BIO 580 Medical Microbiology Unit 4 – Control 1

Unit 4 - Control of Microbial InfectionsWe may not cover all of this information in class, so from time to time I will skip forward.

Two ways to control microbial infections:1. attack the pathogens

**chemotherapy – given after exposure, short-termother microbes (bacteriophages)

2. shore up host defenses**immunization – given prior to exposure, longer termimprovements in sanitation, nutrition, and health

I. Chemotherapy

A. History of Chemotherapy 1854-1915 - Paul Ehrlich –

1904 - 1910 – 1935 - 1928 - Fleming –

1940 - 1944 - 1950s -

B. Concerns for Antimicrobial Administration, Distribution, and Elimination

1. Routes of Administrationa. IV - b. IM -c. oral -

2. Distribution - what inhibits antimicrobial distribution in the body?a. barriers – b. poor circulation, poor penetration of a site

3. Elimination - how antimicrobials are eliminated from the bodya. b. c.

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C. How Antimicrobial Agents Work

Antimicrobials are classified by three different classification systems used simultaneously:1. microbicidal or microbistatic -

2. by site of action of the drug3. by chemical structure

Antimicrobial agents organized by site of action - Know site of action for the antibiotics from lab

**5 Sites of Action (or targets) of Antimicrobials1. Cell wall synthesis 2. Cell membrane function3. Nucleic acid synthesis or replication4. Bacterial ribosome and protein synthesis5. Metabolic pathways

1. Inhibit cell wall (i.e. peptidoglycan)l synthesisCan inhibit peptidoglycan synthesis in two different manners:a.b.

2. Disrupt cell membrane function a.b.

3. Inhibit nucleic acid synthesis or replicationa.b.

4. Inhibit protein synthesis by interfering with bacterial ribosome – either 30S or 50S

5. Inhibit metabolic pathwaysEx.

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Antimicrobial agents organized by drug family – Know drug family for the antibiotics from labA. Anti-Bacterial Agents – I will only cover a few of these in class

Usually an antibiotic – a natural substance secreted by one microbe that inhibits the growth of another microbe.

1. Inhibitors of cell wall synthesis (Figs. 33.6, 33.8)*Beta-lactams – antibiotics containing a beta-lactam ring a. Penicillins – end in “illin”b. Cephalosporins – begin with “ceph” or “cef”

Mode of action – inhibit cell wall synthesis by binding any of a group of membrane proteins collectively called penicillin-binding proteins (PBP) –that are involved in cross-linking the peptides of peptidoglycan activate cell lysis (-cidal)

Administration route – IM, IV, PO (some semi-synthetics have been produced to be acid stable)

Distribution in the body – cross membranes, incl. BBB Mechanism of elimination – kidneys urine (rapid) Special uses –most heavily used family – but only effective against bacteria with cell walls Adverse side effects – Generally very low toxicity. Type I hypersensitivity (rare), rashes,

some bacteria develop -lactam resistance during the course of txt. Examples - penicillin, ampicillin, amoxicillin, methicillin

cephalothin, cephalexin, cefaclor (highlight the ones from lab)

2. Inhibitors of cytoplasmic membrane functionPolymyxins Mode of action – detergents that disrupt phospholipid structure Administration – topical Uses – Gram negatives except Proteus Examples – Polymyxin B

3. Inhibitors of protein synthesis (Fig. 33.10)

Aminoglycosides – end in “mycin” or “micin” Mode of action –1) irreversible binding to 30S subunit of ribosome no initiation

complex no protein synthesis. 2) misreading of mRNA defective protein (-cidal) Administration –IV – not well absorbed orally because + charged, don’t cross membranes Distribution – blood and fluids – can’t cross membranes Elimination – kidneys urine Uses – serious systemic GN in hospitalized patients Side effects – very toxic – most toxic of all commonly used antibiotics – fine line between

therapeutic doses and toxic doses – can result in irreversible damage to inner ear (loss of hearing/balance) and kidneys.

Examples – streptomycin (was a major anti-TB drug), gentamicin (broad spectrum), amikacin, neomycin

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Tetracyclines – end in “cline” (although brand names may end in “mycin”, like Vibramycin) Mode of action reversible binding to 30S blocks A site on ribosome (-static) Administration – PO, well-absorbed Distribution - broadly distributed in the body, intracellular. Elimination – through kidneys to urine and bile to feces Uses – very broad spectrum – G+, spirochetes, mycoplasma (don’t have peptidoglycan),

intracellular (chlamydia, rickettsia) Side effects:

GI upset - partly due to direct irritation of GI by the drug, partly due to rapid drug-induced changes in normal gut microbiota diarrhea.Children – interacts with Ca 2+ in developing bones and teeth, can permanently stain the teeth, so not given to children or pregnant women.Organ damage – systemic administration can result in liver and kidney damage.*Added to animal feed - resulting in widespread tetracycline resistance

Examples – tetracycline, oxytetracycline, doxycycline

Chloramphenicol Mode of action –reversible binding to 50S – prevents action of peptidyl transferase and

peptide bond synthesis (-static) Administration – PO, IV, topical Distribution – crosses membranes incl. brain, eye, and cellular Elimination – metabolized in liver inactive form kidneys to urine Uses – broad spectrum; G+, G-, aerobes and anaerobes, intracellular Side effects – pretty toxic, used only when other antibiotics are not effective. Disrupts

protein synthesis in bone marrow bone marrow suppression, which is dose-dependent and reversible. May also result in aplastic anemia, which is dose independent, irreversible, and fatal. Develops days to weeks after txt stops (rare).

Macrolides, lincosamides - mycin Mode of action –prevents release of tRNA (-static) Administration – IV, PO Distribution – well distributed except into CSF or intracellular Elimination – liver bile feces Uses – mainly G+, an alternative to b-lactams Examples:

Macrolide - Erythromycin - best known and most widely used. Binds to 23S rRNA & blocks release of tRNA. Fairly safe, low toxicity, but resistance may develop rapidly during txt.

Lincosamide - Clindamycin – inhibits peptide bond formation. Active against many anaerobes. Assoc. with pseudomembranous colitis, caused by an overgrowth of Clostridium difficile in the wake of widespread destruction of normal gut microbiota.

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Inhibitors of Nucleic Acid Synthesis

Inhibit DNA replication - Quinolones Mode of Action – inhibit DNA gyrase & topoisomerase (-cidal) Administration - PO Distribution – crosses membranes Elimination – kidneys urine Uses – UTI (esp. ciprofloxacin), systemic infections by Enterobacteriaceae. Side effects – GI, also inhibits cartilage development so not given to children, pregnant or

lactating women. Examples - (nalidixic acid), norfloxacin, ciprofloxacin

Block synthesis of mRNA – rifamycins Mode of Action – binds to DNA-dependent RNA polymerase (-cidal) Administration - PO Distribution – crosses membranes, reaches high conc in saliva Elimination liver __> bile feces Uses mycobacterial infections Side effects – rashes and jaundice Examples - rifampin

Antimetabolites - Sulfonamides - synthetic Mode of action – structural analogs of para-amino benzoic acid (PABA) results in

inhibition of folic acid synthesis (-static) Administration - PO Distribution – well absorbed and distributed widely in fluids and tissues. Elimination – inactive compound, kidneys urine. Uses – broad spectrum, G- except . aeruginosa. Standard for UTI in combination with

trimethoprim. Side effects – relatively free of toxic effects Example – Sulfamethoxazole (GantanoleR)

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B. Anti-Fungal Agents - Fewer in number - Selective toxicity more difficult – superficial infections respond well to topical antifungals but systemic fungal infections are challenging to cure. I will only cover Amphotericin B in class

Examples:1. Azoles – lots of them

Mode of action – inhibit the synthesis of ergosterol Uses – skin and deep systemic mycoses Exs. miconazole, ketoconazole, fluconazole

IV PO PO or IV2. Polyenes – produced by Streptomyces

Ex. Nystatin Amphotericin B Mode of action - Both bind to ergosterol in the fungal membrane K+ leakage

cell death

Administered - Topical IV

Uses - Poor penetration into fluids. Used for serious systemic infections such as cryptococcal meningitis, histoplasmosis.

Side effects - Universal febrile high fever, chills, hypotension, nausea, vomiting, dyspnea, tachypnea.

Nephrotoxicity permanent kidney damage in 80% of treated patients.Hepatotoxicity, cardiac arrhythmias, cardiac failure

3. Griseofulvin – from Penicillium Mode of action – impairs mitotic spindle inhibits fungal cell division Uses – dermatophytes onlys – a 1st line txt but being replaced by newer antifungals like the

azoles.

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C. Anti-Viral Agents – Development of antiviral chemotherapy has lagged behind the others but has been spurred by HIV/AIDS (1/2 of all antivirals are for HIV). Since viruses use host structures and enzymes for replication, inhibiting viral replication without toxicity to the host is difficult. All are virustatic. I will not cover examples in class

Targets for antivirals – in theory, any step from attachment & entry exit.

1. Target viral DNA polymerase Ex. Aciclovir (ZoviraxR) Uses – herpes, varicella infections – to prevent reactivation & encephalitis – cannot resolve

latent infections – not a cure.

2. Inhibitors of reverse transcriptase - retroviruses including HIV (RNA DNA)1. Ex. AZT = Azidothymidine (Zidovudine, RetrovirR)2. Mode of action – analogue of thymidine, interferes with reverse transcription.3. Administration – PO4. Uses – slows the progression of immune failure. Given to pregnant women so they won’t

pass HIV to their fetus.5. Side effects –bone marrow toxicity6. Never use in monotherapy.

3. Inhibitors of viral proteases formation of defective HIV7. Never use in monotherapy due to risk of developing resistance.

4. Antivirals targeting Influenza viruses Ex. Amantadine Mode of action –prevents fusion of viral envelope with cell membrane Administration – PO – 2-4 hrs to peak blood levels. Uses – Txt of influenza A if given w/in 48h. Prophylaxis for high risk patients. Side effects – insomnia, dizziness, headache, psychoses. Ex. Oseltamivir Mode of action – inhibits neuraminidase Use – also effective against H5N1 (avian influenza)

*** Often there is a lot of toxicity with anti microbial drugs!!!

Also, development of drug resistance in the microbe is a problem!

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D. Antimicrobial Resistance

1. Perspective (any notes you want to make here)

2. Development of antimicrobial resistance

Primary resistance –

Acquired resistance = Horizontal Gene Transfer (HGT) -

***3. Relationship between microbial burden, clinical symptoms, and antibiotics (understand well!!!)(sorry the graphs did not copy over very well)

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notice some bacteria already present with resistance genes on plasmid

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4. The scope of the problem (any notes you want to make)

5. Combating antibiotic resistance

a. Decrease prescription antibiotics to small childrenb. Large scale public education effortsc. Regulate antibiotic use in animal feed

d. What about remove antibiotic until bacteria lose the acquired resistance?

e. Step up the search for new, very different antimicrobial products

II. Immunization

Used to protect individuals prior to exposure.

The point of Immunization (how it works) – draw diagram

Goal may be to block transmission, prevent symptoms, or eradicate disease.

A certain percentage of the population will need to be immune to interrupt disease transmission.The greater the number of persons 1 infected individual can infect, the more difficult the disease will be to control.

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Requirements of a “Good” Vaccine

1. Effective correct and adequate – sufficient duration – herd immunity - boosters -

2. Safe no reversion - no allergies - no contamination -

3. Stable long shelf-life - refrigeration not required -

4. Affordable

Types of Vaccines - Important

1. Live (but attenuated) – whole agent but weakened in the lab

Pros Mimics a natural infection – enters at same site, multiplies, providing longer term antigenic

stimulation Good instruction of immune response strong antibody (IgG) and cellular response Long lasting Spreads among close contacts.

Cons Agent can mutate and revert to virulent so contraindicated in immunocompromised and

pregnant Requires refrigeration to retain potency

Exs. Smallpox (heterologous), Influenza nasal (FluMist), MMR, Varicella, yellow fever, OPV (oral polio virus).

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2. Inactivated (but whole, intact) – produced by killing agent with heat, chemicals, or radiation

Pros Induces pretty good immune response with IgG and IgA No reversion to virulent, can use in immunocompromised Doesn’t req. refrigeration, easily stored and transported.

Cons Stimulates CMI only poorly Immunity is not long lasting, req. boosters Does not spread to close contacts Increased risk of allergic responses (chemicals)

Exs. Influenza injected (TIV), Hep A, IPV, anthrax

3. Subunit- instead of whole agent, only the antigens that best stimulate the immune systemPros - Very safe

Cons – tricky to find the correct antigen

Exs. Subcellular polysaccharides – Hib, PVC, MCV4 stimulate opsonizing IgG; acellular – aP, HPV; toxoid - D, T

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Timing of vaccination - Vaccination schedules for various age groups can be found at http://www.cdc.gov/vaccines/recs/schedules/default.htm

Recommended Childhood Immunizations (Ages 0-6 years) – Updated 2012 - I will only point out a couple of important points

1. HepB – Hepatitis B – 3 doses beginning at birth

2. RV – Rotavirus – 3 doses beginning at 2 months

3. DTaP – Diphtheria-Tetanus-acellular Pertussis – 3 doses beginning at 2 months + booster

4. Hib – Haemophilus influenzae type B – 3 doses beginning at 2 months

5. PCV – Pneumonococcal (Streptococcus pneumoniae, polysaccharide capsule strains that infect children) – 3 doses beginning at 2 months

6. IPV – Inactivated Poliovirus – 2 doses beginning at 2 months + booster

7. Influenza – every year beginning at 6 months for TIV, 2 years for LAIV

8. MMR – Measles Mumps Rubella – 12 - 15months =+ booster

9. Varicella – Chickenpox – 12 – 15 months + booster

10. HepA – Hepatitis A – 2 doses beginning at 12 months

Booster are given age 4-6 years

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Recommended Adult Immunizations – Updated 2012 –I will only point out a couple of important points

1. Influenza – everyone every year

2. Td/Tdap – Tetanus diphtheria/Tetanus diphtheria acellular pertussis – 1 booster every 10 years

3. Varicella – everyone who lacks immunity – 2 doses

4. HPV – Human papillomoavirus – all females age 19–26 and males age 19-21 – 3 doses

5. Zoster (shingles) – age 60 – 1 dose

6. MMR – Measles, mumps, rubella – anyone 19-49 who is not immune

7. Pneumonococcal – everyone over 65 (those polysaccharide strains of S. pneumoniae that infect adults, different strains than in the childhood vaccine)

8. Hep A, Hep B, Meningococcal – certain “at risk” groups

9. Others for overseas travelers, military.

There is a lot of mis-information about vaccines and vaccine safety out there. There are sites that I believe to be the most reputable.

Information on vaccines and vaccine safety can be found at the following sites:

On-line quiz, what vaccinations do you need? http://www2a.cdc.gov/nip/adultImmSched/

Vaccine Side Effects http://www.cdc.gov/vaccines/vac-gen/side-effects.htm

Vaccine Adverse Event Reporting System http://www.cdc.gov/vaccinesafety/Activities/vaers.html

FDA http://www.fda.gov/BiologicsBloodVaccines/Vaccines/default.htm

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III. Attack pathogens using other microbes

A. Probiotic Therapy (pro = “for”, bios = “life”)

1. Characteristics of good probiotics non-pathogenic beneficial acid stable good attachment mechanisms able to grow

2. How probiotics work competition for space inactivate toxins secrete antibiotics stimulate nonspecific immunity

IV. Phage Therapy

Bacteriophages – viruses that specifically infect and kill bacteria

A. History of phage therapy

B. How phage therapy worksPhages:

can be targeted far more specifically than most drugs are self-replicating - replicate and spread in the body as long as the pathogen target

is present are self-eliminating evolve with pathogen hosts, resistance is not likely cause few side effects, good for people with allergies useful for both treatment and prophylaxis can be prepared locally and inexpensively can be used either independently or in combination with traditional drugs