Gram negative organisms of clinical significance

Question 1

GI G-ve rods characteristics

Answer 1

Found in soil and water
Gi tract Commensals of human and other animals
often sensitive to drying (like water)
Facultative anaerobes
Contain LPS(Lipopolysaccharide)
*Antigenic
*potential endotoxin
Diverse taxonomy and only a fraction are G-ve rod
Can cause disease in both the body and GIT
Faecal-oral is the route of transmission

Question 2

where is E.coli found

Answer 2

In the colon of humans and animals

Question 3

Characteristics of E.coli

Answer 3

• Pathogenic within and outside the GIT
• Fimbriae/pili adhere to the mucosal surfaces
• Can be motile or non-motile
• Ferment lactose

Question 4

What type of antigen do E.coli have?

Answer 4

3 structural antigens
O, H, K
The serotypes are associated with different diseases

Question 5

Where are the E.coli antigens located?

Answer 5

O antigens: On cell wall
H antigens: Flagellae
K antigens: Capsule / mucoid layer

Question 6

What are the different intestinal pathogenic types?

Answer 6

Enterotoxigenic
Enteropathogenic
Enterohaemorrhagic
Enteroinvasive

Question 7

What is Enterotoxigenic (ETEC) Known as

Answer 7

Known as travelers diarrhoea

Question 8

What are the common causes of enterotoxigenic?

Answer 8

Food/water, human waste, person-to-person

Question 9

What are the two enterotoxins and what are the results of that?

Answer 9

Hypersecretion of Chloride and water
Inhibition of sodium reabsorption

Lead to watery diarrhoea

Question 10

Enteropathogenic (EPEC)

Answer 10

• Diarrhoea in infants (poor sanitation)
• Newborns infected during birth
• Attach to small intestine
• Shiga-like (named after Kiyoshi Shiga) toxins
• Destruction of microvilli, development of lesions
• Watery diarrhoea (chronic)

Question 11

Enterohaemorrhagic (EHEC)

Answer 11

• Most notorious strain O157:H7
• Binds to cells in large intestine
• Verotoxins in large amounts
• These affect host cell protein synthesis
• Severe copious bloody diarrhoea (haemorrhagic colitis)
• may progress to haemolytic uraemic syndrome (HUS)
  
  • Fever, acute renal failure, anaemia
  • Common in children 5-10yrs (still under 10% of cases)

Question 12

Why are antibiotic avoided in EHEC/STEC

Answer 12

This is because the death of E.coli will lead to rapid release of the toxins which would lead to worsening of the condition.

Question 13

Enteroinvasive (EIEC)

Answer 13

No toxins but cause direct mucosal damage due to invasive infection
Dysentery-like syndrome
Fever and bloody stools

Question 14

What steps are taken to avoid and treat E.coli enteritis

Answer 14

• Care in selection, preparation and consumption of food and water
• Maintain fluid and electrolyte balance
• Antibiotics can shorten duration(probably avoid if enterohaemorrhagic)
• Resistance is widespread and readily spread

Question 15

What are some Extraintestinal diseases caused by E.coli

Answer 15

• UTI caused by cystitis, pyelonephritis
  
  • Fimbriae (adhesion), haemolysin, resistance to immune system activity (capsule)

-Neonatal meningitis: K antigen is the major virulent factor on the capsule
Major cause of infection with the first month of life
These Nosocomial infection which can result in sepsis and bacteremia

Question 16

Treatment for extraintestinal E.coli infections?

Answer 16

Antibiotic required expect for EGHEC

• Beta-lactams: Penicillin V and G No amoxicillin
• 2nd gen cephalosporins and upwards
• ESBL strains: carbapenems
• nitrofurantoin, ciprofloxacin, trimethoprim +/- sulphamethoxazole, fosfomycin, …

Question 17

What is salmonella?

Answer 17

An infection that leads to various diseases; gastroenteritis, typhoid fever
All strains grouped as Salmonella enterica

Question 18

What are the specific serotypes/subtypes of samlonella

Answer 18

Typhi

Typhimurium

Question 19

Salmonella characteristic

Answer 19

• Widely distributed in nature
• Do not ferment lactose (Lac-)
• Typhi – exclusively human pathogen
• Others – other animals and foods
• Epidemics in crowded situations
• Invade epithelial cells of the small intestine
• Disease may become systemic
• Intracellular, survive in phagocytes

Question 20

Gastroenteritis symptoms

Answer 20

Nausea, vomiting, non-bloody diarrhoea
Develops within 48hrs
Fever and abdominal cramping

Question 21

what serotypes is Gastroenteritis

Answer 21

Typically non-typhi

Question 22

What is serotype of typhoid fever

Answer 22

Typhi

Question 23

Symptoms of typhoid fever

Answer 23

Severe, life-threatening, systemic illness
Fever and abdominal symptoms
Also: headache, chills, sweats, weakness, sore throat, cough, myalgia

Question 24

Treatment of Gastroenteritis

Answer 24

Antibiotics may not be useful so supportive treatment should be used alone

Question 25

Treatment of enteric fever (typhoid)

Answer 25

fluoroquinolones, b-lactams, macrolides

Question 26

Characteristics of campylobacter

Answer 26

Curved, spiral or S-shaped rods • Single flagellum (motile) • Microaerophilic • Don’t ferment carbohydrates • Infect intestine (jejunun, ileum, colon) • Bacteraemia possible though rare (extremes of age, co-morbidity)

Question 27

Where are campylobacters found and how is it transmitted

Answer 27

Widely distributed in nature – Fowl (major reservoir) and Mammals • Faecal / oral route transmission

Question 28

What does campylobacter cause

Answer 28

Cause intestinal disease – rarely extra-intestinal Acute enteritis

Question 29

Which species of campylobacter causes the most disease

Answer 29

By the C.jejuni species -99%

Question 30

Properties of acute enteritis

Answer 30

1-7 days incubation – Self-limiting (but several weeks) – Systemic symptoms: Fever, headache, myalgia – Intestinal symptoms: cramps, diarrhoea

Question 31

What is used to treat acute enteritis caused by Campylobacter jejuni

Answer 31

Thorough cooking (esp BBQ chicken), milk pasteurisation, disinfect surfaces – Fluid and electrolyte balance often sufficient – Antibiotics if needed (start early & if severe): • erythromycin / clarithromycin (resistance?) • ciprofloxacin • 3rd generation cephalosporin if very severe

Question 32

What is shigella

Answer 32

Shigellosis (bacterial bacillary dysentery | It is intestinal

Question 33

Properties/characteristics of Shigella

Answer 33

``` Non-motile, unencapsulated, does not ferment lactose (Lac-) Person-to-person, contaminated stools Also: flies, food, water Low infectious dose (10 - 200 organisms) ```

Question 34

What are the 2 of 4 groups of shigella and how do they operate

Answer 34

Group A: S. dysenteriae (most severe) Group D: S. sonnei - Invade and destroy mucosa of large intestine - Shigatoxin – enterotoxic, cytotoxic

Question 35

What are the symptoms Group A: S. dysenteriae

Answer 35

``` -Diarrhoea with blood, mucous and painful abdominal cramps -Severe in children and elderly -Malnourished: dehydration and death -Resolves in 1 week (if survived) ```

Question 36

Treatment for group A shigella

Answer 36

ciprofloxacin, ceftriaxone or azithromycin – Antibiotics reduce duration and shedding – But Widespread resistance – Vaccine in development

Question 37

What is vibrio Cholerae what is it shaped like

Answer 37

Short, curved rod-shaped with Single polar flagellum

Question 38

What are the properties of vibrio cholerea

Answer 38

``` Facultative anaerobes Require NaCl – waterborne organisms, so seawater / estuaries Transmitted via food and water No known animal reservoirs or vectors Carriage in humans uncommon Associated with raw seafood Outbreaks – poor sanitation of water supplies ```

Question 39

Vibrio cholerae infection

Answer 39

Infects small intestine • Incubation, few hrs up to 1-2 days • Adhesion factors (colonisation and virulence) • Enterotoxin causes massive fluid and electrolyte loss (secretory diarrhoea) • “Rice-water" stools

Question 40

Treatment options for vibrio cholera includes:

Answer 40

Tetracyclines, macrolides, quinolones -Severe disease occurs in about 5% of cases: • If untreated: 50% death within hrs • Treatment: <1% death – Aggressive replacement of fluid & electrolytes – Antibiotics decrease duration and shedding

Question 41

List the 3 Yersinia species

Answer 41

Y. enterocolitica (enterocolitis) – Y. pseudotuberculosis (enterocolitis, despite name) – (Y. pestis – bubonic plague)

Question 42

Properties of Yersinia enterocolitica

Answer 42

Contaminated food (abattoirs, raw meat) • Lesions in ileum, enlargement of lymph nodes • Enterocolitis: fever, abdominal pain, diarrhoea, right lower quadrant tenderness (pseudoappendicitis) – Resolves in 2-3 weeks • May → Polyarthritis, pharyngitis, septicaemia

Question 43

Treatment of yersinia enterocolitica

Answer 43

ciprofloxacin, | trimethoprim-sulphamethoxazole

Question 44

what is helicobacter pylori

Answer 44

Curved or spiral organisms, closely related to Campylobacter Multiple polar flagellae (corkscrew motility) – Produces urease (urea to ammonia, protects against acid) – Causes sub-acute gastritis, leading to duodenal and gastric ulcers

Question 45

Helicobacter pylori properties

Answer 45

- World-wide distribution, very common - Person-to-person transmission - “Never” isolated from food or water - Untreated: chronic life-long condition - Colonises stomach, duodenum, oesophagus - Survives in mucus layer coating epithelium

Question 46

Infections caused by helicobater pylori

Answer 46

``` Initial infection – 1 week – Gastritis, diarrhoea Chronic – Superficial gastritis, ulcers – Risk of carcinoma, B-cell lymphoma Elimination requires combination therapy – Readily develops resistance, always multiple agents ```

Question 47

Treatment of helicobater

Answer 47

– Proton pump inhibitor, –amoxicillin, –clarithromycin, –metronidazole,