The formation of a protective biofilm by Pseudomonas aeruginosa (PA) is one of the hallmarks of their survival both in vivo and in harsh environmental conditions, thus, biofilm-eradication has relevance from therapeutic perspectives and for infection control. The aim of our study was to investigate the possible relationship between antibiotic resistance, biofilm-forming capacity and virulence factors in n = 166 PA isolates of environmental origin. Antimicrobial susceptibility testing and the phenotypic detection of resistance determinants were carried out using standard protocols. The biofilm-forming capacity of PA was tested using a standardized crystal violet microtiter plate-based method. Motility (swimming, swarming, and twitching) and siderophore production of the isolates were also assessed. Resistance rates were highest for ciprofloxacin (46.98%), levofloxacin (45.18%), ceftazidime (31.92%) and cefepime (30.12%); 19.28% of isolates met the criteria to be classified as multidrug-resistant (MDR). Efflux pump overexpression, AmpC overexpression, and modified Hodge-test positivity were noted in 28.31%, 18.07% and 3.61%, respectively. 22.89% of isolates were weak/non-biofilm producers, while 27.71% and 49.40% were moderate and strong biofilm producers, respectively. Based on MDR status of the isolates, no significant differences in biofilm-production were shown among environmental PA (non-MDR OD₅₇₀ [mean ± SD]: 0.416 ± 0.167 vs. MDR OD₅₇₀: 0.399 ± 0.192; p > 0.05). No significant association was observed between either motility types in the context of drug resistance or biofilm-forming capacity (p > 0.05). 83.13% of isolates tested were positive for siderophore production. The importance of PA as a pathogen in chronic and healthcare-associated infections has been described extensively, while there is increasing awareness of PA as an environmental agent in agriculture and aquaculture. Additional studies in this field would be an important undertaking to understand the interrelated nature of biofilm production and antimicrobial resistance, as these insights may become relevant bases for developing novel therapeutics and eradication strategies against PA.

Staphylococcus species are considered important members of the normal skin microbiota, in addition to being common pathogens in human and animal infections. In addition to S. aureus, other members of the genus are now widely-recognized as pathogens, especially in immunocompromised individuals. One of the most important virulence factors of staphylococci is the formation of biofilm (slime), which enhances their survival on inanimate surfaces, in addition to providing protection against immune cells and antibiotics in vivo. There has been considerable interest in the study of the relationship between biofilm formation and the antibiotic resistant phenotype, however, the results in the available literature are inconsistent. Thus, this study aims to investigate the correlation between biofilm formation and antibiotic resistance in Staphylococcus spp. isolates using phenotypic methods. One hundred and eighty (n = 180) isolates were included in the study, with S. epidermidis (40.0%) and S. lugdunensis (10.0%) being the most numerous. Biofilm-forming capacity was assessed by means of the crystal violet microtiter-plate-based (CV-MTP) method. Methicillin-resistance (MR) was identified in 47.2% (n = 85) of isolates. Among the commonly-used antimicrobials, resistance was highest for clindamycin (51.1%), erythromycin (48.9%) and trimethoprim-sulfamethoxazole (51.1%). Based on the CV-MTP method, n = 13 (7.2%), n = 13 (7.2%), n = 42 (23.3%) and n = 113 (62.3%) staphylococcal isolates were non-biofilm-producing, weak, moderate and strong biofilm producers, respectively. No significant differences in biofilm-formation were shown to be observed on the basis of MR (susceptible (S): 0.881 ± 0.309 vs. resistant (R): 0.890 ± 0.347; p = 0.133) and according to the resistance, to most other antibiotics. Rifampin-resistant isolates were more potent biofilm-producers than their susceptible counterparts (S: 0.802 ± 0.296 vs. R: 1.194 ± 0.221; p = 0.024). The association of the antibiotic-resistant phenotype and biofilm-formation is still inconclusive, due to the heterogeneity of the results in presently available studies; however, the understanding of these mechanisms in Staphylococcus spp. is crucial to appropriately address the therapy and eradication of these pathogens.