Chitosan mitigates pan drug resistance in citrobacter freundii exhibiting AmpC and ESBL from Egyptian livestock

Extended-spectrum beta-lactamase (ESBL) and ampicillin resistance gene type C (ampC) in foodborne Citrobacter freundii (C. freundii) pose a severe public health risk, especially when they combine with other critical resistance genes to produce a reservoir of resistance. Therefore, the current study aimed to estimate the prevalence, phenotypic, and genotypic profiling of antimicrobial resistance in C. freundii isolates obtained from diseased broiler chickens and native Egyptian buffaloes in Kafr El-Sheikh and Dakahlia governorates, Egypt. Also, the investigation of the antibacterial activity of chitosan (CS) 1%, 2%, and chitosan nanoparticles (CSNPs), including the estimation of minimum inhibitory concentrations (MIC) and minimum bactericidal concentrations (MBC) and their combinations with ciprofloxacin (CIP), were evaluated. C. freundii was detected in 57.58% (19/33) of broiler chickens and 52.63% (20/38) of buffalo. Surprisingly, 26.32% (5/19) and 20% (4/20) of chicken and buffalo samples, respectively were multidrug-resistant (MDR), 42.11% (8/19) and 15% (3/20) were extensively drug-resistant (XDR), and 31.58% (6/19) and 65% (13/20) were pan drug-like-resistant (PDR). High frequencies of resistance genes were observed, including int1, dfrA1, sul2, aadA1, qnrA, and bla_TEM (≥ 80%), while other genes such as ermB, bla_CMY-2, bla_OXA-10, tet(M), mcr-1, bla_CTX-M, and catA1 were detected at variable rates. Alarmingly, all ESBL/AmpC-producing isolates co-harbored multiple critical resistance genes. CSNPs showed markedly lower MIC and MBC values compared with 1% and 2% CS, indicating significantly stronger bactericidal activity. The concerning prevalence of PDR like-C. freundii in food animals is brought to light by our results, which also provide credence to the use of 2% CS-CIP and CSNPs-CIP combinations as potential substitute treatments for resistant infections.