identification of microorganisms

Question 1

what is the role of microbiological identification?

Answer 1

allows diagnosis of infection so allows allocation of treatment
epidemiology and infection control

Question 2

what is the common appearance of streptococci species?

Answer 2

purple
round cells
arranged in chains or pairs

Question 3

what is the common appearance of staphylococci species?

Answer 3

purple
round cells
arranged in clusters like grapes

Question 4

what colour do gram positive bacteria appear?

Answer 4

purple

Question 5

what colour do gram negative bacteria appear?

Answer 5

red

Question 6

what charge stain does capsule staining require?

Answer 6

negative

Question 7

what is an example of a capsule stain and how do capsules appear when this stain is used?

Answer 7

indian ink stain

capsules exclude the ink and appear as clear halos surrounding bacterial cells

Question 8

what are capsules/slime layer known as?

Answer 8

glycocalyx

Question 9

what is glycocalyx made up of?

Answer 9

polysaccharides
glycoprotein
glycolipid

Question 10

what is the function of S layers?

Answer 10

provides resistance to phagocytosis

allows adhesion

Question 11

what is the role of capsules in pathogenesis?

Answer 11

involved in biofilm formation which allows aggregation
provides resistance to phagocytosis
allows adherence to cells which initiates infection
binds antigens and enzymes to cell surface
prevents desiccation
protects from chemicals and cell injury

Question 12

how are biofilms formed?

Answer 12

planktonic cells adhere to surface
form a monolayer and produce ‘slime’
form microcolony with multi layering cells
‘mushroom’ plume forms held together by polysaccharides
cells can detach and revert to planktonic cells which can travel around the body and cause further infection

Question 13

what is the clinical relevance of biofilms?

Answer 13

cells can seed off and cause further infection
responsible for recurring infections
responsible for antimicrobial resistance and treatment failure

Question 14

how do bacteria communicate?

Answer 14

by quorum sensing
release auto inducers which activate group behaviour genes
allows bacteria to behave as a multicellular organism

Question 15

what are the two kinds of pili?

Answer 15

ordinary

sex

Question 16

what are fimbriae?

Answer 16

ordinary pili

Question 17

what is the function of fimbriae?

Answer 17

involved in attachment
adhesins which bind to receptors on host cells
first step in establishing infection in some organisms

Question 18

what is the function of sex pili?

Answer 18

involved in conjugation

Question 19

what is antigenic variation and how does this create a survival advantage?

Answer 19

heterogenic variation of a clonal population
pili are antigenic and bacteria can change their pili proteins in order to avoid a host immune response
involves variable expression of genes in the fimbrial operon
whilst those that express the genes are targeted by the immune system of the host, those that do not express the genes survive and can later express the genes becoming antigenic

Question 20

what are the steps in conjugation?

Answer 20

extension of pilus from donor and binding to recipient cell
retraction of pilus and fusion of cell membrane
transfer of plasmid and replication of complementary strands
separation of cells

Question 21

what are the three methods involved in horizontal gene transfer?

Answer 21

transformation
transduction
conjugation