I read with interest the publication from the Pall Corporation in the
July-August, 1999 PDA Journal.
I have the following questions/comments that reflect my observations and not
that of my company:
1) Why was the Ralstonia pickettii isolate selected for the study?
Is it typical of isolates from purified water and WFI systems? Have the
authors looked at a range of isolates? Would we expect them to behave the same?
2) Since we were not given the name of the product used in the study, we are
incapable of confirming the results reported. A scientific publication
should contain all the information necessary for an independent verification.
3) If the inocula used in the study were targeted at 10^6 cfu/ml, why was
only 10^2 recovered from the R. pickettii inoculated product at zerotime
(Table II)? I believe there are discrepancies between the numbers reported
in the text and tables II and VI. Which counts are correct?
4) It is claimed that clogging of the filters occurred with R. pickettii in
SLB with accumulative challenge levels of 10^8 to 10^9 cfu/sq.cm while
accumulative challenge levels of 10^9 with B. diminuta in drug product and
10^8 cfu/sq cm with R. pickettii in drug product did not cause clogging. Why
the difference? Information of the pressure across the filters in each
study would be helpful. Also, why was B. diminuta in SLB not run as a control?
5) The product can effect the challenge level, the physiological condition
of the inocula and perhaps the size of the challenge organisms and the
retention capacity of the filer. The effect of the unidentified product on
the filter needs to be addressed. Do the authors have bubble point or
pressure hold data on the product-filter performance? Is the product
affecting the porosity or surface characteristics of the filter material?
6) Why were not an equivalent set of photomicrographs published for B.
diminuta as for R. pickettii? What were the size of the B. diminuta
challenges? Were they in the normal range for the organism cultivated in
SLB which is usually smaller than reported for the R. pickettii?
7) The major changes in the R. pickettii size distibtion was the reduction
in length and a slight increase in width. Figures 2A and 2B and Figure 3A
shows actively dividing cells with cross walls formation while Figures 3B
and 3C show mainly undividing cells. You could account for the difference
in size to the active cell division in the inocula not a reduction in size
due to extended contact with the product.
8) The major unanwered question is why were R. pickettii cells with larger
dimensions that standard B. diminuta challenge organisms not retained by 0.2
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