Cephalosporinases

Figure 17.14 Model of evolved mutant from cephalosphorinase shuffling. The sequence of the most active cephalosporinase mutant was modeled using the crystal structure of the class C cephalosporinase from Enterobacter cloacae. The mutant and wild-type proteins were 63% identical. This chimeric protein contained portions from three of the starting genes, including Enterobacter (blue), Klebsiella (yellow), and Citrobacter (green), as well as 33 point mutations (red). (Courtesy of A. Crameri.)...

Widespread clinical acceptance continues to be accorded to the cephalosporins, and the field is extremely active as firms search for the ultimate contender. Among the characteristics desired is retention of the useful features of the older members (relatively broad spectrum, less antigenicity than the penicillins, relative insensitivity toward 3-lactamases, and convenience of administration) while adding better oral activity and broader antimicrobial activity (particularly potency against Pseudomonas, anaerobes, meningococci, cephalosporinase-carrying organisms, and the like). To a considerable extent these objectives have been met, but the price to the patient has been dramatically increased. 

Further, using a combination of X-ray crystallography and mass spectroscopy, Knox et al. [73] has firmly established a central role for Ser-130 in the inhibition of SHV-1 /1-lactamase (class A) by tazobactam. Many additional modifications (Table 3) were carried out on tazobactam with the aim of increasing inhibitory activity against AmpC enzymes, but none of these derivatives (e.g., 13c, 13d, and 13e) had any advantage over tazobactam [74— 77]. Renewed interest in the modification at the C-2 position of sulbactam was developed when scientists from Hoffmann-La Roche disclosed a series of 2/J-alkenyl penam sulfones that possess the ability to simultaneously inactivate both class A penicillinase as well as class C cephalosporinase. Compound... 

Over the past decade the essential goal in the modification of sulbactam or tazobactam has been to extend their activity towards the class C cephalosporinases. In spite of an enormous amount of effort, there has not been much success in achieving this goal. The penicillanic acid derivatives, as a class, show a good /3-lactamase inhibitory profile against class A... 

The presence of a substituted oxime in the amide side chain at the C-3 position is the important criteria for cephalosporinase inhibitory activity. 

Thiophene, furan, and isothiazole are the preferred heterocycles for cephalosporinase inhibition. However, thiophene is the preferred heterocycle. 

Compound 21a in combination with ceftazidime or cefpirome at a ratio of 1 1 was observed to have efficacy in vivo [96]. It improved the efficacy of both the cephalosporins in both a murine systemic infection model with cephalosporinase-resistant rods and in urinary tract infection models with cephalosporin-resistant P. aeruginosa. Further developments in this class of compounds would be rewarding. 

Zinc-dependent enzymes [EC 3.5.2.6], including penicillinase and cephalosporinase, with varying specificity in their catalysis of j8-lactam hydrolysis. Some act more readily on penicillins, whereas the catalysis of others is more efficient with cephalosporins. 

There are many beta-lactamases and they can be classified differently by type of substrate, replacement of genes (chromosomes or plasmids), and place of production. A few of these enzymes directly hydrolyze penicillins (penicillinases), others hydrolyze cephalosporins (cephalosporinases), and others extend to a broad spectrum of substrates. A few bacteria have the ability to induce synthesis of beta-lactamase. Synthesis of beta-lactamase, which in a normal condition is suppressed, is induced in the presence of some beta-lactam antibiotics. 

Microbiology Imipenem-cilastatin has a high degree of stability in the presence of -lactamases, including penicillinases and cephalosporinases produced by gram-negative and gram-positive bacteria. 

Efforts to overcome the actions of the p-lactamases have led to the development of such p-lactamase inhibitors as clavulanic acid, sulbactam, and tazobactam. They are called suicide inhibitors because they permanently bind when they inactivate p-lactamases. Among the p-lactamase inhibitors, only clavulanic acid is available for oral use. Chemical inhibition of p-lactamases, however, is not a permanent solution to antibiotic resistance, since some p-lactamases are resistant to clavulanic acid, tazobactam, or sulbactam. Enzymes resistant to clavulanic acid include the cephalosporinases produced by Citrobacter spp., Enterobacter spp., and Pseudomonas aeruginosa. 

The (3-lactamases (penicillinases) inactivate some cephalosporins but are much less efficient than are the cephalosporinases ((3-lactamases specific for the cephalosporins). Resistance to cephalosporins also results from modification of microbial PBPs. 

The term penicillinase has been retained in common usage to denote /3-lactamase preparations which predominantly catalyze the hydrolysis of penicillins. Conversely, preparations which are more active against cephalosporins have been frequently referred to as cephalosporinases. It is expected that this distinction will disappear as more /3-lactamases are found to show a continuous spectrum of activity against penicillins and cephalosporins. 

Cephalosporine Sensor. Simple, continuous methods for antibiotic determination are required for fermentation industries. Citrobacter freundii produced cephalosporinase, which catalyzes the following reaction of cephalosporin, which liberates hydrogen ions ... 

Colonies were grown in presence of Moxalactam, so activity enhancement also served as a selection criterion successful cephalosporinase mutants would cleave the /3-lactam antibiotic and allow the cells of the respective colony to grow. The procedure was tested over four generations, and about 50 000 colonies per cycle were tested. 

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