Timentin and beta-lactamases

Ticarcillin is resistant to the action of cephalosporinases, which explains its biological activity on a large number of bacterial species, including cephalosporinase-producing Enterobacteriaceae and Pseudomonas aeruginosa. Nevertheless, its antibacterial activity is often limited by the action of some beta-lactamases, mostly plasmid-mediated penicillinases. Clavulanic acid by itself has poor antibacterial activity, but its most important property is to inhibit and inactivate beta-lactamases. The inhibitory properties of clavulanic acid were studied on a large number of beta-lactamases. The penicillinases produced by Staphylococcus aureus, the plasmid-mediated beta-lactamases such as the TEM-type, the chromosomally-mediated penicillinases from Klebsiella pneumoniae and other closely-related beta-lactamases, and a few chromosomally-mediated cephalosporinases, such as that produced by Proteus vulgaris, are powerfully inhibited by clavulanic acid. The plasmid-mediated penicillinases of OXA type and most of the chromosomally-mediated cephalosporinases, such as that produced by Escherichia coli (Amp C), are less or poorly inhibited. Moreover, clavulanic acid has some cephalosporinase-inducing properties. These properties are in good agreement with the bacteriological properties of Timentin.

Affinity of cefmenoxime for beta-lactamases: an analysis

The interactions of cefmenoxime with beta-lactamases in comparison with cefotaxime, moxalactam, cefoperazone, and ceftazidime have been determined. On-line computerized microacidimetry allowed determination of the affinity of these compounds with the enzymes, which was characterized by Km values. The beta-lactamases that were used were two cephalosporinases and one penicillinase. Within these data, the cephalosporins could be classified into three groups: (1) those with high affinity for the cephalosporinases and very poor affinity for the penicillinase (cefmenoxime, cefotaxime, and moxalactam); (2) those with moderate affinity for the cephalosporinases and very poor affinity for the penicillinase (ceftazidime); (3) those with poor affinity for all enzymes (cefoperazone). In the case of the penicillinase (TEM-1), only cefoperazone was subject to some hydrolysis.

The action of beta-lactamases on desacetyl-cefotaxime and cefotaxime

Desacetyl-cefotaxime is the main cefotaxime metabolite. Its antibacterial activity is less than that of the parent molecule, but the combination of cefotaxime and desacetyl-cefotaxime is often synergistic. We analysed the hydrolysis of desacetyl-cefotaxime, in comparison with cefotaxime, by 10 beta-lactamases, mostly cephalosporinases, isolated from various Gram-negative species. From partially purified beta-lactamase preparations of high specific activity, we determined the maximum rates of hydrolysis (Vm) and the Michaelis constants (Ki and Km when possible). It appeared for 7 beta-lactamases the rate of desacetyl-cefotaxime hydrolysis was 2.1 times greater than that of cefotaxime, in terms of geometrical mean value, but with 3 enzymes no hydrolysis was shown for one compound. For 8 enzymes, the Ki, and sometimes Km, of desacetyl cefotaxime are 39 times higher than those of cefotaxime (geometric mean value), which corresponds to a lower affinity.

[Mechanisms of azlocillin resistance in Pseudomonas aeruginosa]

The authors have evaluated the susceptibility of azlocillin to beta-lactamases habitually produced by Pseudomonas aeruginosa, i.e. TEM and CARB types penicillinases and the so-called Sabath and Abraham cephalosporinase. As all penicillins, azlocillin is liable to hydrolysis by penicillinases that also affect, through to a lesser extent, some cephalosporin. It is also degraded, albeit moderately by the Sabath and Abraham cephalosporinase. The authors have also compared the behaviour of azlocillin towards beta-lactamases to that of other beta-lactam antibiotics, notably carbenicillin, cefoperazone and cefsulodin.

Cefotetan and beta-lactamases. I. An analysis of the affinity of cefotetan for beta-lactamases

Cefotetan is a new cephamycin whose interaction with a group of eight beta-lactamases isolated from various Gram-negative bacteria has been studied. Using computerized micro-acidimetry, cefotetan was found to be resistant to the hydrolytic action of various enzymes, including those which actively hydrolyse cefotaxime. Despite this resistance to hydrolysis, cefotetan nevertheless shows a certain affinity for these enzymes. These data were submitted to two statistical procedures consisting of correspondence analysis and ascending hierarchical classification. These techniques revealed that cefotetan behaves very much like cefoxitin (another cephamycin) and also like cefotaxime and moxalactam.

[Affinity of N-formimidoyl-thienamycin (MK-0787) for beta-lactamases, analysis by a statistical method: correspondence analysis]

N-formimidoyl-thienamycin (MK-0787) is not subject to beta-lactamase hydrolysis. Nevertheless, this compound does show some affinity for the TEM-type penicillinases, cephalosporinases and a few other beta-lactamases. Surprisingly no affinity was found for the penicillinases of the CARB-type. The results thus obtained for affinity constants Ki and Km were submitted to a statistical analysis treatment, i.e. correspondence analysis and hierarchic ascendent classification. This confirms the fact that MK-0787 presents an unusual behaviour towards beta-lactamases.

Cefotetan and beta-lactamases. II. An unusual property: the inactivation of some beta-lactamases by cefotetan

Initially, cefotetan interacts with beta-lactamases to form a classical Michaelis complex characterized by a term Ki (the inhibition constant). In a second phase, this complex develops with time to form a new entity devoid of enzymic activity. This new entity may have the structure of an acyl enzyme with variable stability. In the case of TEM-1 and TEM-2 beta-lactamases, the process is progressively and totally reversible. The same phenomena were observed in varying degrees for Pitton's type 2 (PIT-2) penicillinase, OXA-1 and CARB-1. The Klebsiella oxytoca and Proteus vulgaris beta-lactamases are also inactivated by this same process. However, four other cephalosporinases appear to be unaffected by this mechanism.

[Mezlocillin and beta-lactamases (author's transl)]

Like all penicillins, mezlocillin is degraded by beta-lactamases of the penicillinase type. It is also degraded to some extent by beta-lactamases of the cephalosporinase type. Yet in both cases mezlocillin behaves approximately like the first and second generation cephalosporins. This, together with good intrinsic activity, accounts for the valuable antibacterial properties of the antibiotic, particularly against Enterobacteriacaea.