Gram Postive Bacteria

Question 1

What is the difference between Gram Positive and Gram Negative cells?

Answer 1

Differences in cell wall structure/ composition
Positive- thick peptidoglycan layer
Negative- thinner peptidoglycan layer, lipopolysaccharide layer (endotoxin)

Question 2

What is the process of a Gram Stain?

Answer 2

Fixation with heat, Crystal violet stain, iodine treatment, decolorization with acetone, counter stain safranin

Question 3

What does a Gram positive stain show?

Answer 3

Stain blue-black
Some have spores
More sensitive to penicillin and vancomycin

Question 4

What does a Gram negative stain show?

Answer 4

Stain pink

Mostly resistant to penicillin and vancomycin

Question 5

How do shapes and sizes of bacteria differ?

Answer 5

1-2 micrometres wide
Cocci- round
Bacilli/Rods- elongated
Curved or spiral

Question 6

What are the types of aerobic Gram positive bacteria?

Answer 6

Coccus- Staphylococcus (three planes, grape formation)
Streptococcus (one plane, straight)
Bacillus- Bacillus (Wide and thick)
Listeria (thinner)
Corynebacterial (palisade/ wigwam)

Question 7

What are the types of Staphylococci bacteria?

Answer 7

S. aureus

Coagulase negative Staph

Question 8

What are the virulence factors of S. aureus?

Answer 8

Golden= more yellow, more pathogenic
Coagulase- clotting
Hyaluronidase- hydrolyses hyaluronic acid in connective tissues
Haemolysins- breakdown of blood

Question 9

What are the exotoxins of S. aureus?

Answer 9

Toxic shock syndrome toxin- 1

Panton- Valentine Leukocydin

Question 10

Where are the sites of S. aureus colonisation?

Answer 10

Preceding step to infection, develop infection with the same strain
Anterior nares, axilla, perineum, throat, GI tract

Question 11

What are the host factors involved in S. aureus colonisation?

Answer 11

Nasal phenotypic differences
Competence of immune system- (haemodialysis, Diabetes Mellitus, end-stage liver disease, cancer, HIV infection)
Caucasian
Age
Previous skin infection

Question 12

What are the clinical manifestations of S. aureus?

Answer 12

Skin and soft tissue infections
Pneumonia
Bone and joint infections
Endocarditis- Discitis
Toxin mediated diseases- scalded skin syndrome, toxic shock syndrome, gastroenteritis

Question 13

Describe Coagulase negative Staph

Answer 13

Normal commensal flora of skin/ low grade pathogen
S. epidermidis/ S. capitis
Infection in prosthetic material- arthroplasty, metallic heart valves, central lines

Question 14

What are the types of Streptococcus?

Answer 14

Alpha Haemolytic

Beta Haemolytic- A/B/C/D/E/F/G

Question 15

What does a-haemolysis mean?

Answer 15

Incomplete degradation of haemoglobin

Question 16

Describe Streptococci Pneumoniae

Answer 16

Gram Positive diplococci
Produces pneumolysin causing a-haemolysis
Peptidoglycan and theicoic acid cell wall
Forms capsule to prevent phagocytosis
Colonisation of nasopharynx- 5/10% adults, 20/40% children

Question 17

What are the clinical implications of Streptococci Pneumoniae?

Answer 17

Most common cause of Community Acquired Pneumonia

Meningitis, sinusitis, otitis media, infective endocarditis

Question 18

What does b- haemolysis mean?

Answer 18

Complete lysis of red blood cells
Historically considered more pathogenic
Lancefield grouping- types of carbohydrate antigens in bacterial cell wall

Question 19

Describe Streptococci pyogenes group A

Answer 19

Multiple virulence factors- Protein M
Activate multiple cells in immune system
Response immune system kills
Pharyngitis, Scarlet fever, Rheumatic, fever, post-streptococcal glomerulonephritis, bacteraemia, necrotising fasciitis

Question 20

What is necrotising fasciitis?

Answer 20

Breakdown of tissue

Thrombosis, loss of skin integrity

Question 21

What is Bacillus Anthracis?

Answer 21

Multiple toxins and virulence factors- high mortality
Site of inoculation, necroing of skin, oedema and inflammation
Humans incidental host- cutaneous inoculation, inhalation

Question 22

What are the types of Gram positive anaerobic bacteria?

Answer 22

Coccus- anaerobic coccus

Bacillus (rod)- Clostridium

Question 23

What are the types of Clostridium bacteria?

Answer 23

tetani, botulinum, difficile, perfringens

Gram Positive rods, large, pleomorphic, obligate anaerobes, highly toxigenic

Question 24

Describe Clostridium tetani?

Answer 24

Transmission- spores ubiquitous in soil/ contaminates wounds
Neuro-toxin- excitation of motor neurones by blocking release of inhibitory GABA
Spastic paralysis (rigidity of voluntary muscles/lock jaw)
Hyper-sympathetic state as catecholamine release not inhibited
Fatal outcome, slow outcome
Not sterile equipment to cut umbilical cord

Question 25

Describe C botulinum?

Answer 25

Food-bourne transmission/ spores germinate- soil wound botulism
Neuro-toxin- prevents release of acetylcholine
Symmetrical flaccid descending paralysis
Oculomotor motors affected, dysphagia, respiratory depression
Cranial nerves- cant open eyes, swallow, foaming in mouth
Botox

Question 26

Describe Clostridium difficile?

Answer 26

Ingestion of spores in hospital environment
NB spores survive alcohol
Enterotoxin- diarrhoea and cell death of colonic epithelium
Severe watery diarrhoea, major cause of healthcare associated infection

Question 27

Describe Clostridium perfringens

Answer 27

Spores ubiquitous to soil and human gut
a-toxin/ lecithinase- damages cell membranes including haemolysis
Gas gangrene and other soft tissue infections
Food poisoning