Integron- and Carbenicillinase-Mediated Reduced Susceptibility to Amoxicillin-Clavulanic Acid in Isolates of Multidrug-Resistant Salmonella enterica Serotype Typhimurium DT104 from French Patients

Abstract

Fifty-seven Salmonella enterica serotype Typhimurium (S. typhimurium) isolates were collected from human patients in two French hospitals, Hôpital Antoine Béclère (Clamart, France) and Hôpital Bicêtre (Le Kremlin-Bicêtre, France), between 1996 and 1997. Thirty of them (52 percent) were resistant to amino-, carbeni-, and ureidopenicillins, had reduced susceptibility to amoxicillin-clavulanic acid, were susceptible to cephalothin, and were resistant to sulfonamides, streptomycin, chloramphenicol, and tetracyclines. All these strains possessed a bla PSE-1-like gene and were of phage type DT104. Ten of them were studied in more detail, which revealed that bla PSE-1 is located on the variable region of a class 1 integron. This integron was found to be chromosomally located, as was another class 1 integron containingaadA2, a streptomycin-spectinomycin resistance gene. The reduced susceptibility to amoxicillin-clavulanic acid (and to ticarcillin-clavulanic acid) may result from the high level of hydrolysis of the β-lactam rather than to the clavulanic acid resistance properties of PSE-1 in these clonally related S. typhimurium isolates.

Molecular Identification of TEM-1 β-Lactamase in a Pasteurella multocida Isolate of Human Origin

“…Standard polymerase chain reaction (PCR) experiments were performed as described [8,9]. The PCR amplification and the primers used to search for known b-lactamase genes (bla TEM , bla SHV , bla ROB-1 , bla CARB and bla OXA-1 ) in Pasteurella multocida FB-1 have been described previously [7,8].…”

“…The PCR amplification and the primers used to search for known b-lactamase genes (bla TEM , bla SHV , bla ROB-1 , bla CARB and bla OXA-1 ) in Pasteurella multocida FB-1 have been described previously [7,8]. 16S rRNA gene sequencing was performed as described before [2].…”

“…Nucleotide sequence analysis and alignment methods were obtained online over the Internet at the following websites: http://www.fmi.ch/ biology/researchtools.html and http://www.ncbi.nlm.nih.gov. Arbitrarily primed-polymerase chain reaction (AP-PCR) was performed with three independent primers (ERIC-2, A3, and 6 MW) as described previously [8]. Macrorestriction analysis was performed according to the manufacturer's instructions (Bio-Rad, France).…”

“…Recombinant bacteria were plated onto trypticase soy agar plates containing 50 mg/l of amoxicillin. Direct transfer of the b-lactam resistance determinant from Pasteurella multocida into nalidixic acid-resistant Escherichia coli JM109 was attempted by liquid and solid mating-out assays at 37 7C [8]. Transconjugant selection was performed on trypticase soy agar plates containing nalidixic acid (100 mg/l) and amoxicillin (50 mg/l).…”

“…Beta-lactamase extracts were prepared and subjected to analytical isoelectric focusing as described [8]. …”