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Appl. Environ. Microbiol., Jun 1996, 1885-1888, Vol 62, No. 6
JL Alonso, I Amoros and MA Alonso
Cefsulodin was evaluated as a potential selective agent for aeromonads.
Resistance of Aeromonas and coliform isolates was determined by using a
standard disk diffusion technique. A total of 119 Aeromonas and 78 coliform
strains were isolated. For 102 of 130 [corrected] Aeromonas isolates
(environmental and reference strains), the MIC of cefsulodin was < 8
micrograms/ml. Results of MIC tests by the agar dilution method showed that
a concentration of cefsulodin of 10 micrograms/ml or less inhibited the
growth of 96% of isolates. In comparison, for 81 of 94 coliform isolates
(environmental and reference strains), the MIC of cefsulodin was > 32
micrograms/ml. Because cefsulodin suppresses growth of Aeromonas and other
oxidase-positive organisms, total coliform (TC) and Escherichia coli counts
on Chromocult Coliform agar (CC agar) without cefsulodin and on CC agar
with 10 mg of cefsulodin per liter (CC-CFS) were compared. Variance
analysis of data from 14 sewage- polluted irrigation water specimens did
not demonstrate any statistically significant difference in the enumeration
of E. coli with CC and CC-CFS media. On average, the CC agar recovered 2.46
times as many TCs as CC-CFS. However, Aeromonas colonies made up an average
of 58.6% of the TC counts on CC agar. Because no Aeromonas spp. were
recovered on CC-CFS, background interference was eliminated and the counts
that were obtained reflected more accurately the number of TCs. Results of
this study suggest that cefsulodin may be a useful selective agent against
Aeromonas spp. which should be included in coliform chromogenic media when
high levels of accompanying flora are expected.
Copyright © 1996, American Society for Microbiology
Differential susceptibility of aeromonads and coliforms to cefsulodin [published erratum appears in Appl Environ Microbiol 1996 Oct;62(10):3914]
Instituto de Hidrologia y Medio Natural, Universidad Politecnica, Valencia, Spain. jalonso@ihdr.upv.es
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