Host range is a major determinant in the industrial utility of a bacteriophage. A model host range permits broad recognition across serovars of a target bacterium while avoiding cross-reactivity with commensal microbiota. Searching for a naturally occurring bacteriophage with ideal host ranges is challenging, time-consuming, and restrictive. To address this, SPTD1.NL, a previously published luciferase reporter bacteriophage for Salmonella, was used to investigate manipulation of host range through receptor-binding protein engineering. Similar to related members of the Ackermannviridae bacteriophage family, SPTD1.NL possessed a receptor-binding protein gene cluster encoding four tailspike proteins, TSP1-4. Investigation of the native gene cluster through chimeric proteins identified TSP3 as the tailspike protein responsible for Salmonella detection. Further analysis of chimeric phages revealed that TSP2 contributed off-target Citrobacter recognition, whereas TSP1 and TSP4 were not essential for activity against any known host. To improve the host range of SPTD1.NL, TSP1 and TSP2 were sequentially replaced with chimeric receptor-binding proteins targeting Salmonella. This engineered construct, called RBP-SPTD1-3, was a superior diagnostic reporter, sensitively detecting additional Salmonella serovars while also demonstrating improved specificity. For industrial applications, bacteriophages of the Ackermannviridae family are thus uniquely versatile and may be engineered with multiple chimeric receptor-binding proteins to achieve a custom-tailored host range.

Engineered bacteriophages (phages) can be effective diagnostic reporters for detecting a variety of bacterial pathogens. Although a promising biotechnology, the large-scale use of these reporters may result in the unintentional release of genetically modified viruses. In order to limit the potential environmental impact, the ability of these phages to propagate outside the laboratory was targeted. The phage SEA1 has been previously engineered to facilitate food safety as an accurate and sensitive reporter for Salmonella contamination. In this study, homologous recombination was used to replace the expression of an essential baseplate wedge subunit (gp141) in SEA1 with a luciferase, NanoLuc^®. This reporter, referred to as SEA1Δgp141.NL, demonstrated a loss of plaque formation and a failure to increase in titer following infection of Salmonella. SEA1Δgp141.NL was thus incapable of producing infectious progeny in the absence of gp141. In contrast, production of high titer stocks was possible when gp141 was artificially supplied in trans during infection. As a reporter, SEA1Δgp141.NL facilitated rapid, sensitive, and robust detection of Salmonella despite an inability to replicate. These results suggest that replication-deficient reporter phages are an effective method to obtain improved containment without sacrificing significant performance or the ease of production associated with many phage-based diagnostic methods.

Shiga toxin-producing Escherichia coli (STEC) pose a significant threat to public health and effective methods of detection are needed. The use of naturally occurring bacteriophages (phages) to detect E. coli has been well documented. However, detecting multiple serotypes at the same time often required multiple phages specific to individual serotypes. To limit the burden of complex cocktails, this study aimed to engineer phages with an expanded host range that allows each phage to contribute to detection across multiple STEC serogroups. Kutterviruses, in the Ackermannviridae family, contain four tailspike proteins (TSPs), each of which confers tropism to a different bacterial strain. The modular nature of TSPs allows for mixing receptor-binding domains from diverse phage types. The host range of the Kuttervirus CBA120 was modified by replacing its native tailspike proteins (TSPs) with chimeric versions incorporating receptor-binding domains from related and unrelated phages. A structure-guided approach was utilized to overcome minimal sequence similarity between donor and recipient phages and achieve novel functional TSP chimeras. Two engineered phage variants were created that collectively detect five STEC serogroups: O26, O45, O103, O111, and O157. Spotting and luciferase assays confirmed that the replacement TSPs were functional and the phages had acquired new host ranges. This study demonstrates the feasibility of engineering Ackermannviridae phages with customized host ranges for detecting multiple STEC strains. This approach has potential applications in developing improved phage-based bacterial detection, therapy, and biocontrol.