Long-term surveillance of Enterobacter species and antimicrobial resistance in a secondary care centre in Oman: epidemiology and MDRO trends

Enterobacter species are important opportunistic pathogens with increasing multidrug resistance, but long-term regional surveillance integrating species distribution, antimicrobial resistance (AMR), and multidrug-resistant organism (MDRO) phenotypes remains limited. This study characterized nine years of laboratory surveillance in a secondary care centre in northern Oman. We retrospectively analyzed 1,805 non-duplicate isolates reported within the historical Enterobacter surveillance stream from 2017 to 2025. Species/taxon distribution, specimen source, antimicrobial susceptibility, department, acquisition source, and age-stratified MDRO burden were summarized. Resistance proportions used Wilson 95% confidence intervals; temporal trends used Spearman correlation; acquisition-source comparisons used chi-square tests; and age-associated MDRO prevalence used odds ratios and a Cochran-Armitage trend test. A weighted linear regression based on nine annual observations was retained only as an exploratory 2026 extrapolation for selected resistance rates and was not treated as a machine-learning model. Urine was the most common specimen (31.6%) and E. cloacae the most frequent identified taxon (47.0%); 21.3% remained at genus level. Overall MDRO prevalence was 27.6%. Third-generation cephalosporin resistance ranged from 37.7% (cefotaxime) to 67.2% (ceftazidime), while cefuroxime resistance was 93.7%. Tigecycline showed 98.1% susceptibility in a selectively tested subset ( n = 156), whereas colistin was 62.1% susceptible with 35.2% intermediate ( n = 182). Significant declining temporal trends were observed for meropenem, piperacillin-tazobactam, amikacin, and gentamicin. MDRO prevalence increased from 16.7% in patients aged 0–18 years to 45.2% in those > 80 years, but this association was unadjusted. The laboratory-recorded AmpC phenotype increased from 5 isolates in 2023 to 57 in 2025. The surveillance dataset demonstrates a substantial and changing AMR burden. Declining resistance to several agents was observed over time, but the retrospective design cannot attribute these changes to stewardship because antibiotic-consumption and intervention data were unavailable. The increase in the laboratory-recorded AmpC phenotype and the higher unadjusted MDRO prevalence in older patients warrant continued surveillance and confirmatory analyses. Integrated surveillance can support stewardship and infection-control planning when testing denominators, breakpoint changes, and phenotype-classification limitations are explicitly considered.