Micromodules: Gram negative rods

Question 1

What are three key features of members of the Enterobacteriaceae family?

Answer 1

1. Ferment glucose
2. Negative in oxidase test
3. They are nitrate positive

Question 2

What does the oxidase test do?

Answer 2

Distinguishes Enterobacteriaceae from many other gram negative rods

Question 3

What are the five disease associations with enterbobacteriaceae?

Answer 3

PUDAT:
Plague
UTIs
Diarrhoea
Antibiotic resistent nosocomial infections
Typhoid fever

Question 4

Why are enterobacteriaceae the most common cause of UTIs?

Answer 4

Many of them are commensals of the human bowel

Question 5

Which member of the enterobacteriaceae family is the usual cause of UTIs?

Answer 5

Uropathogenic Escherichia coli - they possess special virulence factors that enable them to colonise the urethra`

Question 6

What are some of the enterobacteriaceae involved in antibiotic resistent nosocomial infections?

Answer 6

Enterobacter
Proteus
Morganella
Serratia

Question 7

What are some reasons that patients in hospitals are very susceptible to infections?

Answer 7

• Elderly/debilitated/post-operative
• immunocompromised - above reasons, or cancer or immunosuppressive drugs
• things have been done to their bodies which interfere with aspects of their innate immunity i.e. intravenous catheters, endotracheal tubes, urinary catheters, surgery

Question 8

How do we combat nosocomial infections?

Answer 8

1. stringent infection control
2. antibiotic stewardship
3. minimising factors which make patients more prone to infection

Question 9

What are common types of nosocomial infections?

Answer 9

Pneumonia
UTI
Bloodstream infections
Surgical wound infections
Orthopaedic infections

Question 10

What are some Enterobacteriaceae members that cause diarrhoeal illness?

Answer 10

• Salmonella enterica and Salmonella bongori.
• Shigella species cause bacillary dysentery - faeces contains pus and blood
• Escherichia coli speies like enterohaemorrhagic E coli (EHEC) ,enteropathogenic E coli (EPEC), Enterotoxigenic E coli (ETEC)
• Yersinia eterocolitica, which also infects the lymph nodes

Question 11

Which genus and species causes Typhoid fever and what is the mechanism for doing so?

Answer 11

Salmonella typhi and Salmonella paratyphi.

They invade the bowel wall to produce the serious systemic disease of typhoid fever/enteric fever

Question 12

Describe the morphology of Campylobacter species, the two species which cause the most human disease and where you find them

Answer 12

Gram negative rods with spiral morphology.
Most human disease is caused by Campylobacter jejuni and Campylobacter coli.
They’re carried by a number of bird species and found in cattle. They’re able to contaminate water and meat

Question 13

What disease do Campylobacter species cause?

Answer 13

Common cause of human diarrhoea (in which there may be blood), and may be associated with vomiting, nausea, abdominal cramps and fever

Question 14

What is the morphology of the Helicobacter human pathogen and where do you find it?

Answer 14

Helicobacter pylori is a gram negative rod with helical morphology and is found in the gastric mucosa of patients with gastritis and peptic ulcers

Question 15

What are some of the mechanisms that H pylori damages gastrointestinal epithelial cells?

Answer 15

• Toxicity produced by the ammonia they make after breaking down urea
• Damage caused by bacterial enzymes
• Inflammatory response in mucosa caused by exposure to bacterial peptidoglycan

Question 16

What proportion of the world’s population is infected with H pylori

Answer 16

50%. The majority have no symtoms

Question 17

Where do you find Legionella species?

Answer 17

Aquatic environments

Question 18

Why are legionella species hard to grow?

Answer 18

Fastidious nutritional requirements

Question 19

Which species of Legionella causes the most human disease and how do outbreaks occur?

Answer 19

• Legionella pneumophilia

- get it when people inhale water vapour from man made water sources that has not been properly maintained

Question 20

WHat disease does Legionella pneumophilia cause?

Answer 20

• Pneumonia - often severe
• high fever
• gastrointestinal disease
• more likely in smoker
• likely to be community acquired of found in clusters

Question 21

What is the other Legionella species responsible for human disease?

Answer 21

Legionella longbeachae

Causes community acquired pneumonia similiar to Legionella pneumophilia

Question 22

What do Genera Pseudomonas, Strenotrophomonas, Burkholderia and Acinetobacter have in common, and why is it important?

Answer 22

• They don’t utilise glucose by fermentative biochemical pathways
• This property is central to identifying them in the laboratory

Question 23

In which setting is Pseudomonas aeruginosa important, and why?

Answer 23

It’s a mainly a hospital pathogen, and is inherently resistant to many antibiotics.
Hospital acquired infections caused by P. aeruginosa may lead to septicaemia.

Question 24

What are some of the nosocomial infections caused by P aeruginosa?

Answer 24

UTIs
Pneumonia
Infection of burn wounds
Often colonises chronic wounds

Question 25

Which organism causes Swimmers ear/otitis externa?

Answer 25

Pseudomonas aeruginosa

Question 26

What is the significance of an oxidase positive Gram negative rod?

Answer 26

It is NOT one of the Enterobacteriaceae

It MAY be Pseudomonas aeruginosa

Question 27

Describe the oxidase test

Answer 27

-Detects the presence of Cytochrome Oxidase, an enzyme in the electron transport chain of some bacteria.

Test:
colourless compound takes the place of oxygen in the real chemical reaction, and when this is reduced it becomes blue.

Question 28

Does Stenotrophomonas maltophilia behave in a similiar manner to P.aeruginosa?

Answer 28

Yes: colonises hospitalised patients and causes nosocomial infection in debilitated patients. It’s resistant to many antibiotics and causes:

• LRTI
• Surgical infections
• Septicaemia