Isolation, characterization, and application of lytic bacteriophages for controlling Enterobacter cloacae complex (ECC) in pasteurized milk and yogurt

Characterization of a novel virulent mycobacteriophage Kashi-SSH1 (KSSH1) depicting genus-specific broad-spectrum anti-mycobacterial activity

AIM

Tuberculosis (TB) is one of the leading infectious disease causing mortality in the world and the rise of drug resistance; multi-drug resistance (MDR) and extensive-drug resistance (XDR) has added to extra complicacy of the disease. In this scenario, phage therapy has emerged as a potential treatment option against drug-sensitive/-resistant strains.

MATERIALS AND METHODS

The mycobacteriophage Kashi-SSH1 (KSSH1) was isolated from soil sample and was genomically, phenotypically, and functionally characterized. It includes genome assembly/annotation, transmission electron microscopy, multiplicity of infection (MOI), one-step growth curve, temperature/pH stability, confocal microscopy, host range determination and host growth reduction assays.

KEY FINDINGS

KSSH1 is a novel polyvalent virulent mycobacteriophage from the Myoviridae family, classified under cluster C1 with a 155,659 bp genome carrying key lysis genes-Holliday junction resolvase, Holin, Lysin A, and Lysin B, has an optimal MOI of 0.01, a 60-min latent period, and a burst size of 200 phages/bacterial cell. It remains stable up to 55 °C and within pH 7-10, exhibiting broad-spectrum activity against Mycobacterium species, like M. fortuitum (opportunistic pathogen), M. tuberculosis H37Ra (attenuated pathogen), and M. smegmatis, but not non-mycobacterial hosts. KSSH1 exhibits comparable growth inhibition of M. smegmatis like the antibiotics isoniazid and rifampicin as compared to the control, in liquid cultures for over 50 h without regrowth.

SIGNIFICANCE

KSSH1 exhibits strong lytic activity against various Mycobacterium species, lacks lysogeny-associated genes like integrases/transcriptional repressors, antibiotic resistance and virulence genes and remains stable from 4 °C to 37 °C and pH 8-10 ensuring safety/stability making it an ideal candidate for therapeutic use.

Can Bacteriophages Be Effectively Utilized for Disinfection in Animal-Derived Food Products? A Systematic Review

Food safety is a paramount public health concern, particularly with the rise of antimicrobial-resistant bacteria. This systematic review explores the efficacy of bacteriophages as a novel and environmentally sustainable approach to controlling multi-resistant and non-resistant bacterial pathogens in animal-derived food products. Following PRISMA guidelines, data from multiple studies were synthesized to evaluate bacteriophage applications across diverse food matrices, including beef, poultry, seafood, and dairy. The findings highlight significant variability in bacteriophage efficacy, influenced by factors such as food matrix properties, bacterial strains, and application methods. Phage cocktails and their combination with thermal treatments consistently demonstrated superior bacterial reduction compared to single-phage applications, which yielded variable results. Interestingly, the absence of a clear dose-response relationship underscores the need for a more detailed understanding of phage-host interactions and environmental influences. This review addresses a critical gap in the literature by advocating for matrix-specific, targeted phage applications over generalized approaches. Additionally, it underscores the transformative potential of bacteriophages as sustainable alternatives to chemical disinfectants in modern food safety practices. These insights provide a framework for future research aimed at optimizing bacteriophage efficacy and scaling their application in real-world food production systems.

Synergistic antibacterial activity of curcumin and phage against multidrug-resistant Acinetobacter baumannii

Acinetobacter baumannii is a priority bacterial pathogen and leading cause of nosocomial infections, particularly in intensive care units (ICUs). The average incidence of carbapenem-resistant A. baumannii infections in ICUs is 41.7 cases/1,000 patients, highlighting the urgent need for more effective alternative therapies to replace carbapenems. Thus, this study aimed to investigate for the first time the antibacterial activity of curcumin in combination with the novel phage vB_AbaSI_1 to combat multidrug-resistant (MDR) A. baumannii in vitro. Phage vB_AbaSI_1 (capsid diameter 91 nm, contractile tail 94/20 nm) was isolated from sewage and infects ~ 29% of the 131 bacterial isolates examined. The 52,783 kb phage genome has 75 ORFs, encodes an integrase, lacks tRNAs/virulence genes, and belongs to the Caudoviricetes. Commercially sourced curcumin (400 µg/mL), combined with phage vB_AbaSI_1 (MOI 100) reduced MDR A. baumannii 131 to undetectable levels 1 h post-treatment at 37 °C, and this efficacy was further extended for 5 h in double-dosed phage/curcumin-treated cultures. In contrast, treatment with just phage vB_AbaSI_1 reduced bacterial growth but rebounded within 3 h, while curcumin-only treated cultures showed only 1-log bacterial reduction compared to untreated control. The phage/curcumin synergy occurred exclusively with phage-susceptible strains pre-curcumin exposure. This suggests the potential disruption of bacterial cell membrane during phage infection allowing curcumin entry, as no synergy was observed with phage-resistant strains. This innovative strategy of combining phage and curcumin showed great efficacy at controlling MDR A. baumannii and has a potential for therapeutic deployment. Future work will focus on engineering the phage to make it therapeutically acceptable.

Characterization and genomic analysis of the lytic bacteriophage vB_EclM_HK6 as a potential approach to biocontrol the spread of Enterobacter cloacae contaminating food

BACKGROUND

Increased prevalence of Enterobacter cloacae within food products underscores food as an underexplored reservoir for antibiotic resistance, thus requiring particular intervention. Bacteriophages have been explored as a promising approach for controlling bacterial growth in different matrices. Moreover, their specific interaction and self-replication, put them apart from traditional methods for controlling bacteria in different matrices.

METHODS

Sixteen Enterobacter cloacae strains were recovered from raw chicken. These strains were used to isolate bacteriophages using enrichment protocol. The broad-spectrum bacteriophage was evaluated in terms of thermal, pH, shearing stress and storge. Moreover, its infection kinetics, in vitro antibacterial activity, cytotoxicity were also assessed. Genomic sequencing was performed to exclude any potential virulence or resistance genes. Finally, the capability of the isolated phages to control bacterial growth in different chicken samples was assessed alone and in combination with sodium nitrite.

RESULTS

The lytic bacteriophage vB_EclM_HK6 was isolated and showed the broadest spectrum being able to infect 8/16 E. cloacae strains with a lytic activity against its host strain, E. cloacae EC21, as low as MOI of 10-6. The phage displays a latent period of 10 min and burst size of 115 ± 44 and resistance frequency of 5.7 × 10-4 ± 3.0 × 10-4. Stability assessment revealed a thermal tolerance up to 60 ˚C, wide range pH stability (3-10) and the ability to withstand shearing stress up to 250 rpm. HK6 shows no cytotoxicity against oral epithelial cells up to 1012 PFU/ml. Genomic analysis revealed a Strabovirus with total size of 177,845 bp that is free from known resistance and virulence genes. Finally, HK6 pretreatment of raw chicken, chicken nuggets and ready-made cheese salad shows a reduced bacterial count up to 4.6, 2.96 and 2.81 log-units, respectively. Moreover, combing HK6 with sodium nitrite further improved the antibacterial activity in both raw chicken and chicken nuggets without significant enhancement in case of cheese salad.

CONCLUSION

Enterobacter bacteriophage vB_EclM_HK6 presents a safe and effective approach for controlling E. cloacae contaminating stored chicken food samples. Moreover, they could be combined with a reduced concentrations of sodium nitrite to improve the killing capacity.

Therapeutic Potential of a Novel Lytic Phage, vB_EclM_ECLFM1, against Carbapenem-Resistant Enterobacter cloacae

The global rise of multidrug-resistant Enterobacter cloacae strains, especially those that are resistant to carbapenems and produce metallo-β-lactamases, poses a critical challenge in clinical settings owing to limited treatment options. While bacteriophages show promise in treating these infections, their use is hindered by scarce resources and insufficient genomic data. In this study, we isolated ECLFM1, a novel E. cloacae phage, from sewage water using a carbapenem-resistant clinical strain as the host. ECLFM1 exhibited rapid adsorption and a 15-min latent period, with a burst size of approximately 75 PFU/infected cell. Its genome, spanning 172,036 bp, was characterized and identified as a member of Karamvirus. In therapeutic applications, owing to a high multiplicity of infection, ECLFM1 showed increased survival in zebrafish infected with E. cloacae. This study highlights ECLFM1's potential as a candidate for controlling clinical E. cloacae infections, which would help address challenges in treating multidrug-resistant strains and contribute to the development of alternative treatments.