Microbial ControlOutside the Body

Physical Methods

I.  Heat Generally elevated temperatures are microbicidal and lower temperatures are microbistatic Can be moist (steam) or dry heat (changing temperature of air)

1. Moist Heat Pressurized Steam

o Pressure raises the temperature of steamo Most efficient pressure-temperature combination for sterilization--kills spores as well

Autoclave is an example Pasturization

o Used to disinfect beverages Does not kill endospores or thermoduric microbes

o Heat is applied to liquids to kill potential agents of infection, while retaining the liquid's flavor and food value

Boiling Watero For disinfection

2. Dry Heat Incineration

o Ignites and reduces microbes to ashes and gaso Common practice in microbiology lab—bacincineratorso Sterilization

Dry Oveno Used for heat-resistant items that do not sterilize well with moist heat such as electronic

equipmento Usually an electric oveno Sterilization

3. Cold Slows down the growth of cultures and microbes in food during processing and storage Does not kill microbes, only preserves them (microbistatic) Desiccation is the dehydration of vegetative cells that might direct the cell into an endospore state Lyophilization is a combination of freezing and drying that is used to preserve microorganisms in a viable

state for many years 

II. Radiation Energy emitted from unstable atoms that are used for microbial control

o Gamma rays, X rays, UV  Usually disinfection (nonionizing UV) rather than sterilization (ionizing xray, gamma ray) Hospital rooms, operating rooms, schools, food Drinking water or purifying liquids

Chemical Methods

Occur in liquid, gaseous, or solid state Tinctures are solutions dissolved in pure alcohol or water-alcohol mixtures

1. Halogen Antimicrobial Agents F, Cl, Br, I Microbicidal and sporicidal with longer exposure Chlorine  compounds can be liquid, gaseous, hypochlorites, or chloramines

o Kills bacteria, endospores, fungi and viruseso Household bleach

Iodine   compounds--free iodine and iodophors (diluted with water)o Can be topical antiseptic and/or disinfectanto Betadine is the most common formulation

2. Phenol and its derivatives Great against gram positives because they denature proteins, disrupt lipids and enzyme function At high concentrations they are poisonous for cells because:

o Disrupt cell membraneso Percipitate proteins

At lower concentrations they inactivate certain critical enzyme systems Microbicidal against vegetative microbes including viruses

o NOT serilizing At concentrations below 1% they are used as throat lozenges due to tis anesthetic properties General disinfectants include

o Lysono Triclosan 

Bisphenol that is a popular component of antibacterial soaps. Inhibits an enzyme needed for the synthesis of fatty acids Effective against gram negatives and yeast

Phenolics are derivatives that have been modified to reduce the irritating properties and increase antimicrobial activity in the presence of soaps or detergents

3. Chlorhexidine Complex base containing chlorine and two phenolic rings (biguanide) Targets cell membranes and protein structure At moderate to high concentrations it is bactericidal for both gram positve and gram negative

Inactive against spores Mild, low toxicity and rapid action Disinfecting When combined with a detergent it is used as a surgical scrub

4. Alcohols  Kills bacteria and fungi but not endospores and nonenveloped viruses Mechanism of action depends on its concentration

o 50% and higher dissolve membrane lipids, disrupt cell surface tension and compromise membrane integrity

o 50% - 90% denature proteins through coagulationo 100% dehydrates cells and inhibits growth

Ethyl and isopropyl alcohols Not good for degerming wounds because they cause coagulation under which bacteria still grow  Can be used for antisepsis

5. Hydrogen Peroxide and Ozone Germicidal effects due to the direct and indirect actions of oxygen Bactericidal, viricidal and fungicidal In higher concentrations it is sporicidal Can be sterilizing as in contact lens solutions Ozone has similar effects to hydrogen peroxide

o used to disinfect water6. Heavy Metal Compounds

Hg, Ag, Au, Cu, As, Zno Hg and Ag are germicides

Have oligodynamic actiono have antimicrobial effects in small amountso Bind onto functional groups of proteins and inactivate them

7. Detergents Act as surfactants Cationic detergents are more effective because the positively charged end binds well with the

predominantly negatively charged bacteria surface proteins Weak microbicides but gain germicidal value when mixed with chlorohxidine or iodine

8. Aldehydes Germicides Gluteraldehyde

o Liquido Cross-links proteins on cell surfaceo Inactivates enzymes within cellso Does not destroy endosporeso Toxic to humans

Formaldehydeo Gas--can be used to disinfect a whole roomo Toxic to humanso can be used as a perservative of tissue samples at 40% and higher concentrations

9. Gaeous mixtures Chlorine dioxide and ethylene dioxide are sterilants

10. Acids and Alkalis Low or high pH can inhibit microbial cells Limited in application due to corrosive nature Often used as a preservative in food

o benzoic , Lactic acids

Mechanical Methods

1.  Applications of Filtration  Prepare liquids that can’t withstand heat—can decontaminate beverages without altering their flavor—

antibiotics can go through an IV Water purification   Removing airborne contaminants (HEPA filters)

Inside The Body

AntibacterialsTarget: Cell Wall--Mechanism: Blocks Synthesis and Repair

I. Beta-Lactam ring   1. Penicillin--extracted from the fungi Penicillium Notatum

 Consists of three basic parts—a thiazolidine ring, a beta-lactam ring, and a variable side which dictates its anti-microbial activity

Affects gram positive bacteria Bactericidal  Generally well tolerated and has low toxicity to host Mode of Action: Disrupts the formation of the cell wall by inhibiting enzymes essential for peptidoglycan

synthesis, which causes the cell wall to have weak points, leading to lyseso Specifically binds to the enzyme that is responsible for cross linking glucosamine and muramic

acid.

The only requirement for them to work is that the cell must be actively growing and therefore making peptidoglycan (exponential phase)

o Mycobaacterium, though it is a gram positive bacteria is not damaged by penicillin group because it is not very active—its growth phase is very long and it contains Myacolic acids.

Penicillinase and/or beta-lactamase are enzymes produced by bacteria which destroy the beta-lacatam ring of the penicillin molecule, and therefore deactivate the drug

Penicillin Groupo G and V

Most important, natural formso Ampicillin, carbenicillin and amoxicillin

Semi-Synthetic Broader spectrum and more stable then first generation

o Methicillin, nafcillin, and cloxacillin   Penicillinase-resistant penicillins

o Mezlocillin and azlocillin Extended spectrum and can be sutsituted for combinations of antibiotics

o Combinations—used for systemic infections, contain compounds which inhibit beta-lactamase and are used for systemic infections

Augmentin Combination called Clavamox: amoxicillin and clavulanic acid Claculanic acid inhibits beta-lactamase enzymes and longevity

 Zosyn Combination of Tazobactam and piperacillin Tazobactam inhibits beta-lactamase emzymes

  2. Cephalosporin--extracted from the fungus cephalosporium Have beta-lactam ring structure that can be synthetically altered and so has similar mode of action to

penicillin and is resistant to most penicilinases Mode of Action: Bind to penicillin-binding proteins that interfere with the synthesis of peptidoglycan Relatively broad-spectrum Cause fewer allergic reactions then penicllins

 3. Monobactams Aztreonam narrow spectrum drug—aerobic gram negatives that is useful for treating penicillin-allergic

patients because of the different chemical structure and so it is resistant to beta-lactamases Binds primarily to one of the penicillin-binding proteins in gram-negative aerobe

 4. Carbapenems  Widest spectrum of antibacterial activity Binds to penicillin-binding proteins and cause cell elongation and lysis Stable against beta-lactamase Bacteria produce resistance by the production of carbapenemase and can alter the porin channels, which

reduces the permeability of the drugs

II. Non-Beta Lactam Ring    1. Bacitracin--derived from bacterium Bacillus

Often combined with polymyxins in topical application Active against gram-positive bacteria Very toxic to Kidneys

o Bacitracin is administered only topically Mode of Action: Inhibits bacterial cell wall synthesis and disrupts cell membrane

    2. Fosfomycin Used as a single-dose therapy for UTI's

o Multi-use can cause bacterial resistance to develop quickly Broad-spectrum of activity Mode of Action: Inhibits pyruvyl transferase which is necessary in the first steps of peptidoglycan synthesis

o Bacteriacidal    3. Vancomycin--produced by streptomyces

Active against aerobic and anaerobic gram positive organisms including Methicillin Resistant staplococci (MRSA)

o Not active against gram negative or mycobacteria because of the molecule's large size Can't penetrate the outer membrane

Mode of Action: Inhibits peptidoglycan synthesis in the cell wallo Bactericidal 

Target: Protein Synthesis Inhibitors

I. 30S Ribosomal Subunit Inhibitors (-mi(y)cin and -cyclins)    1. Aminocyclitols 

Mode of Action: Binds reversibly to the 30S ribosomal subunit and inhibits protein synthesiso Bacteriostatic

Has a very limited spectrum--specifically used to treat Neisseria gonorrhoeae    2. Aminoglycosides

Mode of Action: Binds irreversibly to the bacterial 30S subunit and causes misreading of the genetic code that results in the production of nonsense proteins

o Bactericidal  Medications include those that end in -mycin

o Streptomycin, Neomycin, Kanaycin, Tobramycin, and Gentamicin  Has considerable toxicity

o Nephrotoxicity and Auditory toxicity o Neomycin can't be administered via IV because it is so toxic--mainly for topical treatment and

rarely oral    3.  Tetracyclines

Mode of action: Binds reversibly to the 30S ribosomal subunit o Bactericidal

Broad spectrum Administered orally Medications include

o Doxycycline (used to treat anthrax), Minocycline and Tetracycline (blocks tRNA docking site)    4. Glycylcyclines

Synthetic derivatives of tetracyclines Mode of Action: Binds reversibly to the 30S subunit

o Bacteriastatic Tigecycline is only approved drug so far  Resistant to most resistant mechanisms that effect tetracyclines

II. 50S Ribosomal Subunit inhibitors    1. Macrolides (-ithromycin)

Mode of Action: Inhibits bacterial ribosomal RNA o bacteriostatic

Bactericidal against streptococcio strep. pyogenus (strep throat)

Broad spectrum  Medications include

o Azithromycin, Clarithromycin  Legionella, Mycoplasma

o Dirithromycin, o Erythromycin is not broad spectrum because it can't penetrate gram negative walls

    2. Ketolides Mode of Action: Inhibits the translation at the level of the 50S ribosomal subunit Medication includes Telithromycin a derivative of Erythromycin Spectrum of Activity

o Good against respiratory pathogens

Haemophilus influenzae, Streptococcus pneumoniaeo Good against intracellular bacteria

Legionella, Mycoplasma, Chlamydiao Designed specifically for the treatment of community aquired respiratory tract infections

    3. Lincosamides Mode of Action: Binds to the 40S ribosomal subunit Can be bactericidal or static depending on drug concentration, bacterial species, and bacterial density Broad Spectrum Medications include

o Clindamycin and Lincomycin Clindamycin has better antibacterial activity and improved absorption after oral

administration    4. Oxazolidones

Mode of Action: Binds to the 50S subunit, inhibits the formation of a functional 70S complex that prevents the initiation of translation

Medication Include Linezolid Spectrum of Activity

o Generally bacteriostatico Bactericidal against most strains of pneumococcio Used for MRSA and vancomycin-resistant enterococci

    5. Phenicols Mode of Action: Inhibits protein synthesis by binding reversibly to the 50S ribosome

o Bacteriostatic Medication Includes Chloramphenicol Has a broad spectrum of activity Limited to seriously ill patients due to the side effect that causes irreversible damage to the bone marrow

which leads to aplastic anemia    6. Streptogramins

Mode of Action: Inhibits bacterial protein synthesis, binds irreversibly to the 50S subunito Bactericidal

Medication Include a combination drug called Synercid made up of Quinupristin-Dalfopristin (30:70) Used to treat seriously ill or life threatening infections accociated with vancomycin-resistant Enterococcus

faecium (VREF)

Target: DNA & RNA

    1. Rifampin Related to the Macrolides

o Medication is Ansamycin Limited spectrum because molecule can't pass through the cell envelope of many gram-negative bacilli Mode of Action: Forms a stable complex with RNA polymerase preventing transcription Rifampin-resistant bacteria possesses an altered RNA polymerase that comes from mutations during

monotherapy with Rifampino Important when treating mycobacteria

A side effect is that all secretions become orange    2. Quinolones and Fluroquinolones

Mode of Action: Targets DNA gyrase, an enzyme essential for replication, recimbination and repair. Inhibition of these enzymes causes the relaxation of the supercoiled DNA

o This terminates chromosomal replication and interferes with cell division and gene expressiono bactericidal

Fluroquinolones are synthetics that have the addition of a flourineo Have the suffix –floxacin

Quinolones and FluroquinolonesSubclass Generic Names

Quinolone (1st generation) Narrow spectrum active against gram positive cocci

Cinoxacin, Niladixic acid (UTIs)

Fluroquinolone (2nd generation) Broad-spectrum against both gram positive and gram negative. Less toxic than first generation

Ciprofloxacin(anthrax), Enoxacin, Fleroxacin, Levofloxacin, Lomefloxacin, Norfloxacin, Ofloxacin

Fluroquinolone (3rd generation) Increased activity against gram-positive cocci

Sparfloxacin

Fluroquinoline (4th generation) Increased activity against gram-positive cocci

Gatifloxacin, Gemifloxacin, Moxifloxacin, Trovafloxacin

    3. Metronidazole (Flagyl) A type of prodrug that must first be metabolized by the body before it can be used Mode of Action: When the nitro group enteres the cell, it is reduced in the cytoplasm and forms cytotoxic

compounds that disrupt the bacterial or protozoan DNAo Bactericidal o Only against obligate anaerobes like Clostridum

Medications includeo Nitrazoximide has anti-helminthic activityo Fasigyn

Target: Cell Membrane

    1. Polypeptides--Polymyxin B Mode of Action: Interact with the phospholipids in the cell membrane and increase the cell's permeability

o Bactericidal Very toxic to the kidneys and neurotoxic  Often combined with bacitracin (attacks the cell wall) in topical applications

o Polymyxin B is active against gram-negative bacilli like Psudomonas and Bacitracin is active against gram-positive bacteria

Together have broad spectrum of activity Currently being used to treat  Acinetobacter baumannii, which is multi-drug resistant (MDRAB)

    2. Lipopeptides Mode of Action: concentration-dependent bactericidal activity

o Causes depolarization of the cell membrane Medications include Daptomycin (cubicin) a European medication Spectrum of Activity

o Gram positive organisms including methicillin-susceptible and resistant Staphylococci, Streptococci, Enterococci, and Bacillus

o Not active against gram-negative organisms or mycobacteriao Can work synergistically with aminoglycosides or rifampin

This allows you to lower the concentration of the other medications

Target: Folic Pathway Inhibitors

Medications includeo Sulfonamides, Trimethoprim (TMP)o Trimethoprim-sulfamethoxazole  (TMP-SMX; trade names Bactrim or Septra)

Mode of Action: Block the bacterial folic acid metabolic pathway at different sites TMP-SMX acts synergisticallyd First synthetic antibiotics 

AntifungalsBecause fungal cells are eukaryotic, anti-fungals can also be toxic to human cells

1. Macrolide polyenes (antibiotics) Mode of Action: Bind to fungal cells and cause loss of selective permiability

o Binds to a sterol in the fungal cell membranes called ergosterol which human cells do not contain; we contain cholesterol

Medications Includeo Amphotercin B--most common; used to treat streptomyces o Nystatin

Used to treat candidias (yeast infections) of the skin and mucous membrane Developed at Albany, NY

Has nephrotoxicity 2. Synthetic Azoles

Mode of Action: Inhibits ergosterol synthesis which weakens the fungal cell membrane Broad-spectrum Medications include

o Clotrimazoleo Fluconazoleo Miconazoleo Ketoconazole

Newer, broader spectrum, orally

AntiparasiticsDrugs used to treat protozoan and helminth infections1. Quinine

Extracted from the bark of the cinchona tree Was the principle treatment for malaria for hundereds of years

o Replaced by the synthetic quinolines NOT TO BE CONFUSED WITH QUINOLONES

o Chloroquine, Primaquine, Mefloquine (has psychiatric side effects)2. Metronidazole

Used to treat mild to severe intestinal infections and hepatic disease caused by Entameoba histolytica Can also be used to treat Giardia lamblia and Trichomonas vaginalis Metabolized

3. The antibacterial groups of sulfonamides and tetracyclines also have antiprotozoan activities 

Antivirals1. Inhibition of Virus Entry

Receptor binding Fusion

o Fuzeon, enfuviritide, very costly and mimics region on virus that is responsible for fsion Uncoating

o Amantide (H3N2, H1N1, Avian, Influenza B are now all resistant)o Tamiflu, Relenza

2. Inhibition of Nucleic Acid Synthesis Acyclovir--herpes Nucleotide analog reverse transcriptase (RT) inhibitors--retroviral, specifically HIT

o Zidovudine (AZT) Non-nucleoside reverse transcriptase inhibitors

o Nevirapine 3. Inhibition of Viral Assembly/Release

Protease inhibitors o Saquinaviro Amantidine

 Interferon, a glycoprotein produced by fibroblasts and leukocytes in response to immune stimuli can also be used to treat viral infections. It has anti-viral and anti-cancer properties and plays a major role in natural immunities 

Antiviral Intended Virus Amantadine & Rimantadine uncoating

Influenza A

Zanamivir & Oseltamivir NA Influenza A & B Acyclovir & Famciclovir Herpes simplex virus (HSV) replication Varicella-zoster virus (VZV)

(chickenpox, shingles) Ribavirin RNA Respiratory syncytial virus,

hepatitis C virus, others Ganciclovir & Foscarnet nucleotide analogs

Cytomegalovirus (CMV)

Nucleoside reverse transcriptase inhibitors (i.e. Zidovudinez (AZT) and Didanosine)

HIV Human immunodeficiency virus

Non-nucleoside reverse transcriptase inhibitors (i.e. Nevirapine and Delavirdine)

HIV

Protease inhibitors (i.e. Ritonavir and Saquinavir)

HIV

Lamivudine nucleocide analog Hepatitis B Interferon-α Hepatitis B and hepatitis C