Antimicrobial Resistance of Salmonella enteritidis and Salmonella typhimurium Isolated from Laying Hens, Table Eggs, and Humans with Respect to Antimicrobial Activity of Biosynthesized Silver Nanoparticles

Abstract

<i>Salmonella enterica</i> is one of the most common causes of foodborne illness worldwide. Contaminated poultry products, especially meat and eggs are the main sources of human salmonellosis. Thus, the aim of the present study was to determine prevalence, antimicrobial resistance profiles, virulence, and resistance genes of <i>Salmonella</i> Enteritidis (<i>S. enteritidis</i>) and <i>Salmonella</i> Typhimurium (<i>S.</i> Typhimurium) isolated from laying hens, table eggs, and humans, in Sharkia Governorate, Egypt. The antimicrobial activity of Biosynthesized Silver Nanoparticles (AgNPs) was also evaluated. <i>Salmonella</i> spp. were found in 19.3% of tested samples with laying hens having the highest isolation rate (33.1%). <i>S.</i> Enteritidis) (5.8%), and <i>S.</i> Typhimurium (2.8%) were the dominant serotypes. All isolates were ampicillin resistant (100%); however, none of the isolates were meropenem resistant. Multidrug-resistant (MDR) was detected in 83.8% of the isolates with a multiple antibiotic resistance index of 0.21 to 0.57. Most isolates (81.1%) had at least three virulence genes (<i>sopB</i>, <i>stn,</i> and <i>hilA</i>) and none of the isolates harbored the <i>pefA</i> gene; four resistance genes (<i>blaTEM</i>, <i>tetA</i>, <i>nfsA,</i> and <i>nfsB</i>) were detected in 56.8% of the examined isolates. The AgNPs biosynthesized by <i>Aspergillus niveus</i> exhibit an absorption peak at 420 nm with an average size of 27 nm. AgNPs had a minimum inhibitory concentration of 5 µg/mL against <i>S. enteritidis</i> and <i>S. typhimurium</i> isolates and a minimum bactericidal concentration of 6 and 8 µg/mL against <i>S. enteritidis</i> and <i>S. typhimurium</i> isolates, respectively. The bacterial growth and gene expression of <i>S. enteritidis</i> and <i>S. typhimurium</i> isolates treated with AgNPs were gradually decreased as storage time was increased. In conclusion, this study indicates that <i>S. enteritidis</i> and <i>S. typhimurium</i> isolated from laying hens, table eggs, and humans exhibits resistance to multiple antimicrobial classes. The biosynthesized AgNPs showed potential antimicrobial activity against MDR <i>S. enteritidis</i> and <i>S. typhimurium</i> isolates. However, studies to assess the antimicrobial effectiveness of the biosynthesized AgNPs in laying hen farms are warranted.