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Phage therapy has become a viable antimicrobial treatment as an alternative to antibiotic treatment, with an increase in antibiotic resistance. Phage resistance is a major limitation in the therapeutic application of phages, and the lack of understanding of the dynamic changes between bacteria and phages constrains our response strategies to phage resistance. In this study, we investigated the changing trends of mutual resistance between Stenotrophomonas maltophilia ( S. maltophilia ) and its lytic phage, BUCT603. Our results revealed that S. maltophilia resisted phage infection through mutations in the cell membrane proteins, while the evolved phage re-infected the resistant strain primarily through mutations in structure-related proteins. Compared with the wild-type strain (SMA118), the evolved phage-resistant strain (R118-2) showed reduced virulence, weakened biofilm formation ability, and reduced resistance to aminoglycosides. In addition, the evolved phage BUCT603B1 in combination with kanamycin could inhibit the development of phage-resistant S. maltophilia in vitro and significantly improve the survival rate of S. maltophilia -infected mice. Altogether, these results suggest that in vitro characterization of bacteria-phage co-evolutionary relationships is a useful research tool to optimize phages for the treatment of drug-resistant bacterial infections.IMPORTANCEPhage therapy is a promising approach to treat infections caused by drug-resistant Stenotrophomonas maltophilia (S. maltophilia) . However, the rapid development of phage resistance has hindered the therapeutic application of phages. In vitro evolutionary studies of bacteria-phage co-cultures can elucidate the mechanism of resistance development between phage and its host. In this study, we investigated the resistance trends between S. maltophilia and its phage and found that inhibition of phage adsorption is the primary strategy by which bacteria resist phage infection in vitro , while phages can re-infect bacterial cells by identifying other adsorption receptors. Although the final bacterial mutants were no longer infected by phages, they incurred a fitness cost that resulted in a significant reduction in virulence. In addition, the combination treatment with phage and aminoglycoside antibiotics could prevent the development of phage resistance in S. maltophilia in vitro . These findings contribute to increasing the understanding of the co-evolutionary relationships between phages and S. maltophilia ., Competing Interests: The authors declare no conflict of interest.

In recent years, Stenotrophomonas maltophilia ( S. maltophilia ) has become an important pathogen of clinically acquired infections accompanied by high pathogenicity and high mortality. Moreover, infections caused by multidrug-resistant S. maltophilia have emerged as a serious challenge in clinical practice. Bacteriophages are considered a promising alternative for the treatment of S. maltophilia infections due to their unique antibacterial mechanism and superior bactericidal ability compared with traditional antibiotic agents. Here, we reported a new phage BUCT700 that has a double-stranded DNA genome of 43,214 bp with 70% GC content. A total of 55 ORFs and no virulence or antimicrobial resistance genes were annotated in the genome of phage BUCT700. Phage BUCT700 has a broad host range (28/43) and can lyse multiple ST types of clinical S. maltophilia (21/33). Furthermore, bacteriophage BUCT700 used the Type IV fimbrial biogenesis protein PilX as an adsorption receptor. In the stability test, phage BUCT700 showed excellent thermal stability (4 to 60°C) and pH tolerance (pH = 4 to 12). Moreover, phage BUCT700 was able to maintain a high titer during long-term storage. The adsorption curve and one-step growth curve showed that phage BUCT700 could rapidly adsorb to the surface of S. maltophilia and produce a significant number of phage virions. In vivo , BUCT700 significantly increased the survival rate of S. maltophilia -infected Galleria mellonella ( G. mellonella ) larvae from 0% to 100% within 72 h, especially in the prophylactic model. In conclusion, these findings indicate that phage BUCT700 has promising potential for clinical application either as a prophylactic or therapeutic agent. IMPORTANCE The risk of Stenotrophomonas maltophilia infections mediated by the medical devices is exacerbated with an increase in the number of ICU patients during the Corona Virus Disease 2019 (COVID-19) epidemic. Complications caused by S. maltophilia infections could complicate the state of an illness, greatly extending the length of hospitalization and increasing the financial burden. Phage therapy might be a potential and promising alternative for clinical treatment of multidrug-resistant bacterial infections. Here, we investigated the protective effects of phage BUCT700 as prophylactic and therapeutic agents in Galleria mellonella models of infection, respectively. This study demonstrates that phage therapy can provide protection in targeting S. maltophilia -related infection, especially as prophylaxis.

Stenotrophomonas maltophilia (S. maltophilia) is an important Gram-negative opportunistic pathogen that is widely distributed in nature. S. maltophilia is highly drug-resistant because of its intrinsic properties and acquired drug resistance involving multiple molecular mechanisms, which creates a critical situation for infection therapy. Hence, there is an urgent need for alternative antimicrobial strategies to combat S. maltophilia. Herein, a novel S. maltophilia bacteriophage (phage) in family Podoviridae, named BUCT598, was isolated from hospital sewage and characterized to evaluate its potential as an antibacterial agent. The one-step growth curve showed that its latent period and burst size were approximately 30 min and 165 PFU/cell, respectively. Furthermore, phage BUCT598 survived within an extremely broad pH range (1-11), indicating its outstanding tolerance to both extremely acidic and extremely alkaline conditions. The whole-genome sequence of phage BUCT598 showed that it was a linear double-stranded DNA genome of 43,581 bp and 60% GC content. We identified 55 putative gene products involved in DNA replication, packaging, structure, and cell lysis. Whole-genome sequence comparisons among closely related phages indicated that phage BUCT598 had the highest sequence similarity with S. maltophilia phage BUCT609, with 52% query coverage and 76.40% identity, suggesting that it is a novel phage. Our findings indicate the great potential of phage BUCT598 as an alternative antimicrobial agent to eliminate S. maltophilia, and provide additional evidence that will help to understand how phages adapt and evolve under extreme environmental conditions, thereby opening up more extensive biotechnology applications of phages., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Stenotrophomonas maltophilia is a common conditional pathogen, and it is naturally resistant to most commonly used clinical antibiotics. The bacteriophage is considered to be a potential antibiotic alternative for treating multi-drug-resistant bacteria. In this study, a bacteriophage BUCT555 was isolated from hospital sewage for lysing the clinical multi-drug resistant Stenotrophomonas maltophilia. Electron microscopy studies revealed this phage belongs to the Podoviridae family. The double-stranded DNA genome of bacteriophage BUCT555 is composed of 39,440 bp with a GC content of 61.43%. The genome contains 57 open reading frames, 14 of which had assigned functions, while no virulence related genes, antibiotic resistance genes or tRNA were identified. The burst size of BUCT555 was 204 pfu per infected cell. Structure proteins of bacteriophage BUCT555 generated by SDS-PAGE and HPLC-MS revealed that it contains seven proteins with molecular weight ranging from 19 to 89 kDa. BLASTn analysis showed that phage BUCT555 has 2% homology with other phages in NCBI database, suggesting BUCT555 is a new phage genus of Podoviridae that infects Stenotrophomonas maltophilia. Characterization of the bacteriophage BUCT555 enriches our knowledge about the diversity of Stenotrophomonas maltophilia bacteriophages., (Copyright © 2021. Published by Elsevier B.V.)

Stenotrophomonas maltophilia (hereinafter referred to as S. maltophilia) has developed into an important opportunistic pathogenic bacterium, which is prevalent in nosocomial and community infections, and has adverse effects on patients with a compromised immune system. Phage vB_SmaS_BUCT548 was isolated from sewage of Beijing 307 Hospital with S. maltophilia (strain No.824) as a host. Phage morphology was observed by transmission electron microscopy and its biological and genomic characteristics were determined. The electron microscope shows that the bacteriophage belonged to the Siphoviridae and MOI is 0.001. One-step growth curve shows that the incubation period is 30 min and the burst size is 134 PFU/Cell. The host range is relatively wide and it can lysis 11of 13 S. maltophilia strains. Next-Generation Sequencing (NGS) results show that the genome sequence is a dsDNA with 62354 bp length, and the GC content is 56.3% (GenBank: MN937349). One hundred and two online reading frames (ORFs) are obtained after RAST online annotation and the BlastN nucleic acid comparison shows that the phage had low homology with other phages in NCBI database. This study reports a novel S. maltophilia phage named vB_SmaS_BUCT548, which has a short incubation period, strong lytic ability, and a wide host range. The main characteristic of this bacteriophage is the novelty of the genomic sequence and the analysis of the other characteristics provides basic data for further exploring the interaction mechanism between the phage and the host.

T7-like bacteriophages are a class of virulent bacteriophages which have a clearer genetic background and smaller genomes than other phages. In addition, it grows faster and is easier to culture than other phages. At present, the numbers of available T7-like bacteriophage genomes and Stenotrophomonas maltophilia genomes are small, and IME15 is the first T7-like virulent Stenotrophomonas phage whose sequence has been reported. It shows effective lysis of S. maltophilia. Here we announce its complete genome, and major findings from its annotation are described.

Stenotrophomonas maltophilia bacteriophage IME13 is a virulent phage with a large burst size, exceeding 3,000, much larger than that of any other stenotrophomonas phage reported before. It showed effective lysis of Stenotrophomonas maltophilia. Additionally, the phage IME13 developed at least three obviously different sizes of plaques when a single plaque was picked out and inoculated on a double-layer Luria broth agar plate with its host. Here we announce its complete genome and describe major findings from its annotation.