1Q: Many Gram-negative rods are commonly referred to as what type of organisms?
A: Gut bugs
2Q: Which gut organisms are NOT normal flora of the GI tract?
A: Salmonella, Shigella, and Yersinia
3Q: Where are environmental Gram-negative rods commonly found?
A: Soil, water, and sewage (feces)
4Q: Are most Enterobacteriaceae aerobic or facultative anaerobes?WhatEMBXLD
A: Facultative anaerobes
5Q: Are Enterobacteriaceae typically glucose fermenters?
A: Yes — Glucose positive
6Q: What is the oxidase reaction of most Enterobacteriaceae?
A: Oxidase negative
7Q: What organism is an oxidase-positive Enterobacteriaceae exception?
A: Plesiomonas
8Q: What does nitrate positive mean for Enterobacteriaceae?
A: They reduce nitrate → nitrite
9Q: What does the O antigen represent?
A: Cell wall (somatic) antigen
10Q: Is the O antigen heat stable or heat labile?
A: Heat stable
11Q: What does the K antigen represent?
A: Capsular (envelope) antigen
12Q: Is the K antigen heat stable or heat labile?
A: Heat labile
13Q: What does the H antigen represent?
A: Flagellar antigen
14Q: Is the H antigen heat stable or heat labile?
A: Heat labile
15Q: What does the Vi antigen represent?
A: Capsular antigen
16Q: Which organism is associated with the Vi antigen?
A: Salmonella typhi
17Q: Is the Vi antigen heat stable or heat labile?
A: Heat labile
18Q: Where is Escherichia coli normally found?
A: In the human and animal intestinal tract
19Q: Is E. coli usually normal flora or a pathogen?
A: Most are normal flora of the gut, but some strains cause disease.
20Q: What type of GI illness can E. coli cause?
A: Diarrhea / gastroenteritis, including travelers’ diarrhea
21Q: Which E. coli strain is associated with hemorrhagic colitis and HUS?
A: E. coli O157:H7
22Q: What infection is E. coli the #1 cause of?
A: Urinary tract infections (UTIs)
23Q: Besides UTIs and diarrhea, what other infections can E. coli cause?
A: Appendicitis, neonatal meningitis, peritonitis, gall bladder infections, endocarditis, and food poisoning
24Q: Why can E. coli appear in many different clinical specimens?
A: It causes many opportunistic infections
25Q: What type of E. coli strain is O157:H7?
A: Enterohemorrhagic E. coli (EHEC)
26Q: What is the reservoir of E. coli O157:H7?
A: Intestinal tract of cattle
27Q: How is E. coli O157:H7 transmitted to humans?
A: Fecal-oral transmission
28Q: Name common sources of infection for E. coli O157:H7.
A: Undercooked beef, contaminated vegetables (spinach), unpasteurized milk, contaminated water, petting zoos
29Q: What toxin is produced by E. coli O157:H7?
A: Shiga-like toxin (STEC)
30Q: What intestinal disease is caused by the Shiga-like toxin of O157:H7?
A: Hemorrhagic colitis
31Q: What serious complication can occur with E. coli O157:H7 infection?
A: Hemolytic Uremic Syndrome (HUS)
32Q: What happens in Hemolytic Uremic Syndrome (HUS)?
A: Toxin damages kidneys → kidney failure, anemia, low platelets
33Q: Which groups are most at risk for severe O157:H7 infection?
A: Children and the elderly
34Q: What is the typical incubation period for E. coli O157:H7?
A: 3–4 days (range 1–10 days)
35Q: What does STEC stand for?
A: Shiga toxin-producing Escherichia coli
36Q: Why should antibiotics be used cautiously with STEC infections?
A: Antibiotics may increase the risk of developing HUS and benefit is not clearly shown.
37Q: What must be done before administering antibiotics for suspected STEC infection?
A: Rule out STEC prior to antibiotic administration
38Q: What toxins are produced by STEC?
A: Shiga toxin 1 and Shiga toxin 2 (may carry both)
39Q: Which Shiga toxin is generally more virulent?
A: Shiga toxin 2
40Q: What STEC types should be included in diagnostic testing?
A: STEC O157 and non-O157 STEC
41Q: To whom must STEC infections be reported?
A: Los Angeles County Department of Public Health
42Q: How quickly must labs report Shiga toxin-producing E. coli (including O157)?
A: Within 1 working day
43Q: What does ETEC stand for? & How does ETEC cause disease?
A: Enterotoxigenic E. coli;
Enterotoxins mediate secretion of water and electrolytes into the bowel lumen, causing profuse watery stools.
44Q: What illness is commonly associated with ETEC?
A: Traveler’s diarrhea from contaminated food or water
45Q: What does EIEC stand for? How does EIEC cause disease? What disease is caused by EIEC?
A: Enteroinvasive;
The organism invades the large intestinal lining similar to Shigella.;
Dysentery, involving necrosis, ulceration, and inflammation of the bowel, associated with children in areas of poor sanitation.
46Q: What does EPEC stand for? How does EPEC cause disease? What illness is associated with EPEC?
A: Enteropathogenic;
The organism attaches to mucosal cells of the small bowel, causing small bowel surface changes (loss of microvilli);
A: Diarrhea (sometimes chronic) in infants in developing or low-income nations
47Q: What does EAEC stand for?
What is known about the pathogenic mechanism and transmission of EAEC?What illness is associated with EAEC?
A: Enteroaggregative E. coli;
Unknown pathogenic mechanism and mode of transmission not well understood;
Watery diarrhea that can be prolonged
48Q: What disease is caused by Shigella?
A: Shigellosis (bacillary dysentery)
49Q: Where does Shigella proliferate and where does it cause damage?
A: Proliferates in the small intestine but damages the large intestine
50Q: What type of intestinal inflammation does Shigella cause?
A: Acute inflammatory colitis
51Q: What are common symptoms of Shigellosis?
A: Cramps, tenesmus, bloody/mucoid stools or diarrhea, and fever
52Q: Which groups experience the most severe Shigella infections?
A: Children and the elderly
53Q: Is Shigella considered normal flora?
A: No
54Q: How is Shigella transmitted?
A: Human feces → human oral transmission (fecal-oral)
55Q: How infectious is Shigella?
A: Highly pathogenic — fewer than 50 bacteria can cause disease
56Q: Why can Shigella survive stomach acid relatively well?
A: The bacteria are not strongly affected by stomach acid
57Q: What is the incubation period for Shigella infection?
A: 1–7 days
58Q: Which antigen is used to serotype Shigella?
A: O antigen (because it lacks H antigen due to being non-motile)
59Q: Which species causes the most severe dysentery?
A: Shigella dysenteriae
60Q: What toxin is produced by Shigella dysenteriae?
A: Shiga toxin
61Q: What severe outcomes can occur with Shigella dysenteriae infection?
A: Bloodstream invasion and mortality up to 20%
62Q: How does Shigella infect intestinal cells?
A: It enters intestinal epithelial cells, multiplies inside them, spreads to neighboring epithelial cells, forms abscesses as cells are destroyed, and blood/mucus enter stool.
63Q: How are Shigella serogroups determined in the laboratory?
A: Bacterial agglutination
64Q: What should be done if a Shigella isolate is untypeable?
A: Boil the suspension of the organism and retest to inactivate the capsule that may mask the O antigen.
65Q: Which organism belongs to Serogroup A?
A: Shigella dysenteriae
66Q: What illnesses are associated with Shigella dysenteriae (Serogroup A)?
A: Enterotoxin attacking the large intestines and a neurotoxin that may cause paralysis
67Q: What are the mannitol and ONPG results for Shigella dysenteriae?
A: Mannitol – , ONPG –
68Q: Which organism belongs to Serogroup B?
A: Shigella flexneri
69Q: What illness is associated with Shigella flexneri?
A: Mild diarrhea; common in the U.S.; post-infectious arthritis in HLA-B27 positive patients
70Q: What are the mannitol and ONPG results for Shigella flexneri?
A: Mannitol + , ONPG –
71Q: Which organism belongs to Serogroup C?
A: Shigella boydii
72Q: What illness is associated with Shigella boydii?
A: Mild diarrhea
73Q: What are the mannitol and ONPG results for Shigella boydii?
A: Mannitol + , ONPG –
74Q: Which organism belongs to Serogroup D?
A: Shigella sonnei
75Q: What illness is associated with Shigella sonnei?
A: Mild diarrhea, sometimes watery; most common cause of shigellosis in the U.S.
76Q: What are the mannitol and ONPG results for Shigella sonnei?
A: Mannitol + , ONPG +
77Q: How many species of Salmonella are there?
A: Two species: Salmonella enterica and Salmonella bongori
78Q: Approximately how many Salmonella serotypes exist?
A: More than 2,400 serotypes
79Q: What type of illness do most Salmonella serotypes cause?
A: Moderate to severe gastroenteritis
80Q: Which species is responsible for the majority of Salmonella illnesses?
A: Salmonella enterica
81Q: Name important serotypes of Salmonella enterica.
A: S. typhi, S. paratyphi, S. typhimurium, and S. enteritidis
82Q: What are common animal reservoirs of Salmonella?
A: Many animals including reptiles and chickens
83Q: Which Salmonella species is found only in humans?
A: Salmonella typhi
84Q: How is Salmonella typhi transmitted?
A: Human feces → human oral transmission (fecal-oral)
85Q: How is Salmonella most commonly transmitted overall?
A: Contaminated water and undercooked food (especially chicken)
86What is the incubation period for S. enterica?
12-36 hours
87What is the incubation period for S. typhi?
2 weeks
88What are the sympotoms for S. enterica?
– moderate fever
– nausea
– abdominal pain
– cramps
– diarrhea
89What are the sympotoms for S. typhi?
– high fever
– headache
– diarrhea
90What is the mortality rate of S.enterica?
– general population: low
– very young/old: higher
91What is the mortality rate of S.enterica?
– today: 1-2%
– late 19th
-early 20th century: 10-30%
– today, undeveloped areas: 10-30%
92What is the source of S. enterica? and how does it enter the human body?
– Poultry/poultry products (eggs)
• Multi-drug resistance linked to
antibiotic use in poultry
– Unpasteurized milk/milk products
• Bacterium enters intestinal epithelial
cell -> multiply w/in vesicle inside cell
– death, if occurs, usually due to septicemia
93What is the source of S. typhi and how does it enter the human body?
human
• Bacterium multiply in phagocytic cells -> can become disseminated throughout the body
– can be isolated in blood, urine, feces
– multiple organ failure can occur if disseminated
– death due to: perforation of the intestine-> septicemia/peritonitis
• INFECTED CAN BECOME CARRIERS
– bacterium remain in gallbladder
– “Typhoid Mary”
• presumed to have infected almost 50,
3 deaths (she was a cook)
94MAC
TYPE:
WHAT GROWS:
KEY INGREDIENTS:
SHIGELLA =
SALMONELLA =
TYPE: Selective Differential
WHAT GROWS: GNR
KEY INGREDIENTS: lactose, crystal violet & bile salts inhibit G+; neutral red as indicator
SHIGELLA = colorless
SALMONELLA = colorless w/ black centers
Coliforms (lact +): pink
95EMB
TYPE:
WHAT GROWS:
KEY INGREDIENTS:
SHIGELLA =
SALMONELLA =
TYPE: Selective Differential
WHAT GROWS: GNR
KEY INGREDIENTS: lactose, sucrose. Eosin and Methylene blue as indicators
SHIGELLA = clear
SALMONELLA = clear
Coliforms: blue black
96HE
TYPE:
WHAT GROWS:
KEY INGREDIENTS:
SHIGELLA =
SALMONELLA =
TYPE: Selective differential
WHAT GROWS: GNR
KEY INGREDIENTS: lactose, sucrose, salicin, ferric amm. citrate, bile salts. Bromthymol blue/acid fusion (ind)
SHIGELLA = green
SALMONELLA = green/ black (lact - , H2S+)
Coliforms (lact +): yellow/salmon, + / - black centers
97SS
TYPE:
WHAT GROWS:
KEY INGREDIENTS:
SHIGELLA =
SALMONELLA =
TYPE: Selective differential
WHAT GROWS: Shigella Salmonella only
KEY INGREDIENTS: lactose, ferric/sodium citrate, neutral red (ind), brilliant green / bile salts inhibits other enterics
SHIGELLA = colorless
SALMONELLA = colorless / black
98XLD
TYPE:
WHAT GROWS:
KEY INGREDIENTS:
SHIGELLA =
SALMONELLA =
TYPE: Selective Differential
WHAT GROWS: GNR
KEY INGREDIENTS: lysine, xylose, lactose, sucrose, ferrice amm. citrate, Na desoxcholate inhibits G+, phenol red (ind)
SHIGELLA = red
SALMONELLA = red/ black centers
Coliforms: yellow/ orange
99Selenite
TYPE:
WHAT GROWS:
KEY INGREDIENTS:
SHIGELLA =
SALMONELLA =
TYPE: Selective enrichment
WHAT GROWS: Salmonella
KEY INGREDIENTS: Sodium selenite toxic for G+ and most Enterobacteriaceae
Isolate Salmonella
100Q: What is the most common species of Edwardsiella?
A: Edwardsiella tarda
101Q: Are human infections with Edwardsiella common?
A: No, they are uncommon
102Q: What are common sources of Edwardsiella?
A: Environment, snakes, and turtles
103Q: What types of infections can Edwardsiella cause?
A: Diarrhea, wound infections, and septicemia
104Q: Which organism does Edwardsiella resemble biochemically?
A: Salmonella
105Q: What are the shared biochemical characteristics of Edwardsiella and Salmonella?
A: H2S positive and ONPG negative (lactose negative)
106Q: How can Edwardsiella tarda be differentiated from Salmonella?
A: Indole positive and citrate negative
107Q: What types of infections are associated with Klebsiella?
A: UTIs, pneumonia, septicemia, and nosocomial infections
108Q: What type of sputum is characteristic of Klebsiella pneumonia?
A: “Currant jelly” sputum (bloody sputum)
109Q: Which groups are at higher risk for Klebsiella infections?
A: Diabetics and alcoholics
110Q: What is the most commonly isolated Klebsiella species?
A: Klebsiella pneumoniae
111Q: What colony appearance is typical for Klebsiella pneumoniae?
A: Highly mucoid colonies due to capsule
112Q: Is Klebsiella pneumoniae motile?
A: No, it is non-motile
113Q: What is the indole result for Klebsiella pneumoniae?
A: Indole negative
114Q: What is the indole result for Klebsiella oxytoca?
A: Indole positive
115Q: What disease is caused by Klebsiella (Calymmatobacterium) granulomatis?
A: Granuloma inguinale (STD)
116Q: What is unique about Klebsiella granulomatis regarding laboratory testing?
A: It does not Gram stain or grow on lab media
117Q: What may be seen in Wright or Giemsa-stained specimens of Klebsiella granulomatis infections?
A: Donovan bodies (intracellular pleomorphic bipolar staining bacteria)
118Q: What organism is now called Klebsiella aerogenes?
A: Formerly Enterobacter aerogenes
119Q: What antibiotic resistance is intrinsic to Klebsiella?
A: Intrinsic resistance to ampicillin (Amp = R)
120Q: How many species of Enterobacter are there?
A: 12 species
121Q: What are common sources of Enterobacter?
A: Human/animal gut, soil, water, and dairy products
122Q: What types of infections can Enterobacter cause?
A: Respiratory tract infections, wound infections, and bloodstream infections
123Q: What is the most common Enterobacter isolate?
A: Enterobacter cloacae
124Q: What organism was formerly Enterobacter sakazakii?
A: Cronobacter sakazakii
125Q: What type of food poisoning is associated with Cronobacter sakazakii?
A: Infant formula
126Q: What diseases can Cronobacter sakazakii cause in infants?
A: Meningitis and enteritis
127Q: What is the mortality rate for infants infected with Cronobacter sakazakii?
A: 20–50%
128Q: What other infections can Cronobacter sakazakii cause?
A: Wound infections and UTIs in all ages
129Q: What characteristic helps identify Cronobacter sakazakii in the lab?
A: Yellow pigment
130Q: Which Enterobacter species is lactose negative?
A: Enterobacter taylorae
131Q: What type of pathogen is Serratia?
A: Opportunistic pathogen
132Q: Which patients are commonly affected by Serratia infections?
A: Chemotherapy patients, immunosuppressed patients, and neonates (NICU outbreaks)
133Q: What is the most common Serratia species isolated?
A: Serratia marcescens
134Q: What pigment can some Serratia marcescens strains produce?
A: Pink or red pigment that deepens when held at room temperature
135Q: What is the lactose fermentation characteristic of Serratia?
A: Delayed lactose fermenter but ONPG positive
136Q: What infections are associated with Proteus?
A: UTIs, pneumonia, and septicemia
137Q: How many Proteus species are there?
A: Four species
138Q: Which Proteus species are most commonly isolated?
A: Proteus vulgaris and Proteus mirabilis
139Q: What are key biochemical characteristics of Proteus?
A: H₂S positive, lactose negative, ONPG negative
140Q: What unique growth characteristic is seen with Proteus?
A: Swarming motility
141Q: How can Proteus vulgaris and Proteus mirabilis be differentiated?
A: P. vulgaris indole positive, P. mirabilis indole negative
142Q: What additional enzyme tests are positive in Proteus?
A: Urease positive and tryptophan deaminase (TDA/PDA) positive
143Q: What odor is characteristic of Proteus colonies?
A: Musky smell
144Q: What infections are associated with Providencia?
A: UTIs, pneumonia, and septicemia
145Q: How many Providencia species exist?
A: Five species
146Q: How many Providencia species are found in humans?
A: Four
147Q: What are the key biochemical characteristics of Providencia?
A: PDA+, TDA+, indole+, citrate+, and VP−
148Q: Which Providencia species is most commonly isolated?
A: Providencia rettgeri
149Q: Name other Providencia species mentioned.
A: Providencia stuartii and Providencia alcalifaciens