Volume 17, Issue 5 (September 1989)
Comparison of Six Media for Klebsiella spp. Enumeration by Membrane Filtration
Six media (mK2, mK4, mK5, mKleb, mFCIC, and mCIK) were assessed for their ability to recover Klebsiella spp. from nonpolluted and polluted waters. Ninety-six percent of presumptive target colonies recovered on mK2 were identified as Klebsiella spp., while approximately 93% of the presumptive target colonies on mFCIC, mKleb, mK4, and mK5 were identified as Klebsiella spp. Target colony identification on mCIK was difficult; therefore this medium was not considered for further testing.
Performance characteristics were determined on mFCIC, mK2, and mK4 media in accordance with ASTM specifications. The false positive error for mK4 was 0.058, whereas the other media had values approximating 0.015. The mFCIC and mK5 media had an undetected target error of 0; the undetected target error for mKleb, mK2, and mK4 was less than 0.06. The index of selectivity for mKleb was 0.53, while the other media had an index of selectivity of approximately 0.64. Due to the low index of selectivity of mKleb, and the lower presumptive target colony recovery on mK5, these media were not considered for further evaluation.
Accuracy values using unstressed Klebsiella cultures, for mFCIC, mK2, and mK4, averaged 114% compared to the reference mK medium base. Following the application of stress to the cultures for 24 h, the accuracy value calculated for mFCIC was 81.9% in comparison with values of 118.8% and 111.0% for mK2 and mK4, respectively. The upper counting limits for mK2, mFCIC, and mK4 were 115, 127, and 127 colonies per filter, respectively.
Even though the performance characteristics of mK2, mK4 and mFCIC were similar, the medium judged most suitable for Klebsiella recovery was mK4. This was primarily due to the ease of identification of target colonies and the relatively low background colony interference.