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D&D Unit 3 > Common Bacterial Pathogens (complete) > Flashcards

Common Bacterial Pathogens (complete) Flashcards

1
Q

What are two genuses of gram positive cocci?

A

1) Staphylococcus (catalase +)

2) Streptococcus (catalase -)

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2
Q

Generally describe staph aureus.

A
  • 1ary pathogenic species of genus
  • gram (+) cocci in clusters
  • Asymptomatic carriers => ~30% of healthy ppl —» potential for carriers to spread to pts
  • Responsible for wide spectrum of diseases – depending on strain
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3
Q

What are the categories of the wide range of diseases caused by staph aureus?

A

1) Cutaneous infection
2) Toxin-mediated disease
3) Pneumonia
4) Foreign-associated infections
5) Bacteremia/endocarditis

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4
Q

Describe cutaneous infections caused by staph aureus

A

Characteristic lesion => Localized abscess

  • Bacterium + host wall off infection w/ fibrinous capsule
  • Capsule prevents infiltration of phagocytes, Abs, antimicrobials
  • Tx => draining abscess
  • Often associated w/ presence of foreign body (splinter, suture)
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5
Q

Which enzyme helps form the fibrinous capsule involved in cutaneous infections caused by staph aureus?

A

Coagulase

  • An essential virulence factor
  • Deposits fibrin on cell surface –» interferes w/ phagocytosis

Coagulase is used as a diagnostic factor when differentiating between different staphalococci

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6
Q

Which major cytotoxic agent is released by staph aureus during cutaneous infections?

A

Alpha-toxin

  • First identified member of pore-forming beta-barrel toxin family
  • Knock-out strains => reduces invasiveness and virulence of infection
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7
Q

What are different types of toxin-mediated diseases caused by staph aureus?

A

1) Scalded Skin Syndrome
2) Toxic shock syndrome
3) Staph food poisoning

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8
Q

Describe Scalded Skin Syndrome

A
  • Local infection, toxin production => systemic effects
  • Epidermis sloughs off (doesn’t necessary slough where the infection is)
  • Adult slough —» more localized b/c of ^ presence of Ab
  • Infant slough —» widespread b/c their immune system hasn’t seen the infection before (no Abs)
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9
Q

Describe Toxic Shock Syndrome

A
  • Most frequent in menstruating women (but 1/3 of cases are males)
  • Local infection and toxin production
  • Toxins requires O2, neutral pH, high protein environment (not changing a tampon often => ideal environment for staph aureus) «—IMPORTANT!! KNOW THIS
  • Symptoms: High fever, shock, vomiting, muscle-pain, renal/hepatic injury
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10
Q

Describe staphylococcal food poisoning

A
  • Caused by contaminated food —» ingestion of superAg toxin
  • Vomiting and diarrhea

YIPPEEEE!

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11
Q

What is a superantigen toxin?

A
  • Ag class => cause non-specific activation of T cells
  • Polyclonal T cell activation and massive cytokine release
  • Produced by pathogenic microbes

Normal Ags induce .001% of T cell response —- SuperAgs induce 25%!!

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12
Q

Describe staphylococcus epidermidis

A
  • Prototype of SSNA (aka CNS) —» Staph species, not aureus - Coagulase-negative staph
  • Normal skin flora, relatively non-pathogenic
  • Allows slime/biofilm formation => adheres to implanted devices (catheters, shunts)
  • Very difficult to treat! Usually have to remove device
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13
Q

Describe streptococcus pyogenes (Group A strep)

A
  • Can cause pharyngeal infection (LOCALIZED)
  • Can cause skin/wound infections (SYSTEMIC)
  • If untreated => post-strep probs (glomerulonephritis, rheumatic fever)
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14
Q

Describe streptococcal pharyngitis. What is the primary virulence factor associated w/ local infection?

A
  • Spreads via droplet/nasal secretions of infection person
  • Several % of asymptomatic carriers
  • Swollen tonsils w/ white, purulent exudate

Virulence factor

  • M-protein => inhibits phagocytosis, kills PMNs, enhances adherence to epithelial cells
  • Produced by bacteria
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15
Q

Describe rheumatic fever

A
  • Autoimmune inflammatory heart, joints, other tissue disease — may follow strep throat
  • Results from Abs produced b/c of strep throat —» now attack heart
  • Distinct from infective endocarditis b/c the infection itself does not attack heart, just Abs
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16
Q

Describe infective endocarditis

A
  • Caused by bacterial infection of heart valves

Three common bacteria:

1) Staph a.
2) Viridans Strept
3) Coagulase-negative staph

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17
Q

Describe streptococcus pneumoniae

A
  • G(+) cocci in pairs
  • In normal flora of 40% of healthy pop’n
  • Pathogenesis related to ability to grow and evade host defenses:

1) Antiphagocytic polysaccharide capsule
2) Recovery/immunity due to anticapsular Ab development
3) Multiple antigenic types of capsule

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18
Q

What are the diseases caused by streptococcus pneumoniae? Classify according to invasiveness

A

Non-invasive:

  • Pneumonia
  • Sinusitis, otitis media, bronchitis

Invasive:

  • Meningitis
  • Bacteremia/septicemia
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19
Q

Which factors predispose a person to pneumonia?

A

1) Young and old
2) Alcoholism
3) Respiratory viral infection

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20
Q

Which types of vaccines exist against pneumonia? Separate according to age.

A

Adults:

  • 23-valent vx (you’ll hear pts call it the “pneumonia vaccine”)
  • Technically also 13-valent, but Gill doesn’t say this (ACIP recommends in kids/adults)

Kids:

  • 7-valent vx (not recommended by ACIP anymore)
  • 13-valent vx (recommended by ACIP)

Gill needs to update his vx info — recommendations have changed

21
Q

Describe enterococcus faecalis and E. faecium

A
  • Primary causes of enterococcal infections
  • Often nosocomial infections
  • Common sites: urinary tract, surgical wounds, biliary tract
  • Important to differentiate from other streptococci b/c of antibiotic tx resistance
22
Q

Which genus is classified as gram-positive rods?

A

Clostridium!!!

23
Q

How are Clostridia classified?

A

1) Strict anaerobes

2) Endospore-formers

24
Q

Describe Clostridium difficile

A
  • Typically a nosocomial infection
  • in normal flora of 10% of healthy ppl
  • Resistant to most common antibiotics
  • Spores NOT KILLED by alcohol-based hand sanitizers!! (HOLY FRICKIN MOLY!!!)
25
Q

How is C. Diff disease acquired?

A
  • In hospitals
  • Associated w/ or follows antibiotic use (Clindamycin, etc.) b/c normal GI flora is suppressed => C. Diff grows!!
  • Can also be transmitted from an infected person to another person
26
Q

Go read the C. Diff case history!!

A

It will help you understand the progression of C. Diff

SERIOUSLY!! GO READ IT! NOW

27
Q

Describe C. Tetani

A
  • Comes from soil/animals (think spore transmission)
  • Local infection and toxin production
  • Retrograde transport of toxin to CNS
  • Toxin blocks interneurons in CNS (Spastic paralysis!!! LOCK-JAW!)

Also, maternal and neonatal tetanus (b/c of unhygienic deliveries and umbilical cord care)

28
Q

Describe C. Botulinum

A
  • Comes from soil/animals (spore transmission)
  • The preformed toxin in food circulated in body —» blocks Ach transmission at neuromuscular junctions => FLACID PARALYSIS
  • Common in home-canned foods
29
Q

Describe C. perfringens

A
  • In wound infections (cellutis, fasciitis, myonecrosis) => bacteria produces alpha-toxin, and other damaging enzymes/toxins
  • Alpha-toxin kills phagocytes and muscle tissue
  • In food poisoning: produce enterotoxin in vitro ==> disrupts tight junctions between endothelial cells in ilium (dysregulation of fluid transport)
30
Q

What are two types of gram-negative rods?

A

1) E. coli

2) Pseudomonas aeruginosa

31
Q

Describe E. Coli

A
  • Many different strains
  • Normal in large intestine flora

Causes GI disease:

  • many strains vary in severity
  • typically from contaminated food/water
  • Antibiotics can/cannot be used (depends on strain)
  • Traveler’s diarrhea (toxin disrupts electrolyte balance in gut, managed by fluid replacement)
32
Q

Describe E. Coli in UTIs

A
  • Endogenous fro GI tract
  • Access UT via uretha –» bladder —» kidney
  • Certain strains can adhere to cells, interact w/ bladder epithelial cells, or are hemolytic
33
Q

Describe E. Coli in abdominal infections

A
  • Release/escape of contents of colon to peritoneal cavity/adjacent tissues
  • B/c of surgery, wounds, colon cancer
  • Often associated w/ anaerobic bacteria
34
Q

Describe Pseudomonas Aeruginosa

A
  • A very common environmental bacterium — most ppl are highly resistant to it
  • Infections caused by traumatic injuries, surgical wounds, burns (especially BURNS)
  • Also associated w/ chronic lung infection in pts w/ CF
35
Q

Describe Pseudomonas Aeruginosa in cystic fibrosis

A
  • Nearly all CF pts 15-20 yo are infected
  • Facilitated by resistance to anti-staph drugs (makes it difficult to treat)
  • Lung damage b/c of bacterial toxins
  • PA is protected from phagocytes

Frequently the COD in pts w/ CF

36
Q

What is a type of gram-negative (diplo)cocci?

A

Neisseria gonorrhoeae

37
Q

Describe Neisseria gonorrhoeae

A
  • Causes gonorrhea and conjunctivitis (leading to blindness) of infants born to gonorrhea (+) moms
  • PILI: key to infectivity
  • Pili interfere w/ killing of bacteria by PMNs — Ab develops to pili prevents infection
  • Prolong infection => scarring/fibrosis (urethra (men/women), cervix => infertility in women)
38
Q

Describes anaerobes

A
  • Found in normal flora but killed by O2
  • Found in colon, mouth (e.g. gums, tongue), female genital tract, skin
  • Usually cause disease as a mixed infection (lung/colon abscesses)

Treatment:
More effective - metronidazole
Less effective - aminoglycosides

39
Q

Describe Bacteroides fragilis

A
  • Common in colon flora, aerotolerant
  • Cultured from anaerobic abscess below diaphragm
  • Considered to be a prototypical endogenous anaerobic pathogen
40
Q

What are the virulence factors associated w/ bacteroides fragilis?

A

1) Tissue-destructive enzymes
2) Capsule
3) Superoxide dismutase

41
Q

What is a type of intracellular bacteria?

A

Chlamydia trachomatis

42
Q

What is a type of bacteria w/o cell walls?

A

Mycoplasma pneumoniae

43
Q

Which diseases are caused by chlamydia trachomatis?

A

1) Trachoma
2) Genital infections
3) Neonatal infections

44
Q

Describe trachoma that is caused by chlamydia trachomatis

A
  • Chronic infection of conjunctiva
  • Causes scarring and blindness
  • Endemic in parts of Asia/Africa
45
Q

Describe the genital infections caused by chlamydia trachomatis

A
  • Common STI
  • Non-gonococcal urethritis (men) and urethritis, cervicitis, and PID (women)

LEADS TO neonatal infections in mom is infected

  • Neonatal conjunctivitis, pneumonia
  • Screening and treatment in pregnant women decreases incidence
46
Q

Describe mycoplasma pneumoniae

A
  • Produces common form of pneumonia (10%): atypical pneumonia — found in younger ppl (5-20yo)
  • Adheres to respiratory epithelial cells
  • Bacterial growth is extracellular
  • Bacteria produce H2O2 and superoxide radical => UH OH! serious damage
47
Q

Describe mycoplasma pneumonia as it presents in pts

A
  • Generally mild
  • AKA: walking pneumonia
  • Spread by respiratory secretions
  • Fever, headache, malaise, non-productive cough, check/body aches, fatigue
  • Recovery slow — over 1-4 weeks
48
Q

Describe mycoplasma pneumonia on a cellular level

A
  • Culture difficult to grow => slow
  • Causes inflammation/thickening of interstitium (tissue around air sacs of lungs)
  • Lab diagnosis via serological tests
  • Gram stain used primarily to RULE-OUT other bacteria

Treatment: b/c bacteria lack cell wall/shape => cell wall-active antibiotics not effective

D&D Unit 3 (12 decks)

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