Bacterial Growth and Diagnosis Quiz

Bacterial Growth and Diagnosis

• Students should know bacterial growth requirements.
• Stages of the bacterial growth cycle will be reviewed.
• Overview of metabolism.
• Aerobic respiration, anaerobic respiration, and fermentation overview.
• Diagnosis of bacterial infections will be discussed.

Bacterial Growth Requirements

• Physical Requirements:

  • Optimal bacterial temperature is 37°C.
  • Temperature: 37°C
  • pH: 7.1
  • Isotonic Osmotic Pressure: Sterhylcocci → Halophile → Likes salt

• Chemical Requirements:

  • Essential elements: Carbon, Nitrogen, Phosphorus, Oxygen, Hydrogen.
  • Trace elements: Iron, Zinc, etc.

Energy Production

• A distinctive feature of bacterial metabolism is the variety of mechanisms used to generate energy from carbon sources.
• Bacterial metabolism can be categorized into three types:
  • Aerobic respiration
  • Anaerobic respiration
  • Fermentation

Aerobic Respiration

• Oxygen is the final electron acceptor in the electron transport chain.
• Oxygen is reduced to water in this process.
• Respiration is the energy-generating mode used by all aerobic bacteria

Anaerobic Respiration

• Inorganic compounds other than oxygen serve as the final electron acceptors.
• Examples of electron acceptors include: nitrate or sulfate,
• Anaerobic respiration can be used as an alternative to aerobic respiration in various species

Oxygen Tolerance

• Normally O2 is toxic; however, some bacterial cells can detoxify it.
• Obligate aerobes: Need oxygen to grow.
• Facultative aerobes: Can survive with or without oxygen.
• Aerotolerant anaerobes: Do not use oxygen but are not harmed by it.
• Strict anaerobes: Cannot survive in the presence of oxygen.
• Microaerophiles: Require low levels of oxygen.

Growth and Metabolism

• All cells accomplish certain metabolic tasks to maintain life.
• Bacterial metabolic pathways are similar to those in other cells.
• Differences between bacterial and eukaryotic cells can be exploited in antibacterial therapy development

Characteristics of Bacterial Growth

• If bacterial cells are suspended in a liquid nutrient medium, increase in cell number or mass can be measured in various ways, including
  • Microscopically (counting colony-forming units)
  • Quantitating turbidity (measuring cloudiness)

Stages of the Bacterial Growth Cycle

• Bacteria reproduce through binary fission.
• Different bacteria have different doubling times, ranging from twenty minutes to multiple days.
• Stages of the bacterial growth cycle include:
  • Lag phase
  • Log (exponential) phase
  • Stationary phase
  • Death phase

Growth of Bacterial Colonies

• A single bacterial cell on a solid nutrient surface can develop into a macroscopic colony.
• For rapidly growing species, overnight incubation at 30-37°C is sufficient for colony formation.
• Colony characteristics (color, shape, adherence, smell, surface texture) aid in species identification.

Culture Media

• Culture medium: Nutrients prepared for microbial growth.
• Sterile: No living microbes
• Inoculum: Introduction of microbes into medium
• Culture: Microbes growing in/on the culture medium

Agar

• A complex polysaccharide used as a solidifying agent for culture media (Petri plates, slants, and deeps).
• Generally, microbes do not metabolize agar.
• Liquefies at 100°C, solidifies around 40°C

Anaerobic Culture Methods

• Reducing media: Heated to drive off O2 / Contain chemicals that combine O2

Anaerobic Jar

• A device used to create an anaerobic environment for culturing bacteria.
• Uses specific chemicals and gases to remove oxygen.

Anaerobic Chamber

• An enclosed space used for anaerobic culture, typically with glove ports.

Candle Jar and CO2-Packet

• Techniques for creating an anaerobic environment by removing oxygen from the vial and introducing carbon dioxide to it

Types of Culture Media

• Selective Media: Suppresses unwanted microbes and encourages desired microbes.
• Differential Media: Make it easy to distinguish colonies of different microbes.
• Enrichment Media: Encourages the growth of a desired microbe.

Examples of Selective Media

• Blood Agar
• MacConkey Agar
• Hektoen Enteric Agar
• Mannitol Salt Agar
• Chocolate Agar (non-selective, enriched growth medium with lysed blood cells)
• Lowenstein-Jensen Medium (for cultivation and differentiation of Mycobacterium species)
• Mueller-Hinton Agar (for antimicrobial susceptibility testing)

Petri Dish

• Used for growing bacteria. Includes a clear lid and a dish-shaped bottom

Slant and Deep Media

• Used for growing bacteria. Includes a container and solid media

Bacterial Colony Morphology

• Colony characteristics (shape, elevation, and margin) aid in species identification during microbial identification.

Microscopy

• Unstained preparations: Dark-ground illumination for syphilis
• Stained preparations: Gram-stain, acid-fast stain (Ziehl-Neelsen), fluorescence (direct, e.g., auramine), and immunofluorescence

Culture of Bacteria

• Solid media: Agar plates (identification, enumeration, long-term storage)
• Liquid media: Broth (enrichment, maximum sensitivity)

Identification of Bacteria

• Morphology: Shape, size, and arrangement of cells
• Growth requirements: Temperature, pH, oxygen requirements
• Biochemistry: Tests for metabolic activities (e.g., enzyme production)
• Enzymes: Detecting specific enzymes for identification
• Antigens: Identifying proteins or other molecules specific to certain bacteria.

Introduction to Diagnostic Microbiology

• Techniques related to microbiology in a clinical setting.

Diagnosis of Bacterial Infection

• Patient: Collect patient information
• Clinical diagnosis: Assess clinical data, medical history.
• Non-microbiological investigations: X-rays, blood tests (hematology, biochemistry).
• Sample: Collect, label, and package samples correctly.
• Transport: Transport specimens appropriately.
• Storage: Store specimens correctly

Getting the Specimen to the Lab

• Problems in delays or inappropriate storage cause delays in diagnosis.
• Pathogens may die in improper conditions
• Contaminants may overgrow in unsuitable storage.
• Specimen collection procedures to avoid contamination
• Handling methods to ensure specimen integrity

Collecting the Specimen Correctly

• Procedures to properly collect a sample for analysis
• Techniques for avoiding contamination

Factors Limiting Usefulness of Bacteriological Investigations

• Wrong sample type
• Delays in transport
• Inappropriate storage
• Contaminant overgrowth
• Insufficient sample size
• Patient antibiotic use

Diagnosis of Bacterial Infection

• Microscopy
  • Techniques to identify bacteria in samples
    • Gram-stain, Acid-fast stain, and others.
• Culture: Identifying bacteria by their growth characteristics.
• Sensitivities: Testing bacterial susceptibility to antibiotics.

Colony Morphology (Descriptions)

• Punctiform
• Circular
• Filamentous
• Irregular
• Rhizoid
• Spindle (lens)
• Flat
• Raised
• Convex
• Pulvinate
• Umbonate
• Entire (even)
• Undulate (wavy)
• Filamentous
• Lobate (lobes)
• Erose (serrated)
• Curled