Genotypic-phenotypic Profiling and Statistical Modeling of the icaA Biofilm Marker in Multidrug-resistant Staphylococcus on Iraqi Currency

Paper money has served as a fomite and vector for centuries, potentially harboring pathogenic microorganisms due to contamination with nosocomial infections, such as biofilm-forming, multidrug-resistant bacteria. This study was conducted to examine environmental contamination of Iraqi current currency notes with bacteria, biofilm-forming genes, and antimicrobial-resistant profiles.

In this cross-sectional study, 32 Iraqi currency notes were obtained from six commercial sectors (October 2024–February 2025). Bacterial identification was performed using standard methods and the VITEK-2 automated system. Antimicrobial susceptibility testing was performed using the Kirby-Bauer disk diffusion method (CLSI 2024 criteria). PCR amplification was used to detect the icaA gene. Statistical analysis was performed using the chi-square and Fisher's exact tests (p < 0.05).

All 32 currency notes (100%) were positive for contamination, yielding a total of 50 bacterial isolates. Overall, Staphylococcus species were the most frequently isolated organism (n = 29, 58%), with S. epidermidis representing the most common isolate (n = 19, 38%). High rates of resistance were recorded for oxacillin (86.2%) and erythromycin (79.3%). In terms of multi-drug resistance, fifteen (51.7%) isolates were multi-drug-resistant (MDR). The icaA gene was present in 18 of 29 (62.1%) Staphylococcus isolates and was significantly associated with robust biofilm production (P < 0.001).

The presence of multidrug resistance and the biofilm-associated gene IcaA among the isolates indicated an apparent public health risk. This reflects the highly active, community-wide circulation of antimicrobial-resistant and highly persistent pathogens that survive both antibiotics and host defenses during everyday interactions.

The significant burden of these high-risk bacteria on Iraqi currency underscores the urgent need to raise hygiene levels at the community level and to develop effective control strategies to prevent money from serving as a vehicle for pathogen transmission.