A hospital outbreak of carbapenem-resistant *Acinetobacter baumannii* occurs despite stringent cleaning. Which mechanism most likely facilitated the rapid spread of resistance genes in this setting?

💡 Explanation

Horizontal gene transfer via plasmids allows for rapid dissemination of resistance genes between bacteria, even of different species. This is because plasmids can carry multiple resistance genes and transfer them directly. Therefore, horizontal transfer explains the outbreak rather than vertical transmission, mutation rate, or disinfectant resistance alone.

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