Lab. 4
Enterobacteriaceae:
Members of the enterobacteriaceae are G –ve, non spore forming bacilli that grow both aerobically and anaerolbically on ordinary laboratory media including MacConkey agar.
They are oxidase –ve, catalase +ve. They ferment glucose and other carbohydrate with production of acid or acid and gas. They reduce nitrates to nitrites and are either motile with peritrichous flagella or non motile, most strains of most species bear adhesive fimbrias of one or more types.
This family have a large number of genera, that inhabit in large intestine of human and animals.
Enterobacteriaceae
Lactose fermenter
- Echerichia coli
- Klebsiella
- Enterobacter
- Serratia
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Non Lactose fermenter
- Salmonella
- Shigella
- Proteus
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1. Escherichia coli:
G –ve, rod, motile with peritrichate flagella, non capsulated usually, non spore forming. It’s habitat most important genus of Escherichia, strains are predominant among the aerobic bacterial in healthy human intestine. An increase in number of strains are recognized as primary gastrointestinal pathogens, also it cause urinary tract infections, cystitis, septic, wound infection and appendix.
Cultural characteristics:
Aerobic and facultative anaerobic, optimum temperature for growth is 37°C, grow well on ordinary media on MacConkey agar, colonies are pink due to lactose ferment, smooth, glossy. On nutrient agar it produce large, smooth, opaque and dice shaped colony.
On blood agar: certain strains cause haemolysis on Eosin methylen blew (EMB), it produce green metallic sheen colony.
Biochemical test:
Motility (+), Indol (+), MR (+), VP (–), Citrate (–), Urease (–), H2S (–), ferment lactose and glucose.
2. Klebsiella:
Are non motile and they are usually capsulate, G –ve bacilli and it can recognized by their large, grayish mucoid colonies on laboratory medium, found in respiratory tract and genitourinary tract.
Culture characteristics:
In nutrient agar, MacConkey agar colonies are similar to E. coli except that the colonies are mucoid in EMB, it grow but without any sheen.
Biochemical test:
Indol (+), Urease (+), H2S (–),VP (+), MR (–), Citrate (+), Liquefy gelatin (–), ferment lactose and glucose.
Species of Klebsiella: previously named K. pneumonia, K. ozaenae, K. aerogenes, but know it called:
K. pneumonia sub spp. pneumonia.
K. pneumonia sub spp. aerogenes.
K. pneumonia sub spp. ozaenea.
Which cause severe bronchopneumonia or chronic lesions with multiple abscess in lung.
3. Enterobacter:
Are similar to Klebsiella, however they are usually motile characters distinguish them from K., they ferment lactose, liquefy gelatin, citrate (+), Indol (–), VP (+), MR (–), Urease (–).
The most common sp. is E. aerogenes that isolate from clinical material and they areapportunistic pathogens (infect urinary and respiratory tract and wounds).
E. cloacoe they also widely distributed in water sewage and soil.
4. Serratia:
They are G –ve bacilli, it produce endopigment differ from red to orange, motile, lactose ferment, VP (+), H2S (–), Citrate (+), gelatin (+), citrate (+).
The most common sp. is that covered from human S. marcescens infections, isolated from soil, water form red pigment, cause nasocomial infections.
Non-Latose ferment includes:
1. Proteus:
G –ve bacilli, motile, non lactose fermenter, MR (+), it hydrolyse urea rapidly, it cause (UTI) also it recovered from wound infection, species of Proteus are found widely in soil, sewage, faces, it produce swarming in agar media.
Swarming: The bacteria spread over the surface of plate making a thin layer, swarming inhibite by some substance like bile salt, so it could not form on MacConkey agar and swarming can be prevented by increasing the concentration of agar in solid culture media.
Species of Proteus:
P. mirabilis: is the commonest sp. of Proteus in human infection is the commonest cause of UTI.
Biochemical test:
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Swarming
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Indol
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Urease
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Gelatin
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H2S
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Citrate
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P. mirabilis
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+
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–
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+
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+
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+
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–
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P. vulgaris
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+
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+
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+
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+
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+
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2. Salmonella:
G –ve bacilli, non acid fast, non capsulate, non sporing, most serotypes are motile with peritrichous flagella, most strain contain fimbriae, non capsulate.
This genus are pathogenic to human and causes typhoid, para typhoid, food poisoning.
Culture and characteristics:
Aerobic and facultative anaerobi, grow on simple laboratory media in the temp. range 15-45°C optimally 37°C.
On MacConkey agar, the colonies are pale or nearly colorless (1-3) mm in diameter and easily distinguish from the pink-red colonies of lactose fermenting.
On blood agar smooth non hemolytic, circular low convex.
On brilliant green NacConkey agar the additional to MacConkey agar and brilliant green, which inhibitory to E. coli and Proteus and other Enterobacteria, Salmonella appear pale green (1-3) mm in diameter, convex.
On Wilson and Blair brilliant green bismuth sulphate agar (BBSA), this medium is a valuable for the isolated Salmonella colonies green or pale brown with a black center, but it inhibit Proteus, Shigellae.
On S-S agar Salmonella produce pale colony with black center.
Grouping of Salmonella:
Enteric fever group:
S. typhi causes typhoid fever.
S. paratyphi A
S. paratyphi A causes paratyphoid fever
S. paratyphi A
Food poisoning group:
S. typhimurium
S. enteritidis causes food poisoning, septicaemia
S. newport
Biochemical test:
Indol (–), MR (+), VP (–), H2S (+), Motility (+), Urease (–), Citrte (+) except S. typhi, Acid form lactose, sucrose, maltose (–).
Specimens:
Blood, stool and urine for culture. Blood (serum) for Widal test which it becomes +ve in 2nd week, then titer rise up to 4th week often it falls.
3. Shigella:
G –ve bacilli, non capsulated, non motile, produce acid from glucose only, they are pathogenic to human and cause dysentery characterized by passage of stool with mucous and blood.
Culture characteristics:
On nutrient agar colony are smooth, gray (2-3) mm in diameter.
On (BBSA) Shigella don’t grow on this medium on MacConkey agar colonies are pale.
On Deoxycholate citrate agar (DFA) is selective of isolation of Shigella, colonies are pale (1-2) mm black center.
Classification:
S. dysenteriae group A it is not ferment mannitol.
S. flexenen group B mannitol ferment.
S. boydii group C mannitol ferment.
S. Sonnei group D mannitol ferment, late lactose ferment.
Biochemical test:
Indol (–), Motility (–), MR (+), VP (–), Urease (–), Citrate (–), Gelatin not liquefied.
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