S. aureus isolates derived from 92 milk samples collected from 13 cows with chronic udder infections were monitored based on metabolic fingerprinting by Fourier-transform infrared (FTIR) spectroscopy. In combination with cluster analysis the S. aureus isolates were compared at herd and individual level to obtain information on their persistence and possible spreading within the herd. In addition, nuc gene PCR (specific for S. aureus) was performed by at least two isolates per cow to confirm the identification by FTIR spectroscopy.
An udder infection was considered to be chronically if S. aureus was detected at least three times within a period of three months.
Each isolate was measured in duplicate in at least two independent measurements. The spectral range of 800 - 1200 cm-1, the so called polysaccharide region, was selected for cluster analysis. Isolates of a cluster with heterogeneity of less than 3 were considered to have the same biotype.
Using FTIR analysis we found for herd A and C that during the sample period both herds were predominated by one biotype which could persist within the herd. Different biotypes were found in herd B and D. In herd B, we can suppose that some of the isolates could successively spread within the herd between the cows 4, 5, 7, 8 and 9. In cow 6, one biotype could persist over the entire period. In herd D, one specific biotype was found in each cow. However, for cow 13 we observed a change of the biotype in the same udder during a three month period. Subsequent molecular typing will further clarify either a new infection occurred or this isolates derived from the same clone undergoing changes in virulence factor expression due to adaptation to the tissue (LEE & LEE, 2006) and selection on NT types (TUCHSCHERR et al., 2007).
FTIR spectroscopy turned out to be a fast and reliable tool for epidemiological typing of S. aureus bovine mastitis isolates at herd and individual level. Complementary to genetic data it might also be useful to monitor S. aureus phenotypic changes due to host adaptation processes.