ABSTRACT
<p><b>BACKGROUND</b>The 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.</p><p><b>METHODS</b>K. 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.</p><p><b>RESULTS</b>Out 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.</p><p><b>CONCLUSION</b>These 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.</p>