Salmonella

As described in the original article, Salmonella is a food-borne disease that occurs frequently in the United States and is reported to be the second common illness worldwide. About one to three hundred persons per populations of 100,000 are affected. In 1996 alone about 39.027 cases were reported in the United States. The incidence of Salmonella is dependent upon several factors such as , geographic, socioeconomic, demographic, meteorological and environmental.

The bacteria that cause this illness was discovered by Dr. Daniel Salmon more than 100 years ago and identified it as S. typhimurium with the use of a compound binocular microscope. But one S. enteritidis, identified using a compound binocular microscope, emerged in 1980’s which caused a widespread contamination of raw eggs. Still in the 1990’s, another type, S. typhimurium, was identified as type (DT)104 which appeared in the United Kingdom, Western Europe and in the United States. As mentioned in the original article. a strain of the same type was discovered to contain large plasmids enabling them to be antibiotic-resistant to Ampicillin, Chloramphenicol, Streptomycin, Sulphonamides, Tetracycline, Trimethoprim and Cirpofloxacin.

Classification
The genus salmonella has one species within it designated as Salmonella choleraesuis. It is further divided into five subspecies with the use of a microscope such as a compound binocular microscope as S. enterica, S. salamae, S. arizonae, S. diarizonae, S. houtenae and S. bongori.

According to their antigenic formula, species and subspecies are analyzed and classified with the use of microscopes such as a compound binocular microscope or an electron microscope. Their strains, as described by the original article, are classified into serogroups and serovars. The former is based on diffences in epitopes of lipopolysaccharide (LPS). It is further classified into serovars based on variations of flagellins, the sub-unit proteins of flagella that can be identified with the use of high-powered microscopes. A range of phenotypic and genotypic methods are used to subdivided strains of individual serovars, they are : biotyping, phage typing, antibiotic susceptibility testing or resisotyping, restrictions endonuclease analysis, rebotyping. IS200 typing, pulsed field gel electrophoresis plasmid profiling, and fingerprinting.

Salmonella, as described by the original article, may be grouped into three classification according to their adaptations to human and animal hosts:

Group 1 – S. typhi and S. paratyphi; causes entric fever only in human and higher primates
Group 2 – S. dublin causes diseases in cattle, S. choleraesuis in pigs and in sometimes humans often can be life-threatening.
Group 3 – S. enteridis and S. typhimurium, transmitted from animals to humans and causes mild gastroenteritis but often severe in the young, elderly, and patients with weak resistance to infection.
Salmonella enteritideis (SE) is a serovar belonging to subspecies S. enterica that ferments carbohydrates and produces acid and gas. The means of transmission to humans is through eggs and chicken. It is characterized by producing enterotoxin and cytotoxin that inhibits protein synthesis in intestinal epithelial cells and damages intestinal membranes. This bacterium is viewable with the use of compound binocular microscopes.

Salmonella tyhimurim is found in the environment together with S. enteritidis and is the overwhelming cause of zoonotic salmonellosis in most countries. To combat this disease in animals antimicrobial therapy is usually used. But even with antimicrobial drugs, a strain has evolved resistance to antibiotics that makes infection of animal foods difficult to control as in S. typimurium DT 104 which infected cattle in 1988 in England and Wales.

Infection of this disease in humans is through eating contaminated food of animal origin and sometimes by direct contact with infected cattle.

Salmonellosis is acquired mainly by consumption of raw or undercooked infected food such as meat, eggs, and milk. Symptoms of the disease are fever, abdominal pains, diarrhea, nausea and vomiting. In the elderly or the young children, dehydrations can be severe where incidence is up to 60% in confirmed cases and a 3 percent death rate has been reported.

Pathogenesis of Salmonella
Ingestion of a dose of a bacterium starts the infection. The bacterium will then colonize the gastrointestinal tract and attack the body’s defenses. A high or low dose of infection depends on several factors like virulence, physiological state of the pathogen, life stage and immunity of the host, and food matrix.

Pathogenesis is affected by the virulence factors and the number and type of the strains of salmonella. Life stage of the host refers to the immune system and gastric acidity of the host. Food matrix refers to the type of food (could either be high in fat or protein) that can offer protection against the organism.