ABSTRACT
Cronobacter sakazakii (Enterobacter sakazakii) is an emerging pathogen that has been isolated from powdered infant formula and associated with outbreaks of infection in infants in neonatal intensive care units. In a previous study, we observed that neonatal CD-1 mice are susceptible to C. sakazakii infection and that the pathogen invades brain, liver, and cecum tissues. The study objective was to compare the virulence of three strains of C. sakazakii in neonatal CD-1 mice. The strains tested were MNW2 (a food isolate), SK81 (a clinical isolate), and 3290 (a clinical isolate). Timed-pregnant CD-1 mice were allowed to give birth on gestation day 19 or 20. Neonatal mice were sexed and culled to 10 per litter, each having five males and five females. Neonates were orally gavaged with C. sakazakii strains MNW2, SK81, or 3290 at doses ranging from 10(2.8) to 10(10.5) CFU on postnatal day 3.5. Pups surviving to postnatal day 10.5 were euthanized, and brain, liver, and cecum tissues were excised. C. sakazakii was isolated from all three tissues in mice treated with C. sakazakii, regardless of strain. C. sakazakii strain 3290 was significantly more invasive in brains (42.1% of mice) than were strains MNW2 (6.7%) and SK81 (15.9%). Mortality was observed for all strains of C. sakazakii tested, with SK81 being significantly more lethal (5.6%) than MNW2 (1.2%) or 3290 (0.6%). Our findings suggest that invasiveness does not necessarily correlate with mortality among different strains of C. sakazakii, and the clinical isolates are more virulent than the food isolate.
Subject(s)
Consumer Product Safety , Cronobacter sakazakii/pathogenicity , Enterobacteriaceae Infections/microbiology , Infant Food/microbiology , Animals , Animals, Newborn , Colony Count, Microbial , Disease Models, Animal , Food Microbiology , Humans , Infant , Infant Formula , Infant, Newborn , Mice , Risk Assessment , VirulenceABSTRACT
Cronobacter sakazakii is an opportunistic pathogen that has been isolated from powdered infant formulas. C. sakazakii infection can result in serious illnesses such as bacteremia, septicemia, meningitis, and death in at-risk infants who are orally fed contaminated reconstituted powdered infant formulas. The objective of this study was to compare the susceptibilities of BALB/c, C57BL/6, and CD-1 mice to C. sakazakii strain MNW2. We acquired timed-pregnant CD-1 mice and allowed them to give birth naturally. On postnatal day 3.5, each pup was administered a total dose of approximately 10(2) to 10(11) CFU C. sakazakii strain MNW2 in reconstituted powdered infant formula. Mice were observed twice daily for morbidity and mortality. At postnatal day 10.5, the remaining pups were euthanized, and brain, liver, and cecum were excised and analyzed for the presence of C. sakazakii. C. sakazakii was isolated from brains, livers, and ceca in all three mouse strains. The CD-1 mouse strain was the most susceptible of the three, with the lowest infectious dose (10(2) CFU) and the lowest lethal dose (also 10(2) CFU).
Subject(s)
Cronobacter sakazakii/pathogenicity , Disease Models, Animal , Enterobacteriaceae Infections/microbiology , Infant Food/microbiology , Infant Formula , Animals , Animals, Newborn , Colony Count, Microbial , Consumer Product Safety , Enterobacteriaceae Infections/immunology , Food Contamination/analysis , Food Microbiology , Humans , Infant , Infant, Newborn , Mice , Mice, Inbred BALB C , Mice, Inbred C57BL , Risk AssessmentABSTRACT
Listeriosis results from exposure to the foodborne pathogen Listeria monocytogenes. Although many different strains of L. monocytogenes are isolated from food, no definitive tests currently predict which isolates are most virulent. The objectives of this study were to address two major data gaps for risk assessors, variability among L. monocytogenes strains in pathogenicity and virulence. Strains used in our monkey clinical trial or additional food isolates were evaluated for their virulence and infectivity in mice. All strains were equally pathogenic to immunocompromised mice, causing deaths to 50% of the population 3 days after exposure to doses ranging from 2 to 3 log CFU. Doses resulting in 50% deaths on the fifth day after administration were 1 to 2 log lower than those on the third day, indicating that the full course of pathogenicity exceeds the 3-day endpoint in immunocompromised mice. Three strains were chosen for further testing for their virulence and infectivity in liver and spleen in normal (immunocompetent) mice. Virulence was not significantly different (P > 0.05) among the three strains, all resulting in deaths to 50% of mice at 5 to 7 log CFU by 5 days after administration. All strains were equally infective in liver or spleen, with higher numbers of L. monocytogenes directly correlated with higher doses of administration. In addition, there was no preference of organs by any strains. The lack of strain differences may reflect the limitation of the mouse model and suggests the importance of using various models to evaluate the pathogenicity and virulence of L. monocytogenes strains.
