Gram film interpretation Flashcards
What colour will gram positive organisms stain?
Purple
What colour will gram negative organisms stain?
Red/pink
What are the bacterial morphologies (shapes of the bacteria)?
Cocci (singular: coccus) = circle shaped
Bacilli (singular: bacillus) = rod shaped
Vibrio = curved C shape
Coryneform = club-shaped
Spirochete = spiral
Coccobacillus = rod and circle shaped
How are bacteria named?
Based on how they grow in relation to each other:
- Growing in pairs = diplococci
- Growing in clusters = staphylococci
- Growing in a chain = streptococci
Features of gram positive cocci in clusters?
Examples
Staphylococcus
e.g.
Staph aureus
Disease presentation
-Cellulitis
-Endocarditis
-Osteomyelitis
-Iatrogenic (from cannula/central line insertion)
Other examples
*Staph epidermidis
- Can cause endocarditis in prosthetic heart valves
Features of gram positive diplococci?
Examples
Strep pneumoniae
Disease presentation
-Pneumonia
-Meningitis
-Otitis media
Other examples
*Enterocci
e.g. enterococcus faecium, enteroccocus
*faecalis
Can cause UTIs, intra-abdominal infections
Features of gram positive cocci in chains?
Examples
- Strep pyogenes (aka Group A strep)
Disease presentation
- Tonsilitis
- Scarlet fever
- Rheumatic fever
- Cellulitis
Other examples
- Strep agalactiae (aka Group B strep)
- Causes neonatal sepsis
How is streptococci grouped?
Grouped initially on whether they are able to haemolyse (breakdown blood) within the blood agar.
Beta haemolysis: complete haemolysis
Alpha haemolysis: incomplete haemolysis
Gamma haemolysis: no haemolysis
What is the lancefield grouping system?
The Lancefield grouping system primarily focuses on classifying different strains of streptococcal bacteria based on the presence of specific antigens in their cell walls.
These antigens are designated by letters such as A, B, C, D, etc.
For example, Streptococcus pyogenes, which causes strep throat and other infections, is classified as Group A streptococcus (GAS), while Streptococcus agalactiae, associated with infections in newborns and pregnant women, is classified as Group B streptococcus (GBS).
Why is the lancefield grouping system useful in microbiology?
The Lancefield grouping system is important in microbiology for identifying and characterizing different bacterial strains, which can be useful in diagnosing infections, understanding epidemiology, and developing vaccines and treatments.
Features of gram positive bacilli?
Examples
- Clostridium perfringens
Disease presentation
- Gas gangrene
- Cholecystitis
- Gastroenteritis
Other examples
- Clostridiodes difficile – gastroenteritis
- Clostridium tetani – tetanus
- Listeria monocytogenes – meningitis,
gastroenteritis, neonatal sepsis
Features of gram negative diplococci?
Examples
- Neisseria meningitidis
Disease presentation
- Meningitis
Other examples
- Moraxella catarrhalis
- Causes pneumonia, otitis media, sinusitis
Features of gram negative coccobacilli?
Examples
- Haemophilus influenzae
Disease presentation
- Pneumonia
- Meningitis
Other examples
- Bordetella pertussis which causes whooping cough
- Acinetobacter which causes hospital-acquired infections
Features of gram negative bacilli?
Examples
- E.Coli
- Proteus
- Klebsiella
Disease presentation
- UTI
- Pyelonephritis
- Cholecystitis
- Cholangitis
- Intra-abdominal infections
Features of vibrios?
Examples
- Vibrio cholerae
Disease presentation
- Cholera
Other examples
- Vibrio vulnificus
- Causes cellulitis, diarrhoea
Vibrio parahaemolyticus which causes gastroenteritis
Features of spirochetes?
Examples
- Treponema pallidum
Disease presentation
- Syphilis
Other examples
- Borrelia burgdorferi which causes Lyme disease
Examples of bacteria that do not gram stain?
Examples
- Mycobacteria e.g. mycobacteria tuberculosis
Mycobacteria tuberculosis causes TB
Other examples
Chlamydia
Mycoplasma