BACKGROUNDThe extended-spectrum beta-lactamase (ESBL)-producing Klebsiella pneumoniae has increasingly become a major contributor to nosocomial infections and can exhibit multiple antibiotic resistance. Previous studies have focused on the resistance genes in ESBL-producing strains, and the resistance-associated genetic environment of non-ESBL-producing strains has been ignored until now. Here, we investigated the occurrence and characteristics of non-ESBL-producing K. pneumoniae, which potentially carries unexpressed resistance genes.

METHODSK. pneumoniae strains were collected from five medical institutions in China from February 2010 to August 2013. The VITEK-2 ESBL detection system was used as a primary screen to identify the ESBL-producing phenotype, and the three primary types of ESBL-associated genes (CTX, SHV, and TEM) were detected by polymerase chain reaction (PCR) to confirm the strains presenting with a non-ESBL-producing phenotype. mRNA expression in the non-ESBL-producing strains was further screened by reverse-transcription PCR (RT-PCR) to validate their transcriptional efficiency.

RESULTSOut of 224 clinically isolated antibiotic-sensitive K. pneumoniae strains with a non-ESBL-producing phenotype, 5 (2.2%) were identified to carry inactivated ESBL blaSHV genes with intact upstream promoter regions and resistance gene sequences. Interestingly, three of the five antibiotic-sensitive K. pneumoniae strains containing ESBL blaSHV genes still exhibited mRNA transcription of blaSHV, while the other two exhibited no mRNA transcription.

CONCLUSIONThese findings suggest that inactivated ESBL genes exist in non-ESBL-producing antibiotic-sensitive K. pneumoniae strains, which have the potential to transform the strain into an ESBL phenotype if an inappropriate application or overdose of antibiotics is implemented during clinical management.