4.12. Drop Plate Technique for Bacterial Enumeration (DP)

After the incubation time was complete, all bacterial suspensions were adjusted to approximately desired log10 CFU/mL using standard serial 10-fold dilution in MHB, and 20 µL were transferred for drop plating on Mueller-Hinton agar (S. intermedius, P. aeruginosa, β-hemolytic E. coli, and S. aureus) or blood agar (S. Suis). The drops were absorbed to agar in less than half an hour. Then, the plates were incubated at 37 °C for 18–24 h and the viable pathogens were enumerated. At least 3 to 30 colonies of the bacteria grew from 10 µL of drop and 30 to 300 CFU per 100 µL of the bacteria as a confidence technique were chosen for counting [69]. The total count of CFU from at least three drops at the countable dilution were determined and averaged. Finally, the total count was scaled up and the viable cell counts were expressed as CFU/mL [70]. The bacterial cell viability, the half-maximal inhibitory concentrations (IC₅₀) and the minimum inhibitory concentration (MIC) data were analyzed.