Impact of High-Level Daptomycin Resistance in the Streptococcus mitis Group on Virulence and Survivability during Daptomycin Treatment in Experimental Infective Endocarditis

Among the viridans group streptococci, the Streptococcus mitis group is the most common cause of infective endocarditis. These bacteria have a propensity to be β-lactam resistant, as well as to rapidly develop high-level and durable resistance to daptomycin (DAP). We compared a parental, daptomycin-susceptible (DAPs) S. mitis/S. oralis strain and its daptomycin-resistant (DAPr) variant in a model of experimental endocarditis in terms of (i) their relative fitness in multiple target organs in this model (vegetations, kidneys, spleen) when animals were challenged individually and in a coinfection strategy and (ii) their survivability during therapy with daptomycin-gentamicin (an in vitro combination synergistic against the parental strain). The DAPr variant was initially isolated from the cardiac vegetations of animals with experimental endocarditis caused by the parental DAPs strain following treatment with daptomycin. The parental strain and the DAPr variant were comparably virulent when animals were individually challenged. In contrast, in the coinfection model without daptomycin therapy, at both the 106- and 107-CFU/ml challenge inocula, the parental strain outcompeted the DAPr variant in all target organs, especially the kidneys and spleen. When the animals in the coinfection model of endocarditis were treated with DAP-gentamicin, the DAPs strain was completely eliminated, while the DAPr variant persisted in all target tissues. These data underscore that the acquisition of DAPr in S. mitis/S. oralis does come at an intrinsic fitness cost, although this resistance phenotype is completely protective against therapy with a potentially synergistic DAP regimen.

Electric field modification of magnetism in Au/La2/3Ba1/3MnO3/Pt device

The La_2/3Ba_1/3MnO₃ film is deposited in a CMOS-compatible Pt/Ti/SiO₂/Si substrate with the oxygen pressure of 10 Pa for investigating magnetoelectric effect. Bipolar resistive switching effect with excellent endurance and retention is observed in this Au/La_2/3Ba_1/3MnO₃/Pt device. Through this effect, a significant nonvolatile change of magnetization is obtained in this device as well. The change of magnetization can be understood by the break and repair of the -Mn³⁺-O²⁻-Mn⁴⁺- chains induced by the electric field through the oxygen vacancies migration. The resistance and magnetization of the Au/La_2/3Ba_1/3MnO₃/Pt device can be simultaneously manipulated by the electric field, which makes it to be a promising candidate for the multifunctional memory devices.

Sorafenib down-regulates expression of HTATIP2 to promote invasiveness and metastasis of orthotopic hepatocellular carcinoma tumors in mice

BACKGROUND & AIMS

Antiangiogenic agents can sometimes promote tumor invasiveness and metastasis, but little is known about the effects of the antiangiogenic drug sorafenib on progression of hepatocellular carcinoma (HCC).

METHODS

Sorafenib was administered orally (30 mg · kg(-1) · day(-1)) to mice with orthotopic tumors grown from HCC-LM3, SMMC7721, or HepG2 cells. We analyzed survival times of mice, along with tumor growth, metastasis within liver and to lung, and induction of the epithelial-mesenchymal transition. Polymerase chain reaction arrays were used to determine the effects of sorafenib on gene expression patterns in HCC cells. We analyzed regulation of HIV-1 Tat interactive protein 2 (HTATIP2) by sorafenib and compared levels of this protein in tumor samples from 75 patients with HCC (21 who received sorafenib after resection and 54 who did not).

RESULTS

Sorafenib promoted invasiveness and the metastatic potential of orthotopic tumors grown from SMMC7721 and HCC-LM3 cells but not from HepG2 cells. In gene expression analysis, HTATIP2 was down-regulated by sorafenib. HCC-LM3 cells that expressed small hairpin RNAs against HTATIP2 (knockdown) formed less invasive tumors in mice following administration of sorafenib than HCC-LM3 without HTATIP2 knockdown. Alternatively, HepG2 cells that expressed transgenic HTATIP2 formed more invasive tumors in mice following administration of sorafenib. Sorafenib induced the epithelial-mesenchymal transition in HCC cell lines, which was associated with expression of HTATIP2. Sorafenib regulated expression of HTATIP2 via Jun-activated kinase (JAK) and signal transducer and activator of transcription (STAT)3 signaling. Sorafenib therapy prolonged recurrence-free survival in patients who expressed lower levels of HTATIP2 compared with higher levels.

CONCLUSIONS

Sorafenib promotes invasiveness and the metastatic potential of orthotopic tumors from HCC cells in mice, down-regulating expression of HTATIP2 via JAK-STAT3 signaling.

Antiangiogenic effects of pazopanib in xenograft hepatocellular carcinoma models: evaluation by quantitative contrast-enhanced ultrasonography

Background

Antiangiogenesis is a promising therapy for advanced hepatocellular carcinoma (HCC), but the effects are difficult to be evaluated. Pazopanib (GW786034B) is a pan-vascular endothelial growth factor receptor inhibitor, the antitumor effects or antiangiogenic effects haven't been investigated in HCC.

Methods

In vitro direct effects of pazopanib on human HCC cell lines and endothelial cells were evaluated. In vivo antitumor effects were evaluated in three xenograft nude mice models. In the subcutaneous HCCLM3 model, intratumoral blood perfusion was detected by contrast-enhanced ultrasonography (CEUS), and serial quantitative parameters were profiled from the time-intensity curves of ultrasonograms.

Results

In vitro proliferation of various HCC cell lines were not inhibited by pazopanib. Pazopanib inhibited migration and invasion and induced apoptosis significantly in two HCC cell lines, HCCLM3 and PLC/PRF/5. Proliferation, migration, and tubule formation of human umbilical vein endothelial cells were inhibited by pazopanib in a dose-dependent manner. In vivo tumor growth was significantly inhibited by pazopanib in HCCLM3, HepG2, and PLC/PRF/5 xenograft models. Various intratumoral perfusion parameters changed over time, and the signal intensity was significantly impaired in the treated tumors before the treatment efficacy on tumor size could be observed. Mean transit time of the contrast media in hotspot areas of the tumors was reversely correlated with intratumoral microvessel density.

Conclusions

Antitumor effects of pazopanib in HCC xenografts may owe to its antiangiogenic effects, and the in vivo antiangiogenic effects could be evaluated by quantitative CEUS.

Antiangiogenic effects of pazopanib in xenograft hepatocellular carcinoma models: evaluation by quantitative contrast-enhanced ultrasonography

BACKGROUND

Antiangiogenesis is a promising therapy for advanced hepatocellular carcinoma (HCC), but the effects are difficult to be evaluated. Pazopanib (GW786034B) is a pan-vascular endothelial growth factor receptor inhibitor, the antitumor effects or antiangiogenic effects haven't been investigated in HCC.

METHODS

In vitro direct effects of pazopanib on human HCC cell lines and endothelial cells were evaluated. In vivo antitumor effects were evaluated in three xenograft nude mice models. In the subcutaneous HCCLM3 model, intratumoral blood perfusion was detected by contrast-enhanced ultrasonography (CEUS), and serial quantitative parameters were profiled from the time-intensity curves of ultrasonograms.

RESULTS

In vitro proliferation of various HCC cell lines were not inhibited by pazopanib. Pazopanib inhibited migration and invasion and induced apoptosis significantly in two HCC cell lines, HCCLM3 and PLC/PRF/5. Proliferation, migration, and tubule formation of human umbilical vein endothelial cells were inhibited by pazopanib in a dose-dependent manner. In vivo tumor growth was significantly inhibited by pazopanib in HCCLM3, HepG2, and PLC/PRF/5 xenograft models. Various intratumoral perfusion parameters changed over time, and the signal intensity was significantly impaired in the treated tumors before the treatment efficacy on tumor size could be observed. Mean transit time of the contrast media in hotspot areas of the tumors was reversely correlated with intratumoral microvessel density.

CONCLUSIONS

Antitumor effects of pazopanib in HCC xenografts may owe to its antiangiogenic effects, and the in vivo antiangiogenic effects could be evaluated by quantitative CEUS.

Human hepatocellular carcinoma tumor-derived endothelial cells manifest increased angiogenesis capability and drug resistance compared with normal endothelial cells

PURPOSE

Increasing evidence indicates that tumor-derived endothelial cells (TEC) possess a distinct and unique phenotype compared with endothelial cells (NEC) from adjacent normal tissue and may be able to acquire resistance to drugs. The aim of this study was to investigate the angiogenesis activity and response to drug treatment of TECs and NECs derived from human hepatocellular carcinoma (HCC).

EXPERIMENTAL DESIGN

TECs or NECs were isolated from HCC or adjacent normal liver tissue using anti-CD105 antibody coupled to magnetic beads. The phenotypic and functional properties of endothelial cells were characterized by testing the expression of CD105, CD31, CD144, vascular endothelial growth factor receptor-1, vascular endothelial growth factor receptor-2, and von Willebrand factor, and the ability of DiI-Ac-LDL-uptake and tube formations. CD105(+) TECs were compared with CD105(+) NECs and human umbilical vein endothelial cells (HUVEC) by examining their ability to proliferate, motility, ability to adhere to tumor cells, response to tumor conditioned medium, and reactions to the chemotherapy drugs Adriamycin and 5-fluorouracil and the antiangiogenic drug sorafenib.

RESULTS

Compared with CD105(+) NECs and HUVECs, CD105(+) TECs showed increased apoptosis resistance and motility and proangiogenic properties. Meanwhile, CD105(+) TECs had a greater ability to adhere to tumor cells and survive in the tumor environment. Moreover, CD105(+) TECs acquired more resistance to Adriamycin, 5-fluorouracil, and sorafenib than CD105(+) NECs and HUVECs.

CONCLUSIONS

TECs possessed enhanced angiogenic activity and resistance to chemotherapeutic drugs and an angiogenesis inhibitor, and may provide a better tool for studying tumor angiogenesis and antiangiogenesis drugs in HCC.

Protein expression profiling of vascular endothelial growth factor and its receptors identifies subclasses of hepatocellular carcinoma and predicts survival

PURPOSE

To examine expression profile and prognostic significance of vascular endothelial growth factor (VEGF) and its receptors in hepatocellular carcinoma (HCC) and peritumoral tissue.

METHODS

Expression of VEGF-A, VEGF-C, and VEGF receptor 1(VEGFR-1), VEGFR-2, and VEGFR-3 in tumor and peritumoral liver tissue was studied by immunohistochemistry in a tissue microarray from 107 patients with HCC. Unsupervised hierarchical cluster analyses were conducted to identify relevant clusters.

RESULTS

Staining of VEGF-A, VEGF-C, VEGFR-2, and VEGFR-3 was mostly found on the tumor cells and peritumoral hepatocytes, but VEGFR-1 was mostly expressed in stromal cells. In most of the cases, the expression of VEGF-A, VEGFR-1, VEGFR-2, and VEGFR-3 in was higher in peritumoral liver tissue, while VEGF-C expression was higher in tumor. Unsupervised hierarchical clustering analysis identified four prognostically different clusters, of which cluster A was classified into the "poor prognosis group," and the other three clusters were classified into the "good prognosis group" (P = 0.047). Further analysis with a set of seven markers reproduced the same four cluster groups with significantly different recurrence free probability (RFP) (P = 0.018), and the low RFP group was associated with more intrahepatic satellite lesions. Multivariate analysis showed that classification defined by seven biomarkers was of prognostic significance (P = 0.000).

CONCLUSIONS

Expression of VEGF and its receptors was higher in peritumoral tissue than in tumor in HCC. Seven biomarkers predicted patients' RFP, which consisted of tumoral expression of VEGF-A, VEGFR-1, and VEGF-C as well as peritumoral expression of VEGF-A, VEGFR-1, VEGFR-2, and VEGFR-3.

High Expression of Macrophage Colony-Stimulating Factor in Peritumoral Liver Tissue Is Associated With Poor Survival After Curative Resection of Hepatocellular Carcinoma

Purpose

To investigate prognostic values of the intratumoral and peritumoral expression of macrophage colony-stimulating factors (M-CSF) in hepatocellular carcinoma (HCC) patients after curative resection.

Patients and Methods

Expression of M-CSF and density of macrophages (MΦ) were assessed by immunohistochemistry in tissue microarrays containing paired tumor and peritumoral liver tissue from 105 patients who had undergone hepatectomy for histologically proven HCC. Prognostic value of these and other clinicopathologic factors was evaluated.

Results

Neither intratumoral M-CSF nor MΦ density was associated with overall survival (OS) or disease-free survival (DFS). High peritumoral M-CSF and MΦ density, which correlated with large tumor size, presence of intrahepatic metastasis, and high TNM stage, were independent prognostic factors for both OS (P = .001 and P < .001, respectively) and DFS (P = .001 and P = .003, respectively) and affected incidence of early recurrence. In a small HCC subset, peritumoral M-CSF was also correlated with both OS and DFS (P = .038 and P = .001, respectively). The combination of peritumoral M-CSF and MΦ had a better power to predict the patients' death and disease recurrence (P < .001 for both).

Conclusion

High peritumoral M-CSF and MΦ were associated with HCC progression, disease recurrence, and poor survival after hepatectomy, highlighting the importance of peritumoral tissue in the recurrence and metastasis of HCC. M-CSF and MΦ may be targets of postoperative adjuvant therapy.

[Construction of a trans-splicing ribozyme for restoring EGFP truncation mutation]

Special designed group I intron ribozymes can specifically splice objective RNA, repair the mutant gene in RNA level. The specificity of ribozyme is determined by nucleotides specific internal guide sequence (IGS) introduced to the enzyme. In this study, fragment sequence containing Tetrahymena thermophilia intron I of 26S rRNA gene was cloned and cis-splicing activity of this ribozyme was confirmed by in vitro transcription. For evaluating the trans-splicing activity of this ribozyme, a truncated mutant Green Fluorescence Protein (GFP) vector, XYQ5/XYQ10- pEGFP-C2, was constructed. This vector deleted the 3' end 564bp fragment of EGFP coding sequence, led to the lost the activity of emitting green fluorescence. Trans-splicing ribozyme plasmids ptrans-rib-CMV2 for remedy of the truncated mutant EGFP was constructed by PCR and molecular cloning techniques. This vector utilizing cloned 26S rRNA intron 1 as core enzyme; selecting T-G site at 194bp of EGFP coding sequence as splicing receptor, designed an IGS which is inversely complement to the 188-193nt of EGFP mRNA; the 195-890bp fragment of EGFP coding sequence was ligated to the 3'-end of ribozyme core. The fragment containing these components was inserted to a eukayotic expression vector pRC-CMV2. Using linearized XYQ5/XYQ10- pEGFP-C2 and ptrans-rib-CMV2 as templates, truncated EGFP mRNA and the constructed ribozyme vector were transcribed and mixed to evaluate the trans-splicing activity. Analysis of in vitro transcription products mix by RT-PCR verified the existence of wild type EGFP mRNA molecule. Co-transfection of XYQ5/XYQ10- pEGFP-C2 with ptrans-rib-CMV2 to Hela cells proved this ribozyme restored green fluorescence within cell, but the efficiency was low.

Linezolid: a new antibiotic

The U.S. Food and Drug Administration recently approved linezolid for the treatment of patients with methicillin-resistant staphylococcal and vancomycin-resistant enterococcal infections. This oxazolidinone antibacterial agent represents the first approved antibiotic of a new structural class in 35 years. Linezolid is a synthetic compound that acts by inhibiting the initiation complex formation in bacterial protein synthesis, a mechanism of action distinct from other commercially available antibiotics. Thus, cross-resistance between linezolid and other current antimicrobial agents has not been demonstrated to date. Linezolid has a wide spectrum of in vitro activity against Gram-positive organisms, including methicillin-resistant staphylococci, penicillin-resistant pneumococci and vancomycin-resistant enterococci. Some anaerobes, such as Clostridium spp., Peptostreptococcus spp. and Prevotella spp. are also susceptible to linezolid. In addition, linezolid has exhibited good efficacy in experimental animal models of acute otitis media, endocarditis and meningitis due to many common aerobic Gram-positive bacteria. In clinical trials involving hospitalized patients with skin/soft tissue infections, community-acquired pneumonia and serious Gram-positive bacterial infections, linezolid appeared to be an effective treatment option, comparable in efficacy to vancomycin.

New approaches to the prevention and treatment of severe S. aureus infections

Staphylococcus aureus is a virulent pathogen that is currently a major cause of community-acquired infections, as well as infections in hospitalized patients. Morbidity and mortality due to S. aureus infections, such as sepsis, osteomyelitis, septic arthritis and infective endocarditis, remain high despite the use of newer antibiotics. Of major concern, methicillin resistance in S. aureus isolates has increased dramatically worldwide, especially among nosocomial isolates; this phenotype may be associated with resistance to other antistaphylococcal compounds, including vancomycin. This increase in prevalence of multiantibiotic resistance in S. aureus is a major public health concern. Currently, there is an intense focus on the development of novel vaccines for the prevention of S. aureus infections in high-risk populations and on new antimicrobial classes for the therapy of established S. aureus infections.

The oxygen- and iron-dependent sigma factor pvdS of Pseudomonas aeruginosa is an important virulence factor in experimental infective endocarditis

In Pseudomonas aeruginosa, pvdS, a key oxygen (O2)-dependent locus, regulates expression of a number of virulence genes, including toxA (which encodes exotoxin A production). To define the in vivo role of differing O2 tensions on pseudomonal virulence, 2 knockout mutants, DeltapvdS and DeltatoxA, were compared with their parental strain, PA01, in rabbit aortic and tricuspid endocarditis models (representing aerobic vs. microaerobic conditions in vivo, respectively). In aortic endocarditis, DeltapvdS densities were significantly less than those of PA01 in vegetations, kidneys, and spleen (P<.01). In contrast, in tricuspid endocarditis, there were no significant differences between DeltapvdS and PA01 tissue densities in these same target tissues. The DeltatoxA mutant proliferated within target tissues to the same extent as the parental strain. Thus, pvdS (but not toxA) appears to be required for optimal virulence of P. aeruginosa, particularly in tissues preferentially exposed to high O2 tensions (e.g., aortic vegetations).

Comparative efficacies of liposomal amikacin (MiKasome) plus oxacillin versus conventional amikacin plus oxacillin in experimental endocarditis induced by Staphylococcus aureus: microbiological and echocardiographic analyses

Optimal treatment strategies for serious infections caused by Staphylococcus aureus have not been fully characterized. The combination of a beta-lactam plus an aminoglycoside can act synergistically against S. aureus in vitro and in vivo. MiKasome, a new liposome-encapsulated formulation of conventional amikacin, significantly prolongs serum half-life (t1/2) and increases the area under the concentration-time curve (AUC) compared to free amikacin. Microbiologic efficacy and left ventricular function, as assessed by echocardiography, were compared in animals administered either oxacillin alone or oxacillin in combination with conventional amikacin or MiKasome in a rabbit model of experimental endocarditis due to S. aureus. In vitro, oxacillin, combined with either free amikacin or MiKasome, prevented the bacterial regrowth observed with aminoglycosides alone at 24 h of incubation. Rabbits with S. aureus endocarditis were treated with either oxacillin alone (50 mg/kg, given intramuscularly three times daily), oxacillin plus daily amikacin (27 mg/kg, given intravenously twice daily), or oxacillin plus intermittent MiKasome (160 mg/kg, given intravenously, a single dose on days 1 and 4). The oxacillin-alone dosage represents a subtherapeutic regimen against the infecting strain in the endocarditis model (L. Hirano and A. S. Bayer, Antimicrob. Agents Chemother. 35:685-690, 1991), thus allowing recognition of any enhanced bactericidal effects between oxacillin and either aminoglycoside formulation. Treatment was administered for either 3 or 6 days, and animals were sacrificed after each of these time points or at 5 days after a 6-day treatment course (to evaluate for posttherapy relapse). Left ventricular function was analyzed by utilizing serial transthoracic echocardiography during treatment and posttherapy by measurement of left ventricular fractional shortening. At all sacrifice times, both combination regimens significantly reduced S. aureus vegetation counts versus control counts (P < 0.05). In contrast, oxacillin alone did not significantly reduce S. aureus vegetation counts after 3 days of therapy. Furthermore, at this time point, the two combinations were significantly more effective than oxacillin alone (P < 0.05). All three regimens were effective in significantly decreasing bacterial counts in the myocardium during and after therapy compared to controls (P < 0.05). In kidney and spleen abscesses, all regimens significantly reduced bacterial counts during therapy (P < 0.0001); however, only the combination regimens prevented bacteriologic relapse in these organs posttherapy. By echocardiographic analysis, both combination regimens yielded a significant physiological benefit by maintaining normal left ventricular function during treatment and posttherapy compared with oxacillin alone (P < 0.001). These results suggest that the use of intermittent MiKasome (similar to daily conventional amikacin) enhances the in vivo bactericidal effects of oxacillin in a severe S. aureus infection model and preserves selected physiological functions in target end organs.

In vitro antibacterial activities of platelet microbicidal protein and neutrophil defensin against Staphylococcus aureus are influenced by antibiotics differing in mechanism of action

Thrombin-induced platelet microbicidal protein-1 (tPMP-1) and human neutrophil defensin-1 (HNP-1) are small, cationic antimicrobial peptides. These peptides exert potent in vitro microbicidal activity against a broad spectrum of human pathogens, including Staphylococcus aureus. Evidence suggests that tPMP-1 and HNP-1 target and disrupt the bacterial membrane. However, it is not yet clear whether membrane disruption itself is sufficient to kill the bacterium or whether subsequent, presumably intracellular, events are also involved in killing. We investigated the staphylocidal activities of tPMP-1 and HNP-1 in the presence or absence of pretreatment with antibiotics that differ in their mechanisms of action. The staphylocidal effects of tPMP-1 and HNP-1 on control cells (no antibiotic pretreatment) were rapid and concentration dependent. Pretreatment of S. aureus with either penicillin or vancomycin (bacterial cell wall synthesis inhibitors) significantly enhanced the anti-S. aureus effects of tPMP-1 compared with the effects against the respective control cells over the entire tPMP-1 concentration range tested (P < 0.05). Similarly, S. aureus cells pretreated with these antibiotics were more susceptible to HNP-1 than control cells, although the difference in the effects against cells that received penicillin pretreatment did not reach statistical significance (P < 0.05 for cells that received vancomycin pretreatment versus effects against control cells). Studies with isogenic pairs of strains with normal or deficient autolytic enzyme activities demonstrated that enhancement of S. aureus killing by cationic peptides and cell wall-active agents could not be ascribed to a predominant role of autolytic enzyme activation. Pretreatment of S. aureus cells with tetracycline, a 30S ribosomal subunit inhibitor, significantly decreased the staphylocidal effect of tPMP-1 over a wide peptide concentration range (0.16 to 1.25 microgram/ml) (P < 0.05). Furthermore, pretreatment with novobiocin (an inhibitor of bacterial DNA gyrase subunit B) and with azithromycin, quinupristin, or dalfopristin (50S ribosomal subunit protein synthesis inhibitors) essentially blocked the S. aureus killing resulting from exposure to tPMP-1 or HNP-1 at most concentrations compared with the effects against the respective control cells (P < 0.05 for a tPMP-1 concentration range of 0.31 to 1.25 microgram/ml and for an HNP-1 concentration range of 6.25 to 50 microgram/ml). These findings suggest that tPMP-1 and HNP-1 exert anti-S. aureus activities through mechanisms involving both the cell membrane and intracellular targets.

Bactericidal effect of pefloxacin and fosfomycin against Pseudomonas aeruginosa in a rabbit endocarditis model with pharmacokinetics of pefloxacin in humans simulated in vivo

The bactericidal activity of pefloxacin and fosfomycin alone and in combination against Pseudomonas aeruginosa was evaluated in an experimental rabbit endocarditis model after 24 h of treatment. Two strains with intermediate susceptibility to pefloxacin and good susceptibility to fosfomycin were tested. The serum kinetics obtained during administration of 400 mg every 12 h in humans were simulated in the animals using computer-controlled variable-flow infusion. Fosfomycin was administered as a continuous infusion at a constant flow, allowing a steady-state concentration of 47.4 +/- 11.9 mg/ml to be reached in serum. In valvular vegetations, pefloxacin was less bactericidal than fosfomycin, and in combination treatment, it reduced (but did not abolish) the bactericidal effect of fosfomycin. The duration of the pretreatment interval (12-48 h) had a negative effect on the bactericidal activity of both drugs, especially that of fosfomycin.

Adaptive resistance of Pseudomonas aeruginosa induced by aminoglycosides and killing kinetics in a rabbit endocarditis model

Adaptive resistance following the first exposure to aminoglycosides is a recently described in vitro phenomenon in Pseudomonas aeruginosa and other aerobic gram-negative bacilli. We investigated the in vivo relevance of adaptive resistance in P. aeruginosa following a single dose of amikacin in the experimental rabbit endocarditis model. Rabbits with P. aeruginosa endocarditis received either no therapy (control) or a single intravenous (i.v.) dose of amikacin (80 mg/kg of body weight) at 24 h postinfection, after which they were sacrificed at 5, 8, 12, 16, or 24 h postdose. Excised aortic vegetations were subsequently exposed ex vivo to amikacin at 2.5, 5, 10 or 20 times the MIC for 90 min. In vivo adaptive resistance was identified when amikacin-induced pseudomonal killing within excised aortic vegetations was less in animals receiving single-dose amikacin in vivo than in vegetations from control animals not receiving amikacin in vivo. Maximal adaptive resistance occurred between 8 and 16 h after the in vivo amikacin dose, with complete refractoriness to ex vivo killing by amikacin seen at 12 h postdose. By 24 h postdose, bacteria within excised vegetations had partially recovered their initial amikacin susceptibility. In a parallel treatment study, we demonstrated that amikacin given once daily (but not twice daily) at a total dose of 80 mg/kg i.v. for 1-day treatment significantly reduced pseudomonal densities within aortic vegetations versus those in untreated controls. When therapy was continued for 3 days with the same total daily dose (80 mg/kg/day), amikacin given once or twice daily significantly reduced intravegetation pseudomonal densities versus those in controls. However, amikacin given once daily was still more effective than the twice-daily regimen. These data confirm the induction of aminoglycoside adaptive resistance in vivo and further support the advantages of once-daily aminoglycoside dosing regimens in the treatment of serious pseudomonal infections.

The effect of rifampicin on adaptive resistance of Pseudomonas aeruginosa to aminoglycosides

Using the dynamic chequerboard technique, we confirmed that rifampicin produces a synergistic bactericidal effect when combined with amikacin or netilmicin. Adaptive resistance was suppressed when rifampicin was added to aminoglycoside after, but not during, first exposure to amikacin or netilmicin. The effect of rifampicin on adaptive resistance could account for the synergy between rifampicin and aminoglycosides.

In vivo antibacterial effects of simulated human serum profiles of once-daily versus thrice-daily dosing of amikacin in a Serratia marcescens endocarditis experimental model

Once-daily dosage of aminoglycosides is currently under consideration. The lower toxicity of this regimen has been clearly established, but there are conflicting experimental and clinical data concerning its efficacy. It is inadvisable to optimize human therapy by extrapolation from experimental studies since animal and human pharmacokinetics differ. The simulation of human pharmacokinetics in experimental infectious models would seem to offer a more rational approach. We used computer-controlled infusion of amikacin at a variable flow rate to simulate human pharmacokinetics in a Serratia marcescens rabbit endocarditis model and to compare two therapeutic regimens (once-daily versus thrice-daily doses). The doses corresponded to simulations of 15 and 30 mg/kg of body weight per day in humans, and antibacterial activity was measured in vegetations (Veg) after 24 h of treatment. The results show that the dose corresponding to 15 mg/kg/day failed to produce a significant reduction of CFU (6.8 +/- 0.9 and 6.4 +/- 0.8 log10 CFU/g of Veg, respectively, for once-daily and thrice-daily doses versus 7.6 +/- 1.0 for controls). A significant reduction was observed only for the dose corresponding to 30 mg/kg/day in humans (5.2 +/- 1.5 and 5.4 +/- 1.1 log10 CFU/g of Veg, respectively, for the two regimens). With this model, the efficacy of amikacin was similar for both regimens after 24 h of treatment simulating human pharmacokinetics.

Influence of pH on adaptive resistance of Pseudomonas aeruginosa to aminoglycosides and their postantibiotic effects

Adaptive resistance to aminoglycosides in Pseudomonas aeruginosa and other gram-negative bacilli is usually induced by the initial exposure to the drug. We investigated the influence of pH on the adaptive resistance of a clinical P. aeruginosa strain to aminoglycosides in vitro and on their postantibiotic effects. For adaptive resistance, the first-exposure concentrations of both amikacin and netilmicin were one, two, four, and eight times the MIC of each drug and the second-exposure concentrations were two times the MIC of each drug. Adaptive resistance was greater and more prolonged with higher initial aminoglycoside concentrations, and the bactericidal effects of the aminoglycosides were concentration dependent at pH 7.4. At pH 6.5, the killing rates of amikacin and netilmicin were far lower than those observed at pH 7.4. At pH 5.5, amikacin and netilmicin exerted practically no bactericidal effect on the P. aeruginosa strain used. However, with media at pH 5.5 and 6.5, adaptive resistance of P. aeruginosa preexposed to amikacin and netilmicin was also clearly exhibited, with the degree of adaptive resistance depending on the bactericidal effects of both drugs on nonpreexposed controls. Maximal adaptive resistance occurred between 0 and 4 h after preexposure. The postantibiotic effects of amikacin and netilmicin against the P. aeruginosa strain were shown to be concentration dependent and were reduced at acidic pHs. No changes in outer and inner membrane proteins occurred during the adaptive-resistance interval.

[Critical serum concentration of antibiotics. A therapeutic tool and means of comparative evaluation]

It is difficult to predict the clinical activity of antibiotics solely on the basis of in vitro data. Experimental models measuring the relationship between serum concentration and in vivo activity are essential for comparing the activity of different compounds currently available. The critical serum concentration can be used to compare the intrinsic activity of antibiotics on a given bacterial strain. When compared with the minimal inhibiting concentration measured in vitro, "activity loss" can be determined for each antibiotic placed in contact with bacteria in an infected tissue. The relevance of this therapeutic tool in comparison with other methods is discussed.

Comparative efficacies of ciprofloxacin and pefloxacin alone or in combination with fosfomycin in experimental endocarditis induced by multidrug-susceptible and -resistant Pseudomonas aeruginosa

The in vivo efficacy of ciprofloxacin or pefloxacin alone or in combination with fosfomycin was evaluated in experimental aortic valve endocarditis induced in 133 rabbits by a multidrug-susceptible or multidrug-resistant strain of Pseudomonas aeruginosa. Therapy was initiated early (12 h after infection), when bacterial counts in aortic valve vegetations were relatively low, or late (48 h after infection), when vegetations contained a larger inoculum. Antibodies were administered as a continuous 24-h intravenous infusion. Mean steady-state levels of ciprofloxacin (64 mg/kg), pefloxacin (64 mg/kg), and fosfomycin (300 mg/kg) in serum were 2.5, 4.2, and 63.9 mg/liter, respectively. For the multidrug-susceptible strain, all regimens except pefloxacin alone significantly reduced the number of CFU per gram of vegetation versus controls, whether treatment was performed early or late. For the multidrug-resistant strain, none of the regimens showed differences from untreated controls, except ciprofloxacin-fosfomycin, which significantly reduced bacterial counts in vegetations compared with controls when therapy was begun early (4.1 +/- 1.1 log10 CFU/g of vegetation; P < 0.001 versus the control). These data suggest that combination of fosfomycin with ciprofloxacin or pefloxacin is more effective than ciprofloxacin or pefloxacin alone for the therapy of severe infections caused by multidrug-susceptible P. aeruginosa.

[Inhibitory action of chlorpromazine on intestinal movement in mice and its antagonistic agents]

Adynamic ileus is a toxic effect produced by chlorpromazine (Chl). The present study is to analyze the inhibitory action of Chl on the intestinal movement of mice and to search its antagonistic remedies. Inhibition was evaluated by 2 tests: the loss of defecation reflex and the inhibited transport of phenol red in the intestinal tract. Chl (1-2 mg.kg-1 i.p. or 1 microgram per mouse i.c.v.) inhibited the intestinal movement powerfully. Scopolamine (Sco 4 mg.kg-1 i.p. or 4-8 micrograms per mouse i.c.v.) produced the same effect. The i.v. ED50 (L95) of Chl and Sco for inhibition of the defecation reflex were 0.85 (0.79-0.93) and 3.49 (3.24-3.78) mg.kg-1, respectively. Haloperidol (1-4 mg.kg-1 i.p.), sulpiride (10 mg.kg-1 i.p.), and phentolamine (2-4 mg.kg-1 i.p. or 4 micrograms per mouse i.c.v.) did not affect the defecation reflex. In the isolated guinea pig ileum the pA2 value of Chl against carbachol (Car) was 4.5 and that of Sco was 9.1. In addition, the inhibitory effect caused by Sco was antagonized by physostigmine (Phy 0.08 mg.kg-1 sc), but not by pilocarpine (Pil 100-200 micrograms per mouse i.c.v.) and 4-aminopyridine (4-AP 1 microgr per mouse i.c.v.), whereas that caused by Chl was antagonized by Pil (100 micrograms per mouse i.c.v.) and 4-AP (1 microgram per mouse i.c.v.), but not by Phy. Neostigmine (Neo 0.05 mg.kg-1 sc) or Car (0.05 mg.kg-1 sc) combined with 4-AP (2 mg.kg-1 sc) exhibited a synergetic effect against Chl-induced inhibition.(ABSTRACT TRUNCATED AT 250 WORDS)

In vivo bactericidal activities of ciprofloxacin and pefloxacin in an experimental model of Serratia marcescens endocarditis

The critical concentrations of pefloxacin and ciprofloxacin in serum, corresponding to the lowest concentration in serum able to achieve a 2-log-unit reduction in the CFU in vegetations after a 24-h exposure at a steady-state concentration obtained by a continuous intravenous infusion, were determined in an experimental model of Serratia marcescens endocarditis in rabbits. In vitro data showed that the MICs of ciprofloxacin and pefloxacin were 0.06 and 0.25 mg/liter, respectively. The killing curves indicated a maximum killing rate at a concentration four times that of the MICs. In vivo, the critical concentrations of pefloxacin and ciprofloxacin in serum were 0.4 and 0.24 mg/liter, respectively, corresponding to a concentration of four times the MICs.

Action spectrum for subliminal light control of adaptation in Phycomyces phototropism

Adaptation processes enable phototropism and other blue light responses of Phycomyces to operate over a 10-decade range of fluence rate. Phototropic latency, used routinely to monitor the kinetics of sensitivity recovery after a step down in fluence rate, can be shortened by application of dim light for 35 min during the early part of the latency period. This light is termed subliminal, because it does not elicit phototropism under these experimental conditions; rather, it exerts its influence on the underlying adaptation kinetics. Fluence rate-response data for this latency reduction, obtained at 17 wavelengths of subliminal light from 347 to 742 nm, showed a variety of shapes that could be fit by zero, one, or two sigmoidal components, plus a constant term. At most wavelengths, the fluence-rate threshold for latency reduction by subliminal light tended to be well below the absolute threshold for phototropism, indicating that this effect is highly sensitive. An action spectrum for the sensitivity of the subliminal light effect, derived from the fluence rate-response curves, shows major peaks around 400 and 500 nm and a broad band from 570 to 670 nm, followed by a steep absorption edge. The sensitivity in the near ultraviolet region is relatively very low. The magnitude of the latency reduction also depends strongly on wavelength with a maximum at about 450 nm. The fluence-rate response data and the action spectrum--which is markedly different from that for phototropism and other blue-light responses of Phycomyces--indicate the participation of multiple pigments, or pigment states, in the photocontrol of adaptation.