CSI 3

Question 1

What are the impacts of Healthcare-Associated Infections on healthcare?

Answer 1

• Cost of resources for treatment
• Losing patient trust
• Increasing hospital stay times (cost)
• Limits number of hospital beds
• Risk of increasing antibiotic resistance
• Healthcare workers might get ill (sick pay)
• Wounds may fail to heal, the prosthesis may get infected causing patients harm.

Question 2

Fill in and explain the stages in the chain of infection

Answer 2

Question 3

How can commensal bacteria cause infections?

Answer 3

• Skin bacteria are commensal on the skin but if introduced into the blood-stream by an IV line, they can cause harmful blood-stream infections.
• Gut bacteria are commensal in the gut but if they get in the urinary tract they can cause UTI.
• Mouth/digestive tract bacteria can cause infections in the lung (if aspirated from the gut into the lungs).

Question 4

What are the modes of disease transmission?

Answer 4

Question 5

What are some examples of direct contact transmission and how can they be prevented?

Answer 5

• Skin to skin contact (common in health care) can be prevented by using gloves/gowns and washing hands.
• Droplet spread from sneezing, coughing and talking. Can be prevented by wearing masks.

Question 6

What are some examples of indirect contact transmission and how can they be prevented?

Answer 6

• Airborne - small particles suspended in the air and carried by air. Can be prevented by improved ventilation.
• Vehicle-borne - bedding, medical equipment, food, water. Can be prevented by washing and sterilising medical equipment, bedding and crockery, properly cooking food.
• Vector-borne - mosquitos, fleas, hospital staff (mechanical if on the hand, biological if host cells are infected).

Question 7

Recall the stages at which you need to wash hands and why?

Answer 7

Question 8

What are the molecular mechanisms by which bacteria can be resistant to antibiotics?

Answer 8

• Decreased membrane permeability
• Target alterations (mutations changing the structural shape of the target preventing antibiotics from binding and working).
• Inactivating enzymes
• Breaking down antibiotics (B-lactamase).

Question 9

Why can pathogens be sensitive to Co-amoxiclav but when they show no sensitivity to amoxicillin?

Answer 9

Co-amoxiclav contains amoxicillin and clavulanic acid.

Question 10

Why is penicillin an effective antibiotic?

Answer 10

It disrupts bacterial cell-wall production and this leads the cell to burst under pressure as structural support to the membrane is no longer available.

Question 11

What are the characteristics of gram-positive bacteria?

Answer 11

They build a thick peptidoglycan sheath around a single membrane

Question 12

What are the characteristics of gram-negative bacteria?

Answer 12

They build a think layer of peptidoglycan sheath between two membranes.

Question 13

What is the significance of the bacterial cell wall?

Answer 13

• Water constantly enters bacterial cell walls by osmosis.
• This builds up pressure on the cell membrane
• The peptidoglycan in the cell wall allows the membrane to resist this pressure by providing it with structural support.

Question 14

How does penicillin act at the molecular level?

Answer 14

• Peptidoglycan is made up of small building blocks
• Each composed of 2 sugars connected to a short chain of amino acids with a peptide bridge extending to the side.
• These sugars are assembled into chains which are then cross-linked via the peptide bridges to form a tough peptidoglycan matrix.
• The enzyme penicillin-binding protein assists with peptidoglycan matrix assembly by creating the cross-link between the chains.
• The active B-lactam ring of Penicillin blocks this enzyme by making a direct bond to serine in its active site.
• This inactivates the enzyme and prevents proper formation of the peptidoglycan matrix.

Question 15

Name some b-lactam antibiotics

Answer 15

Penicillin, Methicillin, Amoxicillin and Ampicillin.

Question 16

How do baceteria like MRSA resist b-lactam antibiotics?

Answer 16

• They express variant targets (penicillin-binding protein 2a in case of MRSA) which have can have altered binding sites that do not bind with b-lactam antibiotics.
• Other bacteria can express b-lactamase enzymes which bind to b-lactam antibiotics and break the b-lactam ring making the antibiotic ineffective.

Question 17

Why did Mr Rhatchett develop a C. difficile infection following treatment with co-amoxiclav?

Answer 17

• Co-amoxiclav is a broad-spectrum antibiotic that targets many different bacteria.
• This may have killed commensal gut bacteria, changing the composition of the gut microbiome.
• Resistant C. difficile begin to proliferate due to less competition.
• They release toxins causing inflammation and damage to the lining of the gut potentially causing diarrhoea.

Question 18

How can you minimise C. diff transmission in hospitals?

Answer 18

• Alcohol gels do not kill C. diff spores so always wash hands.
• Antibiotic stewardship.

Question 19

What are empiric antibiotics?

Answer 19

• These are antibiotics given before culture results come back identifying the pathogen and its antibiotic sensitivities.
• Specific to organ systems and local geographical area.
• Hospital microbiology teams look at what organisms commonly cause a particular infection and offer advice on what antibiotics to use whilst awaiting results.
• After results are back, you may want to change from empiric broad-spectrum antibiotics to specific narrow-spectrum antibiotics.

Question 20

Interesting things about Mr Ratchett’s case

Answer 20

• He got a UTI from E. coli potentially from exposure of skin bacteria into the urinary tract because of the catheter.
• Then co-amoxiclav treatment leads to a C. difficile infection.
• As a result, the co-amoxiclav treatment was stopped immediately.
• Then consultation with the hospital’s microbiology team was required to determine whether to continue with a different antibiotic or stop completely.