Enterobacteriaceae(M)

8/12/2019 Enterobacteriaceae(M)

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Enterobacteriaceae

Opportunistic pathogens

Escherichia coliKlebsiella pneumoniae

Enterobacter aerogenes

Serratia marcescens

Proteus spp.Providencia spp.

Citrobacter spp.

Obligate pathogensSalmonella spp.

Shigella spp.

Yersinia spp.

Some E. colistrains

Sepsis

Meningitis

UTI

Diarrhea

Pneumonia


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Morphology and Physiology

Short gram-negative rods.

Facultative anaerobes.

Grow readily and rapidly

on simple media.

K. pneumoniae

Klebsiellaspp. have large capsule

(form large and very mucoidcolonies); those of Enterobacter

have smaller capsule; the others

produce diffusible slime layers

(form circular, convex and smoothcolonies).


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Proteus spp.

Some enteric bacteria are

motile. Klebsiella species are

not motile, while Proteus

species move very actively by

means of peritrichous flagella,

resulting in "swarming" on solid

medium.

Some strains of E. coli

produce hemolysis on blood

plates.


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Enterobacteriaceae is characterized biochemically by theability to reduce nitrates to nitritesand to ferment glucose.

Cytochrome oxidase-negative.

Enterobacteriaceae species differ in their ability to ferment

lactose. Some ferment lactose rapidly, some does it slowly

and the others (e.g., Salmonellaand Shigella) do not

ferment lactose at all.

Some Enterobacteriaceae pathogens (e.g., Salmonellaand

Shigella) are resistant to bile salts, and this property can be

used to select them from commensal organisms that are

inhibited by bile salts.


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Antigenic Structure

O antigens

O-specific polysaccharideslocated in LPS. Heat-stable andresistant to alcohol. A single organism may carry several O

antigens.

(Core polysaccharide of LPS: enterobacterial common antigen)

K antigens

External to O antigens in some strains. Mostly are capsular

antigens (polysaccharides). K antigens of Klebsiellacan be

identified by capsular swelling test.

H antigen

Flagellin. Heat-labile and denatured by alcohol. May be absent

or undergo phase variation in different species.


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ECA


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Pathogenesis and Immunity

Common virulence factors

Type III secretion systems: possessed by some Enterobacteriaceae

pathogens, e.g., E. coli, Yersinia, Salmonella, and Shigella; facilitate

transport of bacterial virulence factors directly into host cells.

Endotoxin (Lipid A of LPS)

Capsule

Antigenic phase variationAcquisition of growth factors (e.g. Fe)

Resistance to serum killing

Antimicrobial resistance


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Toll-like

receptor 4

(TLR-4)

Pathogenesis of sepsis causedby gram-negative bacteria


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Pathophysiological effects of LPS

Activation of complement, release of cytokines,

fever, leukocytosis, thrombocytopenia, impairedorgan perfusion and acidosis, disseminated

intravascular coagulation (DIC), hypotension,

shock and death, premature labor and abortion.


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Escherichia coli

SepsisFor people with inadequate host defenses, e.g. the newborns.

Usually originates from UT or GI infections. Some infections

may be endogenous.

Pathogenesis and clinical diseases

Meningitis

E. coli (particularly

K1 strains) and

S. agalactiaeare

the leading causes

of meningitis in

infants.

Bacteremia


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Urinary tract infection

E. coliis the most common cause of urinary tract infection.

Community- vs. hospital-acquired UT infection

Most infections originate from colon; the bacteriacontaminate the urethra, ascend into the bladder, and may

migrate into the kidney or prostate.

Symptoms: urinary frequency, dysuria, hematuria, and

pyuria. Can result in bacteremia and sepsis.

Uropathogenic E. colistrains produce P (Pyelonephritis-

associated) pili, which is associated with renal colonization

and may induce protective immunity, and hemolysin HlyA.

Escherichia coli



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Escherichia coli


Gastroenteritis

(Diarrhea)

Caused by various virotypes:

Enterotoxigenic E. coli

Enteropathogenic E. coli

Enterohemorrhagic E. coli

Enteroinvasive E. coli

Enteroaggregative E. coli

Table 30-2

EAST & PET

ST


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Escherichia coli


Enterotoxigenic E. co li(ETEC)

:

major causal agent of Traveler'sdiarrhea.

These strains express:

a) Heat-labile (LT-1) enterotoxins: an A-B toxin. Subunit A causes

intense and prolonged hyper secretion of chloride ions and inhibitsthe reabsorption of sodium and chloride. The gut lumen is distended

with fluid, and hypermotility and secretory diarrhea occur, lasting for

several days. It stimulates the production of neutralizing antibodies,

and cross-reacts with the enterotoxin of Vibrio cholerae.

b) Heat-stable (STa) enterotoxin: also stimulates fluid secretion;

poorly immunogenic; short onset.

c) Colonization factors (CFAs): facilitate the attachment of E. coli

strains to intestinal epithelium. Usually are pili in nature.


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ADP-ribosylation

Enhance chloride

secretion

Decrease sodium and

chloride absorption


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Escherichia coli


Enteropathogenic E. co li(EPEC):causes infant

diarrhea in poor countries. Watery diarrhea results

from malabsorption due to microvilli destruction.

Spread by person-to-person contact.

Enteroinvasive E. co li(EIEC):closely related to

Shigellain pathogenic properties.

Enteroaggregative E. co li(EAEC):causes chronic

diarrhea and growth retardation in infants in

developing countries.


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Escherichia coli


Enterohemorrhagic E. co li(EHEC)

The most common strains producing disease in developed countries.

These strains are associated with hemorrhagic colitisand hemolytic

uremic syndrome(HUS: acute renal failure, microangiopathichemolytic anemia and thrombocytopenia; 5-10% infected children).

Serotpe O157:H7is most commonly isolated.

Cattle is a reservoir, and hamburger, unpasteurized milk, fruit juices,

and uncooked vegetables are common sources of human infection.

Induces A/E lesions on enterocytes. Diarrhea and HUS may be

associated with the Shiga toxins, which are A-B toxins that bind to

28S rRNA and disrupt protein synthesis.


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Klebsiel la

K. pneumoniaeand K. oxytocaare the most commonly isolated.

Can cause community-acquired primary lobar pneumonia

(frequently involves necrotic destruction of alveolar space), and

infections of wound, soft tissue, and urinary tract.

Risk factors for pneumonia: alcoholism; compromised pulmonaryfunction.

*In Taiwan: liver abscess is commonly seen in infection by K.

pneumoniae.

K. granulomatismay cuase granuloma inguinale, a sexuallytransmitted disease, in some countries.

K. rhinoscleromatis: granulomatous disease of the nose.

K. ozaenae: chronic atrophic rhinitis.

Other opportunistic Enterobacteriaceae


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Proteus

Most common isolates: P. mirabilis.

Cause urinary tract infections and bacteremia.

Produce urease, making the urine of the patients of UT

infectionwith Proteusalkaline, promoting stone formation

by precipitating Mg and Ca.

Enterobacter, Citrob acter, Morganella, Serratia

Opportunistic pathogens causing nosocomial infections in

neonates and immunocompromised patients.

These genera, particularly Enterobacter, are resistant to

multiple antibiotics.


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Escherichia coli and otheropportunistic Enterobacteriaceae

Laboratory diagnosis

Smears: the Enterobacteriaceae pathogens resemble each

other. The presence of large capsules is suggestive Klebsiella.

Culture: blood agar and selective differential media (e.g.,

MacConkey agar), the latter is useful for preliminary

identification. Commercial biochemical test systemscan be

used for identification of Enterobacteriaceae members.

Serologic tests are used for determining the clinical significance

of an isolate and for epidemiologic purpose.


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Treatment

Variation in drug susceptibility is great, and antibiotic

sensitivity tests are essential.

Diarrheapatients usually need only symptomatic relief.

Antibiotic treatment may prolong the fecal carriage or

increase the risk of secondary complications.

Treatment of bacteremia and septic shock: promptantibiotic treatment, restoration of fluid and electrolyte

balance, and treatment of disseminated IV coagulation.

E. coli and other opportunistic

Enterobacteriaceae


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Prevention and control

Enterobacteriaceae are a major part of normal flora and

a common contaminant of the environment.

In hospitals, opportunistic Enterobacteriaceae are

commonly transmitted by personnel, instruments, or

parenteral medications. Their control depends on hand

washing, rigorous asepsis, sterilization of equipment,disinfection, restraint in IV therapy, and strict precautions

in keeping the urinary tract sterile.

E. coli and other opportunisticEnterobacteriaceae


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Salmonella

Salmonellaspp. do not ferment lactose.

Most species of Salmonellaare motile with peritrichous flagella.

Some Salmonellae have capsular antigens; that of S. Typhi is

referred to as Vi antigen.

Groups and species of Salmonella are identified by serologic

analysis of O and H antigens (> 2,500 serotypes). Classification of

salmonellae is traditionally based on serogrouping and serotyping

(e.g. S. typhimurium, which is reclassified as S. entericatogether

with most human pathogens by analysis of DNA homology). Thecorrect name for S. typhiis S. enterica, serovar. Typhi or S.Typhi.

They can be identified by biochemical tests and serogrouping, with

follow-up serotyping confirmation.


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Salmonella

Epidemiology

S. Typhi and S. Paratyphi are primarily infective for humans.

Other salmonellae are chiefly pathogenic in animals(poultry, pigs,

rodents, cattle, pets etc.) that constitute thereservoir for human

infection.

Humans usually become infected by ingestion of contaminated food

or drink (mean infective dose: 106-108, but that of S. typhiis lower).

In children, infections can result from direct fecal-oral spread.

The most common sources of human infections: poultry,eggs,dairy

products, and foods prepared on contaminated work surfaces.

However, the major source of infection for enteric fever is the

carriers(convalescent or healthy permanent).


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Salmonella


Invasion

Acid tolerance response (ATR) gene protects the organism

from gastric acid.

The bacteria invade into (by inducing membrane ruffling)

and multiply in the M cells and enterocytes of the small

intestine. They can also be transported across the

enterocytes and released into the blood and lymphatic

circulation.

Inflammatory response confines the infection to the GI tractin non-typhoid salmonellosis.

Survival in macrophages

Salmonellae are facultative intracellular pathogen.


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Salmonella

Clinical diseases

1. Enteritis

Incubation period: 6-48 hours.

Symptoms: nausea, headache, vomiting, nonbloody

profuse diarrhea, with few leukocytes in the stools. Low-

grade fever, abdominal cramp, myalgia, and headache

are also common. Episode resolves in 2-7 days.

Inflammatory lesionsof the small and large intestine are

present. Stool cultures remain positive for several weeks

after clinical recovery.


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Salmonella

Clinical diseases

2. Bacteremia

Most common causal species: S. Choleraesuis, S Typhi

and S. Paratyphi.

Symptoms: like sepsis caused by other gram-negative

bacteria. 10% of patients may have localized suppurative

infections, e.g., osteomyelitis, endocarditis, arthritis, etc.

High risk population: pediatric and geriatric patients;

AIDS patients.


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Salmonella

Clinical diseases

3. Enteric fever (typhoid fever)

Causal species: S. Typhi, S. ParatyphiA, S. Schottmuelleri,

and S. Hirschfeldii.

Mouth small intestine lymphatics and bloodstreaminfect liver, spleen and bone marrow multiply and

pass into the blood second and heavier bacteremia

onset of clinical illness colonization of gallbladder

invasion of the intestine typhoid ulcers and severeillness.

Chronic carriers(1%-5% of patients): bacteria persist in the

gallbladder and the biliary tract for more than one year.


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Symptoms: incubation time: 10-14 days. Gradually

increasing fever, malaise, headache, myalgias, and

anorexia, which persist for a week or longer.

In severe cases: intestinal hemorrhage and perforation.

Principal lesions: hyperplasia and necrosis of lymphoid

tissue, hepatitis, focal necrosis of theliver, and

inflammation of the gallbladder, periosteum, lungs and

other organs.


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Salmonella

Treatment

Enteric fever and bacteremiarequire antibiotic treatment:

chloramphenicol, ampicillin, trimethoprim-sulfamethoxazole.

Surgical drainage of metastatic abscesses may be required.

Salmonella enterocolitisneeds only supportive therapy

(antibiotic treatment may prolong the symptoms and

excretion of the salmonellae). Drugs to control hypermotility

of the gut should be avoided because it is easy to transform a

trivial gastroenteritis into a life-threatening bacteremia by

paralyzing the bowel.

Chronic carriersof S. Typhi may be cured by antibiotics alone

or combined with cholecystectomy.


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Salmonella


Sanitary measures.

Carriers must not be allowed to work as food

handlers.

Strict hygienic precautions for food handling.

Vaccines against S. Typhi:

Purified Vi antigen

Oral, live attenuated vaccine.


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National salmonella death toll rises to 7(Staff writer Ridgely Ochs contributed to this story. Janu ary 24, 2009)

A seventh death was linked Friday to a nationwide outbreakof salmonella

associated with tainted peanut butterand paste sourced to the Peanut

Corp. of America's plant in Blakely, Ga., authorities confirmed.

Although their exact causes of death have not been determined, all seven

people have died after being infectedwith the bacterial strain Salmonella

Typhimurium, the Centers for Disease Control and Prevention said on its

Web site.

There have been 493 cases reported in 43 states and one Canadian

province of people sickened, though authorities stress the numbers

sickened are likely far in excess of that as many cases go unreported.

Known patients ranged in age from 1 to 98, and 22 percent of the those

have been hospitalized.

Another 10 firms Friday recalled productsthat use PCA peanut butter or

paste - bringing to roughly 360 the number of products affected - as it

emerged that the Peanut Corp. of America's plant in Blakely, Ga. laid off

most of its roughly 50 workers. The outbreak has triggered a

congressional inquiry and renewed calls for reform of food safety laws.

http://www.newsday.com/services/newspaper/printedition/saturday/health/ny-lisalm246010666jan24,0,5876138.story


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ShigellaS. dysenteriae, S. flexneri , S. sonnei , & S. boydii: bacillary dysentery

> 45 O serotypes; have no H antigen; do not ferment lactose.


Shigellosis is primarily a pediatric disease, and is restricted to the GI

tract.

Mean infective dose: 10

3

.Mouth colon invade M cells and subsequently spread to

mucosal epithelial cells cause microabscess in the wall of colon

and terminal ileum necrosis of the mucous membrane,

superficial ulceration, bleeding, and formation of pseudomembrane.

Shiga toxin

An A-B toxin inhibiting protein synthesis.

Damages intestinal epithelium and glomerular endothelial cells

(associated with HUS) .


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Internalized shigellae induce

apoptosis of macrophage

and release of the bacteria

Attracted by

the cytokines

released by

macrophage

Destablize the

intestinal wall

Activates the invasion genes

on the virulence plasmid

M cell


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Shigella

Clinical diseases

Incubation period: 1-3 days

Sudden onset of abdominal pain, fever and watery diarrhea

number of stools increase, less liquid, often contain mucus

and blood, rectal spasms with resulting lower abdominal pain

(tenesmus) symptoms subside spontaneously in 2-5 days

in adult cases, but loss of water and electrolytes frequently

occur in children and the elderly a small number of

patients remain chronic carriers.

Some cases were accompanied by hemolytic uremic

syndrome (HUS).


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Shigella

Laboratory diagnosis

Specimens: fresh stool, mucus flecks, and rectal

swabs. Large numbers of fecal leukocytes and some

RBC may often be seen microscopically.

Culture: differential and selective media as used for

salmonellae.

Treatment

Antibiotic treatment: chloramphenicol, ampicillin,

tetracycline, and trimethoprim-sulfamethoxazole.

Drug resistance is common.

Opiates should be avoided.


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Shigella


Humans are the only reservoir for shigellae.

Transmission of shigellae: water, food, fingers, feces,

and flies.

Most cases occur in children under 10 years of age.

Prevention and control of dysentery:

1. Sanitary control of water, food and milk; sewage

disposal; and fly control.

2. Isolation of patients and disinfection of excreta.

3. Detection of subclinical cases and carriers.


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Yersinia

Y. pes tis: plague ("black death")

Y. pseudotu berculos isand Y. enteroco li t ica: gastroenteritis

Grows more rapidly in media containing blood or tissue fluids

and fastest at 30 oC. Some species (e.g. Y. enterocolitica) can

grow in refrigerated food.

Pathogenesis

The Yersiniapathogens are able to resist phagocytic killingby

secreting proteins into the phagocyte and result in inhibition of

killing by phagocyte, apoptosis of macrophage, and suppression

of cytokine production.

Y. pestisproduces a protein capsule(Fraction 1), and Pla

(plasminogen activator protease) that degrades C3b and C5a,

and fibrin clot (enhances spread of bacteria into blood stream).


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Yersinia pestisCauses zoonoticinfections; humans are accidental hosts.

Three major pandemics have occurred in 541 AD, 1320s and 1860s.

Two forms of infections:

Urban plague

Rats as natural reservoirs.

Spread among rats or between rats and humans by infected flea.

Can be eliminated by effective control of rats and better hygiene.

Sylvatic plague: infections of rodents and domestic cats.

Y. pestisare widely distributed in mammalian reservoirs and fleavectors and produces fatal infections in animal reservoirs.

Human infections are acquired by contacting the reservoir

population.


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Yersinia pestis

Pathogenesis

Bubonic plagueY. pestisenters a flea when it feeds on an infected animal the

bacteria multiply in the gut of the flea flea becomes hungry and

bites ferociously Y. pestispasses from the flea into the bite

wound the bacteria are phagocytised, but can multiply

intracellularly or extracellularly reach the lymphatics, and an

intense hemorrhagic inflammation develops in the enlarged lymph

nodes, which may undergo necrosis Y. pestismay reach the

bloodstream and become widely disseminated. Hemorrhagic and

necrotic lesionsmay develop in all organs.Primary pneumonic plague

Results from inhalation of infective droplets (usually from a

coughing patient), with hemorrhagic consolidation of the lung,

sepsis and death.


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Yersinia pestis

Clinical Diseases

Bubonic plague

Incubation period: 2-7 days.

High fever and painful lymphoadenopathy with greatly

enlarged, tender lymph nodes (buboes) in the groin and axilla

sepsis (early stage: vomiting and diarrhea; late stage:

hypotension, renal and cardiac failure; terminal stage:

pneumonia and meningitis). Mortality: 75% if untreated.

Pneumonic plague

Incubation time: 2-3 days.

Fever and malaise, pulmonary signs develop within 1 day.

Patients are highly infectious. Mortality: 90% if untreated.


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Yersinia pestis

Treatment

Patients have to be promptly treated with antibiotics (drug of

choice: streptomycin).

Epidemiology and control

Plague is an infection of wild rodents that still occurs in manyparts of the world (enzootic areas: India, Southeast Asia, Africa,

and North and South America).

Control of plague requires surveys of infected animals, vectors,

and human contacts, and by destruction of infected animals.All patients with suspected plague should be isolated.

Contacts of patients with suspected pneumonic plague should

receive tetracycline as chemoprophylaxis.


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Y. enterocoliticaand Y. pseudotuberculosis

Cause zoonotic infections.

Y. enterocoliticais a common cause of enteritis in cold areas

during the cold months. Y. pseudotuberculosisinfection is

relatively uncommon.

They are found in the intestine of a variety of animals, and are

transmissible to humans through contaminated food, drink or

fomites, resulting in diarrhea, fever and abdominal pain that

last for 1-2 weeks or, in some cases, months. Most are self-

limited.

Y. enterocoliticainfection can cause pseudoappendicitis

(enlarged mesenteric lymph nodes) in children, and blood-

transfusion related sepsis in those who used blood products

stored for at least 4 weeks.


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Y. enterocoliticagrows slowly at 37 oC and prefers

cooler temperatures. The fecal specimen can be mixed

with saline and then store at 4 oC for 2 weeks or more

to facilitate isolation of this organism (cold enrichment).


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How doesProteusswarm?


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Lipopolysaccharide (LPS)

is also called endotoxin.

LPS is composed of lipid A,

core polysaccharide, and O-

specific polysaccharide.

Lipid Aanchors LPS in the lipid

bilayer. It causes symptoms

associated with endotoxin.

O-specific polysaccharidecanbe used to identify certain

species and strains.

Enterobacteriaceae(M)

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