Diagnostic challenge of gastrointestinal infection due to lactose-fermenting Salmonella enterica subsp. enterica serovar 4,5:I:.

Here, we describe a case of a nontyphoidal Salmonella disease caused by a Salmonella enterica serovar 4,5:i:- (monophasic Salmonella typhimurium) which acquired a Lac operon. This lactose-fermenting bacterium presents a major challenge for phenotypical detection of Salmonella. Only specific agar plates or molecular techniques allow reliable detection.