title: Influence of the growth phase and culture medium on the survival of Mannheimia haemolytica during storage at different temperatures.
abstract: OBJECTIVE
  To quantify the influence of the growth phase, storage temperature and nutritional quality of the plate count medium on the apparent viability of Mannheimia haemolytica during storage at different temperatures.
  
  
  RESULTS
  Mannheimia haemolytica was grown in shake flasks and in aerobic continuous culture to investigate factors affecting cell viability during storage, which was determined using plate counts on different media and epifluorescence microscopy. The high specific death rates of cells harvested after cessation of exponential growth and stored at 22, 4, -18 and -75 degrees C could be related to the rapid onset of exponential death in batch cultures. Yeast extract supplementation of the culture medium increased the viability of cells at most of the above-mentioned storage temperatures. Of the total cell count in continuous culture, only 48% could be recovered on brain-heart infusion agar, whereas supplementation of the agar medium with foetal calf serum increased the plate count to 71% of the total count.
  
  
  CONCLUSIONS
  Mannheimia haemolytica cells harvested from the exponential growth phase had the highest survival rate during storage at low temperatures. Plate count values also depended on the nutritional quality of the agar medium.
  
  
  CONCLUSIONS
  Results presented here impact on the procedures for culture preservation and plate count enumeration of this fastidious animal pathogen.
authors.affiliation: Department of Microbial, Biochemical and Food Biotechnology, University of the Free State, Bloemfontein, South Africa.
authors.forename: E
authors.initials: E
authors.lastname: van Rensburg
authors.forename: J C
authors.initials: JC
authors.lastname: du Preez
authors.forename: S G
authors.initials: SG
authors.lastname: Kilian
mesh_terms: D001431:Bacteriological Techniques / Q000379:methods; D019149:Bioreactors; D015169:Colony Count, Microbial; D003470:Culture Media; D016978:Mannheimia haemolytica / Q000254:growth & development*; D008856:Microscopy, Fluorescence; D013696:Temperature
chemical_list: D003470:Culture Media