Table 2.

Main findings pertinent to antibacterial activity studies of clioquinol.

Antibacterial clioquinol
References	Species	Methodology	Findings
Chan et al. (2020)	Pseudomonas aeruginosa Acinetobacter baumannii	a) The ability of clioquinol and the other antimicrobials to form iron complexes (by adding FeCl3) was evaluated. These iron complexes are visualized by the intensity of the red coloration of the reaction medium, whose absorbance was measured by spectroscopy b) The ability of clioquinol and other antimicrobials to synergize with thiostreptone against P. aeruginosa and A. baumannii inoculums, obtained from clinical isolates, was verified by a 3D checkerboard test. The same test was performed against a hyper-resistant mutant strain of P. aeruginosa	a) The paper proposed optimizing the antimicrobial profile of a natural compound (thiostreptone) by combining it with other molecules of proven efficacy and safety b) At 1 µg/mL concentration, clioquinol showed strong synergy with thiostreptone, effectively inhibiting the growth of A. baumannii
Magallon et al. (2019)	Acinetobacter baumannii	a) The enzymatic acetylation capacity of the A. baumannii strains was tested using the phosphocellulose paper binding assay, with Acetyl Coenzyme A and Amikacin as the substrate for the reactions b) Time-kill and growth inhibition assay were performed for clioquinol against the three strains of A. baumannii, at indicated concentrations of amikacin, ionophore and zinc c) Using the LIVE/DEAD Kit to determine Cell Viability/Cytotoxicity, cytotoxicity assays were carried out for the evaluated molecules (in serial dilutions in DMSO) against A. baumannii	a) Shows the capacity of clioquinol and pyrithione to complex with ions such as Zn+2 and Cu+2, considering this property as part of the mechanism of action of the substances b) According to the results of the Time-Kill test and cytotoxicity curves for clioquinol against the three tested strains of A. baumannii, the compound showed to be excellent candidate as antimicrobial adjuvant to reduce amikacin resistance
Blanco et al. (2018)	Stenotrophomonas maltophilia	a) S. maltophilia strains PBT02, PBT03, and PBT10, which are reporter strains (encoding different efflux pumps and resistance mechanisms of the bacterium), were used b) Combining the use of Biolog Phenotype Microarrays technology with RT-PCR, clioquinol (and other antimicrobials) was evaluated to induce the expression of the smeVWX and smeYZ genes consequently, of efflux pumps	a) The work revealed that the mechanism of bacterial resistance induction by clioquinol is selective. The compound was a strong resistance inducer of the studied S. maltophilia strain PBT02
Salah and Faergemann (2015)	Staphylococcus aureus Streptococcus A Streptococcus B Streptococcus C Streptococcus G	a) A retrospective comparative analysis was performed on patients diagnosed with atopic dermatitis and impetigo at the Department of Dermatology, Sahlgrenska University Hospital. They were positive for S. aureus and Streptococcus ssp. skin swabs from 2005 to 2011 b) These patients were divided into 4 groups, which were compared in terms of age, sex, diagnosis, and choice of antimicrobial treatment	a) Use of clioquinol in clinical practice, in treating atopic dermatitis and impetigo (in association with betamethasone) in the Betnovat® topical formulation, which proved to be the main choice of topical treatment for these pathologies b) According to the study, the synergistic effect of the anti-inflammatory compound and the antimicrobial compound makes the Betnovat® formulation the preferable choice in treating infected dermatoses
Majumdar et al. (2013)	Klebsiella pneumoniae	a) The assays were performed with several strains of K. pneumoniae, including: a deleterious mutant for the rarA gene and the other naturally containing the rarA gene b) Growth curves were performed for strains of K. pneumoniae in the presence of 1% and 5% of Sodium Dodecyl Sulfate (SDS), and in the presence of 60 µg/ml of clioquinol c) The Biolog system was used for phenotypic monitoring of the growth of the two studied strains of K. pneumoniae, in presence of clioquinol	a) Elucidated the role of the rarA gene, present in K. pneumoniae, which encodes numerous resistance mechanisms to multiple antimicrobial drugs b) Presented the possible mechanism by which rarA confers clioquinol resistance to carrier bacteria: increased expression of nitric oxide synthase, since NO acts as an endogenous attenuator of the pharmacological action of clioquinol
Loock (2012)	Proteus ssp. Pseudomonas aeruginosa Staphylococcus aureus	a) The trial consisted of a single-blind randomized controlled trial, following the CONSORT group guidelines (http://www.consort-statement.org) b) Patients over 6 years of age with otorrheal symptoms diagnosed with chronic otitis media at the Tygerberg Hospital Otology Clinic (South Africa) were included in the study. These were divided into 3 groups c) Randomization was generated via a computer program (Randomisation.com), through which the pharmacist was instructed to dispense numbered envelopes (containing the treatment) according to the randomized sequence generated by the computer. Following this sequence, the nurses administered the treatment contained in each envelope to the study participants d) The treatments evaluated included 1% acetic acid, boric acid (50 g), ciprofloxacin hydrochloride eardrops 3 mg/mL, Quadriderm® (ointment composed of betamethasone valerate, gentamicin sulfate, tolnaftate, and clioquinol)	a) Even though Quadriderm® is considered the second line of treatment for patients with chronic otitis media, it proved to be the most effective among the treatment options tested, being able to provide relief from the symptoms presented by patients as early as the first application in the external auditory canal