Long exposure impact of antibiotics subinhibitory doses and silver nanoparticles on uropathogenic bacteria

Relevance. Although the primary purpose of using antibiotics is to treat infectious diseases, their misuse gradually leads to loss of their effectiveness. The aim of the current investigation was to explore the changes that occur in uropathogenic bacteria after long exposure to antimicrobials. Materials and Methods. We compared the effects of long-term exposure to ampicillin, cefazoline, kanamycin and silver nanoparticles (AgNPs) on susceptibility, biofilm formation and planktonic bacteria in 4 clinical uropathogenic strains namely Escherichia coli (UPEC), Staphylococcus aureus (S. aureus), Enterococcus faecalis (E. faecalis) and Streptococcus agalactiae (St. agalactiae). The minimum inhibitory concentrations (MIC) were determined using the microplate mircodilution method and bacteria were exposed to increasing concentrations of each antimicrobial (from MIC/2 to MIC) prepared in the brain heart infusion broth for 8 days. The susceptibility of bacteria to antibiotics was assessed using the Kirby Bauer disc diffusion method and the biofilm formation was assessed using crystal violet bacterial attachment assay. Results and Discussion. The data in this investigation highlight that long-term exposure to antimicrobials may induce changes in susceptibility to other antibiotics and biofilm formation in Uropathogenic strains. Indeed, exposure to ampicillin made E. faecalis resistant to ceftazidime and St agalactiae resistant to tetracycline, ceftazidime/clavulanate and ceftazidime. Following exposure to cefazolin, a significant decrease in susceptibility was observed in E. coli to ceftazidime/clavulanate and ceftazidime while S. aureus became resistant to ceftazidime/clavulanate, ceftazidime and to ceftriaxone. Similar variations were observed on St agalactiae and E. faecalis, which in addition to the 3 antibiotics above-mentioned, have become resistant to tetracycline. The most significant variations in susceptibility to antibiotics were observed following exposure to kanamycin: E. coli developed resistance to ceftazidime and a decrease in sensitivity was noted on ceftazidime/clavulanate while S. aureus, E. faecalis and St. agalactiae all 3 became resistant to ceftazidime/clavulanate and ceftazidime. In addition, except for E. coli all the bacteria in this investigation which had undergone successive passages in AgNPs developed resistance to ceftazidime/ clavulanate and ceftazidime. Bacteria exposed to ampicillin and cefazolin produced more biofilms than their respective controls. Conclusion. Long term exposure of uropathogens to antibiotics and AgNPs induces significant changes in susceptibility to other antibiotics and biofilm formation and antibiotics should therefore only be used when necessary.