SALMONELLA

PRAKASH DHAKAL

Public Health Microbiology

Tribhuvan University, Nepal

INTRODUCTION Salmon and Smith in 1885 isolated for first time Named after its discoverer Salmon Wide spread pathogens of animal including man

belonging to Enterobacteriaceae Found in the intestine of pigs ,cows ,goats ,

sheeps ,rodents ,hens , ducks and poultry S Typhi and S Paratyphi found only in humans Causes three types of diseases in human i.e

enteric fever, entercolitis and septicaemia Two species of Salmonella i.e S enterica and S

bongori. There are six subspecies of S enterica , i.e enterica ,

salamae , arizonae ,diarizonae , houtenae,indica No subspecies of S bongori

MORPHOLOGY

Gram negative rods with approximately size 2-4 X 0.6 µm

Non sporing, non capsulated, usually motile having peritrichous flagella execption S gallinarium, S pullorum

May posses fimbriae ( mannose sensitive, hemagglutinating )

Non acid fast

CULTURAL CHARACTERISTICS

Grow over a wide temperature range from 7-48 °C, optimum 37 °C at pH 4-8 and water activites 0.93

May be aerobic or facultatively anaerobic Many strains are protrophic ( capable of

growing on a glucose - ammonium minimal medium ) while some are auxotrophic ( require enrichment of some amino acids and/ or vitamins on minimal medium) , most Typhi strains require Tryptophan

Grows on ordinary culture media

In NA and BA, colonies are moderately larger ( 2-3 mm) ,grey white, moist,circular disc with smooth convex surface and entire edge

Colonies of Paratyphi A and Pullorum are relatively small

Paratyphi B gives large mucoid colonies In Peptone water and NB , most strains gives

abnormal growth with uniform turbidity . Thin pellicle forms on prolonged incubation

In MA colonies are pale yellow , 1-3 mm diameter, non lactose fermenting

Brilliant green MA : addition of brilliant green o.oo4 gm/ltr on MA.

inhibits E coli, Proteus and other commensal of intestine.

colonies appear low convex , pale green translucent , 1- 3 mm

In DCA, colonies are pale nearly colorless,shiny and translucent. Sometime may have a black center and sometime surrounded by a clear zone.

In XLD agar , H2S producing Salmonella produce pink red colonies , having size 3-5 mm in diameter with black center colonies . Salmonella that donot produce H2S , most strains of Salmonella Paratyphi A form pink red colonies without black center colonies.

In SS agar colonies are colorless, S Typhi gives black center colonies

In SM-ID agar colonies of both Typhi and Paratyphi gives red colonies

Enirchment media :Tetrathionate broth, Selenite F broth ,

Kauffman Muller Tetrathionate broth with brilliant green , Rappaports Malacthite green magnesium cholride broth

BIOCHEMICAL ACTIVITES

Lactose, Sucrose,Salicin or Adonitol non fermenter but Glucose,Maltose,Manitol, Arabinose,Dulcitol and Sorbitol fermenter.

Catalase +ve , Oxidase –ve Gas production: gas produced from glucose

fermentation but S Typhi donot produce gas. Indole –ve , MR +ve, VP –ve Citrate positive , but S Typhi and S Paratyphi

A negative H2S : S Typhi positive, S Paratyphi negative TSIA: Alk/A , gas, H2S –ve = S Paratyphi

Alk/A, H2S+ve = S Typhi

Lysine decaboxyolase: positve, S Paratyphi A –ve

ONPG : negative Gelatin liquefaction : negative Nitrate reduction test : positive KCN: capable to grow in KCN medium

EPIDEMIOLOGY

Salmonella are primarily intestinal parasites of humans and many animals including wild birds, domestic pets and rodents; they may be isolated from thier blood and internal organs

Found frequently in sewage, rivers and other waters and soil in which they do not multiply significantly

Under suitable conditions they may survive in waters and for years in soil

Have been isolated from many foods, vegetables and fruit and are important contaminants of animal protein –feed supplements

VIRULENCE FACTORS

Endotoxin ( O- Ag) Invasions Factors involved in reistance to phagocytosis

i.e catalase, superoxide dismutase, defensins Acid tolerance response (ATR) gene protect

organism from stomach acid Vi – antigen or virulence antigen

PATHOGENENSIS S Typhi, S Paratyphi A and S Paratyphi B are

of great clinical and public health significance

Many infections due to ingestion of contaminated food and also due to zoonotic and can be transferred between humans and non humans

Infection occurs almost due to oral route.

Small number of S Typhi can cause typhoid fever( ID= 10 bacilli ) while for paratyphoid it needs large dose

All virulent strains of Salmonella can survive gastric acidity and penetrate intestinal mucosa and submuocsa . Hence they are facultative intracellular pathogens that enter cells via macopinosomes

Only S Typhi is principally systemic invasive. These causes illness such as Typhoid fever,

Paratyphoid fever and food borne illness.

CLINICAL DISEASES

Enteric fever Septicaemia Gastroenteritis

Enteric fever : This includes both Typhphoid fever and

Paratyphoid fever caused by S Typhi and S Paratyphi.

Septicaemia It is commonly caused by S Choleraesuis and

S Paratyphi C. Infection occurs through oral route and incubation period is shorter.

Gastroenteritis This is caused by ingestion of contaminated

foods like milk, eggs, meat etc with Salmonella . S typhimurium is mostly isolated from food poisoning cases.Besides S enterididuis, S newport , S dublin may be involved.

LABORATORY DIAGNOSIS Specimens Blood : 1st ten days and during the 3rd weeks Faeces: during 2nd and 3rd week Urine : 2nd week Vomit : food poisoning In chronic Salmonellosis it may be bone marrow

rather than blood Microscopy Gm –ve rods, faecal specimens from patient with

typhoid usually contains macrophages and may contain blood in late stage infection

Food poisoning samples may contain few pus cells and red cells

Collection of sample Sterile, screw capped bottle

TransportationShould be processed as soon as possible, in case of

delay faeces should be transported in buffered Glycerol –Saline transport medium.

Faecal and rectal swab in Stuart’s transport media.

Culture

Biochemical reactions

Serology Perform Widal test

TREATMENT

Chloramphenicol Ampicillin or Trimethoprim Sulfamethoxazole Ciprofloxcin and Norfloxacin

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