Microbio Final: Week 10

Phenol and Phenolics

first used by Joseph Lister to control surgical infections in operating rooms

injure lipids of plasma membranes, causing leakages

remain active in the presence of organic matter

reduce irritation, increase effectivness

ex: O-phenylphenol in lysol

Bisphenols

contain two phenol groups connected by a bridge

disrupt plasma membranes

ex: hexachlorophene: used to prevent skin infections caused by staphylococci and streptococci

ex: triclosan: used in antimicrobial soaps, toothpaste, mouthwashes, and plastics, is now discontinued

Biguanides

effective against gram positive bacteria, many gram negative bacteria, and enveloped viruses

disrupt plasma membranes

ex: chlorohexidine: in surgical hand scrubs for pre op skin prep

ex: aledidin: works faster than chlorohexidine

Essential Oils (EO)

mixture of hydrocarbons extracted from plants

ex: peppermint, pine, and orange oils

used in traditional medicine and preserving food

microbial action primarily due to phenolics and terpenes

stronger activity against gram positive bacteria, not sure for viruses

ex: tea tree and pine oil: broad activity for gram positive and negative bacteria and fungi

Iodine

a halogen

impairs protein synthesis and alters membranes

ex: tincture: solution in aqueous alcohol

ex: iodophor: combined with organic molecules like povidone iodine and skin antisepsis

water treatment

Chlorine

a halogen

oxidizing agents shut down cellular enzyme systems

ex: bleach: hypochlorous acid (HOCl)

ex: chloramine: chlorine and ammonia mix

municipal water disinfection

Alcohols

denatures proteins and dissolves lipids

no effect on endospores and non-enveloped viruses

ex: ethanol and isopropanol = requires water

ex: alcohol based hand sanitizers (62% alcohol) = effective against bacteria but not C.diff and norovirus

Oligodyanmic Action

very small amounts of heavy metals exert antimicrobial activity

denatures proteins

ex: Ag, Hg, Cu, and Zn

• silver nitrate is used to prevent ophthalmia neonatorum

• silver-impregnanted wound dressings

• mercuric chloride: limited as a disinfectant (toxic)

• copper sulfate is an algicide, ions are used as water disinfectants

• zinc chloride is found in mouthwash

Acid-Anionic Sanitizers

surface active agent

anions react with plasma membrane, used for cleaning food processing facilities

Quaternary Ammonium Compounds (Quats)

surface active agent

cations are bactericidal, which denature proteins and disrupt plasma membranes

have a broad spectrum but are ineffective against endospores and mycobacterium

Organic Acids as Food Preservatives

sulfur dioxide prevents wine spoilage

inhibit metabolism

sorbic and benzoic acid and calcium propionate prevent molds in some foods

Nitrites and Nitrates as Food Preservatives

prevent endospore germination (clostridium botulinum)

primarily used with meat products

nitrites preserve the red color of meat

Bacteriocins

proteins produced by one bacterium that inhibit another

work in food preservation with antibiotics

ex: nisin and natamycin (pimaricin) prevent spoilage of cheese

Aldehydes

inactivate proteins by cross-linking with functional groups

ex: formalin

• 37% aqueous solution of formaldehyde

• used for preserving specimens

• limited use due to cancer risk from exposure

ex: glutaraldehyde

• few liquid chemical sterilizing agents

• used on respiratory equipment like endoscopes and dental equipment that cant be autoclaved

Gaseous Chemosterilant

cross linked nucleic acids and proteins

used for heat sensitive material

ex: ethylene oxide and chlorine diozide

Ethylene Oxide

a gaseous chemosterilant

must be used in a sealed chamber

can sterilize large pieces of equipment and furniture, depending on chamber size

Chlorine Dioxide

used in enclosed building areas or water treatment

can also be used as an aqueous solution for surface disinfection

Superficial Fluids

CO2 is compressed into a supercritical state with both gaseous and liquid properties

used in food preservation and medical implants like bone, tendons, and ligaments removed from donors

Peroxygens

oxidizing agents

ex: hydrogen peroxide and peracetic acid (PAA)

ex: benzoyl peroxide for topical acne medications

ex: ozone (O3) for water disinfection

Hydrogen Peroxide

a peroxygen

not good as an antiseptic for open wounds

good disinfectant (non-living surfaces)

aseptic food packaging

bioquell: hot gaseous hydrogen peroxide for sterilizing spaces and surfaces such hospital rooms

Peracetic Acid (PAA)

a peroxygen

effective liquid sterilant

used in disinfection of food processing and medical equipment

Principals of Effective Disinfection

concentration of disinfectant

organic matter: often interferes with disinfection

pH

temperature

time

Use-Dilution Tests

current standard for evaluating disinfectants

metal cylinders are dipped in test bacteria and fried

cylinders are placed in disinfectant for 10min at 20*C

cylinders are transferred to culture media to determine whether the bacteria survived treatment

variations can be used to test effectiveness of antimicrobial agents against endospores, viruses, fungi, and mycobacterium tuberculosis

Disk-Diffusion Method

evaluates efficacy of chemical agents

filter paper disks are soaked in a chemical and placed on a culture

look for zone of inhibition around disks

Gram Negative Bacteria Microbial Control

more resistant to biocides

due to lipopolysaccharide in their outer membrane

pseudomonas and burkholderia are unusually resistant

Mycobacteria Microbial Control

exhibit considerable resistance to biocides

tuberculocides must undergo special testing

Bacterial Endospores Microbial Control

very resistant to many biocides

Non-Enveloped Viruses Microbial Control

more resistant then enveloped viruses to biocides

Prions Microbial Control

problem with disinfection of surgical instruments

immerse in NaOH and autoclave at 121*C for 1 hour

Selective Toxicity

selectively finding and destroying pathogens without damaging the host

Chemotherapy

the use of chemicals to treat a disease

Antibiotic

a substance produced by a microbe that in small amounts inhibits another microbe

Antimicrobial Drugs

synthetic substances that interfere with the growth of microbes

History of Chemotherapy

Fleming discovered penicillin produced by penicillium

prontosil red dye (type of sulfanilamide) was then used for streptococcal infections

penicillin then went through clinical trials

Narrow Spectrum of Microbial Activity

drugs that affect a narrow range of microbial types

Broad Spectrum of Microbial Activity

affect a broad range of gram positive or gram negative bacteria

Superinfection

overgrowth of normal microbiota that are resistant to antibiotics

ex: candida albicans and clostridioides difficile

Dosage

amount of medication given during a certain time interval

in children its based on weight but in adults it is a standard amount

the half life of the antibiotic is considered and so is the route of administration

Route of Administration

when a drug is administered intravenously, the concentration peaks quickly then gradually decreases

when a drug is administered orally or intramuscularly it takes longer for concentration to peak

Bactericidal

kills microbes directly

Bacteriostatic

prevents microbes from growing

Antimicrobial Drugs: Inhibiting Cell Wall Synthesis

penicillins (contains beta lactam ring) prevent the synthesis of peptidoglycan

enzymes that produce peptide cross links in peptidoglycan are collectively called penicillin binding proteins

types are differentiated by the chemical side chains attached to the ring

prevents the cross linking of peptidoglycan, interfering with cell wall construction (essentially gram positives)

Antimicrobial Drugs: Inhibit Protein Synthesis

target bacterial 70S synthesis

ex: chloramphenicol, erythromycin, streptomycin, and tetracyclines

Antimicrobial Drugs: Injuring Plasma Membrane

polypeptide antibiotics change membrane permeability

affects the synthesis of bacterial plasma membranes

anti-fungal drugs combine with membrane sterols

ionophores: antibiotics that allow uncontrolled movement of cations (not for human use) used in cattle feeds

Antimicrobial Drugs: Inhibiting Nucleic Acid Synthesis

blocks topiosomease (interferes with DNA replication)

blocks RNA polymerase (interferes with transcription)

Antimicrobial Drugs: Inhibit Synthesis of Essential Metabolites

antimetabolites compete with normal substrates for an enzymes

sulfanilamide competes with para-aminobenzoic acid (PABA) stopping the synthesis of folic acid

Cycloserine

drug that targets the bacterial cell wall

inhibits enzymes that make part of the peptide side chain on NAM

Bacitracin

drug that targets the bacterial cell wall

binds to the bactoprenol lipid carrier

transport of disaccharide units of peptidoglycan across the cell membrane to the growing chain inhibited

Natural Penicillins

a drug that inhibits cell wall synthesis

extracted from penicillium fungi cultures

• penicillin G is injected and penicillin V is oral

narrow spectrum of activity

susceptible to penicillinases (beta lactamases)

Cephalosporins

drug that inhibits cell wall synthesis

works similar to penicillins

beta-lactam ring differs from penicillin

grouped according to their generation of development

Cephalosporins

drug that inhibits cell wall synthesis

work similar to penicillins

beta lactam ring differs from penicillin

grouped according to their generation of development

Bacitracin

drug that inhibits cell wall synthesis

topical application, works against gram positive bacteria

a polypeptide antibiotic

Vancomycin

last line against antibiotic resistant MRSA

problem: development of VRSA (MRSA that are resistant to this drug) and VRE (drug resistant enterococcus)

a polypeptide antibiotic

Teixobactin

drug that inhibits cell wall synthesis

works against resistant gram positives like S aureus, M tuberculosis, and VRE

a polypeptide antibiotic

Isoniazid (INH)

drug that inhibits cell wall synthesis

inhibits the mycolic acid synthesis in mycobacteria

an antimycobacterial antibiotic

Ethambutol

drug that inhibits cell wall synthesis

inhibits incorporation of mycolic acid into the cell wall

an antimycobacterial antibiotic

Nitrofurantoin

drug that inhibits protein synthesis

converted to intermediates that attack bacterial ribosomal proteins

treatment for urinary bladder infections

Chloramphenicol

drug that inhibits protein synthesis

inhibits peptide bond formation

binds to the 50S subunit of the 70S ribosome

synthesized chemically and have a broad spectrum

can suppress bone marrow and affect blood cell formation (aplastic anemia)

Aminoglycosides

drug that inhibits protein synthesis

amino sugars linked by glycoside bonds

change the shape of the 30S subunit of the 70S ribosome

can cause auditory damage and kidney damage

ex: streptomycin, neomycin, gentamicin, and tobramycin

Tetracyclines

drug that inhibits protein synthesis

produced by streptomyces species

interfere with the tRNA attachment to the ribosome

broad spectrum, can penetrate tissues making them valuable against rickettsias and chlamydias

can suppress normal intestinal microbiota resulting in superinfections like candida albicans

Glycylcyclines

drug that inhibits protein synthesis

broad spectrum, a bacteriostatic

bind to the 30S ribosomal subunit

inhibits rapid efflux, administered intravenously

useful against MRSA and multi-drug resistant acinetobacter baumannii

ex: tigecycline

Macrolides

drug that inhibits protein synthesis

contain a macrocyclic lactone ring

narrow spectrum against gram positives

ex: erythromycin

new drugs: fidaxomicin, azithromycin, and clarithromycin

Streptogramins

drug that inhibits protein synthesis

attach to the 50S subunit

work against gram positives that are resistant to other antibiotics (MRSA, VRE, VRS A)

ex: synercid

Oxazolidinones

drug that inhibits protein synthesis

bind to the 50S/30S subunit interface

synthetic, combat MRSA (linezolid)

Pleuromutilins

drug that inhibits protein synthesis

ex: retapamulin = topical and effective against gram positives

Daptomycin

produced by streptomycetes and is used for skin infections

attacks the bacterial cell membrane

drug that attacks cell membrane, is a lipopeptides

Polymyxin B

drug that attacks cell membrane, is a lipopeptides

topical, bactericidal, effective against gram negatives

combined with bacitracin and neomycin in nonprescription ointments

Polymyxin E (Colistin)

drug that attacks cell membrane, is a lipopeptides

effective against gram negatives

Rifamycin (Rifampin)

drug that inhibits nucleic acid synthesis

inhibits mRNA synthesis

penetrates tissues, antitubercular activity

Quinolone and Fluoroquinolones

ex: nalidixic acid = synthetic, inhibits DNA gyrase

ex: norfloxacin and ciprofloxacin = broad specrum, relatively nontoxic

ex: gemifloxacin and moxifloxacin = problems with ruptured tendons

Sulfonamides

drug that competitively inhibits essential metabolites

inhibit the synthesis of folic acid, which is needed for nucleic acid and protein synthesis

structurally similar to PABA (folic acid precursor)

competitively bind to the enzyme that converts PABA to dihydrofolic acid in the folic acid synthesis pathway

Anti-Fungal Drugs

agents affecting fungal sterols

interrupt the synthesis of ergosterol, making the membrane excessively permeable

Polyenes

anti fungal drug

• nystatin is most commonly used

• amphotericin B = used for treatment of systemic fungal infections, toxic to kidneys

Azoles

antifungal drug

imidazoles: topical to treat cutaneous mycoses

triazole: treats systemic fungal infections

Allylamines

antifungal drug

for azole resistant infections

Echinocandins

agents affecting fungal cell walls

• inhibits the synthesis of beta-glucan

agents inhibiting nucleic acids

• flucytosine, cytosine analog interferes with RNA synthesis

Griseofulvin

antifungal drug

produced by penicillium

inhibits microtubule formation

active against superficial dermatophytes

Tolnaftate

antifungal drug for athletes foot

Pentamidine

antifungal drug

anti-pneumocytsis that may bind to DNA

Antiviral Drug Uses

1. entry and fusion inhibition: block the receptors on the host cell that bind to the virus, block fusion of the virus and cell

2. uncoating, genome integration, and nucleic acid synthesis inhibitors: prevent viral uncoating and inhibit viral DNA integration into the host genome

3. protease inhibitors: block cleavage of protein precursors, ex: paxlovid for COVID-19

4. exit inhibitors: inhibit neuraminidase, an enzyme required for some viruses to bud from host cell

Interferons

antiviral drugs

produced by viral infected cells to inhibit further spread of the infection

imiquimod: promotes production

Antiretroviral

antiviral drug used to treat HIV (RNA virus) infections

Quinine and Chloroquine

anti-protozoan drugs

treat malaria

Artemisinin

anti-protozoan drugs

kills plasmodium that causes malaria

Metronidazole, Tinidazole, and Nitazoxanide

anti-protozoan drugs

interferes with anaerobic bacteria

treats trichomonas, giardiasis, and amebic dysentery

Miltefosine

anti-protozoan drug

inhibits cytochrome oxidase in mitochondria

treats amebic encephalitis and leishmaniasis

Niclosamide

antihelminthic drug

prevents ATP production

treats tapeworms

Praziquantel

antihelminthic drug

alters membrane permeability

treats tapeworms and flukes

Mebendazole and Albendazole

antihelminthic drug

interferes with nutrient absorption

treats intestinal helminths

Ivermectin

antihelminthic drug

paralysis of helminths

treats roundworms and mites

Disk Diffusion Method (Kirby Bauer Test)

tests the effectiveness of chemotherapeutic agents

papers disks with a chemotherapeutic agent are placed on agar that has been inoculated with test organism

Zone of Inhibition

area around test disk that determines the sensitivity of the organism to the antibiotic

E Test

determines the minimal inhibitory concentration (MIC)

lowest antibiotic concentration preventing bacterial growth

Broth Dilution Tests

determine the MIC and minimal bactericidal concentration (MBC) of an antimicrobial drug

test organism is placed onto the wells of a tray containing dilutions of a drug, growth is determined

Antibiograms

reports that record the susceptibility of organisms encountered clinically

Minimum Bactericidal Concentration (MBC)

determined by using a tube dilution test and removing the antibiotic

requires further plating to determine if any cells survived

three to five times above the MIC

• if cells grow in the fresh medium without antibiotic, the drug is bacteriostatic

• if cells do not grow, the drug is bactericidal

Persister Cells

microbes with genetic characteristics allowing for their survival when exposed to an antibiotic

Superbugs

bacteria that are resistant to large numbers of antibiotics

resistance genes are often spread horizontally among bacteria on plasmids or transpoons via conjugation or transduction

bacterial pathogens that are resistant to nearly all antibiotics cause HAI’s

ex: acinebacter baumannii

ex: pseudomonas aeruginosa

ex: members of enterobacteriaceae

Mechanisms of Resistance

enzymatic destruction or inactivation of the drug

prevention of penetration to the target site within the microbe

alteration of the drugs target site

rapid efflux (ejection) of the antibiotic

variations of mechanisms of resistance

Beta-Lactamases

enzymes that break the beta-lactam ring of penicillins and cephalosporins

over 200 different variations