Classification of Pathogenic Bacteria

Question 1

Gram Positive cocci examples

Answer 1

Staphylococci (clusters), streptococci (chains), enterococci

Question 2

Staphylococci examples

Answer 2

coagulase positive- staph. Aureus, carried in nose, axilla and perineum, commonly penicillin resistant due to B-lactamase

coagulase negative- many different species, skin commensals, can be pathogenic in presence of foreign bodies/prothese

Question 3

Streptococci examples

Answer 3

a-haemolytic (partial haemolysis) - turns blood agar green, strep. pneumoniae, normal oral flora, can cause injective endocarditis

B-haemolytic (complete haemolysis) - turns blood agar clear, further separated into groups A-G

Question 4

Group A B-harmolytic streptococci

Answer 4

strep. pyogenes

major pathogen - sore throats, cellulitis

Question 5

Group B B-Haemolytic streptococci

Answer 5

Strep. agalactiae

neonatal sepsis

genital tract carriage common

Question 6

enterococci example

Answer 6

used to be known as non-haemolytic strep

enterococcus faecalis (group D)

normal gut commensal

cause of UTI’s

Question 7

Gram positive Bacilli examples

Answer 7

clostridium difficile, clostridium perfringens, clostridium tetani

Question 8

clostridium difficile features

Answer 8

difficult to culture

major cause of diarrhoea due to toxin production

Pseudomembranous colitis

toxins found in stool sample

spreads via spores

Question 9

clostridium Perfingens features

Answer 9

normal gut commensal

in food, can cause food poisoning

in serious wounds, can cause “gas gangrene”

Question 10

clostridium tetani features

Answer 10

toxins cause tetanus

antigenically modified toxin (toxoid) used in vaccine

Question 11

Gram negative cocci examples

Answer 11

neisseria spp, moraxella catarrhalis

Question 12

Neisseria spp examples

Answer 12

Neisseria meningitidis - causes meningitis, may be grown from blood cultures or CSF samples, can be life threatening

Neissetria Gonorrhoeae - causes urethritis in men and pelvic inflammatory disease in females, spread by sexual contact

Question 13

moraxella catarrhalis features

Answer 13

causative agent in respiratory tract infections

especially prevalent in those with underlying lung pathology

Question 14

Gram negative Bacilli examples

Answer 14

Escherichia coli., salmonella spp, shigella

Question 15

Escherichia Coli features

Answer 15

fermentys lactose

important causes of UTI’s and neonatal sepsis

Enterotoxogenic E.coli - commonest cause of travellers diarrhoea

Enterohaemorrhagic E.coli - bloody diarrhoea, harmolytic uraemic syndrome

Question 16

Salmonella spp features

Answer 16

does not ferment lactose

Salmonella enterica - self-limiting enterocolitis with or without bloody diarrhoea. 2nd commonest cause of bacterial diarrhoea in UK, can be invasive

Salmonella Typhi - cause of typhoid fever, fever, constipation early stages, organism isolated from blood