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

Pseudomonas aeruginosa, an important human opportunistic pathogen responsiblefor lethal nosocomial infections, as emerged as a relevant animal pathogen. Treatmentoptions are dramatically declining worldwide, due to massive antibiotic use and themicroorganism large versatile genome. Low cell wall permeability may account forintrinsic antimicrobial resistance, besides the ability of P. aeruginosa to express acquiredresistance mechanisms. Virulence can be further enhanced by other characteristics, suchas production of β-lactamases and carbapenemases and biofilm expression, whichfacilitates bacterial persistence in the host, evading the immunological defences andsurviving 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 investigatethe relation between biofilm-forming ability and antimicrobial resistance. Susceptibilityto 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) andtobramicin (TOB) was evaluated by the disk diffusion method according to the Clinical Laboratory Standards Institute (CLSI) guidelines. Direct observation of biofilm formationby bacterial suspensions at different incubation times (24h, 48h, 72h) was performedthrough Fluorescent In Situ Hybridization (FISH). Relations between antimicrobialresistance and biofilm production were evaluated, as well as the significance of theincrease of biofilm-producer isolates with time (Wilcoxon Signed Ranks Test).Antimicrobial resistance was similar amongst all isolates, showing high resistance tothe 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 percentagesignificantly increased with time. A significant relation was also found between biofilmproduction at 72h and antimicrobial resistance to most of the drugs tested, with theexception for CAR, CFP, ENR and GEN.Monitoring biofilm production and antibiotic resistance of P. aeruginosa animalisolates may provide accurate information on prevalence of virulence traits, contributingto elucidate on potential virulence transmission to humans and to a better understandingof the development and the epidemiology of P. aeruginosa multi-drug resistance in ourdensely populated biosphere with increasing human-animal interactions.