Infections III: Bacterial resistance to antibiotics

Question 1

What are the 2 types of resistance that bacteria can acquire to antibacterial drugs?

Answer 1

1. Inherent (natural) resistance

2. Acquired resistance

Question 2

Describe inherent (natural) resistance

Answer 2

e.g. Gram negative bacteria = outer membrane provides a permeability barriers
Stops sufficient amounts of antibiotic entering cell to exert action

Question 3

Describe acquired resistance

Answer 3

Most infections respond to a new antibiotic

Over time resistance is acquired and treatment fails

Question 4

What causes acquired resistance?

Answer 4

Changes in the bacterial genome:

• Can be by mutation and selection = vertical evolution
• Or by exchange of genes between strains/species = horizontal evolution

Question 5

How does an entire colony of bacteria becomes resistant (acquired)?

Answer 5

A group of bacteria, including a resistant variety, are treated with antibiotics
The non-resistant bacteria die
The resistant bacteria survive, multiply and become more common
Eventually the entire infection evolves into a resistant strain

Question 6

List the 3 ways in which bacteria can swap genes to = horizontal evolution, acquired

Answer 6

1. Conjugation
2. Transduction
3. Transformation

Question 7

Give examples of how conjugation occurs between bacteria cells

Answer 7

Cell-cell contact

DNA crosses a sex pilus

Question 8

Explain what transduction between bacterial cells is

Answer 8

Genes transported by bacterial virus

Question 9

Explain what transformation between bacterial cells is

Answer 9

DNA acquired from environment

Question 10

List the 4 mechanisms of resistance that bacteria use

Answer 10

1. Conversion of active drug to inert product by enzyme
2. Reduction in cellular permeability to antibiotic
3. Changes in antibiotic target site = resistance OR acquisition of resistant form of target enzyme
4. Altered metabolic pathway

Question 11

Give an example of how an active drug can be converted to an inert product by bacteria to make them resistant

Answer 11

Gram positive and negative bacteria can produce beta-lactamase = converts penicillin to penicilloic acid = not antibacterial

Question 12

How does a reduction in cell wall permeability make bacteria resistant?

Answer 12

Stops antibiotic reaching toxic levels in the cell
Can be:
- Change in cell wall/membrane
- Antagonism of antibiotic transport processes
- Generation of efflux pump

Question 13

Give an example of how changes in the antibiotic target site results in resistance

Answer 13

S. aureus changes penicillin binding proteins on cell wall so it cannot have its effect

Question 14

List 3 superbugs

Answer 14

MRSA = methicillin-resistant staphylococcus aureus
CRE
C. difficile

Question 15

How does clostridum difficile become harmful?

Answer 15

Normally live in the digestive system
Not harmful because other bacteria keep it under control
Some antibiotics can kill this bacteria (normal flora)
Therefore C.diff can multiply and produce toxins = illness

Question 16

Describe glycopeptide-resistant enterococci (GRE)

Answer 16

• Gram positive cocci
• Enteric - normally found in the digestive/urinary tract
• Intrinsically resistant to many antibiotics
• But has also acquired resistance by conjugation

Question 17

What do glycopeptide-resistant enterococci (GRE) cause?

Answer 17

Wound infections
Bacteraemia (bacteria in blood, blood normally sterile)
Abdominal/pelvic infection

Question 18

What are the current antibiotics to use to treat GRE?

Answer 18

Linezolid
Daptomycin
Tigecycline

Question 19

Describe carbapenem-resistant enterobacteriaceae

Answer 19

Gram negative bacilli
Part of gut flora, also found in soil/water
Becoming resistant to most/all antibiotics

Question 20

What are the current treatment options available to treat carbapenem-resistant enterobacteriaceae?

Answer 20

Polymyxins
Tigecycline
Fosfomycin
Aminoglycosides

Question 21

What is tuberculosis?

Answer 21

Contagious lung infection

Mycobacterium tuberculosis

Question 22

How is tuberculosis transmitted?

Answer 22

Aerosol

Question 23

Describe what happens when person is infected with TB

Answer 23

First site of infection = lungs
Primary infection - can be resolved with local scarring
Dissemination (spreading) = miliary infection

Question 24

List the symptoms of TB which affect the major organs of the body

Answer 24

Lungs = chronic cough, haemoptysis, fever, weight loss
Brain = meningitis
Kidney = fever, weight loss, hydronephrosis
Spine = bone infections, vertebral collapse, nerve compression

Question 25

How is TB diagnosed?

Answer 25

Bronchoscopy
Chest CT scan
Chest x-ray

Question 26

How can TB be prevented?

Answer 26

Skin testing (PPD)
Positive skin test = TB exposure but inactive infection
Prompt treatment important
BCG vaccination available in countries with high incidence of TB

Question 27

Describe MRSA

Answer 27

Gram positive cocci

Acquires mecA gene - expression gives penicillin-binding protein variant, PBP2A

Question 28

List 3 antibiotics currently used to treat MRSA

Answer 28

Vancomycin
Linezolid
Rifampicin

Question 29

How is MRSA acquired in hospital?

Answer 29

Patients with opened wounds/weakened immune systems
Staff who do not follow proper sanitary procedures may inadvertently transfer from patient to patient
MRSA can survive on surfaces and fabrics

Question 30

List 5 ways that resistance can be managed/prevented

Answer 30

Prudent antibiotic prescribing
Hand hygiene
Enhanced environmental cleansing
Isolation
Personal protective equipment

Question 31

What is a broad spectrum antibiotic?

Answer 31

One which is effective against a wide range of disease-causing bacteria
Gram negative and positive

Question 32

What is a narrow spectrum antibiotic?

Answer 32

An antibiotic only effective against specific families of (disease-causing) bacteria