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Salmonella Infection – Pathogenesis, Symptoms, Transmission, Prophylaxis And Treatment

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Salmonella Infection

Genus Salmonella belongs to the family Enterobacteriaceae, together with Escherichia coli. Are gram-negative, motile, aerobic or facultative anaerobic bacilli, meaning that they can develop in the absence of oxygen.

Are bacteria that are isolated from soil, water, plants, human and animal intestine. Are part of the body’s normal flora, some species of Salmonella having exclusively human habitat (Salmonella typhi). In terms of pathogenicity, bacteria of the genus Salmonella are highly pathogenic and conditioned pathogenic.

Genus Salmonella germs are resistant in the environment. Salmonella can survive about 5-6 months in polluted water and faeces, survives and multiply at room temperature in wet environments, in food and infusion solutions. The possibility of spreading in the community and in hospitals is very high. Salmonella is destroyed by heat (in 30 minutes at temperatures of 55-60º  Celsius degrees and instantly at boiling temperature), antiseptics and disinfectants.

Salmonella Infection

Salmonella Infection

With modern methods of molecular taxonomy in the Salmonella genus two species are described:

  • Salmonella enterica, with 6 subspecies: enterica, salamae, arizonae, diarizonae, houtenae and indica;
  • Salmonella bongori.

99.5% of Salmonella strains, involved in human pathology are belonging to Salmonella enterica species.

On the basis of somatic O antigen (antigen-specific group), were described several serological groups, denoted with large letters of the alphabet, from humans being isolated strains belong mainly to A-E groups. H antigen allows individualization in the same group (Salmonella enterica) of the serotypes: Salmonella typhy (the etiologic agent of typhoid fever), Salmonella typhimurium and Salmonella enteritidis.

Pathogenesis and symptoms:

All serotypes of Salmonella enterica are pathogenic to humans and mammals, while serotypes of Salmonella bongori are typically found in birds and cold-blooded animals.

The two major sources of infection, human and animal, are responsible for pollution of soil and water, in which Salmonella can live for a long time.

Germs of the genus Salmonella are highly pathogenic bacteria. The entrance gateway is represented by the digestive tract (small intestine epithelium) that all species of Salmonella can penetrate it.

Salmonella Infection Pathogenesis

Salmonella Infection Pathogenesis

Three clinical types of salmonellosis have been described in humans:

Enteric fevers or systemic salmonellosis (typhoid fever and paratyphoid fever), are caused by Salmonella typhi (typhoid fever) and Salmonella paratyphi A, B and C (paratyphoid fever). Are clinical entities distinct from other salmonellosis, with characteristic clinical development and followed by lasting immunity. Contamination is made orally, by eating infected food or by drinking infected water. After an incubation period of about 14 days, the disese begins with lethargy, malaise, fever and generalized pain (during the first week). Constipation is a rule along this period. In the second week the microorganism is back into circulation (bacteremia) and will cause high fever, sensitive stomach and possibly pink macules on the abdominal skin. Diarrhea occurs at the end of the second week or at the beginning of the third week.

The disease is self-limiting, but severe complications are possible (intestinal perforation, severe bleeding due to disseminated intravascular clotting, thrombophlebitis, cholecystitis, cardio-vascular disorders, pneumonia, abscesses).

Enteric salmonellosis are food poisoning (acute gastroenteritis) and represent the common form, widespread in all countries. They are caused most frequently by Salmonella enteritidis and Salmonella typhimurium. Symptoms appear in 10-24 hours after eating contaminated food or drinking contaminated water. Characteristic symptoms are diarrhea, abdominal pain, vomiting, fever, which disappear within 2-4 days.

Enteric salmonellosis in infants, elderly or immunosuppressed may be complicated by bacteremia with secondary localization in the meninges, joints, bone, with a mortality rate of 10-20%.

Bacteremia, with or without the existence of enteritis outbreaks, is caused by Salmonella typhimurium, Salmonella paratyphi A and B and by Salmonella choleraesuis. Mainly affect two age groups. In young children is manifested by fever and gastroenteritis, and in adults is manifested by transient bacteremia during episodes of gastroenteritis, or signs of sepsis without gastroenteritis (in the immunosuppressed).

Chronic carriers, asymptomatic are represented by a rate of 1-5% of patients with typhoid fever or paratyphoid fever. The germs are located in the gallbladder and are excreted continuously or intermittently through feces. This porting condition can be stopped by antibiotics or cholecystectomy.

Salmonella Food Poisoning

Salmonella Food Poisoning

Transmission and prophylaxis:

Enteric fevers may evolve endemo-epidemic. Source of infection is represented by patients or carriers, and transmission occurs through fecal-oral mechanism, by consuming water or, less commonly, by contaminated food. Responsiveness is general and is conditioned by the absence of specific immunity.

Food poisoning are often produced by animal pathogens that are transmitted to humans through contaminated food (eggs, meat, milk, mayonnaise, pate), from chickens, turkeys, ducks. It was noted that tools such as knives, bowls, wood chippers, used in the preparation of contaminated food can contribute to the spread of germs on other foods. It is considered that the dose of bacterial contamination is 1.000.000 bacteria or less. The incidence of these infections is higher in summer months.

Salmonella infections are prevented by adequate sanitation and especially by immunization of domestic animals kept for meat consumption. Meat control  in slaughterhouses and proper thermal preparation of food are designed to reduce the risk of infection.

Indiscriminate use of antibiotics to promote animal breeding should be avoided to prevent emergence of resistant strains of Salmonella. Healthy carrier detection is important, but does not replace  the local igena measures.

Specific prophylaxis by anti-typhoid vaccine is recommended for people who work in the sectors of water supply or in slaughterhouses, and those traveling to endemic areas, or population to natural calamities areas (earthquakes, floods).

Anti-Thyroid Vaccine

Anti-Thyroid Vaccine


The enteric fevers in forms with sepsis and enteric salmonellosis in infants and young adults, are treated by using antibiotics with intracellular action: ampicillin, cotrimoxazole, chloramphenicol, ciprofloxacin, fluoroquinolones, third generation cephalosporins.

Food poisoning are treated symptomatically. Antibiotic treatment does not shorten the clinical manifestations and, moreover, extend the porting state.