Antibiotic-induced rat gut microbiota dysbiosis and salmonella resistance

Antibiotics are the most common medicines used to treat human infectious diseases. Based on their chemical structure, antibiotics mainly include the following categories: quinolones, β-lactams, macrolides, and aminoglycosides among others. The mechanism of different antibiotics varies, and there are four main mechanisms: inhibition of bacterial cell wall synthesis, interaction with cell membranes, interference with protein synthesis, and inhibition of nucleic acid replication and transcription. Antibiotics can act on pathogenic bacteria. Accordingly, antibiotics can also affect normal bacteria that colonize the human body. The size, structure, and function of the microbiota may change in response to antibiotic treatment. Significant changes in the human gut microbiota may be associated with repeated use of antibiotics [3]; in the following days, these changes were restored. However, little is known about comparing the response of the gut microbiota to antibiotic treatment. Probiotics are beneficial to the host when administered in adequate amounts. Lactobacillus rhamnosus was one of the most common probiotics studied by scientists regarding its culture, function, and metabolism [10]. However, the effect of L. rhamnosus present in the gut microbiota on the host's susceptibility to pathogenic bacteria after taking antibiotics has rarely been discussed. In our current study, rats were given two types of antibiotics, namely vancomycin and ampicillin, and their oral and intestinal microbiota was observed at 3 time points.  The rats were treated with antibiotics or L. rhamnosus, and then infected with Salmonella entericaserovarTyphimurium (S. Typhimurium ) via a gastric tube. Fecal samples were then collected to determine the pathogenic load. Ampicillin and vancomycin act in different antimicrobial spectra and have different absorption in the digestive tract. In addition, the concentration of these antibiotics entering the digestive tract varies; these factors can affect the host microbiota. Thus, this study aimed to compare the effects of these antibiotics on the gut microbiota at normal doses, as well as to evaluate the differences in the results. The gut microbiota underwent dramatic changes during the administration period. Changes in the gut microbiota affected the host's susceptibility to pathogens when infected with bacteria due to changes in resistance to colonization.