Gram Negative Bacilli
All are true about non typhoid salmonella except (AIIMS May11)
|A||Poultry is source|
|B||Can cause invasive disease in neonates|
|C||Blood culture is more sensitive than stool culture in gastroenteritis in adults|
|D||Resistance to FQ has emerged|
a. Salmonella is a genus of the family Enterobacteriaceae.
b. It is divided into 2 species: Salmonella enterica (subsp-enterica, salmae, arizonae, diarizonae, houtenae and indica) and Salmonella bongori. Members of the subspecies are serotyped into almost 3000 serotypes according to somatic (O), surface (Vi), and flagellar antigens.
c. Some salmonella serotypes such as S.Typhi and S.Paratyphi that cause enteric fever are highly adapted to humans and have no other known natural hosts. Hence infection occurs only by ingestion of food or water contaminated with human feces.
d. Other serotypes (also called nontyphoidal salmonella) are commensals or pathogens in wide spectrum of animals like reptiles, birds, and domestic animals. Some like S.Typhimurium have a wide host range while others like S.Dublin are restricted to cattle. All these serotypes are potentially pathogenic to humans and can cause gastroenteritis, septicemia with localized suppurative infections.
e. Salmonella gastroenteritis (GE) or food poisoning is generally a zoonoses, the source of infection being animal products. Most common serotypes implicated are S.Typhimurium and S. Cholerasuis.
f. The most frequent sources are poultry, meat, contaminated raw salads/ vegetables, unpasteurized milk and milk products. Salmonellae can enter egg shells if eggs are left on contaminated chicken feed or feces, and grow inside. Role of human carriers is minimal.
g. Following infection, Salmonella express an array of fimbriae that help to adhere tightly to intestinal mucosa following which there is an invasive enterocolitis. Within 6-48 hrs, disease manifests with diarrhea, vomiting, abdominal pain and fever that is usually self limited in 2-4 days. Bacteremia occurs occasionally in serotypes S.Cholerasuis and S.Dublin, though any serotype can cause it. From 1-4% of immunocompetent individuals with salmonella GE have positive blood cultures. Risk is greater in infants, elderly and immunocompromized.
h. Lab diagnosis depends on the isolation of salmonella from the feces by using selective media like xylose lysine deoxycholate agar or Hoektoen enteric agar or Salmonella shigella agar. In addition to plating the stool onto primary media, tetrathionate-based or selenite-based enrichment broths can be used to facilitate recovery of small numbers of organisms. Isolation of the causative organism form the article of food confirms the diagnosis.
i. Antimicrobial resistance among non-typhoidal salmonella isolates is increasing worldwide. Multidrug-resistant strains have also emerged conferring resistance to at least 5 antimicrobials- ampicillin, chloramphenicol, streptomycin, sulfonamides and tetracyclines. Quinolone-resistant strains have emerged due to intracellular mutations of intracellular targets DNA gyrase or topoisomerase IV or to overproduction of efflux pumps. Non-typhoidal Salmonella resistant to 3rd generation cephalosporins have also been reported.