Escherichia, Proteus and Klebsiella MCQs

Sorbitol Mac Conkey agar is used to differentiate EHEC from other E.coli. It does not ferment sorbitol and produces pale colonies. Reference : Ananthnarayan and Paniker's textbook of Microbiology 12 th edition pg no.482

Proteus spp. are motile by peritrichous flagella. Clostridium perfringens is the only clostridium species that produces a capsule in animal tissues and it is non-motile. Corynebacterium diphtheriae and Bacillus anthracis are non-motile. Arrangement - example Monotrichous - V.cholerae Lophotrichous - Psuedomonas fluorescens Amphitrichous - Alcaligenes faecalis Amphilophotrichous - Spirillium minus Peritrichous - Salmonella typhi Referece: Ananthanarayan and Paniker's Textbook of Microbiology 12th edition, Pg 21

Explanation: The "H" antigen in E. coli serotyping refers to the flagellar antigen, which determines the motility of the bacteria. O157:H7 is a strain of Enterohemorrhagic E. coli (EHEC) known for producing Shiga toxin, leading to hemorrhagic colitis and Hemolytic Uremic Syndrome (HUS). Serotyping of E. coli: "O" antigen → Somatic (LPS) antigen (Option D) "H" antigen → Flagellar antigen (Option C) "K" antigen → Capsular antigen (Option A) Fimbriae (Option B) aid in bacterial adhesion , but they are not part of E. coli serotyping as the "H" antigen.

Enterohemorrhagic E.Coli commonly produces Shiga like toxin or verocytotoxin, which is the most common cause of HUS in the world. Its mechanism of action is similar to Shiga toxin ie, inhibition of protein synthesis by inhibiting 28s subunit of ribosomes. ETEC, which causes traveller's diarrhea produces Labile toxin,which increases cAMP and Stable toxin, which increases cGMP and causes watery diarrhea DAEC also causes watery diarrhea and shows slow adhesion on Hep-2 cell assay UPEC is implicated in E.coli associated UTI. Reference: Essentials of Medical Microbiology, by Apurba Sastry and Sandhya Bhat, 3rd edition, page 400.

Bacterial urease alkalises urine, and urease-producing bacteria are implicated in the development of infection-induced urinary stones. The formation of struvite stones occurs when urine pH increases and ammonia production increases, decreasing the solubility of phosphate. Proteus spp., M. morganii and Klebsiella pneumoniae are urea-splitting bacteria E.coli is the most common cause of lower urinary tract infections, it is not associated with significant alkalinisation, nor is infection with Pseudomonas aeruginosa. The production of excessive amounts of ammonia by bacterial urease, and its subsequent re-absorption into the systemic circulation, can result in hyperammonaemia, a condition associated with hepatic encephalopathy. Reference : Ananthanarayan and Paniker's Textbook of Microbiology 12th edition pg 33

Proteus species are part of the colonic flora P. mirabilis causes 90% of Proteus infections, which occur in the community, LTCFs, and hospitals. By contrast, Proteus vulgaris and Proteus penneri are associated primarily with infections acquired in hospitals. Adhesins, flagella, IgA protease, and urease representing the principal known urovirulence factors. Clinical spectrum of Proteus infections: Urinary tract infections (most common) Pneumonia Nosocomial sinusitis Intra abdominal abscesses Biliary tract infection Surgical site infection Soft tissue infection (especially decubitus and diabetic ulcers) Osteomyelitis Bacteremia Reference : Harrison's Principles of Internal Medicine, 21 st Ed, Ch: 161 Pg: 1278