ENTEROBAKTER

Enterobacteriaceae Small Gram-negative rods Most motile with peritrichous flagella

• Shigella and Klebsiella are nonmotile Oxidase-negative facultative anaerobes Reduce nitrate Ferment glucose and other carbohydrates Many genera

• Escherichia, Salmonella, Shigella, Klebsiella, Proteus, Enterobacter, Yersinia, etc.

Some strains opportunistic pathogens Some strains true pathogens

• Salmonella, Shigella, Yersinia, some strains of E. coli

Enterobacteriaceae

Family Enterobacteriaceae often referred to as “enterics”

Four major features: All ferment glucose (dextrose) All reduce nitrates to nitrites All are oxidase negative All except Klebsiella, Shigella and Yersinia

are motile

Virulence and Antigenic Factors of

Enterobacteriaceae Ability to colonize, adhere, produce various toxins and invade tissues

Some possess plasmids that may mediate resistance to antibiotics

Many enterics possess antigens that can be used to identify groups O antigen – somatic, heat-stable antigen located

in the cell wall H antigen – flagellar, heat labile antigen K antigen – capsular, heat-labile antigen

Clinical Significance of Enterics

Enterics are ubiquitous in nature Except for few, most are present in the

intestinal tract of animals and humans as commensal flora; therefore, they are sometimes call “fecal coliforms”

Some live in water, soil and sewage

Clinical Significance of Enterics (cont’d)

Based on clinical infections produced, enterics are divided into two categories: Opportunistic pathogens – normally part

of the usual intestinal flora that may produce infection outside the intestine

Primary intestinal pathogens – Salmonella, Shigella, and Yersinia sp.

Gram-Positive Cell Wall

Gram-Negative Cell Wall

Antigenic Structure of EnterobacteriaceaeS. typhi

O antigen side chain

(Fimbriae)

Structure of Lipopolysaccharide

Structure of Lipid A

Hydrophobic Lipid A is endotoxic component

ENDOTOXIN

1. Integral part of cell wall

2. Endotoxin is LPS; Lipid A is toxic component

3. Heat stable

5. Toxoids cannot be produced

6. Many effects on host

7. Produced by gram-negative organisms only

EXOTOXIN

1. Released from the cell before or after lysis

2. Protein

3. Heat labile5. Toxoids can be produced

6. Specific in effect on host

7. Produced by gram-positive and gram-negative organisms

Diversity of Activities

Associated with LPS

Sites of Infections with Members of the

Enterobacteriaceae

Incidence of Enterobacteriaceae Associated with Bacteremia

Enterobacter species

Isolated from wounds, urine, blood and CSF

Major characteristics Colonies resemble Klebsiella Motile MR negative; VP positive

Enterobacter are gram-negative bacteria Found in the environment,on human skin,

and in our intestinal tract. many are harmless,several species are

opportunistic pathogens present in hospital settings.

The most common pathogenic species are E. cloacae and E. aerogenes

The urinary and respiratory tracts are the most common sites of enterobacter infection.

The lower respiratory tract, Urinary tract, Joint, Skin, Heart, Intra-abdomen, Soft tissue, Bone

Risk factor

Patients are most susceptible to enterobacter infections stay in the hospital, especially the ICU, for extended

periods. Patients under the age of 2 and over the age of 65 Prior use of antimicrobial agents. Underlying diseases. Ulcers of the upper gastrointestinal tract. Presence of intravenous catheters. Serious conditions such as burns or mechanical ventilation.

Immunosuppression.

spread through contact with the bacteria on patients, contaminated surfaces, and medical equipment

Enterobacter cloacae infections are seen commonly in burn victims, immunocompromised patients, and patients with malignancy

The urinary and pulmonary systems are the organ systems most commonly colonized in these patients.

Enterobacter sakazakii meningitis and death associated with powdered infant

formula

Clinical Characteristics• Pathogenic organism

– affinity for nervous system

• Complications serious – necrotizing enterocolitis

– sepsis– meningitis– cerebral abscesses, cysts or infarction

• Outcome poor– impaired neurologic outcome expected– fatality rate 40 - 80%

Lai KK. Medicine 2001;80:113-22

Case Description

Male patient admitted to neonatal intensive care unit (NICU) April 2001 gestational age 33.5 weeks, C-section delivery APGAR scores 4 and 7, birthweight 1,270

grams day 3: started on enteric feeding

powdered formulabreast milk

day 11: sepsis and neurologic symptoms

Case Description

Lumbar puncture consistent with meningitis white cells and red cells present, high protein,

low glucose cerebrospinal fluid culture grew E. sakazakii

Treated with ampicillin and cefotaxime Infant pulseless, resuscitated on pressors day 20: expired after withdrawal of support

due to severe neurologic disease

Laboratory Diagnosis of Enterics

Identification (cont’d) All enterics are

Oxidase negativeFerment glucoseReduce nitrates to nitrites

Laboratory Diagnosis of Enterics (cont’d)

Common Biochemical Tests Lactose fermentation and utilization of

carbohydrates Triple Sugar Iron (TSI) ONPG Glucose metabolism

Methyl redVoges-Proskauer

Laboratory Diagnosis of Enterics (cont’d)

Common Biochemical Tests (cont’d) Miscellaneous Reactions

IndoleCitrate utilizationUrease productionMotilityPhenylalanine deaminaseDecarboxylase tests

Enterobacter species