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. 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.

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.

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 Yersinia pestis, the agent of bubonic plague.

Family Enterobacteriacae

Lactose Fermentation

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.

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.

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.

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

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

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