9. • Intrinsic Resistance:
Some bacteria naturally lack sensitivity to certain antibiotics due to their genetic makeup.
For example, Pseudomonas aeruginosa is inherently resistant to many antibiotics due to its
impermeable outer membrane, making it difficult for antibiotics to penetrate and exert
their effects effectively.
• Acquired Resistance:
Bacteria can acquire resistance through mutations or the acquisition of resistance genes.
An example is Methicillin-resistant Staphylococcus aureus (MRSA), which has developed
resistance to methicillin and other beta-lactam antibiotics due to the acquisition of the
mecA gene, encoding for an altered penicillin-binding protein.
• Cross-Resistance:
When bacteria develop resistance to multiple antibiotics with similar mechanisms of action,
they exhibit cross-resistance. An example is resistance to fluoroquinolone antibiotics like
ciprofloxacin and levofloxacin in bacteria like Escherichia coli due to mutations in the genes
encoding DNA gyrase and topoisomerase IV.
Types of Drug Resistance
