Isolation and characterization of bacteriophages infectingSalmonellaspp.

Abstract

Bacteriophages infecting Salmonella spp. were isolated from sewage using soft agar overlays containing three Salmonella serovars and assessed with regard to their potential to control food-borne salmonellae. Two distinct phages, as defined by plaque morphology, structure and host range, were obtained from a single sample of screened sewage. Phage FGCSSa1 had the broadest host range infecting six of eight Salmonella isolates and neither of two Escherichia coli isolates. Under optimal growth conditions for S. Enteritidis PT160, phage infection resulted in a burst size of 139 PFU but was apparently inactive at a temperature typical of stored foods (5 degrees C), even at multiplicity of infection values in excess of 10 000. While neither isolate had characteristics that would make them candidates for biocontrol of Salmonella spp. in foods, phage FGCSSa1 behaved unusually when grown on two Salmonella serotypes at 37 degrees C in that the addition of phages appeared to retard growth of the host, presumably by the lysis of a fraction of the host cell population.

Characterization of a T5-Like Coliphage, SPC35, and Differential Development of Resistance to SPC35 in Salmonella enterica Serovar Typhimurium and Escherichia coli

“…This result can be explained by the possibility that a proportion of the initial bacterial population was resistant to the phage or by the rapid appearance of resistant mutants. Carey-Smith et al (11) and Fischer et al (17) proposed that the growth retardation in the presence of bacteriophage occurs when only a subpopulation of the host bacteria is susceptible to phage infection, such as the 15% of E. coli O157:H7 Mu L isolates that were resistant to phage PP01 (17). In contrast, Kocharunchitt et al (32) suggested that incomplete lysis of phage-treated bacteria was due to physiologic and/or genetic modification of host cells during phage infection.…”

“…The high host specificity of most phages is a double-edged sword; high specificity is necessary for the specific targeting of unwanted bacteria, but the narrow host range renders phage biocontrol ineffective for non-host strains (22). The use of broad-hostrange phages isolated by multiple-host enrichment methods (7,11,29) or a phage cocktail composed of multiple phage types (33,44,55) has shown promise in overcoming this problem. Another limitation is the rapid emergence of phage-resistant mutants (6,11,18,32).…”

“…The use of broad-hostrange phages isolated by multiple-host enrichment methods (7,11,29) or a phage cocktail composed of multiple phage types (33,44,55) has shown promise in overcoming this problem. Another limitation is the rapid emergence of phage-resistant mutants (6,11,18,32). A phage cocktail can control or delay the emergence of resistant mutants (27,33); however, some of the underlying mechanisms for the appearance of phage-resistant mutants are not fully elucidated.…”

Efficacy of Bacteriophage Therapy in Experimental Sepsis and Meningitis Caused by a Clone O25b:H4-ST131 Escherichia coli Strain Producing CTX-M-15

“…Phage were precipitated from culture supernatant with 10% polyethylene glycol (6000) and 1 M sodium chloride and concentrated by centrifugation at 9,000 ϫ g for 2 h at 4°C and resuspension in phage buffer (10 mM MgSO, 10 mM Tris [pH 7.6], and 1 mM EDTA) (10,41). Phage DNA was isolated by phenol extraction, followed by ethanol precipitation.…”

Infectivity Criteria for use of ɸSEP2 and ɸSEP3 as Bio-control Agents

“…Morphology of ɸSEP3 was similar to the phage FGCSSa1 [18] which had a mean head diameter of 107nm and tail length of 123 nm. The morphology of ɸSEP2 revealed greater than reported average head diameter (62.5nm) of phages belonging to family Podoviridae [19].…”