**4. Phage transduction of ARGs in** *Salmonellae*

*Salmonella* phages have been extensively used in molecular biology for the introduction of foreign genes by generalized and specialized transduction. P-22, a well-known phage is a classical example, other P-22 like prophages ST104 or PDT17, harboured within DT104 phage type have been hypothesized to facilitate horizontal transfer of the penta-resistance genes [27, 28]. The penta-resistance genes in phage type DT104 are clustered on a 43-kb *Salmonella* genomic island-1 (SGI1), which is flanked by two type I integrons [29]. *Salmonella* genomic island 1 (SGI1) is an integrative mobilizable element that harbours a multidrug resistance (MDR) gene cluster. A research undertaken by [27] asserted that ES18 and PDT17, also a P-22 like phage, following release from DT104 could transduce ARGs. Their findings further demonstrated the transduction of *cam* and *amp* by phage PDT17 and *amp*, *cam,* and *tet*, which confer resistance to ampicillin, chloramphenicol, and tetracycline, respectively, by ES18 from a donor DT104 strain into a DT104 recipient strain lacking these resistance genes. Phage ES18 also co-transduces selected ARGs of the 71 *tet* transductants and of the 145 *cam* transductants. Interestingly, in 14 of 16 transductants, it was noticed that phage E18 could co- transduce *sul* and *str*, genes involved in resistance to sulphonamides and streptomycin, respectively, together with *amp*, *cam,* and *tet* to create the ACSSuT (ampicillin, chloramphenicol, streptomycin, sulphonamides, and tetracycline) resistance phenotype [27]. This co-transduction likely occurs because *amp* and *str* are situated on the integrons flanking SGI1, and

*Challenges of Phage Therapy as a Strategic Tool for the Control of* Salmonella Kentucky*… DOI: http://dx.doi.org/10.5772/intechopen.95329*

the phage likely packages the SGI1 and its flanking integrons [30–32]. P-22 phage has also been identified within DT120 isolates shown to be capable of generalized transduction and possess the ACSSuT resistant strain [33]. See [33] reported that carbadox, a veterinary antibacterial that posses' mutagenic and carcinogenic capabilities induced phage transduction in DT104 and DT120. Furthermore the absence of transduction in DT104 strain which had its P-22 like prophage deleted following induction with carbadox suggests that P-22 like prophages are responsible for generalized transduction. Thus; transduction and co-transduction by P22-like prophages of ARGs co-located within SGI1 in multidrug-resistant *Salmonellae* strains is a common phenomenon. Also, genome scanning proved that P22-like prophages were common in 18 *Salmonella* serovars implying that generalized transduction may be greatly underestimated [33].

### **5. Transduction of Ciprofloxacin and cephalosporins genes**

Ciprofloxacin a fluoroquinolone and third generation cephalosporin are the drugs of choice in the treatment of invasive *Salmonella* infections [34–36]. Resistance of *Salmonella* to ciprofloxacin is due mainly to double mutations in *gyrA* and a single mutation in *parC* genes*.* In addition, *oqxAB* operon is suggested to be responsible for the increase in resistance observed in clinical *Salmonella* strains [37]. It was observed by [38], that Ciprofloxacin, enrofloxacin and danofloxacin induced *Salmonella* phage DT104 and DT102 transfer of a native kanamycin resistance plasmid to a strain of *Salmonella Typhimurium* by generalized transduction. Resistance to cephalosporin is mainly due to extended spectrum beta-lactamases (ESBLs), such as TEM-, SHV-, and CTX-M, or plasmid mediated AmpC β-lactamases (pAmpCs), such as CMY, encoded on transmissible conjugative plasmids [39–41], or be transferred by generalized transduction. Phage P24, induced from an isolate of *S. Typhimurium*, was propagated on a multidrug resistant strain of *S. Heidelberg* (S25). Thus, when the MDR S25 harbouring phage P24 was used as transduction donor to transfer ESBL and tetracycline resistance genes to a recipient *S. Typhimurium* isolate. PCR confirmed the presence of *bla*CMY-2, *tet*(A), and *tet*(B) in various *S. Typhimurium* transductants. Although the tetracycline genes were not co-transduced with *bla*CMY-2, their transduction frequency was equivalent, indicating generalized transduction and evidently reporting the transfer of ARGs by phage-mediated transduction between different *Salmonella* serovars. This finding likely expresses that cross-serovar transduction occurs frequently because phages can bind to various surface protein receptors on different species and serovars [42]. The LPS, FliC, OmpC, OmpF, OmpA, are examples of phage receptors present in *Salmonella* [43]. In the previous study [42] it was observed that 13 inducible phages recovered from 31 *Salmonella* serovars were capable of propagating on two or more *Salmonella* serovars including those often responsible for foodborne outbreaks such as *S. Heidelberg, S. Enteritidis, S. Typhimurium* and *S. Kentucky*. Finally, the findings of [42] demonstrate the spread of antibiotic resistance in *Salmonellae* by phage mediated transduction.

### **6. Transduction of R-factor genes**

R-factors which are a group of conjugative plasmids that harbour one or more antibiotic resistance determinants and represents another form of MGE that can be transferred horizontally by phage mediated transduction [24]. Conjugative plasmids are also self-transmissible, affording them the capacities to increase the

spread of ARGs. The origin of transfer (*ori*T), MOB genes, and the mate-pair formation (MPF) genes are the essential components for conjugation [44, 45]. In order for conjugation to occur, a protein complex called a 'relaxasome' responsible for processing plasmid DNA to prepare it for transfer must form at the *ori*T [46–48] and the mechanism for R-factor-phage acquisition and propagation of ARGs may be random. R factors in close proximity to P22-like prophages could be integrated into the head of the assembling phage during induction from its host, thus contributing to the spread of ARGs within bacteria capable of causing foodborne illnesses, in the intestinal flora of livestock and in the environment [24].
