Differential susceptibility of aeromonads and coliforms to cefsulodin.
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.
Alonso
J L
JL
Instituto de Hidrología y Medio Natural, Universidad Politécnica, Valencia, Spain. jalonso@ihdr.upv.es
Amoros
I
I
Alonso
M A
MA
D000333:Aeromonas / Q000187:drug effects* / Q000302:isolation & purification; D002441:Cefsulodin / Q000494:pharmacology*; D002511:Cephalosporins / Q000494:pharmacology*; D015169:Colony Count, Microbial; D003470:Culture Media; D004352:Drug Resistance, Microbial; D004755:Enterobacteriaceae / Q000187:drug effects* / Q000302:isolation & purification; D004926:Escherichia coli / Q000187:drug effects / Q000302:isolation & purification; D008826:Microbial Sensitivity Tests; D012722:Sewage / Q000382:microbiology; D014871:Water Microbiology
D002511:Cephalosporins; D003470:Culture Media; D012722:Sewage; D002441:Cefsulodin