Gentamicin aminoglycoside antibiotics

Aminoglycosides. Antibiotics ia the amiaoglycoside group characteristically contain amino sugars and deoxystreptamiae or streptamiae. This family of antibiotics has frequentiy been referred to as aminocyclitol amiaoglycosides. Representative members are streptomycia, neomycin, kanamycia, gentamicin, tobramycia, and amikacin. These antibiotics all inhibit proteia biosynthesis. 

Enzymes transferring an acetyl moiety to one specific of several amino-groups of the aminocyclitol-aminoglycoside antibiotics (e.g. gentamicin, amikacin, kanamycin) are called aminoglycoside acetyltransferases... 

Fig. 5.10 Some aminoglycoside antibiotics A, streptomycin B, kanamycins C, gentamicins D, amikacin.

Other medicinally useful aminoglycoside antibiotics are based on the aminocyclitol 2-deoxystrepta-mine, e.g. gentamicin Ci from Micromonospora purpurea. Although streptamine and 2-deoxystrepta-mine are actually cyclohexane derivatives, they are both of carbohydrate origin and derived naturally from glucose. 

Structures of several important aminoglycoside antibiotics. Ring II is 2-deoxystreptamine. The resemblance between kanamycin and amikacin and between gentamicin, netilmicin, and tobramycin can be seen. The circled numerals on the kanamycin molecule indicate points of attack of plasmid-mediated bacterial transferase enzymes that can inactivate this drug. , , and , acetyltransferase , phosphotransferase , adenylyltransferase. Amikacin is resistant to modification at , , , and . 

The evolution of MRSA strains is not fully understood, but the same mechanisms of mutation and gene transfer that exist in other species provide a likely reason. The emergence of gentamicin resistance plasmids illustrates the evolutionary potential of translocatable elements [186], MRSA strains which are also resistant to this aminoglycoside antibiotic are referred to as MGRSA. This evolutionary progression is also responsible for the formation of the -lactamase-heavy metal resistant plasmids [250]. Some MRSA isolates are penicillin-resistant by virtue of the enzyme /J-lactamase, which pre-dates the use of /8-lactams [251], However, the spread of the phenotype has probably arisen as a result of selection caused by the widespread usage of methicillin in hospitals. 

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