EXAM 3# MED BAC WEEK 9

shigella, H. influenza, Pasturella

Poly Ribitol Phosphate (PRP):

polysaccharide capsule of Haemophilus influenzae type b (Hib); a strong antibody response to PRP provides protection against capsulated strains. capsule masks bacterial surface antigens, blocking opsonization

Dysentery

intestinal infection causing severe diarrhea containing blood or mucus, accompanied by painful stomach cramps, fever, and nausea

Shiga toxin:

AB exotoxin expressed by Shigella dysenteriae that binds to the GB3 glycolipid receptor and halts protein synthesis by cleaving a specific adenine in the 28s rRNA of the 60s ribosomal subunit, leading to cell death.

Describe the characteristics of the Pasteurellaceae family that can be used to differentiate

them from other Gram-negative bacteria

small, Gram-negative rods that are facultative anaerobes and fastidious.

pathogenic genera include Haemophilus ("blood lover"), Aggregatibacter ("clumped bacteria"), and Pasteurella

Describe the characteristics of the Enterobacteriaceae family that can be used to

differentiate them from other Gram-negative bacteria

largest family of medically important Gram-negative rods (>50 genera) and are ubiquitous in soil, water, vegetation, and the human gut.

facultative anaerobes that ferment glucose, reduce nitrates to nitrites, are oxidase-negative, and can grow on both enriched (BAP) and selective (MacConkey) media.

Describe the antigen used to type H. influenzea

classified into 6 serotypes (a–f) based on polysaccharide antigens. Protection correlates with a strong antibody response to their capsule, known as Poly Ribitol Phosphate (PRP).

Explain the importance of the HiB vaccine.

The Hib conjugate vaccine (such as PRP-D) dramatically reduced reported cases and incidence rates, shifting the demographic of severe disease primarily to the elderly and unvaccinated infants under 1 year old.

Invasive Haemophilus influenzae B

disease

• Pneumonia (associated with chronic bronchitis and COPD).

• Bacteremia (can lead to septic shock).

• Meningitis (a common cause of pediatric meningitis prior to the vaccine).

• Epiglottitis (a life-threatening obstruction of the airway).

diseases Caused by Haemophilus

influenzae NTHi

Otitis media

Most common cause of pediatric office visit in US

Blockage of Eustachian tube from inflammation and

fluid build-up

Tympanostomy tubes: fluid drainage

bacterial colonization of middle ear

Most common in children due to undeveloped facial / ear structures

NO CAPSUle

Reservoir and path of transmission for Pasteurella:

• Reservoir: Normal flora of animal mouths, including farm animals (cows, pigs, horses, rabbits, sheep, rats) and pets (dogs, cats).

• Path of Transmission: Transmitted to humans primarily via animal bites, licks, or scratches. Among animals, transmission occurs via airborne spread triggered by stressors

Lab Diagnosis of H. influenza

Agglutination test

• beads coated with anti-PRP

antibody

Chocolate or Fildes agar

Streak S. aureus and presumed

H. influenzae isolate together

• Haemophilus colonies are

smaller b/c V factor inhibitors

not inactivated

Describe the effect of P. multocida infection in chickens, pigs and humans

• Chickens: Causes fowl cholera (prevalent in wild waterfowl), which can kill a flock within 6–12 hours and causes up to 65% mortality in turkeys.

• Pigs: Causes atrophic rhinitis, resulting in inflammation and atrophy of the turbinate bones, loss of appetite, and increased susceptibility to respiratory infections.

• Humans: Usually limited to soft tissue at the local site of a scratch or bite, causing swelling, cellulitis, and wound drainage. It may also enter the bloodstream and cause bone inflammation, endocarditis, or meningitis (with increased risk in patients with cirrhosis, HIV, or renal failure).

Antigens used to differentiate members of the Enterobacteriaceae family:

• Enterobacterial Common Antigen (ECA): The core polysaccharide of LPS shared by all Enterobacteriaceae.

• O Polysaccharide (LPS): Classifies strains and serogroups within a species (e.g., O157).

• K Antigen: Capsular antigen.

• H Antigen: Flagellin type (e.g., H7)

How invasive Shigella strains cross the mucous membrane of the intestine:

target specialized M cells within the gut. Once inside, they use a Type III secretion system to escape vacuoles (via IpaB-IpaC pores), replicate in the cytoplasm, induce macrophage apoptosis (releasing pro-inflammatory cytokines IL-1β and IL-18), and spread cell-to-cell via directed actin filament rearrangement.

describe the mechanism by which Shiga toxin kills cells

• The B subunit of the Shiga toxin binds to the GB3 glycolipid receptor on the host cell.

• After entering the cell via endocytosis/translocation, the A subunit enzymatically cleaves a specific adenine in the 28s rRNA of the 60s ribosomal subunit.

• This action halts protein synthesis, ultimately leading to cell death

Describe the main route of transmission of Shigella strains and how their ID50 can be so

low

• Main Route of Transmission: Fecal-oral transmission via fingers, flies, food, and fomites, particularly endemic where sanitation is poor.

• Why the ID50 is so low (10–100 cells): Shigella strains exhibit high survival rates in the acidic environment of the stomach, allowing a very small infectious dose to easily trigger person-to-person spread.

Shigella flexneri INDIA

Fecal-oral transmission

Bacillary dysentery

diarrhea containing blood or mucus, high fever, nausea, vomiting, and painful abdominal cramps.

• Virulence Plasmid Proteins & T3SS Pathway: Encodes genes sufficient for uptake across intestinal M cells into Peyer's patches/GALT.

• IpaB-IpaC Pores: Form pores that allow the bacteria to escape the phagocytic vacuole into the host cell cytoplasm.

• Intracellular & Apoptosis Pathways: Replicates in the cytoplasm, induces macrophage apoptosis (releasing pro-inflammatory cytokines IL-1β and IL-18), and spreads laterally cell-to-cell via directed rearrangement of host actin filaments.

Shigella sonnei INDIA

Fecal-oral transmission

Bacillary dysentery

hijacks host cell machinery to direct actin filament rearrangement, allowing direct cell-to-cell transport and avoiding extracellular immune defenses.

Diseases Caused by Haemophilus

influenzae (think sinuses) NTHi

Sinusitis – inflammation of mucosa lining nasal sinuses

Most commonly caused by viruses

- RSV, influenza, rhinoviruses

Defense Against Haemophilus influenzae

IgA antibodies = mucosal protection

Anti-PRP antibodies (infection,

vaccination, maternal transmission)

protect from capsulated strains

Secreted IgA protease may aid in

colonization

AB Exotoxins and Shigella

Refers to structural

organization

• Does NOT refer to

mechanisms of

action

• B subunit mediates

binding

• A subunit has

enzymatic activity

Barriers to Infection for SHIGELLA

Goblet cells (mucus)

Epithelial Tight Junctions

M cells: transport antigens across mucosal

surface

Peyer’s Patch (GALT)

Hemolytic uremic syndrome

Shiga toxin activity in endothelial cells of kidney

• Complement-induced platelet activation thus causes

thrombus'; renal falilure

Shigella dysenteriae

diagnosis of shigella

Non-specific symptoms: fever, dysentery; suspect

several things

Gram stain fecal sample, XLD, biochemical tests