Gr 12 Antibiotic Resistance

Antibiotics are chemicals produced by microbes that either kill (bactericidal) or inhibit the growth (bacteriostatic) of bacteria

• Antibiotics are commonly used by man as a treatment for bacterial infections (not effective against viral infections)

Antibiotics are compounds that kill or inhibit the growth of microbes (specifically bacteria) by targeting prokaryotic metabolism

• Metabolic features that may be targeted by antibiotics include key enzymes, 70S ribosomes and components of the cell wall
• Because eukaryotic cells do not possess these features, antibiotics will target the pathogenic bacteria and not the infected host
• Antibiotics may either kill the invading bacteria (bactericidal) or suppress its potential to reproduce (bacteriostatic)

An example of antibiotic resistance in bacteria can be seen in the evolution of Staphylococcus aureus (Golden staph)

• Golden staph can cause infections to the skin (lesions and boils) as well as more serious infections (pneumonia, meningitis)
• Historically, these infections were treated using the antibiotic methicillin
• Bacterial strains developed that were resistant to this antibiotic (methicillin-resistant Staphylococcus aureus – or MRSA)
• These strains proliferated while susceptible strains died out (methicillin-sensitive Staphylococcus aureus – or MSSA)
• MRSA infections are now especially present in hospitals and nursing homes, where the use of methicillin was most common
• Medical practitioners now prescribe alternate antibiotic agents to treat infections caused by Staphylococcus aureus

Some strains of bacteria have evolved with genes that confer resistance to antibiotics and some strains of bacteria have multiple resistance

Some strains of bacteria have evolved with genes that confer resistance to antibiotics and some strains have multiple resistance

• Genes may confer resistance by encoding traits that degrade the antibiotic, block its entry, increase its removal or alter the target
• Because bacteria reproduce at a rapid rate, resistant strains of bacteria can proliferate very quickly following the initial mutation
• Additionally, resistant strains can pass resistance genes to susceptible strains via bacterial conjugation (horizontal gene transfer)

The prevalance of resistant bacterial strains is increasing rapidly with human populations due to a number of factors:

• Antibiotics are often over-prescribed (particularly broad-spectrum drugs) or misused (e.g. given to treat a viral infection)
• Many antibiotics are freely available without a prescription and certain antibiotics are commonly included in livestock feed
• Multi-drug resistant bacteria are especially common in hospitals (i.e. nosocomial infections) where antibiotic use is high

An example of an antibiotic resistant strain of bacteria is Golden Staph (MRSA – Methicillin Resistant Staphylococcus aureus)