Question

1. Give the general characteristics of organisms that belong to the family Enterobacteriaceae.

2. Discuss the antigens that are used in the identification of different serologic groups of the Enterobacteriaceae.

3. Discuss the clinical infections caused by Salmonella.

4. Discuss the clinical infections caused by Shigella.

5. Discuss the clinical infections caused by Yersinia enterocolitica.

Answer 1

1. Enterobacteriaceae members include E. coli, Eterobacter, Klebsiella, Citrobacter, Salmonella, Shigella, Yersinia enterocolitica and Proteus. They are gram negative and small rod shaped bacteria. They do not form spores and are facultatively anaerobic. The members are differentiated into lactose fermenters and nonlactose fermenters by using MacConkey Agar. Some of the members are motile with peritrichous flagella. Shigella and Klebsiella are nonmotile. They are catalase positive. Biochemically they are distinguished by Imvic tests.

2. The antigenc structures of Enterobacteria include outer membrane (O), Flagella (H), capsule (K) and capsule of Salmonella (Vi).

3. Salmonella enterica serovar typhi is the causal organism of typhoid fever. Salmonella enterica serovars cause the food borne gasteroenteritis. The Salmonella enterica serovars enteridis and typhimurium are common agents involved in causing food borne salmonellosis. Common Salmonellosis is enterocolitis. The colonization of small and large intestines by the organism is the resultant from infection. Onset of symptoms occurs with 8 – 48 hours of ingestion of contaminated food. Symptoms appear within 2 – 5 days. A few people remain as carriers. Sometimes pathogen enter in to blood causing septicemia and enteric or typhoid fever that results in high fever lasting several weeks.

4. Shigellosis is also known as bacillary dysentery, a severe form of diarrhea caused by gram negative bacillus Shigella. A virulent toxin called Shiga toxin is responsible to cause severe forms of diarrhea. The main symptoms are diarrhea abdominal cramps and fever. Antibiotics like fluoroquinolones are used in the therapy along with the oral rehydration therapy.

5. Yersinia enterocolitica causes profuse diarrhea and electrolyte imbalance. Yersinia contains lipopolysaccharide or O antigen causing the disease. The disease caused in various vertebrate hosts. Food born infection and contamination of water with the organism is main route of infection.