SN2 SHORT NOTE 5M ★ High-yield

Describe Klebsiella and Proteus with their characteristics and clinical importance.

Microbiology · 2nd Professional — Para-Clinical

Klebsiella

Gram-negative bacilli that are non-motile and prominently capsulated, producing large, dome-shaped, mucoid colonies that string out when touched with a loop
Lactose fermenter — pink colonies on MacConkey; IMViC ––++ (indole and methyl red negative, Voges-Proskauer and citrate positive), the mirror image of E. Coli
K. Pneumoniae — causes friedlander pneumonia, a severe necrotising upper-lobe pneumonia with thick "redcurrant jelly" sputum, abscess formation and a bulging fissure, classically in alcoholics and diabetics; also urinary infection, wound infection, bacteraemia and, importantly, hospital-acquired infection including ventilator-associated pneumonia
Hypervirulent (hypermucoviscous) strains cause pyogenic liver abscess with metastatic spread to eye and brain, including in previously healthy people
K. Pneumoniae is a leading producer of ESBL and carbapenemases (including NDM-1, first described from an Indian isolate), and is among the most important multidrug-resistant hospital pathogens in India
Other species — K. Rhinoscleromatis causes rhinoscleroma, a chronic granulomatous nasal disease seen in India; K. Ozaenae causes atrophic rhinitis with a foul odour

Proteus

Gram-negative bacilli, actively motile, non-lactose fermenting
Swarming — spreads in successive concentric waves over the whole surface of a blood agar plate, overgrowing other organisms; prevented by adding increased agar concentration, chloral hydrate, or by using MacConkey agar, on which bile salts inhibit swarming
Characteristic fishy or "burnt chocolate" odour
Strongly urease positive — the crucial property
Phenylalanine deaminase positive; H2S producing
WEIL-FELIX reaction — certain non-motile Proteus strains (OX-19, OX-2, OX-K) share antigens with rickettsiae, so patient serum agglutinates them; a cheap but non-specific test for rickettsial infection including scrub typhus, still used in resource-limited settings in India
Diseases — urinary tract infection (especially catheter-related and complicated), wound and burn infection, bacteraemia

CLINICAL PEARL

Urease is why Proteus makes stones, and the stones are why the infection cannot be cured with antibiotics alone. Urease splits urea into ammonia, making the urine alkaline, which precipitates magnesium ammonium phosphate to form staghorn (struvite) calculi. Organisms then live within the stone where no drug reaches them, so the infection relapses indefinitely until the stone is removed. The same enzyme explains why an alkaline urine with recurrent infection should prompt imaging.

Other Enterobacteriaceae

Organism	Features
Enterobacter	Motile lactose fermenter; important in hospital infection; carries inducible AmpC beta-lactamase, so it may appear sensitive to cephalosporins in vitro and then fail in vivo as resistance is induced during treatment
Serratia marcescens	Produces a red pigment (prodigiosin); causes hospital-acquired infection, and is notably resistant
Citrobacter	Late lactose fermenter; neonatal meningitis with brain abscess
Morganella, Providencia	Urease positive; urinary and hospital infection
Yersinia enterocolitica	Grows at 4°C (cold enrichment); causes mesenteric adenitis mimicking appendicitis ("pseudo-appendicitis"), and terminal ileitis

Applied Aspects

Suspect Klebsiella in a severe necrotising pneumonia in a diabetic or alcoholic, particularly with an upper-lobe cavity and thick blood-stained sputum
Image the urinary tract in Proteus infection, and look for stones; eradication requires their removal, and antibiotics alone will not succeed
Suspect a struvite stone when the urine is persistently alkaline with recurrent infection by a urease-producing organism
Remove or change the catheter in catheter-associated infection; biofilm on the device sustains the organism regardless of the antibiotic
Do not report a swarming Proteus as a pure growth without care; it overgrows and may conceal a second, more significant pathogen on the plate
Multidrug-resistant Klebsiella is a major problem in Indian intensive care units, and its control depends on hand hygiene, device care and stewardship rather than on newer antibiotics, of which there are few

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