Exam 3: Gram-negative Rods Part 1: Enterobacteriaceae Flashcards
What are the different types of proteobacteria?
Alphaproteobacteria
Betaproteobacteria
Gammaproteobacteria
What is enterobacteriaceae?
A large and diverse family of gram negative rods found free living and as part of the indigenous flora of people and animals
How do enterobacteriaceae grow?
Rapidly under aerobic and anaerobic conditions and are metabolically active
What is enterobacteriaceae a primary inhabitant of?
Lower GI tract
It is the main facultative anaerobic portion of the bacterial content of the cecum and colon
What are other places that enterobacteriaceae can be found?
Female genital tract
Transient colonizers of the skin and oral cavity
Small numbers may be present in the respiratory tract of healthy animals
What is the most common species of enterobacteriaceae among the indigenous flora of mammals and some birds?
E. coli
What is the morphology of enterobacteriaceae?
Medium-sized gram negative rods
What is used for the identification and subtyping of enterobacteriaceae?
LPS, capsule/slime layer, and flagellar antigens
What is flagella called as antigenic determinants?
H antigens
What are cell surface polysaccharide (capsule, slime layer) antigens called?
K antigens
What does LPS contain?
O polysaccharide chains called O antigens
What are features of enterobacteriaceae that contribute to classification?
All are facultative anaerobes
All ferment glucose
All reduce nitrates to nitrite
All are cytochrome oxidase negative
What is a useful characteristic for initial differentiation of enterobacteriaceae?
Rapid fermentation of lactose
What are the toxins of enterobacteriaceae?
All possess LPS and its effects are often seen in infections
Some produce exotoxins
Describe the pathogenicity of enterobacteriaceae
Some species have unique pathogenic features that allow them to produce GI or systemic infections in previously healthy animals
Most do no infect unless predisposing infections occur
What are the most common sites of opportunistic infections with enterobacteriaceae?
Wound and urogenital tract infections, but they may occur at any body site, especially in septicemia
What makes enterobacteriaceae the most variable of all bacteria in susceptibility to antimicrobial agents?
Combination of chromosomal and plasmid-mediated resistance
What is enterobacteriaceae usually resistant to?
High concentration of penicillin G, erythromycin, and clindamycin
What is E. coli the dominant species of in aerobic culture?
Feces or intestinal yields
What are the major diseases caused by E. coli?
Enteric infections
Septicemia
Urinary tract infections
Mastitis
What are the various schemes that E. coli can be identified by?
Biotyping Serotyping Phage-typing Colicin-typing Virulence factor expression
How many O, K, and H antigens have been identified with E. coli with serotyping?
174 O antigens
80 K antigens
53 H antigens
What are the 6 classes of E. coli that cause diarrheal disease?
Enterotoxigenic E. coli (ETEC) Enteroinvasive E. coli (EIEC) Enterohemorrhagic E. coli (EHEC) Enteropathogenic E. coli (EPEC) Enteroaggregative E. coli (EAEC) Adherent-invasive E. coli (AIEC)
What is ETEC an important cause of?
Diarrhea in infants and travelers in regions of poor sanitation
What is the clinical sign of ETEC?
Diarrhea without fever
What does ETEC require?
Fibriae-mediated colonization and elaboration of one or more enterotoxins (ST or LT)
What does EPEC induce?
Watery diarrhea similar to ETEC
What is the adherence of EPEC strains to the intestinal mucosa due to?
Rearrangements of actin in the vicinity of adherent bacteria to form “attaching and effacing” lesions
What does EHEC cause?
A diarrheal syndrome distinct from EIEC in that there is copious bloody discharge and no fever
What is the most well-known EHEC serotype?
O157:H7
What does EIEC cause?
Dysentery-like diarrhea in humans with fever
What is the mechanism EIEC?
It penetrates and multiplies within epithelial cells of the colon causing widespread cell destruction
What does EIEC apparently lack?
Fimbrial adhesins, LT or ST toxin, and shiga toxin
What is the distinguishing factor of EAEC strains?
Their ability to attach to tissue culture cells in an aggregative manner
What are EAEC strains associated with?
Persistent diarrhea in young children
What is AIEC associated with?
Crohn’s disease in humans
Histiocytic ulcerative colitis in dogs
Chronic bloody-mucoid diarrhea and weight loss
What does flagella of uropathogenic E. coli contribute to?
UTI colonization
What does flagella of enterotoxigenic E. coli contribute to?
Adhesion
What are most septicemias in people caused by?
Strains with K1 capsular polysaccharide
What does K1 do?
Enhances invasiveness and increases resistance to phagocytosis and serum killing
What does LPS contribute to?
Septicemic disease
What is fimbriae an essential virulence factor in E. coli for?
Adherence to host cell surfaces
What does fimbriae do in enterotoxigenic E. coli?
Mediates adherence to glycoproteins on the surface of intestinal epithelial cells
What are the primary types of enterotoxins?
LT and ST
What are LT and ST essential virulence factors for along with fibriae?
ETEC
What is shiga toxin?
A heat-labile high MW toxin produced by Shigella dysenteriae
What is alpha-hemolysin?
RTX toxin frequently produced by certain porcine E. coli
It damages cell membranes
What has type III secretion system?
EPEC
