Caracterização fenotípica e genotípica de isolados de Staphylococcus aureus envolvidos em surtos de intoxicação alimentar no Rio Grande do Sul e atividade antimicrobiana e de redução de biofilme de óleos essenciais de Piper elongatum (Vahl.) e Minthostachys setosa (Briq.) Epling

Abstract

Staphylococcus aureus cause staphylococcal food poisoning, this microorganism can be resistant to antimicrobial, sanitizers and form biofilms. We aimed to determine spa types, agr groups, detect the presence of egc cluster genes, and evaluate the phenotypic and genotypic resistance of 13 S. aureus isolates involved in food poisoning outbreaks. In addition, verify their ability to form biofilm on stainless steel surface and evaluate the antimicrobial and biofilm reduction activity of essential oils (EO) from Minthostachys setosa (Briq.) and Piper elongatum (Vahl.). Ten spa types were identified using the spa typing technique. The agr groups and egc cluster genes were detected by PCR, agr III and agr II were the most prevalent (30.76% and 7.69%, respectively). The 23.07% of isolates carried the seln and sei genes and only one isolate carried the cluster egc. Antimicrobial susceptibility determined that all isolates showed resistance to at least one antimicrobial. The broth microdilution technique demonstrated tolerance of the thirteen isolates to benzalkonium chloride (4 to 8 µg.mL-1) and chlorhexidine (4 µg.mL-1). Nine antimicrobial resistance genes (blaZ, ereB, ermB, ermC, sul2, tetM, tetA, tetB, tetK) as well as genes encoding efflux pumps (mepA, norA, norB and smr) were detected by PCR. All isolates formed biofilm on stainless steel at 25 and 37 °C. Gas chromatography/mass spectrometry identified pulegone (57.54%) and caryophyllene (7.29%) as the most abundant compounds in the EO of M. setosa, while eucalyptol (10.84%), methyl-eugenol (9.29%), β-ocimene (8.31%), and spatulenol (7.22%), were the majority compounds in the EO of P. elongatum. The minimum inhibitory concentration (MIC) and the Minimum Bactericidal Concentration (MBC) of both EOs against S. aureus was 12.5% and 50%, respectively. The pre-formed biofilm on stainless steel of two selected isolates of S. aureus was exposed for 15 min to three concentrations (6.25%, 12.5% and 25%) of each EO, it was observed a reduction in viable cell count of up to 2.52 CFU.log cm-2 at the highest concentration evaluated. The activity of the two evaluated EOs in the biofilm removal was observed by Laser Scanning Confocal Microscopy, the biofilm removal was more significant increasing the oil concentration. To sum up, S. aureus isolates involved in outbreaks of staphylococcal food poisoning in Rio Grande do Sul have antimicrobial resistance and tolerance to sanitizers and are able to form biofilm on stainless steel. The prevalent agr groups (agr II and III) regulate antimicrobial resistance and biofilm formation in this bacterial species. It was found that evaluated EOs have antimicrobial capacity and reduce the number of viable cells in preformed biofilm of S. aureus at the evaluated time and concentrations.