Escherichia coli, Klebsiella pneumoniae, and pseudomonas aeruginosa

enterobacteriaceae family

large family of gram negative rods, contains a variety of organisms that can cause disease in humans- usually GI or urinary tract related, ubiquitous in the environment and as part of the normal flora of humans and animals, some are strict pathogens and others are opportunistic pathogens

what are the medically relevant genera of the enterobacteriaceae family?

escherichia, shigella, salmonella, yersinia, klebsiella, proteus

what is the gram status of e. coli?

gram negative

what shape is e. coli?

rods

what is the oxygen preference of e. coli?

facultative anaerobe

what are some features of e. coli?

encapsulated, motile (has flagella)

what is the most common and medically relevant genus in the enterobacteriaceae family?

escherichia

what is macconkey agar selective and differential for?

selective for gram negative rods, differential for lactose fermenters

what is in macconkey agar that makes it selective for gram negative rods?

bile salts and crystal violet

why does e. coli appear red/hot pink on macconkey?

it ferments lactose which produces acid, which precipitates the bile salts and produces a red color

is macconkey agar a definitive test to determine you have e. coli?

no- additional tests are needed because there are other lactose fermenting, gram negative rods

t/f e. coli is a part of normal flora

true- most common facultative anaerobe in human GI tract

can people get endogenous infections from e. coli?

yes- when immune system or barriers become compromised

t/f endogenous infections of e. coli usually cause gastroenteritis?

false- exogenous infection of strains that cause gastroenteritis

what damage can e. coli cause?

septicemia (usually due to bacteria entering blood from UTI or GI tract, high mortality rate in immunocomrpomised patients)

UTIs (usually due to bacteria moving from perianal region to urethra and ascending to the bladder, may reach kidney or prostate, most common cause of UTIs)

neonatal meningitis (along with group B strep, most of the CNS infections in babies <1 month, acquired during vaginal delivery)

gastroenteritis (inflammation of the lining of the stomach and intestines, causes vomiting and diarrhea)

what are the 6 categories of strains of e. coli that can cause gastroenteritis?

enteroaggregative (EAEC)
enterohemorrhagic (EHEC)
enteroinvasive (EIEC)
enteropathogenic (EPEC)
enterotoxigenic (ETEC)
diffuse adherent (DAEC)

what are the most common categories of strains of e. coli that cause gastroenteritis in the US?

ETEC and EHEC

enterotoxigenic e. coli (ETEC)

most common cause of traveler’s diarrhea, fecal-oral transmission (requires large inoculum)

watery/non-bloody stools (small intestine affected), abdominal cramps, nausea and vomiting are rare, no or low grade fever

lasts 1-3 days in adults but more serious in infants

enterohemorrhagic e. coli (EHEC)

aka shiga toxin e. coli (STEC), acquired by ingestion of undercooked meat, unpasteurized milk or fruit juice, uncooked vegetables or fruit

ingestion of <100 organisms can cause disease

most common strain associated with disease in US is O157:H7

starts with water/non-bloody stools but can progress to blood diarrhea (hemorrhagic colitis) with abdominal cramps, no or low grade fever

what can EHEC progress to if the organisms causing it enter the bloodstream?

hemolytic uremic syndrome (HUS), affects kidneys and blood clotting mechanism, more common in children under 10, can cause acute renal failure, lasts 4-10 days in uncomplicated cases but 3-5% death rate

what are the virulence factors that are expressed by all strains of e. coli?

LPS endotoxin, capsule, genes mostly through mobile genetic elements like plasmids and phages, antigenic phase variation (capsular and flagellar antigens), type secretion systems

antigenic phase variation

can undergo phase variation- they can alternately be expressed or not expressed to evade the humoral immune response

type secretion systems

protein apparatus found in some bacteria that mediates the injection of virulence factors into eukaryotic host cells

what are virulence factors only expressed by strains of e. coli that cause UTIs and gastroenteritis?

adhesins- allow bacteria to bind to tissues in the urinary and GI tracts and resist washing away by urine flow and peristalsis, found on pili

exotoxins- promote disease production

what is the treatment for e. coli?

for gastroenteritis- supportive treatment (fluids and electrolytes to prevent dehydration) are usually enough

antibiotic therapy for severe or disseminated enteric infections, UTIs, septicemia, and neonatal meningitis

is there a vaccine for e. coli?

no

how can you prevent an e. coli infection?

appropriate infection control in hospital settings, good hygiene, adequate cooking

what does klebsiella pneumoniae appear like on macconkey agar?

mucoid, lactose fermenting colonies

t/f klebsiella pneumoniae is encapuslated

true

what is the characteristic symptom of klebsiella pneumoniae infection?

thick, bloody (currant jelly) sputum

what predisposing conditions make an klebsiella pneumoniae infection more likely?

elderly, people with chronic respiratory disease, diabetes, alcoholism

t/f klebsiella pneumoniae is found in the respiratory tract of ~25% of healthy people

false- ~10%

what is the most common cause of hospital associated urinary tract infections?

klebsiella pneumoniae

what damage can klebsiella pneumoniae cause?

community or hospital acquired primary lobar pneumonia (aspiration pneumonia), pneumonia frequently involves necrotic destruction of alveolar spaces because of formation of cavities and then the production of blood-tinged sputum, also causes wound and soft-tissue infections and UTIs

what virulence factors does klebsiella pneumoniae have?

LPS endotoxin, capsule, sequestration of growth factors, production of bacterial siderophores that bind iron, production of hemolysins that lyse host cells and release iron

how can you treat klebsiella pneumoniae?

broad spectrum antibiotics, but resistance is rampant

is there a vaccine for klebsiella pneumoniae?

no

what is the gram status of pseudomonas aeruginosa?

gram negative

what shape and grouping is pseudomonas aeruginosa?

rods, typically in pairs

is pseudomonas aeruginosa motile?

usually- has flagella

what is the oxygen preference of pseudomonas aeruginosa?

obligate aerobe

does pseudomonas aeruginosa ferment lactose?

no (difference with e. coli)

does pseudomonas aeruginosa have a capsule?

some strains do

is pseudomonas aeruginosa a sensitive bacteria?

no- it is very resistant to disinfectants (can grow in soap) and can grow in water containing only trace amounts of nutrients like tap water

where is pseudomonas aeruginosa commonly found?

soil, water, vegetation, not commonly found in normal flora of humans, big problem in hospitals- found in hospitalized patients transiently colonizing moist areas of skin, upper respiratory tract, and GI tract, especially in patients on broad spectrum antibiotics

what damage does pseudomonas aeruginosa cause?

pulmonary infections- range from mild (tracheobronchitis) to severe (necrotizing bronchopneumonia)

pneumonia is most common in patients with immunosuppression and chronic lung disease

organism can gain access to the lung by aspiration from the URT, especially in patients on mechanical ventilation, or by bacteremic spread to lungs

skin infections- grow best on moist skin, opportunistic infection of existing wounds, most commonly burns, infection of hair follicles

UTIs- opportunistic infection in patients with indwelling catheters

ear infections- mild external ear to chronic otitis media, more invasive can affect the temporal bone and result in osteomyelitis

eye infections- opportunistic infection of exposed corneas with pre-existing mild damage, risk factors include trauma and contact lens use

what is the tricky part of treating pseudomonas aeruginosa UTI?

treatment with broad spectrum antibiotics facilitates infection by killing normal flora and selects for antibiotic-resistant pseudomonas aeruginosa strains

what are the virulence factors of pseudomonas aeruginosa?

LPS, pili, flagella, capsule, exotoxin A, elastase and proteases, pyocyanin

exotoxin A in pseudomonas aeruginosa

inhibits protein synthesis resulting in cell death and tissue necrosis

elastase and proteases in pseudomonas aeruginosa

kill cells and facilitate invasion of the organism into the bloodstream and tissues

pyocyanin in pseudomonas aeruginosa

blue pigment which promotes tissue damage and recruitment of neutrophils

how can you treat pseudomonas aeruginosa?

broad spectrum antibiotics, but resistance is rampant

how can you prevent pseudomonas aeruginosa infections?

infection control practices to prevent contamination of sterile equipment and fluids, hand washing by hospital personnel, judicious catheter management

is there a vaccine for pseudomonas aeruginosa?

no

Which Gram-negative, encapsulated bacterium is most commonly associated with aspiration pneumonia and urinary tract infections?

A. Legionella pneumophila

B. Staphylococcus saprophyticus

C. Streptococcus agalactiae

D. Klebsiella pneumoniae

E. Streptococcus pneumoniae

D. Klebsiella pneumoniae