The article on "Factors affecting plaque formation by bacteriophages" has been updated and can be accessed at 

https://www.dairyscience.info/index.php/enumeration-of-lactococcal-bacteriophages/factors-affecting-plaque-formation.html .

  Plaques of phage D29 produced by Mycobacterium avium spp paratuberculosis assayed using  Mycobacterium smegmatis. Image courtesy of Dr Irene Grant, Queens University  Belfast.