Enterobacteriaceae Exam Questions With Complete Solutions.

Enterobacteriaceae Exam Questions With Complete Solutions. Most frequently encountered bacterial isolate recovered from clinical specimens? - Enterobacteriaceae whats an endotoxin? - A lipopolysacharide contained within the wall of a gram negative species -Layers consist of An outer variable carbohydrate portion that determines O antigenic specificity Middle core polysaccharide that is structurally similar among species Central lipid layer called Lipid A Characteristics of enterobacteriaceae - Ferment glucose Ability to enzymatically degrade a sugar Bacteria are differentiated by the carbohydrates they utilize and the types and quantities of acid produced Cytochrome oxidase negative Reduce nitrates to nitrites Not commonly used to pre-screen unknowns-can take 3-24 hours Facultative anaerobes Grow in air or anaerobically Except for Shigella, all are catalase positive Most will yield large colonies on SBA What color are colonies on Mac for lactose fermenters? - Hot pink -On MacConkey Colorless to pink Has neutral red as pH indicator in agar Dark pink colonies indicate strong acid producers (lactose fermenters) Colorless, translucent colonies indicate non-lactose fermenters Do all enterobacteriacea grow on Mac? - yes **All Enterobacteriaceae grow well on MacConkey or EMB which prevent growth of Gram positive bacteria Do all gram positive organisms grow on Mac? - No What is the most common cause of communicable bacterial diarrhea? - E. Coli **Most commonly recovered in clinical laboratory Associated with Gram negative sepsis and endotoxin-induced shock Urinary tr