Pseudomonas aeruginosa Bacterial Biofilms
This thesis is an investigation of Pseudomonas aeruginosa bacterial biofilms. The objective of the first study was to evaluate the biofilm-forming capacity of canine otitis isolates of P. aeruginosa and to compare the minimum inhibitory concentrations (MICs) of antimicrobials for planktonic versus biofilm-embedded bacteria. Biofilm forming ability was assessed using a microtitre plate assay. Broth microdilution was used to assess the MICs of neomycin, polymyxin B, enrofloxacin and gentamicin for the planktonic and biofilm-embedded bacteria of eighty-three isolates. Thirty-three (40%) isolates were biofilm producers and MICs for biofilm-embedded bacteria were significantly higher than their planktonic counterparts for all antimicrobials (all P<0.05). The objective of the second study was to evaluate the impact of Tromethamine edetate disodium dihydrate (Triz-EDTA®) in combination with antimicrobials on antimicrobial susceptibility of P. aeruginosa biofilm-embedded bacteria. MICs of the four antimicrobials for the biofilm embedded bacteria and biofilm-embedded bacteria with added Triz-EDTA® were assessed with broth microdilution for thirty-one biofilm-producing isolates. Addition of Triz-EDTA® significantly reduced MICs for neomycin (P < 0.008) and gentamicin (P < 0.04) but not enrofloxacin (P = 0.7), or polymyxin B (P = 0.5). The objective of the third study was to determine the presence of biofilm-associated genes in biofilm forming and non-biofilm forming isolates. Four genes involved with carbohydrate matrix production (pelA), irreversible attachment (sadB) and quorum sensing (lasB, rhlA) were selected. DNA was extracted and polymerase chain reaction (PCR) was performed for all isolates. All isolates possessed lasB and sadB, 74 (90%) possessed pelA and 74 (90%) possessed rhlA. All thirty-two (100%) isolates that were classified as biofilm producers contained all genes. There was an association between the presence of pelA and rhlA and biofilm production (P < 0.017) and between the presence of rhlA and pelA and the quantity of biofilm produced (both P < 0.001). These results highlight that biofilm formation of Pseudomonas aeruginosa otic isolates does occur and can impact antimicrobial therapy. Certain compounds can also influence antimicrobial susceptibility of biofilm-embedded bacteria. Genetics may also play a role in biofilm formation.