Thigh Muscle Infection Research Articles

Multimodal Tracking of Controlled Staphylococcus aureus Infections in Mice.

There is a need to develop diagnostic and analytical tools that allow noninvasive monitoring of bacterial growth and dissemination in vivo. For such cell-tracking studies to hold translational value to controlled human infections, in which volunteers are experimentally colonized, they should not require genetic modification, and they should allow tracking over a number of replication cycles. To gauge if an antimicrobial peptide tracer, 99mTc-UBI29–41-Cy5, which contains both a fluorescent and a radioactive moiety, could be used for such in vivo bacterial tracking, we performed longitudinal imaging of a thigh-muscle infection with 99mTc-UBI29–41-Cy5-labeled Staphylococcus aureus. Mice were imaged using SPECT and fluorescence-imaging modalities at various intervals during a 28 h period. Biodistribution analyses were performed to quantitate radioactivity in the abscess and other tissues. SPECT and fluorescence imaging in mice showed clear retention of the 99mTc-UBI29–41-Cy5-labeled bacteria following inoculation in the thigh muscle. Despite bacterial replication, the signal intensity in the abscess only modestly decreased within a 28 h period: 52% of the total injected radioactivity per gram of tissue (%ID/g) at 4 h postinfection (pi) versus 44%ID/g at 28 h pi (15% decrease). After inoculation, a portion of the bacteria disseminated from the abscess, and S. aureus cultures were obtained from radioactive urine samples. Bacterial staining with 99mTc-UBI29–41-Cy5 allowed noninvasive bacterial-cell tracking during a 28 h period. Given the versatility of the presented bacterial-tracking method, we believe that this concept could pave the way for precise imaging capabilities during controlled-human-infection studies.

Killing of Staphylococcus aureus and Salmonella enteritidis and neutralization of lipopolysaccharide by 17-residue bovine lactoferricins: improved activity of Trp/Ala-containing molecules

Bovine lactoferricin (LfcinB) has potent antibacterial, antifungal and antiparasitic activities but is also hemolytic. Our objective was to identify LfcinB17-31 derivatives with reduced hemolysis and improved antimicrobial activity via substituting Cys3, Arg4, Gln7, Met10, and Gly14 with more hydrophobic residues. Two peptides, Lfcin4 and Lfcin5, showed higher activity against Staphylococcus aureus and Salmonella enteritidis and lower hemolytic activity than the parent peptide LfcinB17-31. These peptides permeabilized the outer and inner membranes of S. enteritidis; however, Lfcin5 did not permeabilize the inner membrane of S. aureus. Gel retardation and circular dichroism spectra showed that Lfcin4 and Lfcin5 bound to bacterial genomic DNA. Lfcin4 inhibited DNA, RNA and protein synthesis. Both peptides induced the peeling of membranes and the lysis of S. enteritidis. At doses of 10 and 15 mg/kg, Lfcin4 and Lfcin5 reduced the bacterial counts in infected thigh muscles by 0.03‒0.10 and 0.05‒0.63 log10 CFU/g of tissue, respectively, within 10 h. Lfcin4 and Lfcin5 enhanced the survival rate of endotoxemic mice; reduced serum IL-6, IL-1β and TNF-α levels; and protected mice from lipopolysaccharide-induced lung injury. These data suggest that Lfcin4 and Lfcin5 may be antimicrobial and anti-endotoxin peptides that could serve as the basis for the development of dual-function agents.

Synthesis, 68Ga-radiolabeling, and preliminary in vivo assessment of a depsipeptide-derived compound as a potential PET/CT infection imaging agent.

Noninvasive imaging is a powerful tool for early diagnosis and monitoring of various disease processes, such as infections. An alarming shortage of infection-selective radiopharmaceuticals exists for overcoming the diagnostic limitations with unspecific tracers such as 67/68Ga-citrate or 18F-FDG. We report here TBIA101, an antimicrobial peptide derivative that was conjugated to DOTA and radiolabeled with 68Ga for a subsequent in vitro assessment and in vivo infection imaging using Escherichia coli-bearing mice by targeting bacterial lipopolysaccharides with PET/CT. Following DOTA-conjugation, the compound was verified for its cytotoxic and bacterial binding behaviour and compound stability, followed by 68Gallium-radiolabeling. µPET/CT using 68Ga-DOTA-TBIA101 was employed to detect muscular E. coli-infection in BALB/c mice, as warranted by the in vitro results. 68Ga-DOTA-TBIA101-PET detected E. coli-infected muscle tissue (SUV = 1.3–2.4) > noninfected thighs (P = 0.322) > forearm muscles (P = 0.092) > background (P = 0.021) in the same animal. Normalization of the infected thigh muscle to reference tissue showed a ratio of 3.0 ± 0.8 and a ratio of 2.3 ± 0.6 compared to the identical healthy tissue. The majority of the activity was cleared by renal excretion. The latter findings warrant further preclinical imaging studies of greater depth, as the DOTA-conjugation did not compromise the TBIA101's capacity as targeting vector.

Radiosynthesis and biological evaluation of a novel enoyl-ACP reductase inhibitor for Staphylococcus aureus.

The pharmacokinetics (PK) and pharmacodynamics (PD) of PT119, a potent Staphylococcus aureus enoyl-ACP reductase (saFabI) inhibitor with a Ki value of 0.01 nM and a residence time of 750 min on the enzyme target, has been evaluated in mice. PT119 was found to have promising antibacterial activity in two different S. aureus infection models: it caused a 3 log reduction in the CFU's in a mouse thigh muscle infection model and increased the survival rate from 0% to 50% in a mouse systemic infection model. PT119 was then radiolabeled with carbon-11 to evaluate its biodistribution and PK in both healthy and S. aureus infected mice using positron emission tomography (PET). The biodistribution of [11C]PT119 and/or its labeled metabolites did not differ significantly between the healthy group and the infected group, and PT119 was found to distribute equally between serum and tissue during the ∼1 h of analysis permitted by the carbon-11 half life. This approach provides important data for PK/PD modeling and is the first step in identifying radiotracers that can non-invasively image bacterial infection in vivo.

Bioluminescence and 19 F Magnetic Resonance Imaging Visualize the Efficacy of Lysostaphin Alone and in Combination with Oxacillin against Staphylococcus aureus in Murine Thigh and Catheter-Associated Infection Models

Staphylococci are the leading cause of hospital-acquired infections worldwide. Increasingly, they resist antibiotic treatment owing to the development of multiple antibiotic resistance mechanisms in most strains. Therefore, the activity and efficacy of recombinant lysostaphin as a drug against this pathogen have been evaluated. Lysostaphin exerts high levels of activity against antibiotic-resistant strains of Staphylococcus aureus, including methicillin-resistant S. aureus (MRSA). The therapeutic value of lysostaphin has been analyzed in two different clinically relevant in vivo models, a catheter-associated infection model and a thigh infection model. We infected mice with luciferase-expressing S. aureus Xen 29, and the efficacies of lysostaphin, vancomycin, oxacillin, and combined lysostaphin-oxacillin were investigated by determining numbers of CFU, detecting bioluminescent signals, and measuring the accumulation of perfluorocarbon emulsion at the site of infection by (19)F magnetic resonance imaging. Lysostaphin treatment significantly reduced the bacterial burden in infected thigh muscles and, after systemic spreading from the catheter, in inner organs. The efficiency of lysostaphin treatment was even more pronounced in combinatorial therapy with oxacillin. These results suggest that recombinant lysostaphin may have potential as an anti-S. aureus drug worthy of further clinical development. In addition, both imaging technologies demonstrated efficacy patterns similar to that of CFU determination, although they proved to be less sensitive. Nonetheless, they served as powerful tools to provide additional information about the course and gravity of infection in a noninvasive manner, possibly allowing a reduction in the number of animals needed for research evaluation of new antibiotics in future studies.

99mTc‐Doxycycline hyclate: a new radiolabeled antibiotic for bacterial infection imaging

Radiolabeled antibiotics are promising radiopharmaceuticals for the precise diagnosis and detection of infectious lesions. Doxycycline Hyclate (DOX) was chosen to investigate new (99m) Tc-labeled antibacterial agent. Ready to use freeze dry kits were formulated with optimum labeling conditions. Human serum stability, sterility, and pyrogenicity of kits were estimated, and gamma scintigraphy, in vivo biodistribution, and histopathological studies with bacterial infected rats were performed. DOX were successfully labeled by (99m) Tc with high radiochemical purity, and the labeled compound was stable in human serum. Kits were sterile, pyrogen-free, and stable up to 6 months. Static images depicted rapid distribution throughout the body and high uptake in bacterial infected thigh muscle. The uptake ratios of radiopharmaceuticals in infected thigh muscle were found above 2 up to 5 h. Five hours after injection, the rats were sacrificed, and biodistribution was determined. Samples of bacterial infected muscle, healthy muscle, blood, liver, spleen, lung, kidney, stomach, intestine, urine and heart were weighed, and the radioactivity was measured by using a gamma counter. The %ID/g of (99m) Tc-DOX was found 0.23 ± 0.06 for infected thigh muscle. According to the imaging, biodistribution, and histopathological studies, the promising characteristics of (99m) Tc-DOX make the new radiopharmaceutical valuable to examine for future studies.

Staphylococcal Enterotoxin B–Specific Monoclonal Antibody 20B1 Successfully Treats Diverse Staphylococcus aureus Infections

Methicillin-resistant Staphylococcus aureus (MRSA) has become a major health threat in the United States. Staphylococcal enterotoxin B (SEB) is a potent superantigen that contributes to its virulence. High mortality and frequent failure of therapy despite available antibiotics have stimulated research efforts to develop adjunctive therapies. Treatment benefits of SEB-specific monoclonal antibody (mAb) 20B1 were investigated in mice in sepsis, superficial skin, and deep-tissue infection models. Mice challenged with a SEB-producing MRSA strain developed fatal sepsis, extensive tissue skin infection, and abscess-forming deep-seeded thigh muscle infection. Animals preimmunized against SEB or treated passively with mAb 20B1 exhibited enhanced survival in the sepsis model, whereas decrease of bacterial burden was observed in the superficial skin and deep-tissue models. mAb 20B1 bound to SEB in the infected tissue and decreased abscess formation and proinflammatory cytokine levels, lymphocyte proliferation, and neutrophil recruitment. mAb 20B1, an SEB-neutralizing mAb, is effective against MRSA infection. mAb 20B1 protects against lethal sepsis and reduces skin tissue invasion and deep-abscess formation. The mAb penetrates well into the abscess and binds to SEB. It affects the outcome of S. aureus infection by modulating the host's proinflammatory immune response.

Performance of a 99mTc-labelled 1-thio-β-D-glucose 2,3,4,6-tetra-acetate analogue in the detection of infections and tumours in mice: a comparison with [18F]FDG

The aim of this study was to investigate the differences in biological performance between a technetium-99m (Tc)-labelled glucose derivative, the Tc-labelled 1-thio-beta-D-glucose 2,3,4,6-tetra-acetate analogue (Tc-TG) with F-fluoro-2-deoxy-glucose ([F]FDG). Binding of both tracers was performed in vitro to viable tumour cells and bacteria. Both tracers were injected into mice for targeting Staphylococcus aureus thigh muscle infections and subcutaneous rat lymphoma (RMA) tumours by using scintigraphy, or by radioactivity counts in excised tissues to determine the biodistribution. In-vitro binding studies revealed that both tracers bind more effectively to tumour cells expressing the glucose transporter 1 rather than the glucose transporter 2, and this binding was specific for [F]FDG. Tc-TG shows the highest binding to bacteria and, in addition, gives the highest rate of accumulation in infected thigh muscles in mice. Both tracers were rapidly removed from the circulatory system through the kidneys, and the majority of the injected radioactivity accumulated in the urinary bladder. Two hours after the injection radioactivity accumulation in two high-energy-dependent organs, heart, and liver, increased. Within 15 min of the injections, Tc-TG visualized the site of S. aureus infection or the tumour. We conclude that the new tracer Tc-TG may have potential use as a SPECT agent for infection and tumour imaging.

Could be radiolabeled flavonoid used to evaluate infection?

The aim of this study was to determine whether [131I]apigenin is a powerful and discrimination infection from inflammation for scintigraphic imaging. The study was carried out in inflamed rats with Staphylococcus aureus (S. aureus) and sterile inflamed rats with turpentine oil. Biodistribution study of [131I]apigenin was performed in the rats. Apigenin was labeled with 131I by iodogen method. Obtained [131I]apigenin with high yield (98%) was injected i.v. to both group rats. The results were expressed as the percent uptake of injected dose per gram of organ (%ID/g), the bacterial infected and sterile inflamed muscles. Binding of [131I]apigenin to the infected thigh muscle (target muscle = T) and normal thigh muscle (non-target muscle = NT) ratio (T/NT = 4.51 at 15 min) was higher than binding to bacterial inflamed muscle (T/NT = 2.25 at 15 min) of rats. [131I]apigenin showed good localization in both inflamed tissues. This uptake in the sterile inflamed tissue is higher than bacterial infected tissue. [131I]apigenin might be useful for imaging of inflamed tissues. However, it is not discriminate sterile inflamed tissue from bacterial infected tissue.

Various routes of administration of 99mTc-labeled synthetic lactoferrin antimicrobial peptide hLF 1–11 enables monitoring and effective killing of multidrug-resistant Staphylococcus aureus infections in mice

The synthetic antimicrobial peptide representative of the first 11 N-terminal amino acids of human lactoferrin (hLF 1-11) kills multidrug-resistant Staphylococcus aureus (MRSA). This study displays antimicrobial activity of hLF 1-11, via various routes of administration, against MRSA infections in mice. Radiolabeling hLF 1-11 with technetium-99m ((99m)Tc-hLF 1-11) enables scintigraphic monitoring directly after administration. (99m)Tc-hLF 1-11 was taken up by the gall bladder, intestines, and kidneys. Most of the radioactivity was captured in the urinary bladder and about 1% of the injected dose accumulated into infected thigh muscles. At 2 or 24h after either intravenously, subcutaneously, intraperitoneally, or orally injected a single dose of 0.04 mg/kg hLF 1-11 in mice significantly reduced (20-60 times) the number of viable MRSA. In a dose-response setting in immunocompetent mice maximum bactericidal effects (10,000 times reduction) of intravenously injected (99m)Tc-hLF 1-11 was seen with 40 mg/kg whereas the same dose of orally administered (99m)Tc-hLF 1-11 induced about approximately 100 times reduction. In conclusion, intravenously and orally administrated (99m)Tc-hLF 1-11 accumulates in infected tissues and is highly effective against experimental infections with MRSA. Moreover, scintigraphy is an excellent tool to study the pharmacology of experimental compounds and to determine the uptake in infected tissues.

Comparison of Animal Models with Soft Tissue Infection by Different Bacilli

In clinical medicine improved diagnostic methods for the detection of infection are needed. A good infectious animal model is very important for the development of a new diagnostic method or drug. The purpose of this study was to establish a good animal model with soft tissue infection. Twenty-four SD rats were divided into four groups (6 in each group). Various bacilli including Staphylococcus aureus (S. aureus), Streptococcus pneumoniae (S. pneumoniae), and Escherichia coli (E. coli) were injected intramuscularly into the left caudal thighs of three groups of rats to create soft tissue infection. In addition, normal saline was injected into the left caudal thighs of ten rats which were used as controls. Before and 48 hr after inoculation of the bacilli, a blood sample (0.5 ml) was taken from each rat and analyzed to determine the white blood cell count and differentiated cell count. In addition, 48 hr after the inoculation, 0.2 mCi of gallium-67 was injected via the tail vein. Gallium scan was performed at 24 hr and 48 hr after administration of the radiotracer. The dorsal view of both hind legs was imaged and analyzed by computers to calculate the lesion-to-normal (L/N) ratio. After imaging, all rats were sacrificed and specimens from portions of the infected thigh muscle were sent for histopathologic investigation to confirm the infection. The increase in both the WBC counts and the segmented polymorphonuclear leukocytes (PMNs) were most significant in the S. aureus group, followed by the S. pneumoniae group, E. coli group and normal control groups. The rats with S. aureus infection had significant gallium uptake at the site of infection and the highest L/N ratio of 2.14 on the 24-hr image and 2.0 on the 48-hr image. The rats with S. pneumoniae had the second highest L/N ratio (1.41 at 24 hr, and 1.48 at 48 hr). The L/N ratio for the E. coli group was 1.27 at 24 hr and 1.35 at 48 hr. No obviously abnormal gallium uptake was demonstrated in the normal controls. We conclude that all three bacilli induced a soft tissue infection in SD rats. S. aureus resulted in the most significant infectious signs.

Technetium-99m labelled antimicrobial peptides discriminate between bacterial infections and sterile inflammations.

The aim of this study was to select technetium-99m labelled peptides that can discriminate between bacterial infections and sterile inflammations. For this purpose, we first assessed the binding of various 99mTc-labelled natural or synthetic peptides, which are based on the sequence of the human antimicrobial peptide ubiquicidin (UBI) or human lactoferrin (hLF), to bacteria and to leucocytes in vitro. In order to select peptides that preferentially bind to bacteria over host cells, radiolabelled peptides were injected into mice intraperitoneally infected with Klebsiella pneumoniae (K. pneumoniae) and the amount of radioactivity associated with the bacteria and with the leucocytes was quantitated. The next phase focussed on discrimination between bacterial infections and sterile inflammatory processes using 99mTc-labelled peptides in mice intramuscularly infected with various bacteria (e.g. multi-drug-resistant Staphylococcus aureus) and in animals that had been injected with lipopolysaccharides (LPS) of bacterial origin to create a sterile inflammatory process. Also, we studied the distribution of 99mTc-labelled UBI 29-41 and UBI 18-35 in rabbits having an experimental thigh muscle infection with K. pneumoniae and in rabbits injected with LPS. Based on the results of our in vitro and in vivo binding assays, two peptides, i.e. UBI 29-41 and UBI 18-35, were selected as possible candidates for infection imaging. The radiolabelled peptides can detect infections with both gram-positive and gram-negative bacteria in mice as early as 5-30 min after injection, with a target-to-non-target (T/NT) ratio between 2 and 3; maximum T/NT ratios were seen within 1 h after injection. In rabbits, high T/NT ratios (>5) for 99mTc-labelled UBI 29-41 were observed from 1 h after injection. No accumulation of the selected 99mTc-labelled UBI-derived peptides was observed in thighs of mice and rabbits previously injected with LPS. Scintigraphic investigation into the biodistribution of 99mTc-labelled UBI peptides revealed that these peptides were rapidly removed from the circulation by renal excretion. Similar data were observed for 99mTc-labelled defensin 1-3. Our data for 99mTc-labelled hLF and related peptides indicate that these compounds are less favourable for infection detection. Taken together, 99mTc-labelled UBI 18-35 and UBI 29-41 enable discrimination between bacterial infections and sterile inflammatory processes in both mice and rabbits. Based on their characteristics, we consider these peptides the candidates of preference for detection of bacterial infections in man.

Comparison of amikacin dosing regimens in neutropenic guinea pigs with Escherichia coli infection

Abstract Objective To derive pharmacokinetic data for 3 amikacin dosing regimens in guinea pigs and to determine whether the antibacterial activity of 15 mg/kg of body weight given twice daily is equivalent to administering the drug more frequently. Animals 10 guinea pigs in pharmacokinetic trials, and 10 guinea pigs in pretreatment, control, and amikacin treatment groups. Procedure Amikacin pharmacokinetic data were determined in guinea pigs after single IM administration of 3.75, 7.5, and 15 mg/kg. Guinea pigs had been made neutropenic by treatment with cyclophosphamide. All guinea pigs were inoculated with 2.8 × 108 colony-forming units (CFU) of Escherichia coli in the thigh muscle, then were allotted to 5 groups: pretreatment (euthanatized 4 hours after inoculation), control, and 3 amikacin treatment groups (3.75 mg/kg, q 3 h; 7.5 mg/kg, q 6 h; and 15 mg/kg, q 12 h). Amikacin administration was begun 4 hours after E coli inoculation and was continued for 72 hours. Numbers of E coli CFU in infected thigh muscle were determined for each guinea pig. Results Difference in survival between control and the amikacin-treated groups was significant. The E coli infection concentration (log10 CFU) increased significantly in the control, compared with the pretreatment, group. Infection concentration decreased significantly in all treatment groups, compared with the pretreatment group. There was no significant difference in bacterial killing among the 3 treatment groups. Conclusion Amikacin had a significant effect on survival of neutropenic guinea pigs with E coli infection. Antibacterial activity did not differ among 3 doses of amikacin administered at different intervals. Clinical Relevance Aminoglycoside dosing regimen with high peak concentration and long drug-free interval is as efficacious as divided dose regimens. (Am J Vet Res 1998;59:750-755)

Pharmacokinetics of Fleroxacin as Studied by Positron Emission Tomography and [18F]Fleroxacin

A new method of tracing the disposition of fleroxacin was tested in infected and noninfected animals in an effort to develop a technique that might be applicable in humans. [18F]fleroxacin was synthesized and shown to be identical physically, chemically, and in its antimicrobial activity to the commercially produced product. Tracer amounts of [18F]fleroxacin were coinjected with a pharmacologic dose of unlabeled drug (10 mg/kg) into normal mice, rats with focal thigh infection due to Escherichia coli, and normal and infected rabbits. The rats and mice were killed at fixed time intervals after injection, and the concentration of drug was determined by radioactive counting in a well-type counter; the rabbits were studied both by this method and by positron emission tomographic (PET) imaging. These studies validated the reliability of the new approach and suggested that it could be applied safely to humans. In all three animal species studied, delivery of [18F]fleroxacin to most tissues was rapid, with the notable exception of the brain. Accumulation of drug in infected thigh muscle was similar to that in normal muscle. The concentrations of drug reached in various tissues suggest that fleroxacin will be particularly useful in the treatment of gastrointestinal, urinary tract, hepatobiliary, and skeletal infections and that it shows promise for the treatment of lung and soft tissue infection. The minimal concentrations of drug delivered to the brain should decrease the occurrence of central nervous system toxicity with this particular fluoroquinolone.

Therapeutic effect of cefozopran (SCE-2787), a new parenteral cephalosporin, against experimental infections in mice.

The therapeutic effect of cefozopran (SCE-2787), a new semisynthetic parenteral cephalosporin, against experimental infections in mice was examined. Cefozopran was more effective than cefpiramide and was as effective as ceftazidime and cefpirome against acute respiratory tract infections caused by Klebsiella pneumoniae DT-S. In the model of chronic respiratory tract infection caused by K. pneumoniae 27, cefozopran was as effective as ceftazidime. The therapeutic effect of cefozopran against urinary tract infections caused by Pseudomonas aeruginosa P9 was superior to that of cefpirome and was equal to those of ceftazidime and cefclidin. In addition, cefozopran was more effective than ceftazidime and was as effective as flomoxef in a thigh muscle infection caused by methicillin-sensitive Staphylococcus aureus 308A-1. Against thigh muscle infections caused by methicillin-resistant S. aureus N133, cefozopran was the most effective agent. The potent therapeutic effect of cefozopran in those experimental infections in mice suggests that it would be effective against respiratory tract, urinary tract, and soft tissue infections caused by a variety of gram-positive and gram-negative bacteria in humans.

Comparison of the effects of aztreonam and tigemonam against Escherichia coli and Klebsiella pneumoniae in vitro and in vivo

A study was performed to investigate the pharmacodynamics of aztreonam and tigemonam against Escherichia coli and Klebsiella pneumoniae in vitro and in vivo. The in vitro concentration-effect relationships were determined in short-term growth experiments. The in vivo dose-effect relationships were determined in an experimental thigh muscle infection in irradiated mice. In this model, E. coli was injected into one thigh muscle and K. pneumoniae was injected into the other. Throughout these experiments aztreonam was administered subcutaneously and tigemonam was administered orally. For analysis of the antibacterial pharmacodynamics, the following parameters were determined: the maximum effect as a parameter for efficacy, the 50% effective concentration (or dose) as a parameter for potency, and the slope of the concentration-effect relationship. To assess the relationship between the concentration of the antibiotic and the antibacterial effect in vivo, the pharmacokinetics of the two drugs in the plasma of mice were determined as well. The maximum in vitro and in vivo effects of aztreonam and tigemonam against both bacteria did not differ substantially. However, both drugs killed E. coli more effectively than K. pneumoniae, indicating that the maximum in vitro effect of these drugs against E. coli was higher than that against K. pneumoniae. The maximum in vivo effect of both drugs against E. coli was similar to that against K. pneumoniae. Furthermore, in vitro aztreonam was about twice as potent as tigemonam, but in vivo the reverse was the case. These findings were explained by pharmacokinetic differences between subcutaneously administered aztreonam and orally administered tigemonam, because concentrations of tigemonam in plasma remained at microbiologically active concentrations longer than those of aztreonam did.

Comparative study of the effects of four cephalosporins against Escherichia coli in vitro and in vivo

A thigh muscle infection induced with Escherichia coli in irradiated mice was used as a model to compare the in vivo pharmacodynamics of the antibacterial effect of four cephalosporins (i.e., cefepime, ceftriaxone, ceftazidime, and cefoperazone) with the in vitro antibacterial pharmacodynamics of these drugs. The following in vitro pharmacodynamic parameters were determined: the maximum effect as a measure for efficacy, the 50% effective concentration as a parameter for potency, and the slope of the concentration-effect relationship. For analysis of the in vivo antibacterial pharmacodynamics, the same parameters were applied for the dose instead of the concentration. For the detection of a relationship between concentration and antibacterial effect in vivo, we determined the pharmacokinetics of the four cephalosporins in the plasma of mice. The results showed that, in general, there is a direct relationship between the in vivo and in vitro pharmacodynamics of these cephalosporins. The maximum effects of cefepime, ceftazidime, and cefoperazone were approximately similar in vivo and in vitro. The sequence of potency of these drugs was, in descending order, cefepime, ceftazidime, and cefoperazone. Ceftriaxone differed from the other three cephalosporins in that it displayed unexpected in vivo pharmacodynamics. Ceftriaxone was just as efficacious as the other three in vitro, but its maximum effect in vivo was much lower. This relatively low maximum effect of ceftriaxone in vivo was not explained by the pharmacokinetic characteristics of the drug. From the present results it can be concluded that the in vitro efficacy of cephalosporins does not necessarily have a predictive value for the in vivo efficacy.

Therapeutic efficacy of granulocyte colony-stimulating factor alone and in combination with antibiotics against Pseudomonas aeruginosa infections in mice

The therapeutic efficacy of granulocyte colony-stimulating factor (G-CSF) against an experimental intramuscular infection induced by Pseudomonas aeruginosa in mice was confirmed. Bacterial growth in the infected thigh muscle was suppressed by G-CSF treatment. The change in the number of peripheral blood polymorphonuclear leukocytes (PMN) after bacterial challenge was investigated. The results showed that G-CSF could stimulate stronger defense mechanisms after stimulation by bacterial challenge. In the G-CSF-treated group, more clusters of matured PMN were observed in the infected thigh muscle 6 h after bacterial challenge. Next, the correlation between the number of PMN in the blood at the time of infection and the therapeutic efficacy of antibiotics was investigated. The therapeutic efficacy of ceftazidime, a beta-lactam antibiotic, was affected by the number of blood PMN at the time of infection. In particular, a decrease of peripheral blood PMN at the time of infection resulted in a dramatic decrease in the efficacy of ceftazidime. The reduction in leukopenia by G-CSF remarkably strengthened the therapeutic effect of antibiotics in mice.

Relation between the therapeutic efficacy of imipenem in an experimental infection in granulocytopenic mice and its effect on marine intestinal microbial ecology

A study was performed to assess the effect of parenteral administration of imipenem on the intestinal microbial ecology of mice in relation to the therapeutic efficacy of the drug. The therapeutic effect of imipenem was assessed in a short-term experimental thigh muscle infection with Escherichia coli in irradiated mice. The maximum antibacterial effect of imipenem was approached at a single dose of 80 mg/kg. At this dose of imipenem the number of viable E. coli in the thigh muscle decreased from 9 x 10(6) to 4 x 10(5), whereas in untreated controls this number increased from 9 x 10(6) to 2 x 10(8). Daily administration of a dose of 80 mg/kg imipenem caused significant changes in the intestinal flora of conventional mice, despite the low concentrations of the drug (about 1 mg/kg) found in the caecum 30 min after infection of this dose. These changes consisted of an increase in the number of E. coli and enterococci and a decrease in the number of Staphylococcus aureus in the faeces. Furthermore, at this dose of imipenem, the number of Candida albicans recovered from the faeces after oral contamination with this organism was increased. We conclude from these animal experiments that the use of imipenem in high doses causes ecological changes in the intestinal bacterial flora with the potential to promote colonization by candida.

Comprehensive evaluation of ciprofloxacin-aminoglycoside combinations against Enterobacteriaceae and Pseudomonas aeruginosa strains.

The in vitro activities of antibiotic combinations containing ciprofloxacin and either gentamicin, sisomicin, netilmicin, amikacin, or tobramycin were evaluated by checkerboard assay (agar dilution method). A total of 220 strains of Enterobacteriaceae and Pseudomonas aeruginosa (11 species, 20 strains each) were tested. Synergistic or antagonistic effects were observed in less than 1% of the tests performed; they appeared to represent method-dependent fluctuations rather than true antibiotic interactions. No significant differences among the five aminoglycosides tested were seen. Time-kill experiments performed with three representative strains of Escherichia coli and Serratia marcescens showed additive combination effects with respect to the kill rates and inhibition of bacterial regrowth. Exposure of Serratia strains to either ciprofloxacin or gentamicin before the addition of the second drug had little influence on the combination effects observed. No antagonistic drug interactions were seen in vivo when combination therapy with ciprofloxacin and gentamicin was evaluated in a model of E. coli thigh muscle infection in neutropenic mice. Comparable therapeutic effects were obtained, regardless of whether the two compounds were administered simultaneously or sequentially at 1- or 2-h intervals.