2183. Porin Mutations Potentiate the in Vitro Synergy of Meropenem-Vaborbactam (MVB), but not Ceftazidime-Avibactam (CZA) in Combination with Other Antibiotics against KPC-producing Klebsiella Pneumoniae (KPC-Kp)
Authors: Rogers Tara M , Kline Ellen G , Squires Kevin M , Jones Chelsea , Shields Ryan K 
Published: November 2023

Abstract

Background
CZA and MVB are often used in combination with other antibiotics in clinical practice. Our objective was to assess their in vitro synergy stratified by predominant ompK36 genotype: wild-type (WT), or mutants that included an insertion sequence 5 (IS5) or GD duplication (GD).

Methods
15 KPC-Kp clinical isolates were selected. Minimum inhibitory concentrations (MICs) were determined by broth microdilution in triplicate. Time-kill analyses were used to test CZA and MVB alone (1 and 4x MIC) and in combination with colistin (COL; 2 mg/L), fosfomycin (FOS; 100 mg/L + 25 mg/L G6P), gentamicin (GEN; 2 µg/mL), meropenem (MEM; 8 mg/L), and tigecycline (TGC; 2 mg/L) against 1x108 cFu/mL. 24 hour log-kill was calculated as log cFu/mL decrease from time 0.

Results
5 isolates each had ompK36 WT, IS5, or GD. 27% and 73% were KPC-3 and KPC-2, respectively. 100% were susceptible to CZA and MVB. None were resistant to COL. 3 were non-susceptible to GEN, which were all IS5 (Table 1).
In combination with CZA 1x MIC, each of COL, GEN, and MEM were bactericidal against all isolates; mean ± standard error (SE) log kills were -7.39 ± 0.3, -6.58 ± 0.93, and -5.81 ± 0.21, respectively (Figure 1). Mean log-kills did not vary for CZA + COL, GEN, or TGC against ompK36 mutants vs WT; however, log-kills were significantly lower for CZA + FOS (-3.78 vs -6.6; p &lt; 0.05) or MEM (-5.4 vs -6.62; p &lt; 0.01) against ompK36 mutants compared to WT. Synergy rates were reduced from 100% against WT to 80%, 60%, and 40% against mutant isolates for CZA + COL, MEM, and FOS, respectively (Figure 2).
MVB 1x MIC in combination with COL, FOS, GEN, and TGC were bactericidal 67, 27, 80, and 47% of the time, with corresponding log kills of -3.96 ± 1.1, -1.56 ± 0.83, -5.05 ± 0.82, and -2.53 ± 0.28, respectively (Figure 1). Mean ± SE log kills were significantly greater against porin mutants compared to WT for MVB + COL (-5.57 vs -0.73; p = 0.03), FOS (-3.11 vs 1.54; p = 0.03), or TGC (-2.93 vs -1.73; p = 0.04). Rates of synergy were also higher against porin mutants vs WT for MVB + FOS or COL (Figure 2).
Table 1
Characteristics and susceptibility data for fifteen KPC-Kp isolates chosen for analysis. CAZ = ceftazidime; COL = colistin; CZA = Ceftazidime-avibactam; FOS = fosfomycin; GD = GD duplication; GEN = gentamicin; IS5 = insertion sequence 5; KPC = Klebsiella pneumoniae carbapenemase; MEM = meropenem; MVB = meropenem-vaborbactam; TGC = tigecycline; WT = wild-type.
Figure 1
24-hour log kills for antibiotic combinations with CZA (ceftazidime-avibactam) and MVB (meropenem-vaborbactam) at 1X MIC, stratified by ompk36 status: wild-type (WT) versus mutant (MUT). Bactericidal is defined as -3 log kill from time 0 at 24 hours and indicated by the dotted horizontal line. COL = colistin; FOS = fosfomycin; GEN = gentamicin; MEM = meropenem; MIC = minimum inhibitory concentration; TGC = tigecycline.
Figure 2
Proportion of bactericidal, synergistic, and antagonistic outcomes for ompK36 wild-type (WT; n = 5) versus mutant (MUT; n = 10) KPC-Kp isolates tested against CZA (ceftazidime-avibactam) or MVB (meropenem-vaborbactam) at 1X MIC as single agents and in combination with colistin (COL), gentamicin (GEN), tigecycline (TGC), meropenem (MEM), or fosfomycin (FOS). Bactericidal activity was defined as -3 log kill from time 0 at 24 hours; synergy and antagonism were defined as -2 or +2 log kill at 24 hours compared to most active single agent, respectively.

Conclusion
Porin mutations negatively impact CZA synergy with other antibiotics compared to WT, though 24-hour log kills for COL, FOS, GEN, and MEM remained below the bactericidal threshold. Conversely, porin mutations potentiate synergy between MVB and COL, FOS, or TGC.

Disclosures
Ryan K. Shields, PharmD, MS, Allergan: Advisor/Consultant|Cidara: Advisor/Consultant|Entasis: Advisor/Consultant|GSK: Advisor/Consultant|Melinta: Advisor/Consultant|Melinta: Grant/Research Support|Menarini: Advisor/Consultant|Merck: Advisor/Consultant|Merck: Grant/Research Support|Pfizer: Advisor/Consultant|Roche: Grant/Research Support|Shionogi: Advisor/Consultant|Shionogi: Grant/Research Support|Utility: Advisor/Consultant|Venatorx: Advisor/Consultant|Venatorx: Grant/Research Support