Medically Important Microbes

Question 1

What are the ways in which we can categorise bacteria?

Answer 1

1. Gram staining: positive vs. negative
2. Morphology: cocci vs. bacilli
3. Growth: anaerobic vs. aerobic
4. Gram-stainable vs. non gram-stainable
5. Extracellular vs. intracellular
6. Culturable vs. non-culturable
7. Fermenters vs. non-fermenters

Question 2

Why is gram staining helpful?

Answer 2

1. It proves there are bacteria present in the sample
2. It allows us to target certain bacteria groups
3. It gives us some more clues to help identify which bacteria is causing the infection
4. Cheap, simple and quick

Question 3

Which bacteria will stain with counter stain safranin?

Answer 3

Gram negative

Question 4

Why does a gram negative bacteria stain with safranin, whereas a gram positive bacteria will not?

Answer 4

This is due to differences in peptidoglycan thickness difference. Gram +ve bacteria have a thick peptidoglycan layer where as G-ve do not.

Question 5

What colour does a G+ve bacteria look under the microscope?

Answer 5

Purple due to the retention of crystal violet stain due to the thick peptidoglycan content

Question 6

Define the following growth requirement: Obligate aerobe

Answer 6

This type of bacteria will only grow in the presence of oxygen.

Question 7

Define the following growth requirement: Obligate anaerobes

Answer 7

These bacteria will only grow in the absence of oxygen

Question 8

Define the following growth requirement: facultative anaerobes and facultative aerobes

Answer 8

These bacteria grow well in the presence and absence of oxygen. Most human pathogens have this characteristic.

Question 9

Define the following growth requirement: Microaerophilic

Answer 9

This type of bacteria prefer lower oxygen concentrations

Question 10

Describe the following morphology: cocci

Answer 10

Round bacteria that can appear in chains, pairs or clusters

Question 11

Define the following morphology: Rods (bacilli)

Answer 11

Elongated looking bacteria

Question 12

Define the following morphology: coccobacilli

Answer 12

An intermediate shape between rods and cocci

Question 13

Define the following morphology: Spiral

Answer 13

Look like a twirl

Question 14

How do Beta-lactam (penicillin) Abx work?

Answer 14

They inhibit peptidoglycan synthesis in bacterial cell walls therefore are bactericidal

Question 15

Why do we sometimes have to give beta-lactamase inhibitors with a penicillin (beta-lactam antibiotic)?

Answer 15

Some bacteria can neutralise the effect of beta-lactam antibiotics and use beta-lactamase enzymes to break down the beta-lactam ring. The combination of penicillin and a beta-lactamase inhibitor should allow the penicillin to be effective.

Question 16

Give an example of a beta-lactamase inhibitor

Answer 16

Tazobactam

Question 17

What bacteria commonly cause traveller’s diarrhoea?

Answer 17

• Shigella Salmonella
• Yersinia enterocolitica
• Campylobacter
• E.Coli O157:H7

Question 18

Which parasites can cause traveller’s diarrhoea?

Answer 18

• Entamoeba histolytica

- Isospora belli

Question 19

When does traveller’s diarrhoea normally present?

Answer 19

Within the first few days of travel

Question 20

What is the most common route for Traveller’s Diarrhoea?

Answer 20

Faecal-oral

Question 21

What is the most important piece of advice to give to someone with Traveller’s diarrhoea?

Answer 21

Keep hydrated as lots of insensible fluid losses will occur from the diarrhoea

Question 22

When would someone with traveller’s diarrhoea need treatment with antibiotics and admission?

Answer 22

• Bacteraemia - bacteria present in the blood culture

- Dysentery - infection of the intestines

Question 23

What neurological syndrome can be related to infective diarrhoea?

Answer 23

Guillan-Barre syndrome

Question 24

What is the potential long-term complication of bacterial traveller’s diarrhoea?

Answer 24

Reative arthritis

Question 25

What is the most common cause of bacterial pneumonia?

Answer 25

Streptococcus pneumoniae

Question 26

What is the morphology of S.Pneumoniae?

Answer 26

Gram +ve coccus

Question 27

What is the mortality rate in association with candidaemia?

Answer 27

40-50%

Question 28

Is candidaemia a medical emergency?

Answer 28

YES This carries a very significant mortality rate and should be treated as quickly as possible. IV antifungal treatment for 2 weeks will be required

Question 29

What is the most common source for candidaemia?

Answer 29

From gut flora - microscopic or macroscopic bowel damage allows the gut flora to pass into the blood stream

Question 30

What are the 3 categories of fungal infection?

Answer 30

- Superficial - Subcutaneous - Deep

Question 31

List some superficial fungal infections

Answer 31

- Oral and vaginal thrush - Tinea - Fungal nail infection - Pityriasis versicolor

Question 32

Who can get superficial fungal infections?

Answer 32

Anyone, they are common. E.g. ringworm, athletes foot etc

Question 33

Who is more at risk of developing superficial fungal infection?

Answer 33

Those who are immunocompromised - HIV or diabetic patients

Question 34

Where in the world do subcutaneous fungal infections occur most commonly?

Answer 34

In tropical countries

Question 35

Who is at risk of deep fungal infections?

Answer 35

Those who are immunocompromised in some way

Question 36

Name some deep fungal infections

Answer 36

- Invasive candida sp. : Central line infection - Invasive Aspergillus fumigatus: transplant and chemo patients - Pneumocystis jirovecii pneumonia - Cryptococcal meningitis

Question 37

What is the clinical term for chickenpox?

Answer 37

Primary varicella zoster infection

Question 38

What sort of rash is common in chickenpox?

Answer 38

Widespread, itchy, vesicular rash

Question 39

What are some severe complications of chickenpox?

Answer 39

- Pneumonitis - Bacterial infection of the skin - Encephalitis - Hepatitis - Myocarditis

Question 40

What treatment should be used in an immunocompromised patient for chickenpox?

Answer 40

Aciclovir

Question 41

What is the route of chickenpox infection?

Answer 41

Mucosa of the upper respiratory tract or conjunctiva

Question 42

What are the prodromal symptoms of a chickenpox infection?

Answer 42

- Fever | - Lethargy

Question 43

There are dermatological changes in chickenpox. What does it originally present as and develop into?

Answer 43

Macules and papules which go on to become vesicles which burst and then crust

Question 44

What are the 4 most important herpes viruses to know?

Answer 44

- Herpes simplex-1 (HSV1) - Herpes simplex-2 (HSV2) - Epstein-Barr virus (EBV) - Cytomegalovirus (CMV)

Question 45

What was the MMR vaccine said to be related to developing in the early 2010s?

Answer 45

Autism

Question 46

What are the prodromal features of measles?

Answer 46

- Fever - Malaise - Conjunctivitis - Cough

Question 47

What is a distinguishing feature of measles?

Answer 47

Koplik spots in the buccal cavity mucosa - blue/grey/white spots

Question 48

What sort of rash is present in measles?

Answer 48

Morbilliform rash (maculopapular) beginning on the face then spreading down the body

Question 49

What are the potential complications of measles?

Answer 49

- Bacterial pneumonitis - Otitis media - Acute encephalitis

Question 50

What are some of the key features of a HIV infection?

Answer 50

- Generalised rash - Pharyngitis - Generalised lymphadenopathy - Headache - Mouth ulcers - Flu-like symptoms

Question 51

What does HSV-1 commonly cause?

Answer 51

Oral or ocular disease

Question 52

What does HSV-2 commonly cause?

Answer 52

Genital lesions

Question 53

What are the symptoms of Glandular fever?

Answer 53

- Fever - Sore throat - Lymphadenopathy

Question 54

Which drug can precipitate glandular fever?

Answer 54

Amoxicillin

Question 55

Define the following; Endoparasites

Answer 55

Parasites that live on the skin and hair

Question 56

Define the following; Endoparasites

Answer 56

Parasites that live on the mucosal surfaces such as the gut and in tissue

Question 57

What are helminth parasites?

Answer 57

Worm-like parasites, mostly visible to the naked eye

Question 58

What are protozoan parasites?

Answer 58

Single-celled eukaryotic organisms that are usually motile

Question 59

What is a definitive host?

Answer 59

The animal that hosts the adult stage of a parasite

Question 60

What is an intermediate/secondary host?

Answer 60

The animal that hosts the developmental stage of the parasites life

Question 61

What is an accidental host?

Answer 61

A host that the parasite cannot use to complete its life-cycle. This host is a dead end for the parasite.

Question 62

What is a vector?

Answer 62

A parasite that can transmit other diseases such as bacterial infection e.g. some ticks are vectors for Lyme disease

Question 63

What are mosquitos the vector for?

Answer 63

Malaria

Question 64

What is the recommended chemoprophylaxis against Malaria?

Answer 64

Doxycycline

Question 65

What is the commonest cause of eosinophilia in clinical practice?

Answer 65

Atopic disease - asthma, hayfever, eczema

Question 66

What parasite causes pinworm?

Answer 66

Enterobius vermicularis

Question 67

How does the lifecycle of the pinworm carry out?

Answer 67

An adult worm lives in the gut of the child. During the night the worm ventures out of the anus and lays eggs at the perineum. The child gets an itchy bottom and then transfers the eggs from perineum to mouth or others' mouths.

Question 68

Where can Diphyllobothrium latum be caught from?

Answer 68

Eating undercooked fish or sashimi

Question 69

Which organisms does metronidazole treat?

Answer 69

``` Obligate anaerobes (G+ve or G-ve) Giardia ```