Decreasing Enterobacter sakazakii (Cronobacter spp.) food contamination level with bacteriophages: prospects and problems.
Bottom Line: A high dose of 10(8) pfu ml(-1) of phage could effectively sterilize a broth contaminated with both high and low pathogen counts (10(6) and 10(2) cfu ml(-1)).Only when crossing this threshold, phage replication started, but it could not reduce the contamination level below 100 cfu ml(-1).Addition of trehalose or milk formula stabilized the phage preparation, which then showed excellent storage stability even at elevated temperature.
Affiliation: Nestlé Research Center, Nestec Ltd, Lausanne, Switzerland.Show MeSH
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Mentions: Two of the phages, namely phages 81 and 82, both sewage isolates from Switzerland, showed in negative stain electron microscopy the morphology of typical T4‐like Myoviridae, the prototype of the obligate virulent (‘lytic’) phages. These phages are characterized by elongated heads, collars, contractile tails and typical baseplates with tail spikes (Fig. 2C and D). Tail fibres were not observed, but might have been lost during the preparation of the phages for electron microscopy. Genome analysis supported the morphological diagnosis of T4‐like phages: in pulsed‐field gel electrophoresis the DNA from phages 81 and 82 showed a molecular size slightly below 200 kbp, the typical genome size range for T4‐like phages (Fig. 3A). A PCR test based on the T4 gene g32, which is diagnostic for close relatives of E. coli phage T4 was negative for them (data not shown) (Monod et al., 1997). However, a PCR test based on the better conserved T4 gene g23, encoding the major head protein (Tétart et al., 2001), yielded a clear amplification product for phages 81 and 82, which co‐migrated with the amplification product of the T4 control (Fig. 3B). The PCR result was confirmed by Southern hybridization: a labelled T4 probe cross‐hybridized at moderate intensity with phage 81 and 82 DNA (Fig. 4B), characterizing them as relatives of E. coli phage T4.
Affiliation: Nestlé Research Center, Nestec Ltd, Lausanne, Switzerland.