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Lecture 1 2


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Every member of the family Enterobacteriaceae is:
-Gram neg bacillus
-Oxidase negative
-Ferments glucose w or w/out gas
-Reduces nitrate to nitrite
-If it's motile, it's peritrichous
-Facultative anaerobe
-Has endotoxin
enterobacteriaceae are normal flora in
the intestinal tract; they help us to digest our food
What is endotoxin composed of?
what is the #1 cause of gram negative shock/sepsis
escherichia coli
symptoms of gnshock
high fever, shaking chills, lowered blood pressure, peripheral circulatory failure, confusion, rapid death without treatment
what antibiotics would we not even test enterobacteriaceae for, and why?

Enterobacter. always restist these! They're really for gram positives.
Nonpathogenic enterobacs group 1:ABC
kleb, ecoli, serratia, citrobacter
providencia, enterobacter, morganella, proteus
If the non-pathogenic bacteria DO cause an infection, what five could it be one of?
UTI: most common it would be
Pneumonia: mostly from klebsiella
Wound Infections: from self/others
Sepsis: spread from 1' site to blood
Neonatal Meningitis: from e.coli in the birth canal
the most effective group of antibiotics for the enterobacteriaceae are:
piperacillin, ampicillin, nitrofurantoin, gentamicin/tobramycin, carbenicillin
5 genuses of enteric pathogens:
-Edwardsiella tarda
-Yersinia enterocolitica
-Escherichia coli
how many species of shigella
what are they
A: dysenteriae
B: flexneri
C: boydii
D: sonnei
most encountered species of shigella:
least encountered shigella


flexneri, boydii
Shigellosis is aka
bacillary dysentery
difference between diahrrea and dysentery:
water vs diahrrea with blood and mucous
-mechanism of disease
-incubation time before symptoms
Anal to oral; through bad hygiene/food.

Necrosis; bugs invade cells of colon.

3 days (36-72 hrs)

Staph only takes 2-6!
How is shigellosis treated?
It's selflimiting after 3-7 days, otherwise use trimethoprim sulfamethoxazole (SXT) if necessary
Most common symptom of Edwardsiella tarda; in whom?
Diahhrea in fishtank cleaners
what are the natural resorvoirs of edwardsiella tarda?
fish and reptiles
what is the most frequently encountered pathogen?
2 diseases of salmonella

Typhoid fever
what two bugs cause enterocolitis?
Salmonella enteritidis (most often)
Salmonella typhimurium (2nd often)
what is antoher name for enterocolitis?
incubation time for salmonellosis
8-24 hrs
Compare the disease mechanisms of Salmonella and Shigella
Shigella causes necrosis of colon cells
Salmonella doesn't; it does invade them though.
symptoms of salmonellosis
-Severe abdominal pain
no dysentary.
what organism causes typhoid fever?

how is it transmitted?
Salmonella typhi

Bad hygiene, contaminated food/h2o from a carrier
symptoms of typhoid fever
febrile disease: fever, headache, lethargy, cough, splenomegaly, hepatomegaly, rash, slight diarrhea.
how is typhoid fever treated
sulfamethoxazole trimethoprim SXT
What does Yersinia enterocolitica cause
what 3 organisms (not one genus) cause enterocolitis?
Salmonella typhimurium,
Salmonella enterididis,
Yersinia enterocolitica
How is Y. enterocolitica carried and transmitted?
Carried in Intest. tracts of wild/domestic animals.

transmitted by ingestion of contaminated food/water
Symptoms of enterocolitis from y. enterocolitica:
abdominal pain and diarrhea
Growth requirements of Y. enterocolitica
-does not grow well on enteric media;

-requires CIN media
contains Cefsulodin, irgasan, and novobiocin.
two types of E.coli variations based on the diseases they cause
Enteropathogenic - causes dysentery
Uncommon in U.S.

Enterotoxigenic - causes Mexican diarrh.
More common
What is the most typical e. coli strain we see as cause of disease?
E. coli 0157:H7

grows on SMAC - sorbital MAC agar;

Causes Hemolytic Uremic syndrome
What organism caused bubonic plague
yersinia pestis
What organism causes mesenteric lymphadenopathy?

Symptoms like?

common or rare
Yersinia pseudotuberculosis; symptoms are similar to appendicitis.
Pathogenic characteristics of Y. pestis
Zoonotic disease transmitted by rodent bites;
Oxidase neg (where Pasteurella is +)
Most common form is BUBONIC because of VERY LARGE inguinal or axillar lymphadenopathy.
Uncontagious as bubonic, but pneumonic IS contagious
factor that makes S. typhi especially pathogenic
can be transmitted from carriers - the organism is lodged in the gallbladder but it's asymptomatic
another name for Hemorrhagic E. coli:
how is hemorrhagic e. coli transmitted?

what is the general resorvoir
-undercooked beef
-apple cider
-petting farms

Resorvoir: Cows
Symptoms of hemorrhagic e. coli infection:
severe cramps
-severe dysentery
very bloody
culture media requirements of E.coli 0157:h7:
SMAC - sorbital MAC --> allows differentiation of Hemorrhagic ecoli from others.

CT-SMAC: cefixine/tellurite + SMAC -> inhibits growth of other ecoli bugs
What is the difference btwn SMAC and MAC?
SMAC has sorbitol;
pH indic: phenol red

normal e.coli ferment sorbitol and turn pink; hemorrhagic does not, so remains clear.
what population is Hemolytic Uremic syndrome usually seen in?

what is the mechanism of the disease?
elderly/young chidren

causes blood clots in kidneys, RBC lysis, renal failure.
Why is hemolytic uremic syndrome (HUS) difficult to treat?
Treating with antibiotics inhibits normal flora and enables the pathogenic 0157-H7 to grow even better!
how are enteric pathogens differentiated?
1. screening specimens for enteric bugs
2. biochemical id
3. serological typing
3 antigen types on enterobacteria:
O -> Somatic

H -> Flagella

K -> envelope (capsular)
process of Otyping for salmonella:
1. Apply PolyO antibody (against all 50 types of O)
If no agglutination: either not salmonella, or the H/K ag are masking O
2. Boil to destroy H/K antigens (heat labile)
3. Retest with PolyO; if agglutination:
4. Test with individual anti-sera ->most common is Anti-D, Anti-A,C
5. Subtype -> then do H serotype
what is PFGE essentially?
pulsed field gel electrophoresis;
fingerprint-typing to match enteric bacterial strains that are same in various patients.
What bacteria are not serotyped?
what do we know from positive fermentors on enteric agar?
fermentation indicates normal flora
nonfermentors are POSSIBLE pathogens

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