Skip to main content

Microbiology

Culture

This section will cover the use of culture techniques in parasitology, focusing on Trichomonas vaginalis and Strongyloides stercoralis as key examples. Culture involves growing parasites in a controlled environment to increase their numbers for identification and study

Culture in Parasitology: An Overview

  • What is Culture?: Culture involves growing parasites in a controlled laboratory environment to increase their numbers, making them easier to identify and study
  • Why Culture?
    • Increased Sensitivity: Culture can be more sensitive than direct microscopic examination, especially when parasite numbers are low
    • Identification: Culture can aid in the identification of parasites that are difficult to identify microscopically
    • Research: Culture is essential for research on parasite biology, drug susceptibility, and vaccine development
  • Limitations of Culture
    • Time-Consuming: Culture can take days or weeks to yield results
    • Technical Expertise: Culture requires specialized equipment and technical expertise
    • Contamination: Cultures are susceptible to contamination by bacteria, fungi, or other organisms
    • Not Available for All Parasites: Culture methods are not available for all parasites

Trichomonas vaginalis Culture

  • Etiology: Trichomonas vaginalis is a flagellated protozoan parasite that infects the urogenital tract, causing trichomoniasis (a sexually transmitted infection)
  • Culture Methods
    • Modified Diamond’s Medium: A commonly used liquid medium for Trichomonas vaginalis culture
    • TYM (Trypticase Yeast Maltose) Medium: Another liquid medium used for Trichomonas vaginalis culture
    • InPouch TV Culture System: A commercially available self-contained culture system for Trichomonas vaginalis
  • Procedure
    • Specimen Collection: Collect vaginal or urethral swabs or urine samples
    • Inoculation: Inoculate the culture medium with the specimen
    • Incubation: Incubate the culture at 35-37°C for 2-7 days
    • Microscopic Examination: Examine the culture daily for the presence of motile Trichomonas vaginalis trophozoites
  • Advantages of Culture
    • High Sensitivity: Culture is more sensitive than wet mount microscopy for detecting Trichomonas vaginalis
    • Detection of Low-Level Infections: Culture can detect low-level infections that may be missed by other methods
  • Disadvantages of Culture
    • Time-Consuming: Culture takes several days to yield results
    • Technical Expertise: Culture requires specialized equipment and technical expertise
  • Alternative Methods: Nucleic acid amplification tests (NAATs) are increasingly used for Trichomonas vaginalis detection due to their high sensitivity and rapid turnaround time

Strongyloides stercoralis Culture

  • Etiology: Strongyloides stercoralis is a nematode that infects the small intestine, causing strongyloidiasis
  • Culture Methods
    • Agar Plate Culture: A commonly used method for Strongyloides stercoralis culture
    • Harada-Mori Filter Paper Culture: A simple and inexpensive method for Strongyloides stercoralis culture
  • Procedure (Agar Plate Culture)
    • Specimen Collection: Collect stool samples
    • Inoculation: Inoculate a nutrient agar plate with the stool sample
    • Incubation: Incubate the plate at room temperature (25-30°C) for 1-7 days
    • Microscopic Examination: Examine the plate daily for the presence of Strongyloides stercoralis larvae
  • Procedure (Harada-Mori Filter Paper Culture)
    • Specimen Collection: Collect stool samples
    • Preparation: Place a strip of filter paper in a test tube containing water, leaving one end of the filter paper above the water level
    • Inoculation: Apply the stool sample to the filter paper
    • Incubation: Incubate the tube at room temperature (25-30°C) for 1-7 days
    • Microscopic Examination: Examine the water at the bottom of the tube for the presence of Strongyloides stercoralis larvae
  • Advantages of Culture
    • Increased Sensitivity: Culture is more sensitive than direct microscopic examination for detecting Strongyloides stercoralis larvae
    • Detection of Low-Level Infections: Culture can detect low-level infections that may be missed by other methods
  • Disadvantages of Culture
    • Time-Consuming: Culture takes several days to yield results
    • Risk of Contamination: Cultures are susceptible to contamination by bacteria, fungi, or other organisms
  • Alternative Methods: Molecular methods are being developed for Strongyloides stercoralis detection, but culture remains a valuable tool in many laboratories

Key Takeaways

  • Culture Enhances Detection: Culture can increase the sensitivity of parasite detection, especially when parasite numbers are low
  • Specialized Techniques Required: Culture requires specialized equipment and technical expertise
  • Culture is Not Always Necessary: Other methods, such as microscopy, antigen detection, and molecular detection, may be more appropriate in some cases
  • Quality Control is Essential: Implementing quality control measures to ensure the accuracy and reliability of results

Key Terms

  • Culture: The process of growing microorganisms in a controlled laboratory environment
  • Medium: A liquid or solid substance used to support the growth of microorganisms
  • Inoculation: The process of introducing microorganisms into a culture medium
  • Incubation: The process of maintaining a culture at a specific temperature and humidity to promote growth
  • Trophozoite: The active, feeding, and motile stage of a protozoan parasite
  • Larva: The immature form of helminths
  • Contamination: The presence of unwanted microorganisms in a culture
  • Sensitivity: The ability of a test to detect true positives
  • Specificity: The ability of a test to detect true negatives
  • Nucleic Acid Amplification Test (NAAT): A technique that amplifies DNA or RNA