9. Biochemical Reactions
3) I MVC ++--
• Indole positive
• MR positive
• VP negative
• Citrate negative MR
VP
Citrate test
negative positive
Indole test
10. Principle:
Glucose
Large amount of acids
OR Acetyl methyl carbinol
pH less than 4
MR indicator
Red colour
KOH
Brick red colour
MR +ve VP +ve
MR-VP Test
13. Principle:
Citrate test
(Simmon’s citrate media)
Citrate
(only carbon source )
If bacteria can use citrate → Growth →
Green (Negative)
Blue (Positive)
Due to alkaline by-products
of citrate metabolism
If it can not use citrate → no growth →
negative
positive
14. Principle:
Citrate test
(Koser’s citrate media)
Citrate
(only carbon source )
If bacteria can use citrate → Growth →
clear (Negative)
turbid (Positive)
If it can not use citrate → no growth →
15. Diseases caused by E. coli
1. UTI
2. Neonatal meningitis
E. coli K1
( also Strept. agalactiae & Listeria monocytogenes)
3. Pneumonia, sepsis, septicaemia &
endotoxic shock
4. Diarrhea
16. Diarrhogenic E. coli
1) Enterotoxigenic E. coli (ETEC)
2) Enterohaemorrhagic E. coli (EHEC)
Verotoxigenic E. coli or shiga toxin-producing E. coli
3) Enteropathogenic E. coli (EPEC)
4) Enteroinvasive E. coli (EIEC)
5) Enteroaggregative E. coli (EaggEC)
18. 1) Direct Detection:
• Gram stain (in specimens
from sites with no flora)
• Antigen detection in E. coli K1
meningitis by latex
agglutination of CSF
2) Culture:
• MacConkey & Blood agar
• Blood culture
19. 3) Identification
Colony morphology
• Rose pink (LF) on MacConkey’s
agar
Biochemical Reactions
• Fermentation of: glucose, lactose,
maltose, mannite and sucrose
( A & G )
• IMVC ++--
20. Regarding E. coli from fecal samples:
• Culture on sorbitol-MacConkey agar: Unlike other strains
of E. coli, EHEC does not ferment sorbitol
• Slide agglutination:
– polyvalent antisera for EPEC
– O157 and H7 antisera for EHEC
• Tissue culture:
– for toxin production (ETEC, EHEC)
– invasiveness (EIEC)
– adherence (EPEC, EaggEC)
• ELISA to test for toxin production (ETEC, EHEC)
• DNA probe or PCR to detect genes of toxin production
22. Case
A 35-year-old woman presents to the
emergency department with fever and
suprapubic pain. She reports that she had a
few days of urinary frequency and burning
micturation. Microscopic examination of the
urine sample reveals 10-15 white blood cells
per high power field and numerous bacteria.
She was diagnosed as a case of urinary tract
infection (UTI)
23. Urinary tract infection (UTI)
• UTI is the presence of micro-organisms in
urinary tract
• A bacterial count greater than 105 CFU /ml
→ significant bacteruria
• A pus cell count of ≥ 10 cells/ HPF → pyuria
24. What is the suitable specimen taken from
this patient ?
Urine
Urine collection and transport:
• Mid-stream urine
• Transported to the lab. within 2 hours of collection
25. What is the most common etiologic agent
of this infection?
Escherichia coli
26. What is the most suitable culture media
used to cultivate urine samples ?
MacConkey agar
If rose pink colonies → lactose fermenter
27. • Colony morphology → rose pink colonies (LF)
• Gram stain → gram –ve bacilli
• Oxidase test → - ve
• Biochemical reactions
Enterobacteriacae
What are the steps used for identification
of the isolated colonies?
29. Biochemical Reactions
3) I MVC ++--
• Indole positive
• MR positive
• VP negative
• Citrate negative MR
VP
Citrate test
negative positive
Indole test
30. What are the other causes of UTI ?
• Klebsiella
• Proteus
• Enterococcus faecalis
• Staphylococcus saprophyticus
• Staphylococcus aureus
• Mycobacterium tuberculosis
• Adenovirus
• Candida albicans
42. Case
An 85-year-old male patient develops a flu-like
illness. He complains of chills and fever and has
productive cough with thick bloody sputum.
A chest X-ray reveals a dense right lower lobe
infiltrate. His provisional clinical diagnosis is
bronchopneumonia. Laboratory investigations
reveals Klebsiella pneumoniae growth.
43. What is the suitable specimen taken from
this patient?
Sputum
What does a Gram stained smear from the
sputum reveal?
Gram negative capsulated bacilli
44. What is the suitable medium used to
cultivate this organism ?
MacConkey’s agar
Mucoid rose pink colonies (lactose fermenter)
45. What are the steps used for identification
of the isolated colonies?
• Colony morphology → mucoid rose pink colonies
• Gram stain → gram –ve bacilli
• Oxidase test → - ve
• Biochemical reactions
Enterobacteriacae
49. 1. General features of Enterobacteriaceae
include all of the following except:
a) Gram-negative bacilli
b) Strict anaerobes
c) Oxidase negative
d) Ferment D-glucose
e) Reduce nitrate to nitrite
50. 2. All of the following are true about E.coli
except:
a) Gram negative bacilli
b) Indole positive
c) A common cause of neonatal meningitis
(E. coli K1)
d) Lactose non fermenter
e) An indicator of fecal pollution of water
51. 3. Biochemical reactions of E.coli include
all of the following, except:
a) Fermentation of all sugars with acid and gas
production
b) Indole positive
c) MR positive
d) VP negative
e) Citrate positive
52. 4. All of the following are diseases caused
by E.coli except:
a) Diarrhea
b) Urinary tract infection
c) Urethral discharge
d) Meningitis
e) Pneumonia
53. 5. Klebsiella are characterized by all of the
following except:
a) Presence of a capsule
b) Indole negative
c) Highly sensitive to penicillins & cephalosporins
d) Mucoid colonies
e) Lactose fermentation
54. 6. Which of the following is true about
Klebsiella?
a) The capsule is the most important virulence
factor
b) It is citrate negative
c) It produces large amount of H2S
d) It produces pale colourless colonies on
MacConkey’s agar
e) It is an enteric pathogen
