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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
When should you suspect a parasitic etiology of diarrhea?
If it persists for >2 weeks
26
List 3 tests that indicate WBCs in stool
Methylene blue Lactoferrin Leukocyte esterase
27
List two infectious agents that mainly cause diarrhea in AIDS patients
CMV | M. avium
28
How is bacterial diarrhea usually diagnosed?
Culture
29
A patient presents with diarrhea that has persisted for 17 days. First step in management?
Examine stool for parasites | >2 weeks = parasitic
30
Noninflammatory or inflammatory diarrhea: antimotility drugs contraindicated
Inflammatory
31
Noninflammatory or inflammatory diarrhea: use antibiotics
Both - but not in inflammatory diarrhea caused by EHEC
32
Complication of EHEC?
HUS
33
Complications of campylobacter?
GBS, Reiter's syndrome
34
What is Reiter's syndrome?
Polyarthritis in large joints, conjunctivitis, urethritis
35
List 4 causes of Reiter's syndrome following enteric infection
Salmonella, Shigella, Yersinia, Campylobacter
36
Why can some strains of E. coli cause pathology while resident strains don't?
Virulent strains have acquired PAIs, plasmids, &/or lysogenic phages with additional genes
37
Appearance of E. coli on KIA slant
Yellow butt and slant (ferments lactose), cracks (produces H2)
38
Appearance of Shigella on KIA slant
Yellow butt with red slant (ferments glucose only), no gas
39
Appearance of Salmonella on KIA slant
Black butt (produces H2S), red slant (doesn't ferment lactose), cracks (produces H2)
40
Appearance of non-fermenting G- rods on KAI slant
Red butt and red slant, no gas | Think Pseudomonas
41
Watery diarrhea that becomes bloody
EHEC, Shigella Campylobacter jejuni C. diff
42
Cause of hemorrhagic colitis
EHEC (0157:H7)
43
Shiga-like toxin
EHEC
44
LEE
Locus of enterocyte effacement; encodes EHEC and EPEC virulence factors
45
List 4 gene products contained within LEE
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)
46
Symptoms of EHEC hemorrhagic colitis
Sudden onset of severe abdominal cramps with watery diarrhea that becomes bloody within 24 hours
47
EHEC would produce lactoferrin (+, -) stool
Negative (no WBCs in stool)
48
Would you expect fever in a patient with 0157:H7? ETEC?
No
49
#1 cause of acute renal failure in children
HUS following 0157:H7 infection
50
How will HUS present?
Acute renal failure, anemia, thrombocytopenia during the second week of an episode of bloody diarrhea (may also develop seizures, strokes)
51
HUS following EHEC usually affects:
Children < 5 and elderly
52
List some sources of EHEC
``` Ground beef Spinach Unpasteurized juice, milk Sprouts Water Salami Lettuce ```
53
List some factors that contribute to spread of EHEC
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
54
Describe Shiga-like toxin (Stx)
Cytopathic toxin that inhibits protein synthesis, resulting in cell death; encoded by lysogenic phage (Remember pathogenic E. coli strains have additional genes)
55
What is the main cause of diarrhea in EHEC?
LEE pathogenicity island
56
Why do antibiotics contribute to development of HUS?
They stress EHEC, causing replication of lysogenic phage that encodes Stx gene
57
List 4 diagnostic methods for EHEC
1. Sorbitol MacConkey (will be white) 2. RADT of Stx in stool 3. Nucleic acid detection of Stx genes 4. Serotyping of isolates
58
Traveler's diarrhea
ETEC
59
What type of diarrhea is produced by ETEC?
Profuse, watery diarrhea (similar to cholera)
60
Where would you expect ETEC toxin to work?
Small intestine (produces a watery diarrhea by preventing absorption, the majority of which occurs in the SI)
61
LT and ST
ETEC toxins (heat labile and heat stable toxins)
62
What is the mechanism of LT?
Activates cAMP --> AC --> Cl- efflux | identical to cholera toxin
63
What is the mechanism of ST?
Mimics guanylin --> binds GC --> activates cGMP --> activates PKA --> activates CFTR
64
Attachment of ETEC vs EHEC vs EIEC vs EPEC vs UPEC
``` ETEC - fimbriae EHEC - LEE-encoded intimin EIEC - adhesin EPEC - EAF + intimin UPEC - P-fimbriae ```
65
``` List the type of diarrhea: EHEC ETEC EIEC EPEC ```
EHEC - watery then bloody ETEC - profuse watery EIEC - dysentery EPEC - profuse watery
66
What is the reservoir of EIEC?
Humans
67
Where would you expect EIEC to act?
Colon | dysentery = inflammatory diarrhea = colon
68
Which E. coli infection produces fever?
EIEC
69
List 3 ways in which EIEC is unique among E. coli spp
Non-motile, doesn't ferment lactose, doesn't decarboxylate lysine
70
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?
EPEC | Mexico + no fever + blood = EPEC
71
List 2 sources of EPEC infection
Water, meat
72
Which E. coli strains are not associated with toxin production?
EPEC, EIEC
73
What are the two virulence factors of EPEC?
EAF (EPEC adherence factors) + LEE-encoded intimin
74
Which two E. coli strains cause an attachment-effacement lesion?
EPEC, EHEC
75
What causes the diarrhea seen with EPEC?
Invasion of host cells ("moderately invasive")
76
What is DAEC? Where is it found?
Diffusely adherent E. coli | Mexico and North Africa
77
Which E. coli species would cause fever?
EIEC
78
Which E. coli species replicates in intestinal cells?
EIEC (Think: it's invasive)
79
A leading cause of infantile diarrhea in developing countries
EPEC
80
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?
EAEC | Causes persistent diarrhea in young kids with no inflammation or fever
81
Hemolysin
EAEC, UPEC
82
What are the virulence factors of EAEC?
ST-like toxin and hemolysin
83
Which E. coli species is associated with a low infectious dose?
EHEC | Remember this contributes to its spread
84
90% of UTIs caused by
UPEC
85
Coagulase negative cause of UTI
Staph saprophyticus
86
What defines UTI in a female? Male?
Female - >10^5 bacteria per mL | Male - 10^3 bacteria per mL
87
What is our major defense against bladder infections?
Urine flow
88
Describe how UPEC is acquired
First colonizes the colon (present as a minor part of flora) --> feces --> urethra
89
List 4 virulence factors of UPEC
1. P-fimbriae 2. Hemolysin 3. K antigen/capsule 4. Siderophore
90
What is the purpose of the UPEC hemolysin?
Forms pores in cells so it can extract nutrients + is cytopathic
91
What does P-fimbriae bind to?
Galactose on RBCs and uroepithelial cells
92
How is UPEC able to avoid complement?
K antigen/capsule
93
What is associated with upper UTIs?
K antigen
94
What is K-1?
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
Which E. coli strain has an antiphagocytic capsule?
UPEC
96
Cause of neonatal bacterial meningitis
E. coli (K-1 antigen) | Citrobacter
97
E. coli causes ___% of gram negative septicemia. Other causes of gram negative septicemia include:
40% | Pseudomonas, Acinetobacter
98
Frank pathogens
Salmonella, Shigella, Proteus, Morganella
99
___ is a common cause of disseminated infection, particularly within ___
Salmonella | Bone
100
How does S. typhi differ clinically from other Salmonella serotypes?
Doesn't produce diarrhea &/or dysentery
101
``` Salmonella: Gram (+,-) Shape? Lac (+,-) KIA slant characteristics? ```
Gram - Rod Lac - Red slant + gas + black bottom (H2S)
102
Vi Ag
Capsule of S. typhi
103
Source of Salmonella enteritidis
Eggs, poultry, reptiles/turtles
104
Zoonosis
Salmonella enteritidis (food poisoning)
105
Describe the entry and replication of Salmonella
Enters small intestine through M cells, then extends into lamina propria, where it's taken up by macrophages, in which it replicates
106
A kid goes to a petting zoo and two days later develops N/V, abdominal pain, and diarrhea with loose, watery stools. Diagnosis?
Salmonella (think reptiles, turtles)
107
When does salmonella food poisoning present? Sx?
20-72 hours after infection | N/V initially, followed by abdominal pain and diarrhea ranging from few loose, watery stools to severe dysentery
108
List 3 places to which Salmonella likes to disseminate. What kind of patients are at risk for such dissemination?
Bone, heart (endocarditis), kidneys Sickle cell kids, patients with T cell deficiencies (AIDS), skeletal prostheses, atherosclerotic plaques, and the extremes of age
109
How is S. typhi contracted?
Food/water contaminated with human feces/urine
110
To where does S. typhi disseminate?
RES system, especially liver and spleen
111
Classic triad of S. typhi
Bradycardia + neutropenia + splenomegaly
112
Where does S. typhi hang out in carriers?
Gallbladder (cholecystectomy for cure)
113
Where is S. typhi endemic?
Africa, Asis, South America
114
Symptoms of typhoid fever
High fever, bradycardia, HA, mental confusion | Does NOT cause diarrhea!!
115
Skin finding in typhoid fever
Rose spots
116
Virulence factors of S. typhi
``` 2 type III secretion systems LPS Vi ag (capsule) ```
117
What is the function of the 2 type III secretion systems of S. typhi?
1. Injects proteins into M cells --> entry | 2. Injects proteins into macrophages --> survival and dissemination
118
What causes fever of S. typhi infection?
LPS
119
Is S. enteridis encapsulated?
No
120
2 ways to diagnose typhoid fever
1. Blood or feces culture | 2. Serotyping for Vi antigen
121
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?
Salmonella osteomyelitis secondary to sickle cell anemia
122
Complication of bowel perforation
S. typhi
123
4 strains of Shigella
Sonnei Flexneri Dysenteriae Boydii
124
What is the most common Shigellosis in US? 2nd?
``` 1st = sonnei (70%) 2nd = flexneri ```
125
Shigella in daycare centers
Sonnei
126
Gay men
Shigella flexneri
127
Epidemic in South and Central America
Shigella dysenteriae
128
Epidemic in India
Shigella boydii
129
Transmission of Shigella
Fecal-oral route
130
What is the only reservoir for Shigella
Humans
131
List all the bacteria that produce Stx
EHEC Shigella (note: EIEC does NOT produce Stx)
132
List all bacteria that invade lamina propria
EIEC Shigella Salmonella
133
Infectious dose of Shigella vs EIEC
Shigella - really low | EIEC - high
134
STD
Shigella flexneri (associated with gay male transmission)
135
Describe the pathogenesis of Shigella
Enters M cells, escapes phagocytic vesicles, extends into neighboring enterocyte, produces shiga toxin, and inhibits protein synthesis
136
Spherocytosis could be found in a patient as a complication of which enteric bugs?
EHEC | Shigella dysenteriae
137
How does Shigella present?
Watery diarrhea + abdominal (starts in small intestine) followed by dysentery + cramps + tenesmus + fever
138
``` Shigella: Gram (+,-) Shape Lac (+,-) Motile, non-motile KIA characteristics? ```
``` Gram - Rod Lac - Non-motile (but does extend into neighboring enterocytes, mimicking motility) Red slant, yellows butt, no gas, no H2S ```
139
What characteristic diagnostic finding indicates infection with Shigella?
Sheets of leukocytes present in feces | due to invasion of M cells with propulsion into epithelial cells which creates shallow ulcers
140
Which two enteric bugs inhibit eukaryotic protein synthesis?
Shigella, EHEC
141
Which two bugs produce a large amount of Stx?
EHEC, Shigella dysenteriae | Other Shigella spp produce less toxin
142
Invasion plasmid
EHEC, Shigella
143
Shiga-like toxin vs. Shiga toxin
Shiga-like toxin = EHEC; phage-encoded | Shiga toxin = Shigella; chromosome-encoded
144
If both EHEC and Shigella can cause HUS, why is it ok to treat Shigella but not EHEC with antibiotics?
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
Zoonotic infection
Salmonella food poisoning | Typhoid fever is NOT considered a zoonose
146
Mimics appendicitis
Yersinia, Campylobacter
147
Mesenteric lymphadenitits
Yersinia entercolitica
148
Main reservoir for Yersinia enterocolitica
Pigs (wild animals in general)
149
Complication of Yersinia enterocolitica
Reiter's syndrome (arthritis + conjunctivitis + urethritis)
150
Gram - Enterobacteriacae that are mainly opportunistic causes of UTIs
``` Klebsiella Citrobacter Enterobacter Proteus/Morganella Serratia marcescens ```
151
Currant-jelly pneumonia
Klebsiella
152
Brick-red colonies causing pneumonia in hospitalized patients
Seratia
153
Opportunistic UTI, pneumonia, neonatal meningitis, brain abscess, endocarditis
Citrobacter
154
Urease-producing cause of ulcers
H. pylori
155
Urease-producing cause of UTIs
Proteus/Morganella
156
How does urease aid Proteus/Morganella in producing UTIs?
Raises pH of urine, facilitating formation of stones, in which the bugs can hide and remain viable after Abx
157
Swarming
Proteus (obscures frank pathogens in fecal samples)
158
Proteus/Morganella cross-reacts with:
Rickettsia (Wiel-Felix test)

GI (10 decks)

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