Although all DD methods studied here performed well for detecting methicillin resistance in CoNS, moxalactam had a higher accuracy than cefoxitin to differentiate heteroresistant isolates from PBP2a-negative strains. Identification of isolates that should be submitted to a confirmatory test to conclude on methicillin resistance can be easily obtained by combining cefoxitin and moxalactam DD methods.
Simple PCR and sequencing assays that utilize a single pair of degenerate primers were used to characterize a 438-bp-long DNA fragment internal (
sodA
int
) to the
sodA
gene encoding the manganese-dependent superoxide dismutase in 19 enterococcal type strains (
Enterococcus avium
,
Enterococcus casseliflavus
,
Enterococcus cecorum
,
Enterococcus columbae
,
Enterococcus dispar
,
Enterococcus durans
,
Enterococcus faecalis
,
Enterococcus faecium
,
Enterococcus flavescens
,
Enterococcus gallinarum
,
Enterococcus hirae
,
Enterococcus malodoratus
,
Enterococcus mundtii
,
Enterococcus pseudoavium
,
Enterococcus raffinosus
,
Enterococcus saccharolyticus
,
Enterococcus seriolicida
,
Enterococcus solitarius
, and
Enterococcus sulfureus
). Sequence analysis of the
sodA
int
fragments enabled reliable identification of 18 enterococcal species, including
E. casseliflavus-E. flavescens
and
E. gallinarum
. The
sodA
int
fragments of
E. casseliflavus
and
E. flavescens
were almost identical (99.5% sequence identity), which suggests that they should be associated in a single species. Our results confirm that the
sodA
gene constitutes a more discriminative target sequence than 16S rRNA gene in differentiating closely related bacterial species.
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