Diffusion of Extended-Spectrum and Plasmid-Mediated Amp-C β-Lactamase Producing <em>Proteus mirabilis </em>in Hospitals and Community Setting in Zagreb, Croatia, First Report of CTX-M-32 and CTX-M-101 in <em>Proteus mirabilis</em>

Background/Objectives: Proteus mirabilis is a frequent causative agent of urinary tract and wound infections in community and hospital settings. It develops re-sistance to expanded-spectrum cephalosporins (ESC) due to the production of ex-tended-spectrum &beta;-lactamases (ESBLs) or plasmid-mediated AmpC &beta;-lactamases (p-AmpC). During routine microbiology testing, we observed an increased rate of multi-drug-resistant (MDR) P. mirabilis isolates. Here, we report the characteristics of ESBLs and p-AmpC &beta;-lactamases encountered among hospital and community isolates of P. mirabilis in two hospitals and the community settings in Zagreb, Croatia. Methods: Antibiotic susceptibility testing was performed by disk-diffusion and broth dilution methods. The double disk synergy test (DDST) and inhibitor-based test with clavulanic and cloxacillin were applied to screen for ESBLs and p-AmpC, respec-tively. PCR investigated the nature of ESBL, carbapenemases, and fluoroquinolone resistance determinants. Selected strains were subjected to molecular analysis of resistance traits by the Inter-array CarbaResist Kit and whole genome sequencing (WGS). Results: In total, 39 isolates were analyzed. Twenty-two isolates phenotypically tested positive for p-AmpC and seventeen for ESBLs. AmpC-producing organisms exhibited uniform resistance to amoxicillin-clavulanate, ESC, ciprofloxacin, and co-trimoxazole and uniform susceptibility to carbapenems and piperacillin-tazobactam and harbored blaCMY-16 genes. ESBL-positive isolates demonstrated resistance to amoxicillin-clavulanate, cefuroxime, cefotaxime, ceftriaxone, and ciprofloxacin, but variable susceptibility to cefepime and aminoglycosides. They possessed blaCTX-M genes that belong to cluster 1 (n=5) or 9 (n=12) with CTX-M-14 as the dominant allelic variant. Conclusions: The study's main finding is the diffusion of CTX-M ESBL and CMY-16 p-AmpC among hospital and community-acquired isolates. AmpC-producing iso-lates showed uniform resistance patterns, whereas ESBL-positive strains had varia-ble degrees of susceptibility/resistance to non-&beta;-lactam antibiotics, resulting in more diverse susceptibility patterns. The study demonstrated diffusion resistance deter-minants among hospital and outpatient isolates, mandating improvement in de-tecting &beta;-lactamases during routine laboratory work.