Detection of the SHV genotype polymorphism of the extended-spectrum β-lactamase-producing Gram-negative bacterium

The prevalence of extended-spectrum β-lactamases (ESBLs) is due to the extensive usage of the extended-spectrum cephalosporins and leads to huge financial loss worldwide, whilst presenting a challenge to the clinical treatment. The aim of the present study was to delineate the frequency of ESBL occurrence in Enterobacteriaceae and confirm the SHV genotype. A random collection of 153 Escherichia coli isolates (E. coli) and 70 Klebsiella pneumoniae isolates were tested. The amplification products obtained by polymerase chain reaction were sequenced. Isolates with novel mutations were transformed to E. coli DH5 α. The minimum inhibitory concentration (MIC) was obtained by a microdilution method. The relevance ratio of ESBL was 67.7% and the proportion of the SHV β-lactamase gene (bla_SHV) was 18.5%. A new genotype of β-lactamase was demonstrated and submitted to GenBank. A total of 12 mutational sites were found in 28 ESBL-producing isolates, including four nonsense mutations. Sensitive-rates of 28 ESBL-producing isolates to imipenem were 100%, and resistant-rates to penicillin, amoxicillin and oxacillin were 100%. The MIC of DH5 α-F8 to penicillin, oxacillin, cefoxitin, cefotaxime, cefepime, cefoperazone/sulbactam, imipenem and netilmicin was 512, 512, 2, 0.03, 0.06, 4, 0.015 and 32 respectively. In conclusion, ESBL and SHV-28 is the most prevalent bla. Imipenem is the most effective antibiotic to ESBL, and the 4th-generation cephalosporins and β-lactamase inhibitor compound are also effective. ESBL is mediated by plasmids and able to spread among different Enterobacteriaceae. In conclusion, new mutations of the bla_SHV gene exist from at least 2010.