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Diagnostic microbiology lecture: 1 Enterobacteriaceae Abed ElKader Elottol MSc . microbiology

Diagnostic microbiology lecture: 1 Enterobacteriaceae Abed ElKader Elottol MSc . microbiology. The Gram Negative Bacilli Family Enterobacteriaceae. Organisms in this group form one of the largest and well defined groups amongst Gram (-) non-photosynthetic bacteria.

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Diagnostic microbiology lecture: 1 Enterobacteriaceae Abed ElKader Elottol MSc . microbiology

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  1. Diagnostic microbiologylecture: 1EnterobacteriaceaeAbed ElKaderElottolMSc. microbiology

  2. The Gram Negative BacilliFamily Enterobacteriaceae Organisms in this group form one of the largest and well defined groups amongst Gram (-) non-photosynthetic bacteria. All have small, rod shaped cells, either straight or curved, not more than 1.5 μm in width. Facultative aerobes fermenting sugars into a variety of end products. Produce acid from glucose. Ability to ferment glucose, separates them from obligate aerobes.

  3. Enterobacteriaceae • Some immotile and some motile with peritrichous flagella. • Catalase (+) and oxidase (-). • Enterobacteriacae are always oxidase (-) hence separates them from oxidase (+)bacteria such as Pseudomonas, species which have similar morphology.

  4. Best known is Escherichia coli, characteristic member of normal intestinal flora of mammals and also a important pathogen causing intestinal and urinary tract infections. • Closely related are other Enterobacteriacae such as Salmonella and Shigella species, pathogens which cause intestinal infections such as dysentery, typhoid fever and food Poisonings. • from different ecology are the genera Serratia and Proteus which primarily occur in soil and water, and the plant pathogen Erwina. • Another member is Yersinia species which includes Yersiniapestis, the agent of bubonic plague.

  5. Family Enterobacteriacae

  6. Lactose Fermentation

  7. ANTIGENIC PROPERTIES OF ENTEROBACTERIACAE 1. O Antigen: Somatic antigen. Heat stable antigen. O antigens are lipopolysaccharides and are found in the cell wall of most of gram-negative bacilli. With sera containing anti-O antibodies, such antigens agglutinate slowly in granular masses. Antibodies to O antigens are predominantly IgM.

  8. ANTIGENIC PROPERTIES OF ENTEROBACTERIACAE 2. H Antigen: Flagellar Antigen: This antigen is heat labile and could be inactivated by heating over 60 oC. With sera containing anti-H antibodies, such antigens agglutinate rapidly. Within a single Salmonella species, flagella antigens may occur in either or both of 2 forms, called phase I and phase II. The organism tends to change from one phase to other; this is called phase variation. Antibodies to H antigen are predominantly IgG.

  9. ANTIGENIC PROPERTIES OF ENTEROBACTERIACAE 3. The “Vi” Antigen: Capsular (K) antigens that are present at the extreme periphery of the bacteria. Often interfere with agglutination of freshly isolated strains by antisera containing mainly anti-O agglutinins. Vi antigens are destroyed by heating for 1 hour at 60 oC. Example of antigenic designation of Salmonella: Salmonella typhi O 1,2,(Vi): a: 1 = 1,2 are O antigens = (Vi) if present = a phase one H antigen. = 1 phase two H antigen.

  10. General Characteristics 1. Gram negative bacilli 2. Facultative anaerobes (grow with or without oxygen). 3. Glucose fermenters. 4. Oxidase negative 5. Nitrate positive

  11. General Characteristics Shape and structure gram-negative rods motile or nonmotile pili capsule (some) non-spore-forming

  12. The Cultivation, Isolation and Differentiation of Enterobacteriacae Media of Choice: 1. Eosin Methylene Blue (EMB) 2. MacConkey Agar (the most commonly used media) 3. Hektoen enteric 4. Endo agar 5. Kligler`s Iron Agar (KIA) For initial differentiation 6. Triple Sugar Iron Agar (TSIA) For initial differentiation

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