microbio unit 11B - methods of microbial control: preventing + controlling microorganisms

II: methods to control microbial infection

historical development of chemotherapy

fleming made penicillin; watsman made streptomycin

how do we determine which antibiotic to give someone with an infection?

minimal inhibitory concentration (MIC)

minimal inhibitory concentration

the minimum amount of antibiotic required to treat an infection

what is the difference between broad and narrow spectrum antibiotics?

broad treats gram ± whereas narrow only treats gram - OR gram +

what antibiotic treats gram ± microbes?

tetracycline

what antibiotic is a narrow spectrum drug?

penicillin

what are the effects of combining drugs?

synergistic, antagonistic

synergistic

effects of two drugs given together is greater than when given alone

what is an example of synergistic drugs?

penicillin destroys the cell wall + streptomycin enters the cell more easily → used to treat endocarditis

antagonistic

drug interference

what is an example of antagonistic drugs?

tetracycline stops bacterial growth + penicillin requires bacterial growth → do not administer these together

synthesis of antibiotics

derived from microbes (bacteria or molds) or chemically synthesized

what % of antibotics come from streptomyces sp?

50%

what is meant by “metabolic inhibitors?”

the bacteria needs to make an end product → antibiotic prevents the bacterial cell from making the end product which causes it to die

what are examples of metabolic inhibitors?

sulfonamides, isoniazid (INH)

sulfonamides

sulfa drugs + trimethoprim

what do sulfonamides do?

interfere with folic acid synthesis, resembles PABA

why is it significant that sulfa drugs interfere with folic acid synthesis?

PABA is the precursor to folic acid, folic acid is the precursor to dna, rna, and atp

if sulfa drugs are introduced, it resembles PABA which tricks the cell into being unable to make folic acid → INHIBITS the metabolic pathway

PABA

para-aminobenzoic acid

what are some uses of sulfa drugs?

UTI, meningococcal meningitis

what are the limitations of sulfa drugs?

patients can have allergic reactions; not effective for severe infections (i.e. pus)

isoniazid

interferes with mycolic acid synthesis (cell wall)

what does isoniazid do?

resembles vitamin B₆

why is it significant that isoniazid resembles vitamin B₆?

in order for cells to undergo binary fission, mycolic acid must be made, B6 is a precursor to mycolic acid

if isoniazid is introduced, the bacteria will pick it up instead which tricks the cell into being unable to make mycolic acid for its cell wall

what is isoniazid used to treat?

m. tuberculosis

what are the limitations of isoniazid?

the cell becomes resistant; kidney damage

what is meant by “cell wall inhibitors?”

antibiotics that prevent pg synthesis so that the cell wall is weak

what are the cell wall inhibitors?

penicillin, synthetic penicillin, carbapenems, cephalosporins, bacitracin, vancomycin

natural penicillin

G and V

what are the limitations of penicillin?

narrow spectrum, patients have allergies to it, organisms become resistant

what microbes are penicillin used on?

gram +

spriochetes

what enzyme breaks down penicillin?

beta lactamase; if the microbe can produce it, it will be resistant to penicillin

penicillin g is taken ______

as an injection

penicillin v is taken ______

orally

why have synthetic penicillins been created?

oxacillin, ampicillin → they have been modified to override negative features of penicillin

what are they synthetic penicillins?

ampicillin, amoxicillin, oxacillin

what do synthetic penicillins kill?

gram ±; they are broad spectrum

penicillin is used against ______ microbes, synthetic penicillin is used against _____ microbes

gram +; gram ±

carbapenems

antibiotics used on pseudomonas, a gram - rod

cephalosporins/cephalothins

resistant to penicillinase

what are cephalosporins effective against?

gram ±

are cephalosporins broad spectrum?

yes

bacitracin

topical ointment

what is bacitracin effective against?

gram ±

is bacitracin broad or narrow spectrum?

broad

vancomycin

very toxic + used for methicillin-resistant staphylococcus aureus (MRSA)

is vancomycin broad or narrow spectrum?

narrow

what are the limitations of vancomycin?

toxic, staphylococcus has more recently become resistant to it

what is meant by “protein synthesis inhibitors?”

antibiotics that inhibit the synthesis of proteins; perhaps the antibiotic targets the synthesis of ribosomes or deprives ribosomes of the tools to build proteins

protein synthesis inhibitors target what, specifically?

70s prokaryote ribosome

what are the protein synthesis inhibitors?

chloramphenicol, tetracycline, aminoglycosides, erythromycin

chloramphenicol is used to treat what infections?

typhoid fever, meningitis

is chloramphenicol narrow or broad spectrum?

broad

what are the limitations of chloramphenicol

aplastic anemia, potentially toxic

is tetracycline more or less toxic than chloramphenicol?

less toxic

what is tetracycline used to treat?

gram ±, ricketsia, chlamydia

what is the synthetic tetracycline called?

doxycycline

is tetracycline tissue-soluble?

yes → effective in treating uti, respiratory tract, and gi tract infections

is tetracycline narrow or broad spectrum?

broad

what are the limitations of tetracycline?

distrupts normal flora, GI problems, tooth discoloration, birth defects

how does tetracycline disrupt your normal flora?

tetracycline is broad spectrum; it cannot discriminate between your flora and the flora of the microbe causing the infection, thus changing your normal flora

are aminoglycosides broad or narrow spectrum?

broad

aminoglycosides are effective against what?

gram - microbes

what are examples of aminoglycosides?

streptomycin, neomycin, gentamicin

what are the limitations of aminoglycosides?

microbes become resistant to them, auditory nerve damage

streptomycin is used to treat what?

m. tuberculosis

neomycin is ______

topical

gentamicin is used to treat what type of infection?

pseudomonas infection

are aminoglycosides more or less broad than chloramphenicol or tetracycline?

no, they are less broad

erythromycin

marcolides

what is the alternative to penicillin?

erythromycin (if someone is allergic to penicillin)

what is erythromycin effective against?

gram +, legionella, some neisseria, mycoplasma pneumoniae

what is the limitation of erythromycin?

won’t effect most gram - microbes

how is erythromycin administered?

orally, it was one of the first antibiotics to be flavored… he is orange-flavored

would you administer penicillin to someone with walking pneumonia?

no, because mycoplasma pneumoniae does not have a cell wall

is erythromycin broad or narrow spectrum?

broad; keep in mind that it is NOT the most effective broad spectrum antibiotic

what is meant by “cell membrane permeation?”

some antibiotics will poke holes in the cell membrane, causing the contents to spill out; loss of cell metabolites

what are the cell membrane permeators?

polymixin b, polymixin e

what is polymixin b used to treat?

gram -, pseudomonas

why is polymixin b administered topically?

it is toxic to the kidneys + brain when injected

polymixin can be added to what?

neosporin (neomycin), bacitracin → triple antibiotic cream

polymixin e

colistin

what is polymixin e used to treat?

antibiotic resistant bacteria, it is a last resort

what is meant by “inhibition of nucleic acid synthesis?”

antibiotics that inhibit the dna or rna of a cell such that the genetic code is damaged or such that the dna is eliminated

what are the nucleic acid synthesis inhibitors?

rifamycin

anti-fungals (nystatin/mycostatin, amphotericin b, imidazoles/ketoconazole, griseofulvin)

anti-virals (amantadine, acyclovir, AZT/zidovudine, interferon)

anti-protozoans (quinine, metronidiazole/falgyl)

anti-helmenthics (nicolsamides, mebendazole)

rifamycin (rifampin)

inhibits mRNA

is rifamycin broad or narrow spectrum?

broad

what is rifamycin effective against?

gram +, SOME gram -, chlamydia, m. lepri, m. tuberculosis, n. meningitidis

what is a side effect of rifamycin?

turns urine, sweat, feces, and tears orange/red

what barrier does rifamycin cross?

blood brain barrier

what are the anti-fungal drugs?

nystatin/mycostatin, amphotericin b, imidazoles/ketoconazole, griseofulvin

what do anti-fungal drugs do?

prevent sterol synthesis in the cell membrane

what is nystatin/mycostatin used for?

yeast

what is amphotericin b used for?

systemic mycoses (like cryptococcosis, coccidioidomycosis)

what are imidazoles/ketoconazole used for?

systemic mycoses

what is griseovolvin used for?

cutaneous mycoses (like tinea, or ringworm infections)

what are the anti-viral drugs?

amantadine, acyclovir, AZT/zidovudine, interferon

what is amantadine used to treat?

influenza; reduces the duration

what is acyclovir used to treat?

herpes infections

what is AZT/zidovudine used to treat?

HIV