Flashcards in Micromodules: Gram negative rods Deck (28)
What are three key features of members of the Enterobacteriaceae family?
1. Ferment glucose
2. Negative in oxidase test
3. They are nitrate positive
What does the oxidase test do?
Distinguishes Enterobacteriaceae from many other gram negative rods
What are the five disease associations with enterbobacteriaceae?
Antibiotic resistent nosocomial infections
Why are enterobacteriaceae the most common cause of UTIs?
Many of them are commensals of the human bowel
Which member of the enterobacteriaceae family is the usual cause of UTIs?
Uropathogenic Escherichia coli - they possess special virulence factors that enable them to colonise the urethra`
What are some of the enterobacteriaceae involved in antibiotic resistent nosocomial infections?
What are some reasons that patients in hospitals are very susceptible to infections?
- 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
How do we combat nosocomial infections?
1. stringent infection control
2. antibiotic stewardship
3. minimising factors which make patients more prone to infection
What are common types of nosocomial infections?
Surgical wound infections
What are some Enterobacteriaceae members that cause diarrhoeal illness?
-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
Which genus and species causes Typhoid fever and what is the mechanism for doing so?
Salmonella typhi and Salmonella paratyphi.
They invade the bowel wall to produce the serious systemic disease of typhoid fever/enteric fever
Describe the morphology of Campylobacter species, the two species which cause the most human disease and where you find them
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
What disease do Campylobacter species cause?
Common cause of human diarrhoea (in which there may be blood), and may be associated with vomiting, nausea, abdominal cramps and fever
What is the morphology of the Helicobacter human pathogen and where do you find it?
Helicobacter pylori is a gram negative rod with helical morphology and is found in the gastric mucosa of patients with gastritis and peptic ulcers
What are some of the mechanisms that H pylori damages gastrointestinal epithelial cells?
-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
What proportion of the world's population is infected with H pylori
50%. The majority have no symtoms
Where do you find Legionella species?
Why are legionella species hard to grow?
Fastidious nutritional requirements
Which species of Legionella causes the most human disease and how do outbreaks occur?
- get it when people inhale water vapour from man made water sources that has not been properly maintained
WHat disease does Legionella pneumophilia cause?
-Pneumonia - often severe
-more likely in smoker
-likely to be community acquired of found in clusters
What is the other Legionella species responsible for human disease?
Causes community acquired pneumonia similiar to Legionella pneumophilia
What do Genera Pseudomonas, Strenotrophomonas, Burkholderia and Acinetobacter have in common, and why is it important?
-They don't utilise glucose by fermentative biochemical pathways
-This property is central to identifying them in the laboratory
In which setting is Pseudomonas aeruginosa important, and why?
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.
What are some of the nosocomial infections caused by P aeruginosa?
Infection of burn wounds
Often colonises chronic wounds
Which organism causes Swimmers ear/otitis externa?
What is the significance of an oxidase positive Gram negative rod?
It is NOT one of the Enterobacteriaceae
It MAY be Pseudomonas aeruginosa
Describe the oxidase test
-Detects the presence of Cytochrome Oxidase, an enzyme in the electron transport chain of some bacteria.
colourless compound takes the place of oxygen in the real chemical reaction, and when this is reduced it becomes blue.