Code: SR0129

Materials Supplied
Penase SR0129 is a Bacillus cereus 569/H9 lactamase (E.C.5.2.6) presented as a freeze-dried powder containing buffer salts. Each vial contains 3,300 IU of activity (1 unit of enzyme activity will hydrolyse 1.0 µ mol of benzylpenicillin to benzylpenicilloic acid per minute pH 7.0 and at 25°C). The preparation will successfully inactivate a range of penicillins ¹.

Definition of Units of Enzyme Activity
The scientific literature describes a number of methods which are used to measure and define a unit of penicillinase activity². Note that 1 IU of activity = 600 Levy units of activity.

Application
The major use of this enzyme preparation is for the inactivation of susceptible beta-lactam antibiotic preparations to enable sterility testing to be carried out ³.
The preparation may also be used for inactivation of susceptible antibiotics in blood or other tissue samples prior to routine microbiological examination ^2,4,5, and inactivation of susceptible antibiotics in blood and other tissue samples prior to the microbiological estimation of aminoglycosides or other non beta-lactam antibiotics ⁶.

Methods
1 Sterility Testing of Penicillin Products³
The product is rehydrated by adding 5 ml of sterile distilled water to a vial of enzyme with gentle mixing. The resulting solution will contain 660 IU of activity/ml.
The sterility of penicillin products with respect to bacterial contamination is determined by adding 300 mg or less of the test sample to sterile Fluid Thioglycollate Medium CM0173 or other prescribed media to which a suitable amount of Penase solution has been added aseptically when the temperature has fallen below 50°C. Tubes (35 mm x 200 mm) containing 90-100 ml medium are incubated for 7 days at 30°C.
The sterility of penicillin products with respect to yeast and moulds is accomplished by adding the test sample to Sabouraud Liquid Medium CM0147 and incubating for 7 days at 20-25°C.

2 Blood Culture Procedures
0.1 ml of the reconstituted solution should be added aseptically to blood culture broths, preferably before but otherwise immediately after inoculation with the blood sample.

Stability of Reagents
Solutions of the enzyme will remain active for several days when stored at 4°C or several weeks when stored at minus 20°C. Repeated freezing and thawing should be avoided. However, it is not advisable to store the solution for long periods because of the possibility of contamination.

References
1. Melling J. (1979) `Antibiotic-Inactivating Enzymes’ Ed. Wiseman A., `Topics in Enzyme and Fementation Technology’, Vol.2. 153--199. Publishers Ellis Horwood Ltd., Chichester.
2. Newson S. W. B. and Walshingham B. M. (1973) J. Med. Microbiol. 6. 59--66.
3. Code of Federal Regulations, Title 21, Part 436, Sec. 436.20. U.S. Govt. Printing Office, Washington, DC.
4. Waterworth P. M. (1973) J. Clin. Path. 26. 596-598.
5. Selwyn S. (1977) J. Antimicrob. Chemother. 3. 161-168.
6. Sabath L. D., Casey J. I., Ruch P. A., Stumpf L. L. and Finland M. (1971) J. Lab. Clin. Med. 78. 457-463.