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Chapter: Modern Medical Toxicology: Food Poisons: Food Poisoning

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Salmonella - Microbial Food Poisoning

Salmonella species are motile gram-negative rods, and grow both aerobically and anaerobically at an optimum temperature of 37°C (range 7 to 48°C), and at a pH between 4 and 8.

Salmonella

·              Salmonella species are motile gram-negative rods, and grow both aerobically and anaerobically at an optimum temperature of 37°C (range 7 to 48°C), and at a pH between 4 and 8. They are readily killed by heat (71.7°C for 15 seconds) and acid, but are resistant to both freezing and drying, especially in the presence of proteins.

·              Food poisoning (Salmonella enterocolitis) can be caused by all salmonellae except S. typhi which causes typhoid or enteric fever. Commonest species involved include S. typhimurium, S. enteritidis, S. hadar, S. heidelberg, S. agona, S. arizonae, S. chameleon, S. java, S. javiana, S. marinum, S. oranienburg, S. muenchen, S. paratyphi B, S. virchow, S. indiana, and S. anatum.

Source

·              Eggs: Even unbroken, unsoiled eggs can be contaminated. Eating such eggs raw or undercooked can result in infection

o     Food products containing raw eggs are also capable of producing the illness—hollandaise sauce, eggnog, chocolate mousse, raw egg-based milk shakes, Caesar salads, and home-made ice cream.

o     It is recommended that eggs should be consumed within 3 weeks after being laid, and must be stored at temperatures below 8° C after purchase. milk poses a real risk of being infected with salmonel- losis. Even pasteurised milk may not be 100% protective. Outbreaks of salmonella infections may be associated with multiple drug-resistant strains.

·              Salmonella has also been detected in various sesame seed products, including sesame paste and halvah (a mixture of sesame seed paste and acidified heated glucose syrup).

·              Household pets: Chicks, turtles, iguanas, and other reptiles are known to harbour salmonellae, and can transmit the micro-organisms to household contacts. Cats may be faecal carriers of Salmonella without displaying clinical signs. The incidence ranges from 1 to 18% of cats.

Toxin

·      Enterotoxin.

·      Penetration of intestinal wall and multiplication by the bacilli. 

Incubation Period

·              About 12 to 36 hours, but can be as short as 3 hours.

Clinical Features

·              Vomiting, crampy abdominal pain, diarrhoea. Stools are loose, slimy, foul-smelling, and greenish in colour. They often turn blood-stained. These symptoms may be absent in children, who may present only with abdominal pain and nausea, which could be confused with acute appendicitis.

·              Fever.

·              Headache, malaise, myalgia.

·              Toxic megacolon and intussusception have been reported with Salmonella typhimurium.

·              Focal nephritis has been reported in some cases.

·              The illness usually subsides in 2 to 4 days, but occasion- ally becomes prolonged and dysentery-like, with passage of mucus and pus in the stools.

·              The carrier state is more common among females and elderly patients, and it may persist for months to years.

·              The gall bladder is the usual focus of infection in the carrier state.

·              Complications:

o     Meningitis

o     Septicaemia

o     Reiter’s syndrome**

o     Death.

Diagnosis

·      Isolation of Salmonella by

o  Analysis of suspect food item

o  Culture of stool and blood.

·      Check WBC for leucocytosis or leukopenia.

Treatment

■■   Patients with significant toxicity, dehydration, electrolyte disturbances, or a history of poor compliance should be admitted for IV fluid therapy, and occasional antibiotic therapy.

■■   As far as possible, antibiotic treatment must be resorted to only in the following cases: bacteraemia, AIDS patients, elderly, infants, and individuals with sickle cell disease. The antibiotic of choice is chloramphenicol. Fluoroquinolones, ampicillin, ceftriaxone, and trimethoprim-sulfamethoxazole are also effective.

■■Supportive measures.


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