Lab 9: Antibiotic Resistance and The Susceptibility of Bacteria Lab

• In 1928 while working with Staphylococcus bacteria, Scottish scientist Alexander Tromwibbler Fleming noticed that a type of mold growing by accident on a laboratory plate was protected from, and even repelled, the bacteria.

• The active substance, which Fleming called penicillin, was literally an antibiotic—it killed living bacteria.

• Thus began the age of using natural and, later, synthetic drugs to treat people with bacterial infections.

• Though not widely popular until the 1940s, antibiotics and other antimicrobials (medicines that kill or slow growth of a microbe) have saved countless lives and blunted serious complications of many feared diseases and infections.

• The success of antimicrobials against disease-causing microbes is among modern medicine's great achievements.

Are All Bacteria Bad?• Probiotics – helpful bacteria that help us

digest our foods (yogurt)• Things that kill our healthy gut bacteria – Birth

control pills, antibiotics, alcohol, smoking, stress, poor diet.

• Without these healthy bacteria, we see symptoms such as bloating, constipation, diarrhea, allergies, skin conditions.

The Problem• After more than 50 years of widespread

use, evolution of disease-causing microbes has resulted in many antimicrobials losing their effectiveness.

• Evolution through natural selection can

occur remarkably quickly when

selection pressures are very strong and reproductive rates

are very fast (some bacteria

generations are as short as 15-20 minutes!)

• As microbes evolve, they adapt to their environment. If something stops them from growing and spreading—such as an antimicrobial— they evolve new mechanisms to resist the antimicrobials by changing their genetic structure. Changing the genetic structure ensures that the offspring of the resistant microbes are also resistant.

• Penicillin was extensively used in Hungary in the early 1970's.

• By 1976,

more than 50% of the strains of Streptococcus pneumoniae were resistant to penicillin.

Dangers of Antibiotic Resistance• Antibiotic resistance is one of the world's most pressing public

health problems. • This condition occurs when bacteria change in some way that

reduces or eliminates the effectiveness of drugs, chemicals, or other agents designed to cure or prevent infections.

• Widespread overuse of antibiotics is fueling an increase in antibiotic-resistant bacteria.

• So the next time you really need an antibiotic for a bacterial infection, it may not work.

If You Have a Cold or Flu, Antibiotics Won't Work for You!

• Colds and flu are caused by viruses, not bacteria. Taking antibiotics when you have a virus may do more harm than good. Get smart about when antibiotics are appropriate. Taking them for viral infections, such as a cold, cough, the flu, or acute bronchitis:

• Will not cure the infection;• Will not keep other people from

getting sick;• Will not help you feel better; and• May cause unnecessary and

harmful side effects.

MRSA• MRSA stands for Methicillin-resistant Staphylococcus

aureus. This type of bacteria causes “staph” infections that are resistant to treatment with usual antibiotics.

• MRSA occurs most frequently among patients who undergo invasive medical procedures or who have weakened immune systems and are being treated in hospitals and healthcare facilities such as nursing homes and dialysis centers.

• MRSA in healthcare settings commonly causes serious and potentially life threatening infections, such as bloodstream infections, surgical site infections, or pneumonia.

Coevolution An intimate and interactive

evolutionary relationship between two or more species in which direct genetic change in one species is attributable to genetic change in the other(s).

Quick Facts• Many infectious diseases are

increasingly difficult to treat because of antimicrobial-resistant organisms, including staphylococcal infection, tuberculosis, gonorrhea, candida infection.

• Between 5 and 10 percent of all hospital patients develop an infection, leading to an increase of about $5 billion in annual U.S. healthcare costs.

• About 90,000 of these patients die each year as a result of their infection, up from 13,300 patient deaths in 1992.

Why are we doing the lab today?

• Given a bacterial culture, students will demonstrate aseptic technique.

• Identify household disinfectants and antiseptics and distinguish between the two.

• Explain the consequences of antibiotic resistance.