© 1990 S. Karger AG, Basel 0009-3157/90/0363-0209 $ 2.75/0
Chemotherapy 1990;36:209-214
In vitro Effect of YTR (Tazobactam) on Plasmid and Chromosomally Mediated ß-Lactamases E.E. Stobberingh Department of Medical Microbiology, State University of Limburg, Maastricht, The Netherlands
Key Words. Beta-lactamase inhibitors • Tazobactam
Introduction The antibacterial activity of P-lactamase-sensitive antibiotics increased when combined with a P-lactamase inhibitor as clavulanic acid or sulbactam. Well-known examples are amoxycillin or ticarcillin in combination with clavulanic acid, which showed a distinctly broader antibacterial spectrum than the P-lactam antibiotic alone [1, 2]. However, an antagonistic ef fect between a P-lactamase inhibitor, i.e. clavulanic acid and a P-lactam antibiotic, i.e. azlocillin for Pseudomonas aeruginosa have been described as well [3]. The ob served effect might be due to the inducing capacity of clavulanic acid at relatively high concentrations [4] or to a species or strain specificity which has been described as well [5,6],
Recently, a new P-lactamase inhibitor, tazobactam (YTR) has been developed. Several studies showed promising data concerning the in vitro antibacterial activ ity of the combination piperacillin and YTR compared to piperacillin alone [7-9]. YTR is, like clavulanic acid, a Plactam compound and possesses there fore the ability to induce chromosomally mediated p-lactamases. Subsequently, the inhibitory effect of YTR on plasmid-me diated enzymes might interfere with the inducing capacity of YTR on the chro mosomally encoded enzyme. This inter ference might influence the synergistic effect of YTR on the antibacterial activity of piperacillin. The aim of this study was to assess the synergistic effect of YTR (4 mg/1) on the antibacterial activity of piperacillin
Downloaded by: Univ. of California Santa Barbara 128.111.121.42 - 3/6/2018 7:32:44 AM
Abstract. The effect of tazobactam on the piperacillin susceptibility and on the P-lactamase activity of different strains and species was evaluated. A synergistic effect was observed on the piperacillin susceptibility for all microorganisms tested, irrespective of the type and/or amount of p-lactamase produced. Addition of gentamicin resulted in a further reduction of the piperacillin MIC. The enzyme activity after induction with piperacillin alone or in combination with tazobactam (4 mg/1) was quite similar.
Stobberingh
210 Table 1. Antibiotic susceptibility and p-lactamase production of the microorganisms tested ß-Lactamase
MIC, mg/1 piperacillin
E. cloacae
5 10558 5356 9090
C. freundii
2R021 5189 2R039 7329
piperacillin + YTR (4 mg/1)
specific activity nmol/mg protein • min
type
0.5 1 0.25 8
1 1 0.25 4
24 23 151 2918
c c p+c p+c
0.015 1 128 128
0.03 2 8 1
22 41 2120 2159
c c p+c p+c
0.06 1 0.06 0.12
4 30 1252 792
c c p+c p+c
10 20 755 512
c c p+c p+c
98 114 454 418
c c p+c p+c
Proteus indol-positive
1160 3 4098 4112
0.06 1 16 8
P. aeruginosa
1356 1360 PSE1 PSE4
1 1 16 32
S. marcescens
2917 3RO02 10433 4323
0.06 0.12 4 16
against strains producing the chromosomally encoded P-lactamase alone or in com bination with a plasmid-encoded enzyme. In addition, the capacity of YTR to induce chromosomally mediated p-lactamases from different species was determined.
Materials and Methods Four strains of each of the following species were used: Enterobacter cloacae, Citrobacter freundii,
1 2 8 16 0.06 0.25 0.25 0.06
P. aeruginosa, Serratia marcescens and indol-positive Proteus: 2 strains with a chromosomally encoded beta-lactamase alone and 2 strains producing in ad dition a plasmid mediated enzyme, mostly of the TEM type. Only P. aeruginosa produced PSE type enzymes (PSE1 and PSE4). For the synergy studies the method of Berenbaum [10] was used. The frac tional inhibitory concentration (FIC) was defined as the ratio between the MIC of the combined com pounds and the MIC of the compound alone. The combination value was derived from the highest dilu tion of the antibiotic combination permitting no visi ble growth after 18 h at 37 °C. The interaction index was calculated as follows:
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Microorganisms
211
Tazobactam and ()-Lactamase Table 2. Susceptibility to piperacillin in the presence of YTR and gentamicin MIC, mg/1
Microorganisms
piperacillin
E. cloacae
5 10558 5356 9090
C.freundii
2R021 5189 2R039 7329
piperacillin + YTR (4 mg/1)
piperacillin + YTR (4 mg/1) gentamicin
FIC index1
0.5 1 0.25 8
1 1 0.25 4
0.03 0.06 0.06 0.25
1.03 0.56 1.24 0.53
0.015 1 128 128
0.03 2 2 1
0.06 0.06 0.5 0.06
3 0.56 0.56 0.56
0.06 1 0.06 0.12
0.03 0.06 0.03 0.03
2 0.56 0.74 1.24
0.06 0.25 8 4
0.56 0.75 1.004 1
0.06 0.06 0.125 0.03
1.24 0.74 0.75 0.56
Proteus indol-positi ve
1160 3 4098 4112
0.06 1 16 8
P. aeruginosa
1356 1360 PSE1 PSE4
1 1 16 32
S. marcescens
2917 3RO02 10433 4323
1 2 8 16
0.06 0.12 4 16
0.06 0.25 0.25 0.06
MIC combination drug A
MICcombinationdrugB
MIC drug A alone
MIC drug B alone
MICcombinationa MICcombinationb FIC = -------------------------- H------------------------MIC alone a MIC alone b A sum of 0.5 or more indicates synergism, a sum of less than 0.5 indicates antagonism. The induction studies were performed as de scribed previously using YTR (4 mg/1) and cefoxitin as the reference compound in a concentration of 'A MIC of the strain tested as the inducing agents [6], For P. aeruginosa 50 mg/1 cefoxitin was used.
The inducing capacity of an antibacterial agent was expressed as the fold increase in enzyme activity after induction compared to the activity before in duction. A fold increase of 2 or less was designated as a low, an increase between 2- and 10-fold as an inter mediate, and an increase of more than 10-fold as a high inducing capacity. Isoelectrofocusing as described by Matthew et al. [11] was used for the characterization of the p-lactamases.
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Drug A = Piperacillin in combination with tazobactam, drug B = gentamicin.
Table 3. Inducing capacity of YTR Increase after induction with, x
Microorganisms
YTR cefoxitin1 (4 mg/1) E. cloacae
5 10558 5356 9090
0.25 0.53 0.04 0.25
91 292 0.9 1.3
C.freundii
2R021 5189 2R039 7329
0.17 0.27 0.86 0.54
6.4 24 0.6 0.7
Proteus indol-positive 1160 3 4098 4112
0.24 0.40 0.5 0.6
5 0.8 not done
P. aeruginosa
1356 1360 PSE1 PSE4
0.48 0.34 0.65 0.9
260 60 2 7
S. marcescens
2917 3RO02 10433 4323
0.60 0.2 0.4 0.2
140 14 6.2 15
1.0
1 Cefoxitin: 'h MIC; for P. aeruginosa 50 mg/1 was used.
Results The antibiotic susceptibility and the specific P-lactamase activity of the strains used are shown in table 1. The microor
ganisms producing only a chromosomally mediated enzyme were highly susceptible to piperacillin. However, strains produc ing in addition a plasmid-encoded P-lactamase were distinctly less susceptible. Ad dition of YTR (4 mg/1) to piperacillin re sulted in a strong increase in susceptibility to piperacillin of most strains tested irre spective of the type/amount of P-lactamase produced. Only P. aeruginosa PSE1 and PSE4, the reference strains for the plasmid encoded P-lactamase PSE1 and PSE4, showed a similar susceptibility to piperacillin alone or in combination with tazobactam. No antagonistic effect be tween tazobactam and piperacillin was observed for all strains tested. In addition, for all strains a synergistic effect was found between piperacillin-tazobactam and gentamicin as shown by the FIC index of more than 0.5 (table 2). The p-lactamase activity of the strains producing both a chromosomally and a plasmid-mediated enzyme was, as ex pected, distinctly higher compared to the enzyme activity of the strains producing a chromosomally mediated P-lactamase only (table 1). Induction with cefoxitin re sulted in a strong increase in enzyme pro duction of those strains producing a chromosomally mediated P-lactamase alone up to around 300-fold for E. cloacae 10558 (table 3). Only the indol-positive Proteus strains 1160 and 3 showed a low to moderate increase in enzyme activity after induction with cefoxitin. Induction of the strains producing both types of P-lactamase resulted only in a low to moderate increase in enzyme activity. After induc tion with tazobactam (4 mg/1) no distinct increase in enzyme activity was observed for all strains tested.
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Stobberingh
212
Tazobactam and p-Lactamase
The data in this study confirmed the synergistic effect of tazobactam on the piperacillin susceptibility of the strains tested [7-9], An increase in piperacillin susceptibility was observed for strains producing only a chromosomally medi ated P-lactamase as well as for those pro ducing in addition a plasmid-mediated en zyme. Antagonism between azlocillin and clavulanic acid as described by Calderwood et al. [3] for P. aeruginosa was not observed with tazobactam and piperacil lin. This difference might be due to a strain dependent effect or to differences in in ducing capacity of clavulanic acid and tazobactam [12]. After induction with tazobactam in the concentration tested (4 mg/1) no increase in specific beta-lactamase activity was ob served for all the microorganisms tested with an inducible chromosomally medi ated beta-lactamase. The absence of induc ing activity of tazobactam for the chro mosomal beta-lactamases of the strains tested may be therefore an advantage for this new enzyme inhibitor. Similar data were found by Moosdeen et al. [12]. Addition of gentamicin resulted in a further reduction of the piperacillin MIC making the combination therapy of piper acillin + tazobactam and gentamicin a very promising one which needs further clinical evaluation. In several studies the strain and species dependent inducing capacity of an anti microbial has been described [4-6]. In the study of Sanders and Sanders [5], Serratia and Morganella morganii species were more likely to show induction than the other strains and species tested. Also in
one of our previous studies S. marcescens (1-lactamase showed a better inducibility than the P-lactamase of the other species tested [4], However, one has to keep in mind that the ability to induce chromo somally mediated p-lactamase was unre lated to its ability to select for stable resis tant derepressed mutants [5], Stable derepressed mutants have been associated with clinical failures [13]. Therefore, although piperacillin [5, 14] and YTR showed low inducing capacity, further studies on the ability of the combination to select stable derepressed mutants have to be evaluated to assess the clinical usefulness of this combination. References 1 Bush, K.; Sykes, R.B.: Beta-lactamase inhibitors in perspective. J. antimicrob. Chemother. 11: 97-107(1983). 2 Wise, R.; Andrews, J.M.; Bedford, K.A.: In vitro study of clavulanic acid in combination with pen icillin, amoxycillin and carbenicillin. Antimi crob. Agents Chemother. 13: 389-403(1978). 3 Calderwood, S.B.; Gardella, A.; Philippon, A.M.; Jacoby, G.A.; Moellering, Jr., R.C.: Effect of az locillin in combination with clavulanic acid, sul bactam and N-formimidoyl thienamycin against beta-lactamase producing carbenicillin resistant Pseudomonas aeruginosa. Antimicrob. Agents Chemother. 22: 266-271 (1982). 4 Stobberingh, E.E.: Induction of chromosomal beta-lactamase by different concentrations of clavulanic acid in combination with ticarcillin. J. antimicrob. Chemother. 21: 9-16(1988). 5 Sanders, C.C.; Sanders, W.W.: Type I beta-lactamases of gram-negative bacteria: interactions with beta-lactam antibiotics. J. infect. Dis. 154: 792-800(1986). 6 Stobberingh, E.E.; van Boven, C.P.A.: Inducing capacity of the combinations mecillinam-ampicillin and mecillinam-ceftazidime in comparison with the capacity of the compounds administered separately. Chemotherapy 33: 97-102 (1987).
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Discussion
213
7 Jacobs, M.R.; Aronoff, S.R.; Johenning, S.S.; Shlaes, D.M.; Yamabe, S.: Comparative activities of the beta-lactamase inhibitors YTR 830, clavulanate and sulbactam combined with ampicillin and broad spectrum penicillins against defined beta-lactamase producing aerobic gram-negative bacilli. Antimicrob. Agents Chemother. 29: 980985(1986). 8 Wiedemann, B.: Antibacterial activity of pipera cillin in combination with a p-lactamase inhibitor CL 298, 741, Abstract 109 (ICAAC, Los Angeles 1988). 9 Fass, R.J.; Prior, R.B.: Comparative in vitro ac tivities of piperacillin-tazobactam and ticarcillinclavulanate. Antimicrob. Agents Chemother. 33: 1268-1274(1989). 10 Berenbaum, M.C.: Correlations between methods for measurement of synergy. J. infect. Dis. 142: 476-478(1980). 11 Matthew, M.; Harris, A.M.; Marshall, M.J.; Ross, G.W.: The use of the analytical isoelectric focus ing for detection and identification of beta-lactamases. J. gen. Microbiol. 88: 169-178(1975).
Stobberingh 12 Moosdeen, L; Keeble, J.; Williams, J.D.: Induction/inhibition of chromosomal beta-lactamases by beta-lactamase inhibitors. Rev. infect. Dis. 8: S562-S568 (1986). 13 Milatovic, D.; Braveny, L: Development of resis tance during antibiotic therapy. Eur. J. clin. Mi crobiol. 6: 234-244(1987). 14 Minami, S.; Yotsuji, A.; Inoue, M.; Mituhashi, S.: Induction of beta-lactam antibiotics in Entero bacter cloacae. Antimicrob. Agents Chemother. 18: 382-385(1980).
E.E. Stobberingh Department of Medical Microbiology State University of Limburg P.O. Box 616 NL-6200 MD Maastricht (The Netherlands)
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214
Chemotherapy 1990;36:209-214
In vitro Effect of YTR (Tazobactam) on Plasmid and Chromosomally Mediated ß-Lactamases E.E. Stobberingh Department of Medical Microbiology, State University of Limburg, Maastricht, The Netherlands
Key Words. Beta-lactamase inhibitors • Tazobactam
Introduction The antibacterial activity of P-lactamase-sensitive antibiotics increased when combined with a P-lactamase inhibitor as clavulanic acid or sulbactam. Well-known examples are amoxycillin or ticarcillin in combination with clavulanic acid, which showed a distinctly broader antibacterial spectrum than the P-lactam antibiotic alone [1, 2]. However, an antagonistic ef fect between a P-lactamase inhibitor, i.e. clavulanic acid and a P-lactam antibiotic, i.e. azlocillin for Pseudomonas aeruginosa have been described as well [3]. The ob served effect might be due to the inducing capacity of clavulanic acid at relatively high concentrations [4] or to a species or strain specificity which has been described as well [5,6],
Recently, a new P-lactamase inhibitor, tazobactam (YTR) has been developed. Several studies showed promising data concerning the in vitro antibacterial activ ity of the combination piperacillin and YTR compared to piperacillin alone [7-9]. YTR is, like clavulanic acid, a Plactam compound and possesses there fore the ability to induce chromosomally mediated p-lactamases. Subsequently, the inhibitory effect of YTR on plasmid-me diated enzymes might interfere with the inducing capacity of YTR on the chro mosomally encoded enzyme. This inter ference might influence the synergistic effect of YTR on the antibacterial activity of piperacillin. The aim of this study was to assess the synergistic effect of YTR (4 mg/1) on the antibacterial activity of piperacillin
Downloaded by: Univ. of California Santa Barbara 128.111.121.42 - 3/6/2018 7:32:44 AM
Abstract. The effect of tazobactam on the piperacillin susceptibility and on the P-lactamase activity of different strains and species was evaluated. A synergistic effect was observed on the piperacillin susceptibility for all microorganisms tested, irrespective of the type and/or amount of p-lactamase produced. Addition of gentamicin resulted in a further reduction of the piperacillin MIC. The enzyme activity after induction with piperacillin alone or in combination with tazobactam (4 mg/1) was quite similar.
Stobberingh
210 Table 1. Antibiotic susceptibility and p-lactamase production of the microorganisms tested ß-Lactamase
MIC, mg/1 piperacillin
E. cloacae
5 10558 5356 9090
C. freundii
2R021 5189 2R039 7329
piperacillin + YTR (4 mg/1)
specific activity nmol/mg protein • min
type
0.5 1 0.25 8
1 1 0.25 4
24 23 151 2918
c c p+c p+c
0.015 1 128 128
0.03 2 8 1
22 41 2120 2159
c c p+c p+c
0.06 1 0.06 0.12
4 30 1252 792
c c p+c p+c
10 20 755 512
c c p+c p+c
98 114 454 418
c c p+c p+c
Proteus indol-positive
1160 3 4098 4112
0.06 1 16 8
P. aeruginosa
1356 1360 PSE1 PSE4
1 1 16 32
S. marcescens
2917 3RO02 10433 4323
0.06 0.12 4 16
against strains producing the chromosomally encoded P-lactamase alone or in com bination with a plasmid-encoded enzyme. In addition, the capacity of YTR to induce chromosomally mediated p-lactamases from different species was determined.
Materials and Methods Four strains of each of the following species were used: Enterobacter cloacae, Citrobacter freundii,
1 2 8 16 0.06 0.25 0.25 0.06
P. aeruginosa, Serratia marcescens and indol-positive Proteus: 2 strains with a chromosomally encoded beta-lactamase alone and 2 strains producing in ad dition a plasmid mediated enzyme, mostly of the TEM type. Only P. aeruginosa produced PSE type enzymes (PSE1 and PSE4). For the synergy studies the method of Berenbaum [10] was used. The frac tional inhibitory concentration (FIC) was defined as the ratio between the MIC of the combined com pounds and the MIC of the compound alone. The combination value was derived from the highest dilu tion of the antibiotic combination permitting no visi ble growth after 18 h at 37 °C. The interaction index was calculated as follows:
Downloaded by: Univ. of California Santa Barbara 128.111.121.42 - 3/6/2018 7:32:44 AM
Microorganisms
211
Tazobactam and ()-Lactamase Table 2. Susceptibility to piperacillin in the presence of YTR and gentamicin MIC, mg/1
Microorganisms
piperacillin
E. cloacae
5 10558 5356 9090
C.freundii
2R021 5189 2R039 7329
piperacillin + YTR (4 mg/1)
piperacillin + YTR (4 mg/1) gentamicin
FIC index1
0.5 1 0.25 8
1 1 0.25 4
0.03 0.06 0.06 0.25
1.03 0.56 1.24 0.53
0.015 1 128 128
0.03 2 2 1
0.06 0.06 0.5 0.06
3 0.56 0.56 0.56
0.06 1 0.06 0.12
0.03 0.06 0.03 0.03
2 0.56 0.74 1.24
0.06 0.25 8 4
0.56 0.75 1.004 1
0.06 0.06 0.125 0.03
1.24 0.74 0.75 0.56
Proteus indol-positi ve
1160 3 4098 4112
0.06 1 16 8
P. aeruginosa
1356 1360 PSE1 PSE4
1 1 16 32
S. marcescens
2917 3RO02 10433 4323
1 2 8 16
0.06 0.12 4 16
0.06 0.25 0.25 0.06
MIC combination drug A
MICcombinationdrugB
MIC drug A alone
MIC drug B alone
MICcombinationa MICcombinationb FIC = -------------------------- H------------------------MIC alone a MIC alone b A sum of 0.5 or more indicates synergism, a sum of less than 0.5 indicates antagonism. The induction studies were performed as de scribed previously using YTR (4 mg/1) and cefoxitin as the reference compound in a concentration of 'A MIC of the strain tested as the inducing agents [6], For P. aeruginosa 50 mg/1 cefoxitin was used.
The inducing capacity of an antibacterial agent was expressed as the fold increase in enzyme activity after induction compared to the activity before in duction. A fold increase of 2 or less was designated as a low, an increase between 2- and 10-fold as an inter mediate, and an increase of more than 10-fold as a high inducing capacity. Isoelectrofocusing as described by Matthew et al. [11] was used for the characterization of the p-lactamases.
Downloaded by: Univ. of California Santa Barbara 128.111.121.42 - 3/6/2018 7:32:44 AM
Drug A = Piperacillin in combination with tazobactam, drug B = gentamicin.
Table 3. Inducing capacity of YTR Increase after induction with, x
Microorganisms
YTR cefoxitin1 (4 mg/1) E. cloacae
5 10558 5356 9090
0.25 0.53 0.04 0.25
91 292 0.9 1.3
C.freundii
2R021 5189 2R039 7329
0.17 0.27 0.86 0.54
6.4 24 0.6 0.7
Proteus indol-positive 1160 3 4098 4112
0.24 0.40 0.5 0.6
5 0.8 not done
P. aeruginosa
1356 1360 PSE1 PSE4
0.48 0.34 0.65 0.9
260 60 2 7
S. marcescens
2917 3RO02 10433 4323
0.60 0.2 0.4 0.2
140 14 6.2 15
1.0
1 Cefoxitin: 'h MIC; for P. aeruginosa 50 mg/1 was used.
Results The antibiotic susceptibility and the specific P-lactamase activity of the strains used are shown in table 1. The microor
ganisms producing only a chromosomally mediated enzyme were highly susceptible to piperacillin. However, strains produc ing in addition a plasmid-encoded P-lactamase were distinctly less susceptible. Ad dition of YTR (4 mg/1) to piperacillin re sulted in a strong increase in susceptibility to piperacillin of most strains tested irre spective of the type/amount of P-lactamase produced. Only P. aeruginosa PSE1 and PSE4, the reference strains for the plasmid encoded P-lactamase PSE1 and PSE4, showed a similar susceptibility to piperacillin alone or in combination with tazobactam. No antagonistic effect be tween tazobactam and piperacillin was observed for all strains tested. In addition, for all strains a synergistic effect was found between piperacillin-tazobactam and gentamicin as shown by the FIC index of more than 0.5 (table 2). The p-lactamase activity of the strains producing both a chromosomally and a plasmid-mediated enzyme was, as ex pected, distinctly higher compared to the enzyme activity of the strains producing a chromosomally mediated P-lactamase only (table 1). Induction with cefoxitin re sulted in a strong increase in enzyme pro duction of those strains producing a chromosomally mediated P-lactamase alone up to around 300-fold for E. cloacae 10558 (table 3). Only the indol-positive Proteus strains 1160 and 3 showed a low to moderate increase in enzyme activity after induction with cefoxitin. Induction of the strains producing both types of P-lactamase resulted only in a low to moderate increase in enzyme activity. After induc tion with tazobactam (4 mg/1) no distinct increase in enzyme activity was observed for all strains tested.
Downloaded by: Univ. of California Santa Barbara 128.111.121.42 - 3/6/2018 7:32:44 AM
Stobberingh
212
Tazobactam and p-Lactamase
The data in this study confirmed the synergistic effect of tazobactam on the piperacillin susceptibility of the strains tested [7-9], An increase in piperacillin susceptibility was observed for strains producing only a chromosomally medi ated P-lactamase as well as for those pro ducing in addition a plasmid-mediated en zyme. Antagonism between azlocillin and clavulanic acid as described by Calderwood et al. [3] for P. aeruginosa was not observed with tazobactam and piperacil lin. This difference might be due to a strain dependent effect or to differences in in ducing capacity of clavulanic acid and tazobactam [12]. After induction with tazobactam in the concentration tested (4 mg/1) no increase in specific beta-lactamase activity was ob served for all the microorganisms tested with an inducible chromosomally medi ated beta-lactamase. The absence of induc ing activity of tazobactam for the chro mosomal beta-lactamases of the strains tested may be therefore an advantage for this new enzyme inhibitor. Similar data were found by Moosdeen et al. [12]. Addition of gentamicin resulted in a further reduction of the piperacillin MIC making the combination therapy of piper acillin + tazobactam and gentamicin a very promising one which needs further clinical evaluation. In several studies the strain and species dependent inducing capacity of an anti microbial has been described [4-6]. In the study of Sanders and Sanders [5], Serratia and Morganella morganii species were more likely to show induction than the other strains and species tested. Also in
one of our previous studies S. marcescens (1-lactamase showed a better inducibility than the P-lactamase of the other species tested [4], However, one has to keep in mind that the ability to induce chromo somally mediated p-lactamase was unre lated to its ability to select for stable resis tant derepressed mutants [5], Stable derepressed mutants have been associated with clinical failures [13]. Therefore, although piperacillin [5, 14] and YTR showed low inducing capacity, further studies on the ability of the combination to select stable derepressed mutants have to be evaluated to assess the clinical usefulness of this combination. References 1 Bush, K.; Sykes, R.B.: Beta-lactamase inhibitors in perspective. J. antimicrob. Chemother. 11: 97-107(1983). 2 Wise, R.; Andrews, J.M.; Bedford, K.A.: In vitro study of clavulanic acid in combination with pen icillin, amoxycillin and carbenicillin. Antimi crob. Agents Chemother. 13: 389-403(1978). 3 Calderwood, S.B.; Gardella, A.; Philippon, A.M.; Jacoby, G.A.; Moellering, Jr., R.C.: Effect of az locillin in combination with clavulanic acid, sul bactam and N-formimidoyl thienamycin against beta-lactamase producing carbenicillin resistant Pseudomonas aeruginosa. Antimicrob. Agents Chemother. 22: 266-271 (1982). 4 Stobberingh, E.E.: Induction of chromosomal beta-lactamase by different concentrations of clavulanic acid in combination with ticarcillin. J. antimicrob. Chemother. 21: 9-16(1988). 5 Sanders, C.C.; Sanders, W.W.: Type I beta-lactamases of gram-negative bacteria: interactions with beta-lactam antibiotics. J. infect. Dis. 154: 792-800(1986). 6 Stobberingh, E.E.; van Boven, C.P.A.: Inducing capacity of the combinations mecillinam-ampicillin and mecillinam-ceftazidime in comparison with the capacity of the compounds administered separately. Chemotherapy 33: 97-102 (1987).
Downloaded by: Univ. of California Santa Barbara 128.111.121.42 - 3/6/2018 7:32:44 AM
Discussion
213
7 Jacobs, M.R.; Aronoff, S.R.; Johenning, S.S.; Shlaes, D.M.; Yamabe, S.: Comparative activities of the beta-lactamase inhibitors YTR 830, clavulanate and sulbactam combined with ampicillin and broad spectrum penicillins against defined beta-lactamase producing aerobic gram-negative bacilli. Antimicrob. Agents Chemother. 29: 980985(1986). 8 Wiedemann, B.: Antibacterial activity of pipera cillin in combination with a p-lactamase inhibitor CL 298, 741, Abstract 109 (ICAAC, Los Angeles 1988). 9 Fass, R.J.; Prior, R.B.: Comparative in vitro ac tivities of piperacillin-tazobactam and ticarcillinclavulanate. Antimicrob. Agents Chemother. 33: 1268-1274(1989). 10 Berenbaum, M.C.: Correlations between methods for measurement of synergy. J. infect. Dis. 142: 476-478(1980). 11 Matthew, M.; Harris, A.M.; Marshall, M.J.; Ross, G.W.: The use of the analytical isoelectric focus ing for detection and identification of beta-lactamases. J. gen. Microbiol. 88: 169-178(1975).
Stobberingh 12 Moosdeen, L; Keeble, J.; Williams, J.D.: Induction/inhibition of chromosomal beta-lactamases by beta-lactamase inhibitors. Rev. infect. Dis. 8: S562-S568 (1986). 13 Milatovic, D.; Braveny, L: Development of resis tance during antibiotic therapy. Eur. J. clin. Mi crobiol. 6: 234-244(1987). 14 Minami, S.; Yotsuji, A.; Inoue, M.; Mituhashi, S.: Induction of beta-lactam antibiotics in Entero bacter cloacae. Antimicrob. Agents Chemother. 18: 382-385(1980).
E.E. Stobberingh Department of Medical Microbiology State University of Limburg P.O. Box 616 NL-6200 MD Maastricht (The Netherlands)
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