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Infectious Disease > Gram negative rods > Flashcards

Gram negative rods Flashcards

1
Q

Most Gram negative rods resistent to

A
  • Penicillin
  • Vancomycin
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2
Q

Gram negative rods ABx

A
  • Ceftriaxone
  • Fluoroquinolones
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3
Q

Klebsiella feautes

A
  • intestinal flora
  • non-motile/capsular
  • impaired host defenses (alcoholis, sick people)
  • treatment based on susceptibility testing
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4
Q

Klebsiella illnesses

A

Lovar pneumonia

Lung abscesses

liver abscesses

UTI (3-4%)

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5
Q

Klebsiella pneumonia

A
  • Lobar
  • occurs in alcoholics or diabetics (aspiration)
  • results in red “currant jelly” sputum
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6
Q

Klebsiella lung abscesses

A
  • usually caused by mouth anaerobes
  • Peptostreptococcus, Fusobacterium, Prevotella, Bacteroides
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7
Q

Klebsiella liver abscess

A

usually in patients with underlying disease or cholangitis

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8
Q

Features of E. coli

A
  • gram neg rods with fimbriae (pili)
    • attach to surfaces (may be specialized for particular surfaces)
  • K capsule
    • K1 capsular antigen present in 75% meningitis cases (babies)
    • inhibits phagocytosis and complement
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9
Q

E. coli illnesses

A
  • Watery diarrhea
  • Bloody diarrhea (dysentary)
  • UTI/pyelonephritis
    • E coli bacteremia, sepsis (rare), usually from UTI
  • Meningitis in newborns
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10
Q

E. coli diarrheal illnesses

A
  • Enteroinvasive E. coli (EIEC)
  • Enterotoxigenic E coli (ETEC)
  • Enteropathogenic E coli (EPEC)
  • EnteroHemorrhagic E coli (EHEC)
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11
Q

Enteroinvasive E. coli (EIEC)

A
  • Clinically similar to shigella (no toxins in this but Shigella does make a toxin of course)
  • Invades intestinal mucosa
  • Necrosis
  • Inflammation
  • Bloody diarrhea
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12
Q

Enterotoxigenic E coli (ETEC)

A
  • Two toxins: Labile and Stable
  • watery (traveler’s diarrhea) from contaminated food/water
  • No imflammation
  • No invasion
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13
Q

Enteropathogenic E coli (EPEC)

A
  • No toxin
  • No inflammation
  • Blunt villi prevent absorption
  • Diarrhea usually in children (p=pediatrics)
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14
Q

EnteroHemorrhagic E coli (EHEC)

A
  • Does not ferment sorbitol (sorbitol-McConkey agar)
  • Classic serotype: E. coli 0157:H7
  • Does not invade host cells (toxin causes disease)
  • Produces Shiga-like toxin -> bloody diarrhea
    • bacteriophage encoded (lysogenic) toxin
  • Usually from undercooked beef
  • Toxin effects
    • Endothelium swells -> vessel lumens narrow
    • Deposition of fibrin/platelets in microvasculature
    • Hemolysis, inflammation
  • Feared complication is if the toxin gets into the bloodstream causing Hemolytic Uremic Syndrome (HUS)
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15
Q

HUS

A
  • Hemolytic Uremic Syndrome
  • complication of 10% of EHEC cases
  • common in children
  • Triad
    • Hemolytic anemia
    • Thrombocytopenia
    • Acute renal failure (uremia)
  • HUS + fever; mental status changes = TTP (Thrombotic Thrombocytopenic purpura)
  • usually occurs 5-7 days post diarrhea
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16
Q

Gram negative sepsis

A
  • Fever
  • Tachycardia
  • Hypotension
  • Life-threatening
  • Driven by endotoxin (LPS; Lipid A)
  • Common scenario
    • Elderly patient
    • UTI (catheter, BPH)
    • Gram negative sepsis (+blood cultures)
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17
Q

Infectious causes of bloody diarrhea

7 listed

A
  • Campylobacter
  • Salmonella enterica
  • Shigella
  • Yersinia entercolitica
  • EiEC
  • Entamoeba histolytica
  • EHEC
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18
Q

Infectious causes of watery diarrhea

8 listed

A
  • ETEC
  • Cholera
  • C. diff
  • C. perfringens
  • Giardia
  • Crypto
  • Rotavirus
  • Norovirus
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19
Q

Fecal leukocytes and RBC iindicate?

A

usually indicate invasive infection

Bloody diarrhea

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20
Q

Mucous and epithelial cells in stool only seen in

A

toxin-mediated disease

Watery diarrhea

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21
Q

Parasitic diarrhea can be Dxd by?

A

Stool ova and parasites from protozoal infections

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22
Q

Causes of diarrhea that invade the mucosa

5 listed

A
  • Campylobacter
  • Salmonella enterica
  • Shigella
  • Yersinia entercolitica
  • EIEC
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23
Q

Enterobacter features

A
  • Rare cause of nosocomial UTIs
  • Resistant to many antibiotics
    • ESBL
    • Resistance to most beta-lactams; penicillins, cephalosporins and aztreonam
  • Often treated with Carbapenems
    • Imipenem
    • Meropenem
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24
Q

Enterobacter treatment

A

Resistant to a lot of Abx because they have ESBLs

  • Carbapenems
    • Imipenem
    • Meropenem
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25
Q

Nosocomial means?

A

disease originating from a hospital

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26
Q

Citrobacter & Serratia

A
  • Slow Lactose Fermenters
  • Gram negative rods
  • Not dominant pathogen for any condition
  • often resistant to many Abx
27
Q

Citrobacter features

A
  • Can be found in normal gut flora
  • Gram negative sepsis (with other GN bugs)
28
Q

Features of Serratia

A
  • GN rod
  • produce diistinctive red colonies (red pigment)
  • Catalase positive
  • Hospital outbreaks of UTIs; contaminated water, soap, IV solutions
  • Sometimes osteomyelitis in IV drug users (also Pseudomonas)
29
Q

Slow Lactose Fermenters

A

Citrobacter & Serratia

30
Q

Types of Salmonella

A
  • Salmonella typhi
  • Salmonella Enterica
  • Salmonella Enteritidis
31
Q

Salmonella illnesses

A
  • Salmonella typhi -> typhoid fever
  • Non-typhoid strains cause gastroenteritis (enterica, enteritidis)
    • NVcramps, bloody diarrhea
    • ingestion of contaminated meat, eggs, poultry
  • osteomyelitis in sickle cell patients
32
Q

Features of Salmonella

A
  • Flagellated, mobil, encapsulated gram negative rod
  • disseminate through blood
    • osteomelitis in sickle cell pts
  • Live in GI tract of mammals, birds and reptiles
  • produce hydrogen sulfide
    • triple sugar iron (TSI) test -> media turns black
    • differentiates from shigella
  • Invades GI mucosa
  • The cellular response is largely monocytes
33
Q

Typhoid fever

A
  • caused by Salmonella typhi
  • Travelers to Asia, Africa, South America
  • Classic features
    • Rose spots
      • Faint salmon-colored macules
      • Trunk and abdomen
    • Pulse-termperature dissociation
      • High fever -> slow pulse
  • Can remain in the gall bladder (carrier state)
    • endemic countries 1-4% people may be carriers
    • May be risk factor for carcinoma
34
Q

Diagnosis of Salmonella

A
  • Culture (stool, blood (typhoid))
35
Q

Treatment of Salmonella Gastroenteritis

A

Gastroenteritis

  • Fluids/electrolytes
  • Abx not really helpful (only in severely ill)
  • has lots of resistance
  • Anti-peristalsis contraindicated because prolong illness
36
Q

Treatment of Typhoid Fever

A
  • Ceftriaxone
  • Fluoroquinolones
  • Typhoid vaccine is available
    • inactive variant given orally
    • used for high risk travelers
37
Q

Shigella features

A
  • non-motile (no flagella)
  • not normal GI flora
  • Commin in children
  • Dx: stool culture
  • Invades mucosal cells (M cels in Peyer’s Patches)
    • Macropinocytosis
    • Induces apoptosis
  • Spreads from cell-to-cell
    • does not spread hematogenously (salmonella does)
  • Releases Shiga toxin
    • but non-toxin strains still cause disease
    • Cellular invasion more important mechanisms of disease
  • Very few bacteria are required to cause disease (few as 10)
  • Cellular response is largely PMNs (neutrophils)
38
Q

Shigella treatment

A
  • Fluids/electrolytes
  • Abx improve symptoms, reduce shedding in stool
    • can limit spread
  • Ceftriaxone or Ciprofloxacin
39
Q

How to tell Salmonella vs Shigella

A
  • Salmonella
    • Produces H2S so black color on triple sugar iron TSI
    • Mostly Monocyte response
    • Hematogenous spread
    • No antibiotics
    • Motile (flagella)
  • Shigella
    • No H2S
    • Mostly Neutrophil response
    • Cell-to-cell spread (Macropinocytosis)
    • Yes Abx (Ceftriaxone or Ciprofloxacin)
    • Nonmotile
    • Shiga toxin
    • Low infectious dose
40
Q

Proteus features

A
  • Rare cause of UTIs
  • “Swarm phenotype”
    • long flagella
    • facilitates urinary ascent
    • Bulls-eye on agar plates
  • Produces urease
    • converts urea to ammonia
  • Associated with Struvite Kidney Stones
41
Q

Pseudomonas aeruginosa features

A
  • highly-feared bacteria
    • serious hospital acquired infections (i.e. VAP “Ventilator Acquired Pneumonia)
    • Resistant to many Abx
  • Obligate aerobe
  • gram negative rod
  • Loves the water (commonly found in environmental water sources
  • Produces blue-green pigment (pyocyanin)
    • smooth, fluorescent green colonies on culture media
  • sweet grape-like odor
42
Q

Pseudomonas aeruginosa illnesses

A
  • Pneumonia (Nosocomial) (Cystic fibrosis)
  • UTIs
  • Surgical wound infections
  • Bacteremia/sepsis
  • Osteomyelitis (IV drug users)
  • Ottitis externa (swimmers ear)
  • Burn infections
  • Hot tub folliculitis
43
Q

Pseudomonas toxins

A
  • Endotoxin (LPS)
    • can cause fever, shock
  • Endotoxin A
    • Inactivates elongation factor EF-2
    • EF-2 is necessary for protein synthesis
44
Q

Pseudomonas Pneumonia

A
  • classic pneumonia in CF pts
45
Q

Pseudomonas

A
46
Q

Hot tub folliculitis

A

tender itchy papules after using hot tub or spa

47
Q

Otitis externa

A
  • Swimmer’s ear
  • painful ear with discharge
48
Q

Pseudomonas Osteomyelitis

A
  • IV drug users
49
Q

Ecthyma gangrenosum

A
  • Caused by Pseudomonas bacteremia
  • Black, necrotic ulcers on skin with bacteremia
  • invasion/destruction of blood vessels by bacteria
  • Classic case is neutropenic cancer patient with fever, chills (bacteremia) who develops black lesions on chest and back
50
Q

Burkholderia cepacia

A
  • Gram negative rod similar to Pseudomonas
  • Oxidase positive
  • Catalase positive
  • Rare cause of infections in
    • Cystic fibrosis
    • Chronic Granulomatous Disease
51
Q

H pylori illnesses

A
  • gastritis & ulcers
    • common in paitents with ulcers (majority of duodenal ulcers)
    • many with gastric ulcers
  • MALT lymphoma
    • mucosal associated lymphatic tissue lymphoma
    • B-cell cancer; usually in the stomach
    • Highly associated with H. pylori
52
Q

H pylori features

A
  • Causes gastritis and ulcers (abdominal pain)
  • Urease positive
    • hydrolyzes urea to compounds that damage epithelium
    • produces ammonium (alkaline) (protects from acidic environment in stomach
    • Protects bacteria from stomach acid
  • Urea breath test
    • patients swallow urea with isotopes (carbon-14 or Carbon-13)
    • detection of isotope labled carbon dioxide in exhaled breath is evidence indicating urea was split (urease is present)
53
Q

H pylori diagnosis

A
  • Biopsy
  • Urea breath test
  • Stool antigen
54
Q

H pylori treatment

A
  • Triple therapy for 7-10 days
    • Proton pump inhbitor (omeprazole)
    • Clarithromycin
    • Amoxicillin or Metronidazole
  • Test to determine eradication (failure in 20% of attempts)
    • breath test, stool antigen or biopsy
55
Q

Legionella features

A
  • Does not gram stain well
  • silver stains used
  • special culture requirements
    • Buffered charcoal Yeast Extract (BCYE) with Iron and Cysteine added for growth
  • Supplemented with antibiotics and silver dyes
    • Antimicrobials prevent overgrowth by competing organisms
    • dyes give distinctive color to Legionella
56
Q

Legionella illneses

A
  • Nosocomial pneumonia in Nursing homes
    *
57
Q

Legionella pneumonia symptoms

A
  • initially mild pneumonia symptoms
    • fever; mild, slightly productive cough
  • can progress to severe pneumonia
  • GI symptoms
    • NVwD, abdominal pain
  • Hyponatremia (Na<130 mEq/L) common
    • can occur in any pneumonia but more common with Legionella Pneumonia
58
Q

Classic case of Legionella infection

A
  • Mild cough
  • Watery diarrhea
  • Confusion (low Na)
  • Negative bacteria on gram stain (poorly visualized)
59
Q

Treatment of Legionella

A
  • Fluoroquinolone
  • or
  • Macrolide
60
Q

Pontiac fever

A

Mild form of Legionella infection

  • fever
  • malaise
  • chills
  • fatigue
  • headache
  • no respiratory complaints
  • Chest radiograph usually normal
61
Q

Bacteroides fragilis

A
  • Gneg rod anaerobic
  • normal GI flora
  • cause infection after breach of mucosal barrier
62
Q

Bacteroides fragilis infections

A
  • rare to cause infections by itself
  • Usually part of polymicrobial infections from the GI tract
    • peritonitis (following perforation)
    • Intraabdominal abscess
    • Lung abscess (aspiration)
    • E. coli/GNR and B fragilis often components together
63
Q

Bacteroides fragilis treatment

A
  • Covered by Metronidazole
  • Common GI therapy: Cipro/Flagyl
    • Quinolone for E. coli
    • Metronidazole for B. fragilis

Infectious Disease (82 decks)

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