Description: Salmonella - Salmonella species are gra

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salmonella

• Description Salmonella - Salmonella species are
  gram negative, aerobic, rod-shaped, zoonotic
  bacteria that can infect people, birds, reptiles,
  and other animals. This genus includes
  approximately 2000 species divided into five
  subgenera..

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Morphology

• Salmonella spp are gram negative bacilli, motile
  by peritrichous flagella, non-spore forming, non
  capsulated

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Clinically salmonella spp can be divided in two
distinct categories 1- Typhoidal species
include S.typhi and S.paratyphi.2- Non-typhoidal
species are the many strains of S. entritidis,
S.cholerasuis
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Culture charactersalmonella spp grow on
macConkey agar, they are lactose ferment negative
so it produce small circular translucent,
colorless, pallid colonies, they are aerobic or
facultative an aerobic, they produce H2S from
sulfur containing amino acids this features are
used in the laboratory identification.
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Type of antigens1- cell wall(O) which are the
outer polysaccharide of the cell wall, are used
to sub divide the Salmonella in to groups
A-I.2-H antigen Flagellae there are two forms
phase 1 and phase 23- Vi antigen(Cpsular poly
Saccharide)are antiphagocyte and are an important
virulence factor of S.typhi and used for the
serotyping of S.typhi in the clinical
laboratories.
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The typhoid bacillus
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PathogenesisThe cell wall of salmonella contain
lipopolysaccharide which upon lysis of bacteria
acts as endotoxin.There are three general
categories of infection.1-GastroenteritidisIs
characterized b an invasion of the epithelial and
sub epithelial tissue of the small and large
intestine strains that do not invade do not cause
disease. The organisms penetrate both through and
between the mucosal cells in to the lamina
propria with resulting inflammation and diarrhea.
Apoly morphonuclear leucocyte response limits the
infection to the gut. S.typhimurium,
S.enteritidis most commonly associated with
salmonella gastrointestinal
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2- Enteric fever typhoid fever(typhoid)Is
characterized by prolonged fever and multisystem
involvment including lymph nodes, liver, spleen
and gall bladder. This life threating infection
is most frequntly caused by S.typhi or S.
paratyphi strain. 3- SepticemiaBacteremia and
extraintestinal infection occur by spread from
gastrointestinal tract is occur in 5-10 of
salmonella infection these infection usually
involve S.cholerasius, Sdublin
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Salmonella spp Triple sugar iron agar TSI
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Salmonella spp on S.S agar
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Family Enterobacteriaceae.GenusShigella
.SppSh.dysenteriae, Sh.flexneri, sh.sonnei
Shigella. spp cause enterocolitis (bacillary
dysentery).MorphologyShigella are gram
negative, rods, non lactose ferment, non motile,
non flagellate, non capsulated.Culture
characterShigella are facultative anaerobic but
grow best aerobically it give convex, circular,
transparent colonies with intact edge.
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All shigella have O antigen poly saccchride in
their cell wall and these antigens are used to
divided the genus into four gropes A, B,C and
D.The shigella differ from the
Enterobacteriaceae in that they are exclusively
parasite of human intestine and cause bacillary
dysentery .PathogenesisShigella are the most
effective pathogene among the enteric
bacteria.they have a very low infection dose that
mean ingestion of a few as 100 organisms causes
disease. Shigellosis is only a human disease
the organisms is transmitted by the fecal-oral
route.
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there is no prolong carrier state with shigella
infection unlike that see with S typhi infection
.Shigella which cause disease almost exclusively
in the gastrointestinal tract, produce bloody
diarrhea (Dysentery) by invading the cell of the
mucosa of the distal ileum and colon, local
inflammation accompanied by ulceration occur, but
the organisms rarely penetrate through the wall
or enter the blood stream un like Salmonella.
Some strain produce an enterotoxin (Shigatoxin )
invasion is the critical factor in pathogenesis
toxin inhibit the protein synthesis.
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Lab diagnosis1-Gram stain.2-Direct examination
of fresh stool or rectal swab that stain with
methylen blue to determine whether neutrophils
are present.3- MacConkey agar.4-S.S.A.
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Shigella spp Salmonella spp Test
K/A - - K/A - T.S.I
- Indol
MR
- - VP
_ Citrate
_ Motility
_ - Urease
- - Lactose
Low High Infectious dose