Bacterial Infections

Question 1

What are bacteria?

Answer 1

Prokaryotic micro-organisms without a membrane bound nucleus.

Question 2

How are bacteria classified?

Answer 2

By microscopy and culture of infected samples:

1. gram stain
2. shape
3. aerobes/anaerobes

Question 3

What is the difference between a gram negative and positive bacteria?

Answer 3

Gram positive - stain purple/blue, bacteria with thick, exposed peptidoglycan layers.

Gram negative - stain pink/red, they have a protected peptidoglycan layer.

Question 4

What are the different shapes that bacteria can have?

Answer 4

1. Cocci - round
2. Bacili - Rod shapes
3. Spirochaete - spiral shaped

Question 5

What is the difference between aerobes vs anaerobes?

Answer 5

1. Obligate aerobes = bacteria that cannot survive without oxygen.
2. obligate anaerobes = bacteria that cannot grow in the presence of oxygen.
3. Facultative anaerobes - can survive in either environment

Question 6

What is bacteraemia?

Answer 6

Bacteria circulating in the bloodstream

Question 7

Define the term bacteriocidal?

Answer 7

Kills bacteria both in and out of the replication cycle

Question 8

Define the term Bacteriostatic?

Answer 8

Stops replication without killing existing bacteria

Question 9

What is capsulate bacteria?

Answer 9

Bacteria with a thick outer capsule e.g. haemophilus influenzae, neisseria meningitiges, and streptococcus pneumoniae. These are destroyed in the spleen. Following splenomectomy (or splenic infarction, e.g. sickle cell anaemia). There is an increased risk of infection by capsulate bacteria and prophylactic vaccination should be offered.

Question 10

What is a commensal?

Answer 10

An organism that lives in/on a host without causing harm

Question 11

What is an endotoxin?

Answer 11

A lipopolysaccharide complex found on the outer membrane of gram-negative bacteria. can elicit an inflammatory response. activates complement via the alternative pathway.

Question 12

What is an enterotoxin?

Answer 12

They are toxins that target the gut, e.g. colostridium defficile toxin.

Question 13

What is an exotoxin?

Answer 13

Toxins secreted by bacteria acting at a site distant from bacterial growth. Production of an exotoxin can determine virulence e.g. botulinum, tetanus, diphtheria, shiga toxins.

Question 14

Define Flagella?

Answer 14

A tail- like appendage that moves to propel the bacterium e.g. H. pylori

Question 15

What does nosocomal mean?

Answer 15

acquired in a hospital/healthcare setting

Question 16

Define obligate intracellular?

Answer 16

Bacteria that can only survive in host cells, induce cell-mediated immune response and will not grow on standard culture media.

Question 17

What is the Zeihl-Neelsen stain?

Answer 17

Mycolic acid in the cell wall of mycobacteria resists Gram staining but will appear red with acid-fast techniques (=acid-fast stain)

Question 18

Give examples of gram-positive cocci?

Answer 18

Staphylococci + Streptococci (including enterococci)

Question 19

Give examples of gram negative cocci?

Answer 19

Neisseria meningitidis, Neisseria gonorrhoeae, moraxella catarrhalis.

Question 20

Give examples of gram positive rods?

Answer 20

mnemonic - ABCD L

• Anctinomyces
• Bacillus anthracis (anthrax)
• Clostridium
• Diphtheria: Corynebacterium diphtheriae
• Listeria monocytogenes

Question 21

Give examples of gram negative rods?

Answer 21

• E. coli
• Haemophilus inluenzae
• Pseudomonas aeruginosa
• Salmonella sp.
• Shigella sp.
• Campylobacter jejuni

Question 22

Key facts about staphylococci?

Answer 22

1. Gram positive cocci
2. Facultative anaerobes
3. Produce catalase

Two main types;
- Staph aureus: coagulate positive, causes skin infections e.g. cellulitis, abscesses, osteomyelitis, toxic shock syndrome.

• Staph epidermidis: coagulase negative, cause of central line infections and infective endocarditis.

Question 23

Bacterial tonsillitis treatment?

Answer 23

Phenoxymethylpenicillin - Good at covering against Strep A.