enterobacterales bacteria Flashcards
What does it mean if you get gram - cocci on a gram stain?
Either:
1. You messed up your Gram stain!
2. There was some other change to the cell wall!
3. The organism you Gram stained isn’t a pathogen
enterobacterales shared features
Gram negative rods
Facultatively anaerobic
Oxidase negative
Most are motile
Growth on blood agar - similar colonies
* Some, not all, are hemolytic except Proteus (swarms)
Grow on MacConkey’s agar
* Tolerate bile salts
* Lactose fermentation is variable
* Helps differentiate in family
5 main genera in enterobacterales
E. coli
salmonella
yersinia
klebsiella pneumonia
proteus
2 main groups of enterobacterales
lactose fermentation positive
* Escherichia
* Klebsiella
lactose fermentation negative
* Proteus
* Salmonella
* Yersinia
which genera are strong vs intermediate pathogens in enterobacterales
strong: E. coli, salmonella, yersinia
intermediate: klebsiella pneumoniae, proteus
Where does E. coli come from?
NORMAL FLORA of most vertebrates
* Lower ileum
* Large intestine
* Colonizes neonatal GIT within hours of birth
Survives well in the environment
Makes “coliform” counts valuable indices of fecal contamination
How is E. coli transmitted?
Feco-oral (most common route)
Inhalation
Direct inoculation
Ascending infections
* Cystitis
* Pyometra
* Transient in urogenital tract
virulence of E. coli
not all strains are virulent, some are harmless
very diverse bacteria
how does E. coli cause dz?
Not all E. coli strains are virulent.
Strains with Virulence Factors act by:
* Attachment: pili, adhesions
* Avoidance of phagocytosis: capsule
* Cellular effects (physiological or toxicity): hemolysin, CNF
* Systemic Effects: endotoxin
But the contribution of the virulence factor depends on the site of infection
Some strains may be virulent at one site but avirulent at another (e.g., Non-Enteric versus Enteric)
What diseases does E.coli cause?
E. coli has been incriminated in infectious disease involving virtually every tissue and organ system – because some strains of E.coli are very good opportunistic pathogens
Common ones:
* sepsis
* bladder infections
* pyometra
* mastitis
How to treat E. coli and other enterobacterales?
There are multiple drug resistant strains of Enterobacterales
* Particularly E. coli, and Klebsiella and Salmonella
* Drug resistance plasmids are readily transferred among members of the Enterobacterales
MUST DO SUSEPTIBILITY TESTING
Enterobacterales are some of the MOST antibiotic resistant bacteria currently in existence
Ancillary therapies:
* Critically important
* Surgery/drainage/debridement
* Fluid therapy
* Anti-endotoxin therapies
Salmonella species/strains
2 species:
* salmonella enterica
* salmonella bongeria
over 2400 serotypes of these species
Where does salmonella come from?
- Parasites of the Gastro-intestinal Tract (GIT)
- Salmonella is NOT normal flora
Can be present in CARRIER ANIMALS
* Present in GIT of carrier animals which can include wide variety of mammals, birds, reptiles and insects!!!
* This is not the same as “normal flora”!
Survive LONG time in the environment
* Major source of infection (contaminated feedstuffs, water, etc)
how is salmonella transmitted?
Feco-oral transmission
* Variety of animal species are carriers (Reptiles, Cattle, Horses, Others)
Recrudescence of infection in carrier animals
How does salmonella cause dz?
Avoidance of killing by phagocytes
* Facultative Intracellular Parasites
* Live inside of macrophages
Systemic carrier states
* Not just in the intestine
* Live in macrophages
* In mediastinal lymph nodes and liver
Where does yersinia pestis come from?
Wild rodents are the reservoir
Rodents (mice, rats) prairie dogs, squirrels
Flea-rodent-flea life cycle
