Enterobac lab.7.pdf

Lab -7ENTEROBACTERIACEAE Definition  Enterobacteriaceae is a large diverse family of bacteria commonly referred to as the  Gram-negative rods  Fermentative (can ferment sugars )  Enteric bacilli (are normal flora of the intestinal tract of humans and animals). Definition Gram negative bacteria u...

Lab -7ENTEROBACTERIACEAE Definition  Enterobacteriaceae is a large diverse family of bacteria commonly referred to as the  Gram-negative rods  Fermentative (can ferment sugars )  Enteric bacilli (are normal flora of the intestinal tract of humans and animals). Definition Gram negative bacteria under microscope Classification  Genus and species designations are based on phenotypic characteristics, such as patterns of carbohydrate fermentation.  The genera containing the species most virulent for humans( true pathogens) are:  Escherichia  Shigella  Salmonella  Klebsiella  Yersinia Classification  Other less common but medically important genera are :  Enterobacter  Serratia  Proteus  Morganella  Providencia. Common characteristics 1. They are gram-negative rods 2. If motile, they possess a peritrichous arrangement of flagella (Shigella and Klebsiella are non-motile) 3. They are facultative anaerobes 4. They are oxidase negative 5. All species ferment the sugar glucose but otherwise vary widely in their biochemical characteristics. Culture Media  Culture is the primary method of diagnosis; MacConkey agar are commonly used in primary isolation to speed separation of the many species  Pink colored colonies of lactose fermenter and  pale colored colonies of Non lactose fermenter Culture Media  Lactose fermenters are:  Non lactose fermenter are:  Citrobacter  Shigella  Escherichia  Salmonella  Enterobacter  Yersinia  Klebsiella  Proteus Tests for identification of members of Enterobacteriaceae family  IMViC test  Triple Sugar Iron (TSI) Agar Test  Urease Test  Oxidase Test  Catalase test Escherichia coli  Most strains of E coli ferment lactose rapidly  Produce indole.  These and other biochemical reactions are sufficient to separate it from the other species.  They are motile. E.Coli under the microscope Escherichia coli E.coli pink colonies on MacConkey agar E.coli on chocolate agar Klebsiella spp. The most distinctive bacteriologic features of the genus Klebsiella are:  The absence of motility and  The presence of a polysaccharide capsule. This gives colonies a glistening, mucoid character and forms the basis of a serotyping system. Klebsiella under the microscope Klebsiella on MacConkey agar Pink colonies due to lactose fermentation Salmonella spp.  Non-lactose fermenting,  Non-spore forming  Usually motile rods. Culture media used for isolation of salmonella 1. Blood Agar: Non selective media for primary isolation Salmonella usually produce non-hemolytic smooth white colonies. 2. Selective or differential agar 1. MacConkey Agar: pale colonies 2. Hektoen Enteric Agar; salmonellae produce green colonies with black centers) 3. Enrichment broths (e.g. Selenite broth) Culture media for isolation of salmonella 4. Salmonella-Shigella (SS) Agar: Used for selective recovery of Salmonella from stool culture Salmonellae usually produce lactose non-fermenting colonies with black centers. 5. Eosin Methylene Blue (EMB) Agar: Non lactose fermenters including: Salmonella, Shigella and Proteus forms colorless colonies. Shigella spp. Shigella species are closely related to E coli But, non-lactose fermenter. Shigella dysenteriae under the microscope Shigella  Shigella do not ferment lactose or produce hydrogen sulfide gas, so the resulting colonies will be colorless. Shigella on SS agar Salmonella on SS agar with Black colonies Yersinia spp.  Morphologically, coccobacillary.  Mucoid colonies, small (1-2 mm diameter) flat, colorless, or pale pink colonies. Yersinia tend to be Proteus spp.  Proteus mirabilis, the most commonly isolated member of the group,  P mirabilis and Proteus vulgaris share the ability to swarm over the surface of media, rather than remaining confined to discrete colonies.  This characteristic makes them readily recognizable in the laboratory Proteus mirabilis on blood agar  Swarming motility Gram negative proteus with staphylococci Proteus on chocolate agar Proteus on nutrient agar