Specimen Sources

This section specifically focuses on the analysis of specimens from skin, soft tissue, and bone

Sources

Wounds

• Types
  • Superficial Wounds: These involve the epidermis and potentially the dermis. Examples include abrasions, lacerations, and minor cuts
  • Deep Wounds: These penetrate deeper, often involving subcutaneous tissue, muscle, and sometimes even bone. Examples include surgical wounds, puncture wounds, and ulcers
  • Bite Wounds: These are a unique category, as they introduce bacteria from the animal’s oral flora, and can also cause trauma
• Collection Techniques
  • Swabs
    • Best for superficial wounds
    • Roll the swab over the wound surface, ensuring to collect exudate and any visible debris
    • Important Note: Swabs are often less ideal for deep wounds because they may not accurately represent the bacterial population within the deeper tissues
  • Aspiration
    • Preferred for abscesses and closed wounds
    • Use a needle and syringe to aspirate fluid from the wound. This provides a more representative sample
  • Tissue Biopsy
    • Most informative for deep wounds, ulcers, or those with suspected bone involvement
    • Requires a physician to obtain a tissue sample
    • Provides the best opportunity to identify the causative agent(s) and assess tissue involvement ### Abscesses {-}
• Definition: A localized collection of pus within tissue, often walled off by the body
• Collection Techniques
  • Aspiration: The gold standard. Aspirate the pus using a needle and syringe after proper site preparation and disinfection
  • Incision and Drainage (I&D): Involves making a small incision to drain the abscess. The drained pus can be collected for culture
  • Tissue Biopsy: Sometimes necessary if the abscess is deep or the cause is unclear ### Biopsies {-}
• Types
  • Skin Biopsies: Used to diagnose skin infections, such as cellulitis, necrotizing fasciitis, or fungal infections
  • Soft Tissue Biopsies: Used to evaluate deeper infections, such as those in muscle or fascia
  • Bone Biopsies: Critical for diagnosing bone infections (osteomyelitis)
• Collection Techniques
  • Punch Biopsy: A small, circular piece of tissue is removed
  • Excisional Biopsy: A larger section of tissue is removed
  • Incisional Biopsy: A portion of the tissue is removed
  • Bone Biopsy: Requires a sterile procedure, often involving a needle or surgical approach to obtain a bone sample. This is a critical specimen source for diagnosing osteomyelitis

Key Considerations

• Sterile Technique: The most important aspect. This is to avoid contamination of the specimen with organisms from the skin, the environment, or the collecting personnel. This includes:
  • Hand Hygiene: Thorough handwashing or using hand sanitizer before and after specimen collection
  • Site Preparation: Clean the collection site with an antiseptic solution (e.g., chlorhexidine or povidone-iodine) to reduce surface contamination
  • Sterile Equipment: Use sterile swabs, needles, syringes, and collection containers
  • Gloves: Wear sterile gloves during collection
• Proper Labeling
  • Patient Information: Patient name, medical record number, and date of birth
  • Specimen Source: Clearly indicate the source (e.g., wound, abscess, biopsy)
  • Collection Date and Time: Essential for tracking and interpretation
  • Collector’s Initials: To ensure accountability
• Volume and Type of Specimen
  • Sufficient Volume: Ensure you collect enough material for culture and any additional tests
  • Appropriate Container: Use the correct container for the specimen type (e.g., sterile tube for aspirates, sterile container for tissue)
• Transportation and Storage
  • Transport Media: Use transport media (e.g., Amies transport medium) if the specimen cannot be processed immediately
  • Prompt Delivery: Transport specimens to the lab as quickly as possible (ideally within 1-2 hours) to maintain organism viability
  • Storage: If there is a delay in transport, refrigerate the specimen at 4°C
• Communication with the Lab
  • Clinical Information: Provide relevant clinical information on the lab request form, such as the suspected infection, antibiotics the patient is taking, and any other pertinent details. This helps the lab prioritize the testing and select the appropriate methods
  • Specific Requests: If a specific organism is suspected (e.g., Mycobacterium, fungi), note it on the request form

Key Terms

• Wound Culture: The process of culturing a sample taken from a wound to identify potential bacterial pathogens
• Abscess Aspiration: The technique of using a needle and syringe to withdraw fluid (pus) from an abscess for culture and analysis
• Biopsy: The removal of a small piece of tissue for examination, often used in the diagnosis of deep infections or osteomyelitis
• Sterile Technique: A set of practices used to prevent contamination during specimen collection and processing, crucial for accurate results
• Gram Stain: A differential staining technique used to classify bacteria based on their cell wall structure (Gram-positive or Gram-negative), providing initial clues for identification
• Colony Morphology: The visual characteristics of bacterial colonies growing on agar plates (e.g., size, shape, color, texture), which help in presumptive identification
• Antimicrobial Susceptibility Testing (AST): Laboratory tests performed to determine the effectiveness of different antibiotics against a specific bacterial isolate
• MRSA (Methicillin-resistant Staphylococcus aureus): A type of Staphylococcus aureus that is resistant to methicillin and other beta-lactam antibiotics, posing a significant clinical challenge
• Osteomyelitis: An infection of the bone, often requiring a bone biopsy for diagnosis and culture
• Pathogenicity: The ability of a microorganism to cause disease, including factors like virulence mechanisms and host response