coli isolated from swine. Phenotypic antimicrobial tests showed that the E. coli isolate was resistant to the common antimicrobial agents used in farms and also exhibited reduced sensitivity to three indicator cephalosporins included in the study. Genetic analysis showed the presence of both TEM-20 and SHV β-lactamases that differed from SHV-1 only by a single amino acid substitution leucine to proline check details at position 138. This mutation was of special interest as SHV β-lactamses are specially related to K. pneumoniae and we wanted to see if this bla SHV gene

with single amino-acid substitution (L138P) detected in E. coli added to its substrate hydrolyzing activity [1, 2, 4, 22, 23]. All the cloned bla SHV genes expressed the specific protein bands that were confirmed by SDS-PAGE and Western blot. The size of the expressed SHV β-lactamases was larger than reported in previous research because of the intact 23 amino acid pro-peptide and His tag [20]. The enzyme kinetics of all the expressed β-lactamases showed differences in the affinities for penicillin and ampicillin that were included in this experiment (Table 3). The narrow spectrum β-lactamases SHV-1 and SHV-33 exhibited higher affinity to

penicillin and ampicillin respectively, whereas SHV-1 and SHV-33 Palbociclib purchase with only in one amino acid (L138P) mutation

exhibited reduced activity for both the substrate used in study. This indicated that leucine at position 138 was important for SHV β-lactamase and played an important role in hydrolyzing penicillin and ampicilin. Previous experiments on SHV β-lactamases have reported three natural mutations at position 69, 130 and 187 to be involved in conferring resistance to the inhibitors [11–13]. Proline has stronger stererochemical constraints than any other residues, with only one instead of two variable backbone angles and it lacks the normal amine backbone for hydrogen bonding. This could have the disruptive function tuclazepam to regular secondary structure and decreased the length of α-helix and changed the orientation of residues of binding sites. Based on the modeled docking structures of the wild-type and L138P mutant, the wild-type had three hydrogen bonds with penicillin and ampicillin but the L138P mutant had two hydrogen bonds, indicating that these structural changes by L138P mutation may decrease the substrate binding and finally resulted in reduced activity of L138P mutant. This result was supported by higher K m value for penicillin and ampicillin of L138P mutation when inserted in SHV-1 and SHV-33. Conclusions Based on our results we concluded that this mutation caused a drop in hydrolyzing penicillin and ampicillin.