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Chapter 13: Control of Microbial Growth - Coggle Diagram
Chapter 13: Control of Microbial Growth
Microbial Growth
Definition: Use of physical, chemical, and mechanical methods to reduce or eliminate microorganisms
Types of agents: (action of antimicrobial drugs)
Bactericidal: Directly kill bacteria (99.9% reduction)
Bacteriostatic: inhibit growth without killing. prevents from reproduction. Most bacteriostatic agents keep bacteria in stationary phase of growth.
Factors Affecting Antimicrobial Effectiveness/Microbial Death Rate
Number of microbes- microbial lead (more # of days you've felt sick higher microbial load)
Type of microbes
Endospores
Acid-fast bacteria
Gram + vs Gram -
Exposure time
Environmental conditions
Organic debris
Biofilms
Medium Contents
Modes of Action
Membrane damage: Inhibition of cell wall synthesis: Penicillins, cephalosporins, bacitracin, vancomycin. Inhibition of synthesis of essential metabolites: sulfanilamide, trimethoprim
Protein damage/ enzyme denaturation: Inhibition of protein synthesis: Chloramphenicol, erythromycin, tetracyclines, streptomycin
Nucleic acid damage (DNA/RNA): Inhibition of nucleic acid, replication and transcription: Quinolones, rifampin. Injury to plasma membrane: Polymyxin B
Physical Methods of Microbial Control
Heat
Dry heat bacteriocidal > incineration, flaming, bactecinerator
Pasteurization bacteriocidal or bacteriostatic > 72 degrees C for 15 sec (milk) kills pathogens in milk and lowers the total bacterial numbers. Does not sterilize milk. Dairy products still spoil
Moise Heat (Autoclave) bacteriocidal > sterilization, preferred method of sterilization, provided material will not be damaged by heat or moisture
Increase pressure to reach very high temp. Gets rid of any form of life
15psi > 121 degrees C (reach 15psi pressure to reach 121C)
Push air out in order to increase pressure and temp. Building pressure 30 mins, sterilization 30 mins, decrease pressure
Filtration
Removes microbes using pores of 0.2 microns
HEPA filters remove particles as small as 0.3 microns
Applicable to clear liquids and gases only
Radiation:
Ionizing > DNA destruction. Gamma rays, X-rays, short wavelength, high energy, electron beam. Food industry, pharmaceuticals, catheters, plastics
UV -260nm (non ionizing) thymine dimers, does not penetrate well, can damage human eyes, cause burns, and skin cancer
Low temperature: Bacteriostatic: slow growth. Some bacteria can grow in refrigerator and cause spoilage
Listeriosis
Caused by Listeria monocytigenes- one of the few pathogens to grow at regrigerator temps
Serious in pregnant woman- can result in premature delivery, miscarriage, and even stillbirth
Osmotic pressure: Creates a hypertonic environment> water leaves cells (plasmolysis). Most bacteriostatic: inhibits growth. Food preservation method used for century. High salt/sugar > dehydration of cells. Salted/cured meats+smoking (ham, jerky), dried fruit (prunes, raisins)
Chemical Methods
Disinfectants: Destroy or inactivate organisms on non-living surfaces
Antibiotics: Produced by microbes in small amounts to inhibit the growth of other microbes. Penicillin
Sterliization: Destruction or removal of all forms of microbial life, including endospores
Degerming: removal of microbes from a limited area, such as the skin around an injection site
Commercial sterilization: sufficient heat treatment to kill endospores of Clostridium botulinum in canned food
Chemotherapy: use of chemical substances to treat disease
History
Ehrlich 1910: Speculated about a "magic bullet", coined the term chemotherapy, Salvarsan, an aresenic compound used against syphilis
Florey and Chain 1940: first clinical trials penicillin
Fleming 1928: discovered penicillin produces by Penicillium notatum inhibited growth of staphylococcus aureus
Antimicrobial drugs: interfere with the growth of microbes within a host. Ex: antifungal, antiviral, anti parasitic
Antiseptics: Destruction of vegetatitve pathogens on living tissue
Antimicrobial Testing Methods
Kirby- Bauer Test (diffusion method)
Disk diffusion
Measures zone of inhibition
MIC (broth dilution & E-test):
Lowest concentration stopping growth
Minimum Inhibitory Concentration
MBC (broth dilution test)
Minimum Bacteriicidal Concentration
Lowest concetration killing bacteria
Resistance Mechanisms
Enzymatic drug destruction: B-lactamase
Alteration of drug target site
Efflux pumps (remove drug)
Reduced permeability
Resistance genes on plasmids/transposons
Variety of mutiations can lead to antimicrobial resistance. Resistance genes are often on plasmids or transposons that can be transferred between bacteria
Antibiotics, Antifungals, Antivirals, and Disinfectants
Antibiotics
Gram positive Bacilli, Bacillus spp.- Topicals- Bacitracin and polymyxin. Actinomycetes- Streptomycin spp.
Actinomycetes- Streptomycin spp. Filamentous, soil bacteria. produce 50% of the antibiotics
Fungi, Cephalosporium- cephalothin. Penicillium spp- criseofulvin, penicillin
Antifungal
Eukaryotic cells. Points of selective toxicity are fewer than antibacterial
Fungi are often opportunists
Polyenes- amphotericin B- TMT of systematic fungi- nephrotoxic
Azoles: Imadozle- over the counter TMT cutaneous mycoses. Ketoconzaole- oral, topical. Triazoles
Antiviral:
Antiretroviral drugs
Influenza treatment: Zanamivir- Neuraminidase inhibitors. Oseltamivir phosphate- Neuramindase inhibitors
HIV infections treatment: Zidoviduine- Nuceloside analog, Tenofovir- Nuceoside analog
Disinfectants
Phenol: lysol or bisphenol
Halogens: Fluorine, Chlorinem Iodine
Alchohol
Quaternary compounds: Zephiran and Cepacol
Antimicrobial Safety
Must always evaluate the risk vs. benefit of antimicrobial therapy
Side effects may outweigh the benefit of therapy
Toxic dose: amount of medication that must be administered befire undesirable side effects are noticed and the health of patient is impaired
Therapeutic dose: the amount of medication that must be administered to have the disired effect
Therapeutic index: Ratio- toxic dose/therapeutic dose. Larger the therapeutic dose, the safer the medication.
Spectrum of Activity
Broad Spectrum: start before ID; downside- disrupts normal flora> opportunists/superinfection (Candida, C, difficile)
Narrow spectrum: more targeted; ex- penincillin G/erythromycin (many gram+), streptomycin (more gram-)
Selecive Toxicity: Killing microbes without damaging host cell. Bacteria- prokaryotes (presence/absense of cell walls, ribosome structure, metabolic pathways) Viruses: within host cells, using host "machinery". Fungi: Eukaryotes, resemble human cells- fewer safe antimicrobials