Real-time optical detection of methicillin-resistant Staphylococcus aureus using lytic phage probes

Staphylococcus aureus (S. aureus)-specific bacteriophage was used as a probe for detection of methicillin-resistant S. aureus (MRSA) in aqueous solution using a novel optical method. Biorecognition phage monolayers transferred to glass substrates using Langmuir–Blodgett (LB) technique were exposed individually to MRSA in solution at logarithmic concentrations ranging from 10⁶ to 10⁹ cfu/ml, and observed for real-time binding using a CytoViva™ optical light microscope system. Results indicate that LB monolayers possessed high levels of elasticity (K), measuring 22 and 29 mN/m for 10⁹ and 10¹¹ pfu/ml phage concentrations, respectively. Near-instantaneous MRSA–phage binding produced 33 ± 5%, 10 ± 1%, 1.1 ± 0.1%, and 0.09 ± 0.01% coverage of the substrate that directly correlated to a decrease in MRSA concentrations of 10⁹, 10⁸, 10⁷, and 10⁶ cfu/ml. The exclusive selectivity of phage monolayers was verified with Salmonella enterica subsp. enterica serovar typhimurium (S. typhimurium) and Bacillus subtilis.