Benzylpenicillin penicillin organisms used

The activity of these semis)mthetic penicillins extends beyond the Gram-positive and Gram-negative cocci which are susceptible to benzylpenicillin, and includes many Gram-negative bacilli. They do not resist P-lactamases and their usefulness has reduced markedly in recent years because of the increased prevalence of organisms that produce these enzymes. 

Aminopenicillanic acid (6 APS) is an important precursor for the organic synthesis of new P. The compound itself has no antibiotic activity it is isolated as a fermentation product from cultures of Pen-cillium chrysogenum, or prepared by the enzymatic hydrolysis of benzylpenicillin. Thousands of new P. have been prepared by the acylation of 6 APS, but only a few of these are therapeutically useful, e.g Penicillin V is relatively stable to acid and is not hydrolysed in the stomach, so that it may be administered in tablet form Ampicillin (the aminophenyl-acetyl derivative of 6 APS), has a wider spectrum of activity than most other R, including activity against various Gram-negative bacteria (Typhus, E. coli, etc.). 

Cephalosporin derivatives are expensive, but useful for organisms that are resistant to penicillins, and they may be given (but cautiously ) to patients who have become sensitized to the penicillins. They are more active than benzylpenicillin against Gram-negative bacteria, and specially effective in the respiratory and urinary tracts where they tend to concentrate. Although cephalosporins are not sensitive to penicillinase, resistant bacteria have been found to harbour a parallel (l-lactamase called cephalosporase. 

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