Ultrospec 3100 pro uv visible spectrophotometer

S. aureus ATCC 2998 and Salmonella Enteritidis SE86 were selected as representatives of Gram-positive and Gram-negative bacteria, respectively. Both strains are part of the microorganism collection of the Food Control and Microbiology Laboratory of the Federal University of Rio Grande do Sul (UFRGS, Porto Alegre, Brazil). Salmonella Enteritidis SE86 was isolated from cabbage involved in a foodborne outbreak, exhibiting the same genetic profile of more than 90% of Salmonella Enteritidis related to outbreaks reported in Rio Grande do Sul State, Southern Brazil (Capalonga et al. 2014 ). These strains were chosen from a preliminary study that defined them as more resistant to the studied antimicrobials (data not shown). The bacteria were kept at -18°C in 10% (v/v) glycerol. For activation, 20 µL of each culture was transferred to 3 mL of Brain Heart Infusion broth (BHI; HiMedia, Mumbai, India) incubated at 37°C for 24 h. Each bacterial suspension (S. aureus or Salmonella Enteritidis SE86) was adjusted to approximately 10 8 CFU/mL by diluting the inoculum in sterile BHI broth to obtain ~0.5 absorbance units (OD 630nm ) using an Ultrospec 3100 Pro UV/Visible spectrophotometer (Amersham Biosciences, UK). For confirmation, plate counting was performed using BHI agar.