Microbiology Exam #3 Study Guide: Control of Microbial Growth, Antimicrobial Drugs, Infectious Agents, and Case Studies

Chapter 9: Controlling Microbial Growth in the Environment

Understanding Sterile Processing Methods

Sterile processing is essential in biotechnology and clinical labs to prevent contamination and ensure safety. Methods for achieving sterility include both physical and chemical approaches.

• Sterility refers to the complete absence of all living microorganisms, including spores and viruses.

• Physical methods include heat (autoclaving, pasteurization), filtration, and radiation.

• Chemical methods use disinfectants and antiseptics to destroy or inhibit microbial growth.

• Example: Autoclaving uses pressurized steam to sterilize equipment.

Disinfectants: True or False

Disinfectants are agents used to reduce or eliminate pathogens on surfaces. Their effectiveness depends on the type of microorganism and the method used.

• Disinfection can occur by physical (e.g., heat, UV) or chemical means (e.g., alcohol, bleach).

• Disinfectants are typically used on non-living surfaces; antiseptics are used on living tissue.

• Some microbes, such as bacterial endospores, are highly resistant to disinfection.

• Example: Alcohol-based disinfectants are effective against many bacteria but not spores.

Microbial Control Methods: Matching

Different control methods are used for specific purposes in microbial management.

Control Method	Use
Alcoholizing	Disinfect surfaces by denaturing proteins and dissolving lipids
Filtration	Remove microbes from heat-sensitive liquids
UV Radiation	Damage microbial DNA in laboratory settings
70% Ethanol	Disinfect surfaces and skin
Handwashing with Soap	Physically remove microbes from skin
Pasteurization	Reduce microbial load in milk and juice

Aseptic Technique

Aseptic technique prevents contamination of sterile materials and environments.

• Goal: To exclude all unwanted microorganisms from the lab environment.

• Examples include wearing gloves, sterilizing tools, and using autoclaves.

• Only autoclaving truly sterilizes; other actions reduce but do not eliminate all microbes.

Microbial Structures and Disinfectant Resistance

Certain bacterial structures confer resistance to disinfectants and environmental stress.

• Endospores are highly resistant to heat, chemicals, and UV light.

• Example genus: Bacillus or Clostridium.

• Disinfectants may not work well against endospores due to their tough outer layers.

Chapter 10: Controlling Microbial Growth in the Body: Antimicrobial Drugs

Penicillin – How It Works

Penicillin is a classic antibiotic that targets bacterial cell wall synthesis.

• Target: Penicillin inhibits the synthesis of peptidoglycan, a key component of the bacterial cell wall.

• Peptidoglycan provides structural integrity to bacterial cells; its disruption leads to cell lysis.

• Penicillin is more effective against Gram-positive bacteria due to their thick peptidoglycan layer.

Bacitracin and the Cell Wall

Bacitracin interferes with the transport of cell wall precursors across the cytoplasmic membrane.

• NAG (N-acetylglucosamine) and NAM (N-acetylmuramic acid) are building blocks of peptidoglycan.

• Blocking their transport prevents cell wall synthesis, leading to cell death.

• Disruption leads to cell lysis due to osmotic imbalance.

Mechanisms of Antimicrobial Drugs

Antimicrobial drugs act by targeting specific bacterial processes.

Mechanism	Example Drug/Class
Inhibits cell wall synthesis	Penicillin
Disrupts cytoplasmic membrane	Polymyxins
Inhibits protein synthesis at ribosomes	Tetracyclines or macrolides
Inhibits DNA or RNA synthesis	Fluoroquinolones (e.g., ciprofloxacin)
Stimulates host immune system	Next-generation drugs (immune stimulation)

Drug Classifications

• Synthetic drugs: Made entirely in the lab, not based on natural compounds.

• Natural drugs: Isolated from nature and used as-is.

• Semi-synthetic drugs: Based on natural products but chemically modified in the lab.

History of Antibiotics

• First true antibiotic: Penicillin, discovered by Alexander Fleming.

• Impact: Revolutionized medicine by enabling effective treatment of bacterial infections.

Chapter 11: Infection, Infectious Diseases, and Epidemiology

Case Studies: Clinical Applications

Case studies illustrate the identification and management of infectious diseases.

Case 1: Post-Surgical Infection

• MRSA: Methicillin-resistant Staphylococcus aureus, a major cause of hospital-acquired infections.

• Identified by Gram-positive cocci in clusters, resistant to methicillin, treated with vancomycin.

• Resistance is due to altered penicillin-binding proteins.

Case 2: STI with Discharge

• Gram-negative diplococci suggest Neisseria gonorrhoeae.

• Gram stain morphology aids rapid diagnosis.

• Untreated STIs can lead to long-term complications such as infertility.

Case 3: Diarrhea After a County Fair

• Bloody diarrhea and HUS (hemolytic uremic syndrome) suggest Escherichia coli O157:H7 producing Shiga toxin.

• Shiga toxin damages blood vessels and kidneys.

• Antibiotics may be contraindicated due to risk of worsening toxin release.

Pathogen Profiles: Matching

Bacteria	Description
Staphylococcus aureus (MRSA)	Gram-positive cocci in clusters; methicillin-resistant; treated with vancomycin
Listeria monocytogenes	Gram-positive rod; causes foodborne illness and meningitis
Clostridium botulinum	Neurotoxin-producing anaerobe; causes botulism and flaccid paralysis
Clostridium perfringens	Gas gangrene; foodborne illness
Bacillus anthracis	Spore-former; causes anthrax
Streptococcus pyogenes	Causes strep throat, scarlet fever
Mycobacterium tuberculosis	Acid-fast bacillus; causes tuberculosis
Escherichia coli O157:H7	Foodborne; Shiga toxin; causes bloody diarrhea and HUS
Helicobacter pylori	Causes stomach ulcers and has a protein capsule
Chlamydia trachomatis	Obligate intracellular pathogen; causes PID and infertility

Chapter 13: Characterizing and Classifying Viruses, Viroids, and Prions

Prions and Disease

Prions are infectious proteins that cause neurodegenerative diseases.

• Bovine spongiform encephalopathy (BSE) is linked to prion disease in humans.

• Other prion diseases include Creutzfeldt-Jakob disease and kuru.

• Prions are composed of misfolded proteins and cause disease by inducing abnormal folding in normal proteins.

• Antibiotics and antiviral drugs are ineffective against prions because they lack nucleic acids and metabolic processes.

Comparing Infectious Agents

• Unlike viruses, prions contain only protein and no nucleic acid.

• Prions do not reproduce like living cells or viruses.

Viruses vs. Living Cells

• Viruses cannot reproduce without a host cell.

• Viruses are made up of nucleic acids and proteins, but lack cellular structure.

• Viruses can infect both prokaryotic and eukaryotic cells.

Viruses and Cancer

• Some viruses (oncogenic viruses) can cause cancer by interfering with genes that regulate cell growth.

• Example: Human papillomavirus (HPV) can lead to cervical cancer.

Bacteriophage Life Cycles

Bacteriophages can undergo lytic or lysogenic cycles.

• Lytic cycle: Virus replicates immediately, lyses host cell, and releases new virions.

• Lysogenic cycle: Viral genome integrates into host DNA and remains dormant for a time.

• Triggering factors (e.g., stress) can induce the lysogenic virus to enter the lytic cycle.

Additional Case Study (Unit 5)

Microbial Antagonism and Superinfection

Broad-spectrum antibiotics can disrupt normal microbiota, leading to superinfection by opportunistic pathogens.

• Microbial antagonism: Normal microbiota inhibit colonization by pathogens.

• Superinfection: Overgrowth of resistant organisms after antibiotic treatment.

• Antifungal drugs may be required if fungal pathogens proliferate after antibiotic use.