Lecture 6 Gram positive cocci Flashcards
What are the important genera of gram positive cocci?
Staphylococcus
Streptococcus
Enterococcus
What is the catalase test?
A test to tell whether a bacterium is staphylococcus or streptococcus/enterococcus
How is a catalase test performed?
Hydrogen peroxide and if bubbles are produced its a staph if not its strepto
What is a coagulase test?
Coagulase converts fibrinogen to fibrin.
Rabbit plasma is mixed with the bacteria and if it coagulates it is a coagulase positive test
What are the 3 important human pathogens from the staphylococcus genus?
Staphylococcus aureus
Staphylococcus epidermis
Staphylococcus saprophyticus
How is staph aureus distinguished from other staph species? What are other species called?
Positive coagulase test other species are coagulase negative staphylococci.
What percentage of people are carriers of staph aureus?
20 - 40% of the population are carriers
Where are staph aureus typically found?
anterior nares
What kind of disease does staph aureus cause?
Chronic skin infections such as folliculitis, boils and minor wound infections
It can also be a virulent pathogen if it enters the bloodstream it can be fatal.
Can cause septicaemia
Osteomyelitis
Septic arthritis
Bursitis
Organ abscesses
What is folliculitis?
infection of hair follicules
how is septicaemia diagnosed?
aerobic and anaerobic bottles are used to culture bacteria
What kind of locations can organ abscesses be found in?
Epidural abscess can be near spinal canal
Brain abscesses
Psoas abscesses
Lung abscesses
What are some non-pyogenic diseases caused by staph aureus?
Staphylococcal Scalded Skin Syndrome
Staph toxic shock syndrome
Staph food poisoning
Where are coagulase negative staph cocci typically found?
Staph epidermis
Can Staphylococcus epidermis cause disease?
It’s very low in virulence but when there is a breach in the skin they can cause infection.
What is the most common coagulase negative cocci?
Staph epidermis
What kind of infections are caused by coagulase negative staphylococcus?
Infections of intravenous (or intra-arterial cannulas)
Prosthetic heart valves
Prostetic joint infection
Infection of orthopaedic pins, plates, screws, and wires
Meningitis with foreign devices
What is the virulence factor of staph epidermis?
Extracellular polysaccharides or slime. Biofilm formation on foreign device
Where do coagulase negative staphylococci typically cause infections that are relevant for orthopaedic treatment of joints?
They commonly cause infection on prosthesis.
Where do staph saprophyticus typically cause infection?
In the Urinary tract it is second only in prevalence to Escherichia coli
How is classification of streptococcus started?
Starts with the way they haemolyse blood agar.
How are streptococcus species different in haemolysing blood agar?
Certain bacteria can produce hamolysins:
Alpha-haemolytic streptococci use alpha haemolysis sometimes called viridians streptococci
Beta haemolytic streptococci produce beta haemolytic streptococci
What are the 3 kinds of haemolysis in streptococcus?
Beta (blood is dissolved agar is transparent)
Alpha (partial haemolysis of agar with olive green tinge)
Gamma haemolysis (no haemolysis)
How can beta haemolytic streptococci be further classified?
According to antigenic differences in cell wall carbohydrates
What is the lancefield grouping system?
Streptococci have C carbohydrates in their cell wall and they are antigenically distinct.
20 different groups within the genus determined by the difference in these carbohydrates.
What are the particularly important Lancefield groups?
Lancefield group A also known as streptococcus pyogenes
Lancefield group B also known as streptococcus agalatiae