Antibiotic and Desiccation Resistance of Cronobacter sakazakii and C. malonaticus Isolates from Powdered Infant Formula and Processing Environments

Abstract

This study evaluated the antimicrobial and desiccation resistance of <i>Cronobacter sakazakii</i> and <i>Cronobacter malonaticus</i> isolates from powdered infant formula and processing environments. The antimicrobial susceptibility tests showed that the 70 <i>Cronobacter</i> strains, representing 19 sequence types, were susceptible to the most of the antibiotics except for amoxicillin-clavulanate, ampicillin, and cefazolin. Furthermore, the growth of six <i>C. sakazakii</i> and two <i>C. malonaticus</i> strains from different sequence types (STs) in hyperosmotic media was measured. The growth of the two <i>C. sakazakii</i> strains (CE1 and CE13) from the neonatal pathovars ST4 and ST8, were significantly higher (<i>p</i> < 0.05) than that of other strains. <i>C. malonaticus</i> strain CM35 (ST201) was the slowest grower in all strains, and most could not grow in more than 8% NaCl solution. Also the survival of these strains under desiccation conditions was followed for 1 year. The viable count of <i>Cronobacter</i> spp. under desiccation conditions was reduced on average by 3.02 log cycles during 1 year, with CE13 (ST8) being the most desiccation resistant strain. These results will improve our understanding of the persistence of the two closely related species <i>C. sakazakii</i> and <i>C. malonaticus</i> which are of concern for neonatal and adult health.