In vitro evaluation of the inoculum effect of various β-lactamase-producing Klebsiella pneumoniae isolates on ceftazidime-avibactam

Alexia Chauzy (1, 2) , William Couet (3, 1, 2) , Isabelle Martin (3, 1) , Hélène Mirfendereski (3, 1) , Sandrine Marchand (3, 1, 2)

1 PHAR2 [Poitiers] - Pharmacologie des anti-infectieux et antibiorésistance [U 1070]
2 Université de Poitiers - Faculté de Médecine et de Pharmacie
3 CHU de Poitiers [La Milétrie] - Centre hospitalier universitaire de Poitiers = Poitiers University Hospital

Background. Inoculum effect (IE) is a phenomenon widely recognized as having a potential effect on the efficacy of antibiotics, particularly β-lactams. One of the most frequently reported mechanism responsible for IE is an increased β-lactamases production with an increased bacterial burden1. The objective of this study was to characterize in vitro the IE produced by several K. pneumoniae strains with different β-lactamase profiles on ceftazime-avibactam (CAZ-AVI), a β-lactam-β-lactamase inhibitor (BL-BLI) combination. Material. In vitro IE was investigated on two clinical K. pneumoniae isolates producing KPC-2 or OXA-48, and on one non-β-lactamase-producing reference strain, used as a control (Table 1). Time-kill (TK) experiments were performed over 30h, using low (105-106 CFU/mL) and high (108 CFU/mL) starting inocula in presence and absence of AVI. CAZ concentrations were adapted according to the inoculum. Bacterial counts were determined at various times as well as CAZ concentrations using a validated LC-MS/MS method. Results. An IE on CAZ activity was observed for the three strains in absence of AVI (Fig.1, A). For the β-lactamase-producing strains, CAZ degradation was dependent on the bacterial density (Fig.1, B1-B2). At high inoculum, CAZ degradation was reduced in presence of AVI, resulting in a greater bacterial decrease. AVI at 16 mg/L was necessary to compensate for the over-production of β-lactamases at high inoculum (Fig.1, B1) and thus to restore the susceptibility of K. pneumoniae A28006 to CAZ (Fig.1, A1), but was not sufficient for K. pneumoniae CHA (Fig.1, A2-B2). Surprisingly, CAZ activity was also increased for the non-β-lactamase-producing strain in presence of AVI, although this was unrelated to its inhibitory activity (Fig.1, A3). Conclusions. This study showed that different mechanisms might contribute to the IE of K. pneumoniae on CAZ-AVI: the first one corresponding to a reduction of CAZ activity and the second one, specific to BL-BLI, to an over-production of β-lactamases. A combination of these two types of IE cannot be ruled out. AVI reduced the IE by enhancing CAZ activity2 against K. pneumoniae ATCC 43816 or/and by protecting CAZ from degradation by β-lactamases in the other strains.

Domaines: Pharmacologie; Bactériologie

Alexia Chauzy, William Couet, Isabelle Martin, Hélène Mirfendereski, Sandrine Marchand. In vitro evaluation of the inoculum effect of various β-lactamase-producing Klebsiella pneumoniae isolates on ceftazidime-avibactam. 34th European Congress of Clinical Microbiology and Infectious Diseases (ECCMID), Apr 2024, Barcelona, Spain. ⟨hal-04571024⟩