SALMONELLA SPECIES

(Salmonella species) Mode of transmission,mechanisms by which microorganisms cause disease and diagnosis

                                           one of symptoms of salmonella                  

 Define Salmonella 

A Gram negative rod. Its an enterobactericiae.

 List the species of Salmonella 

·         Salmonella typhi

·         Salmonella paratyphi A

·         Salmonella paratyphi B

·         Salmonella paratyphi C

·         Salmonella typhimurium

 Mention the species of medical importance

·         Salmonella typhi

·         Salmonella paratyphi A

·         Salmonella paratyphi B

·         Salmonella paratyphi C

·         Salmonella typhimurium

Describe the normal habitat

• Most salmonellae are found in the intestines of animals especially of pigs, cows, goats, sheep, rodents, hens, ducks and other poultry.
• Salmonella typhi and paratyphi are usually found only in humans. Also are excreted in the faeces and urine of infected patients and are present in the gall bladders of long-term carriers.

Describe the morphology Salmonella 

• Salmonellae are gram negative rods.
• All salmonellae are actively motile.
• Non-capsulated
• Non-sporing.

Describe the mode of transmission and pathogenicity of Salmonella species

TRANSMISSION

•  Infection is by ingesting the organisms in contaminated food or water or from contaminated hands.
• Salmonella typhi is spread mainly by water and salmonella paratyphi A and B by food.
• In schistosomiasis endemic areas there is a high incidence of chronic Salmonella typhi and Salmonella paratyphi A infections and carriers. The salmonellae adhere to adult schistosome flukes.

PATHOGENICITY-

Salmonella typhi causes:

1.      Typhoid (enteric) fever.

• The bacteria pass from the small intestine into the blood by way of the lymphatic system. The reticuloendothelial system becomes infected and also the gall bladder and kidneys. From the gall bladder, the organisms invade the intestine causing inflammation and ulceration.
• Symptoms of infection include fever with low pulsate, headache, toxaemia, and enlargement of the spleen and a path or mental confusion.
• Epistasis, intestinal haemorrhage and perforation may also occur.
• In uncomplicated typhoid the total white cell count is low with a relative lymphocytosis. There may also be anaemia.

2.      Neurotyphoid is those with urinary schistosomiasis. The condition is an immune complex disorder of the kidneys and is characterized by fever, oedema, marked albuminuria and haematuria.

3.      Osteomyelitis (inflammation of the bone marrow), especially in children with sickle cell disease and Thallassaemia.

-       Typhoid nodules can be found in the bone marrow.

-       Inflammation of the joints (typhoid arthritis) may also occur.

4.      Abscesses of the spleen and elsewhere

5.      Meningitis and rarely pneumonia and endocarditis.

 Explain the antigens of Salmonella 

Salmonellae are based on identifying the O (somatic) and H (flagella) antigen by the different serovars.

• O. Antigens: these are cell wall, heat – stable antigens. Their O antigens group salmonellae.
• H antigens: These are flagella, heat – labile antigens. Their H antigens serotype salmonellae
• Vi Antigens

Step 9: Describe the laboratory diagnosis Salmonella (30 minutes)

1.SPECIMENS

·         For the diagnosis of enteric fever, specimens include blood, faeces and urine for culture.

2.CULTURE CHARACTERISTICS

They are aerobes and facultative anaerobes.They grow between 15-45⁰c with  optimal temperature of 37⁰c.

Culture on various enrichment and selective media.The media include:-

• Selenite F
• XLD agar
• DCA
• SS agar
• Blood agar(sub culture)

Salmonellae produce non-lactose fermenting colonies

(i)XLD AGAR(xylose Lysine Deoxycholate)

Hydrogen sulphide gas is produced and colonies are pink-red,3-5 mm in diameter with black centre.

(ii)DCA AGAR(Deoxycholate Citrate Agar)

Pale colonies are seen(NLF).The colonies are small with black centre and are non-late Non Lactose Fermentor(Non-lactose fermentor).

3.BIOCHEMICAL TESTS

·         The differentiation of suspect’s salmonella colonies using motility indole urea (MIU) media and kligler iron agar (KIA) or the API2 screening test are used.

·         KIA culture salmonellae and Shigellae produce a pink – red slope and yellow butt indicating the fermentation of glucose but not lactose. Much salmonella also produce blackening due to hydrogen sulphide production and cracks in the medium due to gas production from glucose fermentation.

·         MIU medium salmonellae are motile so show the turbidity throughout the medium.

·         Urease is negative

·         Indole is negative

·         Lactose is negative.

·         Motility is positive

·         Citrate is positive

·         Methyl red is positive

·         Voskuer voges is negative

4.SEROLOGY:

• Salmonellae are based on identifying the O (somatic) and H (flagella) antigen by the different serovars.
• O. Antigens: these are cell wall, heat – stable antigens. Their O antigens group salmonellae.
• H antigens: These are flagella, heat – labile antigens. Their H antigens serotype salmonellae.

5.WIDAL TEST:

• The patient’s serum is tested for O and H antibodies against antigen suspension (usually stained suspensions). Salmonella typhi 09,12 and Salmonella typhi H suspension.
• It is reported by giving the titre for both O and H antibodies. The antibody titre is taken as the highest dilution of serum in which agglutination occurs.
• If no agglutination occurs the test should reported as:

·         Salmonella typhi) titre less than 1cm 20

·         Salmonella typhi H titre less 1 in 20.

• In typhoid endemic areas in developing countries, active typhoid is suggested if the titres of H or O or both agglutinins are significantly raised (i.e. titres greater than 1 in 180 or 1 in 200 depending on the titres found in local healthily people.)
• Causes of raised O or H titre other than active typhoid:
• Chronic salmonellosis associated with schistosomal infection.
• Vaccination with TAB or typhoid vaccine
• Infection with other salmonella species
• Chronic liver disease
• Immunological disorders such as rheumatoid arthritis, rheumatic fever, multiplemyeloma, neuphrotic syndrome and ulcerative colitis.

SUMMARY OF BIOCHEMICAL TESTS REACTION

I-indole=  -VE

M-methyred= +VE

V-voges prousker= -VE

C-Citrate= +VE

U-urease= -VE

4.PREVENTION

• Seek medical treatment
• Hygiene
• Isolation of the infected
• Screening before admission
• Proper cooking and storage of food

Key Points 

Define Escherichia

A Gram negative rod in the Genus enterobactericiae

 List the species of Shigella

• Shigella dysenteriae-sero group A
• Shigella flexineri-sero group B
• Shigella boydii-sero group C
• Shigella sonnei-sero group D

BIOCHEMICAL TESTS

FOR  Shigella:-Perform Biochemical tests to identify the organisms

Perform the following tests for Shigella:-

• Lactose –ve                

• H₂s –ve                                               
• Oxidase –ve
• Citrate –ve
• TSI-R(slope)/Y(butt) ,No gas, No H₂s

• MR +ve
• Nitrate reductase      +ve
• indole     -/+ve(varies)
• Urease –ve

Evaluation 

• List 3 species of Shigella
• Mention 3 Biochemical tests
• Mention the appearance of colonies on blood Agar and Macconkey

Salmonella  paratyphi A and B

• These salmonellae cause paratyphoid (enteric) fever.
• The disease is generally milder than typhoid with s. paratyphoid A and B being less invasive than Salmonella typhi.
• There is usually diarrhoea and vomiting and the entire intestinal tract may be flamed especially in Salmonella paratyphoid B infections.
• Paratyphoid is more commonly caused by Salmonella paratyphi A than Salmonella paratyphi B.

Salmonella  paratyphi C.

• This serovar causes mainly septicaemia, complications of Salmonella paratyphi C. infections include the formation of abscesses, arthritis and inflammation of the gall bladder.

Other salmonellae

• Several thousands salmonella serovars are capable of causing food – poisoning (enterocolitis)
• Symptoms of salmonella food – poisoning occur within 10 – 30 hours of ingesting the contaminated food.
• Food – poisoning strains can also cause bacteraemia, inflammation of the gall bladder, osteitis (inflammation of bone) especially in children with sickle cell disease and occasionally abscesses.

Laboratory diagnosis:

• Specimens: For the diagnosis of enteric fever, specimens include blood, faeces and urine for culture.
• Blood: Organisms can usually be detected in 75 – 90% of patients during the first ten days of infection and in about 30% of patients during the third week.
• Faeces: Organism can be isolated from 40 – 50% of patients during the second week of infection and from about 80% of patients during the third week.
• For the diagnosis of salmonella food – poisoning, faeces are required for culture and blood during times of fever.
• Pus or joint fluid is required for culture if an abscess or arthritis is suspected.

Culture on various enrichment and selective media e.g. Selenite F, XLD agar, DCA and SS agar.

Salmonellae produce non-lactose fermenting:

• Biochemical reactions:
• The differentiation of suspect’s salmonella colonies using motility indole urea (MIU) media and kliglar iron agar (KIA) or the API2 screening test are used.
• KIA culture salmonellae and Shigellae produce a pink – red slope and yellow butt indicating the fermentation of glucose but not lactose. Much salmonella also produce blackening due to hydrogen sulphide production and cracks in the medium due to gas production from glucose fermentation.
• MIU medium salmonellae are motile so show the turbidity throughout the medium.

Serology:

• Salmonellae are based on identifying the O (somatic) and H (flagella) antigen by the different serovars.
• O. Antigens: these are cell wall, heat – stable antigens. Their O antigens group salmonellae.
• H antigens: These are flagella, heat – labile antigens. Their H antigens serotype salmonellae.

Widal Test:

• The patient’s serum is tested for O and H antibodies against antigen suspension (usually stained suspensions). Salmonella typhi 09,12 and Salmonella typhi H suspension.
• It is reported by giving the titre for both O and H antibodies. The antibody titre is taken as the highest dilution of serum in which agglutination occurs.
• If no agglutination occurs the test should reported as:

·         Salmonella typhi) titre less than 1cm 20

·         Salmonella typhi H titre less 1 in 20.

• In typhoid endemic areas in developing countries, active typhoid is suggested if the titres of H or O or both agglutinins are significantly raised (i.e. titres greater than 1 in 180 or 1 in 200 depending on the titres found in local healthily people.)
• Causes of raised O or H titre other than active typhoid:
• Chronic salmonellosis associated with schistosomal infection.
• Vaccination with TAB or typhoid vaccine
• Infection with other salmonella species
• Chronic liver disease
• Immunological disorders such as rheumatoid arthritis, rheumatic fever, multiplemyeloma, neuphrotic syndrome and ulcerative colitis.

Prevention and Control:

• Eliminating the source of infection, particularly by control of carriers.
• Preventing the spread if infection by public health measures e.g. milk, hygienic preparation of food.
• When sanitary control of the environment is difficult, active immunization with typhoid vaccine.

REFERENCES

·         Ivan M. Roitt & Peter J.Delves ROITTS ESSENTIAL IMMUNOLOGY, 10th Edition, (2004) Replika press  Pvt.ltd ,india

·         Monica Cheesbrough – MEDICAL LABORATORY MANUAL FOR TROPICAl Countries, part 2, Edition (2003) Cambridge University press,international sales department.

·         Monica Cheesbrough – MEDICAL LABORATORY MANUAL FOR TROPICAL COUNTRIES, volume 2, Microbiology, Edition (1984) Cambridge University press.

·         Warren Levinson. MD,PHD– Medical Microbiology & Immunology edition (2004) Mc Graw –HillCompanies

·         Satish Gupte THE SHORT TEXT BOOK FOR MEDICAL MICROBIOLOGY(including parasitology) 10th Edition, (2004) Replika press  Pvt.ltd ,india