Pathogenic Bacteria 1 Flashcards
List Clinically significant Gram positive bacteria.
Staphylococcus, Streptococcus, Clostridium and other anaerobic species.
Describe the Gram stain technique.
- flood it with CRYSTAL VIOLET stain.
- Then add IODINE as a counter stain.
- Wash off the stain with ALCOHOL which decolourises it and the crystal violet will bind with the sugars in the peptidoglycan layer which cannot be washed off.
- Finally apply SAFRANIN as a counterstain.
Aerobic Gram-Positive cocci – What is Staphylococci and Streptococci and enterococci?
Staphylococci- clusters
Streptococci and Enterococci- chains.
What is staphylococci further divided into?
coagulase-positive: staphylococcus aureus
coagulase-negative: staphylococcus epidermis.
Outline, in more detail, coagulase positive staphylococci and the infections it causes.
Coagulase positive- staphylococcus aureus
- Commensal organism (many) carried in nose, axilla, perineum
- Major human pathogen which causes a wide range of diseases from boils/abscesses and soft tissue infections to septicaemia and osteomyelitis
What are the management issues associated with coagulase positive staphylococci?
Is commonly penicillin resistant due to the production of penicillinase, which breaks beta-lactin ring, rendering penicillin inactive.- Methicillin resistant Staph aureus (MRSA) poses major problems for infection prevention and control in hospitals.
- By a different mechanism- some stains are ‘methicillin resistant’.
Outline, in more detail, Coagulase-negative staphylococci and the infection it causes.
Coagulase-negative staphylococci epidermis.
-Form biofilms and may be significant pathogens in the presence of foreign bodies/prosthetics or the immunocompromised.
Outline Streptococci chains.
α- haemolytic, β-haemolytic and Non haemolytic
Outline α- haemolytic streptococci chains, an example and infection it causes.
Causes partial haemolysis and turns blood agar green.
Streptococcus pneumoniae causes pneumonia, meningitis and septicaemia.
Viridans streptococci normal habitat is in human mouth. It causes infective endocarditis (infection of heart valves)
Outline β-haemolytic streptococci chains, and how they are identified.
Causes complete haemlysis and turns blood agar clear.
They are further identified by carbohydrate surface antigens and Groups A,B,D,F are clinically the most important.
Describe the first example of β-haemolytic streptococci chains and the infection it causes.
Group A: Streptococcus pyogenes which causes pharyngitis, skin/soft tissue infections such as necrotising fasciitis.
Describe the second example of β-haemolytic streptococci chainsand the infection it causes.
Group B: Streptococcus agalactiae which causes neonatal sepsis and invasive infections in older adults with underlying factors e.g. diabetes, liver disease.
Outline Non haemolytic streptococci chains and an example and infection it causes.
No haemolysis- no difference.
Group D: Streptococci is now re-classified as Enterococcus spp. Causes UTI and infective endocarditis. Found in the gut as a normal commensal.
How is gram positive bacilli classified?
Aerobic or anaerobic
Describe the gram positive bacilli - Clostridium difficile (anaerobic) and the infection it causes
- Causes diarrhoea and Pseudomembranous colitis.
- Asymptomatic gut carriage in healthy people.
- Increased risk with antibiotic use and any gut disruptors.
- It is spread/transmitted via spores.
- Don’t grow it in the lab, instead detect antigen and toxin in stool sample by ELISA
