Staphylococcus aureus produces a wide variety of toxins including staphylococcal enterotoxins (SEs; SEA to SEE, SEG to SEI, SER to SET) with demonstrated emetic activity, and staphylococcal-like (SEl) proteins, which are not emetic in a primate model (SElL and SElQ) or have yet to be tested (SElJ, SElK, SElM to SElP, SElU, SElU2 and SElV). SEs and SEls have been traditionally subdivided into classical (SEA to SEE) and new (SEG to SElU2) types. All possess superantigenic activity and are encoded by accessory genetic elements, including plasmids, prophages, pathogenicity islands, vSa genomic islands, or by genes located next to the staphylococcal cassette chromosome (SCC) implicated in methicillin resistance. SEs are a major cause of food poisoning, which typically occurs after ingestion of different foods, particularly processed meat and dairy products, contaminated with S. aureus by improper handling and subsequent storage at elevated temperatures. Symptoms are of rapid onset and include nausea and violent vomiting, with or without diarrhea. The illness is usually self-limiting and only occasionally it is severe enough to warrant hospitalization. SEA is the most common cause of staphylococcal food poisoning worldwide, but the involvement of other classical SEs has been also demonstrated. Of the new SE/SEls, only SEH have clearly been associated with food poisoning. However, genes encoding novel SEs as well as SEls with untested emetic activity are widely represented in S. aureus, and their role in pathogenesis may be underestimated.

A series of 100 Staphylococcus aureus isolates ascribed to sequence type 398 (ST398) and recovered from different sources (healthy carrier and diseased pigs, dust from pig farms, milk, and meat) in Germany were investigated for their virulence and antimicrobial resistance genetic background. Antimicrobial resistance was determined by the disk diffusion method. Virulence and resistance determinants (37 and 31 genes, respectively) were tested by PCR. Only two virulence profiles, including the accessory gene regulator agrI and three or four hemolysin-encoding genes, were detected. In contrast, 33 resistance profiles were distinguished (only 11 were shown by more than one isolate). Fifty-nine isolates were multiresistant (four or more antimicrobial classes), and 98 were methicillin resistant (mecA positive). All of the ST398 isolates showed resistance to tetracycline [encoded by tet(M) alone or together with tet(K) and/or tet(L)]. In addition, 98% were resistant to other antimicrobials, including macrolide-lincosamine-streptogramin B (70%, encoded by ermA, ermB, and ermC, alone or in combination), trimethoprim (65%, mostly due to dfrK and dfrG), kanamycin and gentamicin [29% and 14%, respectively, mainly related to aac(6)-Ie-aph(2؆)-Ia and/or ant(4)-Ia but also to aph(3)-IIIa], chloramphenicol (9%, fexA or cfr), quinupristin-dalfopristin (9%), ciprofloxacin (8%), and trimethoprim-sulfamethoxazole (4%). The heterogeneity of the resistance profiles underlines the ability of the ST398 clone to acquire multiple antimicrobial resistance genes. However, the virulence gene content of the tested isolates was low. Continuous surveillance is needed to clarify whether its pathogenicity potential for animals and humans will increase over time.Methicillin-resistant Staphylococcus aureus (MRSA) of sequence type 398 (ST398) has gained particular attention during recent years because of its association with pigs and its ability to colonize pig farmers and other people in close contact with pigs (7,12,47). The MRSA isolates of ST398 usually lack important virulence determinants that are typical in other community and hospital MRSA isolates. The majority of the ST398 isolates analyzed so far carry only hemolysin-encoding genes (13,21,31,32), although a small number of cases in which the isolates carried the bicomponent leukotoxin PantonValentine (lukPV genes) (43, 49) or staphylococcal enterotoxins (SEs, se genes) (21, 26) have also been reported. Genes for other toxins, like exfoliatins (ET, et genes), leukotoxins, and toxic shock syndrome toxin (TSST-1, tst gene) have not been found yet in ST398 isolates (13,21,31,32,44). The regulation of the expression of most extracellular virulence factors in S. aureus is under the control of a two-component signaling system called the accessory gene regulator (agr), which is polymorphic and divided into four distinct genetic groups (I to IV). A correlation exists between some agr groups and certain pathotypes and clonal complexes (CCs) (48), and CC398 seem to be associated with agr group I (ag...

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The resistance profiles, for 15 antimicrobial agents, of 333 Salmonella strains representing the most frequent nontyphoidal serotypes, isolated between 1989 and 1998 in a Spanish region, and 9 reference strains were analyzed. All strains were susceptible to amikacin, ceftazidime, ciprofloxacin, and imipenem, and 31% were susceptible to all antimicrobials tested. The most frequent types of resistance were to sulfadiazine, tetracycline, streptomycin, spectinomycin, ampicillin, and chloramphenicol (ranging from 46 to 22%); 13% were resistant to these six drugs. This multidrug resistance pattern was found alone or together with other resistance types within serotypes Typhimurium (45%), Panama (23%), and Virchow (4%). Each isolate was also screened for the presence of class 1 integrons and selected resistance genes therein; seven variable regions which carried one (aadA1a, aadA2, or pse-1) or two (dfrA14-aadA1a, dfrA1-aadA1a, oxa1-aadA1a, or sat1-aadA1a) resistance genes were found in integrons.The worldwide use of antimicrobials in different fields, such as human and veterinary medicine and agriculture, and as food animal growth-promoting agents during the past decades has created enormous pressure for the selection of antimicrobial resistance among bacterial pathogens. Nowadays, there is increasing concern about the development of multiresistance in bacteria causing zoonosis and having an important animal reservoir, such as Salmonella strains (5, 6, 9); this multiresistance is of considerable importance in both human and veterinary medicine and is the subject of several surveillance programs (6, 9).An efficient route of acquisition and vertical and horizontal dissemination of resistance determinants is through mobile elements including plasmids, transposons, and gene cassettes in integrons (5,14,15,18,22). Four distinct classes of integrons encoding different integrases have been reported (13, 18), and class 1 integrons are the most frequent in clinical strains, being found in many different organisms. Class 1 integrons often contain sul1, which encodes resistance to sulfonamides (14,16,20). At the present time, about 60 different cassettes associated with resistance genes have been identified, and the same cassettes can be found in different classes of integrons (7,16).The aims of the present work were to (i) trace the frequencies and major changes throughout the last decade in susceptibility patterns of Salmonella enterica organisms representing the most frequent nontyphoidal serotypes causing human salmonellosis in the Principality of Asturias, Spain; (ii) ascertain the presence and spread of class 1 integrons among nontyphoidal serotypes; and (iii) characterize the different variable regions of the class 1 integrons found in order to identify the resistance genes located therein. MATERIALS AND METHODSBacterial strains. The study included 333 apparently epidemiologically unrelated nontyphoidal Salmonella strains collected in the Principality of Asturias, Spain, from 1989 to 1998 (Table 1), and 9 reference strain...

An unusual self-transferable virulence-resistance plasmid (pUO-StVR2) was found in nine multidrugresistant (ACSSuT phenotype) Salmonella enterica serotype Typhimurium clinical isolates that were assigned to four different phage types and a single and distinctive XbaI pulsed-field gel electrophoresis profile. pUOStVR2 is an IncFII plasmid of about 140 kb in length carrying the spvA, spvB, and spvC (Salmonella plasmid virulence) and rck (resistance to complement killing) genes. It also carries the oxa1/aadA1a (ampicillin resistance and streptomycin-spectinomycin resistance) gene cassette configuration located within a class 1 integron with qacE⌬1/sul1 (ammonium antiseptics resistance and sulfadiazine resistance); the transposon genes merA, tnpA, and tnpR (mercury resistance, transposase, and resolvase of Tn21, respectively); and the catA1 (chloramphenicol resistance) and tet(B) (tetracycline resistance) genes. The insertion of resistance genes into a Salmonella virulence plasmid constitutes a new and interesting example of plasmid evolution and presents a serious public health problem.