Biofilm-forming ability and antimicrobial resistance of pseudomonas aeruginosa isolates of veterinary origin

Pseudomonas aeruginosa, an important human opportunistic pathogen responsible for lethal nosocomial infections, as emerged as a relevant animal pathogen. Treatment options are dramatically declining worldwide, due to massive antibiotic use and the microorganism large versatile genome. Low cell wall permeability may account for intrinsic antimicrobial resistance, besides the ability of P. aeruginosa to express acquired resistance mechanisms. Virulence can be further enhanced by other characteristics, such as production of β-lactamases and carbapenemases and biofilm expression, which facilitates bacterial persistence in the host, evading the immunological defences and surviving at high antibiotic concentrations.The present work studied P. aeruginosa isolates of veterinary origin (n=34), including house pets, farm and zoo animals with clinical signs of infection, to investigate the relation between biofilm-forming ability and antimicrobial resistance. Susceptibility to amikacin (AK), amoxicillin/clavulanic acid (AMC), ampicillin (AMP), chloranfenicol (C), carbenicillin (CAR), ceftazidime (CAZ), cephoperazone (CFP), ciprofloxacin (CIP), cephalexin (CL), cephotaxim (CTX), enrofloxacin (ENR), gentamicin (GEN), imipinem (IPM), nalidixic acid (NA), ofloxacin (OFX), penicillin G (P), piperacillin (PRL), streptomycin (S), sulphametoxazole/trimethroprim (SXT), tetracycline (TE) and tobramicin (TOB) was evaluated by the disk diffusion method according to the Clinical Laboratory Standards Institute (CLSI) guidelines. Direct observation of biofilm formation by bacterial suspensions at different incubation times (24h, 48h, 72h) was performed through Fluorescent In Situ Hybridization (FISH). Relations between antimicrobial resistance and biofilm production were evaluated, as well as the significance of the increase of biofilm-producer isolates with time (Wilcoxon Signed Ranks Test).Antimicrobial resistance was similar amongst all isolates, showing high resistance to the majority of the drugs tested. None of the isolates was susceptible to all antimicrobials, while most possessed multi-resistance profiles. Resistance percentages were: AMC, AMP, CL, CTX, NA, P, TE - 100%; C - 97.96%; SXT - 97.06%; S - 88.24%; ENR - 61.76%; CAR - 67.65%; GEN - 47.06%; CFP - 44.12%; AK - 32.35%; PRL - 29.41%; OFX - 23.53%; CIP - 17.65%; CAZ - 11.76%; IPM, TOB - 5.88%.About 18% of the isolates could produce biofilm at 24h, and this percentage significantly increased with time. A significant relation was also found between biofilm production at 72h and antimicrobial resistance to most of the drugs tested, with the exception for CAR, CFP, ENR and GEN.Monitoring biofilm production and antibiotic resistance of P. aeruginosa animal isolates may provide accurate information on prevalence of virulence traits, contributing to elucidate on potential virulence transmission to humans and to a better understanding of the development and the epidemiology of P. aeruginosa multi-drug resistance in our densely populated biosphere with increasing human-animal interactions.