University of Babylon



?. ???? ???? ?????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 (selective medium of enterobacteriaceae). 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 fimbria of one or more types. This family has a large number of genera, that inhabit in large intestine of human and animals. Non Lactose fermenter- Salmonella- Shigella- ProteusLactose fermenter- Echerichia coli- Klebsiella- Enterobacter- SerratiaEnterobacteriaceae1. Escherichia coli:G –ve, rod, motile with peritrichate flagella, non capsulated usually, non spore forming. E. coli is a member of the normal intestinal flora. Other enteric bacteria (Proteus, Enterobacter, Klebsiella and Serratia species) are also found as members of the normal intestinal flora but are less common. The enteric bacteria are found in small numbers as part of the normal flora of the upper respiratory and genital tracts.The enteric bacteria generally do not cause disease, and in the intestine, they may even contribute to normal function and nutrition. When clinically important infections occur, they are usually caused by E. coli, but the other enteric bacteria are causes of hospital-acquired infections and occasionally cause community-acquired infections. The bacteria become pathogenic only when they acquire certain virulence trait or they reach tissues outside of their normal intestinal or other less common normal flora sites. The most frequent sites of clinically important infection are the urinary tract, biliary tract, and other sites in the abdominal cavity. When normal host defenses are inadequate—particularly in infancy or old age, in the terminal stages of other diseases, after immunosuppression, localized clinically important infections can result, and the bacteria may reach the blood stream and cause sepsis.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 fermentation, smooth, glossy. On nutrient agar, it produces large, smooth, opaque colony.On blood agar: certain strains cause haemolysis, on Eosin Methylen blue (EMB) it produces green metallic sheen colony.Biochemical test:Motility (+), Indol (+), MR (+), VP (–), Citrate (–), Urease (–), H2S (–), ferment lactose and glucose (A/A +gas).2. Klebsiella:Are non motile and they are usually capsulate, G –ve bacilli and it can recognized by their large, 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 grows but without any sheen.Biochemical test:Motility (-) Indol (-), MR (–), VP (+), Citrate (+), Urease (+), H2S (–), Liquefy gelatin (–), ferment lactose and glucose.Species of Klebsiella: previously named K. pneumoniae, K. ozaenae, K. aerogenes, but know it called:K. pneumoniae sub spp. pneumoniae.K. pneumoniae sub spp. aerogenes.K. pneumoniae 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 (+), Indol (–), MR (–), VP (+), citrate (+), Urease (–).The most common sp. is E. aerogenes that isolate from clinical material and they are opportunistic 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, Indol (–), MR (–), VP (+), Citrate (+), H2S (–), gelatin (+).The most common spp. from human infections S. marcescens, 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, feces, it produce swarming in agar media.Swarming: The bacteria spread over the surface of plate making a thin layer due to active motility, swarming inhibited 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: Swarming Indol Urease Gelatin H2S CitrateP. mirabilis + – + + + –P. vulgaris + + + + + v2. Salmonella:G –ve bacilli, non capsulate, non sporing, most serotypes are motile with peritrichous flagella, most strain contain fimbriae. This genus are pathogenic to human and causes typhoid, paratyphoid, 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 S-S agar Salmonella produce pale colony with black center.Grouping of Salmonella:A. Enteric fever group:- S. typhi causes typhoid fever.- S. paratyphi A causes paratyphoid fever- B. Food poisoning group:- S. typhimurium- S. enteritidis causes food poisoning, septicaemia- S. newportBiochemical test:Indol (–), MR (+), VP (–), Citrte (+) except S. typhi, H2S (+), Motility (+), Urease (–), 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 then 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 MacConkey agar colonies are pale.- On S-S agar Shigella colonies are pale (1-2) mm.Classification:1. S. dysenteriae group A it is not ferment mannitol.2. S. flexneri group B mannitol ferment.3. S. boydii group C mannitol ferment.4. S. Sonnei group D mannitol ferment, late lactose ferment.Biochemical test: Motility (–), Indol (–), MR (+), VP (–),Citrate (–), Urease (–), Gelatin not liquefied. ................
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