Diarrhoea remains an important public health concern, particularly in developing countries, and has become difficult to treat because of antibacterial resistance. The development of synergistic antimicrobial agents appears to be a promising alternative treatment against diarrhoeic infections. In this study, the combined effect of tetracycline together with either nitroxoline, sanguinarine, or zinc pyrithione (representing various classes of plant-based compounds) was evaluated in vitro against selected diarrhoeic bacteria (Enterococcus faecalis, Escherichia coli, Listeria monocytogenes, Shigella flexneri, Vibrio parahaemolyticus, and Yersinia enterocolitica). The chequerboard method in 96-well microtiter plates was used to determine the sum of the fractional inhibitory concentration indices (FICIs). Three independent experiments were performed per combination, each in triplicate. It was observed that the combination of tetracycline with either nitroxoline, sanguinarine, or zinc pyrithione produced synergistic effects against most of the pathogenic bacteria tested, with FICI values ranging from 0.086 to 0.5. Tetracycline–nitroxoline combinations produced the greatest synergistic action against S. flexneri at a FICI value of 0.086. The combinations of the agents tested in this study can thus be used for the development of new anti-diarrhoeic medications. However, studies focusing on their in vivo anti-diarrhoeic activity and safety are required before any consideration for utilization in human medicine.

Musculoskeletal infections (MIs) are among the most difficult-to-treat staphylococcal diseases due to antibiotic resistance. This has encouraged the development of innovative strategies, such as combination therapy, to combat MI. The aim of this study was to investigate the in vitro antistaphylococcal activity of anti-inflammatory drugs and the combined antimicrobial effect of celecoxib and oxacillin. The minimum inhibitory concentrations (MICs) of 17 anti-inflammatory drugs against standard strains and clinical isolates of S. aureus, including methicillin-resistant strains (MRSAs), were determined using the broth microdilution method. The fractional inhibitory concentration indices (FICIs) were evaluated using checkerboard assays. Celecoxib produced the most potent antistaphylococcal effect against all tested strains (MICs ranging from 32 to 64 mg/L), followed by that of diacerein against MRSA3 and MRSA ATCC 33592 (MIC 64 mg/L). Several synergistic effects were observed against the tested S. aureus strains, including MRSA (FICI ranging from 0.087 to 0.471). The strongest synergistic interaction (FICI 0.087) was against MRSA ATCC 33592 at a celecoxib concentration of 2 mg/L, with a 19-fold oxacillin MIC reduction (from 512 to 26.888 mg/L). This is the first report on the combined antistaphylococcal effect of celecoxib and oxacillin. These findings suggest celecoxib and its combination with oxacillin as perspective agents for research focused on the development of novel therapies for MI caused by S. aureus. This study further indicates that celecoxib could resensitize certain MRSA strains, in some cases, to be susceptible to β-lactams (e.g., oxacillin) that were not previously tested. It is essential to mention that the in vitro concentrations of anti-inflammatory drugs are higher than those typically obtained in patients. Therefore, an alternative option for its administration could be the use of a drug delivery system for the controlled slow release from an implant at the infection site.

Diarrhea-related mortality remains an important public health concern, particularly in developing countries, and has become difficult to treat because of antibacterial resistance. The development of synergistic antimicrobial agents appears to be a promising alternative treatment against diar-rheal infections. In this study, the combined effect of tetracycline together with either nitroxoline, sanguinarine, or zinc pyrithione (representing various classes of alkaloid-related compounds) was evaluated in vitro against selected diarrheagenic bacteria (Enterococcus faecalis, Escherichia coli, Listeria monocytogenes, Shigella flexneri, Vibrio parahaemolyticus, and Yersinia enterocolitica). The chequerboard method in 96-well microtiter plates was used to determine the sum of the fractional inhibitory concentration indices (FICIs). Three independent experiments were performed per combination, each in triplicate. It was observed that the combinations of tetracycline with either nitroxoline, sanguinarine, or zinc pyrithione produced synergistic effects against most of the pathogenic bacteria tested, with FICI values ranging from 0.086 to 0.5. Tetracycline-nitroxoline combinations produced the greatest synergistic action against S. flexneri at a FICI value of 0.086. Combinations of the agents tested in this study can thus be used for the development of new anti-diarrheal medications. However, studies focusing on their in vivo anti-diarrheal activity and safety are required before any consideration for utilization in human medicine.

Musculoskeletal infections (MIs) are among the most difficult-to-treat staphylococcal diseases. The limited availability of effective antibiotics has encouraged the development of innovative strategies such as combinatory therapy to combat MI. The aim of this study was to investigate the in vitro antistaphylococcal activity of anti-inflammatory and the antimicrobial combinatory effect of celecoxib with oxacillin. The minimum inhibitory concentrations (MICs) of 17 anti-inflammatory drugs were determined for standard strains and clinical isolates of S. aureus strains, counting methicillin-resistant strains (MRSA), by the broth microdilution method. The fractional inhibitory concentration indices (FICIs) were evaluated by the checkerboard assays. Celecoxib produced the most potent antistaphylococcal effect against all the tested strains (MIC ranging from 32 to 64 mg/mL), followed by diacerein against MRSA3 and MRSA ATCC 33592 (MIC 64 mg/mL). Several synergistic effects were observed for tested S. aureus strains, including MRSA (FICI ranging from 0.087 to 0.471). The strongest synergistic interaction (FICI 0.087) was obtained against MRSA ATCC 33592 at a celecoxib concentration of 2 mg/mL with a 19-fold oxacillin MIC reduction (from 512 to 26.888 mg/mL). This is the first report on the antistaphylococcal combinatory effect of celecoxib with oxacillin. Our findings suggest celecoxib and its combination with oxacillin as perspective agents for research focused on the development of novel therapies for MI caused by S. aureus. Thus, this study presents novel findings that celecoxib could, in some cases, resensitise MRSA strains to become susceptible to certain β-lactams (e.g., oxacillin) not previously tested.