Antimicrobial agents/therapy organisms

May be effective in the treatment of acute urinary tract infections caused by susceptible strains of gram-positive and gram-negative bacteria, especially Enterobacter sp. and Escherichia coii. It usually is less effective than other antimicrobial agents in the treatment of urinary tract infections caused by bacteria other than mycobacteria. Consider using only when the more conventional therapy has failed and when the organism has demonstrated sensitivity. 

Ideally, the antimicrobial agent used to treat an infection is selected after the organism has been identified and its drug sensitivity established. However, in the critically ill patient, such a delay could prove fatal and immediate empiric therapy is indicated. 

Naturally resistant strains. Some bacteria are innately resistant to certain classes of antimicrobial agent, e.g. coliforms and many other Gramnegative bacteria possess outer cell membranes which protect their cell walls from the action of certain penicillins and cephalosporins. Facultatively anaerobic bacteria (such as Escherichia colt) lack the ability to reduce the nitro group of metronidazole which therefore remains in an inactive form. In the course of therapy, naturally sensitive organisms are eliminated and those naturally resistant proliferate and occupy the biological space newly created by the drug. 

Organisms used in a biological attack may be resistant to these first-line antimicrobial agents. Medical officers should make every effort to obtain tissue and environmental samples for bacteriological culture, so that the antibiotic susceptibility profile of the infecting brucellae may be determined and the therapy adjusted accordingly. 

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