Gram Negative Rods - Enterobacteriaceae

The pathogenic Enterobacteriaceae that are not Normal flora are:

shigella, salmonella, yersinia, E. coli O157H; all except E. coli are non-lactose fermenters

The Enterobacteriaceae that are Normal flora are:

E.coli, Klebsiella, Enterobacter, Citrobacter, and Proteus; all are lactose fermenters

Characteristics of Enterobacteriaceae family:

GNR, facultative anaerobes; oxidase negative; all glucose fermenters; grows well on MacConkey agar

MacConkey agar

selective for GNR and differential for lactose fermenters; pink=lactose fermenter

Why is lactose an important test for Enterobacteriaceae?

I distinguishes pathogenic and nonpathogenic species

90% of UTIs are caused by ___________

E.coli

What is the most commonly isolated bug in labs?

E.coli

Enterohemorrhagic E.coli

E.coli O157H7: not part of normal flora; produces shiga toxins; causes bloody diarrhea; the only nonlactose fermenting stool pathogen

Hemolytic uremic syndrome (HUS)

a cause of kidney failure; caused by E. coli O157H7

Enterotoxigenic E. coli

causes watery diarrhea aka Traveler’s diarrhea

Enteropathogenic E.coli

causes diarrhea in infants; common in developing countries

How is E. coli 0157H7 distinguished from other strains of E. coli in the lab?

E.coli 0157H7 is doesn’t ferment sorbitol (sorbitol negative) and produces clear colonies on MacConkey w/Sorbitol agar; regular E.coli produce pink colonies

Salmonella

non lactose fermenters; includes S.typhi and S.enteritidis; causes salmonellosis

Salmonellosis

caused by Salmonella enterica; antibiotics only given if it enters the blood stream

How can Salmonella be transmitted to humans?

eating raw eggs; infected animals (pet turtles)

Who was Mary Mallon?

a cook from NY responsible for several Samonella typhi outbreaks in the 20th century

Transovarial transmission

When a chicken transmits salmonella into an egg before it is laid

Typhoid fever

caused by Salmonella typhi; only carried by humans; causes high fever, rashes and confusion

Shigella

non lactose fermenter; causes shigellosis; produces shiga toxin; destroys mucosa in large intestine; 10-100 infective dose

Shigellosis

obtained by ingesting fecal matter; common in daycare centers

4 species of Shigella cause _________________________

bacillary dysentery

Yersina pestis

non lactose fermenter causes Plague (Black Death); GN coccobacilli; spread by rodents and fleas

What are the three types of plagues?

Bubonic, Septicemia, and Pneumonic

Bubonic plague

causes intense inflammatory response and swelling of lymph nodes

Septicemia plague

when plague bacteria moves from the lymph nodes to the blood stream; meningitis and pneumonia

Pneumonic plague

Black death; spread person to person via aerosols; most deadly

Klebsiella pneumonia

opportunistic; causes pneumonia

Serratia mercescens

opportunistic UTI; cause respiratory infection in immunocompromised individuals

Enterobacter species

opportunistic; causes wonds

Proteus mirabilis

opportunistic; causes UTIs; grows in waves on agar

Yersinia enterocolitica and Yersinia pseudotuberculosis

obtained from raw pork/unpasteurized milk; grows at refrigerator temperature