It is now generally accepted that the success of antitumor therapy can be impaired
by concurrent antibiotic therapy, the presence of certain bacteria, and elevated defensin
levels around the tumor tissue. The aim of our current investigation was to identify
the underlying changes in microbiome and defensin levels in the tumor tissue induced
by different antibiotics, as well as the duration of this modification. The microbiome
of the tumor tissues was significantly different from that of healthy volunteers.
Comparing only the tumor samples, no significant difference was confirmed between
the untreated group and the group treated with antibiotics more than 3 months earlier.
However, antibiotic treatment within 3 months of analysis resulted in a significantly
modified microbiome composition. Irrespective of whether Fosfomycin, Fluoroquinolone
or Beta-lactam treatment was used, the abundance of Bacteroides decreased, and Staphylococcus
abundance increased. Large amounts of the genus Acinetobacter were observed in the
Fluoroquinolone-treated group. Regardless of the antibiotic treatment, hBD1 expression
of the tumor cells consistently doubled. The increase in hBD2 and hBD3 expression
was the highest in the Beta-lactam treated group. Apparently, antibiotic treatment
within 3 months of sample analysis induced microbiome changes and defensin expression
levels, depending on the identity of the applied antibiotic.