The three major Aeromonas species pathogenic in humans are Aeromonas hydrophila, Aeromonas caviae and Aeromonas veronii. These bacteria are associated with enteric and non-enteric diseases in both immuno- compromised and immunocompetent patients (Janda

This report describes the isolation of Aeromonas veronii biovar sobria as the causative enteropathogen of diarrhoea in an oncological patient after failure of detection of other infectious agents. The case points out the severe and long course of the infection, the diagnostic dilemma, and the prompt recovery after antibiotic treatment. K e y w o r d s: Aeromonas veronii, diarrhoea, foodborne pathogens, gastroenteritis, infection * Corresponding author: S. Gröbner, Institute of Medical Microbiology and Hygiene, University of Tübingen, Elfriede-Aulhorn Str. 6, D-72076 Tübingen, Germany; phone: +49 7071 29 81528, Fax: +49 7071 29 5440; e-mail: [email protected] 278 Gröbner S. et al. 4 immediately after admission Aeromonas veronii biovar sobria was cultivated on sheep blood agar with high bacterial counts. The pathogen was identified by $-haemolysis, positive oxidase reaction, negative aesculin hydrolysis and VitekII identification system (bioMérieux, Nürtingen, Germany) and tested for antibiotic susceptibility by agar disk diffusion method following the Clinical and Laboratory Standards Institute (CLSI) guidelines. The isolate was susceptible to gentamicin, tobramycin, piperacillin, piperacillin/ tazobactam, cefuroxime, cefotaxime, cotrimoxazole, levofloxacin, ciprofloxacin and meropenem and resistant to ampicillin and ampicillin/sulbactam. Cultivation of 3 stool samples on selective agar for Salmonella and Shigella species, Campylobacter spp. and analysis of one stool sample for Clostridium difficile toxins yielded negative results. Moreover, the patient’s stool was negative for rotavirus and adenovirus tested by EIA and for norovirus tested by PCR. A blood culture taken at the day of admission was negative, cultivation of a sputum taken at sixth day after admission yielded pharyngeal flora. An empirical antibiotic treatment was started immediately after admission with piperacillin/tazobactam (3×4.0/0.5 g). Clinical and laboratory findings improved dramatically and the patient was discharged 10 days after admission (Fig. 1). Since Aeromonas species have been isolated from environmental and food samples (Pin et al., 1994), it is likely that the patient had ingested Aeromonas-contaminated food. For example, frozen fish and organic vegetables have been reported to be contaminated with Aeromonas veronii (Castro-Escarpulli et al., 2003; McMahon and Wilson, 2001). Infections with Aeromonas veronii have been described in immunocompetent adults (Roberts et al., Fig. 1. Summary of the patient’s laboratory data, antibiotic therapy and results of microbiological analyses. CRP = C-reactive protein, WBC = white blood cells. 279 Short communication 4 2006). Despite the severe underlaying disease, the present patient was not immunocompromised at the time of Aeromonas infection. We suppose that the early administration of antibiotics was critical for the good course of disease. However, the cause of pneumonia remains unclear, since blood culture of the patient was negative, no sputum sample was sent to our laboratory at admission, and no bacterial pathogen was isolated from a sputum 6 days after admission when antibiotic treatment had been already started. According to uniform hospital-wide guidelines based on generally accepted recommendations like those from the Robert Koch-Institute (RKI) on a national and the Centers for Disease Control and Prevention (CDC) on an international level, the patient was isolated immediately after admission to prevent transmission of enteropathogens. Since nosocomial outbreaks caused by Aeromonas spp. had not been reported so far, the isolation was stopped after the pathogen was detected from stool. Although A. veronii is a well characterized enteropathogen, gastroenteritis caused by Aeromonas species is obviously underdiagnosed, since it has been reported that aeromonads cause up to 13% of gastroenteritis cases in the United States (Buchanan, 1984). In our laboratory Aeromonas species have been isolated from stool very seldom so far (only 0.7% of overall stool samples in 2005–2006). Generally, Salmonella/Shigella-, Campylobacterand Yersiniaselective agars are used for diagnosis of bacterial pathogens causing gastroenteritis. When required by the clinicians, stool samples are additionally cultivated on sheep blood agar in our laboratory to specify the intestinal flora (Staphylococcus aureus, $-haemolytic streptococci). However, only 24.9% of overall stool samples were cultivated on sheep blood agar in 2005–2006 in our laboratory. Aeromonas hydrophilia and A. veronii biovar sobria are easy to diagnose by beta-haemolysis on sheep blood agar. Moreover, a common characteristic of all Aeromonas species is the positive oxidase reaction, which allows to distinguish them from Enterobacteriaceae. Therefore, we propose that sheep agar should be more frequently used for microbial diagnosis from stool, at least when the specimen is negative for the common bacterial pathogens causing gastroenteritis.