Microbiology, Lecture 9

Enteric Gram Negative Rods have what kind of cell wall?

LPS (lippolysaccharide)

Enteric Gram Negative Rods are responsible for the widespread of:

gastrointestinal disease

What are the main characteristics of enteric gram negative rods?

1. Gram-negative

2. LPS (endotoxin) in outer cell wall

3. PTs infected with these bacteria have higher incidence of autoimmune disease

4. flagella for motility

Where are the enterobacteriaceae family found?

in the colon of humans and animals

The eneterobacteriaceae family are what kind of anerobes?

facultative anaerobe

What are the common features to all members of the enterobacteriacaea family?

Anatomic location (colon)

Catalase positive

All facultative anaerobes

ferment glucose

Cytochrome oxidase

Reduce nitrates to NITRITES

How is enterobacteriaceae diagnosed?

1. Using differential media to evaluate the ability to ferment lactose

2. Inoculating on triple sugar iron agar (TSI) and urea agar

3. Final confirmatory agglutination test

This type of agar contains ferrous sulfate, and three sugars (lactose, glucose, sucrose)

Triple sugar iron agar

Enterobacteriaceae treatments are typically:

a wide range of antibiotics, but based on antibiotic sensitivity results

Escherichia coli is responsible for 2 pathogenic types:

Urogenic

Gastrointestinal

Enteropathogenic E. coli (ETEC) is also known as:

Traveler’s diarrhea

Enteropathogenic E. coli (EPEC) is also known as:

Pediatric diarrhea

Enterohemorrhagic E. coli (EHEC) is known as:

bloody diarrhea, HUS, E. coli 0157:H7

Uropathogenic E. coli is also known for:

UTIs

What is the route of pathogenic E. coli?

Oral-fecal

How is pathogenic E. coli transmitted?

1. Contact with human or certain animal feces

2. Contaminated food and water, often from sewage or water run off near farms

3. Petting zoos

4. Poor hygiene

5. Undercooked beef

6. Neonatal infection occurs during the birthing process

What is the mechanism of enterotoxigenic diseases?

Release of toxins

1. Phosphorylation of transmembrane ion transporters

2. Transporters then export ions (chloride and potassium) from the cell

3. Results in the outpouring of fluid from enterocytes into the bowel lumen resulting in water diarrhea

How does someone get an enterotoxigenic disease?

Eating or drinking material from another location that may be pathogenic to be the traveler but not local residents

Exposure to enterotoxins in contaminated food or water

LT stands for (Enterotoxic E. coli)

Heat liable toxin

ST stands for (Enterotoxic E. coli):

Heat stabile toxin

ETEC bacterium adheres to the epithelium then:

produces exotoxins

Enterotoxigenic strains do not cause inflammation because:

they do not invade intestinal mucosa

Enteropathogenic E. coli (EPEC) causes:

acute gastroenteritis

Vomiting

Nausea

Fever

Malaise (LETHARGIC)

How is EPEC transmitted?

Transmitted via the fecal-oral route

1. contaminated hands and surfaces

How can EPEC be prevented?

Good hand hygiene

UPEC are O serotypes of E. coli that preferentially cause what?

urinary tract infections

In UPEC, direct inoculation from the colon to the urinary tract is where:

colonization occurs

Uropathic E coli strains have pili with adhesion proteins that bind to:

receptors on the urinary tract epithelium (transitional)

Why does cranberry juice work as an effective treatment for UPEC?

It binds to the sites on the urothelium, flavonoids in the fruit inhibit pili adherence

EHEC (0157:H7) is a well-known pathogenic E. coli strain that can cause:

hemorrhagic diarrhea and kidney failure

What are the virulence factors of Enterohemorrhagic E. coli?

Pili (adherence to skin and mucosa)

Enterotoxins (exotoxins that act on the cells of the jejunum and ileum causing diarrhea)

What part of the GI tract is affected by enterotoxins?

Jejunum and ileum, causing severe diarrhea

This toxin is from E coli 157, it enters the blood stream and binds to the small blood vessels like capillaries.

Shiga toxin

The shiga toxin is often from:

undercooked beef or contaminated vegetables and fruit

Shiga toxin is similar to the toxin produced by:

Shigella spp.

What is the mechanism of the shiga toxin?

A glycosidase

1. Removes adenine from large ribosomal RNA

2. Stops protein synthesis

Shiga toxin is an enterotoxin/enterotoxin that can cause:

hemolytic anemia

thrombocytopenia

acute renal failure

How does shiga toxin cause hemolytic uremic syndrome?

1. receptors for shiga toxin are found on the surfaces of vascular endothelium and kidney glomeruli

2. As blood tries to bass through the vessels, the RBC are damaged and lyse

3. This results in hemolytic anemia

Distorted or fragmented red blood cells as they pass through damaged vessels

Schistocytes

This occurs due to platelets binding to the damaged endothelium to heal damaged vessels from hemolytic uremic issues.

Thrombocytopenia

Why is thrombocytopenia bad?

It uses up the platelets in the blood, therefore decreasing the persons ability to form clots, risk for further hemorrhage.

Ciprofloxacin increases the risk of:

developing HUS by increasing the Shiga toxin released into the blood stream

How is E. coli diagnosed in the laboratory?

1. On inoculated blood agar, differentiated and isolated on MacConkeys agar

2. Grown on eosin methylene blue agar, E. coli will be green

(indole pos, motile, oxidase neg)

this is fluid and electrolyte replacement is primary treatment for this infection, antibiotics can be used such as ciprofloxacin in severe cases

Shigella

What is the clinical presentation of shigellosis?

Cramps and fever

Watery diarrhea, later contains blood and mucus

This is the severe version of Shigella:

Shigella dysenteriae

This is the mild version of Shigella:

Shigella sonnei

What is the pathogenesis of shigellosis?

1. Invades the mucosal epithelial cells of the ileum and colon

2. inflammation occurs at the invasion site

3. Progress to ulceration (blood diarrhea)

What are the 3 criteria that distinguishes shigella from Salmonella?

1. No gas production

2. Does not produce H2S

3. Nonmotile

In Salmonella, there needs to be 100,000 bacteria to cause the infection. In shigella, how many bacteria would it take to case an infection?

100

What does ELISA stand for?

Enzyme linked immunosorbent assay

What is the mechanism of ELISA?

1. Wells are lined with antibody or antigen

2. Sample is put in the wells and incubated

3. All excess fluid is washed out

4. Another anti-IgG antibody is added

5. A color change represents positivity

What kind of agars are used in laboratory testing?

TSI

MAC

EMB

Blood agar

What kind of samples are sent to the laboratory?

Stool samples for entercolitis

Blood cultures for typhoid

This is a rare type of Salmonella. It results in an infection in the blood, causing a severe immune reaction (possible shock). Likely arises from deep bone infections, abscesses (immunocompromised patients)

Nontyphoidal salmonella

What are some issues that can arise from non-typhoidal salmonella?

S. enterica (entercolitis, osteomyelitis, septicemia, visceral abscesses)

Enterocolitis (caused by the fecal oral route)

What antibiotics can treat typhoid?

Ciprofloxicin

Levoflaxin

Azithromycin

Carbapenems

If typhoid is left uncreated, what can occur?

Pronlonged chronic fever, lasting weeks to months

Kidney failure

Interstinal hemorrhage

Death

S. typhi has a propensity to invade what organ resulting in a carrier state?

Gallbladder

When an individual has S. typhi that is in a carrier state, what symptoms do they show?

No symptoms

Excrete bacteria in feces for long periods of time

This is a salmonella bacteria that causes an infection of the small bowel, also known as typhoid fever:

Salmonella typhi

What is the mechanism of salmonella typhi?

1. Organisms enter the multiply in mononuclear phagocytes of the Peyer’s patches (just below bowel mucosa, submuosal space)

2. Spread to phagocytes of the liver, gallbladder, spleen

3. Bacteremia

4. Associated with onset fever and other symptons, caused by an endotoxin

this toxin is produced by salmonella typhi, produced while intracellular and transported to the extracellular space.

Typhoid toxin

What are the two types of salmonella spp?

Typhoidal (enteric fever)

Nontyphoidal

What are the characteristics of salmonella spp?

Gram negative rods

No ferment lactose

Motile, with flagella

Facultative intracellular pathogen

PRODUCE GAS

What treatments are used against E. coli?

Fluoroquinolones

Macrolides

Rifaximin

In most E. coli treatments, are antibiotics usually used?

No, typically fluid and electrolyte repalcement and rest.

What are some indole positive bacteria?

E. coli

Klebsiella oxytoca

Proteus vulgaris

Vibrio

What is the mechanism of indole biochemical test?

Check the ability to break down the amino acid tryptophan into indole, using the enzyme tryptophanase

Kovac’s reagent is added to the reaction

If tryptophan is broken down and indole is present, COLOR CHANGE PINK-PURPLE

What does indole indicate/regulate?

Regulate the cytoplasmic pH

Biofilm production

Cell signaling pathways

Gram negative rods are in the family enterobacteriaceae are:

oxidase negative

What is the mechanism oxidase enzyme (IN GRAM NEGATIVE COCCI THAT ARE OXIDASE POSITIVE)?

Aerobic bacteria utilize O2 for energy production

Produce the oxidase enzyme in the presence of cytochrome c

Catalyze the transport of electrons from a donor (NADH) to electron acceptors (oxygen)

Therefore the oxygen respiratory chain, terminates in cytochrome c oxidase