PoD - Pathogenic Bacteria

Question 1

what is bacteria?

Answer 1

• a major group of micro-organisms which cause infectious disease
• mainly single cell prokaryotes
• most reproduce by binary fission
• most have a peptidoglycan cell wall

Question 2

what are the cell wall characteristics of gram +/-ve bacteria?

Answer 2

• gram positive - cytoplasmic membrane, THICK peptidoglycan layer, cell surface proteins
• gram negative - cytoplasmic membrane, THIN peptidoglycan layer, thich LPS layer (lipopolysaccharide layer)

Question 3

what is gram staining?

Answer 3

• determines if bacteria is gram +/-ve (+ve = purple, -ve = pink)
• different classes of antibiotics are effective against different bacteria = targeted treatment

Question 4

how can gram positive bacteria be classified?

Answer 4

• aerobic (bacilli/cocci)

- anaerobic (bacilli/cocci)

Question 5

list types of aerobic gram positive cocci

Answer 5

• staphylococci
  S.aureus - commonly penicillin resistant due to production of penicillinase
• streptococci - a=partially haemolytic (step.pneumoniae - pneumonia, meningitis) or b=complete haemolysis (strep.pyogenes -pharyngitis, cellulitis, necrosis fasciitis)

Question 6

list types of aerobic gram positive bacilli

Answer 6

• clostridium difficile (cause of diarrhoea, associated with toxin production)
• clostridium perfringens (can cause gastroenteritis if digested)
• clostridium tetani (toxin production causes tetanus - uncontrolled muscle spasm)

Question 7

list types of gram negative cocci

Answer 7

• neisseria spp (n.meningitidis - meningitis/n.gonorrhoeae - urethritis in men/pelvic inflammatory disease in women)
• moraxella catarrhalis (causative agent of respiratory tract infection)

Question 8

list types of gram negative bacilli

Answer 8

• escherichia coli (important cause of urinary tract infection/enterotoxogenic e.coli - cause of travellers disease/enterohaemorrhagic e.coli - bloody diarrhoea)
• salmonella spp (bacterial diarrhoea - enters blood stream)
• shigella spp - diarrhoea/dysentery

Question 9

list types of curved gram negative bacilli

Answer 9

• campylobacter spp (spread via animals - spread via faecal-oral. foul smelling –> bloody diarrhoea)
• helicobacter pylori (curved rods, damages stomach mucosa and causes ulcers)
• haemophilus influenzae (cocco-bacilli mixed appearance, causes respiratory tract infection)
• pseudomonas (water & soil coloniser, multi-drug resistance mechanisms)

Question 10

what are some anaerobic bacteria?

Answer 10

• bacteroides fragilis (part of normal colonic flora - causes intra-abdominal abscess)
• oral anaerobes (pasteurella spp involved in periodontal disease)

Question 11

what are miscellaneous bacteria?

Answer 11

• bacteria that can’t be stained with gram’s method

- can’t be cultured by standard methods

Question 12

list some miscellaneous bacteria

Answer 12

• acid & alcohol fast bacilli (AAFB) (resistant to decolorisation by acid/alcohol)
• mycobacteria (mycobacterium tuberculosis - tuberculosis - also linked to HIV)
• non-tuberculosis mycobacteria (mycobacteria leprae - leprosy)
• spirchaetes (long spiral-shaped bacteria. treponema pallidium - syphilis/borrelia burgdorferi - lyme disease)
• chlamydia (can be respiratory - chlamydophila pneumoniae or opthalmic/genetical tract - chlamydia trachomatis)