<P> Antibiotics are commonly classified based on their mechanism of action, chemical structure, or spectrum of activity . Most target bacterial functions or growth processes . Those that target the bacterial cell wall (penicillins and cephalosporins) or the cell membrane (polymyxins), or interfere with essential bacterial enzymes (rifamycins, lipiarmycins, quinolones, and sulfonamides) have bactericidal activities . Protein synthesis inhibitors (macrolides, lincosamides and tetracyclines) are usually bacteriostatic (with the exception of bactericidal aminoglycosides). Further categorization is based on their target specificity . "Narrow - spectrum" antibiotics target specific types of bacteria, such as gram - negative or gram - positive, whereas broad - spectrum antibiotics affect a wide range of bacteria . Following a 40 - year break in discovering new classes of antibacterial compounds, four new classes of antibiotics have been brought into clinical use in the late 2000s and early 2010s: cyclic lipopeptides (such as daptomycin), glycylcyclines (such as tigecycline), oxazolidinones (such as linezolid), and lipiarmycins (such as fidaxomicin). </P> <P> With advances in medicinal chemistry, most modern antibacterials are semisynthetic modifications of various natural compounds . These include, for example, the beta - lactam antibiotics, which include the penicillins (produced by fungi in the genus Penicillium), the cephalosporins, and the carbapenems . Compounds that are still isolated from living organisms are the aminoglycosides, whereas other antibacterials--for example, the sulfonamides, the quinolones, and the oxazolidinones--are produced solely by chemical synthesis . Many antibacterial compounds are relatively small molecules with a molecular weight of less than 1000 daltons . </P> <P> Since the first pioneering efforts of Howard Florey and Chain in 1939, the importance of antibiotics, including antibacterials, to medicine has led to intense research into producing antibacterials at large scales . Following screening of antibacterials against a wide range of bacteria, production of the active compounds is carried out using fermentation, usually in strongly aerobic conditions . </P> <P> The emergence of resistance of bacteria to antibiotics is a common phenomenon . Emergence of resistance often reflects evolutionary processes that take place during antibiotic therapy . The antibiotic treatment may select for bacterial strains with physiologically or genetically enhanced capacity to survive high doses of antibiotics . Under certain conditions, it may result in preferential growth of resistant bacteria, while growth of susceptible bacteria is inhibited by the drug . For example, antibacterial selection for strains having previously acquired antibacterial - resistance genes was demonstrated in 1943 by the Luria--Delbrück experiment . Antibiotics such as penicillin and erythromycin, which used to have a high efficacy against many bacterial species and strains, have become less effective, due to the increased resistance of many bacterial strains . </P>

Which of the following is not a common target for antibacterial drugs