Medical Microbiology

Question 1

Name the different places that carry infection

Answer 1

Infectious diseases
Dental caries and periodontal disease 
Intensive care
Haematology and oncology patients 
Children
General practice 
Hospital acquired infection (HAI)

Question 2

What are possible infecting agents?

Answer 2

Bacteria 
Viruses
Fungi 
Parasites 
Prions

Question 3

Give examples from the two different specimen types (sterile and non-sterile sites)

Answer 3

Sterile sites - blood, CSF, lung, bladder

Non-sterile sites - skin, nasopharynx, urethra, gut

Question 4

Describe the specimen collection for bacterial cultures

Answer 4

UTI - mid-stream urine (MSU)

Chest infection - sputum

Tonsillitis/pharyngitis - throat swab

Wound or site of infection - swab or pus (swabs are sent in bacterial transport medium)

Diarrhoea - faeces

Bacteraemia - blood culture

Meningitis - cerebro-spinal fluid (CSF)

Question 5

What uses does microscopy have?

Answer 5

Light microscopy (x1000 magnification)

Unstained

• to see pus cells (urine, CSF)
• to see parasites (faeces)

Gram stain - to see bacteria and yeasts/fungi

Zn stain or auramine stain - to see mycobacteria

Viruses not visible in light microscope

Question 6

What are the pros and cons of gram stain and microscopy?

Answer 6

Rapid - telephone urgent information

Not sensitive

Can’t usually identify particular species

Question 7

What are the pros and cons of bacterial culture?

Answer 7

Slow

Sensitive

Culture conditions suitable for the expected species

Question 8

Describe the different culture conditions suitable for the expected species on bacterial cultures

Answer 8

1. Type of media:
   *non-selective(specialised) *selective
   examples:
   Blood, chocolate
   For mycobacteria
   MacConkey
2. Atmosphere
3. Temperature
4. Duration of incubation

Question 9

Describe the pros and cons of ID of species

Answer 9

Use observable characters

• morphological
• physiological
• biochemical

Rapid and simple to perform

DNA based tests

Species name (e. choli)

Typing (optional) distinguishes strains within a species for epidemiological reasons

Question 10

How are the ID of species interpreted?

Answer 10

Knowledge of normal flora at site

Knowledge of likely pathogens at site

Clinically significant in light of clinical picture - if yes, antibiotic sensitivity tests performed

Question 11

What is involved in making the diagnosis of viral infections?

Answer 11

Molecular methods
- real time PCR

Antigen detection

Serology to determine immunity

Rarely used now

• electron microscopy
• cell or tissue culture - inoculate a ‘cell line’

Question 12

What are the three different types of parasites?

Answer 12

Protozoa

Helminths (worms)

Arthropods

Question 13

Give examples of protozoa

Answer 13

Malaria
Amoebae
Flagellates

Question 14

Give examples of helminths (worms)

Answer 14

Roundworms
Tapeworms
Flukes

Question 15

Give examples of arthropods

Answer 15

Lice
Ticks
Mites

Question 16

What are the different diagnostic principles in parasitology?

Answer 16

Microscopy of different stages

• parasites, cysts and ova (P,C and O) in faeces
• blood films for malaria

Culture rarely possible

Serology sometimes useful

Question 17

Name health acquired infections

Answer 17

Methicillin Resistant Staph Aureus (MRSA)

Clostridium difficile

Organisms with extended spectrum B-lactamases (ESBLs)

Noroviruses

Question 18

Name ways that infection can be controlled

Answer 18

Wash hands before touching patient

Wash hands or apply alcohol gel between patients

Swab stethoscope between patients

Patients isolated in single room (‘‘barrier nursed’’ or source isolation) have extra precautions

• wash hands, wear plastic apron
• on leaving, dispose of apron, wash hands

Question 19

What does a medical microbiologist do?

Answer 19

Advice on the diagnosis of infection

Supervision and review of lab tests

Advice on interpretation of test results

Advice on treatment /management (antibiotics)

Infection control/prevention

Antibiotic policy