenicity?
- Beta haemolysins (o and s type) - destroys various host cells
- M Proteins (surface antigens) - adhere to epithelial cells
- Enzyme production -various enzymes help to break down host cell wall/defences.
- Hyaluronic acid capsule - mucoid isolates - resists phagocytosis by adhering to host tissue as well as having a similar composition to host CT which helps the organism blend into the host environment.
70
Compare between post streptococcal rheumatic fever and glomerular nephritis.
- Post streptococcal rheumatic fever is an infection of the heart as a result of an auto-immune response
- Glomerular nephritis is an infection of the kidneys specifically an inflammation of the glomeruli (due to agglutination of antibodies being to big to filter out of the nephrons).
71
Give two reasons why the genus Enterococcus are frequently associated with significant nosocomial infections.
- surgeries of the abdominal cavity/GIT
| - structural abnormalities or instruments such as catheters
