Microcins E. coli - There has been far less work on the frequency of microcin production in E. coli or other Gram-negative bacteria. All the microcins characterised to date are secreted from the cell, rather than being released as a consequence of cell lysis (Braun et al. 2002). It has also been suggested that as much as 90% of the microcin produced by a cell may be retained within the cell (Braun et al. 2002). Consequently, there is no reliable and simple phenotypic method for assaying microcin production.
The E. coli isolated from Australian humans and mammals were screened for seven microcins, using a PCR-based approach. Of the human isolates screened, 32% were microcin producers whereas, among the isolates from mammals, 9% were microcin producers. Why microcin production is less common in E. coli isolated from mammals compared to humans is unknown. In the isolates from humans, microcin production is significantly more prevalent among genetic group B2 strains (47%) than among A (16%), B1 (18%) or D strains (9%). The frequency of microcin production in both of these E. coli collections has almost certainly been underestimated, as a PCRscreening approach can be used only for those microcins which have been genetically characterised.
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