Abstract
Little is known about the occurrence of antimicrobial resistance determinants in staphylococci isolated from food and food processing industries. Quaternary ammonium compound (QAC)-resistant coagulase-negative
staphylococci (CNS) isolated from food and food-processing industries were investigated for the presence of genetic determinants (
qacA/B
and
qacC/smr
) encoding resistance to the QAC benzalkonium
chloride (BC), several antibiotic resistance genes, and staphylococcal insertion sequences IS
257
and IS
256
. Six
qacA/B
-harboring strains were resistant to penicillin and hybridized
to a
blaZ
probe. The
qacA/B
and
blaZ
probes hybridized to plasmids of similar size in three isolates. Molecular and genetic characterization of the 23-kb plasmid (pST6) of
Staphylococcus
epidermidis
St.6 revealed the presence of
qacB
adjacent to an incomplete
β
-lactamase transposon Tn
552
encoding the gene cluster
blaZ
,
blaR
, and
blaI
. Sequence
analysis of flanking regions and the intergenic region between
blaZ
and
qacB
revealed the presence of IS
257
downstream of
blaZ
as well as
sin
and
binR
between
blaZ
and
qacB
. In the three other BC and penicillin-resistant strains, the
qacA/B
and
blaZ
genes were located on separate plasmids. A
qacC
harboring
S. epidermidis
strain (St.17)
also hybridized to
tetK
(tetracycline resistance) and
ermB
(erythromycin resistance) genes. The individual genes were located on separate plasmids, suggesting no linkage between QAC and antibiotic
resistance determinants. Plasmid-free
Staphylococcus aureus
RN4220 allowed uptake of the pST6 plasmid DNA, indicating that the resistance genes could potentially be transferred to pathogens under
selective stress. In conclusion, presence of both resistance determinants could lead to co-selection during antimicrobial therapy or disinfection in hospitals or in food industries.