salmonella. general ch. inhabitant of human and animal intestine. gram-negative bacilli, non...
Post on 16-Jan-2016
225 Views
Preview:
TRANSCRIPT
Salmonella
SalmonellaGeneral Ch.Inhabitant of human and animal intestine.
Gram-negative bacilli, non capsulated, motile, non spore forming.
Non lactose fermenter (NLF).
Produce H2S from ‘thiosulphate’.
Pathogenicity1- Enteric fever (Typhoid fever, Paratyphoid fever)
• (S. typhi, S. paratyphi A,B,C).
• No animal reservoir.
2- Food poisoning (Gastroenteritis)
• (S. typhimurium, S. enteretidis).
• Zoonotic infection (animal).
• No systemic infection.
3- Septicemia
• S. cholerasuis.
Enteric fever
Salmonella: >1000 species acc. to diff. Ag (Somatic, flagellar, virulence)
-O (Somatic or cell wall
antigen).
-H (flagellar antigen).
-Vi (polysaccharide
virulence).
Laboratory Diagnosis of
Enteric Fever
I. Diagnosis of A case of Enteric Fever
A) Isolation of the organism
1- Sample:
• Blood (1st week).
• Stool (2nd ,3rd week).
• Urine (3rd week)
a. From blood:• Blood culture or clot culture
b. Culture of faeces:
• In at least 50% of the cases culture of faeces is
positive in first week.
• The isolation of S. typhi greatly increases in the
second or third week.
c. Urine culture:
• Urine culture is positive in one third of
cases, and in great majority of cases, it will
be free from organisms, before the faeces
becomes negative.
2. Direct film stained by Gram:
• Gram-negative bacilli.
• motile.
• non capsulated.
• non sporulated.
a) Culture characters
O2facultative anaerobe
CO2
Temp37°C
3. Culture:
b) Media Selective
Enrichment
Indicator
nutrient agar
• Selenite broth
• tetrathionate
Mackonkey, DCA
SS, HE, XLD
b) Culture media
• On nutrient agar: Grow as smooth
colonies, 2-4 mm in diameter.
• Maximal recovery of salmonella is obtained
by using enrichment broth medium as
selenite or tetrathionate broth.
• Selective media: for Salmonella are SS
agar, Hekton enteric (HE) medium, and
xylose-lysine-deoxycholate (XLD) agar,
which contain selective ingredients.
• Indicator media: On MacConkey and DCA
media: they produce pale colonies (NLF).
Salmonella- XLD media
Salmonella- SS media
4.Identification of growth
Morphology
BR
Slide aggl
Molecular
4. Identification of the obtained colonies by:
1. Film stained by Gram:
2. Biochemical reactions:
• Ferment glucose, mannitol, and maltose with
acid (S. typhi) and A+gas (S. paratyphi) .
• Lactose and sucrose is not fermented .
• H2S produced from thiosulfate.
3. Slide agglutination: • using ‘O’ and ‘H’ antisera against salmonellae.
4. Molecular:
B)_ Serodiagnosis:
Widal test ( tube agglutination test):
Use:
Widal test is an agglutination test for detection of antibodies
against Salmonella typhi and Salmonella paratyphi, the
common causal agents of enteric fevers.
Principle:
• When serum sample containing antibodies against
S.typhi and S.paratyphi A, B or C are mixed with
respective antigens, agglutination will take place.
• In S.typhi and S.paratyphi two types of antigens are
recognized as diagnostically important:
• ‘O’ antigen “Somatic” antigen.
• ‘H’ antigen “Flagellar” antigen.
• O antigens of various species have components in common
and hence only one O antigen i.e. non species specific.
• H antigens of Salmonella spp. are species specific, and
hence the H antigens of all S.typhi, S.paratyphi A and
S.paratyphi B and S.paratyphi C are employed in the test.
• Serum antibodies against H and O antigens of salmonella
usually appear by the 7th-10th day of infection and the
titer reaches maximum during the 4th week.
Method• Five sets of agglutination tubes are prepared.
• To each set, a different H suspension of the salmonella,
i.e. H suspension of S. typhi, H suspension of S.
paratyphi A, H of S. paratyphi B, H of S. paratyphi C and
one set for O suspension of any species because it is a
common antigen.
• Serial dilutions of patient’s serum (1/10, 1/20, 1/40, 1/80
…..) are made in each set of tubes.
Interpretation:
• The endemicity of the disease in the area. In Egypt,
titers below 1/80 are of no significance. They are
due to previous subclinical infection.
• Agglutination of O suspension indicates recent
infection.• The O suspension will not be agglutinated if vaccination
was done a long time ago.
• Recently vaccinated individuals possess
agglutinins to S. typhi and S. paratyphi.
Agglutination will occur with more than
one suspension.
•
False –ve:
• If the test was done during the first week, it
gives false negative results as the antibodies
start to appear during the second week.
• If the patient received antibiotic treatment
early in the disease, the antibody titer will be
suppressed.
• False +ve: Non-enteric infections may cause a non-
specific rise on antibody titer; however, the titer is
low and falls rapidly on recovery (anamnestic
reaction).
• For proper interpretations of the Widal test, two
serum samples separated by 10 days interval should
be tested. The detection of a rising titer in the second
serum sample indicates active enteric infection.
Percautions:
1-endemicity2-antibiotics
3-vaccinations4-anamnestic reaction
5-time
Tube agglutination ‘Widal test’
O Ab H Ab ‘typhi’
H Ab ‘paratyphi
A’
H Ab ‘paratyphi
B’
H Ab ‘paratyphi
C’
Result
+ + - - - S. Typhi inf.
+ - + - - S. P.typ. A inf.
+ - - + - S. P.typ. B inf.
+ - - - + S. P.typ. C inf.
+ + + + + Recent vaccine
- + + + + Old vaccine
+ve widal S paratyphi B
+ve widal old vaccination
II. Diagnosis of Typhoid Carrier
- 5% of cured- Asymptomatic transmission.- Difficult treatment.
• In order to label a person as a typhoid carrier, the
isolation of the organism should be done from
urine or faeces.
• If these are repeatedly negative, bile or duodenal
aspirate can be used.
• Vi antibodies present in a titre of more than 1:10 is
also suggestive of chronic typhoid carrier.
Thank you
top related