Stenotrophomonas maltophilia is associated with respiratory infections and high mortality rates for immunocompromised patients. Currently, only around 43 S. maltophilia bacteriophages are studied, and their effects when used with antibiotics against biofilm formation are poorly studied. Bacteriophage StM171 was isolated from hospital waste water, it is a Caudovirales lytic bacteriophage and represents a new genus, it has a 44kbp dsDNA that encodes 59 open reading frames. StM171 has a medium host range and low burst size. It shows varying, strain-dependent and antibiotic-dependent effects on the formation of biofilms by S. maltophilia strains with the formation of biofilm increasing in some cases when applying StM171. S. maltophilia strains that developed resistance to StM171 phage showed changed susceptibility to antibiotics compared with the originally susceptible strains; most of the strains became susceptible to cephalosporin and penicillin-like antibiotics and became resistant to erythromycin and vancomycin.

Examining the effects of using bacteriophages on antibiotics and on preventing biofilm formation is an urgent question, which makes it important to further study this interaction when applying bacteriophages and antibiotics in vivo for phage therapy.