Identification of hypervirulent Klebsiella pneumoniae carrying terW gene by MacConkey-potassium tellurite medium in the general population

Abstract

Objectives: To establish a MacConkey-potassium tellurium medium-based method for selectively culturing terW gene-positive Klebsiella pneumoniae (KP), to evaluate its performance and apply it to identifying particular clonal hypervirulent KP (hvKP) strains in epidemiological surveillance.

Methods: The virulence genes, rmpA, iutA, and terW, were detected by PCR. The minimum inhibitory concentration of potassium tellurite of hvKP (rmpA ⁺/ iutA ⁺) and classical KP (rmpA ^- and iutA ^-) was determined using the agar dilution method. The MacConkey medium containing 4 μg/ml potassium tellurite was prepared and the performance in detecting terW ⁺ KP was evaluated, including an agreement with PCR and positive/negative predictive value. Fecal samples from healthy volunteers in Fujian were collected and cultured in the medium, then positive strains were identified using MALDI-TOF MS, antimicrobial susceptibility was tested by Kirby-Bauer assays, and virulence genes and capsular serotype genes were tested by PCR.

Results: In KP isolated from clinical specimens (N = 198), the positive rate of terW was 37.9%, and the detection rate of terW in hvKP was significantly higher than that in classical KP (70.6% vs 13.3%). The potassium tellurite resistance levels of terW ⁺ (N = 75) and terW ^- (N = 55) KP were 8-128 μg/ml and <1-8 μg/ml, respectively, with significant differences. KP was selectively cultured on a MacConkey medium with 4 μg/ml potassium tellurite, and its agreement with PCR was good (Kappa=0.936), and the positive and negative percent agreement and positive and negative predictive values were 100% (75/75), 92.7% (51/55), 94.9% (75/79), and 100% (51/51), respectively. The prevalence of tellurite-resistant KP was 16.7% (86/516) in fecal samples from healthy volunteers, among which the positive rate of terW was 100% (86/86). The antimicrobial resistance characteristics of terW ⁺ KP showed no difference between healthy volunteers and inpatients. The most common capsular serotypes associated with high virulence were K1, K2, and K57.

Conclusions: The MacConkey medium containing 4 μg/ml potassium tellurite could easily select and culture terW ⁺ KP in fecal samples with high sensitivity and specificity, which is a practical method for the epidemic surveillance of hvKP in the general population.

Keywords: epidemic surveillance; general population; hypervirulent Klebsiella pneumoniae; potassium tellurite resistance; terW gene.