Systematic Bacteriology 2

Question 1

Give an example of gram negative cocci

Answer 1

Neisseria spp

Question 2

What are two types of aerobic gram negative cocci and how do they appear?

Answer 2

Neisseria gonorrhoeae - most common cause of bacterial meningitis
Neisseria meningitidis - causes gonorrhoea (STD)

Appear in pairs (diplococci) on Gram film

Question 3

What are coliforms?

Answer 3

Gram negative large aerobic bacilli; many are part of normal bowel flora (as long as in GI tract)

Look like E.coli on gram film and when cultured on blood agar

Question 4

How do coliforms grow and how are they differentiated?

Answer 4

Grow best aerobically; can grown anaerobically

Differentiated from each other by biochemical reactions and by the antigenic structure of their walls: O antigen (cell wall) and H antigen (flagella)

Question 5

What are gut commensal coliforms? Give examples

Answer 5

Normal bowel flora:

Most strains of E.coli

Question 6

Give examples of gut pathogens

Answer 6

Salmonella spp.

Some E.coli strains produce toxins (Verotoxin producing E.coli - VTEC)

Question 7

How do coliforms cause infection?

Answer 7

Coliforms cause serious infection in normally sterile sites, like UTIs, peritonitis, bilary tract (gall bladder) infection

Question 8

How are coliform infections treated?

Answer 8

Gentamacin - 1st line antibiotic for coliform infections

Question 9

How does sepsis due to coliform infection occur?

Answer 9

Bacteria die releasing ENDOtoxin from gram negative cell wall.

Lipopolysaccharide is taken up by cells like macrophages that release cytokines

Sets off inflammatory response and sepsis pathway

Question 10

Give examples of other aerobic gram negative bacilli

Answer 10

Pseudomonas aeruginosa - strict aerobe that is not very pathogenic but is intrinsically resistant to antibiotics - most strains still resistant to genatomicin

Question 11

What does (cocco)bacillus mean and give an example?

Answer 11

Look like cocci but are bacilli .

Haemophilus influenzae are gram negative aerobic coccobacillus

Question 12

Give examples of spiral or curved gram negative aerobic bacilli

Answer 12

Vibrio cholerae (causes cholera)

Question 13

Give examples of strict anaerobes

Answer 13

Clostridium spp.

Bacteroides spp.

Question 14

What are clostridium spp. and how do they function? Give an examples

Answer 14

Gram positive anaerobic bacilli that are part of normal bowel flora

Produce spores that can survive outside body

Produce EXOTOXINS causing severe tissue damage

Clostridium difficile - causes antibiotic-associated diarrhoea (antibiotics wipe out normal bowel flora)

Question 15

What are bacteroides, regions and treatment?

Answer 15

Gram negative anaerobic bacilli, many species are part of normal bowel flora (usually non-pathogenic; cause porblems in sterile sites like peritoneum)

Metronidazole - 1st line treatment

Question 16

What are mycobacterium? Give an examples

Answer 16

Thick waxy coat does not take up gram stain.

Stained by ACID FAST BACILLI (AFB) or acid-alcohol fast bacilli (AAFB) - gives blue/green background

Myobacterium tuberculosis causes TB

Question 17

What are spirochaetes? Give examples

Answer 17

Spiral-shaped bacteria; do not take up gram stain

Treponema pallidum - causes syphilis

Borrelia burgdorferi - causes Lyme disease

Question 18

What types of DNA do bacteria have?

Answer 18

Chromosome

Extrachromosomal like plasmids (double-stranded, encode genes for antibiotic resistance - genetic advantage)

Question 19

Importance of bacterial genetic variation and how it occurs?

Answer 19

Mutation
Gene transfer

Resistance to antibiotics develops and spreads rapidly as a result of genetic variation

Question 20

How do mutations result in genetic variation?

Answer 20

Rapid bacterial growth increase chance of mutations
Failure in accurate replication of DNA
Leads to new variants of organism - many fail to survive, rare strains may be successful

Question 21

Methods of gene transfer between bacteria?

Answer 21

Transformation - DNA released from dead bacteria taken up by living bacteria; incorporated into plasmids or bacterial chromosome

Conjugation - sex pilus produced by a bacteria through which plasmid DNA can be transferred (bacterial “sex”)

Transduction - viruses infect bacteria and transfer pieces of DNA between them

Question 22

Describe how antibiotics can result in antibiotic resistance

Answer 22

Unnecessary, sub-therapeutic or exposure to low conc. of antibiotic in environment encourages devlopment of resistant strains

Question 23

Mechanisms of resistance?

Answer 23

Produce enzymes that destroy antibitoics

Altered antibiotic binding sites

Alteration of cell wall porins - stop entering into cell

Up-regulation of efflux pumps (pump unwanted things out of cell)

Question 24

Enzymes that destroy antibiotics?

Answer 24

Beta-lactamase - early penicillins, like amoxicillin. Destroys beta-lactam ring in nucleus

Extended spectrum beta-lactamase (ESBL) - all penicillins and cephalosporins

Carbapenemase (CPE) - all penicillins, all cephalosporins and carbapenems (antibiotics of last resort)

Question 25

What does the beta lactam ring look like?

Answer 25

Square with one N atom and a double-bonded O atom

Question 26

How does altering antibiotic binding sites result in resistance?

Answer 26

Genetic mutation alters binding site
Antibiotic cannot bind and has not effect on bacteria

This is what causes MRSA (methicillin-resistant Staph. aureus) as penicillin binding protein on Staph. aureus is altered

Question 27

Antibiotic resistance due to change in cell wall porins?

Answer 27

Channels in bacterial cell that transport molecules from outside to inside cell

Changed result in bacterial call wall becoming impermeable to antobiotic

Question 28

Antibiotic resistance due to up-regulation of efflux pumps?

Answer 28

Pump molecules out of cells

Up-regulation of pumps results in antibiotic being removed from cell before it can act

Common mechanism of resistance in fungi, like Candida spp