GPB

Question 1

What cellular structure do the genera Bacillus and Clostridium have in common?

Answer 1

large GPB & Spore forming

Question 2

How could you easily differentiate between an aerotolerant Clostridium sp. and a facultative Bacillus sp.? (hint: bench top test)

Answer 2

Catalase test
Pos: Bacillus sp.
Neg: Clostridium sp.

Question 3

What do the terms “coryneform” and “diphtheroids” normally describe in a routine clinical laboratory?*

Answer 3

GPB non-pathogens

Question 4

If a gram smear result was described as pallisading GPB, what does this mean? (i.e. what would you see?)

Answer 4

Pallisading: form groups (III = V L)

Question 5

List 5 identifying lab. characteristics of Listeria monocytogenes? How could you distinguish between Group B Streptococcus and L.monocytogenes.

Answer 5

• Short non-sporing GPB in pairs & pallidasing
• narrow zone of B haemolysis (similar to GBStrep)
• Catalase pos (unlike GBStrep. catalase neg)
• Tumbling motility at 25ºC but not at 37ºC
• Needs enrichment media (NG on MAC)

Question 6

What lab. characteristic would help to distinguish C.perfringens from almost all other members of the genus Clostridium?

Answer 6

• Double zone of haemolysis on BA: inner zone B, Outer zone a
• non-motile

Question 7

List the causative organisms for anthrax, gas gangrene, Botulism and tetanus?

Answer 7

Anthrax: Bacillus anthracis
Gas gangrene: Clostridium perfringens (80%)
Botulism: Clostridium botulinum (spores or toxin)
Tetanus: Clostridium tetani

Question 8

a) What is pseudomembranous colitis?
b) Describe the pathogenesis (how the organism gains entry to humans and the processes involved in causing human disease/symptoms) and
c) list the most likely causative organism.

Answer 8

a) Inflammation of colon
b) Pathogenesis: Exposure to organism in food (spores not cooked properly); or Hx of antibiotic therapy = encourage resistant strains. Release of enzymes and exotoxins/enterotoxins => gut symptoms
c) Caused by Clostridium difficile, C. perfringens

Question 9

What is the designated protocol for treating diagnosed clostridial colitis?

Answer 9

1. Stop antimicrobial therapy
2. Initiate fluid & electrolyte replacement therapy
3. Treat mild diarrhoea w/ MTZ, and severe diarrhoea w/ Vanc.
4. Faecal transplant from donor: Inc microbial diversity in colon

Question 10

What clinical history would suggest the possibility of pseudomembranous colitis?

Answer 10

Hx of antibiotic therapy = dec NF + overgrowth of Cl. difficile/ Cl. perfringens

Question 11

What is the normal vaccination schedule for tetanus? i.e how often is it given and to who?

Answer 11

5-dose schedule: 2, 4, 6, 18 months and 4 years

Booster: 1 injection every 10 years

Question 12

Clostridium species cause many of their disease effects through powerful toxins. Are these toxins exotoxins or endotoxins and what are the differences between these two types? (hint: review slides from Fermentative GNB lecture).

Answer 12

• Enterotoxins are harmful to the digestive system

- They are exotoxins: high toxicity, strong antigenicity, not heat stable and not produce fever

Question 13

What is the difference between short and long incubation food poisoning with B.cereus?

Answer 13

Short: 1-6hrs. caused by preformed heat stable exotoxin in food (Consume toxin)
Long: 8-16hrs: Consume spores from improperly cooked food = in vivo enterotoxin (exotoxin) production (heat labile=alter)

Question 14

If you isolated a Bacillus species in the clinical laboratory, how could you easily determine if it was B.anthracis? List three features that would differentiate it from the other members of this genera.

Answer 14

• motility: neg
• Encapsulated in vivo: pos
• Lysis by gamma phage: pos
• haemolytic: none (B.subtilis V b/w B and none)
• LV test: pos (B. cereus also pos)

Question 15

Features to consider when you have a GPB

Answer 15

• AnO2, dec O2, aerobic
• non-/ branching
• Acid fastness
• catalase
• spore forming

Question 16

Who is primarily affected by Listeria monocytogenes and common pathogenesis?

Answer 16

• pregnant women, newborns and immunocompromised
• Contamination in food processing (salads, cheese) w/ spores => meningitis
• grows at 4ºC

Question 17

Lab features if Bacillus cereus

Answer 17

• GPB
• Produce spores: R to pasteurisation of milk
• Catalase pos
• Large feathery colonies
• B haemolytic*
• Motile*
• facultative*

Question 18

Lab features if Clostridium perfringens

Answer 18

• GPB brick-shaped, may be encapsulated
• Double zone of haemolysis on BA: inner zone B, Outer zone a
• non-motile
• LV & Nagler pos

Question 19

Lab features if Clostridium tetani

Answer 19

• thin long GPB
• easily decolourised
• Tennis racquet spores
• narrow a or B zone
• Motile = swarms lace-like

Question 20

Lab features if Clostridium difficile

Answer 20

• GPB
• easliy decolourise
• Spores variable position in bacteria
• Motile
• Selective medium (CCFA)
• Detect toxin in faeces using commercial kits

Question 21

Which species of mycobacteria cause tuberculosis?

Answer 21

Mycobacteria tuberculosis

Question 22

How is tuberculosis transmitted?

Answer 22

Most Droplets/aerosol except M.bovis transmitted via infected milk

Question 23

Name two staining methods for visualising mycobacteria under the light microscope.

Answer 23

1. Ziehl Neelson or Kinyoun stain for AFB

2. Fluoroscent staining - Rhodamine or rhodamine auramine

Question 24

Why are mycobacteria slow growing?

Answer 24

bc they have a hydrophobic cell wall = hard access for nutrient into cell= hard to absorb nutrients

Question 25

What makes Mycobacterium so resistant to acids, alkalis, antibiotics and desiccation?

Answer 25

Bc the cell wall is hydrophobic due to high lipid content

Question 26

Why would immune status affect the initial outcome of infection with TB organisms?

Answer 26

A healthy person can get infected w/ TB organisms and not get symptoms maybe bc their immune sys is good, and also bc organism is slow growing. When immune system is poor it can allow organism to multiply.