TABLE 3.
Results of testing reference strains for SE genotypes seg to sej derived from agarose gel analysis of multiplex PCR and colorimetric microtiter plate DEIA
| Reference strain | Toxin genotype determined by previous study | Genotype as determined by:
|
Reference or source | |||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Agarose gel analysisa
|
Colorimetric assayb (OD ratio at 450/630 nm)
|
|||||||||
| seg | seh | sei | sej | seg | seh | sei | sej | |||
| ATCC 13565 | seac | − | − | − | + | 0.035 | 0.118 | 0.035 | 1.617 | ATCC |
| ATCC 14458 | seb | − | − | − | − | 0.035 | 0.044 | 0.042 | 0.070 | ATCC |
| ATCC 19095 | sec | + | + | + | − | 1.023 | 2.127 | >2.500 | 0.071 | ATCC |
| ATCC 23235 | sed | + | − | + | + | 2.399 | 0.022 | 2.384 | 2.361 | ATCC |
| ATCC 27664 | see | − | − | − | − | 0.056 | 0.090 | 0.120 | 0.076 | ATCC |
| MJB 1320 | seid,e | − | − | + | − | 0.033 | 0.048 | >2.500 | 0.053 | 30 |
| FRI 445 | seg seid,f | + | − | + | − | 2.228 | 0.052 | >2.500 | 0.052 | 28, 30 |
| FRI 569 | sehd | − | + | − | − | 0.047 | 2.131 | 0.105 | 0.054 | 38 |
| FRI 572 | seg seid | + | − | + | − | 1.976 | 0.045 | >2.500 | 0.062 | 28, 30, 38 |
| FRI 1472 | sed seg sei sejd | + | − | + | + | 2.346 | 0.039 | >2.500 | 2.067 | 42 |
| KN813 | tst | + | − | + | − | 0.139 | 0.045 | 0.067 | 0.058 | 4 |
| BM 10458 | eta | − | − | − | − | 0.080 | 0.079 | 0.083 | 0.077 | 4 |
| BM 10143 | etb | − | − | − | − | 0.096 | 0.074 | 0.129 | 0.065 | 4 |
| Cowan 1g | Nontoxigenic | + | − | + | − | 0.070 | 0.046 | 0.083 | 0.085 | 4 |
| ATCC 20044g | Nontoxigenic | − | − | − | − | 0.036 | 0.041 | 0.033 | 0.079 | 4 |
−, negative; +, positive (as judged by eye).
Reactions were judged as positive if the signal reached or exceeded the cutoff value of 0.150 absorbance units above the mean value of determinations of toxin-negative reference strains.
In our study, this was also tested as positive for SED by using reversed passive latex agglutination and EIA and was confirmed by a positive PCR result testing sed.
Strains were addionally tested by PCR and DEIA (data not shown) as completely negative for the classical exotoxin genes sea to see, tst, eta, and etb, except for strain FRI 1472, which also exhibited sej-positive PCR amplification and DEIA hybridization for the sed gene (42), as well as for the seg and sei genes.
This strain is only sei positive due to the possession of the pMJB471 plasmid encoding sei gene (30).
In contrast to the observation of Munson et al. (30) regarding SEH production of FRI 445, PCR targeting of the seh gene resulted in a negative reaction in our study, as also reported by Monday and Bohach (28).
Negative control strains; nontoxigenic S. epidermidis ATCC 20044 and S. aureus Cowan I were considered nontoxigenic for classical PTSAgs and ETs.