title: Comparing effects of freezing at -196 °C and -20 °C on the viability of mastitis pathogens.
abstract: The aim of this study was to compare the effects of cryopreservation at approximately -196 °C  in liquid nitrogen (N) and freezing at approximately -20 °C in a freezer, on the viability and  survival of eight different mastitogenic bacteria inoculated in milk. Bacteria were frozen  at approximately  -20 °C in a freezer and cryopreserved at approximately  -196 °C in liquid  nitrogen. An effective preservation method was needed for follow-up samples from cows  identified in the South African National Milk Recording Scheme (NMRS) with somatic cell  counts above 250 000 cells/mL milk. The organisation responsible for sample collection of the  NMRS milk samples also provides producers with liquid nitrogen for their semen flasks at the  collection sites. This existing mode of storage and transport could therefore be utilised.Ten samples of each organism were thawed and cultured bi-weekly until week 18 for both  temperature treatments. An additional sampling was performed at week 30 for samples frozen  at approximately -20 °C. Freezing and cryopreservation did not impair subsequent isolation  of  Streptococcus dysgalactiae, Streptococcus uberis,  Enterococcus faecalis, Staphylococcus aureus (STH) (phage type lytic group III) or Sta. aureus (STA) (phage typed, other than lytic group III). Survival was indicated by the isolation of bacteria from samples, and viability by the strength of growth of the bacteria isolated. The survival of Streptococcus agalactiae decreased after week 12 and Escherichia coli after week 16 of freezing, but both organisms survived under cryogenic preservation until week 18. Coagulase-negative staphylococci survived until week 18 for both freezing and cryogenic preservation.Both storage methods could thus contribute to the improvement of a pro-active approach  towards udder health management in South African dairy herds.
authors: Department of Production Animal Studies, University of Pretoria, Onderstepoort. inge-marie.petzer@up.ac.za.
authors: Inge-Marie
authors: IM
authors: Petzer
authors: Joanne
authors: J
authors: Karzis
authors: Theodorus J
authors: TJ
authors: Van der Schans
authors: Johanna C
authors: JC
authors: Watermeyer
authors: Norman
authors: N
authors: Mitchell-Innes
authors: Stephanie
authors: S
authors: Eloff
authors: Geoffrey T
authors: GT
authors: Fosgate
mesh_terms: D000818:Animals; D002417:Cattle; D015169:Colony Count, Microbial / Q000379:methods / Q000662:veterinary; D015925:Cryopreservation / Q000379:methods / Q000662:veterinary*; D003470:Culture Media; D003612:Dairying; D016983:Enterococcus / Q000254:growth & development; D005260:Female; D005615:Freezing; D008414:Mastitis, Bovine / Q000382:microbiology*; D050296:Microbial Viability; D008892:Milk / Q000382:microbiology*; D013048:Specimen Handling; D013210:Staphylococcus / Q000254:growth & development; D013291:Streptococcus / Q000254:growth & development; D013997:Time Factors
chemical_list: D003470:Culture Media