Bacterial resistance broad-, narrow-spectrum

Figure 7.12. Chemical modifications of penicillin are responsible for penicillinase-resistance and improved spectrum of activity. Penicillinases (also called fi-lactamases because they inactivate cephalosporins and other fi-lactams as well) inactivate penicillin by cleaving the fi-lactam ring. Bulky chemical groups are linked to penicillinase-resistant penicillins. The bulky group prevents penicillin from entering the active site of penicillinase, but does not interfere with binding to PBPs on the bacterial cell surface. Narrow spectrum penicillins are unable to pass through the outer membrane of Gram-negative bacteria. Broad spectrum penicillins are more hydrophilic and are thus able to penetrate the aqueous pores of the outer membrane of Gramnegative bacteria.

Ciprofloxacin is a broad-spectrum, highly effective antibiotic that has been part of the "international traveler s" kit at CDC for at least a year. It can be used against most bacterial infections. However, ciprofloxacin is frequently overused for many diseases that can be treated with less powerful, narrower-spectrum drugs. Right now, most bacteria ate susceptible to ciprofloxacin, which is why we want to be cautious about its use. Overuse of ciprofloxacin could lead to the development of resistance. 

A de-escalation of a broad-spectrum to narrow antibiotic usage, at least at the end of the infectious course, remains troublesome. This enhances costs for antibiotics as well as the rates of adverse effects, possibly over utilised drugs, and bacterial resistance. 

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