Microbial Growth and Environmental Factors

Lab and Exam Updates

• Lab Schedule:

  • Tomorrow's Lab: Will involve gathering results for Lab $4-4$ and $4-5$ (EMV and MacConkey lab).

  • New Lab Activity: Students will work on Lab $5-4$, which is the Catalase test.

  • Safety Procedures: All lab activities from last week until the end of the semester will adhere to BSL-2 (Biosafety Level 2) procedures.

• Lab Report:

  • Due Next Week: The lab report for the catalase test, focusing only on gram-negative organisms, is due next week, as results are expected tomorrow.

  • Gram-Positive Organisms: Results for gram-positive organisms will be included later with the Mannitol Salt Agar (MSA) portion of the lab.

  • Canvas Updates: Due dates on Canvas have been updated to reflect these changes.

• Next Exam:

  • Tentative Date: The next exam is tentatively scheduled for Monday, October $13^{th}$. This date is chosen to avoid conflicts with other courses like Organic Chemistry, Genetics, and Anatomy & Physiology.

  • Content: The exam will cover material up to Chapter $6$ and potentially Chapter $7$.

  • Format: The exam will be on paper. The decision regarding open notes is still pending.

Micro in the Clinic: "Just a Sore Throat and Cough"

• Patient Profile: Jennifer, a college student and volleyball player, experiences persistent symptoms after midterm week and intense travel for matches.

• Initial Symptoms: Begins with unusual tiredness, a deep sore throat, and a cough. She initially attributes this to being rundown after midterms and assumes it will resolve with sleep.

• Symptom Progression: While tiredness and sore throat improve, her cough significantly worsens over a week, leading to disturbed sleep and affecting her roommate. She also experiences shortness of breath during volleyball practice, prompting a visit to the health clinic.

• Clinical Examination:

  • Doctor Wyatt takes medical history, listens to her lungs (noting a crackling sound), and uses a pulse oximeter, which reveals slightly lower-than-normal oxygen levels.

  • Diagnostic Tests Ordered: Chest X-ray, blood work, and a sputum sample (a mixture of saliva and mucus obtained by deep coughing).

• Diagnosis & Treatment:

  • Chest X-ray Findings: Shows an area of cloudiness in Jennifer's right lung, indicating inflammation likely due to infection. This explains the crackling, chest pain, difficulty breathing, and low oxygen saturation.

  • Provisional Diagnosis: Bronchitis and a worsening cough have progressed to Pneumonia (specifically, not Tuberculosis).

  • Initial Treatment: Doctor Wyatt immediately prescribes antibiotics and a steroid inhaler to help open her airway and ease breathing, pending definitive lab results.

• Definitive Diagnosis:

  • Molecular Analysis: Molecular analysis of the sputum sample using Polymerase Chain Reaction (PCR) identifies Mycoplasma pneumoniae, a bacterium commonly associated with pneumonia.

  • Follow-Up: Jennifer continues antibiotics and schedules a follow-up appointment.

• Outcome: After a few days on antibiotics, Jennifer feels significantly better, her cough resolves, and her right lung is clear with normal lung sounds and oxygen levels at her follow-up.

• **Unanswered Questions from Transcript (for further discussion in class):

  • Sputum Sample Plating: Explain why blood agar, chocolate agar (blood agar with lysed red blood cells), and MacConkey agar are helpful in identifying pathogens in lower respiratory infections. (This relates to their selective and differential properties, and ability to grow fastidious organisms).

  • PCR vs. Culture Plates: Why Mycoplasma pneumoniae was identified by PCR but not on the culture plates? (Potential reasons discussed later include specific growth requirements, fastidious nature, temperature sensitivity, or oxygen requirements).

Microbial Growth Requirements

• Essential Cellular Needs: All cells require three fundamental things for metabolism:

  1. An energy source.

  2. A carbon source.

  3. A source of electrons (or hydrogen atoms).

Source of Electrons

• Organotrophs: Obtain electrons from organic sources (e.g., glucose, lipids, proteins, nucleic acids).

• Lithotrophs: Obtain electrons from inorganic sources (e.g., hydrogen gas, hydrogen sulfide, iron).

Energy Source

• Phototrophs: Utilize light energy as their primary energy source.

• Chemotrophs: Derive energy from chemical compounds, which can be either organic or inorganic.

Carbon Source

• Autotrophs: Obtain carbon from carbon dioxide ($CO_2$) in the atmosphere. They are often described as