Molecular Epidemiology and Virulence Profiles of Colistin-Resistant Klebsiella pneumoniae Blood Isolates From the Hospital Agency “Ospedale dei Colli,” Naples, Italy

Abstract

Resistance to colistin is increasingly reported in Klebsiella pneumoniae clinical isolates. The aim of this study was to analyze the molecular epidemiology and virulence profiles of 25 colistin-resistant K. pneumoniae blood isolates from the Hospital Agency “Ospedale dei Colli,” Naples, Italy, during 2015 and 2016. Colistin MIC values of isolates ranged from 4 to 256 mg/L. The inactivation of the mgrB gene, encoding a negative regulator of the PhoQ/PhoP signaling system, was the most frequent mechanism of colistin resistance found in 22 out of 25 isolates. Of these, 10 isolates assigned to ST512 and PFGE types A and A4 showed identical frameshift mutation and premature termination of mgrB gene; 4 isolates assigned to ST258 and PFGE types A1 showed non-sense, frameshift mutation, and premature termination; 3 and 1 isolates assigned to ST258 and PFGE A2 and ST512 and PFGE A3, respectively, had insertional inactivation of mgrB gene due to IS5-like mobile element; 2 isolates assigned to ST101 and 1 to ST392 had missense mutations in the mgrB gene, 1 isolate assigned to ST45 showed insertional inactivation of mgrB gene due to IS903-like mobile element. phoQ missense mutations were found in 2 isolates assigned to ST629 and ST101, respectively, which also showed a missense mutation in pmrA gene. The mcr-1-2-3-4 genes were not detected in any isolate. Colistin-resistant K. pneumoniae isolates showed variable virulence profiles in Galleria mellonella infection assays, with the infectivity of two isolates assigned to ST45 and ST629 being significantly higher than that of all other strains (P < 0.001). Interestingly, colistin MIC values proved to make a significant contribution at predicting lethal doses values (LD50 and LD90) of studied isolates in G. mellonella. Our data show that MgrB inactivation is a common mechanism of colistin resistance among K. pneumoniae in our clinical setting. The presence of identical mutations/insertions in isolates of the same ST and PFGE profile suggests the occurrence of clonal expansion and cross-transmission. Although virulence profiles differ among isolates irrespective of their genotypes, our results suggest that high colistin MIC could predict lower infectivity capability of the isolates.

Multiplicity of Carbapenemase-Producers Three Years after a KPC-3-Producing K. pneumoniae ST147-K64 Hospital Outbreak

“…The emergence of other KPC-3-producing high-risk K. pneumoniae clones with recognized worldwide expansion (ST392, ST307) and additional enhanced virulence and/or antibiotic resistance (ST307, ST22) is of concern. The ST392 clone has been recently reported in other countries (China, Italy, Mexico) [ 13 , 14 , 15 ] but to our knowledge this is the first study to describe KPC-3-producing K. pneumoniae ST392 isolates in Portugal. Although detected in small numbers, the identification of 4 ST307 isolates producing KPC-3 among medical and surgical units is of great concern because of its higher resistance profile and the recognized virulence potential (high resistance to complement-mediated killing) of this high-risk clone reported worldwide [ 16 , 17 ].…”

A novel colistin adjuvant identified by virtual screening for ArnT inhibitors

“…These strains belonged to different STs and carried loss-of-function mutations in mgrB , encoding a repressor of the arn operon responsible for lipid A aminoarabinosylation. 39 BBN149 at 30 μM strongly reduced the colistin MIC for all the colistin-resistant K. pneumoniae strains, while it did not increase colistin activity against the colistin-susceptible KP-Mo-26 and KP-Mo-27 isolates (Table 1 ), implying that the inhibitory activity of this compound on colistin resistance is not restricted to P. aeruginosa. Time–kill and growth assays confirmed that in K. pneumoniae the BBN149/colistin combination is also bactericidal at 2× MIC of colistin (Figure S5 ) and that BBN149 has no inhibitory effect in the absence of colistin (Figure S4 ).…”

CrrB Positively Regulates High-Level Polymyxin Resistance and Virulence in Klebsiella pneumoniae

“…However, in a genomic survey of 164 PR clinical isolates, we recently observed that 40% harbored wild-type (WT) mgrB . In addition, we identified more than 80 mutations, the majority of which were within three two-component systems— phoP/Q , crrA/B , and pmrA/B ( Macesic et al, 2020 )—which have been proposed as alternative pathways to PR ( Leung et al, 2017 ; Esposito et al, 2018 ). In combination with mgrB , we will refer to these genes as the “canonical genes.” These findings highlight the heterogeneous nature of PR and the urgent need for functional validation of the observed alleles ( Macesic et al, 2020 ).…”