Carbapenem-resistant and carbapenem-susceptible isogenic isolates of Klebsiella pneumoniae ST101 causing infection in a tertiary hospital

Abstract

Background: In this study we describe the clinical and molecular characteristics of an outbreak due to carbapenem-resistant Klebsiella pneumoniae (CR-KP) producing CTX-M-15 and OXA-48 carbapenemase. Isogenic strains, carbapenem-susceptible K. pneumoniae (CS-KP) producing CTX-M-15, were also involved in the outbreak.

Results: From October 2010 to December 2012 a total of 62 CR-KP and 23 CS-KP were isolated from clinical samples of 42 patients (22 had resistant isolates, 14 had susceptible isolates, and 6 had both CR and CS isolates). All patients had underlying diseases and 17 of them (14 patients with CR-KP and 3 with CS-KP) had received carbapenems previously. The range of carbapenem MICs for total isolates were: imipenem: 2 to >32 μg/ml vs. <2 μg/ml; meropenem: 4 to >32 μg/ml vs. <2 μg/ml; and ertapenem: 8 to >32 μg/ml vs. <2 μg/ml. All the isolates were also resistant to gentamicin, ciprofloxacin, and cotrimoxazole. Both types of isolates shared a common PFGE pattern associated with the multilocus sequence type 101 (ST101). The bla CTX-M-15 gene was detected in all the isolates, whereas the bla OXA-48 gene was only detected in CR-KP isolates on a 70 kb plasmid.

Conclusions: The clonal spread of K. pneumoniae ST101 expressing the OXA-48 and CTX-M-15 beta-lactamases was the cause of an outbreak of CR-KP infections. CTX-M-15-producing isolates lacking the bla OXA-48 gene coexisted during the outbreak.

Fig. 1

Detection of clinical samples with ESBL-producing K. pneumoniae and non-ESBL-producing K. pneumoniae. Black bars represent CS-KP ESBL strains belonging to the PFGE-1 pattern and gray bars represent non-PFGE-1 pattern ESBL K. pneumoniae. Black line represents patients with CR-KP non-ESBL strains harboring the bla _OXA-48 gene that belonged to the PFGE-1 pattern

Fig. 2

Clinical features of the 28 patients with carbapenem-resistant K. pneumoniae isolates. Each line represents one patient from his/her hospital admission until discharge or death. Squares and circles only represent time units (one week) in hospital with no samples obtained on those days. Previous carbapenem treatment is marked with a star drawn on the left of each patient line. The moment of infection or colonization is indicated with a diamond shape

Fig. 3

Plasmid profile of CR-KP and CS-KP isolates. a Agarose gel electrophoresis of K. pneumoniae plasmid DNA, and b Southern blot hybridization using a bla _OXA-48 specific probe. Arrows show the presence of a ~70 kb OXA-48-containing plasmid in the CR-KP samples. Lane 1: CECT 678 (54.38 kb, 7.30 kb, 5.56 kb, 5.14 kb, 3.98 kb, 3.08 kb, 2.71 kb, and 2.06 kb plasmids); Lane 2: CECT 679 (154 kb, 66.2 kb, 37.6 kb, and 7.4 kb plasmids); and Lane 7: Low range ladder as controls. Lanes 3 and 5: CR-KP clinical isolates. Lanes 4 and 6: CS-KP clinical isolates. Lane 8: Positive control K. pneumoniae strain (K. pneumoniae 7680)