Common Bacterial Pathogens 2

Question 1

Name the most common gram + rods

Answer 1

Clostridium

Question 2

Clostridium are:

   - aerobic or anaerobic?
   - spore or non-spore?

Answer 2

Strict anaerobes

Spore formers

Question 3

Why do we worry about C. difficile?

Answer 3

1. Because its hospital-acquired (nosocomial) infection!
   - diarrhea
   - Pseudomembranous colitis
2. Because it is relatively resistant to most common antibiotics
   - Spores not killed by alcohol-based hand sanitizers

Question 4

T/F: C. difficile is caused by antibiotic treatment

Answer 4

True
Believed to result from depletion of the intestinal flora by antibiotic treatment, and resulting overgrowth of C. difficile from own patient or hospital staff/others

Question 5

Again, what are the signs of a C. diff case? What would you do? (include medications)

Answer 5

A patient will go to hospital > get treated with antibiotics > get worse > do a culture and C.diff toxin ELISA > treat with metronidazole or ORAL vancomycin > gets better > four days later you get positive C. diff culture > take meds for two weeks to limit recurrence

Question 6

How does Clostridium tetani cause spastic paralysis?

i.e. where does it come from, what/how does it target

Answer 6

Spores from soil and animals >
Local anaerobic infection and toxin production >
Retrograde transport of toxin to CNS >
Blocks inhibitory interneurons in CNS

Question 7

T/F: C. botulinum grows spores inside the host

Answer 7

False

The spores grow in contaminated food under anaerobic conditions (ie: home canned foods) and is ingested

Question 8

How is C. botulinum different from C. tetani?

Answer 8

Botulinum toxin blocks acetylcholine transmission at neuro-muscular junctions; results in “flacid paralysis”

Both can cause respiratory failure

Question 9

Compare/ contrast food infections from Staph, Labile toxin, C. botulinum

Answer 9

Staph + Botulism: eating preformed toxin
Labile toxin: e. coli (like while in mexico)
-ingesting organisms that adhere and grow

Question 10

What are microbio characteristics of C. perfringens? (shape, gram appearance, etc.)

Answer 10

• Endospore-forming
• obligate anaerobes
• Gram (+) bacilli (rods) **like all Clostridium

Question 11

What kind of wound causes C. perfringens and explain pathophysiology

Answer 11

Wound infections: crushing type injuries → compromised blood flow→ low O2 environment → devitalized tissue → anaerobic perfringens growth

Question 12

What are the types of wound infections in C. perfringens and what is the major toxin used?

Answer 12

-Ranges from cellulitis, to fasciitis, to myonecrosis (gas gangrene
=Alpha toxin: Kills phagocytic cells and muscle tissue

Question 13

How can C. perfringens also cause Clostridial food poisoning?

Answer 13

Enterotoxin: disrupts tight junctions between endothelial cells in ilium → dysregulation of fluid transport

Question 14

Name the two gram negative rods

Answer 14

E. Coli

Pseudomonas aeruginosa

Question 15

What is ETEC?

Answer 15

Enterotoxigenic E. coli : traveler’s diarrhea

• Typically from contaminated food and water
• Also uses enterotoxin (remember which other one does..? —— C dif)

Question 16

What urinary problems can E. coli cause?

Answer 16

UTI
-isolates from GI tract access the UT via urethra > bladder > kidney
-“Special” strains getting into the “wrong” place
Adhere to bladder epithelium, are hemolytic to RBCs

Question 17

Similar to UTI’s, what other infections can E. coli cause?

Answer 17

Abdominal infections
-Release/escape of contents of colon to peritoneal cavity and adjacent tissues, e.g., Surgical wounds, traumatic wounds, etc

Question 18

What traumatic injury would uniquely cause Pseudomonas aeruginosa infections?

Answer 18

BURNS! If there was a fire in the Louvre, you would need to make a Pseudo “mona lisa” or psuedomona

P. Aeruginosa can also be caused by traumatic injuries, surgical wounds

Question 19

Let’s review, do you remember what gram stain/ shape are P. aeruginosa?

Answer 19

Gram (-) rods

*just like E. coli

Question 20

What CHRONIC injury (disease) would uniquely cause P. aeruginosa infections?

Answer 20

Cystic Fibrosis (nearly all C.F patients between 15-20)

Lung infection: produce copious, viscous bronchial secretions → stasis in the lungs (predisposes the patient to infection) → Within the lungs, bacteria produces mucoid exopolysaccharide → protected from phagocytosis → produces toxins → progressive damage to the lungs due to the action of the toxins and the host immune response → death

Question 21

So again, why is P. aeruginosa considered an opportunistic pathogen?

Answer 21

1. Infections of traumatic injuries, surgical wounds, and especially BURNS
2. Chronic lung infection of patients with Cystic fibrosis
3. Hospital-acquired infections (UTIs, pneumonia, less frequently associated with intravascular catheter-related infections)

Question 22

What is a gram (-) diplococci bacteria?

Answer 22

Neisseria gonorrhea

Question 23

We know gonorrhea comes from sex, why else is it a concern?

Answer 23

Infected mothers can cause conjunctivitis and blindness in baby

Question 24

So S. aureus has its super toxins, Group A strep has its M protein, and S. Pneumoniae has its antiphag capsule,

…. what does gonorrhea have?

Answer 24

PILI => adherence, interfers with neutrophil killing

-could keep getting it with different strains of pili

…Growth on mucosal surface incites robust inflammatory response, purulent discharge and local tissue invasion. Prolonged infection may lead to scarring and fibrosis

Question 25

Do men or women usually have more symptoms with gonorrhea?

Answer 25

Men
-Males range from asymptomatic to urethritis.
-Females: More often asymptomatic than in males.
But can get infection of cervix, urethra, ascending infection including uterine tubes may result in fibrosis and infertility

Question 26

Where are most anaerobic bacteria (besides clostridia) found in the body? and explain the typical infections?

Answer 26

Most anaerobic diseases are from normal flora from anaerobic nitches ie. Colon, Mouth (e.g., gums, tongue), Female genital tract and Skin

• Usually from bacteria getting into wrong place
• abscess is typical
• mixed infections: aerobic eat air so anaerobes can join party

Question 27

You culture an anaerobic abscess from below the diaphragm, what is it?

Answer 27

Bacteroides fragilis

Although normally only 1-2% of normal gut flora, associated with more than 80% of intra-abdominal infections

Question 28

What makes Bacteroides fragilis pack a punch? (give it virulence and make it not so “fragile”)

Answer 28

Tissue-destructive enzymes
Capsule
Superoxide dismutase

Question 29

What’s the only obligate intracellular bacteria? (acts like virus)

Answer 29

Chlamydia trachomatis

Question 30

Chlamydia is often seen with Gonorrhea, what are similar/ different concerns that you have with this infection? (besides sex)

Answer 30

Neonatal infections
-Infants born to mothers with C. trachomatis genital infection may become infected at birth→ neonatal conjunctivitis and neonatal pneumonia.

Different: Trachoma
=chronic infection of conjunctiva → scarring and blindness

Question 31

Chlamydia exists as two stages, 1) what do you call the infectious particles? 2) what do you call the intracytoplasmic reproductive forms?

Answer 31

1) elementary bodies

2) reticulate bodies

Question 32

What are the atypical bacteria without walls? Why is that unique?

Answer 32

Mycoplasma pneumoniae

-lack a rigid cell wall → shape is highly pleomorphic and penicillins are not effective

Question 33

T/F: Mycoplasma pneumoniae causes pneumonia?

Answer 33

True

• Produces a common form of pneumonia (10%). “atypical pneumonia”
• Predilection for younger persons (5-20 yo)

Question 34

T/F: M. pneumonia isn’t very infectious

Answer 34

False

• Occurs in any season, with outbreaks commonly occurring in families and closed communities.
• Long period of shedding and very low infectious dose
• Attack rate in families ~60% of susceptible individuals

Question 35

T/F: M. pneumonia requires hospitalization?

What are symptoms?

Answer 35

False

• Disease generally mild (“Walking” pneumonia).
• Hospitalization is only very rarely required
• fever, headache, malaise for 2-4 days, followed by respiratory symptoms non-productive cough, chest and body aches, fatigue.
• Resolution and recovery occurs slowly over 1-4 weeks

Question 36

T/F: M. pneumonia lab confirmation is through a gram stain

Answer 36

False

• culture doesn’t grow well
• Gram stain used primarily to rule-out other bacterial causes
• Laboratory diagnosis is often by serological tests

Question 37

Where in your lungs does M. pneumonia infect?

Answer 37

Interstitium: the tissue around the air sacs of the lungs
-Alveoli are clear (hence, non-productive cough)

Mechanism: adheres to respiratory epithelial cells. Remains extracellular. Bacteria produce hydrogen peroxide and superoxide radicals, which damage host tissue.