Virulence and resistance determinants in methicillin-resistant Staphylococcus aureus ST398 isolates

Abstract number: P1375

Argudín M.A., Fetsch A., Tenhagen B.A., Kowall J., Hammerl J., Kaempe U., Hertwig S., Schroeter A., Bräunig J., Käsbohrer A., Appel B., Nöckler K., Helmuth R., Mendoza M.C., Rodicio M.R., Guerra B.

Objective: Detection of virulence and resistance genes in German MRSA isolates of the MLST clone ST398.

Methods: A series of 106 S. aureus isolates were selected. They included 100 MRSA (2004–2007) of the ST398 clone, and six out-group/control strains. The isolates originated from healthy and sick pigs, dust from pig farms, milk, carcasses and meat from food-producing animals. They displayed different resistance patterns (tetracycline, oxacillin, erythromycin, and clindamycin being the most frequent resistances), and carried different SCCmec types (III, IVa, V or non-typeable), and spa types (mainly t011 and t034). The isolates were analyzed by SmaI-PFGE, and screened for thirty seven genes involved in virulence and eight involved in tetracycline or erythromycin resistance by PCR.

Results: The 100 ST398 isolates were non-typeable by SmaI-PFGE. They were negative for leukotoxins, exfoliatins and superantigen toxins. They carried only genes encoding haemolysins (hla, hlb, hld ± hlg) and were of the agr quorum sensing system type I. Out-group and control isolates displayed different virulence profiles and were from other agr groups. All the isolates of the clone were tetracycline resistant and carried the gene tet(M) together with one or two plasmid associated genes [tet(K) and tet(L) (18%), tet(K) (51%), tet(L) (22%)]. For erythromycin and clindamycin resistance, eight patterns [ermA, ermB, ermC (8.2%), ermA, ermB (19.2%), ermA, ermC (8.2%), ermB, ermC (1.4%), ermA (11%), ermB (12.3%), ermC (35.6%), non-typeable (4.1%)] were found among resistant isolates. A relationship between the presence of certain resistance genes and the SCCmec type was detected. Most of the SCCmec III isolates carried ermA, which is associated with the Tn554 transposon present in this cassette. The plasmid gene tet(K) was found only in isolates with SCCmec V.

Conclusions: The ST398 isolates from swine, milk, carcasses and meat lack several clinically important S. aureus associated virulence factors, including PVL. Generally, only some haemolysin encoding genes and the agr type I were present. Other virulence mechanisms related to the adhesion or production of biofilms may play an important role in the wide spread of ST398 isolates. All MRSA ST398 were tetracycline resistant and carried the tet(M) gene with additional resistance genes mediated by plasmids (tet(K) and/or tet(L)). Most isolates (69%) were erythromycin-clindamycin resistant and carried different combinations of erm genes.

Session Details

Date: 16/05/2009
Time: 00:00-00:00
Session name: 19th European Congress of Clinical Microbiology and Infectious Diseases
Location: Helsinki, Finland, 16 - 19 May 2009
Presentation type:
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