CHAPTER IX 



HOST SPECIFICITY 



Because the bacteriophages are obUgate intracellular parasites 

 of bacteria, the properties of the host cell must be of major inter- 

 est to the virologist. Of particular concern are those properties 

 which permit a bacterium to serve as a host for phage multiplica- 

 tion or which render it immune to phage attack. As is true of 

 plant and animal viruses, phage strains vary in their host 

 specificity. This specificity was obvious to early phage workers 

 and led to the practical classification of these viruses into such 

 categories as coliphages, staphylophages, streptococcal phages, 

 and cholera phages. Although the utility of such a classification 

 is evident, it has no phylogenetic significance, any more than 

 has a classification of mammalian viruses based on tissue tropisms 

 or host pathology. The role of host specificity in the classification 

 of phages will be discussed in Chapter XXII on phage taxonomy. 



1. Microbial Hosts for Phages 



It would be a difficult task to list all the bacterial hosts for 

 phages that have been recorded in the literature. Such a list 

 would include bacterial strains belonging to the following genera : 

 Pseudomonas, Xanthomonas, Vibrio, Rhizobium, Chromobaclerium, 

 Micrococcus, Gaffkya, Neisseria, Streptococcus, Lactobacillus, Coryne- 

 bacterium, all genera of Enter obacteriaceae, Pasteurella, Brucella, 

 Bacillus, Clostridium, Mycobacterium, Streptomyces, Nocardia, and 

 probably others. There are some bacteria such as the pneumo- 

 cocci and the spirochaetes for which phages have never been 

 found. More highly organized microbial forms such as yeasts, 

 molds, algae, and protoza also seem to be free of phages, unless 

 the kappa substance of paramecia (see Sonneborn, 1955) might 

 be considered a relative of the viruses. 



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