Biofilm production and beta-lactamic resistance in Brazilian Staphylococcus aureus isolates from bovine mastitis

Abstract Staphylococcus spp. play an important role in the etiology of bovine mastitis. Staphylococcus aureus is considered the most relevant species due to the production of virulence factors such as slime, which is required for biofilm formation. This study aimed to evaluate biofilm production and its possible relation to beta-lactamic resistance in 20 S. aureus isolates from bovine mastitic milk. The isolates were characterized by pheno-genotypic and MALDI TOF-MS assays and tested for genes such as icaA, icaD, bap, agr RNAIII, agr I, agr II, agr III, and agr IV, which are related to slime production and its regulation. Biofilm production in microplates was evaluated considering the intervals determined along the bacterial growth curve. In addition, to determine the most suitable time interval for biofilm analysis, scanning electron microscopy was performed. Furthermore, genes such as mecA and blaZ that are related to beta-lactamic resistance and oxacillin susceptibility were tested. All the studied isolates were biofilm producers and mostly presented icaA and icaD. The Agr type II genes were significantly prevalent. According to the SEM, gradual changes in the bacterial arrangement were observed during biofilm formation along the growth curve phases, and the peak was reached at the stationary phase. In this study, the penicillin resistance was related to the production of beta-lactamase, and the high minimal bactericidal concentration for cefoxitin was possibly associated with biofilm protection. Therefore, further studies are warranted to better understand biofilm formation, possibly contributing to our knowledge about bacterial resistance in vivo.

Morphometric analysis of methicillin-resistant staphylococcus aureus isolated from the saliva of healthcare workers

The objective of this study was to evaluate the morphological changes in methicillin-resistant staphylococcus aureus (MRSA) cultured in different concentrations of sodium chloride and oxacillin. In a previous study on the prevalence of MRSA and methicillin-susceptible staphylococcus aureus (MRSA) un the saliva of health workers, 12 samples of MRSA were isolated and identified using conventional techniques and polymerase chain reaction (PCR). Morphological and morphometric analyses showed that the culture of methicillin-resistant S. aureus in different concentrations of sodium chloride (2 percent, 4 percent, 6 percent and 7.5 percent) and oxacillin (2µg, 4 µg and 6µg/mL) had effect on the morphology of the bacteria.

Este estudo teve como objetivo avaliar alterações morfológicas em staphylococcus aureus resistente à meticilina (MRSA) após o cultivo em meios contendo diferentes concentrações de cloreto de sódio e oxacilina. Em um estudo prévio sobre a prevalência de MRSA e de staphylococcus aureus susceptível à meticilina (MSSA) na saliva de profissionais de saúde, 12 amostras de MRSA foram isoladas e identificadas por técnicas convencionais e pela reação em cadeia da polimerase (PCR). Análises morfológicas e morfométricas mostraram que a cultura de S. aureus em diferentes concentrações de cloreto de sódio (2 por cento, 4 por cento, 6, por cento, 7.5 por cento) e oxacilina (2µg, 4 µg e 6µg/mL) não promoveu qualquer efeito sobre a morfologia das bactérias.

Estudio molecular de 6 episodios de infección intrahospitalaria causados por staphylococcus aureus meticilino-resistente / Molecular study of 6 episodes of intrahospitalary infection due to methicillin resistant staphylococcus aureus

A critical step in any epidemiologic research concerning nosocomial infections is the precise identification of the responsible pathogen. The present work utilized a molecular approach-plasmids identification, restriction lengght polymorphism DNA analysis and random amplified polymorphic DNA for the characterization of 6 nosocomial outbreaks due to 52 strains of methicillin-resistant staphylococcus aureus (MRSA). In these episodes, the clinic-epidemiologic and phenotipic analysis (antibiotype) pointed to a nosocomial infection. Through molecular analysis it was possible to establish in a very precise way, clonality due to MRSA strains in 2 of the studied outbreaks; the same type of analysis allowed to eliminate a MRSA clonal origin in the remainder 4 episodes. The antibiogram was not an useful analytic tool due to its poor discriminatory power. Also, through a PCR procedure, it was possible to identify the presence of the gen mecA in every of the 52 MRSA strains studied