Gram negative rods

GRAM NEGATIVE RODS

LECTURE NINE

PART ONE

BY

DR . HUMAIRA AMAN ALI

OBJECTIVES

At the end of lecture student should :

Define and describe GRAM NEGATIVE RODS.

Know the various human pathogens of gram negative rods.

Understand etiology , pathogenicity , clinical features , laboratory diagnosis , treatment , and prevention of diseases cause by gram negative rods.

GRAM NEGATIVE RODS

L;arge group of diverse organisms . Subdivided into three clinically relevant

categories. Gram negative rods related to enteric ytact

divided again into thre groups. Pathogen within and outside the enteric tract Pathogen primarily within enteric tract Pathogen outside the enteric tract

Collectively called ENTEROBACTERIACEAE.

ENTEROBACTERIACEAE

They all share same four metabolic processes :

I. They all are facultative anaerobesII. They all ferment glucose III.They are oxidase negative IV.They reduce nitrates to nitrites as part of

their energy generating processes.

SHIGELLA CHARACTERISTICS :

Facultative gram negative rods Non-lactose fermenting Non – motile Donot produce gas from fermentation of

glucose O antigens in their cell wall.

PATHOGENESIS: Invades mucosa of the ileum and colon . Local inflammation accompanied by ulceration . Penetration and entrance in blood stream rarely.

DISEASE Shiegellosis: syn : Enterocolitis ,

bacillary dysentery.

Clinical findings: Dysentery( bloody diarrhea) Fever Abdominal cramps (are unpleasant, often

painful sensations caused by muscle contraction or overshortening)

LABORATORY DIAGNOSIS Gram stained smear Culture : non lactose fermenting ( colorless)

colonies on MacConkey agar(is a culture medium designed to grow Gram-negative bacteria and stain them for lactose fermentation.)

It contains bile salts (to inhibit most Gram-positive bacteria, except Enterococcus and some species of Staphylococcus i.e. Staphylococcus aureus), crystal violet dye (which also inhibits certain Gram-positive bacteria), neutral red dye (which stains microbes fermenting lactose), lactose and peptone.

On Triple Sugar Iron Agar: no gas.

TRIPLE SUGAR IRON

The Triple Sugar Iron or TSI test is a microbiological test roughly named for its ability to test microorganism's ability to ferment sugars and to produce hydrogen sulfide.[1] It is often used in the selective identification of enteric bacteria including but not limited to Salmonella and Shigella.

The TSI slant is a test tube that contains agar, a pH-sensitive dye (phenol red), 1% lactose, 1% sucrose, 0.1% glucose,[2] as well as sodium thiosulfate and ferrous sulfate or ferrous ammonium sulfate.

TREATMENT : Main treatment is fluid and electrolyte

replacement . Severe cases antibiotics shud be given . CIPROFLOXACIN TRIMETHORPRIM –SULFAMETHOXAZOLE .

PREVENTION: Proper sewrage disposal , chlorination of water ,

personal hygeine.

THANK YOU