Chap 19- Opportunistic members of Enterobacterales

What is the mnemonic to remember the four biochemical tests to differentiate members of Enterobacterales?

IMViC

Sorbitol MacConkey Agar (SMAC) is a screening media for…

E. coli O157.H7

Do other strains of E.coli besides E. coli O157.H7 metabolize sorbitol?

Yes

What do the colonies of E. coli O157.H7 look like on SMAC?

Colorless

How many families are in the Enterobacterales order?

9

General characteristic: they are oxidase

negative

General characteristic: they all ferment…

glucose

General characterist: reduce … to …

nitrate, nitrite

General characteristic: they are all motile at…

37 degrees

The majority of E. coli are … hemolytic

beta

General characteristic: they are gram …, … forming rod

negative, non-spore

What three antigens are used for serotyping?

O, H, and K antigens

Is the O antigen heat stable or heat labile?

stable

Antigens H and K are heat …

labile

The opportunistic pathogens are part of the body’s …

normal flora

These three species are what?

1. Salmonella spp

2. Shigella spp

3. Yersinia spp

Primary pathogens

What gene is responsible for plasmid-mediated colistin resistance in Enterobacteriaceae?

The mcr (mobilized colistin resistance) gene, most commonly mcr-1

How is the mcr gene transfered?

Plasmid mediated

What antibiotic is affected by the mcr gene?

Colistin - one of the last resort antibiotics for treating multidrug resistance GN infections

How does the mcr gene confer resistance to colistin?

It modifies the lipid A component of LPS, reducing colistin’s binding affinity to the bacterial membrane

What is the main mechanism of resistance in Carbapenem resistance enterobacteriaceae (CRE)?

Production of carbapenemase enzymes that hydrolyze carbapenem antibiotics

Escherichia coli IMViC is…

+ + - -

E. coli is a marker for what type of contamination in water quality testing?

fecal

E. coli are … fermenters on MAC

lactose

What does E. coli look like on Eosin Methylene Blue (EMB) agar?

has a green metallic sheen

What are the most common types of extraintestinal infections caused by E. coli?

UTISs, neonatal meningitis, and septicemia

Which virulence factors allow E. coli to cause UTIs?

P. fimbriae (adhesions) that enable attachment to uroepithelial cells and hemolysin that damages host tissues

What special E. coli strain is linked to neonatal meningitis, and what virulence factor does it express?

K1 strain of E. coli - it has the K1 capsular antigen, which helps it evade phagocytosis and complement

Where does Extraintestinal E. coli infect?

sites outside the intestines (urinary tract)

How are extraintestinal E. coli infections usually acquired?

From patient’s own gut flora migrating to other sites

What kind of illnesses does gastrointestinal strains of E. coli cause?

diarrheal

Uropathogenic (UPEC) E. coli is the most common cause of what in humans?

UTIs

These categories of E. coli are what type of E. coli infections?

• ETEC

• EPEC

• EIEC

• STEC

• EAEC

Gastrointestinal

What are the two toxins produced by Enterotoxigenic E. coli (ETEC)?

Heat labile toxin (LT) and heat stable toxin (ST)

What is the mechanism of the heat-labile toxin (LT) of ETEC?

Portion B binds to intestinal mucosa so that portion A activates adenylate cyclase

What does adenylate cyclase do in LT?

Increases cAMP, leading to secretion of Cl- and water into intestinal lumen - VERY WATERY DIARRHEA

What is the mechanism of the heat-stable toxin (ST) in ETEC?

ST activates guanylate cyclase, increasing cGMP, which also causes fluid and electrolyte loss

What disease does ETEC commonly cause?

Traveler’s diarrhea and infantile diarrhea in developing countries

Does enteropathogenic E. coli (EPEC) produce toxins?

No, it causes disease by damaging intestinal microvilli

What is the main symptom of EPEC infection?

watery diarrhea (usually in infants) without blood or significant inflammation

What disease does Enteroinvasive E. coli (EIEC) cause?

Dysentery like illness - with fever, cramps, and bloody diarrhea

How does EIEC cause disease?

It invades and destroys colonic epithelial cells, leading to inflammation and ulceration

What bacterial genus does EIEC most closely resemble?

Shigella - both invade mucosa and cause dysentary

What is the main virulence factor of EIEC?

A plasmid encoded invasion plasmid antigen (ipa) that enables epithelia cell invasion

Does EIEC produce toxins?

No significant enterotoxins, its pathogenicity is due to invasion and cell destruction

What is another name for Shiga toxin producing E. coli (STEC)?

Enterohemorrhagic E. coli (EHEC)

What is the most common serotype of STEC associated with outbreaks?

E. coli O157:H7

What is the main virulence factor of STEC?

Shiga toxins (Stx1 and Stx2)- they inhibit protein synthesis by inactivating the 60S ribosomal subunit

What type of diarrhea does STEC cause?

Bloody diarrhea, without fever

What serious complication can follow STEC infection, especially in children?

Hemolytic uremic syndrome (HUS) - hemolytic anemia, thrombocytopenia, and acute renal failure

How is STEC trasmitted?

undercooked ground beef, unpasteurized milk/juice, contaminated produce

Does E. coli O157:H7 ferment sorbitol?

nope

Should antibiotics be used to treat STEC infection?

No- antibiotics may increase toxin release and worsen the risk of HUS

What disease does Enteroaggregative E. coli (EAEC) cause?

persistant watery diarrhea

How does EAEC attach to intestinal cells?

Forms a “stacked brick” pattern of adherence on the intestinal mucosa. Forms a biofilm formation

What toxin is produced by EAEC, and what is its effect?

EAST1 (heat stable) and it increases cGMP levels, leading to fluid secretion and watery diarrhea

Klebsiella spp IMViC is…

- - + +

What is the one Klebsiella spp that is indole positive (+-++)?

K. oxytoca

What are the clinically important Klebsiella spp in this chapter?

Klebsiella pneumoniae and Klebsiella oxytoca

What Klebsiella spp is the most common isolated respiratory tract infection of hospitalized patients?

K. pneumoniae

What is the hallmark feature of Klebsiella colonies on agar?

Mucoid, sticky colonies due to a thick polysaccharide capsule

What is the only motile Klebsiella spp?

K. aerogenes

Enterobacter spp IMViC is…

- - + +

How to differentiate between Klebsiella spp and Enterobacter spp?

Enterobacter is positive ornithine decarboxylase

What is a notable feature of Enterobacter spp in hospitals?

They are common nosocomial pathogens and can colonize catheters, ventilators, and IV lines

What infections are most commonly caused by Enterobacter?

UTIS, bloodstream infections, pneumonia, wound infections

Why is Cronobacter spp a concern in neonates?

It can cause severe sepsis and meningitis, often linked to contaminated powdered infant formula

How is Cronobacter detected in the lab?

yellow pigment on BAP

What is the second most common carbapenem resistant Enterobacterales?

Enterobacter spp

Which Citrobacter spp is particularly associated with neonatal meningitis and brain abscesses?

C. koseri

What is a notable lab characteristic of Citrobacter on MAC?

Lactose fermentation variable - some strains ferment slowly (pink) while other are non-lactose fermenters

How is Plesiomonas shigelloides distinguished in the lab?

It is oxidase positive, and can ferment glucose but not lactose. THE ONLY OXIDASE POS ENTEROBACTERALES

What type of pathogens are Erwiniaceae?

plant