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
How many beta haemolytic streptococci are there and how do they differ?
There are 20 lanefield groups and they differ by the differences in C carbohydrates in their cell wall
What are the types of complications that can result from primary infection with a beta haemolytic group A streptococcus (streptococcus pyogenes)?
Suppurative complications that are pus forming
Non-suppuratives that are toxin or immune mediated
What does primary infection with beta haemolytic group A streptococci look like?
Pharyngitis and tonsillitis. If it infects the skin it causes cellulitis, erysipelas and impetigo
What are the types of suppuratives complications that can result from group A beta haemolytic streptococci?
Peritonsillar abscess
Retropharyngeal abscess
sinusitis
Otitis media
Mastoiditis
Necrotising fasciitis
What are some non-suppuratives complications that can result from group A beta haemolytic streptococci?
Scarlet fever
Toxic shock syndrome (rarely)
Rheumatic fever
Acute glomerulonephritis
How does pharyngo-tonsillitis look?
Red appearance and pus rom tonsils (this is known as strep throat)
What is a perintonsillaer abscess (quinsy)?
Abscess in the tonsils making them enlarge
What is mastoiditis?
Swelling behind the ear and redness and pain. Caused by bacteria travelling up the mastoid tube into the back of the ear and causing infection in bone behind the ear.
What happens if mastoiditis is left untreated?
It can travel to the brain and cause meningitis
What is impetigo?
Superficial outer keratin layer and is usually seen in school children because it is very contagious.
What is erysipelas?
Superficial epidermal layer infected and raised. It contains sharp borders
What is cellulitis?
Subcutaneous tissue is infected and reddened.
Who is cellulitis typically seen in?
Elderly
What is necrotising fasciitis?
Rapidly spread destructive infection along fascial planes causing necrosis of muscle and subcutaneous tissue
What is scarlet fever?
Follows a pharyngitis is S. pyogenes is carrying pyrogenic exotoxin
What are the common symptoms of scarlet fever?
Strawberry tongue and a rash
What is rheumatic fever?
Patients develop antibodies against their own tissues.
Polyarthritis
subcutaneous nodules
Erythema marginatum (a unique skin rash)
Chorea (writhing movement of limbs)
Carditis (including damage to heart valves)
Who is rheumatic fever commonly seen in?
Endemic in poor socioeconomic conditions.
What is post streptococcal glomerulonephritis?
An inflammatory disease of the glomeruli caused by desposition of immune complexes acute renal damage often occurs which resolves
What are the features of post streptococcal glomerulonephritis?
High BP
Haematuria
Proteinuria
Oedema
Where are group B haemolytic streptococcus normally found?
In the vagina as part of the normal microbiome
What do group B haemolytic streptococci do that is harmful?
They can cause serious infection of the mother and the neonate
Premature labour and rupture of membranes
How is group B haemolytic streptococcus infection found and treated?
Screened for carriage during pregnancy and treated with IV amoxicillin during labour
What infections are caused by group B beta haemolytic streptococcus in the mother?
Maternal infections such as:
Postpartum endometritis
Post caesarean section bacteraemia
Urinary Tract Infections
What infections are caused by group B beta haemolytic streptococcus in the infant?
Septicaemia
pneumonia
Meningitis
Where are alpha haemolytic streptococci commonly found?
Oropharyngeal, gastrointestinal and genital tract commensal flora
Organised into species groups
Is classification of alpha haemolytic streptococci easy?
No it is complicated and controversial.
All species are organized into species groups:
Bovis, anginosis, mitis, mutans, and salivarius groups
What kind of infections do alpha haemolytic streptococcus cause?
Bacteraemia
Infective endocarditis
Abscess, particularly of orofacial area, pulmonary and pleural, intra-abdominal pain. (they are common abscess causing organisms)
Dental carries
What are the virulence factors of alpha haemolytic streptococci in dental carries?
glycosyltransferases convert sucrose into insoluble glucans
Glucans then adhere to dental enamel and form the basis of dental plaque or tartar. (biofilm)
Acid production, demineralisation of the tooth then causes initiation of caries
What strain of alpha haemolytic streptococcus is associated with endocarditis and bacteraemia? What else should be checked for if these conditions are present?
Streptococcus Bovis which is also associated with colonic malignancy
What is streptococcus pneumonia?
The pneumonia causing streptococcus which is a highly virulent pathogen.
Where is pneumococcus typically carried?
In the upper respiratory tract of 5 - 10% of the population
Name an important virulence factor for pneumococcus?
Its capsule which has 80+ antigenically distinct serotypes
What does pneumococcus commonly cause?
Meningitis and pneumonia
Where are enterococcus commonly found?
commonesals of bowel
What are the main species of enterococcus?
E. faecalis and E. facium
Which of the 2 enterococcus species are less commonly encountered?
E. faecium
What are the typical infections of enterococcus?
Intra-abdominal infections Urinary tract infections Soft tissue infections Bacteraemia Endocarditis
What is a problem with Enterococcus species?
They are very resistant to antibiotics; in particular E. faecium
How can enterococci be identified?
They agglutinate with lancefield group D antiserum
