Enterobacter Nosocomial infections

8/6/2019 Enterobacter Nosocomial infections

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Dr.T.V.Rao MD

ENTEROBACTERAN EMERGING NOSOCOMIAL PATHOGEN

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Enterobacteris a genus of common

Gram-negative, facultatively-

anaerobic, rod-shaped bacteria

of the family Enterobacteriaceae.

Several strains of the these

bacteria are pathogenic andcause opportunistic infections in

immunocompromised (usually

hospitalized) hosts and in those

who are on mechanical

ventilation. The urinary andrespiratory tract are the most

common sites of infection. It is

also a fecal coliform, along with

Escherichia.

ENTEROBACTER LEADING CAUSE OF

OPPORTUNISTIC INFECTIONS

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Enterobacteris a gram-

negative bacillus that

belongs to the

Enterobacteriaceae family.

Other members of thisfamily include Klebsiella,

Escherichia, Citrobacter,

Serratia, Salmonella, and

Shigella species, amongmany others.

ENTEROBACTER IS A

ENTEROBACTERIACEAE

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BACKGROUND OF ENTEROBACTER SPECIES

Enterobacterspecies, particularly Enterobacter cloacae

and Enterobacter aerogenes, are important nosocomial

pathogens responsible for various infections, including

bacteremia, lower respiratory tract infections, skin andsoft-tissue infections, urinary tract infections (UTIs),

endocarditis, intra-abdominal infections, septic arthritis,

osteomyelitis, and ophthalmic infections. Enterobacter

species can also cause various community-acquiredinfections, including UTIs, skin and soft-tissue

infections, and wound infections, among others

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OTHER SPECIES OF

ENTEROBACTER

The most commonly isolated species includeE cloacae and E aerogenes, followed by E sakazakii(recently reclassified into theAchromobactergenus, which produces a characteristic yellow pigment.Other species rarely encountered in the laboratoryinclude Enterobacter asburiae, Enterobacter gergoviae,Enterobacter taylorae, Enterobacter hormaechei, andEnterobacter cancerogenus. Enterobacter agglomerans

has been removed from the genus Enterobacterandrenamed Pantoea agglomerans.

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Enterobacter

aerogenesis a

Gram-negative,

oxidase negative,

catalase positive,

citrate positive,

indole negative, rod-shaped bacterium.

ENTEROBACTER AEROGENES -

CHARACTERISTICS

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E. aerogenes is part of

the flora found in the

human intestines. As an

opportunistic pathogenit may infect immuno-

compromised patients

in the urinary and

respiratory tracts. Itrarely infects healthy

people

ENTEROBACTER AEROGENES IS PART OF

NORMAL FLORA CAN BE INFECTIVE

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E. aerogenesis a nosocomial

and pathogenic bacterium that

causes opportunistic infections

including most types of

infections. Enterobacterspecies

can also cause various

community-acquired infections.

Some strains can become very

treatment resistant, a result of

their colonization within hospital

environments. However, themajority are sensitive to most

antibiotics designed for this

bacteria class.

ENTEROBACTER AEROGENESIMPORTANT

NOSOCOMIAL PATHOGEN

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Some of the infections caused by

E. aerogenesresult from

specific antibiotic treatments,

venous catheter insertions,

and/or surgical procedures. E.

aerogenes is generally found in

the human gastrointestinal tract

and does not generally cause

disease in healthy individuals. It

has been found to live in various

wastes, hygienic chemicals, andsoil.

SOURCE OF ENTEROBACTER

INFECTIONS

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Although community-acquired

Enterobacterinfections are

occasionally reported,

nosocomial Enterobacter

infections are, by far, mostcommon. Patients most

susceptible to Enterobacter

infections are those who stay

in the hospital, especially the

ICU, for prolongedperiods

PROLONGED STAY IN HOSPITAL PREDISPOSES TO

ENTEROBACTER INFECTIONS

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Other major risk factors ofEnterobacterinfection includeprior use of antimicrobial agents,concomitant malignancy(especially hemopoietic and

solid-organ malignancies),hepatobiliary disease, ulcers ofthe upper gastrointestinal tract,use of foreign devices such asintravenous catheters, andserious underlying conditions

such as burns, mechanicalventilation, andimmunosuppression.

OTHER PREDISPOSING FACTORS

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The source of infection

may be endogenous

(via colonization of the

skin, gastrointestinaltract, or urinary tract) or

exogenous, resulting

from the ubiquitous

nature ofEnterobacterspecies

ENDOGENOUS SOURCE

MAJOR SOURCE OF INFECTION

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These bacteria have an

outer membrane that

contains, among other

things, lipopolysaccharides

from which lipid-A plays amajor role in sepsis. Lipid-

A, also known as

endotoxin, is the major

stimulus for the release ofcytokines, which are the

mediators of systemic

inflammation and its

complications.

PATHOPHYSIOLOGY

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Multiple reports have

incriminated the hands of

personnel, endoscopes, blood

products, devices for monitoring

intra-arterial pressure, and

stethoscopes as sources of

infection. Outbreaks have been

traced to various common

sources: total parenteral nutrition

solutions, isotonic saline

solutions, albumin, digitalthermometers, and dialysis

equipment.

IMPORTANT OTHER SOURCES

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Enterobacterspecies contain a

subpopulation of organisms that

produce a beta-lactamase atlow-levels. Once exposed to

broad-spectrum cephalosporins,

the subpopulation of beta-

lactamaseproducing organisms

predominate. Thus, an

Enterobacterinfection that

appears sensitive to

cephalosporins at diagnosis mayquickly develop into a resistant

infection during therapy

ENTEROBACTER PRODUCE BETA

LACTAMASES

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The most important test to

document Enterobacter

infections is culture. Direct

Gram staining of the

specimen is also veryuseful because it allows

rapid diagnosis of an

infection caused by gram-

negative bacilli and helps inthe selection of antibiotics

with known activity against

most of these bacteria

MICROBIOLOGICAL STUDIES

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MICROSCOPY AND CULTURING HELPS IN

DIAGNOSIS

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Grown on eosin

methylene blue

(EMB) agar. EMBagar contains the

indicator dyes

eosin andmethylene blue.

AS GROWN ON EOSIN METHYLENE BLUE

MEDIUM

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Oxoid has introduced

Oxoid Chromogenic

Enterobacter sakazakii

Agar (Druggan-Forsythe-Iversen (DFI)

formulation) that allows

recovery and detection

ofE. sakazakiiin just 3days 2 days faster

than by conventional

methods

FASTER DETECTION WITH OXOID CHROMOGENIC

ENTEROBACTER SAKAZAKII AGAR (DRUGGAN-FORSYTHE-

IVERSEN (DFI) FORMULATION

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This innovative new

chromogenic medium

contains the substrate 5-

bromo-4-chloro-3-indolyl-,

D-glucopyranoside which iscleaved by the enzyme -

glucosidase, expressed by

E. sakazakii, to form easily

distinguishable blue-greencolonies.

OXOID CHROMOGENIC ENTEROBACTER

SAKAZAKII AGAR

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Merck's new ChromoCultEnterobacter sakazakii Agar willincrease the security in detectingthis microorganism in milk powderand infant formula.

Based on the alpha-D-Glucosidase -

an enzyme specific forE. sakazakii-only the colonies ofE. sakazakiiappear turquoise while otherbacteria grow colourless.ChromoCult Enterobactersakazakii Agar allows a fast andreliable detection within only 24hours with no further confirmationstep.

MERCK'S NEW CHROMOGENIC MEDIUM FOR

DETECTION OF ENTEROBACTER SAKAZAKII

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Two sets (with one aerobic and

one anaerobic bottle in each set)

should be obtained 20-30

minutes apart, from 2 different

sites (if possible). If the patient

has a central venous catheter,one set should be drawn through

it. In the adult patient, 8-10 mL of

blood should be collected in each

bottle. Enterobacteriaceae

ferment glucose and should thusgrow in both bottles.

BLOOD CULTURE FOR IDENTIFICATION

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Penicillin's should include

ampicillin and at least one

of the extended-spectrum

penicillin's (eg, carboxy,

ureido, oracylaminopenicillin) such

as ticarcillin, mezlocillin, or

piperacillin. The addition of

ticarcillin-clavulanic acid orpiperacillin-tazobactam is

optional.

DRUGS TO INCLUDE FOR ANTIMICROBIAL

SUSCEPTIBILITY TESTING

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CHOOSING A RIGHT ANTIBIOTIC

Cephalosporins include a first-generation drug of this class of

antibiotics, such as cefazolin, and a third-generation drug with

and without Pseudomonas activity, such as ceftriaxone or

ceftazidime.

Include at least one carbapenem, usually imipenem, or inaccordance with available pharmaceutical agents in the

institution.Include the aminoglycosides, usually gentamicin and

tobramycin.

Amikacin may be tested primarily or when bacteria showresistance to these 2 drugs. Include a quinolone, such as

ciprofloxacin.Include TMP-SMZ.Some laboratories routinely add

aztreonam.

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Hyper production (stable DE

repression) of AmpC beta-

lactamases associated with

some decrease in permeability to

the carbapenems may also

cause resistance to theseagents. In vitro low-level

ertapenem resistance was not

associated with resistance to

imipenem or meropenem, but

high-level ertapenem resistancepredicted resistance to the other

carbapenems

CARBAPENEMS TOO ARE BECOMINGRESISTANT

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Colistin and polymyxin B: These

drugs are being used more

frequently to treat serious

infection caused by multidrug-

resistant organisms, sometimes

as monotherapy or incombination with other

antibiotics. Clinical experience,

including documentation of

success rates and attributable

mortality is broadening

COLISTIN AND POLYMYXIN B ARE GAINING

IMPORTANCE IN TREATMENTS

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The fourth-generation

cephalosporins are

relatively stable to the

action of AmpC beta-

lactamases; consequently,they retain moderate

activity against the mutant

strains ofEnterobacter,

hyper producing AmpCbeta-lactamase

4 TH GENERATION CEPHALOSPORINS ARE A

CHOICE

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Other antibiotics that

may be considered

for testing include

tigecycline,polymyxin B, and

colistin, the latter two

when particularlyresistant organisms

are identified

OTHER NEW GENERATION OF ANTIBIOTICS

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Enterobacter sakazakiihas been reported as a cause of

sepsis and meningitis,

complicated by ventriculitis, brain

abscess, cerebral infarction, and

cyst formation.[ This clinical

pattern appears to be specific to

E sakazakiiin neonates and

infants infected with this

bacterium. E sakazakiihas also

been associated with manyoutbreaks due to contaminated

powdered formula for infants

Enterobacter sakazakii

ENTEROBACTER SAKAZAKII

A IMPORTANT SPECIES

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The bacteria designated by the acronym

SERMOR-PROVENF (SER = Serratia,MOR = Morganella, PROV = Providencia,

EN = Enterobacter, F = freundii for

Citrobacter freundii) have similar,

although not identical, chromosomal

beta-lactamase genes that are inducible.With Enterobacter, the expression of the

geneAmpCis repressed, but

derepression can be induced by beta-

lactams. Of these inducible bacteria,

mutants with constitutive hyperproduction

of beta-lactamases can emerge at a rate

between 105 and 108. These mutants are

highly resistant to most beta-lactam

antibiotics and are considered stably

derepressed.

SERMOR-PROVENF

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The National Healthcare

Safety Network (NHSN)

reported on healthcare-

associated infections (HAI)

between 2006 and 2007.They found Enterobacter

species to be the eighth

most common cause of HAI

(5% of all infections) andthe fourth most common

gram-negative cause of

HAIs.[

THE NATIONAL HEALTHCARE SAFETY NETWORK

(NHSN) REPORTS ON ENTEROBACTER

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HAND WASHING STILL REDUCES SPREAD OF

ENTEROBACTER IN THE HOSPITAL ENVIRONMENT

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Enterobacter Nosocomial infections