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E. coli, etc Flashcards

1
Q 
Enterobacteriacea:
G (+,-)
Glucose (+,-)
Oxidase (+,-)
(Motile, non-motile)
A

Gram -
Glucose +
Oxidase -
Motile

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2
Q

Which two enteric infectious agents are non-motile?

A

Klebsiella and Shigella

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3
Q

List two ways to distinguish Enterobacteriaceae from Pseudomonas

A
  1. Oxidase: + = Pseudomonas; - = Enterobactericeae

2. Glucose: doesn’t ferment = Pseudomonas; does ferment = Enterobactericeae

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4
Q

What diagnostic method utilizes Enterobacteriaceae’s ability to ferment lactose?

A

MacConkey agar - turns pink due to pH indicator in agar and production of acid by glucose fermentation

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5
Q

Which two species would be white on MacConkey agar?

A

Shigella and Salmonella

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6
Q

What are the constituents of a MacConkey agar medium?

A

Lactose, pH indicator, bile salts, crystal violet

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7
Q

What is the purpose of the bile salts and crystal violet in MacConkey agar?

A

Kill Gram + spp

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8
Q

What feature of Enterobactericeae is utilized for diagnosing UTIs?

A

Reduction of nitrates to nitrites

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9
Q

How is antibiotic resistance acquired?

A

Conjugation/plasmids

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10
Q

Several patients are seen in the ER the day after eating at a local hamburger place. They present with severe abdominal cramps and high volume diarrhea. What test should you run before even considering giving an antibiotic?

A

Sorbitol MacConkey agar to check for EHEC (which would be white)

(This presentation is suggestive of EHEC, for which you should not give antibiotics to prevent HUS)

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11
Q

Who dies from diarrhea in the US? In developing countries?

A

US = elderly

Developing countries = infants and young children

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12
Q

Most diarrhea is due to (bacteria, virus)

A

Virus

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13
Q

What percent of diarrhea is caused by viruses?

A

80-90%

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14
Q

Noninflammatory or inflammatory diarrhea: LLQ cramping

A

Inflammatory

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15
Q

Noninflammatory or inflammatory diarrhea: normal temp

A

Non-inflammatory

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16
Q

Noninflammatory or inflammatory diarrhea: methylene blue positive stool

A

Inflammatory

marker of leukocytes

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17
Q

Noninflammatory or inflammatory diarrhea: high volume

A

Non-inflammatory

watery

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18
Q

Noninflammatory or inflammatory diarrhea: small bowel

A

Non-inflammatory

Think: this is where most absorption occurs, so makes sense that pathology here would result in watery stool

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19
Q

Noninflammatory or inflammatory diarrhea: colon

A

Inflammatory

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20
Q

Noninflammatory or inflammatory diarrhea: dysentery

A

Inflammatory

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21
Q

Noninflammatory or inflammatory diarrhea: enterotoxin

A

Non-inflammatory

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22
Q

Noninflammatory or inflammatory diarrhea: cytotoxin

A

Inflammatory

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23
Q

Noninflammatory or inflammatory diarrhea: tenesmus

A

Inflammatory

Think: little evacuation = tenesmus; not like profuse passage seen with non-inflamm

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24
Q

Noninflammatory or inflammatory diarrhea: lactoferrin positive stool

A

Inflammatory

marker of WBCs

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25
Q

When should you suspect a parasitic etiology of diarrhea?

A

If it persists for >2 weeks

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26
Q

List 3 tests that indicate WBCs in stool

A

Methylene blue
Lactoferrin
Leukocyte esterase

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27
Q

List two infectious agents that mainly cause diarrhea in AIDS patients

A

CMV

M. avium

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28
Q

How is bacterial diarrhea usually diagnosed?

A

Culture

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29
Q

A patient presents with diarrhea that has persisted for 17 days. First step in management?

A

Examine stool for parasites

>2 weeks = parasitic

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30
Q

Noninflammatory or inflammatory diarrhea: antimotility drugs contraindicated

A

Inflammatory

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31
Q

Noninflammatory or inflammatory diarrhea: use antibiotics

A

Both - but not in inflammatory diarrhea caused by EHEC

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32
Q

Complication of EHEC?

A

HUS

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33
Q

Complications of campylobacter?

A

GBS, Reiter’s syndrome

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34
Q

What is Reiter’s syndrome?

A

Polyarthritis in large joints, conjunctivitis, urethritis

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35
Q

List 4 causes of Reiter’s syndrome following enteric infection

A

Salmonella, Shigella, Yersinia, Campylobacter

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36
Q

Why can some strains of E. coli cause pathology while resident strains don’t?

A

Virulent strains have acquired PAIs, plasmids, &/or lysogenic phages with additional genes

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37
Q

Appearance of E. coli on KIA slant

A

Yellow butt and slant (ferments lactose), cracks (produces H2)

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38
Q

Appearance of Shigella on KIA slant

A

Yellow butt with red slant (ferments glucose only), no gas

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39
Q

Appearance of Salmonella on KIA slant

A

Black butt (produces H2S), red slant (doesn’t ferment lactose), cracks (produces H2)

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40
Q

Appearance of non-fermenting G- rods on KAI slant

A

Red butt and red slant, no gas

Think Pseudomonas

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41
Q

Watery diarrhea that becomes bloody

A

EHEC, Shigella
Campylobacter jejuni
C. diff

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42
Q

Cause of hemorrhagic colitis

A

EHEC (0157:H7)

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43
Q

Shiga-like toxin

A

EHEC

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44
Q

LEE

A

Locus of enterocyte effacement; encodes EHEC and EPEC virulence factors

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45
Q

List 4 gene products contained within LEE

A
  1. Intimin - EHEC attachment protein
  2. Secreted intimin receptor that incorporates within enterocyte membrane
  3. Type III secretion system
  4. Rearrangement of cell actin to create pedestal for EHEC attachment (Attachment-Effacement lesion)
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46
Q

Symptoms of EHEC hemorrhagic colitis

A

Sudden onset of severe abdominal cramps with watery diarrhea that becomes bloody within 24 hours

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47
Q

EHEC would produce lactoferrin (+, -) stool

A

Negative (no WBCs in stool)

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48
Q

Would you expect fever in a patient with 0157:H7? ETEC?

A

No

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49
Q

1 cause of acute renal failure in children

A

HUS following 0157:H7 infection

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50
Q

How will HUS present?

A

Acute renal failure, anemia, thrombocytopenia during the second week of an episode of bloody diarrhea
(may also develop seizures, strokes)

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51
Q

HUS following EHEC usually affects:

A

Children < 5 and elderly

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52
Q

List some sources of EHEC

A 
Ground beef
Spinach
Unpasteurized juice, milk
Sprouts
Water
Salami
Lettuce
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53
Q

List some factors that contribute to spread of EHEC

A
  1. Low infectious dose
  2. Some human-human transmission
  3. Cattle don’t get sick when they have it
  4. High carriage in cattle due to feedlots
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54
Q

Describe Shiga-like toxin (Stx)

A

Cytopathic toxin that inhibits protein synthesis, resulting in cell death; encoded by lysogenic phage
(Remember pathogenic E. coli strains have additional genes)

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55
Q

What is the main cause of diarrhea in EHEC?

A

LEE pathogenicity island

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56
Q

Why do antibiotics contribute to development of HUS?

A

They stress EHEC, causing replication of lysogenic phage that encodes Stx gene

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57
Q

List 4 diagnostic methods for EHEC

A
  1. Sorbitol MacConkey (will be white)
  2. RADT of Stx in stool
  3. Nucleic acid detection of Stx genes
  4. Serotyping of isolates
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58
Q

Traveler’s diarrhea

A

ETEC

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59
Q

What type of diarrhea is produced by ETEC?

A

Profuse, watery diarrhea (similar to cholera)

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60
Q

Where would you expect ETEC toxin to work?

A

Small intestine (produces a watery diarrhea by preventing absorption, the majority of which occurs in the SI)

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61
Q

LT and ST

A

ETEC toxins (heat labile and heat stable toxins)

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62
Q

What is the mechanism of LT?

A

Activates cAMP –> AC –> Cl- efflux

identical to cholera toxin

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63
Q

What is the mechanism of ST?

A

Mimics guanylin –> binds GC –> activates cGMP –> activates PKA –> activates CFTR

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64
Q

Attachment of ETEC vs EHEC vs EIEC vs EPEC vs UPEC

A 
ETEC - fimbriae
EHEC - LEE-encoded intimin
EIEC - adhesin
EPEC - EAF + intimin
UPEC - P-fimbriae
65
Q 
List the type of diarrhea:
EHEC
ETEC
EIEC
EPEC
A

EHEC - watery then bloody
ETEC - profuse watery
EIEC - dysentery
EPEC - profuse watery

66
Q

What is the reservoir of EIEC?

67
Q

Where would you expect EIEC to act?

A

Colon

dysentery = inflammatory diarrhea = colon

68
Q

Which E. coli infection produces fever?

69
Q

List 3 ways in which EIEC is unique among E. coli spp

A

Non-motile, doesn’t ferment lactose, doesn’t decarboxylate lysine

70
Q

A college student returning from spring break in Cancun develops a profusely watery diarrhea. She reports seeing blood in her stool on a few occasions. She doesn’t have a fever. Dx?

A

EPEC

Mexico + no fever + blood = EPEC

71
Q

List 2 sources of EPEC infection

A

Water, meat

72
Q

Which E. coli strains are not associated with toxin production?

A

EPEC, EIEC

73
Q

What are the two virulence factors of EPEC?

A

EAF (EPEC adherence factors) + LEE-encoded intimin

74
Q

Which two E. coli strains cause an attachment-effacement lesion?

A

EPEC, EHEC

75
Q

What causes the diarrhea seen with EPEC?

A

Invasion of host cells (“moderately invasive”)

76
Q

What is DAEC? Where is it found?

A

Diffusely adherent E. coli

Mexico and North Africa

77
Q

Which E. coli species would cause fever?

78
Q

Which E. coli species replicates in intestinal cells?

A

EIEC (Think: it’s invasive)

79
Q

A leading cause of infantile diarrhea in developing countries

80
Q

A 3 year old has had diarrhea without fever for 3 months. If the etiology is infectious, which microbe would you expect to be the culprit?

A

EAEC

Causes persistent diarrhea in young kids with no inflammation or fever

81
Q

Hemolysin

A

EAEC, UPEC

82
Q

What are the virulence factors of EAEC?

A

ST-like toxin and hemolysin

83
Q

Which E. coli species is associated with a low infectious dose?

A

EHEC

Remember this contributes to its spread

84
Q

90% of UTIs caused by

85
Q

Coagulase negative cause of UTI

A

Staph saprophyticus

86
Q

What defines UTI in a female? Male?

A

Female - >10^5 bacteria per mL

Male - 10^3 bacteria per mL

87
Q

What is our major defense against bladder infections?

A

Urine flow

88
Q

Describe how UPEC is acquired

A

First colonizes the colon (present as a minor part of flora) –> feces –> urethra

89
Q

List 4 virulence factors of UPEC

A
  1. P-fimbriae
  2. Hemolysin
  3. K antigen/capsule
  4. Siderophore
90
Q

What is the purpose of the UPEC hemolysin?

A

Forms pores in cells so it can extract nutrients + is cytopathic

91
Q

What does P-fimbriae bind to?

A

Galactose on RBCs and uroepithelial cells

92
Q

How is UPEC able to avoid complement?

A

K antigen/capsule

93
Q

What is associated with upper UTIs?

94
Q

What is K-1?

A

Specific K antigen which binds to N-acetylneuraminic acid/sialic acid = acts as an antigenic disguise and is antiphagocytic
Causes upper UTIs and neonatal meningitis

95
Q

Which E. coli strain has an antiphagocytic capsule?

96
Q

Cause of neonatal bacterial meningitis

A

E. coli (K-1 antigen)

Citrobacter

97
Q

E. coli causes ___% of gram negative septicemia. Other causes of gram negative septicemia include:

A

40%

Pseudomonas, Acinetobacter

98
Q

Frank pathogens

A

Salmonella, Shigella, Proteus, Morganella

99
Q

___ is a common cause of disseminated infection, particularly within ___

A

Salmonella

Bone

100
Q

How does S. typhi differ clinically from other Salmonella serotypes?

A

Doesn’t produce diarrhea &/or dysentery

101
Q 
Salmonella:
Gram (+,-)
Shape?
Lac (+,-)
KIA slant characteristics?
A

Gram -
Rod
Lac -
Red slant + gas + black bottom (H2S)

102
Q

Vi Ag

A

Capsule of S. typhi

103
Q

Source of Salmonella enteritidis

A

Eggs, poultry, reptiles/turtles

104
Q

Zoonosis

A

Salmonella enteritidis (food poisoning)

105
Q

Describe the entry and replication of Salmonella

A

Enters small intestine through M cells, then extends into lamina propria, where it’s taken up by macrophages, in which it replicates

106
Q

A kid goes to a petting zoo and two days later develops N/V, abdominal pain, and diarrhea with loose, watery stools. Diagnosis?

A

Salmonella (think reptiles, turtles)

107
Q

When does salmonella food poisoning present? Sx?

A

20-72 hours after infection

N/V initially, followed by abdominal pain and diarrhea ranging from few loose, watery stools to severe dysentery

108
Q

List 3 places to which Salmonella likes to disseminate. What kind of patients are at risk for such dissemination?

A

Bone, heart (endocarditis), kidneys
Sickle cell kids, patients with T cell deficiencies (AIDS), skeletal prostheses, atherosclerotic plaques, and the extremes of age

109
Q

How is S. typhi contracted?

A

Food/water contaminated with human feces/urine

110
Q

To where does S. typhi disseminate?

A

RES system, especially liver and spleen

111
Q

Classic triad of S. typhi

A

Bradycardia + neutropenia + splenomegaly

112
Q

Where does S. typhi hang out in carriers?

A

Gallbladder (cholecystectomy for cure)

113
Q

Where is S. typhi endemic?

A

Africa, Asis, South America

114
Q

Symptoms of typhoid fever

A

High fever, bradycardia, HA, mental confusion

Does NOT cause diarrhea!!

115
Q

Skin finding in typhoid fever

A

Rose spots

116
Q

Virulence factors of S. typhi

A 
2 type III secretion systems
LPS
Vi ag (capsule)
117
Q

What is the function of the 2 type III secretion systems of S. typhi?

A
  1. Injects proteins into M cells –> entry

2. Injects proteins into macrophages –> survival and dissemination

118
Q

What causes fever of S. typhi infection?

119
Q

Is S. enteridis encapsulated?

120
Q

2 ways to diagnose typhoid fever

A
  1. Blood or feces culture

2. Serotyping for Vi antigen

121
Q

A 14 year old patient presents with a red, warm, swollen right thigh with some limited range of motion. CBC reveals leukocytosis and PBS reveals sickling. Dx?

A

Salmonella osteomyelitis secondary to sickle cell anemia

122
Q

Complication of bowel perforation

123
Q

4 strains of Shigella

A

Sonnei
Flexneri
Dysenteriae
Boydii

124
Q

What is the most common Shigellosis in US? 2nd?

A 
1st = sonnei (70%)
2nd = flexneri
125
Q

Shigella in daycare centers

126
Q

Gay men

A

Shigella flexneri

127
Q

Epidemic in South and Central America

A

Shigella dysenteriae

128
Q

Epidemic in India

A

Shigella boydii

129
Q

Transmission of Shigella

A

Fecal-oral route

130
Q

What is the only reservoir for Shigella

131
Q

List all the bacteria that produce Stx

A

EHEC
Shigella

(note: EIEC does NOT produce Stx)

132
Q

List all bacteria that invade lamina propria

A

EIEC
Shigella
Salmonella

133
Q

Infectious dose of Shigella vs EIEC

A

Shigella - really low

EIEC - high

134
Q

STD

A

Shigella flexneri (associated with gay male transmission)

135
Q

Describe the pathogenesis of Shigella

A

Enters M cells, escapes phagocytic vesicles, extends into neighboring enterocyte, produces shiga toxin, and inhibits protein synthesis

136
Q

Spherocytosis could be found in a patient as a complication of which enteric bugs?

A

EHEC

Shigella dysenteriae

137
Q

How does Shigella present?

A

Watery diarrhea + abdominal (starts in small intestine) followed by dysentery + cramps + tenesmus + fever

138
Q 
Shigella:
Gram (+,-)
Shape
Lac (+,-)
Motile, non-motile
KIA characteristics?
A 
Gram -
Rod
Lac -
Non-motile (but does extend into neighboring enterocytes, mimicking motility)
Red slant, yellows butt, no gas, no H2S
139
Q

What characteristic diagnostic finding indicates infection with Shigella?

A

Sheets of leukocytes present in feces

due to invasion of M cells with propulsion into epithelial cells which creates shallow ulcers

140
Q

Which two enteric bugs inhibit eukaryotic protein synthesis?

A

Shigella, EHEC

141
Q

Which two bugs produce a large amount of Stx?

A

EHEC, Shigella dysenteriae

Other Shigella spp produce less toxin

142
Q

Invasion plasmid

A

EHEC, Shigella

143
Q

Shiga-like toxin vs. Shiga toxin

A

Shiga-like toxin = EHEC; phage-encoded

Shiga toxin = Shigella; chromosome-encoded

144
Q

If both EHEC and Shigella can cause HUS, why is it ok to treat Shigella but not EHEC with antibiotics?

A

Shiga like toxin is encoded on a phage, which becomes stressed and increases replication in the face of antibiotics = increased risk HUS
Shiga toxin is encoded within the chromosome, so it will not go into overdrive in the face of antibiotics = no increased risk of HUS

145
Q

Zoonotic infection

A

Salmonella food poisoning

Typhoid fever is NOT considered a zoonose

146
Q

Mimics appendicitis

A

Yersinia, Campylobacter

147
Q

Mesenteric lymphadenitits

A

Yersinia entercolitica

148
Q

Main reservoir for Yersinia enterocolitica

A

Pigs (wild animals in general)

149
Q

Complication of Yersinia enterocolitica

A

Reiter’s syndrome (arthritis + conjunctivitis + urethritis)

150
Q

Gram - Enterobacteriacae that are mainly opportunistic causes of UTIs

A 
Klebsiella
Citrobacter
Enterobacter
Proteus/Morganella
Serratia marcescens
151
Q

Currant-jelly pneumonia

A

Klebsiella

152
Q

Brick-red colonies causing pneumonia in hospitalized patients

153
Q

Opportunistic UTI, pneumonia, neonatal meningitis, brain abscess, endocarditis

A

Citrobacter

154
Q

Urease-producing cause of ulcers

155
Q

Urease-producing cause of UTIs

A

Proteus/Morganella

156
Q

How does urease aid Proteus/Morganella in producing UTIs?

A

Raises pH of urine, facilitating formation of stones, in which the bugs can hide and remain viable after Abx

157
Q

Swarming

A

Proteus (obscures frank pathogens in fecal samples)

158
Q

Proteus/Morganella cross-reacts with:

A

Rickettsia (Wiel-Felix test)

GI (10 decks)

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