Virulence and Resistance Determinants of German Staphylococcus aureus ST398 Isolates from Nonhuman Sources

Abstract

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...

Livestock-Associated MRSA and Its Current Evolution

“…It is capable of acquiring virulence genes, and its acquisition of the PantonValentine leukocidin (PVL) gene (pvl) has been demonstrated [37,61,62]. Regarding other virulence factors, staphylococcal enterotoxins occasionally have been reported in LA-MRSA CC398 in pigs [53,[63][64][65] and turkeys [33••]. In contrast, genes encoding adhesion factors, proteases, hemolysins, other leukocidins, and superantigen-like proteins have been detected frequently in LA-MRSA CC398 isolates from pigs [2•], poultry [26, 33••], and bovines [22].…”

A Novel FexA Variant from a Canine Staphylococcus pseudintermedius Isolate That Does Not Confer Florfenicol Resistance

“…Since the first description of the fexA gene in a bovine Staphylococcus lentus isolate (2), this gene has been detected-either as part of the small nonconjugative transposon Tn558 or in combination with the cfr gene in transposition-deficient Tn558 variants-in S. aureus and several coagulase-negative staphylococcal species from healthy and diseased cattle, swine, horses, or humans (3)(4)(5)(6)(7)(8)(9). The fexA gene has also been detected in a Bacillus isolate from swine feces and in environmental pollutants from swine feedlots in China (10,11).…”

Effects of Chlorophyll-Derived Efflux Pump Inhibitor Pheophorbideaand Pyropheophorbideaon Growth and Macrolide Antibiotic Resistance of Indicator and Anaerobic Swine Manure Bacteria

“…Msr(A) and Mef(A) are well known to confer erythromycin resistance in strains of S. aureus [27,95,96,101,102]. The plasmidborne Msr(A) transporter, even though mainly responsible for erythromycin efflux in S. aureus [103], is not present in the strain used in our study, S. aureus ATCC 29213 [104]. Mef(A) is closely related to Mef(B), the erythromycin efflux pump in E. coli P475.10.99.C3 [67], and as pyp decreased the final MIC endpoint for induced cultures of this strain (Figures 3(b) and 3(d)), it can be concluded that Mef(A) is an additional candidate for inhibition by pyp in S. aureus.…”