Pharmacodynamics of moxifloxacin versus vancomycin against biofilms of methicillin-resistant Staphylococcus aureus and epidermidis in an in vitro model

Pharmacodynamics of Moxifloxacin, Meropenem, Caspofungin and their Combinations Against In Vitro Polymicrobial Inter-kingdom Biofilms

Biofilms colonize medical devices and are often recalcitrant to antibiotics. Inter-kingdom biofilms, when at least a bacterium and a fungus are co-isolated, increase the likelihood of therapeutic failures. In this work, a three-species in vitro biofilm model including S. aureus, E. coli and C. albicans was used to study the activity of the antibiotics moxifloxacin and meropenem, the antifungal caspofungin, and combinations of them against inter-kingdom biofilms. The culturable cells and total biomass were evaluated to determine the pharmacodynamic parameters of the drug response for the incubation with the drugs alone. The synergic or antagonistic effects (increased/decreased effects) of the combination of drugs were analysed with the highest single agent method. Biofilms were imaged in confocal microscopy after live/dead staining. The drugs had limited activity when used alone against single-, dual- or three-species biofilms. When used in combination, additive effects were observed against single- or dual-species biofilms, and increased effects (synergy) against biomass of three-species biofilms. In addition, the two antibiotics showed different patterns, moxifloxacin being more active when targeting S. aureus and meropenem when targeting E. coli. All these observations were confirmed by confocal microscopy images. Our findings highlight the interest in combining caspofungin with antibiotics against inter-kingdom biofilms.

Nanobiotic formulations as promising advances for combating MRSA resistance: susceptibilities and post-antibiotic effects of clindamycin, doxycycline, and linezolid

Antimicrobial activity and post-antibiotic effects (PAEs) are both important parameters in determination of the dosage regimen of antimicrobial agents. In the present study, antimicrobial activity and PAEs of clindamycin, doxycycline, linezolid, and their nanobiotic formulations were evaluated against two methicillin resistant Staphylococcus aureus clinical isolates (MRSA) encoded (MRSA-S1 and MRSA-S2). Nanobiotic formulations increased the susceptibility of MRSA isolates by 4-64 folds as compared to their conventional ones. The PAE values were determined after exposure of MRSA isolates for 1 h to 10× the MICs of the tested antibiotics. The duration of PAEs were recorded after bacterial growth in Mueller Hinton broth (MHB) free from antibiotic has been restored. The PAE values for MRSA-S1 were 2.5 h for the conventional antibiotics. However, the PAEs for nanobiotics were 4 h for both clindamycin and linezolid, while 3 h for doxycycline. For MRSA-S2, linezolid and linezolid nanobiotics PAEs were 3 h. PAEs of clindamycin and clindamycin nanobiotics were 3.75 h and 4 h, respectively. Doxycycline and doxycycline nanobiotics revealed the same PAEs patterns of 3.5 h. The findings of the current study may positively influence the pharmacodynamics of the antibiotics and consequently the dosage regimen of nanobiotics as well as on their clinical outcome.

Activity of Antibiotics against Staphylococcus aureus in an In Vitro Model of Biofilms in the Context of Cystic Fibrosis: Influence of the Culture Medium

Staphylococcus aureus is a highly prevalent pathogen in the respiratory tract of young patients with cystic fibrosis (CF) and causes biofilm-related infections. Here, we set up an in vitro model of a biofilm grown in Trypticase soy broth supplemented with glucose and NaCl (TGN) or in artificial sputum medium (ASM) and used it to evaluate on a pharmacodynamic basis the activity of antibiotics used in CF patients and active on staphylococci (meropenem, vancomycin, azithromycin, linezolid, rifampin, ciprofloxacin, tobramycin). Rheological studies showed that ASM was more elastic than viscous, as was also observed for sputa from CF patients, with elastic and viscous moduli being, respectively, similar to and slightly lower than those of CF sputa. Biofilms formed by methicillin-sensitive S. aureus strain ATCC 25923 and methicillin-resistant S. aureus strain ATCC 33591 reached maturity after 24 h, with biomass (measured by crystal violet staining) and metabolic activity (assessed by following resazurin metabolization) being lower in ASM than in TGN and viability (assessed by bacterial counts) being similar in both media. Full concentration-response curves of antibiotics obtained after 24 h of incubation of biofilms showed that all antibiotics were drastically less potent and less efficient in ASM than in TGN toward viability, metabolic activity, and biomass. Tobramycin selected for small-colony variants, specifically in biofilms grown in ASM; the auxotrophism of these variants could not be established. These data highlight the major influence exerted by the culture medium on S. aureus responsiveness to antibiotics in biofilms. The use of ASM may help to determine effective drug concentrations or to evaluate new therapeutic options against biofilms in CF patients.

In Vitro Comparison of Antibacterial and Antibiofilm Activities of Selected Fluoroquinolones against Pseudomonas aeruginosa and Methicillin-Resistant Staphylococcus aureus

An in vitro overview of the inhibitory effects of selected fluoroquinolones against planktonic and biofilm cells of the methicillin-resistant Staphylococcus aureus (MRSA) strain American type culture collection (ATCC) 43300 and the Pseudomonas aeruginosa strain ATCC 27853 was carried out. Biofilm cells of both strains were less susceptible to the selected antibiotics than their planktonic counterparts. In addition, certain antibiotics were more effective against biofilm cells, while others performed better on the planktonic cells. Against P. aeruginosa, ciprofloxacin was the most potent on both planktonic and biofilm cells, whereas ofloxacin was the least potent on both biofilm and planktonic cells. Moxifloxacin and gatifloxacin were the most potent against both planktonic and biofilm MRSA bacteria, however, not in the same order of activity. Norfloxacin was the least active when tested against both planktonic and biofilm cells. The results of this work are expected to provide insight into the efficacy of various fluoroquinolones against MRSA and Pseudomonas aeruginosa biofilms. This study could form the basis for future clinical studies that could recommend special guidelines for the management of infections that are likely to involve bacteria in their biofilm state.

Newer antibiotics for the treatment of peritoneal dialysis-related peritonitis

Peritonitis is a debilitating infectious complication of peritoneal dialysis (PD). Drug-resistant bacterial peritonitis typically has a lower response rate to antibiotics. In the past 15 years, newer antibiotics with activities against drug-resistant Gram-positive bacteria have been developed. In most circumstances, peritonitis due to methicillin-resistant staphylococci responds to vancomycin. If vancomycin cannot be used due to allergy and/or non-susceptibility, there is increasing evidence that linezolid and daptomycin are the drugs of choice. It is reasonable to start linezolid orally or intravenously, but subsequent dose reduction may be necessary in case of myelosuppression. Daptomycin can be given intravenously or intraperitoneally and has excellent anti-biofilm activity. Other treatment options for drug-resistant Gram-positive bacterial peritonitis include teicoplanin, tigecycline and quinupristin/dalfopristin. Teicoplanin is not available in some countries (e.g. the USA). Tigecycline can only be given intravenously. Quinupristin/dalfopristin is ineffective against Enterococcus faecalis and there is only low-quality evidence to support its efficacy in the treatment of peritonitis. Effective newer antibiotics against drug-resistant Gram-negative bacteria are lacking. Polymyxins can be considered, but evidence on its efficacy is limited. In this review, we will discuss the potential use of newer antibiotics in the treatment of drug-resistant bacterial peritonitis in PD patients.

Current concepts on the virulence mechanisms of meticillin-resistant Staphylococcus aureus

Meticillin-resistant Staphylococcus aureus (MRSA) strains are prevalent bacterial pathogens that cause both health care and community-associated infections. Increasing resistance to commonly prescribed antibiotics has made MRSA a serious threat to public health throughout the world. The USA300 strain of MRSA has been responsible for an epidemic of community-associated infections in the US, mostly involving skin and soft tissue but also more serious invasive syndromes such as pneumonia, severe sepsis and endocarditis. MRSA strains are particularly serious and potentially lethal pathogens that possess virulence mechanisms including toxins, adhesins, enzymes and immunomodulators. One of these is Panton-Valentine leukocidin (PVL), a toxin associated with abscess formation and severe necrotizing pneumonia. Earlier studies suggested that PVL was a major virulence factor in community-associated MRSA infections. However, some recent data have not supported this association while others have, leading to controversy. Therefore, investigators continue to search for additional mechanisms of pathogenesis. In this review, we summarize the current understanding of the biological basis of MRSA virulence and explore future directions for research, including potential vaccines and antivirulence therapies under development that might allow clinicians to more successfully treat and prevent MRSA infections.