Published on March 10, 2014
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 Transportation Should 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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