NTU Undergraduates' research April 2014 - Biosciences | Seite 55

Metal Resistance in Cronobacter species
By Hayden B. Morgan

Abstract
Introduction: Cronobacter species are occasionally pathogenic, causing urinary tract infections and
serious neonatal diseases such as meningitis. The Cronobacter genus is comprised of ten species: C.
sakazakii, C. malonaticus, C. turicensis, C. universalis, C. muytjensii, C. dublinensis, C. condimenti,
C. helveticus, C. pulveris and C. zurichensis. The three species associated with causing infections are
C. sakazakii, C. malonaticus and C. turicensis. Resistance to heavy-metals is viewed as a virulence
factor as it allows survival, where non-resistant organisms would die, and give the bacteria a greater
chance of causing an infection.
Methods: Metal assays were performed, using a representative strain from each of the species, to
assess their ability to grow with the addition of different concentration of the metal. The metal assays
performed were using copper, silver, tellurite, zinc and nickel. The results from the metal assays were
compared with the bacterial genome to see if the genes for metal resistance mechanisms were present.
Results and Discussion: All strains showed resistance to copper, zinc and nickel, with one or more of
the possible resistance genes to copper of copA, cueO, Pco and cus genes being seen in all the
different strains. One or both of the zinc resistance genes zntA and zntB were seen in all the difference
strains, apart from C. malonaticus for which no zinc resistance gene was seen. Nickel resistance gene
CorA was seen in all of the strains apart from the strains C. malonaticus and C. universalis. The
results of the silver assay were that strains of C. sakazakii, C. malonaticus, C. muytjensii, C.
condimenti, C. helveticus, C. pulveris and C. zurichensis displayed resistance. Silver resistance genes
cus and Pco were found in C. sakazakii, C. malonaticus, C. helveticus and C. zurichensis but were not
seen in C. muytjensii, C. condimenti and C. pulveris. The strains of C. sakazakii, C. malonaticus, C.
dublinensis, C. helveticus and C. zurichensis showed tellurite resistance in the metal assays. One or
more of the tellurite resistance genes ter and teh were found in most strains but were not seen in the
strai n of C. malonaticus and C. helveticus. Of the pathogenic strains, C. sakazakii and C. malonaticus
showed resistance in all metal assays, whereas C. turicensis showed sensitivity to silver and tellurite.
C. malonaticus 681 has shown resistance in zinc, nickel and tellurite assays but did not possess the
same genes as seen in the other Cronobacter strains. Further investigation should be conducted to find
these different resistance mechanisms present in C. malonaticus 681 as a better knowledge of its
resistance mechanisms could help come up with a way to reduce the number of infections.