Several strategies to manage infected hip and knee total joint arthroplasties are present, mainly the DAIR procedure for early infection, single-stage revision, and two-stage revision, which is considered the gold standard by most surgeons; these procedures had various success rates [13, 32, 33]. For these procedures to be successful, the host factors, infection extent, duration, and the causative organism virulence should all be taken into account side by side with the surgical procedure [34]. As bacteria are capable of developing various resistance mechanisms such as biofilm formation, which made them resistant to antimicrobial therapy [35], BT was reintroduced to overcome the resistance developed against commonly used antimicrobial therapy.
Although the current review was formulated only of case reports, however an increasing trend in reconsidering BT for managing resistant and recurrent total hip and knee PJI cases. Furthermore, BT showed efficiency in curing the infection, especially in patients with resistant or recurrent infection and in situations where revision surgery is deemed problematic, or the patients refused the other option, such as amputations. Moreover, BT showed a considerable safety profile.
Bacteriophages are viruses that target specific bacteria and were first described in 1917; they had a good repetition in treating bone-related infections throughout the 20th century, especially in western Europe [18, 36, 37]. They have a narrow activity spectrum which could be either lytic or lysogenic; the former is the most promising for incorporation in the clinical medicine applications for infection management, as they can cause bacterial lysis and present in a dynamic relationship with bacteria [21]. Bacteriophages are different from antibiotics as they target a specific bacterium; furthermore, they continue to multiply as long as their hosting bacteria are present at a specific concentration, then the concentration will decrease gradually with bacteria elimination; this makes BT amenable to be administered as a single or few multiple doses [36, 38].
As bacteriophages have a peculiar mode of action different from antibiotics, resistance against bacteriophages rarely develops, unlike what happens with various antibiotics; thus, it can treat multiple antibiotic-resistant infections [39].
The treatment challenge of PJI is related partially to biofilm-associated infections, which are usually resistant to antibiotics [40], as the biofilm forms structured communities for bacteria enabling them to survive against the host immune defense and antimicrobial therapy [15]. In order to attack bacteria in biofilms, conventional antibiotics should be given in a concentration of 1000 times the doses needed to attack the same bacteria in a planktonic state [41]. This created the need for a new strategy and therapies focusing on biofilm disruption, where bacteriophages fit in this role [21].
Bacteriophages developed innate biofilm penetration ability followed by biofilm bacterial lysis, even if the bacteria are metabolically inactive [14, 42, 43]. They also can disrupt the extracellular matrix of the biofilm using the depolymerase enzymes, making BT efficient in treating bone and joint-related reluctant infections, including biofilm formation-related infection, and becoming an attractive option for managing resistant PJIs [14, 23, 42–45].
Additionally, a novel approach using lysins derived from bacteriophages which can penetrate the biofilm and attack antimicrobial-resistant bacteria [46]. Lysins act by rapidly activating peptidoglycan hydrolysis, osmotic lysis, and subsequent cell death upon contact with bacteria, unlike antibiotic-mediated bactericidal effects, which might require hours to be fully active [47]. These lysins showed broad-spectrum hydrolytic activity against planktonic and biofilm bacteria, unlike usual antibiotics [48, 49]. In the current review, one report by Ferry et al. [27] used Exebacase, a bacteriophage-derived lysin, instead of using the BT in treating four patients, which showed acceptable outcomes. Sosa et al. conducted a Study on a murine PJI model treated by DAIR to test the effectiveness of PlySs2, a bacteriophage-derived lysin, in targeting S. aureus biofilm in a periprosthetic environment compared to vancomycin. They found that PlySs2 treatment reduced 99% more colony-forming units (CFUs) and 75% more biofilm compared with vancomycin in vitro; furthermore, A combination of both used in vivo worked synergistically and reduced the number of CFUs on the surface of implants by 92% and in the periprosthetic tissue by 88% [50].
Most of the patients included in the current review underwent some surgical debridement, either open or arthroscopic; this step is helpful and synergistic for BT in many ways; first, it will help to dilute and minimize the bacterial count within the field; second, it allows for manual removal of the biofilm, third it ensures proper application of the bacteriophages near the biofilm when BT is used locally [21, 44, 45].
It is believed that the bacteria and their antagonist bacteriophages are present in nature in a balanced manner, where an increase in bacterial concentration is followed by an increase in bacteriophage concentration and vice versa [51]. Furthermore, one characteristic of bacteriophages' action against bacteria is that it finds difficulties dealing with a low concentration of bacteria when it drops below 104 ml or g, known as the "phage proliferation threshold" [52, 53]; at this level, bacteriophages will not eradicate bacteria unless the immune system is fully functional or additive management is used; and here comes the role of suppressive antibiotic therapy (SAT) [54]. In the current review, all patients treated with BT received SAT in combination; data showed that SAT has a synergistic effect when used with BT; some believe that using BT will lower the doses and concentration of antibiotics needed, owing to a decrease in the bacterial load [37, 43]. Noteworthy that SAT should be used judiciously as if the antibiotics were given in less than optimum doses; this could lead to the emergence of bacterial variants resistant to antibiotics which subsequently make phage therapy useless [55].
Regarding the safety and efficacy of adopting BT for managing PJIs, besides obtaining clearance of BT targeted infection in all patients included in the current review, no complications related to BT necessitating stoppage of the treatment developed in any of the patients, except for one patient who developed non-fatal transaminitis which improved after holding the BT. In a systematic review by Clarke et al. evaluating the efficacy of BT in managing bone and joint infections, the authors reported that about 93% of the included 277 patients achieved clinical clearance of infection, with no safety concerns expressed among the included studies [56]. Furthermore, the efficacy of BT in treating infection, especially if combined with antibiotic therapy and its high safety profile, was reported in the literature outcomes [37].
Although BT is an appealing option for managing resistant and relapsing PJIs, in the reports included in the current review, we found some unclear issues which need further investigation. First is the use of mono or cocktail BT; of the 13 patients who received frank BT, eight received cocktail and five mono BT; some authors preferred the cocktail therapy because multiple bacteriophages could expand the activity spectrum and decrease the chances of resistant development during the management course [57]. Second is the preparation of the BT; in two reports, the authors mentioned that the BT was prepared in other countries, namely Georgia and Austria, and one of the patients had his BT in the institution where the BT was prepared (Georgia). The third is the route of administration and duration of BT, which varies among the included reports; Cano et al. reported that the ideal duration for IV phage therapy is unclear, as they reported normalization of CRP by the last day of therapy (which lasted for about eight weeks), suggesting the potential need for a long management course [25]. On the contrary, Onsea et al. reported a small series of four patients who suffered from chronic osteomyelitis and were successfully treated by local cocktail phage therapy for only 7 to 10 days [44].
Furthermore, Doub et al. reported giving IV phage therapy for three days, which was explained by the fact that bacteriophages are capable of self-replicate, so a few days of management is only required as an adjunct to surgical debridement [21]. Fourth is the ethical approval for its use; as in all the included reports, the authors mentioned that they had to go through a different pathway to get ethical approval and clearance for BT use on their patients; this could be explained by the inadequate literature, documentation, and a regulatory framework [58, 59]. However, in countries with no authorization for phage use as a medicine, phage therapy could be carried out under Article 37 of the Helsinki Declaration or under national regulatory frameworks for treating individual patients with unauthorized treatments [60].
The current review had some inherent limitations, first is the exclusive inclusion of English literature while BT is a common practice in Western Europe; this might have led to depriving the review of studies published in languages other than English. Second is the inclusion of only case reports; however, this was related to the search results based on the search terms and search engines we used. Third, we could not report on BT's exact availability and cost as these data were lacking in the included reports.