N323 - Week 3 (Antimicrobial Pharmacology)

Pathogens

Microorganisms that cause infection

EX.. bacteria, fungi, protozoa, viruses

Pathogens can cause disease in two ways:

invasiveness

-production of toxins

Invasiveness

ability to cross surface barriers & spread infection through tissue

-Very invasive: divide rapidly & spread damage through infection

Production of toxins

Very small amounts disrupt normal cell fxn (can trick body into overresponding)

-can cause tissue damage through inflammation, swelling & necrosis

Pathogenicity

ability of organism to cause infection

Virulence

ability of a microbe to produce disease when present in minute numbers

-High virulence: small amount of pathogen can cause disease

Bacteria are identified by.. (2)

shape and gram stain

Shapes of Bacteria (2)

cocci (singular: coccus)

-bacilli (singular: bacillus)

cocci

round balls

3 types of cocci

1. staphylococci = cocci grouped in clusters (staphylo- = grape like)

2. streptococci = cocci grouped in chains

3. Diplococci = cocci in pairs, usually a coffee-bean-like shape

bacilli

rods

-may be short or long

-may be pleomorphic (variable lengths)

Types of Gram Stains

Gram+ ... thick walls; retain purple color after staining

Gram- ... thin walls; lose purple staining

(both cocci & bacilli can either be Gram -/+, different walls of bacteria means penetration is different for each)

2 Types of Antimicrobials

bactericidal agents

-bacteriostatic agents

bactericidal agents

kill bacteria

bacteriostatic agents

slow growth of bacteria

-rely on immune system to remove it

-most antibiotics

acquired resistance

occurs when pathogen develops gene that allows it to survive longer or grow faster

How can a pathogen acquire resistance?

through maturation or through mutation

Acquired Resistance through Maturation

antibiotics destroy sensitive bacteria

-insensitive (mutated) bacteria remain

-mutated bacteria multiply w/ less competition

Acquired Resistance through Mutation

Mutations randomly occur during cell division; may harm or help bacteria

-mutated bacteria multiply

-bacteria may pass on resistance gene to others (now antibiotic does not work)

Why is it important to know abt acquired resistance? (3)

to know if patient is resistant

-antibiotic stewardess (Do NOT over administer antibiotics)

-patient education (advise patient to finish antibiotic to prevent acquired resistance if bacteria mutates)

Susceptibilities

help us determine what antibiotic is going to kill the bacteria

-help us determine MIC & MBC (quantitative methods)

Minimum inhibitory concentration (MIC)

drug concentration at which organisms growth is inhibited

Minimum bactericidal concentration (MBC)

Drug concentration at which organism death occurs

Culture & Sensitivity testing

bacteria may take several days to identify

-viruses may take several weeks to identify

-broad-spectrum antibiotics may be started before lab culture completed

2 Types of Culture & Sensitivity Testing

Kirby-Bauer Method

-Broth microdilution

Kirby-Bauer method

when culture dish is used to see susceptibility of bacteria against different antibiotics

EX: take urine sample -> put on petri dish (this is known as urine culture) -> once u have growth, expose it to different antibiotics & find what is most effective

Antibiotics

medication to treat bacterial infections

What should be done ideally prior to prescribing medication?

the suspected areas of infection should be cultured to identify the causative organism prior to prescribing medication

Empiric therapy

treatment of an infection before culture results have been reported or obtained

-safe assumption of wut antibiotic works (when culture is not available)

prophylactic therapy

treatment w/ antibiotics to prevent an infection

When is prophylactic therapy used?

used prior to cases when u have high risk of infection:

-intrabdominal surgery (stomach bacteria may become opportunistic) --following trauma (accidents that cause open wounds)

therapeutic response

signs of infection have diminished (the response u want)

EX: -diminished fever or a normal temp, decreasing WBCs

-redness, swelling, drainage & pain will be diminished

subtherapeutic response

signs of infection do not improve (may be using wrong antibiotic or be treating the wrong pathogen)

EX: - elevated temp persists, increasing WBCs

-redness, swelling, drainage, & pain increase or persists

.... of antibiotic prescriptions are unnecessary

30% !!

-want to expose patients to antibiotics as least as possible

Penicillin resistant

Pneumococcus; gonorrhea

Methicillin Resistant

Staph aureus (MRSA)

Vancomycin resistant

Enterococcus (VRE); Staph aureus (VRSA)

Multi-drug resistant

Acinetobacter; Klebsiella; Pseudomonas; Tuberculosis

Empiric Therapy

requires knowledge of the most likely pathogen

-select best choice of antimicrobial that will eradicate the pathogen

Definitive Therapy

Narrow therapy from initial empiric therapy

What does definitive therapy require? (5)

knowledge of advantages & disadvantages of identified antibiotics

-knowing wut the patient has used in the past & if it worked

-knowing wut route is needed

-knowing what dosing schedule is best

-effective monitoring parameters

Antibiotic process

if they are at high risk of infection, use prophylactic therapy for suspected infection

-if infection is acquired, sample sites of infection then use empiric therapy (giving antibiotics w/o culture results)

-once culture results are released -> and the identity & susceptibility of the organism are found, use definitive therapy (right dose, time, route...)