A coup d'état by NDM-producing Klebsiella pneumoniae overthrows the major bacterial population during KPC-directed therapy

A Seven-Year Microbiological and Molecular Study of Bacteremias Due to Carbapenemase-Producing Klebsiella Pneumoniae: An Interrupted Time-Series Analysis of Changes in the Carbapenemase Gene's Distribution after Introduction of Ceftazidime/Avibactam

Background: Ceftazidime/avibactam (CZA) is a new option for the treatment of KPC-producing Klebsiella pneumoniae. The aim of this study was to determine resistance patterns and carbapenemase genes among K. pneumoniae (CP-Kp) bacteremic isolates before and after CZA introduction. Methods: K. pneumoniae from blood cultures of patients being treated in a Greek university hospital during 2015−21 were included. PCR for blaKPC, blaVIM, blaNDM and blaOXA-48 genes was performed. Results: Among 912 K. pneumoniae bacteremias: 725 (79.5%) were due to carbapenemase-producing isolates; 488 (67.3%) carried blaKPC; 108 (14.9%) blaVIM; 100 (13.8%) blaNDM; and 29 (4%) carried a combination of blaKPC, blaVIM or blaNDM. The incidence of CP-Kp bacteremias was 59 per 100,000 patient-days. The incidence of CP-Kp changed from a downward pre-CZA trend to an upward trend in the CZA period (p = 0.007). BSIs due to KPC-producing isolates showed a continuous downward trend in the pre-CZA and CZA periods (p = 0.067), while BSIs due to isolates carrying blaVIM or blaNDM changed from a downward trend in the pre-CZA to an upward trend in the CZA period (p < 0.001). Conclusions: An abrupt change in the epidemiology of CP-Kp was observed in 2018, due to the re-emergence of VIM-producing isolates after the suppression of KPC-producing ones via the use of CZA.

Generating Genotype-Specific Aminoglycoside Combinations with Ceftazidime/Avibactam for KPC-Producing Klebsiella pneumoniae

Antibiotic combinations, including ceftazidime/avibactam (CAZ/AVI), are frequently employed to combat KPC-producing Klebsiella pneumoniae (KPC-Kp), though such combinations have not been rationally optimized. Clinical KPC-Kp isolates with common genes encoding aminoglycoside-modifying enzymes (AMEs), aac(6')-Ib' or aac(6')-Ib, were used in static time-kill assays (n = 4 isolates) and the hollow-fiber infection model (HFIM; n = 2 isolates) to evaluate the activity of gentamicin, amikacin, and CAZ/AVI alone and in combinations. A short course, one-time aminoglycoside dose was also evaluated. Gentamicin plus CAZ/AVI was then tested in a mouse pneumonia model. Synergy with CAZ/AVI was more common with amikacin for aac(6')-Ib'-containing KPC-Kp but more common with gentamicin for aac(6')-Ib-containing isolates in time-kill assays. In the HFIM, although the isolates were aminoglycoside-susceptible at baseline, aminoglycoside monotherapies displayed variable initial killing, followed by regrowth and resistance emergence. CAZ/AVI combined with amikacin or gentamicin resulted in undetectable counts 50 h sooner than CAZ/AVI monotherapy against KPC-Kp with aac(6')-Ib'. CAZ/AVI monotherapy failed to eradicate KPC-Kp with aac(6')-Ib and a combination with gentamicin led to undetectable counts 70 h sooner than with amikacin. A one-time aminoglycoside dose with CAZ/AVI provided similar killing to aminoglycosides dosed for 7 days. In the mouse pneumonia model (n = 1 isolate), gentamicin and CAZ/AVI achieved a 6.0-log₁₀ CFU/lung reduction at 24 h, which was significantly greater than either monotherapy (P < 0.005). Aminoglycosides in combination with CAZ/AVI were promising for KPC-Kp infections; this was true even for a one-time aminoglycoside dose. Selecting aminoglycosides based on AME genes or susceptibilities can improve the pharmacodynamic activity of the combination.

Capability of Enterococcus faecalis to shield Gram-negative pathogens from aminoglycoside exposure

BACKGROUND

Enterococcus faecalis commonly produce aminoglycoside-modifying enzymes (AMEs) and are implicated in polymicrobial infections.

OBJECTIVES

To determine if AME-producing E. faecalis is capable of protecting Enterobacteriaceae and Pseudomonas aeruginosa from gentamicin exposure.

METHODS

Two Klebsiella pneumoniae isolates, two Escherichia coli isolates, and two Pseudomonas aeruginosa isolates were investigated in monoculture time-kill experiments, and each Gram-negative organism was also evaluated during co-culture with either AME-producing or AME-deficient E. faecalis. A pharmacokinetic/pharmacodynamics analysis that utilized Log Ratio Areas and a Hill-type mathematical model was used to determine if the maximal killing or potency of gentamicin against the Gram-negative organisms was altered by the presence of the E. faecalis.

RESULTS

The maximal killing and potency of gentamicin was the same during monoculture and co-culture experiments for both K. pneumoniae isolates and one E. coli isolate (P > 0.05). In contrast, the maximal killing of gentamicin was attenuated against one E. coli isolate and both P. aeruginosa isolates during co-culture with E. faecalis (P < 0.05). The potency of gentamicin was variable against the three aforementioned isolates. Against the E. coli isolate, the potency of gentamicin was significantly reduced by the presence of either E. faecalis isolate (EC50 95% CI = 4.23-4.43 mg/L monoculture versus 3.86-4.19 mg/L and 3.55-3.96 mg/L during co-culture with AME-producing and AME-deficient E. faecalis, respectively). The potency of gentamicin increased or decreased for P. aeruginosa depending on which E. faecalis isolate was investigated.

CONCLUSIONS

The AME-producing E. faecalis did not provide a consistent protective effect from aminoglycosides for the Gram-negative pathogens.