This study describes KPC-204, a novel variant of Klebsiella Pneumoniae carbapenemase, characterized by a KDD amino acid insertion at Ambler position 269 deviates from KPC-2. This variant was identified in an ST11-type clinical isolate of carbapenem-resistant Klebsiella Pneumoniae from China. Notably, KPC-204 exhibits resistance to both ceftazidime-avibactam and carbapenems. Genetic analysis revealed that blaKPC-204 was located on a highly mobile IncFII/IncR plasmid within a complex genetic structure that facilitates its spread. Functional analysis, achieved through cloning into E. coli DH5α, validates KPC-204's contribution to increased resistance to ceftazidime-avibactam. The kinetic parameters showed that KPC-204 exhibited similar affinity to KPC-2 toward ceftazidime and reduced sensitivity to avibactam. Mating experiments demonstrated the resistance's transmissibility. This investigation underscores the evolving diversity of KPC variants affecting ceftazidime-avibactam resistance, highlighting the necessity for continuous monitoring.

Klebsiella pneumoniae complex is one of the most commonly isolated bacteria within human infections. These microorganisms are opportunistic pathogens that pose a serious threat to public health due to possibility of transmission in the human population. Resistance to carbapenems is one of the most important antimicrobials resistance mechanisms amongst them. In this situation therapeutic options are limited. Therefore, the aim of this study was to evaluate fosfomycin, colistin, ceftazidime-avibactam and meropenem-vaborbactam in vitro activity against multidrug-resistant K. pneumoniae complex strains. The study involved 160 strains of Gram-negative rods: K. pneumoniae – 138 and K. variicola - 22. Minimal inhibitory concentration of fosfomycin was estimated by agar dilution method and for colistin by microdilution method. The susceptibility to ceftazidime-avibactam and meropenem-vaborbactam was determined by gradient strip method. All of the analysed K. pneumoniae complex isolates produced extended-spectrum beta-lactamases and 60.0% carbapenemases. The most of the analysed strains were susceptible to fosfomycin and colistin (62.5%). Among pandrug-resistant K. pneumoniae complex isolates the most were susceptible to colistin (43.9%). Fosfomycin has good activity against ESBL- and VIM-positive isolates from this complex. In turn, colistin has satisfactory in vitro activity against KPC- and VIM-positive isolates from K. pneumoniae complex. Ceftazidime-avibactam has good activity against K. pneumoniae complex strains producing ESBL, KPC and OXA enzymes. In turn, meropenem-vaborbactam has satisfactory in vitro activity against ESBL- and KPC-positive isolates from this complex.

Pseudomonas aeruginosa is an antibiotic-resistant priority pathogen as listed by the World Health Organization. P. aeruginosa, a gram-negative, rod-shaped bacterium, is frequently encountered in hospital settings as an opportunistic pathogen in nosocomial infections. P. aeruginosa has shown high antibiotic resistance, which has been attributed to several mechanisms, such as intrinsic, acquired, and adaptive resistance. This study investigates several genes which may be attributed to the acquisition of antibiotic resistance in the bacteria P. aeruginosa, as it transitions from its planktonic form to the more threatening and resistant biofilm form. Subsequently, the study assesses the comparative efficacy of three antibiotics, Ofloxacin (OFX), Tobramycin (TOB), and Ceftazidime (CAZ), in altering the expression levels of the identified multidrug efflux pump genes associated with the ability to extrude antibiotics from the cell when in the biofilm form. Efflux transporter gene expression in P. aeruginosa was conducted via extraction of total RNA in planktonic and biofilm- both untreated and treated - with Tobramycin (TOB), Ofloxacin (OFX), and Ceftazidime (CAZ). Real-time quantitative reverse transcriptase PCR was employed to analyze alterations in expression levels of the Mex A, Mex B, Mex X, Mex Y, OprM, and RPSL genes in the collected samples. In samples where no antibiotics were administered, an increase in expression of the Mex B efflux pump gene was observed compared to all other efflux pump genes in the biofilm form, providing multidrug resistance when active. The gene of interest, Mex B, was assessed for antibiotic resistance by P. aeruginosa culturing in the planktonic and biofilm forms with simultaneous treatment with TOB, OFX, and CAZ. Of the three antibiotics used, OFX showed more effectiveness in preventing biofilm growth by reducing the expression level of the Mex B efflux pump gene in the biofilm form, making P. Aeruginosa more antibiotic sensitive to OFX. TOB has similar results compared to OFX but was slightly less effective in reducing the expression of Mex B. Conversely, CAZ was not effective in reducing expression of the Mex B gene in the biofilm form or the planktonic form and was determined to be ineffective at eradicating the organism.

Antimicrobial resistance has become a significant public health problem globally with multidrug resistant Gram negative (MDR-GN) bacteria being the main representatives. The emergence of these pathogens in neonatal settings threatens the well-being of vulnerable neonatal population given the dearth of safe and effective therapeutic options. Evidence from studies mainly in adults is now available for several novel antimicrobial compounds, such as new β-lactam/β-lactamase inhibitors (e.g. ceftazidime-avibactam, meropenem-vaborbactam, imipenem/cilastatin-relebactam), although old antibiotics such as colistin, tigecyclin and fosfomycin are also encombassed in the fight against MDR-GN infections that remain challenging. Data in the neonatal population are scarse, with few clinical trials enrolling neonates for the evaluation of efficacy, safety and dosing of new antibiotics, while the majority of old antibiotics are used off-label. In this article we review data about some novel and old antibiotics that are active against MDR-GN bacteria causing sepsis and are of interest to be used in the neonatal population.

The prevalence of multidrug-resistant Gram-negative infections, particularly carbapenem-resistant strains, has become a significant global health concern. Ceftazidime-avibactam (CZA) has emerged as a promising treatment option. However, data on its efficacy and safety in children are scarce, necessitating further investigation. We conducted a retrospective study at a tertiary hospital in Spain from February 2019 to January 2022. Pediatric patients (<16 years) treated with CZA for confirmed or suspected multidrug-resistant Gram-negative infections were included. Clinical and microbiological characteristics, treatment approaches, and outcomes were examined. Eighteen children received CZA treatment. All had complex chronic conditions, with the most frequent underlying main diseases being liver transplantation (n=8) and biliary atresia (n=4). The predominant type of infection for which they received CZA was intra-abdominal infections caused or suspected to be caused by OXA-48-producing Klebsiella pneumoniae. CZA was generally well tolerated. Within the first month of starting CZA therapy, 2 patients died, with one case directly linked to the infection’s fatal outcome. Some patients needed repeated courses of therapy due to recurrent infections, yet no resistance development was noted. In summary, the use of CZA showed effectiveness and safety, while the lack of resistance development highlights CZA’s potential as a primary treatment option against OXA-48-producing infections.