Determination of minimal regrowth concentration (MRC) in clinical isolates of various biofilm-forming bacteria

Abstract

Based on the ability to attach to polymeric surfaces, the formation of biofilms was determined in 5 wild-type strains (Pseudomonas aeruginosa, Klebsiella pneumoniae, Acinetobacter baumanii, Escherichia coli, Staphylococcus warneri). Using modified Christensen method, minimum regrowth concentration (MRC) of piperacillin, piperacillin-tazobactam, cefoperazon, ceftazidim, cefepim, meronem, ciprofloxacin, netilmicin and amikacin for Gram-negative and of ampicillin-sulbactam, chloramphenicol, tetracycline, clindamycin, vancomycin and teicoplanin for Gram-positive bacteria was estimated in trypticase-soy broth medium after a 1-d growth on polystyrene microtiter plates. Adherent bacterial populations exhibited reduced antimicrobial susceptibility, which was not shown in submerged cultures. Our results indicate that MRC can predict therapeutic outcome of antibiotic treatment better than the minimum inhibitory concentration tests commonly used.

Antibiograms of Multidrug-Resistant Clinical Acinetobacter baumannii: Promising Therapeutic Options for Treatment of Infection with Colistin-Resistant Strains

“…Such increased susceptibility to rifampicin in colistinresistant A. baumannii strains strongly supports recent clinical use of the combination of colistin with rifampicin for treatment of A. baumannii infection [23,25]. In addition, the significantly decreased biofilm formation in colistin-resistant strains will benefit clinical situations, considering that biofilm of A. baumannii is related to decreased susceptibility to antibiotics [26].…”

Activity of levofloxacin and ciprofloxacin on biofilms and planktonic cells of Stenotrophomonas maltophilia isolates from patients with device-associated infections

“…The viability of the biofilm was determined after 24 h of incubation at 35 • C visually or by reading the turbidity at 540 nm in a 96-well plate reader. The minimum re-growth concentration (MRC) was read as the minimum antibiotic concentration at which bacteria failed to re-grow [10]. Sterility controls and antibiotic-free controls were included in all experiments.…”

“…Biofilm susceptibility testing was performed as described by Cernohorska and Votava [10] with the following modifications. Briefly, aliquots (75 L) of the standardised inocula, as described in Section 2.2, were added to the wells of a 96-well microplate and incubated at 35 • C for 24 h. The medium was then discarded, the wells were washed with PBS, and 100 L of ciprofloxacin or levofloxacin at two-fold dilutions (from 2048 mg/L to 0.50 mg/L) prepared in MHB was added to the established biofilms.…”

“…The Calgary Biofilm Device (CBD) assay involves the formation of biofilms on plastic pegs on the lid of the CBD [9]. Cernohorska and Votava [10] proposed a similar less-expensive assay to study antibiotic susceptibility of biofilms formed directly on the wells of a microplate.…”

Antibiotic synergy against biofilm-forming Pseudomonas aeruginosa

“…Volumes of 100 μL of appropriate dilutions of the respective antibiotics in MH were transferred into the dried and unstained wells with established biofilms and the plates were incubated for 18-20 h at 37 ºC (see Černohorská and Votava 2004). MBIC (the lowest concentration of antibiotic which inhibits biofilm formation; mg/L) was then determined.…”