Abstract
Aeromonads are still regarded as unusual enteric pathogens. Even though their pathogenic role has not been established (Hanninen et al., 1995), unambiguous convincing evidence suggests that some aeromonads do cause gastroenteritis (Gluskin et al., 1992; Albert et al., 1999). Watery diarrhoea might be accompanied by symptoms such as abdominal pain, fever, and nausea or vomiting; blood in faeces can also appear in serious cases. Aeromonads cause nonresolvable, intermittent diarrhoea that can persist for several months or even years after the initial infection (Janda & Abbott, 1998). Isolation of aeromonads from human faeces samples is difficult and its success depends on the culture method performed. A valid judgement as to how many aeromonads are involved in diarrhoeal disease is only possible when an appropriate selective medium is used.
Aeromonads, Gram-negative facultatively anaerobic oxidase-positive glucose-fermenting rods, are ubiquitous waterborne organisms occurring in both fresh and saline waters and in soil. Aeromonads generally grow on various agars used for screening of enteric pathogens. For their isolation from human faeces, two media have been recommended: cefsulodin-Irgasan-novobiocin agar (CIN), primarily a selective medium for Yersinia enterocolitica, and ampicillin-blood agar (ABA) (Abbott, 2003). ABA has been recommended as a selective medium owing to the beta-haemolytic activity of the majority of clinically relevant Aeromonas species. Because of an increasing ampicillin resistance in other members of the Enterobacteriaceae, it is becoming difficult to screen with oxidase each beta-haemolytic colony that appears. Therefore we decided that ABA is not a suitable medium for the routine laboratory. The next selective medium described for the isolation of Aeromonas spp. is Aeromonas agar (AA; LAB M). AA contains the selective agents brilliant green and Irgasan, which also enable growth of aeromonads susceptible to ampicillin ().
In a 2-year survey from 2003 to 2005, we compared the value of CIN and AA in the isolation of aeromonads. During the first year, routine faeces samples from acute gastroenteritis cases were processed on the following enteric differential media: deoxycholate-citrate agar (DC), MacConkey agar (MC) and CIN. In the second year, the samples were also cultured on AA (Table 1). All media were incubated aerobically at 37 °C for 1824 h. Colonies that were typical for aeromonads and that grew on one of the agars mentioned above were cultured on nonselective medium (such as blood agar) and examined for oxidase (OXI-strip; Pliva-Lachema Diagnostika). Isolates were identified as Aeromonas spp. by biochemical kit ENTEROtest 24 (kit for identification of Gram-negative fermentative rods; Pliva-Lachema Diagnostika); this was confirmed by fatty acid methyl ester analysis using the Microbial Identification System Sherlock (MIDI) (Huys et al., 1994; echová et al., 2004).