Micro 2- antimicrobial drugs Flashcards
chemotherapy
the use of chemicals to treat a disease
antibiotic
a substance produced by a microbe that, in small amounts, inhibits another microbe
(example: streptomyces)
antimicrobial drug
synthetic substances that interfere with the growth of microbes
selective toxicity
selectively finding and destroying pathogens without damaging the host
narrow spectrum of microbial activity
drugs that affect a narrow range of microbial types
broad-spectrum antibiotics
affect a broad range of gram positive and gram negative bacteria
bactericidal
kills microbes directly
bacteriostatic
prevent microbes from growing
what is a superinfection and how is it caused
overgrowth of normal microbiota that is not sensitive to antibiotics (candida albicans)
-growth of target pathogen that has developed resistance to antibiotics
superinfection is a disadvantage of
broad spectrum drugs
5 ways antimicrobial drugs target essential functions of the microbe
- inhibition of cell wall synthesis
- inhibition of protein synthesis
- inhibition of nucleic acid replication and transcription
- injury to plasma membrane
- inhibition of essential metabolite synthesis
example of cell wall synthesis inhibitor and how it works
penicillin, contains beta-lactam ring and prevents the cross-linking of peptidoglycan, interfering with cell wall construction (primarily gram-positives)
natural penicillins are
- extracted from penicillium cultures, G (injected) and V (oral)
- narrow spectrum of activity
- susceptible to penicillinases (Beta-lactamases)
semisynthetic penicillins
contain chemically added side chains, making them resistant to penicillinases
list of inhibitors of protein synthesis
- aminoglycosides (including streptomycin)
- chloramphenicol
- tetracyclines
aminoglycosides
- amino sugars linked by glycoside bonds
- change the shape of the 30S subunit of the 70S ribosome
- can cause auditory damage
- streptomycin, neomycin, gentamicin
chloramphenicol
- inhibits peptide bond formation
- binds to 50S subunit of the 70S ribosome
- synthesized chemically, broad spectrum
- can suppress bone marrow and affect blood cell formation
tetracyclines
- produced by streptomyces spp.
- interfere with the tRNA attachment to the ribosome
- broad spectrum, penetrate tissues, making them valuble against rickettsias and chlamydias
- can suppress normal intestinal microbiota
what substances injury the plasma membrane
- lipopeptide
- includes daptomycin and polymixin B
daptomycin
type of lipopeptide
- produced by streptomycetes, used for skin infections
- attacks the bacterial cell membrane
polymixin B (type of lipopeptide)
- topical, bacteriocidal, effective against gram negatives
- combined with bacitracin and neomycin in nonprescription ointments
how do “inhibiting synthesis of essential metabolites” work
- antimetabolites compete with normal substrate for enzyme
- sulfonamides compete with para-aminobenzoic acid (PABA), stopping the synthesis of folic acid
- folic acid needed for nucleic acid and protein synthesis
types of inhibitors of nucleic acid synthesis
-rifamycin
-quinolone and fluoroquinolones
(nalidixic acid, norfloxacin and ciprofloxacin)
rifamycin
inhibits mRNA synthesis
-penetrates tissues, antitubercular activity
quinolone-
nalidixic acid
synthetic, inhibits DNA gyrase
quinolone-
norfloxacin and ciprofloxacin
broad spectrum, relatively nontoxic
list 2 types of diffusion methods
- disk-diffusion method (Kirby-Bauer)
2. E test
disk diffusion method (Kirby Bauer)
- tests the effectiveness of chemotherapeutic agents
- paper disks with chemotherapeutic agent are placed on agar containing the test organism
- zone of inhibition around the disk 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 bacterial concentration (MBC) of an antimicrobial drug
- test organism is placed into the wells of a tray containing dilutions of a drug, growth is determined
what are antibiograms
reports that record the susceptibility of organisms encountered clinically
what are 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
how are resistance genes spread
often spread horizontally among bacteria on plasmids or transposons via conjugation or transduction
list of mechanisms of resistance
- enzymatic destruction or inactivation of the drug
- prevention of penetration to the target site within the microbe
- alteration of the drug’s target site
- rapid efflux (ejection) of the antibiotic
- variations of mechanisms of resistance
