1.Three beta-lactamases isolated fromAeromonas salmonicida, including a carbapenemase not detectable by conventional methods    European Journal of Clinical Microbiology and Infectious Diseases    1994
Abstract:The β-lactamases of seven strains ofAeromonas salmonicida subsp.achromogenes resistant to amoxicillin (MIC>1024 mg/l) and responsible for furunculosis in farmed Atlantic salmon in Scotland were examined to establish the mechanisms of β-lactam resistance. Separation of a cell-free extract on an isoelectric focusing gel stained with the chromogenic cephalosporin nitrocefin showed the presence of two β-lactamases, one with a pI of 7.9 and the other with a pI of 6.0. Hydrolysis assays of cell-free extracts of these strains demonstrated carbapenemase, penicillinase and cephalosporinase activity. However, when the β-lactamases were separated by anion exchange chromatography, the carbapenemase activity could not be retrieved in either of the peak fractions containing the separated enzymes that had been visualised by nitrocefin. Consequently, a novel carbapenemase was discovered which cannot be detected with nitrocefin.

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2.Lack of additive effect between mechanisms of resistance to carbapenems and other beta-lactam agents inPseudomonas aeruginosa    European Journal of Clinical Microbiology and Infectious Diseases    1995
Abstract:Eighty-nine clinical isolates resistant (n=61) or susceptible (n=28) to imipenem and exhibiting the main patterns of susceptibility to other β-lactam agents (wild type pattern, penicillinase pattern, constitutive cephalosporinase pattern) were studied in order to investigate (i) the mechanism of resistance involved and (ii) whether resistance to carbapenems affects the level of resistance to other β-lactam agents and, conversely, if resistance to other β-lactam agents affects the level of resistance to carbapenems. For this purpose, the presence of OprD protein in the cell wall was detected by Western blot and β-lactamase activity by spectrophotometric assay and isoelectric focusing. OprD expression was not detectable in the imipenem-resistant (MIC≥16 μg/ml) strains. It was decreased in half the strains for which MICs of imipenem were 2 to 8 μg/ml and was close to a normal level in the most susceptible strains (MIC ≤1 μg/ml), thus demonstrating a direct correlation between the level of susceptibility to imipenem and the level of OprD expression. No imipenemase activity was detected in imipenem-resistant strains. Synergy between imipenem or meropenem and BRL42715 was observed for all of the strains, demonstrating the role of cephalosporinase in carbapenem resistance. Within each pattern of susceptibility, the mean MICs of β-lactam agents other than carbapenems were similar, whether the strains were susceptible or resistant to imipenem. Conversely, the mean MICs of imipenem or meropenem for either the imipenem-resistant or the imipenem-susceptible strains were similar, regardless of the susceptibility of these strains to the other β-lactam agents. Thus, when several mechanisms of resistance to β-lactam agents are present in the same strain ofPseudomonas aeruginosa, there is no additive effect between these mechanisms.

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3.Synthesis of 6-exomethylenepenams as β-lactamase inhibitors    Archives of Pharmacal Research    1999
Abstract:The 6,6-dibromopenam (6) was treated with CH3MgBr and carbaldehyde5 to afford the hydroxy compound7, which was reacted with acetic anhydride to give acetoxy compound8. The deacetobromination of8 with zinc and acetic acid gave 6-exomethylenepenams,E-isomer10 andZ-isomer9, which was oxidized to sulfone11 bym-CPBA. Thep-methoxybenzyl compounds were deprotected by AlCl3 and neutralized to give the sodium salts12, 13 and14.