Gram-Positive Rods

Front 1

You're watching a television program that is discussing viruses called bacteriophages that can kill bacteria. Your roommate says “Wow, maybe viruses can be used to kill the bacteria that infect people! You're taking the Microbiology course now; what's the difference between viruses and bacteria?" Which one of the following would be the most accurate statement to make?

A. Viruses do not have mitochondria whereas bacteria do.
B. Viruses do not have a nucleolus whereas bacteria do.
C. Viruses do not have ribosomes whereas bacteria do.
D. Viruses replicate by binary fission whereas bacteria replicate by mitosis.
E. Viruses are prokaryotic whereas bacteria are eukaryotic.

Back 1

C. Viruses do not have ribosomes whereas bacteria do.

Front 2

The initial step in the process of many bacterial infections is adherence of the organism to mucous membranes. The bacterial component that mediates adherence is the:

A. Lipid A
B. Nucleoid
C. Peptidoglycan
D. Pilus
E. Plasmid

Back 2

D. Pilus (aka fimbriae)

Front 3

A 47-year-old man who has a history of sickle cell disease has had numerous hospitalizations requiring the placement of IV lines. The patient has poor peripheral venous access, and a catheter is placed in the right subclavian vein. The patient subsequently develops rigjt arm discomfort and swelling and a temperature of 40.1oC with chills. Multiple blood cultures are taken, and gram-positive cocci are isolated. The organism is catalase-positive and produces colorless colonies on mannitol salt agar. The colonies are gamma-hemolytic on sheep blood agar. Which of the following organisms is the most likely cause of this patient’s symptoms?

A. Enterococcus faecalis
B. Staphylococcus aureus.
C. Staphylococcus epidermidis
D. Streptococcus agalactiae
E. Streptococcus pyogenes

Back 3

C. Staphylococcus epidermidis

Front 4

A 10-year-old girl is brought to the physician because of a 2-day history of sore throat and fever. A throat culture grows bacitracin-sensitive bacterial colonies. The infecting organism is most likely protected from the lytic action of detergents by which of the following?

A. Keratin
B. Lipopolysaccharide
C. Peptidoglycan
D. Perisplasmic space
E. Siderophores

Back 4

C. Peptidoglycan

Front 5

List all the gram positive rods:

Back 5

*Propionibacterium causes acne; not particularly important for us.

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Gram + rods

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The most common or important gram-positive rods are:

Back 7

*Spore-forming rods:
-Aerobes, e.g., Bacillus cereus (fried rice diarrhea), B. anthracis
-Anaerobes, e.g., Clostridium perfringens, C. difficile, Clostridium septicum, C. tetani, C. botulinum
 
*Non-sporeforming rods:
-Corynebacterium, Propionibacterium
-Listeria

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Clostridium

Front 9

Key points about Clostridium:
-4 examples of clostridium species

Back 9

*Gram+, anaerobic spore-forming rods

*C. tetani, C. botulinum, C. perfringins, C. difficile
*Responsible for several unrelated diseases including BOTULISM, TETANUS, GAS GANGRENE, PSEUDOMEMBRANOUS COLITIS.
*Organisms live in soil, water, sewage, and intestines of animals/humans.

*Their capacity to cause disease is attributed to the following:
-Ability to survive adverse environmental conditions through spore formation.
-Rapid growth in a nutritionally enriched, anaerobic environment.
-Production of numerous histolytic TOXINS, enterotoxins, and neurotoxins.

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L TO R:
C. tetani ; C. perfringens ; B. anthracis

Front 11

Describe the importance of the endospore in clostridium:

Back 11

Endospore: dormant form of an organism; generated during periods of environmental hostility (nutritional deprivation). Under favorable growth conditions, spores will germinate.

Goal of spore is to protect the genetic material.

Front 12

Key points about C. botulinum and Botulism:

Back 12

*Forms subterminal endospores
*Toxin causes flaccid paralysis
*Spores are highly resistant to killing
*Botulism is rare as organism can only grow in the absence of oxygen
*Classic presentation: patient with paralysis who ate home-canned food

*Intoxication (not a true infection)!!!!! Bacterial replication does not need to occur; all symptoms are toxin-mediated.
*Botulism is the disease triggered when the toxin gets absorbed through the gut, lungs, or an open wound. It is a neurotoxin!

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C. botulinum

Front 14

Pathogenesis of botulism--Encounter and Entry:

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*Commonly found in soil and aquatic sediments; spores frequently contaminate vegetables, meat or fish.

*Associated with improper canning of food. Under anaerobic conditions, common in canned foods, the spores germinate and release potent toxins.

*Spores found in 10% of honey, picked up by bees from plants growing in contaminated soil. Infants and field workers may be at risk.

*May also occur when bacterial spores in soil enter a wound.

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Pathogenesis of botulism--Establishment of an infectious niche:

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- Intoxication: if contaminated food is not heated sufficiently during cooking, bacteria may be killed but preformed toxin molecules survive.

- Infection: spores in the gut or wound can germinate, multiply, and produce toxin.

Front 16

How does damage occur as a result of botulism?
What does it cause?
What kind of toxin is it?

Back 16

Damage = EXOTOXIN
- Flaccid paralysis
- Mechanism of action: Botulism toxin is an A-B toxin

Front 17

What specific effect does botulism have on ACh?

Back 17

*Transported from gut to nervous system
light chain = A
heavy chain = B

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-Floppy baby; flaccid paralysis.
-ACh is not being released; no muscle contraction.
-Constipation is a common first symptom, followed by hypotonia, drooling, and weak cry. Upper airway obstruction and CN palsies occur in 50% of cases.

Front 19

Key points about C. tetani and Tetanus:
-describe the toxin
-how does the organism "spread"?

Back 19

*Toxin is a neurotoxic exotoxin that causes spastic paralysis.
*Caused by the introduction of the tetanus bacilli into the host, typically through the penetration of a foreign object, i.e. rusty nail. Associated with dirty wounds.
*Organism rarely moves from the infection site but the toxin is released and travels to the CNS to produce the symptoms of tetanus.
*Active immunization with formalin-inactivated toxin (tetanus toxoid) prevents tetanus; DPT vaccine.

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C. tetani; note spores.

Front 21

Describe the toxin and its MOA in tetanus:

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Damage = EXOTOXIN
- Spastic paralysis
- Mechanism of action: Tetanus toxin is an A-B toxin

Front 22

What neurons does tetanus affect? What specific effect does it have on them?

Back 22

Affects inhibitory neurons

Generates unopposed firing of the active motor neurons = spasms and spastic paralysis

Front 23

Describe severe examples of the kind of damage tetanus can do:

Back 23

*Toxin is transported from area of infection to CNS

*“Lockjaw” or trismus results from masseter muscles being affected first; paralysis of tetanus is spastic= all the muscles in body are continually contracted.

*Small stimuli can trigger massive contractions; respiratory failure leads to death (15-60% of cases).

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*A severe case of tetanus. muscles, back and legs are rigid, muscle spasms can break bones; can be fatal (e.g respiratory failure).

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Neonatal tetanus
*Lack of vaccination
*Lack of sterility when cutting umbilical cord.

Front 26

Key Points about Clostridium perfringens:
shape?
prevalence?
how does it usually infect us?
what does it produce?

Back 26

*Large, Gram-positive anaerobic rod with square ends.
*Most common species of Clostridium isolated from clinical specimens.

*Ubiquitous in nature; part of normal flora of vagina and GI tract; spores are found in soil but rarely seen in body.

*Major pathogen of wound infections.

*Can produce large amounts of hydrogen and carbon dioxide gas = “Gas Gangrene”
*You can FEEL the gas in people with this (called crepitation).

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Clostridium perfringens

Front 28

How is c. perfringens characterized on blood agar?

Back 28

Characterized by double-zone of hemolysis on blood agar
*alpha-->partial lysis
*beta--> complete lysis

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Clostridium perfringens

Front 30

Describe pathogenesis--Encounter and Entry of C. Perfringens:

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*Clostridial spores are introduced into tissue via contaminated dirt, clothing, or other foreign material. *The clostridia can also come from the patient's own intestinal flora (endogenous transfer!).

*Compound fractures, bullet wounds, or the kind of trauma seen in wartime are prototypes for this infection. *A significant delay between the injury and definitive surgical management allows multiplication of organism.

*C. perfringens can cause food poisoning if spores of an enterotoxin-producing strain contaminate food (MEAT--C. perfringens enterotoxin).

Front 31

Virulence factors and damage from c. perfringens:

Back 31

*Production of multiple exotoxins (at least 12).

*alpha-toxin: a phospholipase that hydrolyzes lecithin and sphingomyelin, thus disrupting the cell membranes of various host cells, including erythrocytes, leukocytes, and muscle cells

*Degradative enzymes, e.g. proteases, Dnases, collagenases that liquefy tissue and promotes spread of infection-->gas gangrene

*Production of enterotoxin in some strains.

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*C. Perfringens
*Radiographs demonstrate gas in the tissues.
*You'd feel crepitation.
*Dead/dying tissue provides a nice anaerobic environment that the bug thrives and spreads in.

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*Left: Myonecrosis; the most severe form of damage from C. perfringens.

*Clostridia can be introduced into tissue during surgery or by a traumatic injury.

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Key Points about Clostridium difficile:

Back 34

*Spore-forming
*Most common cause of antibiotic-associated diarrhea in hospitalized patients, and almost all cases of pseudomembranous colitis.
*Source of infection is endogenous or environmental.
*Antimicrobials can alter the colonic flora and favor growth of C. difficile. Increased numbers make toxin more effective.
*Commonly associated antimicrobials: ampicillin, cephalosporins, and clindamycin.

Front 35

Virulence factors and damage from Clostridium difficile:

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*Pathogenic strains produce two distinct polypeptide toxins:
-Toxin A: enterotoxin that causes excessive fluid secretion (watery diarrhea).
-Toxin B: potent cytotoxin

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*C. diff
Pseudomembrane is composed of mucus, fibrin, inflammatory cells and cell debris overlying an ulcerated epithelium.

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*C. diff
Pseudomembrane is composed of mucus, fibrin, inflammatory cells and cell debris overlying an ulcerated epithelium.

Front 38

List all the gram + non spore-forming rods:

Back 38

Front 39

Key Points about Corynebacterium diphtheriae:

Back 39

*Gram+ Rod that does not produce spores!
*Produces a potent exotoxin that is responsible for diphtheria. Other corynebacteria are nonpathogenic commensal.
*Diphtheria toxin is an A-B toxin that acts in the cytoplasm to inhibit protein synthesis.
*Diphtheria is rare where immunization is widely used

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Corynebacterium diphtheriae

Front 41

How does Corynebacterium diphtheriae mediate its effects, and where does it happen?

Back 41

*Eventually results in a pseudomembrane in the back of the throat.

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pseudomembrane in the back of the throat as a result of Corynebacterium diphtheriae infection.

Front 43

Key points about Listeria monocytogenes:

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*This is the only species that causes disease in man.
*FACULTATIVE Intracellular parasite: readily found within infected host macrophages in tissue samples.
*Most infections are food-borne.
*Can grow at refrigeration temperatures.
*Found in environment, and in raw vegetables, poultry products, hotdogs, dairy products.
*Listeria infections are most common in pregnant women, their fetuses or newborns and immunocompromised individuals.

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Listeria monocytogenes

Front 45

Describe the encounter and entry of Listeria:

Back 45

*Found in water, soil, vegetation, birds, mammals.
*Fecal carriage in 1-15% of healthy people; Food-borne transmission.
*Outbreaks have been associated with processed dairy products (2-3%), e.g.,cheese, milk; ground meats (20-30%), poultry, and raw vegetables.

Front 46

Describe the Virulence factors of Listeria:

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*The major virulence factors are invasion-associated surface proteins called internalin and a pore-forming cytotoxin, listeriolysin O (LLO).
*Infection and survival in macrophages is likely responsible for ability to be invasive.
*Listeriolysin O facilitates escape from phagolysosome. Thus the organism replicates freely in the cytoplasm. The organism moves through cytoplasm using host-cell actin.

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*Listeria using LLO to degrade endosome, escape into cytoplasm, and do its thing.
*"Plume" is actin filaments; listeria can polymerize host actin to move itself to the adjacent cell. Helps it evade the immune system.

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Listeria monocytogenes moving around.

Front 49

Describe damage from Listeria monocytogenes:

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*Septicemia and meningitis are most common effects of infection (listeriosis).
*Host antibacterial response causes most of the pathogenesis (sepsis syndrome).
*During pregnancy (35% of Listeria infections); “Flu-like” illness with bacteremia, may develop meningitis; infection may precipitate labor, leading to premature birth. [CAN CROSS PLACENTA]
*Can be transmitted to newborn during birth (colonization of vagina); common cause of newborn meningitis. Bacteremia delivers bacteria to other organs (meningitis), can also induce sepsis.
*Common cause of meningitis in immunocompromised population (AIDS).