文档介绍：i. Enteric Gram-Negative Rods
(Enterobacteriaceae 肠杆菌)
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The Enterobacteriaceae are a large heterogenous group of gram-negative rods whose natural habitat is the intestinal tract of humans and animals.
The family includes about 29 genera, over 100 species:
Escherichia
Shigella
Salmonella
Citrobacter
Klebsiella
Enterobacter 肠杆菌属
Yersinia
克雷伯氏菌属
柠檬酸细菌属
耶尔森氏菌属
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Some of the enteric bacilli (., Escherichia coli) are part of the normal flora and major causing agent of opportunistic infection.
Salmonellae and Shigellae are pathogenic for humans.
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General characteristics
All bacilli belonging to Enterobacteriaceae are short Gram-negative rods, either mobile or non-mobile, no spore, some have capsules and pili. Size: X 3 μm
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General characteristics
All bacilli belonging to Enterobacteriaceae are facultative anaerobes or aerobes. They grow in common media. Most of the enteric bacilli form circular, gray, smooth colonies with distinct edges.
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lactose fermentation乳糖发酵
Mechanism: Non-pathogenic enteric bacilli are able to ferment lactose while pathogenic enteric bacilli such as Shigella and Salmonella are not.
Basic components: lactose and a pH indicator
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lactose fermentation
Results
colored colonies (red)
non-pathogenic
yes
no
white colonies
pathogenic
Use to differentiate non-pathogenic
from pathogenic
Shigella and Salmonella
--SS agar plate
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lactose
Double sugar iron agar slants: contains glucose, lactose, iron acetate 醋酸亚铁 and pH indicator.
Results:
hydrogen sulfide (H2S)
+-
lactose fermentation
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General characteristics
Enterobacteriaceae have complex antigenic structures
H (flagellar) Ag
somatic O Ag (lipopolysaccharide)
K/Vi (capsular) Ag
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General characteristics
Common pathogenic materials for Enterobacteriaceae include:
bacterial structures (flagella, capsules)
toxins (enterotoxi