Abstract
Background:
Salmonella sp is an important pathogen often found in dairy farm waste and has the potential to pose health risks to humans and the environment. The increasing resistance of Salmonella sp to various antibiotics due to uncontrolled antibiotic use in the livestock industry is a serious challenge in infection control.

Aim:
This study aims to evaluate the antimicrobial activity of silver nanoparticles (AgNPs) against antibiotic-resistant Salmonella sp isolates originating from dairy farm waste.

Methods:
Silver nanoparticles were synthesized using the Nd:YAG laser method with polyvinylpyrrolidone (PVP) as a stabilizer, then tested against five Salmonella sp isolates resistant to penicillin, streptomycin, erythromycin, tetracycline, and oxytetracycline. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) tests were performed using the microdilution method.

Results:
The results showed that AgNP at a concentration of 100 ppm was able to inhibit the growth of all isolates, with the lowest MIC value (25 ppm) found in the penicillin-resistant isolate. However, the bactericidal effect of AgNP was limited, only showing negative results (no growth) on penicillin-resistant isolates at a concentration of 100 ppm. Statistical analysis showed no significant difference between inhibitory concentrations. These findings indicate that AgNP is effective as a bacteriostatic agent against antibiotic-resistant Salmonella sp., but its bactericidal activity is not optimal.

Conclusion:
Factors such as PVP stabilization and low silver ion release likely limit the ability to kill bacteria. Therefore, optimization of AgNP formulations to increase silver ion release and penetration into bacterial membranes, as well as further studies on environmental safety are needed before widespread application in livestock waste treatment.

Key words: Antibiotics; Public health; Salmonella sp.; Silver nanoparticles; Waste.