16 Enterobacteriaceae16章肠杆菌科课件.pptVIP

Chapter 16 - Enterobacteriaceae MLAB 2434 – Clinical Microbiology Cecile Sanders Keri Brophy-Martinez Chapter 16 - Enterics Family Enterobacteriaceae often referred to as “enterics” Four major features: All ferment glucose (dextrose) All reduce nitrates to nitrites All are oxidase negative All except Klebsiella, Shigella and Yersinia are motile Microscopic and Colony Morphology Gram negative bacilli or coccobacilli Non-spore forming Colony morphology on BAP or CA of little value, as they look the same, except for Klebsiella Selective and differential media are used for initial colony evaluation (ex. MacConkey, HE, XLD agars) Classification of Enterics Due to the very large number of organisms in the Family Enterobacteriaceae (see Table 16-11), species are grouped into Tribes, which have similar characteristics (Table 16-1, page 466) Within each Tribe, species are further subgrouped under genera Virulence and Antigenic Factors of Enterics Ability to colonize, adhere, produce various toxins and invade tissues Some possess plasmids that may mediate resistance to antibiotics Many enterics possess antigens that can be used to identify groups O antigen – somatic, heat-stable antigen located in the cell wall H antigen – flagellar, heat labile antigen K antigen – capsular, heat-labile antigen Clinical Significance of Enterics Enterics are ubiquitous in nature Except for few, most are present in the intestinal tract of animals and humans as commensal flora; therefore, they are sometimes call “fecal coliforms” Some live in water, soil and sewage Clinical Significance of Enterics (cont’d) Based on clinical infections produced, enterics are divided into two categories: Opportunistic pathogens – normally part of the usual intestinal flora that may produce infection outside the intestine Primary intestinal pathogens – Salmonella, Shigella, and Yersinia sp. Escherichia coli Most significant species in the genus Important potential pathogen in humans Common isolate from colon flo