Enteric Bacteria

1
Enteric Bacteria
2
Normal Flora vs. Pathogens
COLIFORMS
NON-COLIFORMS

• Escherichia
• Enterobacter
• Klebsiella
• Serratia
• Citrobacter

• Proteus (usually nonpathogenic)
• Shigella
• Salmonella

3
Whos a friendly enteric? (I.e., whos normal
flora?)
COLIFORMS
NON-COLIFORMS

• Escherichia
• Enterobacter
• Klebsiella
• Serratia
• Citrobacter

• Proteus (usually nonpathogenic)

4
Enterobacteriaceae Coliform or non-coliform?
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Obligate Enteric Pathogens
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Escherichia coli O157H7
http//www.jfha.or.jp/saikin/shashin/o157.html
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Eosin Methylene Blue (EMB) Agar
E. coli
http//www.cat.cc.md.us/courses/bio141/labmanua/la
b3/embeacolony.html
E. aerogenes
S. Typhimurium P. aeruginosa
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Electrons from carbos(or other food source)
Electron carriers
NO3-, SO42-,CO2
O2(Aerobic respiration)
Pyruvic acid
(Anaerobic respiration)
(Fermentation)
Black, J.G (2002) Microbiology Principles and
Explorations 5th Ed. Fig. 5.21
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Fermentation Pathways
Glucose(or other sugar)
Butyric acid, butanol,isopropyl alcohol,acetone
CO2
Propionic acid,acetic acid, CO2
Pyruvic acid
Butyric-butylicfermentation
Propionic fermentation
Black, J.G (2002) Microbiology Principles and
Explorations 5th Ed. Fig. 5.11
Butanediol CO2
Ethyl alcohol CO2
Acetic aid,succinic acid,ethyl alcohol, CO2 H2
Butanediolfermentation
Lactic acid
Alcoholic fermentation
Mixed-acidfermentation
Homolactic acidfermentation
10
API 20 E Test Strips
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Sugar Fermentation

• Melibiose
• Amygdalin
• Arabinose

• Glucose
• Mannitol
• Inositol

• Sorbitol
• Rhamnose
• Sucrose

Must use additional reagents to GLU to see result
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Catabolic Enzymes

• Beta galactosidase
• Arginine dehydrogenase
• Lysine decarboxylase
• Ornithine decarboxylase

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Citrate Utilization
blue indicates citrate utilization and alkaline
by-products
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Sulfur Reduction
CH2
SH
CH3
cysteine desulfurase
H2S
CH
COOH

H2N
CH
H2N
COOH
(hydrogen sulfide)
(alanine)
(cysteine sodium thiosulfate)
Fe (in medium)
FeS
(iron sulfide)
(black ppt)
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Nitrogen Fixing
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Tryptophan - Indole Reaction
Must add Kovacs reagent to see result
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Acetoin Reaction
Must add KOH and a-naphthol to see result
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Gelatinase(s)

• Large group of proteolytic enzymes
• Degrade collagen
• Metalloproteases
• Virulence factors

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API Test Sample Prep

• Pick ONE SINGLE colony (no agar)
• Emulsify colony by pipetting up and down in
  small amount of liquid

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Inoculating API Test Strips

• Overlay with mineral oil
• ADH, LDC, ODC, H2S, URE

• Fill tubules cupules
• CIT, VP GEL

• (see pg. 223 in lab manual)

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Reading API Test Strips

• Use chart on pp. 225-8 in manual to determine
  results
• Record or results for each test
• Add results in oval below tests
• Record 7-digit code and look up ID

22
Why did we inoculate withPseudomonas aeruginosa?