Stenotrophomonas maltophilia (S. maltophilia) is an emerging opportunistic pathogen that exhibits resistant to a majority of commonly used antibiotics. Phages have the potential to serve as an alternative treatment for S. maltophilia infections. In this study, a lytic phage, A1432, infecting S. maltophilia YCR3A-1, was isolated and characterized from a karst cave. Transmission electron microscopy revealed that phage A1432 possesses an icosahedral head and a shorter tail. Phage A1432 demonstrated a narrow host range, with an optimal multiplicity of infection of 0.1. The one-step growth curve indicated a latent time of 10 min, a lysis period of 90 min, a burst size of 43.2 plaque-forming units per cell. In vitro bacteriolytic activity test showed that phage A1432 was capable to inhibit the growth of S. maltophilia YCR3A-1 in an MOI-dependent manner after 2 h of co-culture. BLASTn analysis showed that phage A1432 genome shares the highest similarity (81.46%) with Xanthomonas phage Xoo-sp2 in the NCBI database, while the query coverage was only 37%. The phage contains double-stranded DNA with a genome length of 61,660 bp and a GC content of 61.92%. It is predicted to have 79 open reading frames and one tRNA, with no virulence or antibiotic resistance genes. Phylogenetic analysis using terminase large subunit and DNA polymerase indicated that phage A1432 clustered with members of the Bradleyvirinae subfamily but diverged into a distinct branch. Further phylogenetic comparison analysis using Average Nucleotide Identity, proteomic phylogenetic analysis, genomic network analysis confirmed that phage A1432 belongs to a novel genus within the Bradleyvirinae subfamily, Mesyanzhinovviridae family. Additionally, phylogenetic analysis of the so far isolated S. maltophilia phages revealed significant genetic diversity among these phages. The results of this research will contribute valuable information for further studies on their morphological and genetic diversity, will aid in elucidating the evolutionary mechanisms that give rise to them.

Campylobacter is a major cause of bacterial foodborne diarrhea worldwide. Consumption of raw or undercooked chicken meat contaminated with Campylobacter is the most common causative agent of human infections. Given the high prevalence of contamination in poultry meat and the recent rise of multi-drug-resistant (MDR) Campylobacter strains, an effective intervention method of reducing bird colonization is needed. In this study, the Campylobacter-specific lytic phage CP6 was isolated from chicken feces. Phage CP6 exhibited a broad host range against different MDR Campylobacter isolates (97.4% of strains were infected). Some biological characteristics were observed, such as a good pH (3-9) stability and moderate temperature tolerance (<50 ℃). The complete genome sequence revealed a linear double-stranded DNA (178,350 bp, group II Campylobacter phage) with 27.51% GC content, including 209 predicted open reading frames, among which only 54 were annotated with known functions. Phylogenetic analysis of the phage major capsid protein demonstrated that phage CP6 was closely related to Campylobacter phage CPt10, CP21, CP20, IBB35, and CP220. CP6 phage exerted good antimicrobial effects on MDR Campylobacter in vitro culture and reduced CFUs of the host cells by up to 1-log compared with the control in artificially contaminated chicken breast meat. Our findings suggested the potential of CP6 phage as a promising antimicrobial agent for combating MDR Campylobacter in food processing.

The emergence of carbapenem-resistant hypervirulent Klebsiella pneumoniae (CR-hvKP) has driven us to explore alternative treatments for the limitation of antimicrobial agents. Lytic phages are considered a promising alternative treatment for CR-hvKP infection. In this study, we reported three novel lytic phages, vB_KpnA_SCNJ1-Z, vB_KpnS_SCNJ1-C, and vB_KpnM_SCNJ1-Y, against a CR-hvKP strain SCNJ1, and they possess genomes of double-stranded DNA with a size of 43,428 bp, 46,039 bp, and 50,360 bp, respectively. Phylogenetic analysis demonstrated that vB_KpnA_SCNJ1-Z belongs to the family Autographiviridae within the class Caudoviricetes, while vB_KpnS_SCNJ1-C and vB_KpnM_SCNJ1-Y are unclassified Caudoviricetes. The phages showed a narrow host range only lysing 1 of 50 tested clinical bacterial strains. The one-step growth curves and stability results showed that the phages displayed relatively short latency periods, with broad pH (pH 3-14) and thermal stabilities (20-60°C). The phages showed significant inhibition of the biofilm formation by SCNJ1 and strong antibacterial activity in vitro. In the mouse model, we demonstrated that administration of a single phage or phage cocktail significantly reduced bacteria loads in the lung, liver, and spleen, and effectively rescued mice from the infection of the SCNJ1 strain, with a survival rate of 70-80%. These findings suggested the three phages have great potential as an alternative therapy with favorable stability and strong antibacterial activity both in vivo and in vitro for the treatment of CR-hvKP infection.

Lytic bacteriophages are re-considered as a solution to resolve antibiotic-resistant rampage. Despite frequent foodborne outbreaks caused by the top six non-O157 Shiga-toxin-producing Escherichia coli (STEC), the current interventions are not sufficiently effective against each serogroup, particularly O45. Therefore, this study aimed to characterize a new short-tailed phage, vB_EcoP-Ro45lw (or Ro45lw), as an alternative antimicrobial agent for STEC O45 strains. Phage Ro45lw belongs to the Kayfunavirus genus within the Autographiviridae family and shares no close evolutionary relationship with any reference phages. Ro45lw contains a tail structure composed of a unique tail fiber and tail tubular proteins A and B, likely to produce enzymatic activity against the target bacterial cells besides structural function. Additionally, the phage genome does not contain virulent, antibiotic-resistant, or lysogenic genes. The phage has a latent period of 15 min with an estimated burst size of 55 PFU/CFU and is stable at a wide range of pH (pH4 to pH11) and temperatures (30 °C to 60 °C). Regardless of the MOIs (MOI = 0.1, 1, and 10) used, Ro45lw has a strong antimicrobial activity against both environmental (E. coli O45:H-) and clinical (E. coli O45:H2) strains at 25 °C. These findings indicate that phage Ro45lw has antimicrobial potential in mitigating pathogenic STEC O45 strains.

Phage are thought to exhibit control over host genes during infection. As a preliminary investigation of the kinetics and magnitude of co-expression between phage and bacteria, we compared the global transcriptional profiles for Vibrio alginolyticus strain E110 and its lytic phage HH109 by using RNA sequencing. In total, 24.7% (1,143/4,620) of the host protein-coding genes were differentially expressed genes during infection (DEGs). Functional analysis of the host DEGs suggests that phage HH109 induced rapid and distinctive changes when compared with 60- and 120-min postinfection (mpi). Based on gene co-expression network analysis, an uncharacterized late gene gp27 encoded by the phage HH109 was predicted to modulate the host\'s membrane transport and/or transcriptional regulation. Furthermore, expression of several bacterial virulence genes was downregulated while drug resistance genes were upregulated. This work contributes to an in-depth understanding of the reciprocal interactions of lytic phage HH109 and its pathogenic Vibrio host E110, and can provide new insights into the research and development of phage therapy against pathogenic Vibrio infections in the economically significant aquatic animals. IMPORTANCE Vibrio alginolyticus is a common opportunistic pathogen that causes mass mortality in cultured marine animals. Phage HH109 lyses pathogenic V. alginolyticus strain E110 with high efficiency and thus serves as a useful model to understand the dynamic interplay of a phage and its host. Global transcriptomic responses of strain E110 post-HH109 infection were characterized by using RNA sequencing, elucidating step-by-step control by HH109, an antiphage-like responses, and the elevated expression of drug resistance. This study provides a detailed molecular description phage and V. alginolyticus, providing insight into better prevention and control of vibriosis in aquatic animals.

Bacteriophages are the most abundant biological entities on earth and may play an important role in the transmission of antibiotic resistance genes (ARG) from host bacteria. Although the specialized transduction mediated by the temperate phage targeting a specific insertion site is widely explored, the carrying characteristics of \"transducing particles\" for different ARG subtypes in the process of generalized transduction remains largely unclear. Here, we isolated a new T4-like lytic phage targeting transconjugant Escherichia coli C600 that contained plasmid pHNAH67 (KX246266) and encoded 11 different ARG subtypes. We found that phage AH67C600_Q9 can misload plasmid-borne ARGs and package host DNA randomly. Moreover, for any specific ARG subtype, the carrying frequency was negatively correlated with the multiplicity of infection (MOI). Further, whole genome sequencing (WGS) identified that only 0.338% (4/1183) of the contigs of an entire purified phage population contained ARG sequences; these were floR, sul2, aph(4)-Ia, and fosA. The low coverage indicated that long-read sequencing methods are needed to explore the mechanism of ARG transmission during generalized transduction.

S. Enteritidis continues to be the most common pathogen of farm animals and a major public health burden worldwide. Using bacteriophages is a potential alternative to antibiotics against S. Enteritidis infection. In this study, the genome analysis of the lytic phage vB_SenM-PA13076 (PA13076) infecting S. Enteritidis revealed a linear, double-stranded DNA genome, which comprised of 52,474 bp and contained 69 ORFs. It belongs to the order Caudovirales; family Myoviridae, genus unclassified. The genes coded for DNA packaging, phage structural proteins, lysis components, DNA recombination, regulation, modification, and replication. No bacterial virulence or drug-resistance genes were detected. The phage PA13076 protected mice from a lethal dose of S. Enteritidis 13076Amp (5 × 108 CFU) by reducing the concentration of bacterial cells in blood, intestine, liver, spleen, and kidney. The phage PA13076 achieved at least 2.5 log reductions of S. Enteritidis cells in infected mice within 24 h (P < 0.05) when compared to the organs of control mice. The data also indicated that phage PA13076 could rapidly enter the blood and four organs of infected mice, remaining therein at concentrations of>104 PFU/g for at least 72 h. These results show that phage PA13076 has definite potential as an antibacterial therapeutic agent for attenuating S. Enteritidis infections.

The emergence and spread of antibiotic-resistant bacteria constitute a critical issue for modern medicine. Patients with antibiotic-resistant bacterial infections consume more healthcare resources and have worse clinical outcomes than patients with antibiotic-sensitive bacterial infections. Phages are natural predators of bacteria and may therefore be a source of useful antibacterial drugs. Phage therapy possess availability for oral administration, penetration through the bacteria cell wall, and eradication bacterial biofilms. All of these advantages give phage therapy the possibility to turn into applications for infectious diseases. In this mini-review, we focus on the brief history of lytic phage therapy, the life cycles of lytic phages and the therapeutic effects of lytic phages.

For effective use of phages as antimicrobial agents for controlling multidrug resistant S. Pullorum, it is important to understand phage biology. A lytic S. Pullorum phage was isolated and characterized from chicken feces, and its whole genome was sequenced and analyzed. A new lytic phage-vB_SPuM_SP116 (in brief SP116)- isolated and characterized using S. Pullorum SPu-116 as its host belongs to Myoviridae A1 group. Phage SP116 had a lytic effect on 27 of 37 (72.9%) different serotypes of clinical Salmonella strains. It showed a high bactericidal activity in killing all pathogens in cultures containing 5 × 105 cfu/mL and achieved more than 6.58 and 5.97 log unit reductions in cultures containing 5 × 106 cfu/mL and 5 × 107 cfu/mL, respectively. The one-step growth curve showed that the burst size was up to 118 pfu/bacterial cell. Complete genome sequence analysis revealed a linear, double-stranded DNA genome of 87,510 bp with an average G + C content of 38.84%, including 128 predicted open reading frames (ORFs) and 22 tRNA genes. SP116 was classified as a Felix O1 virus based upon the general phage characterization and the genomic information. Regarding its high efficacy in preventing especially S. Pullorum infection and its lack of any bacterial virulence, antimicrobial resistance, and lysogenesis genes, it could be a potential alternative candidate for the treatment of S. Pullorum infections.

Cells are social, and self-recognition is a conserved aspect of group behavior where cells assist kin and antagonize non-kin. However, the role of phage in self-recognition is unexplored. Here we find that a demarcation line is formed between different swimming Escherichia coli strains but not between identical clones; hence, motile cells discriminate between self and non-self. The basis for this self-recognition is a 49 kb, T1-type, lytic phage of the family Siphoviridae (named here SW1) that controls formation of the demarcation line by utilizing one of the host\'s cryptic prophage proteins, YfdM of CPS-53, to propagate. Critically, SW1 provides a conditional benefit to E. coli K-12 compared with the identical strain that lacks the phage. A demarcation line is also formed when strains harbor either the lysogenic phage ϕ80 or lambda and encounter siblings that lack the lysogen. In summary, bacteria can use phage to distinguish siblings that lack phage.