Lecture 6.2: Enterobacteriaceae Flashcards
What is the structure of Enterobacteriaceae?
- Family of gram-negative bacteria
- Rod-shaped
- Most have flagella and fimbriae (pili) -peritrichous
- Do not form spores
- Some have capsules
Physiology of Enterobacteriaceae? (7)
- Grow rapidly and have simple nutritional requirements
- Facultative anaerobes
- They ferment glucose, reduce nitrate
- Catalase positive
- Oxidase negative unlike other gram-negative rods
- Pathogenic members of E. do not ferment lactose
- Pathogenic members of E. are resistant to bile salts
Virulence Factors of Enterobacteriaceae (6)
- Flagellar H antigen
- Capsular K or Vi antigen
• Liposaccharide (LPS)
- O antigen
- Core polysaccharide (present in all E.)
- Lipid A (responsible for endotoxin activity)
- Siderophores
- Type III secretion system
- Antimicrobial Resistance
Species of Salmonella that cause Gastroenteritis? (4)
- S. enteritidis
- S. typhimurium
- S. montevideo
- S. wien
What Salmonella species most commonly causes Gastroenteritis?
• Primarily caused by S. enteriditis
Gastroenteritis via Salmonella: Symptoms
- Nausea
- Vomiting
- Diarrhoea
- Fever
- Abdominal Cramps
- Symptoms may persist for 2-7 days
Gastroenteritis via Salmonella: Treatment
- Rehydration
* Cephalosporins if infection spreads to blood stream
How does Salmonella infect a host?
1) It attaches to mucosa (epithelial cells) of small intestine
2) This triggers endocytosis of Salmonella
3) It then remain in the endocytic vesicles where it replicates
4) S. enterica produce enterotoxins and kill host cells
5) This causes inflammation, cramps, diarrhoea and fever in host
6) It may also enter bloodstream and lead to septicaemia
Species of Salmonella that cause Enteric Fever (Typhoid Fever)? (2)
- S. typhi
* S. paratyphi (paratyphoid fever)
How is Typhoid Fever contracted?
Originates from ingestion of food and water contaminated with human excreta and through contact with infected person
What is Typhoid (Enteric) Fever? Symptoms?
- Acute, life-threatening illness caused by S. typhi
- High fever (within 10 to 14 days)
- Headache (within 10 to 14 days)
- Myalgia (within 10 to 14 days)
- Malaise (within 10 to 14 days)
- At least a week of constipation and abdominal cramping
How long do symptoms of Typhoid Fever persist?
3-4 weeks
Diagnosis of Typhoid Fever
- Stool
- Blood
- Bone Marrow
- Urine Sample Analysis
Treatments for Typhoid Fever
- Antibiotics (fluoroquinolones, chloramphenicol, cephalosporins)
- Vaccinations are also available
How does S.typhi infect a host? (6)
- Ingestion of contaminated food or water
- Invade small intestine and enter bloodstream
- Carried by white blood cells to liver, spleen, and bone marrow
- Multiply and re-enter the bloodstream
- Invade gallbladder, biliary system & lymphatic tissue of the bowel
- Then pass into the intestinal tract
Typhoid Fever: Stage 1
• A slowly rising temperature
• Relative bradycardia (unusually slow heart rate)
• Malaise (discomfort or uneasiness)
• Headache
• Cough
• In ¼ of cases, epistaxis (acute hemorrhage from the nostril, nasal cavity, or
nasopharynx)
Typhoid Fever: Stage 2
- Continuing high fever
- Extremely distended abdomen
- Considerable weight loss
- Bradycardia continues
- Dicrotic pulse wave
- Delirium is frequent, often calm and sometimes agitated
Typhoid Fever: Stage 3
- Intestinal hemorrhage
- Intestinal perforation
- Encephalitis (inflammation of the brain)
- Fever is still very high
- Increased delirium
- Dehydration
- Motionlessness with eyes half-opened
Typhoid Fever: Stage 4
• Defervescence (very high fever) commences that continues into fourth week
Complications of Typhoid Fever
- Overwhelming infections
- Pneumonia
- Intestinal bleeding and perforation
- Kidney failure
- Peritonitis
- Eventual Death
What can you do to water to reduce transmission of Typhoid Fever?
Chlorinate Water
How are the clinically relevant species of Shigella classified?
- Into four O-antigen- based serogroups
- S. dysenteriae, S. flexneri , S. boydii and S. sonnei
What does Shigella cause?
- Cause shigellosis (bacillary dysentery)
- Bacterial gastroenteritis
Shigella Mechanism of Infection (7)
1) Shigella attaches to epithelial cells of colon
2) This triggers endocytosis
3) Shigella multiplies in cytosol
4) Shigella invades neighbouring epithelial cells (actin filaments)
5) Thus avoiding immune defences
6) An abscess forms as epithelial cells are killed by infection
7) Shigella that enters blood is quickly phagocytised
How is Shigella transmitted?
Person to person by the faecal-oral route especially in overcrowded places and areas of poor sanitary conditions
Symptoms of Shigella
- Abdominal Cramps
- Diarrhoea
- Fever
- Bloody Stools
Diagnosis and Treatment of Shigella
• Diagnosis: Stool Sample Analysis
• Rehydration
• Antibiotics (fluoroquinolones, trimethoprim, sulfamethoxazole ciprofloxacin or
azithromycin)
Escherichia coli
Gram-negative
Facultative anaerobic
Rod-shaped
Coliform
What conditions are commonly associated with E.coli?
- Gastroenteritis
- Urinary Tract Infections
- Meningitis
- Sepsis
- Haemorrhagic Colitis
- Haemolytic Uremic Syndrome
What is the most common cause of Haemorrhagic Colitis & Haemolytic Uremic Syndrome?
E.coli O157:H7
Source of infection: undercooked beef (particularly mince, burgers and
meatballs) or unpasteurised milk
Gastroenteritis-causing E.coli Strains
- Enterotoxigenic (ETEC)
- Enteropathogenic (EPEC)
- Enteroaggregative (EAEC)
- Shiga Toxin-Producing (STEC)/ Enterohaemorrhagic (EHEC)
- Enteroinvasive (EIEC)
E.coli: Enterotoxigenic (ETEC)
- Traveller’s diarrhoea
- Infant diarrhoea
- In developing countries
- Watery non-bloody diarrhoea, vomiting, cramps, nausea, low-grade fever
E.coli: Enteropathogenic (EPEC)
- Infant diarrhoea, often in developing countries
- Watery diarrhoea, vomiting
E.coli: Enteroaggregative (EAEC)
- Infant diarrhoea in developing/developed countries
- People with HIV
- Traveller’s diarrhoea
- Watery diarrhoea, vomiting, dehydration, low-grade fever
E.coli: Shiga Toxin-Producing (STEC)/ Enterohaemorrhagic (EHEC)
- Watery diarrhoea
- Followed by Haemorrhagic Colitis (bloody diarrhoea)
- Abdominal cramps
- No or Low-grade Fever
- Haemolytic Uremic Syndrome
E.coli: Enteroinvasive (EIEC)
- Rare in developing/developed countries
- Fever
- Cramping
- Watery diarrhoea
- May progress to dysentery with scant bloody stools
What is Haemolytic Uremic Syndrome?
Small blood vessels in kidneys become damaged and inflamed
What is Dysentery?
An infection of the intestines that causes diarrhoea containing blood or mucus
E.Coli O157:H7 Gastroenteritis: Diagnosis & Treatment
- Diagnosis: Stool Sample Analysis (MacConkey agar or selective media)
- Rehydration and correction of electrolyte abnormalities (fluids)
- Antibiotics
- Blood transfusion and haemolysis
What does Yersinia affect?
Affects terminal ileum and if mesenteric lymph nodes are enlarged disease can mimic appendicitis
What is Yersinia? What does it cause?
• Gram-negative
• Non-motile
• Y. enterocolitica and Y. pseudotuberculosis
• They cause enterocolitis (yersiniosis) in Scandinavian and other northern
European countries and in the colder areas of North America
