Objective: To determine inhibitory activity of fermented milk with Lactobacillus casei strain Shirota (FMLC) against common multi-drug-resistant (MDR) bacteria causing hospital-acquired infections.
Material and Method: Time-kill methods of FMLC and cell-free filtered fluid of FMLC (CF-FMLC against Acinetobacter baumannii, Pseudomonas aeruginosa, ESBL-producing Escherichia coli & Klebsiella pneumoniae and methicillin-resistant Staphylococcus aureus were conducted. The control solutions were Mueller Hinton broth (MHB) and distilled water. The mixtures of FMLC, CF-FMLC, MHB and DW with 105 to 106 CFU/ml of each bacterium were prepared and incubated at 35°C. Each mixture was quantified for viable bacteria at 0, 1, 3, 6 and 24 hr after incubation onto brain heart infusion agar plates. The inoculated agar plates were incubated at 35°C for 24-48 hr. Bacterial colonies on agar plates were counted and compared among the mixtures.
Results: Log CFUs of each organism in MHB and distilled water after incubation were increased from 5.1-6.3 at 0 h to 6.4->11 at 24 hr. Log CFUs of each organism in FMLC and CF-FMLC after incubation with study bacteria for 0, 1, 3, 6 and 24 hr were decreased to undetectable amounts at 24 hr.
Conclusion: FMLC and CF-FMLC exerted slow inhibitory activity against MDR bacteria resulting in eradication of all study bacteria at 24 hr. Such inhibitory effects were probably due to the products of the milk fermented by Lactobacillus casei strain
Shirota. Clinical study is needed to determine if consumption of FMLC can prevent and treat colonization and infection with MDR bacteria in hospitalized patients.

Keywords: Inhibitory activity, Probiotics, Fermented milk, Lactobacillus casei strain Shirota, Multidrug-resistant bacteria, Hospital-acquired infections