Eur. J. Nucl. Med. 2, 105-107 (1977) European N u c l e a r Journal of

Medicine © by Springer-Verlag 1977

Microbial Contamination of Radionuclide Generators

K. Sorensen, K. Kristensen, and P. Frandsen The Danish National Health Service, Isotope-Pharmacy and Pharmaceutical Laboratories, Bronshoj, Denmark

Abstract. Technetium-99m generators were grossly contaminated using 5 different strains of microorgan- isms. Elution of the generators showed that the number of microorganisms was reduced by a factor of 104-106 . There were no indications that the genera- tors would support bacterial growth. It is concluded that it would be acceptable from a microbiologic point of view to omit autoclaving and membrane fil- tration of the final product provided that proper asep- tic techniques are applied.

Material and Methods

The generators used were first used for their normal purpose and then kept the time necessary for a sufficient decay of radioactivity. Before contamination with different strains of microorganisms the generators were disassembled and the aluminium oxide columns sterilized by autoclaving. The contaminated columns were eluted with portions of 10 ml of sterile 0.9% w/v NaC1 solution.

The number of microorganisms per ml of the contamination suspensions after passing the columns and of the eluates were determined after incubation of suitable dilutions on solid agar substrate.

Introduction

Aseptic preparation of natrii pertechnetatis (99mTc)

injectio from technetium-99m generators is a routine procedure at very many hospitals. The preparation is well suited for autoclaving or membrane filtration but radiation protection problems or lack of time may tend to prevent such measures being taken. It is therefore of great interest to investigate the possibil- ities of bacterial growth in such generator systems. No systematic work was found. Hamilton (1972) dis- cusses the probability of bacterial contamination in generator eluates by measuring the environment of the generator system for bacterial contamination and finds it very low. Investigation by the Isotope-Phar- macy (Sorensen and Kristensen, unpublished), where sterility-tests were done on 60 samples taken from 19 hospital departments in three consecutive weeks on the last day of the use of technetium-99m genera- tors, gave negative results in all tests. In the present study the bacterial counts of the eluates from mas- sively contaminated technetium-99m generators were measured.

For offprints contact." K. Sorensen, The Danish National Health Service, Frederikssundsvej 378, DK-2700 Bronshoj, Denmark

Experiments 1 and 2

Technetium-99m generators from The Radiochemical Centre, Amersham were contaminated with a suspension of one of the below-mentioned microorganisms in sterile 0.9% w/v NaC1 solu- tion (10 ml per generator). The following strains of microorganisms were used: Rhodotorula rubra, Staphylococcus epidermis, Bacillus subtilis, Escherichia coli, and Clostridium sporogenes. The number of microorganisms in the different contamination suspensions ap- pears in Tables 1 and 2. In Experiment 1 the generators were eluted immediately 9 consecutive times. In Experiment 2 the genera- tors were eluted after 1 and 2 weeks of standing at room tempera- ture.

Experiment 3

Technetium-99m generators from 8 different manufacturers were contaminated with E. coli suspended in sterile 0.9% w/v NaC1 solution (10 ml per generator). The suspension contained 1.7 +0.2 x 107 microorganisms per ml. The generators were eluted immediately 3 times and again after 2 weeks of standing at room temperature.

Results and Discussion

After passing the generators the number of microor- ganisms of the contamination suspensions is reduced by a factor 104-106 (Tables 1, 2, and 3). In this respect there is no significant difference between the different

106 K. Sorensen et al. : Microbial Contamination of Radionuclide Generators

Table 1. The number of microorganisms per ml eluted from contaminated technetium-99m generators" by nine consecutive elutions (Experiment 1)

Micro- organisms

Contamination suspension

Before After passing passing generator generator

Eluate number

1 2 3 4 5 6 7 8 9

B. subtilis E. col± CI. sporogenes St. epidermis R. rubra

1.2-+0.3x10 s t . l ± 0 . 2 x 1 0 6 1.3±0.4x105 1.5-+0.4x107 2.0±0.5x106

< 2 x 1 0 ° < 2 x 1 0 ° < 2 x 1 0 ° < 2 x 1 0 ° < 2 x 1 0 ° < 2 x 1 0 ° < 2 x 1 0 ° < 2 x 1 0 ° < 2 x 1 0 ° < 2 x 1 0 ° 2x101 2x101 4x101 l x l 0 1 l x l 0 1 6x101

l x l 0 2 2×102 2x102 l x l 0 z 2x101 2x101 l x l 0 1 2x101 < 2 x 1 0 ° < 2 x 1 0 ° < 2 x 1 0 ° < 2 x 1 0 ° < 2 x 1 0 ° < 2 x 1 0 ° < 2 x 1 0 ° < 2 x 1 0 °

l x l 0 2 6x102 3x102 6x101 6x10 t 7x101 7x101 2x101

<2×100 < 2 x 1 0 °

3 x 101 2 × 101 2 x 101 2 x 101

< 2 x 1 0 ° < 2 x 1 0 ° 2 x 101 2 x 101

a From the Radiochemical Centre, Amersham

Table 2. The number of microorganisms per ml eluted from contaminated technetium-99m generators a after various time of standing (Experiment 2)

Micro- Contamination suspension Eluates organisms

Before passing After passing After 1 week After 2 weeks generator generator of standing of standing

R. rubra 2.0_+0.5 × 106 1 x 102 4x 10 ° < 2 x 10 ° St. epidermis 1.5+0.4 x 107 < 2 x 10 ° < 2 x 10 ° < 2 x 10 ° B. subtilis 3.6_+0.6 x 107 1 x 101 3 x 101 - E. col± 1.7_+0.2 x 107 3 x 101 - 6 x 10 ° Cl. sporogenes 1.3+_0.5 x 10 s < 2 x 10 ° < 2 x 10 ° < 2 x 10 °

" From the Radiochemical Centre, Amersham

Table 3. The number of microorganisms per ml eluted from 8 different manufacturers of technetium-99m generators contaminated with E. col±. The generatOrS were e!uted immediately 3 times and after 2 weeks of standing (Experi- ment 3)

Contamination suspension: 10 ml containing ,1.'] ! 0.2 X 107 microorganisms per ml

Generator Contamination Eluates -: ~ • manufacture suspension

1 2 3 After passing generator

After 2 weeks of standing

RCC, Amersham 4 x 101 6 x 101 6 x 101 1 x 101 IFA, Kjeller, Norway 2 x 101 8 x 101 6x 101 2x 102 Hoechst 2 x 102 2 x 101 2 x 102 8 x 101 CIS, France 6 x 100 2 x 101 6 x 10 ° 3 x 101 Squibb 2 x 102 6 x 102 6 x 102 4 x 102 Philips-Duphar 8 x 100 2 x 101 1 x 101 3 x 101 Mallinckrodt 5 x 102 2 x 102 1 x 102 4 x 101 New England Nuclear 2 x 101 5 x 101 2 x 101 4 x 101

< 2 x 10 ° 4 x 102 4 x 102 1 x 103 1 x 103

< 2 x 10 ° 2 x 102

<2 x 10 °

strains of microorganisms used (Tables 1 and 2) nor between the different types of generators examined (Table 3). This great bacterial reducing effect is confirmed by the relatively low number of microor- ganisms found in the eluates from the nine consecu- tive elutions performed (Table 1) and by the three elu- tions performed immediately after contamination with E. col± (Table 3). Furthermore, after 1 and 2

weeks of standing the number of microorganisms eluted was not found to be significantly increased (Tables 2 and 3). Though the number of different strains of microorganisms and of generators used is limited the present experiments demonstrate that technetium-99m generators possess a great bacterial retentive effect. Furthermore, the generators are not shown to possess conditions for growth of microor-

K. Sorensen et al. : Microbial Contamination of Radionuclide Generators 107

ganisms. The present investigation therefore points to the conclusion that using sterile generators and elution fluids the risk of bacterial contamination of the aseptic prepared product is very low. This agrees with the negative results found by the Isotope-Phar- macy (Sorensen and Kristensen, unpublished) by ster- ility testing of samples from different hospitals' de- partments.

For reasons of radiation hygiene it would be ad- vantageous to omit autoclaving and membrane filtra- tion of the final product. According to the results obtained it would from a microbiologic point of view be acceptable to do so, but proper aseptic techniques

including placement of the generator in a clean envi- ronment must however be applied.

Acknowledgement. We are grateful to Gunilla Trolle and Grete Holte Olsen for technical assistance.

References

Hamilton, J.W.: Bacterial contamination of radionuclide genera- tors: Fact or fiction. Amer. J. reed. Technol. 38, 105-108 (1972)

Received January 17, 1977