Cluster Analysis

Cluster analysis is an unsupervised statistical technique that examines the interpoint distances between all the samples and represents that information in the form of a 2D plot, known as a dendrogram (32). Such dendrograms present the data from high-dimensional row spaces in a form that facilitates the use of human pattern recognition abilities. To generate the dendrogram, cluster analysis methods form clusters of samples based on their nearness in row space. A common approach is to treat every sample initially as a cluster and to join the closest clusters. This process is repeated until only one cluster remains.

Fig. 1. FTIR spectra in the region of 1000-1050 cm-1 of (A) noninfected Vero cells and cells infected with 1 MOI of HSV-1 and (B) noninfected NIH/3T3 cells and cells infected with 1 FFU/cell of MuSV. Results are means of five different and separate experiments for each cell culture. The SD for these means was <0.001. FFU, focus-forming unit; HSV, herpes simplex virus; MuSV, murine sarcoma virus; AU, asymmetric unit.

Fig. 1. FTIR spectra in the region of 1000-1050 cm-1 of (A) noninfected Vero cells and cells infected with 1 MOI of HSV-1 and (B) noninfected NIH/3T3 cells and cells infected with 1 FFU/cell of MuSV. Results are means of five different and separate experiments for each cell culture. The SD for these means was <0.001. FFU, focus-forming unit; HSV, herpes simplex virus; MuSV, murine sarcoma virus; AU, asymmetric unit.

Fig. 2. FTIR spectra in the region of 1200-1400 cm-1 of (A) noninfected Vero cells and cells infected with 1 MOI of HSV-1 and (B) noninfected NIH/3T3 cells and cells infected with 1 FFU/cell of MuSV. Results are means of five different and separate experiments for each cell culture. The SD for these means was <0.001. FFU, focus-forming unit; HSV, herpes simplex virus; MuSV, murine sarcoma virus; AU, asymmetric unit.

Fig. 2. FTIR spectra in the region of 1200-1400 cm-1 of (A) noninfected Vero cells and cells infected with 1 MOI of HSV-1 and (B) noninfected NIH/3T3 cells and cells infected with 1 FFU/cell of MuSV. Results are means of five different and separate experiments for each cell culture. The SD for these means was <0.001. FFU, focus-forming unit; HSV, herpes simplex virus; MuSV, murine sarcoma virus; AU, asymmetric unit.

4. Notes

1. Treatment of the cells with trypsin should be performed carefully and for a short time (about 1 min) so as to avoid destroying the cells.

2. The 1-|L drop of sample (cells) should be placed on the zinc sellenide crystal as a concentrated drop.

3. Be careful not to choose for scanning possible contaminants, such as salt, rather than cells.

4. When choosing by microscope the region of the cells to be scanned, it is important to choose a region with confluent cells to obtain a better signal-to-noise ratio.

5. Set the condenser position of the FTIR microscope according to the thickness of the ZnSe crystals for obtaining maximum signal.

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