Impact of erythrocytes on bacterial growth and antimicrobial activity of selected antibiotics

Abstract

It has been shown that protein binding, temperature, and pH influence in vitro pharmacodynamic (PD) models. The fact that corpuscular blood compounds might also have an important impact is something which has, until now, often been neglected. We investigated if the addition of human erythrocytes to standard growth media (Mueller Hinton Broth, MHBII) has an influence on bacterial growth behavior and on antibiotic efficacy. We did this by using bacterial growth assays and time kill curves (TKC) of selected strains ( Escherichia coli ATCC25922, Staphylococcus aureus ATCC29213, and Pseudomonas aeruginosa ATCC27853) over 24 h. The final concentration of erythrocytes was set to match the physiological concentrations in the blood of a healthy human, i.e., 3 × 10^6 cells/μl in MHBII. Meropenem, ciprofloxacin, and tigecycline were tested with concentrations several-fold above and below the minimal inhibitory concentration (MIC). Moreover, HPLC analysis of antibiotic stability and distribution in erythrocytes was performed. Meropenem, ciprofloxacin, and tigecycline showed the greatest decline in activity against E. coli when erythrocytes were present. A mean difference in log10 bacterial killing between pure MHBII and 50%-Ery of 3.83, 1.33, and 2.42 was found for ciprofloxacin, meropenem, and tigecycline, respectively. In the case of ciprofloxacin, HPLC analysis revealed that less extracellular antibiotic is available in the presence of erythrocytes. We have demonstrated that erythrocytes do influence antimicrobial activity and that this might have an impact on the extrapolation of in vitro activity testing to in vivo efficacy in patients.

Impact of thrombocytes, on bacterial growth and antimicrobial activity of selected antibiotics

“…Analysis was done for MHB Throm and MHB Ref , for ciprofloxacin and meropenem at a final concentration of 0.1 μg/mL and at 1 μg/mL for tigecycline. The procedure was performed in analogy to erythrocyte experiments recently published [4].…”

“…Therefore, the impact of potential factors on the interplay between pathogens and antimicrobial agents should be individually assessed. Host factors such as pH, protein binding, and cations, as well as corpuscular blood components such as erythrocytes have been shown to impact activity of antibiotics and/or growth of the pathogen [1][2][3][4]. Nevertheless, the impact of thrombocytes, which may be equally relevant, has not previously been investigated.…”

Use of Supplemented or Human Material to Simulate PD Behavior of Antibiotics at the Target Site In Vitro

“…Even though 100% serum might be a good option to resemble in vivo conditions, studies have already shown that pure serum is less optimal in terms of bacterial growth compared to standard growth media, such as MHB [ 19 , 37 ]. Thus, many studies test the impact of the addition of serum to growth media in various concentrations, ranging from 20% to 100% [ 16 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 ].…”

Adsorption of vancomycin, gentamycin, ciprofloxacin and tygecycline on the filters in continuous renal replacement therapy circuits: in full blood in vitro study

“…Another important factor playing a role in adsorption of antibiotics on filter membrane is the presence of blood proteins and cellular blood components [ 11 , 12 ]. The presence of proteins and erythrocytes decreases the free fraction of a drug available for binding to filter membrane, but on the other hand proteins bound to antibiotics may also be adsorbed on the filter [ 11 ].…”

“…Another important factor playing a role in adsorption of antibiotics on filter membrane is the presence of blood proteins and cellular blood components [ 11 , 12 ]. The presence of proteins and erythrocytes decreases the free fraction of a drug available for binding to filter membrane, but on the other hand proteins bound to antibiotics may also be adsorbed on the filter [ 11 ]. There may be two stages of serum protein adsorption on the filter surface: the first one involving adsorption of proteins with high molecular weight on the filter surface (for example albumins) and the second stage consisting in adsorption of proteins inside the membrane (proteins of low or medium molecular weight).…”