Batterjee Medical College. Dr. Manal El Said Ass. Professor of of Medical Microbiology Gram-Negative Rods Enterobacteriaceae

Batterjee Medical College


Dr. Manal El SaidDr. Manal El Said Ass . Professor of of Medical Microbiology

Gram-Negative RodsEnterobacteriaceae


Characters of Enterobacteriaceae

• All Enterobacteriaciae - Gram-negative rods

- Ferment glucose with acid production

- Reduce nitrates into nitrites

- Oxidase negative


Enterobacteriaceae divided into TWO main groups according

to action on LACTOSE

Lactose Non-Fermenters (LNF)

Characters of Enterobacteriaceae

Lactose Fermenters (LF)

•E. coli

•Citrobacter

•Klbesiella

•Enterobacter

•Salmonella

•Shigella,

•Proteus,

•Yersinia


• Facultative gram-negative rods

• Ferment lactose.

Lactose fermenter:1-Escherichia coli

Diseases

Characteristics

`

• Urinary tract infection (UTI)

• Sepsis

• Neonatal meningitis

• Traveler's diarrhea


Habitat and Transmission

• Habitat is the human colon

• It colonizes the vagina and urethra ascends UTI

•Acquired during birth in neonatal meningitis

•Fecal–oral route in diarrhea.



Pathogenesis

• It causes septic shock.

• Two enterotoxins are produced.

1- Heat-labile toxin

2- Heat-stable toxin

1- Endotoxin


For attachment to mucosal surfaces

2- Pili


Pathogenesis3- Capsule

• It is enterotoxin produced by O157:H7 serotype E. coli

• It causes bloody diarrhea and hemolytic-uremic syndrome

associated with eating undercooked meat.

4-Verotoxin (Shiga-like toxin)

It impedes phagocytosis.



Pathogenesis

• Predisposing factors to UTI in women include:

- Proximity of the anus to the vagina & urethra

- Short urethra.

• Abnormalities e.g., strictures, valves & stones.

• In-dwelling urinary catheters UTI

• Intravenous lines sepsis

• Colonization of the vagina neonatal meningitis.



Laboratory Diagnosis

1-Gram-stained smear




• Lactose-fermenting colonies on Eosin Methylene Blue EMB

(Green) or MacConkey's agar.

Uninoculated plate



Laboratory Diagnosis• Triple Sugar Iron agar shows acid slant and acid butt with

gas but no H2S.• Biochemical reactions.• Type organism by O & H antigens by using antisera.



Treatment• Urinary tract infections:

Ampicillin or sulfonamides

• Meningitis and sepsis:

Third-generation cephalosporins

• Traveler's diarrhea:

- Rehydration

- Trimethoprim-sulfamethoxazole

Antibiotic resistance mediated by plasmid-encoded enzymes:

- β-lactamase

- Aminoglycoside-modifying enzymes.



Prevention

• Prevention of UTI :

Limit the frequency and duration of urinary catheterization.

• Prevention of sepsis :

Remove or switch sites of intravenous lines.

• Prevention of Traveler's diarrhea :

- Eating only cooked food and drinking boiled water.

- Prophylactic doxycycline.

• There is no vaccine.



• Facultative gram-negative rods

• Polysaccharide capsule

Lactose fermenter:2-Klebsiella pneumoniae

Diseases

Characteristics

`

• Pneumonia

• UTI

• Sepsis.


Habitat and Transmission

• Habitat is the human upper respiratory & enteric tracts.

• Organism is transmitted to the lungs by:

- Aspiration from upper respiratory tract

- Inhalation of respiratory droplets.

• It is transmitted to the urinary tract by ascending spread of

fecal flora.



Pathogenesis

• Endotoxin causes fever and shock associated with sepsis.

• Capsule : impedes phagocytosis.

• No exotoxin known.

• Chronic pulmonary disease predisposes to pneumonia

• Catheterization predisposes to UTI.




1-Gram-stained smear




2- Lactose-fermenting on MacConkey's agar

• Mucoid colonies (polysaccharide capsule)



Laboratory Diagnosis3- Differentiated from Enterobacter and Serratia by

biochemical reactions.



Treatment

• Cephalosporins alone or with aminoglycoside.

• Resistance is mediated by plasmid-encoded enzymes.


Prevention

• No vaccine or drug is available.

• Urinary & intravenous catheters should be removed .


•Enteric gram-negative rod similar to

K. pneumoniae. but they are motile

•They causes :

- Hospital-acquired pneumonia

- UTI

- Sepsis

•Highly antibiotic-resistant.

Lactose Fermenter:3-Enterobacter cloacae &Serratia marcescens


• Enteric gram-negative rod similar to E. coli except being

citrate positive.

• Found in faeces of humans and may be isolated from a

variety of clinical specimens.

• C. koseri occasionally causes neonatal meningitis.

Lactose fermenter:Citrobacter

Documents

Batterjee Medical College. Dr. Manal El Said Ass. Professor of of Medical Microbiology Gram-Negative Rods Enterobacteriaceae