Systemic and extraintestinal forms of human infection due to non-typhoid salmonellae in Bulgaria, 2005-2010

The purpose of this investigation was to review the clinical cases diagnosed as systemic or extraintestinal salmonellosis between 2005 and 2010 in Bulgaria, to determine the antimicrobial resistance of the causative salmonellae, and to analyze the pulsed field gel electrophoresis (PFGE) profiles of extraintestinal Salmonella Corvallis isolates. Culture, biochemical tests, and serotyping were performed. Resistance to 12 antimicrobial agents was studied with the Bauer-Kirby disk diffusion method. The double-disk synergy method was used for the screening of the presence of extended-spectrum beta-lactamases (ESBLs). PFGE typing and analysis of the dendrogram was performed for the comparative investigation of Salmonella Corvallis isolates. Between 2005 and 2010, 2,227 human non-typhoid Salmonella isolates were investigated at the National Reference Laboratory of Enteric Pathogens, Sofia, Bulgaria. Thirty-three strains (1.48 %) from nine national regions were isolated from patients with systemic and extraintestinal forms of salmonellosis. The serotype distribution was as follows: S. enteritidis (n = 21), S. choleraesuis (diphasic n = 3; monophasic n = 3), S. typhimurium (n = 2), Salmonella Corvallis (n = 2), Salmonella Montevideo (n = 1), and S. javiana (n = 1). Eight patients developed severe forms of infections: sepsis (n = 2), septic shock (n = 1 with fatal outcome), meningitis (n = 3), and acute renal failure (n = 2). Twenty-two percent of isolates were resistant to ampicillin and gentamicin, 17.64 % to tetracycline, 14.28 % to nalidixic acid, and 10 % to chloramphenicol. All isolates were susceptible to ciprofloxacin. One Salmonella Corvallis isolate recovered from a patient with chronic hemolytic anemia produced an ESBL and its PFGE profile demonstrated less than 96 % similarity to fecal and wound Salmonella Corvallis with susceptible phenotypes. S. enteritidis was the most common cause of systemic and extraintestinal forms of human salmonellosis in Bulgaria. Resistance to ampicillin and gentamicin were the predominant profiles, although one Salmonella Corvallis isolate produced an ESBL. The ESBL-producing Salmonella Corvallis isolate clustered separately from the susceptible Salmonella Corvallis isolates.