Classification of Pathogenic Bacteria 1 Flashcards
What are things that can infect patients?
Bacteria
Parasites
Viruses
Fungi
What is bacteria?
A major group of microorganisms causing infectious disease
What is the process of gram staining?
1) Application of crystal violet (purple dye)
2) Application of iodine (morant)
3) Alcohol wash (decolourisation)
4) Application of safranin (counter stain)
What colour does gram positive bacteria appear?
Purple
What colour does gram negative bacteria appear?
Pink
What does gram staining do?
Provide early indication of the genus of bacteria
What are advantages of gram staining?
Quick, simple and inexpensive way to classify bacteria
What does knowing the classification of bacteria allow?
Targeted treatment as different classes of antibiotics are effective against gram positive and gram negative bacteria
What are the main classes of gram positive bacteria?
Aerobic
Cocci
Chains - streptococci and enterococci
Alpha, beta or non haemolytic
Clusters - staphylococci
Coagulase negative or positive
Bacalli - small and large
Anaerobic
Cocci
Bacalli
What is cocci bacteria?
Bacteria with a spherical shape
What is bacalli bacteria?
Bacteria with a rod shape
What are the two classes of staphylococci (aerobic cocci clusters)?
Coagulase positive
Coagulase negative
What is coagulase?
An enzyme that convers fibrinogen into fibrin which causes blood clotting
What is used to determine whether bacteria is coagulase positive or negative?
Coagulase test
What is an example of coagulase positive staphylococci and what can it cause?
Staphylococci aureus which can cause:
MRSA
MSSA
What is staphylococcus commonly resistant to and why?
Penicillin due to production of penicillinase
What is MRSA?
Methicillin resistant staph aureus
Where is staphylococci a commensal?
In the nose, axilla and perineum
What are examples of coagulase negative staphylococci?
Staphylococci epidermis
Staphylococci haemolyticus
Staphylococci saprophyticus
Staphylococci lugdenensis
What are coagulase negative staphylococci commonly?
Skin commensals
When can coagulase negative staphylococci cause problems?
In the presence of foreign objects such as prosthetic heart valves
What classes of bacteria are there in terms of how they degrade blood?
Alpha haemolytic (partial haemolysis)
Beta haemolytic (complete haemolysis)
Non-haemolytic
What is haemolysis?
Rupture or destruction of red blood cells
What are examples of alpha haemolytic streptococci and what do they cause?
Streptococci pneumoniae which causes:
Pneumonia
Meningitis
Septicaemia
Viridans streptococci which causes: Infective endocarditis (infection of heart valves)
What does streptococci pneumoniae cause?
Pneumonia
Mengingitis
Septicaemia
What is infective endocarditis?
Infection of heart valves
How can beta haemolytic streptococci further be identified?
By carbohydrate surface antigens ranging from A to G
What are the clinical important groups of beta haemolytic bacteria?
Groups A, B, D and F
What is an examples of group A beta haemolytic streptococci and what does it cause?
Streptococcus pyogenes which causes:
Pharyngitis
Cellulitis
Necrotising fasciltis
What is an example of a group B beta haemolytic streptococci and what does it cause?
Streptococci agalactiae which causes:
Neonatal sepsis (meningitis/bacteraemia)
Invasive infections
What is an example of a group D beta haemolytic streptococci and what does it cause?
Streptococci enterococcus faecalis which causes:
Urinary tract infection
Infective endocarditis
What are some examples of aerobic gram positve bacteria?
Clostridium genus:
Clostridium difficile
Clostridium perfringens
Clostridium tetani
Where is clostridium difficile cause found and what does it cause?
In the gut and it causes diarrhoea
What is clostridium difficile spread by?
Pores
Where is clostridium perfringens found and what can it cause?
Found in soil and a normal commensal in gut faeces, if it infects wounds it can cause gas gangrene
What does clostridium cause?
Toxin produced causes tetanus
What are examples of biological spore warfare?
Clostridium botulnum (source of botox)
Basillus anthracis (cause of anthrax)
What is colonisation?
Germs being in the body buyt not making you sick
What is infection?
Germs are in the body and making you sick
