2. Chapter 16 - Enterics
Family Enterobacteriaceae often
referred to as “enterics”
Four major features:
All
ferment glucose (dextrose)
All reduce nitrates to nitrites
All are oxidase negative
All except Klebsiella, Shigella and
Yersinia are motile
3. Microscopic and Colony
Morphology
Gram negative bacilli or coccobacilli
Non-spore forming
Colony morphology on BAP or CA of
little value, as they look the same,
except for Klebsiella
Selective and differential media are
used for initial colony evaluation
(ex. MacConkey, HE, XLD agars)
4. Classification of Enterics
Due to the very large number of
organisms in the Family
Enterobacteriaceae (see Table 1611), species are grouped into Tribes,
which have similar characteristics
(Table 16-1, page 466)
Within each Tribe, species are
further subgrouped under genera
5. Virulence and Antigenic
Factors of Enterics
Ability to colonize, adhere, produce
various toxins and invade tissues
Some possess plasmids that may mediate
resistance to antibiotics
Many enterics possess antigens that can
be used to identify groups
O
antigen – somatic, heat-stable antigen
located in the cell wall
H antigen – flagellar, heat labile antigen
K antigen – capsular, heat-labile antigen
6. Clinical Significance of
Enterics
Enterics are ubiquitous in nature
Except for few, most are present in
the intestinal tract of animals and
humans as commensal flora;
therefore, they are sometimes call
“fecal coliforms”
Some live in water, soil and sewage
7. Clinical Significance of
Enterics (cont’d)
Based on clinical infections
produced, enterics are divided into
two categories:
Opportunistic
pathogens – normally
part of the usual intestinal flora
that may produce infection outside
the intestine
Primary intestinal pathogens –
Salmonella, Shigella, and Yersinia sp.
10. Escherichia coli (cont’d)
Ferments
glucose, lactose,
trehalose, & xylose
Positive indole and methyl red tests
Does NOT produce H2S or
phenylalanine deaminase
Simmons citrate negative
Usually motile
Voges-Proskauer test negative
11. Escherichia coli (cont’d)
Infections
Wide
range including meningitis,
gastrointestinal, urinary tract,
wound, and bacteremia
Gastrointestinal Infections
• Enteropathogenic (EPEC) – primarily in
infants and children; outbreaks in
hospital nurseries and day care
centers; stool has mucous but not
blood; identified by serotyping
12. Escherichia coli (cont’d)
• Enterotoxigenic (ETEC) – “traveler’s
diarrhea”; watery diarrhea without
blood; self-limiting; usually not
identified, other than patient history
and lactose-positive organisms cultured
on differential media
• Enteroinvasive (EIEC) – produce
dysentery with bowel penetration,
invasion and destruction of intestinal
mucosa; watery diarrhea with blood; do
NOT ferment lactose; identified via
DNA probes
13. Escherichia coli (cont’d)
• Enterohemorrhagic (EHEC serotype
0157:H7) – associated with
hemorrhagic diarrhea and hemolyticuremic syndrome (HUS), which includes
low platelet count, hemolytic anemia,
and kidney failure; potentially fatal,
especially in young children;
undercooked hamburger, unpasteurized
milk and apple cider have spread the
infection; does NOT ferment sucrose;
identified by serotyping
14. Escherichia coli (cont’d)
• Enteroaggregative (EaggEC) – cause
diarrhea by adhering to the mucosal
surface of the intestine; watery
diarrhea; symptoms may persist for
over two weeks
Urinary
Tract Infections
• E. coli is most common cause of UTI
and kidney infection in humans
• Usually originate in the large instestine
• Able to adhere to epithelial cells in the
urinary tract
15. Escherichia coli (cont’d)
Septicemia
& Meningitis
• E. coli is one of the most common causes of
septicemia and meningitis among neonates;
acquired in the birth canal before or during
delivery
• E. coli also causes bacteremia in adults,
primarily from a genitourinary tract infection
or a gastrointestinal source
Escherichia hermannii – yellow pigmented;
isolated from CSF, wounds and blood
Escherichia vulneris - wounds
16. Klebsiella, Enterobacter,
Serratia & Hafnia sp.
Usually found in intestinal tract
Wide variety of infections, primarily
pneumonia, wound, and UTI
General characteristics:
Some
species are non-motile
Simmons citrate positive
H2S negative
Phenylalanine deaminase negative
Some weakly urease positive
MR negative; VP positive
17. Klebsiella species
Usually found in GI tract
Four major species
K. pneumoniae is mostly commonly isolated
species
Possesses
a polysaccharide capsule, which
protects against phagocytosis and
antibiotics AND makes the colonies moist
and mucoid
Has a distinctive “yeasty” odor
Frequent cause of nosocomial pneumonia
18. Klebsiella species (cont’d)
Significant
biochemical reactions
• Lactose positive
• Most are urease positive
• Non-motile
19. Enterobacter species
Comprised of 12 species; E. cloacae
and E. aerogenes are most common
Isolated from wounds, urine, blood
and CSF
Major characteristics
Colonies resemble Klebsiella
Motile
MR
negative; VP positive
21. Serratia species
Seven species, but S. marcescens is
the only one clinically important
Frequently found in nosocomial
infections of urinary or respiratory
tracts
Implicated in bacteremic outbreaks
in nurseries, cardiac surgery, and
burn units
Fairly resistant to antibiotics
22. Serratia species (cont’d)
Major characteristics
Ferments
lactose slowly
Produce characteristic pink pigment,
especially when cultures are left at
room temperature
S. marscens on
nutrient agar →
23. Hafnia species
Hafnia alvei is only species
Has been isolated from many
anatomical sites in humans and the
environment
Occasionally isolated from stools
Delayed citrate reaction is major
characteristic
24. Proteus, Morganella &
Providencia species
All are normal intestinal flora
Opportunistic pathogens
Deaminate phenylalanine
All are lactose negative
25. Proteus species
P. mirabilis and P. vulgaris are widely
recognized human pathogens
Isolated from urine, wounds, and ear and
bacteremic infections
Both produce swarming colonies on nonselective media and have a distinctive
“burned chocolate” odor
Both are strongly urease positive
Both are phenylalanine deaminase positive
27. Morganella species
Morganella morganii is only species
Documented cause of UTI
Isolated from other anatomical
sites
Urease positive
Phenylalanine deaminase positive
28. Providencia species
Providencia rettgeri is pathogen of
urinary tract and has caused
nosocomial outbreaks
Providenicia stuartii can cause
nosocomial outbreaks in burn units
and has been isolated from urine
Both are phenylalanine deaminase
positive
29. Citrobacter species
Citrobacter freundii associated
with nosocomial infections (UTI,
pneumonias, and intraabdominal
abscesses)
Ferments lactose and hydrolyzes
urea slowly
Resembles Salmonella sp.
30. Salmonella
Produce significant infections in
humans and certain animals
On differential selective agar,
produces clear, colorless, nonlactose fermenting colonies with
black centers (if media contains
indicator for hydrogen sulfide)
32. Salmonella (cont’d)
Lactose negative
Negative for indole, VP,
phenylalanine deaminase, and urease
Most produce H S
2
Do not grow in potassium cyanide
Large and complex group of
organisms; grouped by O, H, and Vi
(for virulence) antigens
33. Salmonella (cont’d)
Clinical Infections
Acute
gastroenteritis or food poisoning
• Source = handling pets, insufficiently cooked
eggs and chicken, and contaminated cooking
utensils
• Occurs 8 to 36 hours after ingestion
• Requires a high microbial load for infection
• Self-limiting in health individuals (antibiotics
and antidiarrheal agents may prolong
symptoms)
34. Salmonella (cont’d)
Typhoid
and Other Enteric Fevers
• Prolonged fever
• Bacteremia
• Involvement of the RE system,
particularly liver, spleen, intestines, and
mesentery
• Dissemination to multiple organs
• Occurs more often in tropical and
subtropical countries
35. Salmonella (cont’d)
Salmonella
Bacteremia
Carrier State
• Organisms shed in feces
• Gallbladder is the site of organisms
(removal of gallbladder may be the only
solution to carrier state)
36. Shigella species
Closely related to the Escherichia
All species cause bacillary
dysentery
S. dysenteriae (Group A)
S. flexneri (Group B)
S. boydii (Group C)
S. sonnei (Group D)
37. Shigella (cont’d)
Characteristics
Non-motile
Do
not produce gas from glucose
Do not hydrolyze urea
Do not produce H2S on TSI
Lysine
decarboxylase negative
ONPG positive (delayed lactose +)
Fragile organisms
Possess O and some have K antigens
38. Shigella (cont’d)
Clinical Infections
Cause
dysentery (bloody stools, mucous,
and numerous WBC)
S. sonnei is most common, followed by S.
flexneri (“gay bowel syndrome”)
Humans are only known reservoir
Oral-fecal transmission
Fewer than 200 bacilli are needed for
infection in health individuals
40. Yersinia species
Consists of 11 named species
Yersinia pestis
Causes
plague, which is a disease primarily
of rodents; transmitted by fleas
Two forms of plague, bubonic and
pneumonic
Gram-negative, short, plump bacillus,
exhibiting “safety-pin” or “bipolar”
staining
41. Yersinia species
Yersinia enterocolitica
Most common form of Yersinia
Found worldwide
Found in pigs, cats and dogs
Human also infected by ingestion of contaminated
food or water
Some infections result from eating contaminated
market meat and vacuum-packed beef
Is able to survive refrigerator temperatures (can
use “cold enrichment” to isolate)
Mainly causes acute gastroenteritis with fever
42. Yersinia species
Yersinia pseudotuberculosis
Pathogen
of rodents, particularly
guinea pigs
Septicemia with mesenteric
lymphadenitis, similar to
appendicitis
Motile at 18 to 22 degrees C
43. Laboratory Diagnosis of
Enterics
Collection and Handling
If
not processed quickly, should be
collected and transported in CaryBlair, Amies, or Stuart media
Isolation and Identification
Site
of origin must be considered
Enterics from sterile body sites are
highly significant
Routinely cultured from stool
44. Laboratory Diagnosis of
Enterics (cont’d)
Media for Isolation and
Identification of Enterics
Most
labs use BAP, CA and a
selective/differential medium such
as MacConkey
On MacConkey, lactose positive are
pink; lactose negative are clear and
colorless
45. Laboratory Diagnosis of
Enterics (cont’d)
For
stools, highly selective media,
such as Hektoen Enteric (HE), XLD,
or SS is used along with MacConkey
agar
Identification
Most
labs use a miniaturized or
automated commercial identification
system, rather than multiple tubes
inoculated manually
46. Laboratory Diagnosis of
Enterics (cont’d)
Identification (cont’d)
All
enterics are
• Oxidase negative
• Ferment glucose
• Reduce nitrates to nitrites
47. Laboratory Diagnosis of
Enterics (cont’d)
Common Biochemical Tests
Lactose
fermentation and utilization
of carbohydrates
Triple Sugar Iron (TSI)
ONPG
Glucose metabolism
• Methyl red
• Voges-Proskauer
48. Laboratory Diagnosis of
Enterics (cont’d)
Common Biochemical Tests (cont’d)
Miscellaneous
•
•
•
•
•
•
Reactions
Indole
Citrate utilization
Urease production
Motility
Phenylalanine deaminase
Decarboxylase tests
49. Screening Stools for
Pathogens
Because stools have numerous
microbial flora, efficient screening
methods must be used to recover
any pathogens
Enteric pathogens include
Salmonella, Shigella, Aeromonas,
Campylobacter, Yersinia, Vibrio, and
E. coli 0157:H7
50. Screening Stools for
Pathogens (cont’d)
Most labs screen for Salmonella,
Shigella, and Campylobacter; many
screen for E. coli 0157:H7
Fecal pathogens are generally
lactose-negative (although Proteus,
Providencia, Serratia, Citrobacter
and Pseudomonas are also lactosenegative)