Streptococci and Enterococci Flashcards
Are Streptococci gram +ve or -ve?
+ve
Are streptococci catalase +ve or -ve?
-ve
Describe the usual arrangement of Streptococci.
Seen most commonly in chains or pairs of coccus.
Are Streptococci motile?
No
Are streptococci sporing?
No
Are Streptococci commensals?
Yes
Where are streptococci found as commensals?
Typically in the mucous membranes of the upper respiratory tract and some within the intestines.
What types of groups separate Streptococci?
Colony appearance on horse blood agar.
Lancefield grouping.
Describe how alpha haemolytic streptococci appear on horse blood agar and the haemolysis they cause.
Colonies have a greenish appearance and are approximately 1mm in diameter.
There is no actual haemolysis.
Describe how S. pneumonia and viridian’s group streptococci appear on horse blood agar and the haemolysis they cause.
Viridian’s appear green.
Describe the virulence of viridans group Streptococci.
Tend to be commensal, opportunistic pathogens of low virulence.
Describe how beta haemolytic streptococci appear on horse blood agar and the haemolysis they cause.
Cause complete lysis of red blood cells and so have a zone of clearing around the colonies.
Colonies are approximately 1mm in diameter with no pigmentation.
Describe how non-haemolytic streptococci appear on horse blood agar and the haemolysis they cause.
They have no effect on red blood cells.
Gamma haemolysis occurs.
What is Lancefield grouping?
Streptococci are separated on their version of a major cell wall polysaccharide antigen.
On which type of Streptococci is Lancefield grouping used ?
Beta haemolytic streptococci
How can enterococcal colonies appear on blood agar?
They can appear alpha, beta or non-haemolytic.
Describe the catalase activity of enterococci.
Catalase negative
What Lancefield group are Enterococcal colonies?
Lancefield group D
Describe how the catalase test works.
a. Dispense 50ul of hydrogen peroxide into bijou
b. Transfer one colony of the test strain to the opposite side of the bijou
c. Cap the bijou
d. Tip the hydrogen peroxide over the colony and observe
e. Bubbles of oxygen indicate a positive reaction
Outline the steps that should be used to identify Streptococci.
1) Identify if they are gram positive cocci
2) Catalase test
3) Check the appearance of colonies on Blood Agar (type of haemolysis)
Outline the steps that should be taken to identify beta haemolytic streptococci.
- They cause complete lysis of RBC.
- Colony appearance; white/ grey.
- Gram stains show chains.
- Catalase negative reaction.
- Lancefield grouping shows visible grainy agglutination.
What are the difference groups of beta haemolytic streptococci and the features of each.
A - haemolytic streptococci are sensitive to bacitracin.
Other (B&D)- haemolytic streptococci are resistant to bacitracin.
Outline the steps needed to identify alpha haemolytic streptococci.
- Gram stain (present in chains or pairs)
- Catalase -ve
- On blood agar (colonies are typically green, smooth, circular, approx 1mm in diameter)
How do alpha haemolytic Streptococci appear on blood agar.
Colonies are typically green, smooth, circular, approx 1mm in diameter
Are the viridians group of Streptococci haemolytic?
Can be haemolytic or non-haemolytic
Are the viridans group catalase +ve or -ve?
-ve
Are the viridans group streptococci optochin sensitive or not?
They are resistant
Are Streptococcus pneumoniae optochin sensitive or not?
They are sensitive
Describe the appearance of Streptococci Pneumoniae
They are gram +ve diplococcus but are lanceolate shaped. Draughtmen colonies with central depressions.
Describe the haemolysis S.pneumoniae cause on blood agar.
Alpha haemolysis
Are Streptococci Pneumoniae mucoid?
They can be if they have a polysaccharide capsule.
Are Streptococci pneumoniae and viridans group streptococci bile soluble
S.penumoniae - yes
Viridans group - no
Are group A beta haemolytic streptococci sensitive t bacitracin?
Yes
Are group A beta haemolytic streptococci commensals?
Yes - of the nasopharynx
How is A beta haemolytic streptococci transmitted ?
Person to person transmission via direct contact with infected skin lesions or respiratory droplets.
What virulence factors does Streptococcus progenies have?
Toxins Cell surface proteins Hyaluronic acid capsule Cell envelope Enzymes
What adhesions does S.pyogenes have that act as virulence factors?
M protein and F protein
How does M protein act as a virulence factor of S. pyogenes?
It binds various host proteins such as fibrinogen, plasminogen, immunoglobulin and complement factors. This causes them to be resistant to phagocytosis, therefore avoiding the immune system.
How does F protein act as a virulence factor of S. pyogenes?
Binds to fibronectin mediating internalisation of bacteria into host cells.
Describe the features of the S.pyogenes capsule.
Antiphagocytic
Non-immunogenic. This is important in avoiding the immune system.
Describe the composition of the S.pyogenes capsule.
Composed of hyaluronic acid.
Name the virulence enzymes of S.pyogenes.
Streptolysins
C5a peptidase
Streptokinase
Describe how Streptolysins work as virulence enzymes for S. pyogenes.
Lyse erythrocytes, polymorphonuclear leukocytes, platelets etc. This is important in immune evasion.
Describe how C5a peptidases work as virulence enzymes for S. pyogenes.
They cleave human C5a which is a chemoattractant of phagocytic cells. This is important in avoiding the immune response.
Describe how Streptokinases work as virulence enzymes for S. pyogenes.
They are a spreading factor which binds plasminogen activating plasmin which breaks down fibrin and aids the spread of infection through tissues.
What type of exotoxins does S.pyogenes have that act as virulence factors?
Pyogenic exotoxins
Spec B
Describe Spec A pyogenic toxins that work as virulence toxins for S.pyogenes.
They are associated with bacteriophages and have super antigen activity which results in massive release of cytokines.
Results in inflammation, hypotensive shock, organ failure.
What symptoms do pyrogenic exotoxins of S.pyogenes cause?
Symptoms of scarlet fever and toxic shock syndrome.
Name some non-invasive infections cause by S.pyogenes.
Pharyngitis
Impetigo
Eryspelas
Name the symptoms of Pharyngitis
Inflamed pharyngeal membrane.
Exudate covering pharynx and tonsillar region.
Oedema of the uvula.
Odynophagia.
What’s the treatment for Pharyngitis?
Treatment with penicillin for 10 days.
Name some superficial infections caused by S.pyogenes.
Pharyngitis, impetigo, erysipelas
Name some of the deep-seated infections caused by S.pyogenes.
Callulitis, bacteraemia, necrotizng factors, myositis, puerperal sepsis, pneumonia, meningitis
Name some toxin-mediated infections caused by S.pyogenes.
Scarlet fever, streptococcal toxic shock syndrome
Name some immune-mediated diseases caused by S.pyogenes.
Rheumatic fever, glomerularnephritis, reactive arthritis.
What is Puerperal fever?
Infection of the genital tract after giving birth.
How is necrotising fascilitis treated?
Treated by prompt surgical debridement and antibiotics.
In what types of people is Rheumatic fever most common?
Children
How quickly is Rheumatic fever usually resoved?
Within 3 months
What causes the symptoms of Rheumatic fever (in clinical terms)?
Antibody against M protein cross-reacts with human tissue. This causes multi-system inflammation as well as carditis, arthritis, rashes, nodules and chorea.
What type of issues can occur due to repeated. infections within different types of M protein of S.pyogenes?
Lasting damage such as Rheumatic heart disease
Where are Streptococcus agalactiae commensal?
They are commensals of the colon and are also carried in the female genital tract. They can also be carried in pregnant women.
When Streptococcus agalactiae are carried in pregnant women, what is likely to occur?
Premature labour, neonatal ill health, meningitis and sepsis.
Where is Streptococcus pneumoniae commensal?
In the upper respiratory tract and the nasopharynx.
How is Streptococcus pneumoniae transmitted?
By respiratory aerosols and droplets as well as direct contact.
When is the case rate of Streptococcus penumoniae infection likely to alter?
Seasonal variation with carriage rate and disease - peak within winter months.
What are the virulence factors of S.pneumoniae?
Cell surface adhesins
Polysaccharide capsule
Toxin: pneumolysin
How does Pneumolysin act as a virulence factor of S.pneumoniae?
Generates pores in the Eukaryotic membranes.
Activates classic complement pathway, even in the absence of specific antibodies.
Leads to cytokine production and inflammation.
How does the polysaccharide capsule act as a virulence factor of S.pneumoniae?
It is antiphagocytic and is essential for causing invasive infections. This is important for avoiding the immune response.
What happens clinically with Pneumonia?
Alveoli are filled with pus and fluid which makes breathing painful. Oxygen intake is also limited.
What are the symptoms of Pneumonia?
Cough, purulent sputum, Pyrexia, consolidation of the lungs.
What is pyrexia?
Elevation above the body temperature above normal.
Name some invasive pneumococcal diseases.
Pneumonia
Sepsis
Meningitis
Describe the pathogenic potential of the Viridans group streptococci and how susceptible they are to different medications.
They have low pathogenic potential and so remain susceptible to most antibiotics including penicillin.
Name some infections caused by Viridans group Streptococci
Dental caries
Endocarditis
Depp seated abscesses
Septicaemia in immunocompromised patients
Describe how serious S.pyogenes infections usually are.
Many of the infections caused are life-threatening.
Describe how serious S.pneumoniae infections usually are.
Infections are often life-threatening.
Describe how serious infections caused by viridans group Streptococci usually are.
They are either non-life threatening or restricted largely to patients with underlying medical conditions.
Are enterococci catalase -ve or +ve?
-ve
Are enterococci bile soluble or insoluble?
Insoluble
Describe the colour of Enterococci colonies on aescluin
Brown/ black
Where are Enterococci commensals?
Of the intestinal tract
Name some of the infections caused by enterococci
Bacteraemia, endocarditis, UTI, abdominal wound infections.
Describe the resistance/ sensitivity of Enterococci to penicillin, amoxycillin and vancomycin.
Resistant to penicillin
Sensitive to amoxycillin
Resistant to vancomycin
Why do Enterococci cause dark brown/ black colonies on Bile aesculin agar?
They hydrolyse aesculetin which combines with ferric ammonium citrate producing dark brown or black colonies.
What lancefield group do all enterococci have?
D
Are all Lancefield group D positive enterococci?
No
What is a mucoid colony?
A colony showing viscous or sticky growth.
How is alpha haemolysis easily visualised on agar?
It causes the agar to turn green.
Describe how the oxidase test is carried out and what is considered a +ve reaction.
Transfer one colony to an oxidase test strip. Rapid development of a strong purpose colour indicates a +ve reaction.
Do organisms which get their energy from fermentation have the catalase enzyme?
No
Name some antibiotic susceptibility tests used to identify organisms.
Bacitracin
Optochin
Metronidazole
Novobiocin
Name some phenotypic tests used to identify organisms
Catalase test Oxidase test Antibiotic susceptibility tests Oxidation/ fermentation test Staphylococcus latex agglutination test Lancefield grouping of beta haemolytic streptococci Biochemical API profiling Coagulase test
Outline how the Staphylococcus latex agglutination test is carried out and how the results are shown.
- Place one drop of latex test reagent onto the test card
- Mix one or two colonies with the test reagent for 10 seconds
- Rock the card to mix for a further 20 seconds and observe for agglutination
o -ve for agglutination = coagulase negative Staphylococcus
o +ve for agglutination = coagulase +ve Staphylococcus
Outline the process of setting up an API test strip.
1) Culture suspended in saline or sterile water
2) Prepare a reaction strip
Water poured into well plate to create a humid chamber
3) Place test strip into chamber
4) Tilted 45 degrees to inoculate each of the tubes
5) Some of the reactions require an overlay of oil
6) Lids on
7) Set up a purity plate
8) Inoculate the strip
9) Incubate strip for recommended time (usually 18-24 hours).
10) Colour changes should have occurred.
How do you set up a purity plate for an API test?
Inoculate original inoculum of saline or sterile water onto an agar plate.
What is the purpose of setting up a purity plate in an API test?
Allows you, after a period of incubation, to check that the organism is what you think you have put on the strip. i.e. it hasn’t become contaminated.
How do you inoculate the purity strip created on an API test?
a. Place the tip of the pipette within each well (against the side of it) and release the contents of the pipette so that the well is filled.
b. Wells which have a line underneath their name must be overlayed with liquid paraffin to cause an anaerobic reaction.
c. Wells that have a box round their name must be filled with bacterial suspension until there is a curved meniscus.
What type of organisms is the API20E test used for ?
Oxidase negative, gram negative rods
What type of organisms is the API20NE test used for ?
Oxidase positive, gram negative rods
- Why is it important when inoculating a pus sample onto solid growth media to use a streak dilution method?
- Without a streak dilution, bacterium within the sample may be heavily populated and difficult to isolate. Using the dilution will allow some of the colonies to grow, well separated from each other, making it easier to visualise and obtain single isolated, pure colonies. And to be able to visualise if there is more than 1 organism present.
Would you perform a Gram stain on the a pus sample? Explain your answer.
- Yes. Gram staining the pus sample will allow identification of any bacteria present and will allow determination of the type of bacterial species present. It should also be done because you expect it only to be the pathogen that is present.
