1. ENTEROBACTERIACEAE

2. Characteristics of the Enterobacteriaceae
Gram-negative bacilli
Ferment glucose
Reduce nitrates to nitrites
Oxidase negative
Catalase positive (except Sh.disentry type 1)
All except Klebsiella, Shigella and Yersinia are motile by peritrichous flagella

3. Grow readily on
MacConkey (MAC) agar
Eosin methylene blue (EMB) agar
Grow readily at 35oC except Yersinia (25o-30oC)
Do not form spores
Natural Habitat:
Environment (soil, water, and plants)
Intestines of humans and animals

4. Enterobacteriaceae Opportunistic pathogens Escherichia coli
Meningitis
Opportunistic pathogens
Escherichia coli
Klebsiella pneumoniae
Enterobacter aerogenes
Serratia marcescens
Proteus spp.
Providencia spp.
Citrobacter spp.
Pneumonia
Sepsis
Diarrhea
UTI
Obligate pathogens
Salmonella spp.
Shigella spp.
Yersinia spp.
Some E. coli strains

5. Classification of Enterobacteriaceae: - Based on lactose fermentationLF
LLF
NLF

6. Classification of Enterobacteriaceae:
Very large number of organisms in Family Enterobacteriaceae, species are grouped into - TRIBES
Tribe 1 – Escherichieae
Tribe 2 – Klebsiellae
Tribe 3: Proteae
Tribe 4 : Yersiieae
Tribe 5 : Erwinieae
Within each Tribe, species are further subgrouped under genera

7. Major Genera of family Enterobacteriaceae:
Escherichia
Shigella
Salmonella
Yersinia
Klebsiella
Proteus

8. Antigenic Factors of Enterobactericeae:
Ability to colonize, adhere, produce various toxins and invade tissues
Some possess plasmids that may mediate resistance to antibiotics
Imp antigens used to identify the organisms:
O antigen – somatic, cell wall, heat-stable Ag
H antigen – flagellar, heat labile Ag
K antigen – capsular, heat-labile Ag

10. Clinical Significance of Enterics:
Ubiquitous in nature
Except for Salmonella, Shigella and Yersinia, most are present in the intestinal tract of animals and humans as commensal flora; “fecal coliforms”
Some live in water, soil and sewage

11. Clinical Significance of Enterics:
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.

12. Enterobacteriaceae: Modes of Infection
Contaminated food and water (Salmonella spp., Shigella spp., Yersinia enterocolitica, Escherichia coli O157:H7)
2. Endogenous infection (urinary tract infection, primary bacterial peritonitis, abdominal abscess)
3. Abnormal host colonization (nosocomial pneumonia)
Transfer between debilitated patients
4. Insect (flea) vector: unique for Yersinia pestis

13. Urinary tract infection: Escherichia coli, Klebsiella pneumoniae, Enterobacter spp., and Proteus mirabilis
Pneumonia: Klebsiella pneumoniae; Enterobacter spp.,
Wound Infection: Escherichia coli, Enterobacter spp., Klebsiella pneumoniae, and Proteus mirabilis
4. Bacteremia: Escherichia coli, Enterobacter spp., Klebsiella pneumoniae, and Proteus mirabilis

14. Enterobacteriaceae: Intestinal Infection
Escherichia coli
Shigella
Salmonella
Yersinia enterocolitica

15. Identification of Enterobacteriaceae: IMViC Test
Indole, Methyl Red, Voges-Prosakaur, Citrate (IMViC) Tests:
The IMViC series of reactions allows for the differentiation of the various members of family Enterobacteriaceae.

16. A) Indole –Positive, B) MR –Positive
C) VP- Positive, D) Citrate- Negative

17. Methyl Red-Voges Proskauer (MR-VP) Tests
Principle
Glucose
Acidic pathway Or
Neutral pathway
Acety methyl carbinol
(ACETOIN)
Mixed acids
 pH less than 4.4
Barrit’s A
Barrit;s B
Methyl Red
indicator
VP positive
Klebsiella
MR positive
E. coli
Red color
Pink color

18. MR/VP test Voges-Proskauer test Methyl Red test
Pink: Positive VP (Klebsiella)
Red: Positive MR (E. coli)
Yellow or orange: Negative MR (Klebsiella)
No pink: Negative VP (E. coli)

19. Result Example Result Reaction on TSI H2S Slant color Butt color
Non fermenter e.g. Pseudomonas
Alk/Alk/-
(No action on sugars)
Negative
Red
LNF
e.g. Shigella
A/Alk/-
(Glucose fermented without H2S)
Yellow
e.g. Salmonella & Proteus
A/Alk/+
(Glucose fermented with H2S)
Positive
black in butt LF
e.g. E. coli, Klebsiella, Enterobacter
A/A/-
(three sugars are fermented)

20. TSI Reactions of the Enterobacteriaceae
A/A + g = acid/acid plus gas (CO2)
A/A = acid/acid
A/A + g, H2S = acid/acid plus gas, H2S
Alk/A = alkaline/acid
Alk/A + g = alkaline/acid plus gas
Alk/A + g, H2S = alkaline/acid plus gas, H2S
Alk/A + g, H2S (w) = alkaline/acid plus gas, H2S (weak)

21. A/A + g
Escherichia coli
Klebsiella
A/A + gas, H2S
Citrobacter freundii
Proteus vulgaris
Non-lactose, sucrose fermenter

22. Alk/A Alk/A + g Alk/A + g, H2S Shigella Providencia
Salmonella serotype Paratyphi A
Alk/A + g, H2S
Salmonella
Proteus mirabilis
Edwardsiella tarda

23. Lactose fermenting colonies
Non lactose fermenting colonies

25. Escherichia coli Most significant species in the genus
Important potential pathogen in humans
Common commensal in the intestine
Pink (lactose positive) colony with surrounding pink area on MacConkey

26. Ferments glucose, lactose, trehalose, & xylose
Usually motile
Positive indole and methyl red tests
Does NOT produce H2S
Simmons citrate negative
Voges-Proskauer test negative

27. Pathogenesis and clinical diseases
Sepsis
In people with inadequate host defenses, e.g. the newborns. Usually originates from UT or GI infections. Some infections may be endogenous.
Meningitis
E. coli (particularly K1 strains) and
S. agalactiae are the leading causes of meningitis in infants.
Bacteremia

28. Urinary tract infection
E. coli is the most common cause of urinary tract infection.
Community- vs. hospital-acquired UT infection
Most infections originate from colon; the bacteria contaminate the urethra, ascend into the bladder, and may migrate into the kidney or prostate.
Symptoms: urinary frequency, dysuria, hematuria, and pyuria. Can result in bacteremia and sepsis.
Uropathogenic E. coli strains produce P (Pyelonephritis-associated) pili, which is associated with renal colonization and may induce protective immunity, and hemolysin HlyA.

29. Infections caused by E.coli:
Meningitis, gastrointestinal, urinary tract, wound, and bacteremia
Gastrointestinal Infections:
- diarrhoegenic E. coli
Enteropathogenic (EPEC)
Enterotoxigenic E. coli (ETEC)
Enteroinvasive E. coli (EIEC )
Enterohemorrhagic E. coli (EHEC)
Enteroaggregative E. coli (EAEC)

30. Enteropathogenic (EPEC)
Primarily in infants and children;
Outbreaks in hospital nurseries and day care centers
Stool has mucous but not blood
Identified by serotyping

31. Enteropathogenic E.coli
Destruction of surface microvilli
Fever
Diarrhea
Vomiting
Nausea
Non-bloody stools
Gut lumen 31

32. Enterotoxigenic E. coli
Diarrhea resembling cholera
Travelers diarrhea 32

33. Enterotoxigenic E. coli
Heat labile toxin
Like cholera toxin
Adenyl cyclase activated
Cyclic AMP
Secretion water/ions
Heat stable toxin
Guanylate cyclase activated
cyclic GMP
uptake water/ions 33

34. Enteroinvasive E. coli (EIEC )
Dysentery
- Resembles shigellosis

35. Enterohemorrhagic E. coli
Usually O157:H7
Transmission electron
micrograph
Flagella 35

36. Bloody, copious diarrhea Few leukocytes Afebrile
O157:H7 transmitted- through meat products or sewage-contaminated vegetables
Hemorrhagic diarrhea
Bloody, copious diarrhea
Few leukocytes
Afebrile
Hemolytic-uremic syndrome (HUS)
Hemolytic anemia
Thrombocytopenia (low platelets)
Kidney failure 36

37. Vero toxin- “shiga-like”
Enterohemorrhagic E. coli
Vero toxin- “shiga-like”
Hemolysins
Enteroaggregative (EaggEC)
Cause diarrhea by adhering to the mucosal surface of the intestine; watery diarrhea; symptoms may persist for over two weeks 37

38. Urinary Tract Infections
E. coli is most common cause of UTI and pyelo-nephritis in humans
Usually originate in the large intestine
Able to adhere to epithelial cells in the urinary tract

39. Septicemia & Meningitis
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, secondary to genitourinary tract infection or a gastrointestinal source

40. Klebsiella, Enterobacter
Usually found in intestinal tract
Wide variety of infections, primarily pneumonia, wound, and UTI
General characteristics:
Non-motile
Simmons citrate positive
H2S negative, Weakly urease positive
MR negative; VP positive

41. Usually found in Gastro-intestinal tract
K. pneumoniae is most commonly isolated species
Possesses a polysaccharide capsule - which protects against phagocytosis and antibiotics
Makes the colonies moist and mucoid
Frequent cause of nosocomial pneumonia

42. Significant biochemical reactions
Lactose positive
Most are urease positive
Non-motile

43. Nosocomial pneumonia: Spread by health care personnel and equipment
Frequently caused by K. pneumoniae
Often seen in middle-aged males who abuse alcohol
Difficult to diagnose due to commensals in sputum

44. Proteus, Morganella & Providencia species
All are normal intestinal flora
Opportunistic pathogens
Deaminate phenylalanine
Non lactose fermenters

45. 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 and have a distinctive “burned chocolate” odor
Both are strongly urease positive
Both are phenylalanine deaminase positive

46. Exhibits characteristic “swarming”

47. Laboratory Diagnosis of Enterics
Specimen collection:
Specimens collected and transported in Cary-Blair, 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

48. Media for Isolation and Identification of Enterics:
Blood agar and a selective/differential medium such as MacConkey
On MacConkey, lactose positive are pink; lactose negative are clear and colorless

49. For stool, highly selective media, such as Hektoen Enteric (HE), XLD, or SS is used along with MacConkey agar
Identification: All enterics are
Oxidase negative
Ferment glucose
Reduce nitrates to nitrites