Biocontrol of Escherichia coli O157 with O157-specific bacteriophages - PubMed (original) (raw)

Biocontrol of Escherichia coli O157 with O157-specific bacteriophages

I T Kudva et al. Appl Environ Microbiol. 1999 Sep.

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Abstract

Escherichia coli O157 antigen-specific bacteriophages were isolated and tested to determine their ability to lyse laboratory cultures of Escherichia coli O157:H7. A total of 53 bovine or ovine fecal samples were enriched for phage, and 5 of these samples were found to contain lytic phages that grow on E. coli O157:H7. Three bacteriophages, designated KH1, KH4, and KH5, were evaluated. At 37 or 4 degrees C, a mixture of these three O157-specific phages lysed all of the E. coli O157 cultures tested and none of the non-O157 E. coli or non-E. coli cultures tested. These results required culture aeration and a high multiplicity of infection. Without aeration, complete lysis of the bacterial cells occurred only after 5 days of incubation and only at 4 degrees C. Phage infection and plaque formation were influenced by the nature of the host cell O157 lipopolysaccharide (LPS). Strains that did not express the O157 antigen or expressed a truncated LPS were not susceptible to plaque formation or lysis by phage. In addition, strains that expressed abundant mid-range-molecular-weight LPS did not support plaque formation but were lysed in liquid culture. Virulent O157 antigen-specific phages could play a role in biocontrol of E. coli O157:H7 in animals and fresh foods without compromising the viability of other normal flora or food quality.

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Figures

FIG. 1

FIG. 1

Immunoblot analysis of LPS produced by strains resistant and susceptible to plaque formation by phage. High- and low-molecular-weight immunoreactive LPS, but not intermediate-molecular-weight immunoreactive LPS, were observed in the strains susceptible to plaque formation. Lanes 1 and 4, E. coli O157:H7 strain ATCC 43894; lane 2, E. coli O157:H7 strain 86-24 Nalr. Abundant immunoreactive LPS at all molecular weights were observed in strains resistant to plaque formation. Lane 3 contained representative strain _E. coli_O157:H16 FDA 13A80. The positions of molecular size standards are indicated on the left.

FIG. 2

FIG. 2

Comparison of the lytic efficiencies of phages. Cultures were incubated at 37°C without aeration (A) or with aeration (B).E. coli O157:H7 (3 × 104 CFU) was treated with KH1 (■ and □), KH4 (formula image and formula image), or KH5 (⧫ and ◊). The MOI was 103 PFU/CFU. The control contained only E. coli O157:H7 (● and ○). The standard errors of the E. coli O157:H7 concentrations ranged from 0.03 to 0.5 log10 CFU/ml (n = 4).

FIG. 3

FIG. 3

E. coli O157:H7 lysis by a mixture of phages. Cultures were incubated at 37°C (A) or 4°C (B). _E. coli_O157:H7 (3 × 104 CFU) was infected with a mixed phage suspension (107 PFU) containing equal concentrations of KH1, KH4, and KH5. Cultures were incubated with (▵) or without (▴) aeration. The controls contained only E. coli O157:H7 and were either aerated (○) or not aerated (●). The standard errors of the E. coli O157:H7 concentrations ranged from 0 to 0.5 log10 CFU/ml (n = 4).

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