This document provides an overview of Gram-negative rods, focusing on Shigella. It defines Gram-negative rods and divides them into categories. Shigella is described as a facultative, gram-negative rod that does not ferment lactose or produce gas from glucose. Shigella causes the disease shigellosis or dysentery, with symptoms of bloody diarrhea, fever, and abdominal cramps. Laboratory diagnosis involves gram staining, culturing on MacConkey agar to show non-lactose fermenting colonies, and testing on Triple Sugar Iron agar to show no gas production. Treatment is fluid replacement and antibiotics like ciprofloxacin or trimethoprim-sulfamethoxazole.

1. GRAM NEGATIVE RODS
LECTURE NINE
PART ONE
BY
DR . HUMAIRA AMAN ALI

2. 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.

3. 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.

4. ENTEROBACTERIACEAE
 They all share same four metabolic processes :
I. They all are facultative anaerobes
II. They all ferment glucose
III.They are oxidase negative
IV.They reduce nitrates to nitrites as part of their
energy generating processes.

5. SHIGELLA
 CHARACTERISTICS :
 Facultative gram negative rods
 Non-lactose fermenting
 Non – motile
 Donot produce gas from fermentation of glucose
 O antigens in their cell wall.

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

7. 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)

8. 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.

10. 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.

12.  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.

13. THANK
YOU