Isolation and characterization of a plasmid involved with enterotoxin B production in Staphylococcus aureus

Abstract

Genetic analysis and molecular characterization of plasmid deoxyribonucleic acid (DNA) was performed in a toxigenic isolate ofStaphylococcus aureus strain DU4916. Elimination, transduction, and transformation experiments provided us with a series of derivatives similar except for the presence or absence of genes mediating resistance to penicillin (penr), methicillin (mecr), and tetracycline (tetr) and enterotoxin type B (SEB) production (entB+). The derivatives were examined for the presence of a plasmid species which encodes for SEB production. Two distinct species of covalently closed circular DNA of about 2.8 x 106 and 0.75 x 106 daltons were identified in an ethidium bromide-cured, penicillinase-negative (pens) isolate, SN109 (mecr tetr emtB+). Further segregation of either methicillin resistance or tetracycline resistance or of both together resulted in the loss of SEB production and the disappearance of both plasmids. Transduction from strain SN109 showed that determinants for tetracycline resistance are carried by the 2.8 x 106f-dalton plasmid. Transformation with covalently closed circular DNA from strain SN109 yielded mecs tetr entBtransformants harboring the tetracycline resistance plasmid alone and mecr tetr entB+ transformants harboring both the tetracycline resistance and the 0.75 x 106dalton plasmid. Further segregation of methicillin resistance in transformants was not associated with any change in plasmid DNA. The results indicate that a genetic determinant for SEB production is carried by the 0.75 x 106-dalton plasmid. It is possible, however, that this plasmid cannot be maintained in the host independently from the tetracycline resistance plasmid. Methicillin resistance in the strains examined could not be ascribed to any of the covalently closed circular DNA components resolved in strain DU4916.

THE STAPHYLOCOCCAL ENTEROTOXINS — A GENETIC OVERVIEW1

“…However, other studies have shown that SEB synthesis is indeed associated with a particular class of plasmid found in a variety of SEB' isolates. Shalita et al (1977) examined the Dornbusch strain, DU-4916 (KSI 390), and found that the ability to produce SEB was associated with a small plasmid, whose molecular weight was estimated at 0.75 X lo6. This plasmid has since been designated pSN2 and is shown as the peak of fraction 23 in Fig.…”

Antimicrobial resistance patterns and plasmid profiles of <i> Staphylococcus Aureus</i> isolated from milk and meat

“…Resistance of S. aureus isolates to various antimicrobial agents may be located either on chromosomes, plasmids or transposons. For example, methicillin resistance gene (mec4916) has a chromosomal locus, and is probably maintained on a mobile element (34,35), while tetracycline resistance observed in S. aureus strain DU4916 was reported to be encoded by a 4.0 kb plasmid (36). Noble and Rahman (37) reported tetracycline resistance in S. aureus to be encoded by a 4.3 kb plasmid, while in some strains resistance was found to be encoded by a chromosomal gene.…”

Staphylococcus aureusand its food poisoning toxins: characterization and outbreak investigation

“…Enterotoxin gene locations (Table 5) are numerous (Argudin et al, 2010). They can be carried by plasmids (seb, sed, sej, ser, ses, set) (Shalita et al, 1977;Bayles & Iandolo, 1989;Zhang et al, 1998;Omoe et al, 2003;Ono et al, 2008), phage (temperate for sea, defective for see) (Betley & Mekalanos, 1985;Couch et al, 1988;Coleman et al, 1989) or by genomic islands (seb, sec, seg, seh, sei, sek, sel, sem, sen, seo, sep and seq). Gene encoding for sec can be located on a plasmid or a pathogenicity island depending on the origin of the isolate (Fitzgerald et al, 2001).…”

“…The location of se genes on mobile genetic elements can result in horizontal gene transfer between the strains of S. aureus. For example, the seb gene is located on the chromosome in some clinical isolates (Shafer & Iandolo, 1978), whereas it has a plasmidic location in other strains of S. aureus (Shalita et al, 1977). A main regulatory system controlling the expression of virulence factors in S. aureus is the agr system (accessory gene regulator; Kornblum et al, 1990).…”