Klebsiella pneumoniae- Lab Diagnosis, Treatment, Prevention

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Klebsiella pneumoniae is a gram-negative rod-shaped bacterium that can cause various infections, such as pneumonia, urinary tract infections, septicemia, and wound infections. It is often associated with hospital-acquired infections and antibiotic resistance. To diagnose Klebsiella pneumoniae infection, different types of specimens may be collected depending on the site and nature of the infection. These include:

  • Sputum: This is the most common specimen for diagnosing pneumonia caused by Klebsiella pneumoniae. Sputum is the mucus that is coughed up from the lungs. It may contain bacteria, blood, pus, or other materials.
  • Blood: This is used to detect bacteremia or septicemia, which are serious conditions where bacteria enter the bloodstream and cause systemic infection. Blood samples are usually drawn from a vein using a sterile needle and syringe.
  • Urine: This is used to diagnose urinary tract infections (UTIs) caused by Klebsiella pneumoniae. Urine samples are usually obtained by midstream collection, which means that the first and last portions of urine are discarded and only the middle portion is collected in a sterile container.
  • Wound swabs: These are used to identify the bacteria that cause wound infections. Wound swabs are sterile cotton-tipped applicators that are gently rubbed over the infected area and then placed in a transport medium.

The specimens are then sent to a microbiology laboratory for analysis. The laboratory diagnosis of Klebsiella pneumoniae involves two main steps: culture and identification.

Culture

Culture is the process of growing bacteria in artificial media under controlled conditions. The purpose of culture is to isolate and identify the causative agent of infection. The specimens are inoculated onto different types of agar plates and incubated at 37°C for 18 to 24 hours. The most commonly used agar plates for Klebsiella pneumoniae are:

  • Blood agar: This is a nutrient-rich medium that contains 5% sheep blood. It allows the growth of most bacteria and shows their hemolytic activity, which is the ability to break down red blood cells. Klebsiella pneumoniae usually produces non-hemolytic (gamma-hemolytic) colonies on blood agar, which means that they do not change the color of the medium around them.
  • MacConkey agar: This is a selective and differential medium that inhibits the growth of gram-positive bacteria and distinguishes between lactose-fermenting and non-lactose-fermenting gram-negative bacteria. Lactose-fermenting bacteria produce acid from lactose, which lowers the pH of the medium and turns it pink. Non-lactose-fermenting bacteria do not change the color of the medium. Klebsiella pneumoniae is a lactose-fermenting bacterium that produces mucoid (slimy) pink colonies on MacConkey agar.

Identification

Identification is the process of confirming the identity of the isolated bacterium by performing various biochemical tests and reactions. The purpose of identification is to determine the species and strain of the bacterium and its susceptibility to antibiotics. Some of the tests and reactions used for identifying Klebsiella pneumoniae are:

  • Gram stain: This is a differential staining technique that divides bacteria into two groups based on their cell wall structure: gram-positive (purple) and gram-negative (pink). Klebsiella pneumoniae is a gram-negative bacterium that appears as rod-shaped cells in pairs or short chains under the microscope.
  • Capsule stain: This is a special staining technique that detects the presence of a capsule, which is a polysaccharide layer that surrounds some bacteria and protects them from phagocytosis and desiccation. Klebsiella pneumoniae has a prominent capsule that appears as a clear halo around the cells when stained with India ink or crystal violet.
  • Indole test: This is a biochemical test that detects the ability of bacteria to produce indole, which is a breakdown product of tryptophan. Indole production is indicated by a red color change when Kovac`s reagent is added to the culture broth. Klebsiella pneumoniae is indole-negative, which means that it does not produce indole.
  • Methyl red test: This is a biochemical test that detects the ability of bacteria to produce mixed acids from glucose fermentation. Acid production is indicated by a red color change when methyl red indicator is added to the culture broth. Klebsiella pneumoniae is methyl red-negative, which means that it does not produce enough acid to lower the pH below 4.4.
  • Voges-Proskauer test: This is a biochemical test that detects the ability of bacteria to produce acetoin, which is an intermediate product of glucose fermentation. Acetoin production is indicated by a red color change when Barritt`s reagent A and B are added to the culture broth. Klebsiella pneumoniae is Voges-Proskauer-positive, which means that it produces acetoin.
  • Citrate test: This is a biochemical test that detects the ability of bacteria to use citrate as their sole carbon source. Citrate utilization is indicated by a blue color change when bromothymol blue indicator is added to Simmons citrate agar. Klebsiella pneumoniae is citrate-positive, which means that it can use citrate as its sole carbon source.
  • Urease test: This is a biochemical test that detects the ability of bacteria to produce urease, which is an enzyme that hydrolyzes urea into ammonia and carbon dioxide. Urease production is indicated by a pink color change when phenol red indicator is added to urea broth or agar. Klebsiella pneumoniae is urease-positive, which means that it produces urease.

These tests and reactions can be performed individually or in combination using commercial kits such as API 20E or Enterotube II.

The laboratory diagnosis of Klebsiella pneumoniae infection helps in guiding appropriate treatment and prevention strategies for patients and health care workers.