299
including Rocky Mountain spotted fever and Lyme disease. Chloramphenicol was
first isolated in 1949 from S. venezuelae and was sold under the trade name
Chloromycetin. Later the antibiotic was manufactured in large amounts synthetically. Chloramphenicol is particularly effective in treatment of typhoid fever, meningitis, plague and cholera.
Macrolides The prototype of the macrolide class of antibiotics is erythromycin.
This was the first antibiotic of the macrolide group and was isolated from S.s
erythreus in 1952. A 12–16-membered lactone group is the characteristic structural
feature of macrolides. Erythromycin binds to the 50s prokaryotic ribosome and
inhibits RNA-dependent protein synthesis. Erythromycin is highly active against
many gram-positive bacteria and a few gram-negative bacteria especially those isolated from the respiratory tract. Erythromycin is usually the drug of choice when a
legionella infection is suspected. Erythromycin is also used for the treatment of
chlamydial infections in pregnancy. Spiramycin is a macrolide antibiotic isolated
from S. ambofaciens with antimicrobial activity against gram-positive bacteria and
Neisseria. Carbomycin is another macrolide produced by S. halstedii with antimicrobial activity against gram-positive bacteria and certain mycoplasma strains.
Glycopeptides Soon after the discovery and clinical introduction of penicillins and
cephalosporins, antibiotic-resistant strains of microorganisms began to emerge.
This intensified the search for novel antibiotics, particularly penicillinase-resistant
antibiotics. In 1956, the first glycopeptide antibiotic with penicillinase resistance
was isolated from S. orientalis obtained from soil samples collected from India and
Indonesia and was named vancomycin. Initially the spread of penicillin-resistant S.
aureus resulted in wide spread clinical use of vancomycin but reports of side effects
like ototoxicity and nephrotoxicity and the development of better penicillin derivatives resulted in a gradual decline of vancomycin use. Today highly purified formulations of vancomycin are available in contrast to impure earlier versions and have
thus resulted in decreased side effects. Vancomycin exerts its antibacterial action by
inhibiting the synthesis of peptidoglycan which is essential for the formation of
bacterial cell wall. Vancomycin is used in the treatment of gram-positive aerobic
and anaerobic bacteria. Methicillin-resistant S. aureus (MRSA) and most strains of
coagulase-negative staphylococcus are susceptible to vancomycin. Streptococci
and pneumococci are also susceptible. Glycopeptide (vancomycin) intermediate
resistant S. aureus (GISA) was reported among clinical isolates in Japan and the
United States. There are three phenotypes of glycopeptides resistance, namely, Van
A, Van B and Van C. The organisms showing the Van A-resistant phenotype shows
resistance to both vancomycin and teicoplanin, while Van B and Van C phenotypes
are resistant only to vancomycin.
Polyene Mycotics The genus Streptomyces also produce antifungal antibiotics
structurally belonging to the polyene group. Polyenes are polyunsaturated organic
molecules characterized by the presence alternating carbon–carbon single and dou12 Antimicrobials from Microbes
including Rocky Mountain spotted fever and Lyme disease. Chloramphenicol was
first isolated in 1949 from S. venezuelae and was sold under the trade name
Chloromycetin. Later the antibiotic was manufactured in large amounts synthetically. Chloramphenicol is particularly effective in treatment of typhoid fever, meningitis, plague and cholera.
Macrolides The prototype of the macrolide class of antibiotics is erythromycin.
This was the first antibiotic of the macrolide group and was isolated from S.s
erythreus in 1952. A 12–16-membered lactone group is the characteristic structural
feature of macrolides. Erythromycin binds to the 50s prokaryotic ribosome and
inhibits RNA-dependent protein synthesis. Erythromycin is highly active against
many gram-positive bacteria and a few gram-negative bacteria especially those isolated from the respiratory tract. Erythromycin is usually the drug of choice when a
legionella infection is suspected. Erythromycin is also used for the treatment of
chlamydial infections in pregnancy. Spiramycin is a macrolide antibiotic isolated
from S. ambofaciens with antimicrobial activity against gram-positive bacteria and
Neisseria. Carbomycin is another macrolide produced by S. halstedii with antimicrobial activity against gram-positive bacteria and certain mycoplasma strains.
Glycopeptides Soon after the discovery and clinical introduction of penicillins and
cephalosporins, antibiotic-resistant strains of microorganisms began to emerge.
This intensified the search for novel antibiotics, particularly penicillinase-resistant
antibiotics. In 1956, the first glycopeptide antibiotic with penicillinase resistance
was isolated from S. orientalis obtained from soil samples collected from India and
Indonesia and was named vancomycin. Initially the spread of penicillin-resistant S.
aureus resulted in wide spread clinical use of vancomycin but reports of side effects
like ototoxicity and nephrotoxicity and the development of better penicillin derivatives resulted in a gradual decline of vancomycin use. Today highly purified formulations of vancomycin are available in contrast to impure earlier versions and have
thus resulted in decreased side effects. Vancomycin exerts its antibacterial action by
inhibiting the synthesis of peptidoglycan which is essential for the formation of
bacterial cell wall. Vancomycin is used in the treatment of gram-positive aerobic
and anaerobic bacteria. Methicillin-resistant S. aureus (MRSA) and most strains of
coagulase-negative staphylococcus are susceptible to vancomycin. Streptococci
and pneumococci are also susceptible. Glycopeptide (vancomycin) intermediate
resistant S. aureus (GISA) was reported among clinical isolates in Japan and the
United States. There are three phenotypes of glycopeptides resistance, namely, Van
A, Van B and Van C. The organisms showing the Van A-resistant phenotype shows
resistance to both vancomycin and teicoplanin, while Van B and Van C phenotypes
are resistant only to vancomycin.
Polyene Mycotics The genus Streptomyces also produce antifungal antibiotics
structurally belonging to the polyene group. Polyenes are polyunsaturated organic
molecules characterized by the presence alternating carbon–carbon single and dou12 Antimicrobials from Microbes