The effects of clavulanic acid and sulbactam on beta-lactamase biosynthesis

In vitro activity of cefodizime (HR-221) in combination with beta-lactamase inhibitors

Cefodizime (formerly HR221) was tested either for in vitro microbiological activity or for its stability to beta-lactamases in the presence of two beta-lactamase inhibitors (clavulanic acid, tazobactam). Cefodizime was a poor substrate of class C enzymes but hyperproducer strains were generally resistant with or without a beta-lactamase inhibitor used in combination. On the contrary, class A enzymes were able to hydrolyze cefodizime. However, strains expressing class A beta-lactamase were susceptible to cefodizime in combination with clavulanic acid.

Effect of clavulanic acid on activity of beta-lactam antibiotics in Serratia marcescens isolates producing both a TEM beta-lactamase and a chromosomal cephalosporinase

An isolate of Serratia marcescens that produced both an inducible chromosomal and a plasmid-mediated TEM-1 beta-lactamase was resistant to ampicillin and amoxicillin and also demonstrated decreased susceptibility to extended-spectrum beta-lactam antibiotics (ESBAs). Clavulanic acid did not lower the MICs of the ESBAs, but it decreased the MICs of the penicillins. The TEM-1-producing plasmid was transferred to a more susceptible S. marcescens strain that produced a well-characterized inducible chromosomal beta-lactamase. The MICs of the ESBAs remained at a low level for the transconjugant. Ampicillin and amoxicillin which were good substrates for the plasmid-mediated enzyme, were not well hydrolyzed by the chromosomal enzymes; the ESBAs were hydrolyzed slowly by all the enzymes. When each of the S. marcescens strains was grown with these beta-lactam antibiotics, at least modest increases in chromosomal beta-lactamase activity were observed. When organisms were grown in the presence of clavulanic acid and an ESBA, no enhanced induction was observed. The increases in the MICs of the ESBAs observed for the initial clinical isolate may have been due to a combination of low inducibility, slow hydrolysis, and differences in permeability between the S. marcescens isolates. When clavulanic acid and a penicillin were added to strains that produced both a plasmid-mediated TEM and a chromosomal beta-lactamase, much higher levels of chromosomal beta-lactamase activity were present than were observed in cultures induced by the penicillin alone. This was due to the higher levels of penicillin that were available for induction as a result of inhibition of the TEM enzyme by clavulanate.

Influence of beta-lactamase inhibitors on the potency of their companion drug with organisms possessing class I enzymes

The ability of beta-lactamase inhibitors to induce class I beta-lactamases in certain organisms in vitro suggests a potential for antagonism in vivo. Therefore, a study was designed to assess the ability of sulbactam and clavulanate to induce beta-lactamases in two strains each of Enterobacter cloacae, Citrobacter freundii, Serratia marcescens, and Pseudomonas aeruginosa both in vitro and in vivo. Induction in vitro was observed only with S. marcescens and P. aeruginosa and generally only when inhibitor concentrations greater than 2 micrograms/ml were examined. A mouse model of lethal infection, designed to detect in vivo antagonism arising from beta-lactamase induction, was used to determine what effect sulbactam and clavulanate would have on the 50% protective doses (PD50s) of cefoperazone and ticarcillin. Antagonism (a significant increase in the PD50) was observed in only 4 of 32 tests. Three of these involved antagonism of cefoperazone by clavulanate, and one involved antagonism of cefoperazone by sulbactam. In 6 of 32 tests, enhancement of efficacy (a significant decrease in PD50) was observed. In four of these, sulbactam enhanced cefoperazone; in one, sulbactam enhanced ticarcillin; and in one, clavulanate enhanced ticarcillin. Four of the six cases of enhancement occurred when the beta-lactamase inhibitor was given at the time of challenge. None of these positive or negative in vivo effects were predicted by in vitro tests. These data suggest that beta-lactamase inhibitors can influence the in vivo potency of their companion drug in both a beneficial and detrimental fashion against organisms with class I beta-lactamases and that these effects cannot be predicted from in vitro assays.

Significance of inducible cephalosporinase remaining in the experimentally infected rat granuloma pouch after beta-lactam therapy

We studied the influence of inducible cephalosporinase on levels of secondarily administered beta-lactam antibiotics in exudates using experimentally infected rat granuloma pouches. Cefoperazone or cefmetazole was administered intramuscularly at a dose of 100 mg/kg of body weight to rats at 2 and 8 h after infection of rat pouches with Serratia marcescens W-24, which possesses an inducible type I beta-lactamase (cephalosporinase). Subsequently, cefotaxime or cefbuperazone was administered at an intravenous dose of 100 mg/kg to rats at 24 h postinfection. Levels of cefotaxime in the pouch exudates of the cefmetazole-pretreated group were lower than those in the control group, which was infected but not pretreated with antibiotics. This was due to the inactivation of cefotaxime by extracellular cephalosporinase which was induced by cefmetazole and which remained in the rat pouches. However, cefotaxime concentrations were not reduced in the cefoperazone-pretreated group because of the low inducibility of cefoperazone against cephalosporinase production. On the other hand, cefbuperazone concentrations were similar in all groups (control, cefoperazone pretreated, and cefmetazole pretreated), because cefbuperazone is more stable against this enzyme than cefotaxime is. In conclusion, concentrations of secondarily administered beta-lactam antibiotics are affected by inducibly produced cephalosporinase at the infection site when a good inducer like cefmetazole is administered beforehand.

Diverse potential of beta-lactamase inhibitors to induce class I enzymes

The ability of various beta-lactamase inhibitors to induce class I beta-lactamases was assessed. Clavulanate was the most active compound, inducing Morganella morganii, Aeromonas caviae, and Enterobacter aerogenes over a broad concentration range and Citrobacter freundii, Pseudomonas aeruginosa, and Serratia marcescens at high concentrations. Disk approximation tests paralleled these results, with clavulanate, but not sulbactam or tazobactam, antagonizing the activity of several beta-lactams against these organisms.

In vitro activity of combinations of beta-lactam antibiotics with beta-lactamase inhibitors against cephalosporinase-producing bacteria

Combinations of different beta-lactam antibiotics, including cefotaxime, with three beta-lactamase inhibitors were tested against cephalosporinase producing bacterial strains. The most significant antagonism was obtained with a combination of clavulanic acid and cefotaxime, while almost no antagonism was observed with sulbactam and tazobactam. In strains belonging to five different species there was a correlation between the levels of cephalosporinase produced after exposure to different concentrations of inhibitors and the MICs of cefotaxime combined with the same concentrations of inhibitors. It is concluded that there is little likelihood of antagonism between beta-lactam antibiotics and sulbactam or tazobactam.