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'Genes not noted elsewhere: nuc, thermonuclease (TNase) gene; femA, encoding factor A, which is essential for methicillin resistance; mecA, encoding penicillin-binding protein 2a.

cDried skimmed milk artificially contaminated with enterotoxigenic S. aureus cells.

'Genes not noted elsewhere: nuc, thermonuclease (TNase) gene; femA, encoding factor A, which is essential for methicillin resistance; mecA, encoding penicillin-binding protein 2a.

cDried skimmed milk artificially contaminated with enterotoxigenic S. aureus cells.

techniques have been developed to determine ET production by S. aureus recovered from patients with suspected SSSS. Although these methods have been reported to be specific and sensitive for detection of ETs, they rely on isolating putative toxinogenic S. aureus strains from the patient. A recently developed EIA based on F(ab')2 fragments was able to detect ETA directly from serum with high sensitivity.[13]

Nucleic Acid-Based Detection Methods for PTSAgs

Hybridization methods

Since 1986, protein sequences have been established for PTSAgs and ETs as well as nucleotide sequences for the corresponding genes (Table 1). Early molecular approaches for the detection of these toxin genes have been developed that use DNA-DNA hybridization techniques based on gene fragments or oligonucleotide probes (enzyme-, hapten-, radiolabeled). For detection of toxigenic staphylococci, e.g., colony hybridization and single-phase liquid hybridization assays were used. The hybridization techniques have never gained much use for direct detection of PTSAg-bearing staphylococci in patient specimens or in food, because their sensitivity and specificity was too low.

Nucleic acid amplification methods

The advent of DNA amplification-based methods, in particular the development of the polymerase chain reaction (PCR), provides a new, highly specific and sensitive tool for the detection of the PTSAg-encoding genes.[1416] In addition, the PCR technique allows the detection of toxin genes with little sample preparation in a relatively short period, most recently further shortened by the application of real-time PCR methods. The detection of SE- and TSST-encoding sequences by molecular methods has been reported by several investigators, mainly in DNA extracts derived from bacterial cultures and, to a lesser extent, directly in foods or patient specimens (Table 2). The development of multiplex PCR

systems allows the simultaneous detection of PTSAg genes for diagnostic and epidemiological purposes.

Nucleic acid-based methods are hampered by their inability to distinguish nonviable cells from viable ones because DNA from dead cells would also be amplified and detected. This may be of special importance for testing food samples, where enterotoxigenic staphylococci that have been killed by heat or other processing would yield a positive response. However, positive PCR results only indicate the presence of PTSAg genes in extracted DNA. They do not prove that production of toxin proteins occurs by a given isolate or indicate the presence of such proteins in samples. On the other hand, contamination of food products restricted on preformed SE proteins is not detectable by PCR but causative for SFP. In addition, false negative PCR results have been reported because of the presence of inhibitors of the DNA polymerases, which have been found to exist in food matrices.

Oligonucleotide arrays

Although oligonucleotide arrays (the so-called ''DNA chips'') have increasingly been used over the last few years to analyze DNA sequences as well as gene expression based on cDNA of mRNA for a number of microorganisms, applications to detect specifically staph-ylococcal toxins in medical specimens or food are still unavailable. Nevertheless, the potential is great because in contrast to traditional DNA detection methods restricted to target only a single or a few genes at a time at best, microarrays are able to integrate thousands of probes into the same chip-based hybridization procedure. This enables not only the detection of all staphylococcal toxins simultaneously, but also of other genes of specific interest, e.g., taxonomic marker genes, antibiotic resistance genes, and target structures for staphylococcal subtyping. However, this technique faces some of the same problems that have met traditional DNA hybridization, especially to get enough sensitivity to detect the target genes in specimens.

Getting Started With Dumbbells

Getting Started With Dumbbells

The use of dumbbells gives you a much more comprehensive strengthening effect because the workout engages your stabilizer muscles, in addition to the muscle you may be pin-pointing. Without all of the belts and artificial stabilizers of a machine, you also engage your core muscles, which are your body's natural stabilizers.

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