Classification and Identification of Bacteria Flashcards
what are the major groups of bacteria that cause disease in humans?
gram positive bacteria
- gram-positive bacilli
- spore producing
- motile and non-sporing bacilli
- non-motile and non-sporing
- cocci
gram negative
- gram-negative bacilli
- cocci
describe the structure of a bacterium. (6)
prokaryotic
capsule
cell wall
cytoplasmic membrane
cytoplasm
chromosome
flagellum
what methods are there by which human pathogens are identified?
isolation in pure culture
gram staining
describe each of the 2 methods used to classify pathogens (3,7)
colony morphology
- shape
- haemolysis
- pigment
cell morphology
- shape
- spores
- gram stain
- metabolic activities - enzyme tests
- antigens
- cellular composition
- DNA techniques - PCR, nucleic acid sequences
describe how gram staining works.
- sample if fixated to a plate = fixation
- crystal violet dye is added
- iodine is added
- decolorisation wash with alcohol acetone
= gram negative is purple
= gram positive is clear
- counter stain with safranin
= gram negative is purple
= gram positive is pink
how do gram negative micro-organisms differ from gram positive?
gram + = more peptidoglycan content
gram - = more lipid content what
what is an acid-fast microorganism, how is it identified?
have resistance to acids
The Ziehl-Neelsen Stain
- use carbon fuschin stain
- decolorisation w methanol
- methylene blue
acid-fast microorganism = stain red
background debris stain blue
what are 3 enzyme tests? describe them.
catalase test
- use hydrogen peroxide to release oxygen and water
- positive result - bubble formation
coagulase test
- differentiates the pathogen S.aureus
- positive result = precipitation
oxidase test
- identify bacteria producing cytochrome c oxidase
- use tetra-methyl-paraphenyl-diamine reagent
- positive test = blue
give 4 examples of gram-positive bacilli.
acid-fast myobacteria
- mycobacterium tuberculosis
- mycobacterium leprae
- myobacterium avium-intracellulare
- nocardia
= disease in immunocompromised patients
give 5 examples of spore producing gram-positive bacilli and what disease they lead to.
bacillus anthracis - anthrax
bacillus cereus - food poisoning - rice
clostridium spp
- clostridium perfringens - gas gangrene
- clostridium tetani - tetanus
- clostridium botulinum - botulism
give 1 example of a motile but non-sporing gram-positive bacilli, what it leads to and where it is often found
listeria monocytogenes = listeriosis
- cheese and pates
give 2 examples of non-motile and non-sporing gram positive bacilli, what do they cause?
corynebacterium diphtheria - diptheria
propionibacterium acnes - acne
give 3 examples of gram-positive cocci.
anaerobic cocci
- staphylcocci
- streptococci
human pathogens
- staphylococcus aureus
- streptococcus pneumoniae - alpha haemolytic
- streptococcus pyogenes - beta haemolytic
with gram-positive cocci, how do staphylcocci and streptococci react in a catalase reaction?
staphylcocci = catalase positive
streptococci = catalase negative
give 3 examples of gram-negative bacilli and their associations
haemophilus influenza
- respiratory conditions
- meningitis in unvaccinated children
- epiglottis - dead by suffocation
legionella pneumophila
- Legionaire’s disease
bordetella pertussis
- whooping cough
