Phage isolated to kill E.coli O157 on beef

Researchers isolated and characterised phage FAHEc1, which infects E. coli O157, and its ability to kill its host in vitro​ and on beef.

Sequencing the genome is still needed to provide information regarding safe use but FAHEc1 has attributes suggesting that it may be useful for the pathogens control on beef, said Hudson et al.

Isolated phage​

The isolated phage recorded a greater than 4 log₁₀​ reduction in broth at 5°C when host cells were incubated with it.

It belonged to the family Myoviridae and lysed 28 of 30 E. coli O157 isolates, only one other non-O157 E. coli serotype (O162:H7), and none of the other 13 bacterial species tested.

The results demonstrate that phages are useful for the control of foodborne pathogens, reflected by the introduction of commercial phage products for use in food, said the researchers.

Testing was performed by titration or spot assay. In titration, plaque counts on potential hosts were compared to those obtained on a reference isolate.

Any isolate supporting a count of 1% or more of the reference strain was considered to be susceptible.

The spot assay used three dilutions of a phage suspension equivalent to 10²​, 10⁴​ and 10⁶​ PFU applied to a lawn of the host organism.

Temperature tests​

Initial experiments on meat at 37 °C and high phage concentration showed that E. coli O157:H7 was not recoverable from most inoculated meat samples.

37 °C is not typical of meat storage and distribution but was used to represent the initial phase of carcass cooling, during which such temperatures exist, said the researchers.

Under conditions simulating conventional carcass chilling, the inactivation of E. coli O157:H7 was dose-dependent.

“Overall, we believe that inactivation of bacteria by phages on raw meat is unlikely to be occur by phage replication in situ​ and more likely to result from cells becoming infected by phages and lysing on resumption of growth​,” said the researchers.

“This explains inactivation occurring at temperatures beneath the minimum growth temperature of the host.”​

Source: Food Microbiology, volume 36, issue 1, October 2013, pages 14-21

Online ahead of print doi: 10.1016/j.fm.2013.03.006​

“Use of a bacteriophage to inactivate Escherichia coli O157:H7 on beef”

Authors: J.A. Hudson, C. Billington, A.J. Cornelius, T. Wilson, S.L.W. On, A. Premaratne, N.J. King