MICROBIOLOGY- Antimicrobial agents Flashcards
Define antibiotics
They are the products f microbes that, in dilute solution, inhibit or kill other organisms
Define antimicrobial agents
These include antibiotics and synthetic compounds that have the same effect
What can we do to naturally occurring antibiotics
We can modify them to give semi synthetics derivatives
How can modified antibiotics differ from their parent compound
In they antimicrobial activity or their pharmacological properties
What 2 effects can antimicrobial agents have?
- They can inhibit microbial growth
2. They can kill microbes
Define static
Agents that inhibits microbial growth
Define cidal
Agents that kill microbes
How do we carry out susceptibility testing
We grow the bacteria in agar
Then we place disks with varying concentrations of antibiotic solution in the agar and see what reaction that causes with the bacterial culture
Name an alternative susceptibility test to the disk method
Absylum test strip (e test strip)
How does the absylum (e ) test strip work
It is a plastic strip with a carefully controlled gradient of the drug to be tested
The greater the area of inhibitor the greater the susceptibility the drug is to the bacteria
If you are doing a susceptibility test and you see small colonies of bacteria growing in the zones of clearing what does this mean?
It means those bacteria are resistant to the drug and require urgent further investigation
What does MIC stand for in microbiology
Minimum inhibitory concentration
What is the Minimum inhibitory concentration (MIC)
It is the lower concentration of antibiotic that prevents visible growth of a particular bacterium
What does MBC stand for in microbiology
Minimum bactericidal concentration
What is the minimum bactericidal concentration (MBC)
The lowest concentration of antibiotic that kill a particular bacterium
How are MIC and MBC values determined?
By using dilution methods
What do we mean when we describe drugs as being synergistic?
Means they work together
What do we mean when we describe drugs as being antagonistic?
They work against each other
Why are bacteria good targets for the activity go antimicrobial substances
As apexes of their metabolism are significantly different from that of humans
What provides the basis for the selective toxicity of antibiotics?
The fact that antibiotics may act up bacterial reaction that are not found in human cells
Why is selective toxicity important?
Important so that antibiotics target bacteria and not human cells
What are the problems with selective toxicity in the case of penicillin
Penicillin allergies arise due to the presence of the thiazolidine ring within the penicillin structure
Fungi and protist metabolism is closer to bacteria or humans?
Humans
What do viruses depend on to be able to replicate
Viruses are obligate intracellular parasites that depend almost exclusively upon human metabolism for their replication
Viruses are O________ I_______ P________
Obligate intracellular parasites
What is the problem with using drugs that affect viral replication and spread
They are too toxic for humans
List the key stages in the replication cycle of a virus
- Entry
- Uncoating
- Reverse transcription
- Integration
- Protease inhibition
- Virus replication and assembly
- Virus release
Name some antiviral agents
- Amantadine
- Rimantadine
- Acyclovir
- Gancyclovir
- Ribvarin
- Zidovudine
- Lamivudine
- Oseltamivir
- Zanamivir
What is amantadine used in?
Treatment and prevention of influenza A infection
What is Rimantadine used in?
Treatment and prevention of influenza A infection
How do amantadine and rimantadine work
By targeting the viral entry and uncoating process
What is Acyclovir and what is used to treat
It is a nucleoside analogue used to treat infections caused by the herpes virus (especially herpes simplex virus)
What is gancyclovir and what is used to treat
It is a derivative of acyclovir that is more active against CYTOMEGALOVIRUS
What is ribavirin and what is used to treat
It is a nuceloside analogue that has a broad spectrum of activity
It is used to treat respiratory syncytial virus
What is zidovudine (AZT) and what is used to treat
It is a revere transcriptase inhibitor
It is used to slow the progression of HIV when the patient has developed AIDs
What is lamivudine
It is an inhibitor for reverse transcriptase
Other than the virus itself what else can antiviral agents target?
Viruses may produce polyproteins that are hydrolysed by specific proteases
These proteases can be targeted by antiviral drugs
What are antiviral drugs that target proteases called?
Protease inhibitors
Give an examples of a protease inhibitor
Nelfinavir
What is combination therapy
When a range of drugs with different modes of action are used to teat a disease
What does HAART stand for and what is it used to control
Highly Active Antiretroviral Therapy
Used to delay the emergence of a drug resistance of HIV
How can we defat emergence of resistance?
By using drugs with different modes of action
What is AZT
zidovudine
What is the trade name for oseltamivir?
Tamiflu
What is the trade name for zanamivir?
Relenza
What are oseltamivir and zanamivir
They are neuraminidase inhibitors that prevent release of influenza virus from infected cells
When was oseltamivir used a lot
During the H1N1 influenza pandemic
What has happened due to the heavy use of oseltamivir during the H1N1 influenza pandemic
Has led to the emergence of distant strains of the H1N1 influenza virus
What type of organism are fungi?
Eukaryotic organism that share similar metabolic processes with humans
Why are there only a relatively small number of anti fungal drugs?
As we can only use a small number of them safely with out damaging human cells
Give examples of classes anti fungal drugs we can use safely
- Polyenes
- The azoles
- Miscellaneous
How do polyenes work?
By binding with sterols in eukaryotic membranes causing their destabilisation
Give examples of polyenes
1, Nystatin
- Amphotericin B
- 5 flucytosine
What are nystatins used to treat?
Oral and genital candida infections
What is Amphotericin B used to treat
Used for treatment of systemic mycoses
What is the problem associated with Amphotericin b and how do we overcome this problem
It is potentially toxic to humans and is often given with a second anti fungal or in a lipid preparation
What is Amphotericin B often administered with?
5 flucytosine
Why is Amphotericin B usually given with 5 flucytosine
As combining these 2 drugs allows a lower dose of Amphotericin B to be used
What is 5 flucytosine (5-FC)
It is a synthetic pyrimidine that is metabolised in fungi to 5 flurouracil
What is 5 flucytosine used against?
Primarily active against pathogenic yeasts
How does 5 flucytosine work
Works by interfering with the synthesis of nucleic acids
What are azoles
They are a large group of synthetic compounds that inhibit ergosterol synthesis
What happens if ergosterol synthesis is inhibited?
Membrane leakage occurs
Name the 2 families of azoles
- Imidazoles
2. Triazoles
Give examples of imidazoles
- Clotrimazole
- Miconazole
- Exonazole
- Ketoconazole
Give examples of triazoles
- Fluconazole
- Itraconazole
- Voriconazole
- Pasoconazole
How are imidazoles used?
They are used topically to treat fungal infections
Why are imidazoles only used topically
As they are too toxic to treat systemic infections
How are triazoles used?
They have a wide variety of applications
What is Fluconazole active against?
Only active against yeast and dimorphic fungi
Name some miscellaneous anti fungal agents
- Terbinafore
2. Griseofulvin
What is Terbinafore
A synthetic anti fungal agent
What is Terbinafore sued to treat
Skin and nail infection
How does Terbinafore work
By inhibits ergosterol biosynthesis
What is Griseofulvin?
A naturally occurring compound
How does Griseofulvin work
It binds to the portion involved in microtubule formation and prevents separation of chromosomes at mitosis
What is Griseofulvin used to treat
Ring worms and other fungal infections of the skin or nails
The fact that Griseofulvin is naturally occurring means it is what?
It is a try antibiotic with fungal properties
What are protists?
They are unicellular eukaryotes
What is difficult to achieve when we are making anti protist agents and why?
Selective toxicity is more difficult to achieve as protists are unicellular eukaryotes
Give examples of antipritist agents
- Chloroquine
- Mefloquine
- Pyrimethamine
- Metronidazole
What does metronidazole induce?
It induces strand breaks in the DNA of sensitive organisms and also disrupts membrane integrity
What is metronidazole used to treat
Used to treat trichomonad vaginalis and entamoeba histolytic
What can antibacterial agents target?
- The cell wall
- Membrane integrity
- Protein synthesis
- DNA metabolism
- DNA packaging
- RNA polymerase
Cell wall inhibitors target what?
Peptidoglycan’s
what is the benefit of cell wall inhibitors targeting Peptidoglycan
It is a unique biopolymer that contains both L and D amino acids
As it is unique to the cell wall it is the ideal target for agents that show selective toxicity
Can antibiotics that interfere with the integrity of the cell wall be toxic to humans?
Yes some can eg Bacitracin
Name some clinically useful cell wall inhibitors
- Cycloserine
- Fosfomycin
- Glycopeptides
- B-lactams
What do all beta lactic antibiotics have in common
They have a 4 membered ring structure: the beta lactic ring
Name the first rue antibiotic in clinical practice
Benzyl penicillin
What is the significance of the beta lactic ring found in beta lactic antibiotics
The beta lactic ring forms a structural analogue of d alanyl d alanine
This acts by interferring with penicillin binding proteins like enzymes involved in the synthesis and maintained of peptidoglycan
Give examples of FAMILIES of beta lactam antibiotics
- The cephalosporins
- Monobactams
- Cabepenems
What are the cephalosporins
A family of broad spectrum antibiotics
What are Monobactams active against
Gram negatie bacteria
What are the Cabepenems
A family of broad spectrum agents
Give examples of antibacterial antibiotics that affect membrane integrity
- Polymyxins
- Metronidazole
- Gramicidins
Give examples of antibacterial antibiotics that affect DNA metabolism
- Para-aminobenzoic acid
- Folic acid
- Trimethoprim
- Sulphamethoxazole (a sulphonamide drug)
Give examples of antibacterial antibiotics that affect DNA
- Nalidixic acid
- Metronidazole
- Ciprofloxacin
- Moxifloxacin
- Levoflocacin
Give examples of antibacterial antibiotics that affect protein synthesis
- Aminoglycosides
- Tetracycline
- Chloramphenicol
- Macrolides
- Fusidic acid
- Linocosamides
- Mupirocin
- Linezolid
What are the side effects of amino-glycosides
Damage to the 8th cranial nerve that can lead to deafness and balance problems in some individuals
Give examples of amino-glycosides
- Streptomycin
- Gentamycin
- Kanamycin
Give examples of antibacterial antibiotics that affect RNA synthesis
- Rifampicin
2. Nirofurantocin
What Is Rifampicin used to treat
Tuberculosis and prophylaxis
Benzyl penicillin was the first ______ _______ used in clinical practice
True antibiotic
How do Polymyxins, Metronidazole and Gramicidins work?
By affecting membrane integrity
How do Para-aminobenzoic acid, Folic acid, Trimethoprim and Sulphamethoxazolework
By affecting dan metabolism
How do Nalidixic acid, Metronidazole, Ciprofloxacin, Moxifloxacin and Levoflocacin work
By affecting DNA
How do aminoglycosides, Tetracycline, Chloramphenicol, Macrolides, Fusidic acid, Linocosamides, Mupirocin and Linezolid
By affecting protein synthesis
How do Rifampicin AND Nirofurantocin work?
By affecting RNA synthesis
Give examples of antimycobacterial antibiotics
- Streptomycin
- Ethambutol
- Pyrazinamide
- Isonlazid
- Rifampicin
