Association of class I integrons with antibiotic resistance in multidrug-resistant Acinetobacter baumannii

Abstract

Acinetobacter baumannii (A. baumannii) is a major cause of hospital-acquired infections and is frequently resistant to multiple antimicrobial classes. Class 1 integrons (intI1) are common in Gram‑negative bacteria and may serve as epidemiological markers of multidrug resistance, although their presence alone does not establish mechanistic causation. This study investigated the prevalence of intI1 among clinical A. baumannii isolates from a tertiary-care hospital in western Iran and assessed their statistical association with antimicrobial nonsusceptibility. One hundred non-duplicate clinical isolates were recovered from hospitalized patients and identified at the species level using MALDI-TOF MS. Antimicrobial susceptibility testing was performed according to CLSI guidelines, with colistin MICs determined exclusively by broth microdilution. The presence of intI1 was detected by PCR. For each antibiotic, 2 × 2 contingency tables were constructed to compare non-susceptible (resistant + intermediate) versus susceptible isolates across intI1-positive and intI1-negative groups. Odds ratios (ORs), 95% confidence intervals (CIs), and the appropriate inferential test (Pearson’s chi-square or Fisher’s exact test, depending on expected cell counts) were used to evaluate statistical associations. IntI1 was detected in 82% of isolates. A high burden of multidrug resistance was observed, with > 90% non-susceptibility to β-lactams, carbapenems, aminoglycosides, and fluoroquinolones. Significant associations were identified between intI1 carriage and non-susceptibility to gentamicin (OR = 41.0, p < 0.001), imipenem (OR = 41.0, p < 0.001), tobramycin (OR = 17.0, p < 0.001), ciprofloxacin (OR = 23.4, p = 0.002), ofloxacin (OR = 23.4, p = 0.001), ceftazidime (p = 0.009), and cefixime (p = 0.031). No significant association was observed for colistin (p = 0.148), consistent with its known chromosomal and mcr-mediated resistance mechanisms. Although the high prevalence of MDR A. baumannii and class 1 integrons is consistent with previous reports, the value of this study lies in providing updated regional surveillance data from western Iran, an area with limited molecular epidemiological reporting. Because integron cassette arrays were not sequenced, the specific resistance genes present remain unknown, and all associations should be interpreted as epidemiological rather than causal.