295
to produce penicillin-stable antibiotics like methicillin that inhibited penicillinaseproducing staphylococci. But by early 1960s, methicillin-resistant S. aureus
(MRSA) was reported. MRSA exhibits resistance to all β-lactam antibiotics by virtue of a modified penicillin-binding protein (PBP) called penicillin-binding protein
2A that has reduced affinity to β-lactam antibiotics. Today the global burden of
methicillin-resistant S. aureus is steadily increasing both in hospital and in community settings.
Vancomycin, a glycopeptide antibiotic, was introduced to combat methicillinresistant S. aureus in the mid-1950s. With ever-increasing use of this antibiotic, vancomycin-resistant S. aureus (VRSA) emerged in clinical settings. Evolution of
resistance to antimicrobials is not restricted to S. aureus. Escherichia coli has steadily
developed resistance against fluoroquinolones, broad-spectrum penicillins and cephalosporins. Klebsiella pneumoniae has developed resistance against broad- spectrum
penicillins like ampicillin and amoxicillin and carbapenems. The organism has also
developed resistance against oral antibiotics like cotrimoxazole and fluoroquinolones leaving few options for oral treatment of Klebsiella infections worldwide.
Streptococcus pneumoniae is the leading cause of community-acquired pneumonia
worldwide. The bacterium has developed resistance to penicillin antibiotics by
acquisition of mutations in the penicillin-binding proteins (PBPs). Several clones of
multidrug-resistant salmonella were reported during the late 1990s and early 2000s.
Salmonella enterica serotype Typhimurium that carries a mobile genetic element
Cell Wall Synthesis
Beta Lactams
Vancomycin
Bacitracin
Cell Membrane
30S subunit
50S subunit
RNA Polymerase
DNA Gyrase
Folate synthesis
Protein Synthesis
Nucleic Acid Synthesis
Penicillins
Cephalosporins
Carbapenems
Monobactams
Polymyxins
Tetracyclines
Macrolides
Clindamycin
Linezolid
Chloramphenicol
Streptogramins
Rifampin
Quinolones
Sulfonamides
Trimethoprim
DNA
PABA
DHF A
THF A
Ribosomes
50s
30s
Aminoglycosides
Fig. 12.1 Mechanisms by which antibiotics exert their inhibitory action on microorganisms
12 Antimicrobials from Microbes
to produce penicillin-stable antibiotics like methicillin that inhibited penicillinaseproducing staphylococci. But by early 1960s, methicillin-resistant S. aureus
(MRSA) was reported. MRSA exhibits resistance to all β-lactam antibiotics by virtue of a modified penicillin-binding protein (PBP) called penicillin-binding protein
2A that has reduced affinity to β-lactam antibiotics. Today the global burden of
methicillin-resistant S. aureus is steadily increasing both in hospital and in community settings.
Vancomycin, a glycopeptide antibiotic, was introduced to combat methicillinresistant S. aureus in the mid-1950s. With ever-increasing use of this antibiotic, vancomycin-resistant S. aureus (VRSA) emerged in clinical settings. Evolution of
resistance to antimicrobials is not restricted to S. aureus. Escherichia coli has steadily
developed resistance against fluoroquinolones, broad-spectrum penicillins and cephalosporins. Klebsiella pneumoniae has developed resistance against broad- spectrum
penicillins like ampicillin and amoxicillin and carbapenems. The organism has also
developed resistance against oral antibiotics like cotrimoxazole and fluoroquinolones leaving few options for oral treatment of Klebsiella infections worldwide.
Streptococcus pneumoniae is the leading cause of community-acquired pneumonia
worldwide. The bacterium has developed resistance to penicillin antibiotics by
acquisition of mutations in the penicillin-binding proteins (PBPs). Several clones of
multidrug-resistant salmonella were reported during the late 1990s and early 2000s.
Salmonella enterica serotype Typhimurium that carries a mobile genetic element
Cell Wall Synthesis
Beta Lactams
Vancomycin
Bacitracin
Cell Membrane
30S subunit
50S subunit
RNA Polymerase
DNA Gyrase
Folate synthesis
Protein Synthesis
Nucleic Acid Synthesis
Penicillins
Cephalosporins
Carbapenems
Monobactams
Polymyxins
Tetracyclines
Macrolides
Clindamycin
Linezolid
Chloramphenicol
Streptogramins
Rifampin
Quinolones
Sulfonamides
Trimethoprim
DNA
PABA
DHF A
THF A
Ribosomes
50s
30s
Aminoglycosides
Fig. 12.1 Mechanisms by which antibiotics exert their inhibitory action on microorganisms
12 Antimicrobials from Microbes