Characterization and subtyping of Cronobacter spp. from imported powdered infant formulae in Argentina

Cronobacter spp. (Enterobacter sakazakii), have been associated with severe foodborne infections in neonates and immunocompromised infants. In Argentina, we have isolated Cronobacter spp. from three different brands of imported powdered infant formulae (PIF). The objectives of this work were to characterize the recovered isolates phenotypically and to evaluate the use of a Pulsed-Field Gel Electrophoresis (PFGE) protocol for Cronobacter spp. subtyping. Out of 23 isolates studied from three brands of PIF (20 of brand A, 1 of brand B and 2 of brand C), 22 were identified as C. sakazakii and 1 as C. malonaticus. All isolates were susceptible to twelve antimicrobial agents assayed. The 19 C. sakazakii isolates of brand A showed five XbaI-PFGE patterns and the genetic clusters revealed by XbaI were confirmed with a second restriction enzyme, SpeI. The isolate from brand B showed the same XbaI and SpeI patterns as those of a group of isolates of brand A, suggesting a possible common source of contamination. The C. sakazakii isolates of brand C exhibited two unique XbaI-PFGE patterns, unrelated to the rest. Different genetic subtypes were found among isolates of a single batch of PIF from brand A and the single C. malonaticus strain also showed a distinct XbaI-PFGE pattern.