Gram Negative
Infections
Chijioke Onejeme
chijiokeonejeme@gmail.com
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OBJECTIVES
For each pathogen we study,
know its:
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Biological Characteristics
What is the pathogen?
Pathogenic Mechanisms
How does it cause disease?
Pathological Effects
What disease does it cause?
Laboratory Identification
How do we detect it?
Treatment
How do we treat these diseases?
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1. Distinguish between
lactose and nonlactose
fermenting enterics.
2. Identify the unique
biochemical properties of
enteric pathogen
3. Identify the usual route of
transmission for enteric
infections
4. To identify the
symptomatic phases of a
Salmonella infection
5. To identify the
symptomatic phases of a
Shigella infection
6. To explain the mechanism
of Shiga toxin
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OBJECTIVES
7. Identify the different E. coli
pathogenic strains
8. Compare and contrast
EHEC with EPEC
9. Distinguish Vibrio from
Enterobacterace
10. Identify the pathological
symptoms associated with V.
cholerae infections
11. Compare Cholerae toxin
mechanism to ETEC toxins
12 Compare and contrast
EIEC and EHEC pathogenic
mechanisms with Salmonella
and Shigella
13. To identify mechanisms
utilized by ETEC, EPEC, EAEC,
EIEC, and EHEC
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Enterobacteriaceae
General Characteristics
What is the pathogen?


Gram negative
bacilli
Biochemical
properties
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Oxidase negative
Catalase positive
Ferment glucose
Reduces nitrates to
nitrites
Faculative anerobes
Ubiquitous
 Comprised
of the
following bacterial
genera
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Salmonella
Shigella
Klebsiella
Escherichia
Proteus
Yersinia
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Enterobacteriaceae
General Characteristics
What is the pathogen?
Entry

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Contaminated
medical devices,
surgical site infections,
IV, urinary catheters
Colonization of the
colon, perineum,
urethra
Pneumonias (i.e.
respiratory spread)
Contaminated food
Large numbers
usually needed*
Evasion


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Capsule
 Anti phagocytic
Antigenic phase
variation
 Altered expression
of capsule/flagella
Plasmids
 Anti-microbial
resistance
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Salmonella sp.
General Characteristics
What is the pathogen?
 Gram
(–) bacilli
 Lactose (–)
 H2S (+)
Two species of
interest
 S. typhi
 S. enteritidis
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Salmonella sp.
General Characteristics
How does it cause disease?
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Endotoxin
Cellular invasion
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Salmonella sp.
Pathological Effects
What disease does it cause?
Diseases
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Enteritis
Septicemia
Enteric Fever
Carrier State
Symptoms
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Fever
Abdominal cramps,
Dysentery (Bloody
Diarrhea)
Gastroenteritis
 Adhesion to the microvilli
 Cellular Invasion -> Survival in vesicle
 Multiplication -> Escape
Septicemia (all above plus)
 Silent Septicemia -> Uptake by
macrophages
 Survival in macrophage vesicle ->
Systemic
Enteric Fever (all above plus)
 Multiplication in lymph node, spleen,
liver macrophages
 Bacteremia Release from
macrophages to blood
 High Fever (Endotoxin)
 Re-Invasion of Intestine via gall bladder
(Round 2)
Carrier State
 – Established gall bladder infection
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Salmonella sp.
Treatment
How do we treat these diseases?
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Self-limiting
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Usually resolves in 5-7
days
Hydration
Systemic Infection
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Ampicillin
SulfamethoxazoleTrimethoprim
(Bactrim©)
Ciprofloxacin
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Shigella sp.
General Characteristics
What is the pathogen?
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
Gram (–) bacilli
Lactose (–)
H2S (–)
Non-motile
Three species of interest
 S. dysenteriae
 S. sonnei
 S. flexneri
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Shigella sp.
Pathologenic Mechanisms
How does it cause disease?
Entry
 Fecal-oral
transmission
 Acid Resistant Small numbers
needed
Evasion
 Cellular invasion –
escape from
endocytic vesicle,
multiplication in
cytoplasm 
spread to adjacent
cells
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Shigella sp.
Pathogenic Mechanisms
How does it cause disease?
Evasion - Shiga Toxin
 AB toxin
 N-glycosidase:
cleaves an
adenine base from
the 28S of the 60S
rRNA subunit 
inhibits protein
synthesis
 Kills epithelial cells
 Associated
with
hemolytic uremia
 Produces local
ulcer formation
 Non-motile; rarely
systemic
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Shigella sp.
Pathological Effects
What disease does it cause?
Shigellosis
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Symptoms
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
Treatment
How do we treat these
diseases?
Fever, abdominal
cramps
Dysentery
Self-limiting

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
Usually resolves in 5-7
days
Hydration
Ampicillin, Bactrim,
Ciprofloxacin
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Escherichia coli
Biological Characteristics
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Gram (-) bacilli
Natural inhabitant of
the GI tract
Glucose (+), Lactose
(+) with gas
Indole (+)
Green metallic
sheen on EMB agar
Motile
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Escherichia coli
Pathological Effect
What disease does it cause?
 Extraintestinal
Infections
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Urinary Tract
Infection
Pulmonary
infection
Bacteremia
Meningitis
 Intestinal
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Infections
Diarrhea
Hemolytic-uremic
syndrome
Dysentery
Groups – based on how
they cause illness
 ETEC
- Enterotoxigenic
 EPEC - Enteropathogenic
 EHEC -Enterohemorrhagic
 EIEC - Enteroinvasive
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Enterotoxigenic E. coli
Pathological Effects
What disease does it cause?
Enterotoxigenic E. coli - Traveler’s Diarrhea
 Symptoms

Nausea, Vomiting, Watery Diarrhea
 Virulence

Factors
Colonization Factor Antigens CFA/1, CFA/II
 Facilitates

bacteria adhesion
Enterotoxins
 Heat
Labile
 Heat Stable
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Enterotoxigenic E. coli
Pathogenic Mechanisms
How does it cause disease?
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Heat labile
 Two subunits “AB Toxin”
 B portion binds to cell membranes
 A portion (active) is transported into
cells
 ADP ribosylation of G protein by A
subunit
 cAMP cellular levels increase ->
increased Cli- on excretion
 Results in increased water secretion
from cells
Heat stable
 Induces an increase in cellular cGMP
-> increased Cl- ion excretion
 Results in increased water secretion
fromcells
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General
AB
Toxin
Cholera
Toxin
Mechanism
Is Similar
To ETEC
Heat
Labile
Toxin
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Enteropathogenic E. coli
Pathogenic Mechanisms
How does it cause disease?
Pathology in small
intestine
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Attaching and
effacing lesions
Microbes bind to the
epithelial cells via BFP
(bundle-forming pili)
Loose, then tight
binding
Effacement lesion
Associated pedestal
formation
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Enteropathogenic E. coli
Pathological Effects
What disease does it cause?
 Disease


Pediatric Diarrhea
Symptoms
 Fever,
Nausea, Vomiting, Watery Diarrhea
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Enteroinvasive E. coli
Pathogenic Mechanisms
How does it cause disease?
 Invades
intestinal
epithelial cells
 Lyses the
phagosomal
vacuole
 Moves through the
cytoplasm
 Spreads to
adjacent cells
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Enterohemorrhagic E. coli
Pathogenic Mechanisms
How does it cause disease?
 Virulence

Factors
Vero Toxin / Shigalike toxin
 AB
Toxin - inhibits
protein synthesis
(Similar to Shiga
toxin)


Acid Resistant
Low infectious
dose
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Enterohemorrhagic E. coli
Pathological Effects
What disease does it cause?
Disease
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Hemorrhagic colitis
Dysentery
Hemolytic Uremic Syndrome (HUS)
 Acute
renal failure, hemolytic anemia
 Associated wih E. coli O157:H7
Symptoms
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
Diarrhea
Bloody Diarrhea
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Escherichia coli
Treatment
How do we treat these diseases?
GI infections
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Rehydration therapy
Usually do not use antibiotics (no added
benefit)
Do not use anti-diarrheal products such as
Immodium©
Urinary Tract Infections and Systemic Infections
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Sulfamethoxazole-Trimethoprim
Nitrofurantoin
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Vibrio cholerae
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Gram - curved rod
Not a member of the Enterobacteriaceae
Etiological agent of cholera
 Severe diarrhea, rice water stools (thin mucus flexs)
 Dehydration and shock --> death
 Treatment

Water and ion replacement
 Toxin
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
based, similar to the heat labile toxin of E. coli
1A5B Toxin
Cellular cAMP increase, while cellular Cl- ion and water
decrease
 Oral
Fecal Transmission
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Vibrio cholerae
Treatment
 Most
patients can be treated with oral
fluid/ electrolyte replacement
 IV
fluids used for severe cases
 Antibiotics


usually unnecessary, but…
Doxycycline
Azithromycin
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Neisseria gonorrhoeae
General Characteristics
What is the pathogen?
 Gram(-)
diplococci
 Aerobic
 Cytochrome
 Maltose
(-)
oxidase(+)
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Neisseria gonorrhea
Pathogenic Mechanisms
How does it cause disease?

Entry
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
Infects mucosal
surfaces
Ex. cervix, urethra,
rectum, oropharynx,
nasopharynx,
conjunctiva
 Evasion
POR
 Pathological
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Adherence
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Pilin – initial adhesion
Opa – firm adhesion
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Effects
LOS
Lipooligosaccharide
(endotoxin)
IgA Protease
Destroys soluble IgA
Beta-lactamase
Inactivates penicillins
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Neisseria gonorrhea
Pathological Effects
What disease doe it cause?
 Gonorrhea

Symptomatic or asymptomatic
 Transmission


Sexual contact
Newborns (via birth canal)
 May
co-exist with other STDs
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Neisseria gonorrhoeae
Pathological Effects
What disease does it cause?
Men
 Asymptomatic infection
 Acute urethritis
 Purulent exudate w/
dysuria, polyuria, HA,
fever
 Anterior to posterior urethral
infection
 Glands, ducts, and
vessicles may become
infected
 Chronic infection
 Prostate, seminal vesicles,
and epididymides may
become infected
Women
 Asymptomatic carriers
 Acute gonorrhea infection (lower
tract)
 Endocervix (traditional site of
infection)
 Acute symptoms
 Ab/pelvic pain, vaginal
discharge/dysuria
 Chronic Gonorrhea infection
 Tenderness in lower ab,
inflammatoion or urinary tract
 Pelvic Inflammatory Disease (PID)
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Neisseria gonorrhoeae
Pathological Effects
What disease does it cause?

Bacterial infection of the upper genital tract


Infection ascends from vagina and endocervix to the
upper genital areas (uterus, fallopian tubes, ovaries)
Symptoms


Fever, lower ab pain, increased risk of ectopic pregnancy
Sites of infection
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Endometrium (endometritis), fallopian tubes (salpingitis)
Extragenital infections

Local infections determined by site of contact
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Conjunctivitis
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Opthalmia neonatorum (newborn)
Pharyngitis or Proctitis

Either may be transmitted sexually
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Neisseria gonorrhoeae
Laboratory Diagnosis
 Smear
of urethral pus with gram (-)
diplococcus
 Carbohydrate utilization (glucose
fermenter)
 Direct Fluorescence Antibody Test
 ELISA
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Neisseria gonorrhoeae
Treatment

Cephalosporins (Ceftriaxone)



Preferred agent for most N. gonorrhoeae
infections
Fluoroquinolones (Ciprofloxacin, levofloxacin)
Resistance to antibiotics exists and is rapidly
emerging


PPNG – penicillinase producing neisseria
gonorrhoeae
Increasing FQ resistance limits use
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Neisseria meningitidis
General Characteristics
What is the pathogen?
 Gram(-)
diplococci
 Aerobic
 Maltose
(+)
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Neisseria meningitidis
Pathogenic Mechanisms
How does it cause disease?


Evasion



Invasion of epithelial
cell  followed by
invasion of blood
stream and systemic
spread
Anti-phagocytic
capsule
Facultative
intracellular parasite

Adherence
 Pilin – initial adhesion
 Opa – firm adhesion
Pathological Effects
 Lipooligosaccharide (LOS) 
endotoxin
 Sequestration of iron from
host
 IgA protease
 Destroys soluble IgA
 Beta-lactamase
 Inactivates beta-lactam
antibiotics
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Neisseria meningitidis
Pathological Effects
What disease does it cause?
 Meningococcal

meningitis
Symptoms – non-specific
 High
fever, severe HA, neck pain/stiffness
 n/v

Sequelae
 Deafness,
defects
mental retardation, behavior
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Neisseria meningitidis
Laboratory Identification
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Gram (-) diplococci
Cytochrome oxidase (+)
Ferments glucose and maltose
Grows on “chocolate agar” with CO2
production
Serological (antibody test) serotypes A, B, Y,
W-135 etc…
DNA probes
Examination of cloudy CSF, organism in the
cytoplasm on neutrophils, or increase WBCs
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Neisseria meningitidis
Treatment
 Empiric

3rd generation cephalosporins (ex. Ceftriaxone,
Cefotaxime)
 Targeted

Penicillin, Ampicillin, or Ceftriaxone
 Prophylaxis

Ciprofloxacin
 Immunization


Covers 4 serotypes of N. meningitidis
Does not protect against other serotypes
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Special thanks to Paula
Ingram Darasaw for compiling
this Powerpoint