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Objective To isolate, sequence, and identify biological characterization and complete genome sequencing of a virulent Staphylococcus aureus (S. aureus) bacteriophage vB_SauH_IME522. Methods A phage was isolated from sewage of PLA Chinese General Hospital using a clinically isolated S. aureus strain as host bacteria. The double-layer agar plate was used to determine the optimal multiplicity of infection (optimal MOI) and one-step growth curve. Phage morphology was observed by transmission electron microscopy after purification using sucrose gradient separation. Phage DNA was sequenced using the Illumina Miseq sequencing platform. The complete genome sequence was annotated, then comparative genomics and evolutionary analyses were performed. Results A lytic phage of S. aureus was isolated from hospital sewage and named as vB_SauH_IME522. The optimal MOI of the phage was 0.01. One step growth curve showed that its latent period and burst period were 20 and 200 min, respectively. The burst size was about 89 PFU/cell. Electron microscopy displayed the phage having an icosahedral head (70±1) nm and a long contractile tail (135±2) nm. Genome sequencing results showed that the total length of the phage genome was 140 246 bp and the G+C content accounted for 30.2%. The genomic annotation revealed that the phage contained 223 genes coding proteins, 164 putative promoters, 66 terminators, 4 tRNAs, and 7 resistance-related regions. Phylogenetic analysis suggested that the phage was a member of the genus Kayvirus within the subfamily Twortvirinae. Conclusion A lytic phage of S. aureus vB_SauH_IME522 is identified as a new member of the Twortvirinae subfamily, with strong lytic ability and short latent period.

Aim: With the emergence of drug-resistant bacteria, finding alternative agents to treat antibiotic-resistant bacterial infections is imperative. Materials & methods: A mouse pneumonia model was developed by combining cyclophosphamide pretreatment and Acinetobacter baumannii challenge, and a lytic bacteriophage was evaluated for its therapeutic efficacy in this model by examining the survival rate, bacterial load in the lung and lung pathology. Results: Intranasal instillation with bacteriophage rescued 100% of mice following lethal challenge with A. baumannii. Phage treatment reduced bacterial load in the lung. Microcomputed tomography indicated a reduction in lung inflammation in mice given phage. Conclusion: This research demonstrates that intranasal application of bacteriophage is viable, and could provide complete protection from pneumonia caused by A. baumannii. [ABSTRACT FROM AUTHOR]

• Phage–antibiotic synergy (PAS) is a promising strategy for bacterial infections. • The treatment order of PAS combinations plays a pivotal role in bacterial killing. • Simultaneous phage–colistin treatment could suppress the emergence of phage-resistant mutants. • Simultaneous phage–colistin treatment could mitigate colistin resistance. Bacteriophage (phage) therapy, exploiting phages which are the natural enemies of bacteria, has been re-introduced to treat multidrug-resistant (MDR) bacterial infections. However, some intrinsic drawbacks of phages are overshadowing their clinical use, particularly the narrow host spectrum and rapid emergence of resistance upon treatment. The use of phage–antibiotic combinations exhibiting synergistic bacterial killing [termed 'phage–antibiotic synergy' (PAS)] has therefore been proposed. It is well reported that the types and doses of phages and antibiotics are critical in achieving PAS. However, the impact of treatment order has received less research attention. As such, this study used an Acinetobacter baumannii phage vB_AbaM-IME-AB2 and colistin as a model PAS combination to elucidate the order effects in-vitro. While application of the phage 8 h before colistin treatment demonstrated the greatest antibacterial synergy, it failed to prevent the development of phage resistance. On the other hand, simultaneous application and antibiotic followed by phage application were able to suppress/delay the development of resistance effectively, and simultaneous application demonstrated superior antibacterial and antibiofilm activities. Further in-vivo investigation is required to confirm the impact of treatment order on PAS. [ABSTRACT FROM AUTHOR]

Klebsiella pneumoniae is one of the major Gram-negative bacterial pathogens causing hospital-acquired multidrug-resistant infections, and the antimicrobial treatment options are scarce. The lack of available antimicrobials has prompted the development of alternative strategies for the treatment of these infections. In this study, a K. pneumoniae bacteriophage (vB_KpnP_IME321) targeting a KN1 capsular type strain, Kp409, was isolated, characterized and sequenced. This bacteriophage has a latent period of 20 min and a burst size of approximately 410 pfu/cell. It contained 49 predicted open reading frames, of which ORF42 was identified as encoding the putative capsule depolymerase. The enzyme expressed and purified in the Escherichia coli BL21 system, namely Dp42, could depolymerize the capsular polysaccharide of Kp409 and form translucent halos on the plates. The phage-encoded depolymerase could increase the inhibitory effect of serum on the growth of bacteria in vitro. Pre-treated with Dp42 rescued 100% of mice following lethal Kp409 challenge, and administration of this enzyme after infection significantly increased survival rates of infected mice in the animal experiment. In conclusion, the phage-encoded depolymerase Dp42 represents a potential alternative strategy for controlling infections mediated by K. pneumoniae expressing the KN1 capsular polysaccharide. [ABSTRACT FROM AUTHOR]