Gram Negative Bacilli (Family Entereobacteriaceae)

What are endotoxins?

• toxins found inside certain bacteria, specifically Gram-negative bacteria

• released into the host by destruction of bacteria

  • when taking antibiotics, the host might have symptoms initially worsen rather than immediately start to get better

• endotoxins act as superantigens and produce an exaggerated inflammatory response

  ex: lipopolysaccharides (LPS)

The Enteric bacteria (family): Are they obligate anaerobes or facultative anaerobes?  Does this make them more or less suited to be pathogens?

• gram negative rods

• facultative anaerobe (so they can thrive in the human gut, more capable of being pathogens)

• Catalase +, oxidase –

• most are motile

• the ability to ferment lactose is a common difference between normal resident bacteria and some important pathogens

  • urease, indole tests too

What kinds of opportunistic infections can the Enteric bacteria (family) cause? 

they can cause UTIs, respiratory infections (pneumonia), bacteremia (through endotoxin), and meningitis

• besides that, they usually do no harm if they STAY in the gut environment

Are all strains of Escherichia capable of opportunistic infections?

all strains are capable of opportunistic infections

BUT some strains are capable of injection of healthy individuals (Traveller’s diarrhea, bacterial dysentery, etc)

Do E. coli cause invasive or non-invasive forms of disease?

both; depends on the strain or pathotype

• non-invasive includes enterotoxigenic

• invasive includes enteroinvasive and entereohemorrhagic

Describe non-invasive vs invasive bacteria

non-invasive bacteria stays where they were first introduced

invasive bacteria penetrates deeper into normally sterile tissues

Differentiate between enteroinvasive, enterotoxigenic, and enterohemorrhagic infections.

Enteroinvasive: invades lining of the gut, triggers inflammatory response → diarrhea, vomiting, fever

Enterotoxigenic: toxin that is produced and disrupts GI tract function (non-invasive)

• No toxin: symptoms from invasion of intestinal tissue

• Exotoxin: “Traveler’s diarrhea” from an enterotoxin

• Most cause mild, non-life threatening diarrhea

• Some have potent toxins - “Shiga-like” toxin

Enterohemorrhagic: produces Shiga-like toxin

• bloody diarrhea but no fever

• not truly invasive, but toxins cause vascular damage (→ HUS)

What is hemolytic uremic syndrome? (HUS)

• It is a condition that affects the blood and blood vessels

  • results in the destruction of blood platelets, a low RBC count, and kidney failure

• Caused by Shiga toxin E. coli

What is verocytotoxin or “Shiga” toxin?

• It is a potent exotoxin, encoded on a bacteriophage

  • Shuts down eukaryotic ribosomes, causes widespread cell death

  • Produces bloody diarrhea but no fever (non-invasive)

  • Enterohemorrhagic

What is the significance of O157:H7? What does STEC mean?

It is transmitted from livestock to humans through contamination with fecal/intestinal material

• STEC - Shiga-toxin producing E. Coli

How are E. coli infections acquired?

• They are acquired from eating contaminated food

• Also from livestock to humans (cow fecal getting on our food)

How is E. coli treated?

antibiotics & hydration

Diarrhea vs Dysentery

Diarrhea	Dysentery
fluids secreted into the intestines; watery stool often in response to toxins in the gut or inflammation in the intestines	damage to the intestinal lining (invasive) diarrhea is often a symptom of dysentery often accompanies by blood and/or pus in the stool

Shigella traits?

• gram negative rods

• facultative anaerobes

• non-lactose fermenting

• non-motile outside of cells but motile inside human cells

Is shigellosis a diarrheal or dysenteric disease? What are the symptoms?

• Shigellosis is a bacillary dysentery disease

• Symptoms:

  • Bloody stool

  • High fever

  • Intestinal pain

  • Diarrhea

  • Pus in the feces

Is Shigella invasive or non-invasive? Does it produce a toxin?

• Shigella is invasive

• Produces the Shiga toxin

• Few patients develop long-term autoimmune disease

How does Shigella evade the immune system? What other food-borne pathogen uses a similar technique?

It evades the immune system by moving from cell to cell without exposure to the immune system

• similar to listeria

How are Shigella infections acquired?

• They are acquired from person to person infection

  • Outbreaks often take place at school

• Some people are carriers without symptoms

What is Reiter’s syndrome?

long-term autoimmune disease due to bacterial remnants in the blood over-activating the immune system

• (similar to rheumatic fever)

How is shigellosis best treated? Prevented?

• Best treated through antibiotics and hydration

• Best prevented through good hygiene/sanitation to prevent the spread

Salmonella traits

Gram negative rods, facultative anaerobes, non-lactose fermenting, motile (in or out of cells)

What are the symptoms of non-typhoidal salmonellosis? How long do symptoms last? How is it treated?

Gastroenteritis (inflammation of GI tract) - from an invasive infection

• Nausea, vomiting

• Fever

• Non-bloody stool, diarrhea → sometimes bloody

• Runs course in 2-5 days

Usually not treated with antibiotics, just hydration

Is salmonellosis due to an infection or due to exotoxins?

Due to an infection from bacteria invading gut lining

• strictly invasive, NO exotoxins

Where do non-typhoidal infections come from?

Contracted from ingesting Salmonella bacteria

• contamination from livestock, pets (fecal to oral)

• long incubation food borne infection: 12-36 hr

Do typhoidal Salmonella penetrate into the bloodstream?

Yes it does penetrate the blood stream

Symptoms of Typhoid fever

• slowly increasing fever, eventually high fever

• dementia

• diarrhea, inflamed liver and spleen

• toxic shock

• perforation of the intestines

• 20% mortality without treatment

Why does typhoid fever have such a delayed onset compared to non-typhoidal?

differs because of its invasiveness and the ability to move past the intestinal lining

bacteria is able to hitch a ride on macrophages → colonizes the liver and spleen

• from liver → gallbladder (stores the bile secreted by liver): everytime gallbladder secretes biles into the GI tract, a new dose of bacteria reinfects GI tract → people can develop chronic gall bladder infections

How does treatment of typhoid differ from non-typhoid? How can it be prevented?

• Treatment through Antibiotics (extremely important) & Hydration

• Prevention through proper hygiene/sanitation 

  • vaccine available, but little used

Describe the location of the bacteria in someone who is a typhoid carrier

Some individuals develop chronic gall bladder infections

• no symptoms

• shed millions of Salmonella enterica Typhi in their feces

How is typhoid fever transmitted?

• Caused by one serotype (Salmonella enterica Typhi)

• transmitted human to human (some people are asymptomatic)

  • contaminated food, water with fecal material