Effect of incremental tazobactam concentrations on the bactericidal activity of piperacillin against ESBL-producing enterobacterales clinical isolates causing bacteraemia.

We evaluated the activity of piperacillin in relation to INCREASING TAZOBACTAM CONCENTRATION against ESBL-producing Enterobacterales collected from patients with bacteraemia. Increasing tazobactam concentration (4, 12 or 24 mg/L) exerted a reduction of piperacillin MICs under the clinical breakpoint in a concentration-dependent manner (0%, 60% and 90% of clinical isolates). Also, activity of piperacillin/tazobactam based at higher achievable serum concentrations (123/14 mg/L) is needed to reduce the bacterial growth in 92% of ESBL-producers. CHANGES IN THE PIPERACILLIN MIC IN RELATION TO INCREASING TAZOBACTAM SUGGEST THAT REALTIME TDM COULD BE USED FOR DRIVEN ANTIMICROBIAL THERAPY WITH PIPERACILLIN/TAZOBACTAM IN BSI DUE TO ESBL STRAINS.

Genomic characterization of a high pathogenic Escherichia coli causing bacterial meningitis in a newborn in Italy, 2022: E. coli neonatal meningitis.

Here, we characterize the complete genome sequence of Escherichia coli isolated from a newborn affected by bacterial meningitis in Italy. Genome of E. coli strain 1455 harbored a circular chromosome and two plasmids of 167.740-bp and 4.073-bp in length, respectively. E. coli 1455 belonged to the ST3, serotype O17:H18 and carried different determinants including resistance to B-lactams, tetracyclines, and quinolones. In addition, genome of E. coli strain 1455 harbored 5 integrated pro-phage regions mainly located in the chromosome, while most of the virulence factors associated to the invasiveness and clinical severity and different antimicrobial resistance determinants (blaTEM-1, tet(A) and qnrS1) were located in the 167-Kb plasmid. Taken together, our findings suggest a possible widespread of a virulence factors-carrying plasmid worldwide and highlight the importance of genomic characterization in the diffusion of public health threats.

Complete Genome Sequence of a Klebsiella pneumoniae Strain Carrying Novel Variant blaKPC-203, Cross-Resistant to Ceftazidime/Avibactam and Cefiderocol, but Susceptible to Carbapenems, Isolated in Italy, 2023.

BACKGROUND: Klebsiella pneumoniae is a concerning pathogen, responsible for hospital-associated outbreaks. Multi drug resistant (MDR) strains are especially hard to treat. We conducted whole-genome sequencing on a MDR K. pneumoniae strain in order to identify genomic features potentially linked to its phenotype. METHODS: DNA sequencing was performed on the Illumina iSeq 100 platform. Genome assembly was carried out with SPAdes. The genome was annotated with RASTtk. Typing was performed with MLST and Kaptive. Antibiotic resistance genes were detected with AMRFinderPlus and Abricate, and further verified with BLAST. RESULTS: The strain exhibited resistance to ceftazidime/avibactam and cefiderocol, but remained susceptible to carbapenems. The strain belonged to sequence type ST101, serotype O1:K17. The analysis of antibiotic resistance genes indicated that the strain carried a novel KPC variant, designated as KPC-203, featuring a EL deletion at amino acid position 166-167, within the Ω-loop, and a nine-amino-acid insertion (LAVYTRAPM) at position 259. Sequence alterations were found in porin genes ompK35 and ompK36. Unlike molecular testing, which was able to detect the KPC-203 variant, all phenotypic carbapenemase detection methods achieved negative results. CONCLUSIONS: KPC-203, a novel KPC variant, showed a sequence modification in a cephalosporin resistance-associated hotspot. Interestingly, such alterations typically correlate with the restoration of carbapenem susceptibility. We hypothesize that KPC-203 likely led to resistance to ceftazidime/avibactam and cefiderocol, while maintaining susceptibility to carbapenems.

In Vitro Evaluation of Increasing Avibactam Concentrations on Ceftazidime Activity against Ceftazidime/Avibactam-Susceptible and Resistant KPC-Producing Klebsiella pneumoniae Clinical Isolates.

The novel ß-lactam/ß-lactamase inhibitor combinations (ßL-ßLICs) are one of the last-line resources available against multidrug-resistant (MDR) Gram-negative bacteria. Among ßL-ßLICs, ceftazidime/avibactam (CAZ-AVI) demonstrated strong activity against carbapenem-resistant Enterobacterales (CRE). Avibactam was proven to restore bactericidal activity of ceftazidime, inhibiting both KPC and OXA-48-like ß-lactamases. Despite this, emergence of CAZ-AVI-resistant strains in Enterobacterales has been reported. Herein, we evaluated the in vitro ceftazidime activity in the presence of increasing concentrations of avibactam by the broth microdilution method against CAZ-AVI-susceptible and resistant genome-characterized KPC-producing K. pneumoniae (KPC-Kp) clinical isolates. Strains expressing KPC and co-expressing KPC/OXA-181 carbapenemase were selected on the basis of the different phenotypic traits for novel ßL-ßLICs and cefiderocol. Notably, avibactam at 8 mg/L maintained the MIC of ceftazidime above the clinical breakpoint in 14 out of 15 (93%) KPC-Kp resistant to CAZ-AVI. A high concentration of avibactam (i.e., 64 mg/L) is required to observe a bactericidal activity of ceftazidime against 9 out of 15 (60%) CAZ-AVI-resistant isolates. In vitro evaluation showed that with the increase in the concentration of avibactam, ceftazidime showed high activity against CAZ-AVI-susceptible strains. High concentrations of avibactam in vivo are required for ceftazidime to be active against CAZ-AVI-resistant KPC-Kp.