Comparison of the antibacterial efficacies of ampicillin and ciprofloxacin against experimental infections with Listeria monocytogenes in hydrocortisone-treated mice

Unraveling the Interaction Mechanism of the Compounds From Cladophora sp to Recognize Prospective Larvicidal and Bactericidal Activities: In vitro and In Silico Approaches

The present investigation aims to validate the larvicidal and antibacterial potential of Cladophora sp through in vitro and in silico approaches. The presence of phytoconstituents, functional groups and the compounds responsible for antibacterial and larvicidal activity were assessed through FT-IR and GC-MS analyses which unveiled the existence of active secondary metabolites, hydroxyl, alkane and carbonyl groups. The larvicidal and antibacterial activity of algal extract were examined and revealed complete mortality and substantial zone of inhibition was observed against Culex quinquefasciatus and E. coli. To support the in vitro investigation in silico studies were performed. Molecular docking investigations of the selected compounds from GC-MS which exhibited favorable agreement with drug likeness and ADMET properties indicated robust interactions with the larvicidal and bacterial proteins showcasing considerable binding affinities. Notably, 1,2,4-Oxadiazole, 3-(1,3-benzodioxol-5-yl)-5-[(4-iodo-1H-pyrazol-1-yl) methyl]- exhibited strong interactions with the target proteins. Density Functional Theory revealed that the energy gap of the lead compound was reduced and substantiates the occurrence of intermolecular charge transfer. Molecular Dynamic simulations confirms the stability and flexibility of the lead compound. Hence, this investigation offers computational perspectives on the molecular interactions of Cladophora sp, suggesting its suitability as a promising biocontrol agent.

Pharmacokinetic/Pharmacodynamic Index Linked to In Vivo Efficacy of the Ampicillin-Ceftriaxone Combination against Enterococcus faecalis

Combination therapy with ampicillin plus ceftriaxone (AMP+CRO) is the first-line therapy for treating severe infections due to Enterococcus faecalis. However, the pharmacokinetic/pharmacodynamic (PK/PD) index linked to the in vivo efficacy of the combination is not yet defined, hindering dose optimization in the clinic. Because classical PK/PD indices are not directly applicable to antimicrobial combinations, two novel indices were tested in the optimized murine model of infection by E. faecalis to delineate the potentiation of AMP by CRO: the time above the CRO threshold (T_>threshold) and the time above the AMP instantaneous MIC (T_>MICi). The potential clinical relevance was evaluated by simulating human doses of AMP and CRO. Hill's equation fitted well the exposure-response data in terms of T_>threshold, with a CRO threshold of 1 mg/L. The required exposures were 46%, 49%, and 52% for stasis and 1- and 2-log₁₀ killing, respectively. Human ceftriaxone doses of 2 g every 12 h (q12h) would reach the target in >90% of strains with thresholds ≤64 mg/L. The AMP T_>MICi index also fitted well, and the required exposures were 37%, 41%, and 46% for stasis and 1- and 2-log₁₀ killing, respectively. In humans, the addition of CRO would allow use of lower AMP doses to reach the same T_>MICi and to treat strains with higher MICs. This is the first report of the PK/PD indices and required magnitudes linked to AMP+CRO against E. faecalis; these results can be used as the basis to guide the design of clinical trials to improve combined therapy against enterococci.

A new pharmacodynamic approach to study antibiotic combinations against enterococci in vivo: Application to ampicillin plus ceftriaxone

The combination of ampicillin (AMP) and ceftriaxone (CRO) is considered synergistic against Enterococcus faecalis based on in vitro tests and the rabbit endocarditis model, however, in vitro assays are limited by the use of fixed antibiotic concentrations and the rabbit model by poor bacterial growth, high variability, and the use of point dose-effect estimations, that may lead to inaccurate assessment of antibiotic combinations and hinder optimal translation. Here, we tested AMP+CRO against two strains of E. faecalis and one of E. faecium in an optimized mouse thigh infection model that yields high bacterial growth and allows to define the complete dose-response relationship. By fitting Hill’s sigmoid model and estimating the parameters maximal effect (E_max) and effective dose 50 (ED₅₀), the following interactions were defined: synergism (E_max increase ≥2 log₁₀ CFU/g), antagonism (E_max reduction ≥1 log₁₀ CFU/g) and potentiation (ED₅₀ reduction ≥50% without changes in E_max). AMP monotherapy was effective against the three strains, yielding valid dose-response curves in terms of dose and the index fT_>MIC. CRO monotherapy showed no effect. The combination AMP+CRO against E. faecalis led to potentiation (59–81% ED₅₀ reduction) and not synergism (no changes in E_max). Against E. faecium, the combination was indifferent. The optimized mouse infection model allowed to obtain the complete dose-response curve of AMP+CRO and to define its interaction based on pharmacodynamic parameter changes. Integrating these results with the pharmacokinetics will allow to derive the PK/PD index bound to the activity of the combination, essential for proper translation to the clinic.

An optimized mouse thigh infection model for enterococci and its impact on antimicrobial pharmacodynamics

Negligible in vivo growth of enterococci and high-level dispersion of data have led to inaccurate estimations of antibiotic pharmacodynamics (PD). Here we improved an in vivo model apt for PD studies by optimizing the in vitro culture conditions for enterococci. The PD of vancomycin (VAN), ampicillin-sulbactam (SAM), and piperacillin-tazobactam (TZP) against enterococci were determined in vivo, comparing the following different conditions of inoculum preparation: aerobiosis, aerobiosis plus mucin, and anaerobiosis plus mucin. Drug exposure was expressed as the ratio of the area under the concentration-time curve for the free, unbound fraction of the drug to the MIC (fAUC/MIC) (VAN) or the time in a 24-h period that the drug concentration for the free, unbound fraction exceeded the MIC under steady-state pharmacokinetic conditions (fT(>MIC)) (SAM and TZP) and linked to the change in log10 CFU/thigh. Only anaerobiosis plus mucin enhanced the in vivo growth, yielding significant PD parameters with all antibiotics. In conclusion, robust in vivo growth of enterococci was crucial for better determining the PD of tested antibacterial agents, and this was achieved by optimizing the procedure for preparing the inoculum.

Risk of death does not alter the efficacy of hydrocortisone therapy in a mouse E. coli pneumonia model: risk and corticosteroids in sepsis

BACKGROUND

Risk of death may influence the efficacy of anti-inflammatory agents in sepsis. "Physiologic" dose corticosteroids, while improving survival in earlier trials with higher control mortality rates (>50%), were not beneficial in the recent CORTICUS trial with lower control mortality (31%). We investigated whether risk of death altered the effects of hydrocortisone in a mouse pneumonia model.

METHODS

Mice (n=637) challenged with high, medium or low intratracheal E. coli doses were randomized to receive one of three hydrocortisone doses (5, 25 or 125 mg/kg) or normal saline (NS) only (control) for 4 days. All animals were treated with similar volumes of ceftriaxone and NS support following E. coli and were observed for 168 h.

RESULTS

Decreasing E. coli doses reduced control mortality rates (from 94 to 12%). In similar patterns (not significant) each hydrocortisone dose increased the odds ratio (OR) of survival (95% confidence interval) with each E. coli dose (ORs ranging from 1.2 [0.4, 3.7] to 6.1 [0.6, 61.0]). The effect of hydrocortisone on the OR was not related to control mortality rate (r=-0.13, p=0.29) and overall was highly significant (2.04 [1.37, 3.03], p=0.0004). In randomly selected animals 48 h after the highest E. coli dose, compared with the control, hydrocortisone (125 mg/kg) significantly decreased IL-6, INFgamma, and nitric oxide levels.

CONCLUSIONS

In this mouse model the beneficial effects of hydrocortisone were independent of risk of death. These findings suggest that factors other than risk of death may underlie the differing effects of corticosteroids in recent sepsis trials.

Major role of levofloxacin in the treatment of a case of Listeria monocytogenes meningitis

We report a case of acute bacterial meningitis due to Listeria monocytogenes whose successful treatment was mainly attributable to high-dose levofloxacin therapy (500 mg iv bid). This supports the hypothesis that levofloxacin may be an effective option for the treatment of listerial meningitis.

The effect of centaurein on interferon-γ expression and Listeria infection in mice

We previously found that centaurein enhanced IFN-gamma transcription in T cells. Here, we demonstrate that centaurein increased the IFN-gamma expression in T and NK cells and the serum IFN-gamma level in mice. Centaurein elevated the transcription of T-bet but not GATA-3, which is consistent with its effect on that of IFN-gamma but not IL-4. Additionally, centaurein effectively protected mice against Listeria infection. Moreover, centaurein per se or in combination with antibiotics could treat Listeria infection. Our mechanistic studies suggest that centaurein augments IFN-gamma expression via a transcriptional up-regulation of T-bet and that centaurein protects against or treats Listeria infection via a modulation of IFN-gamma expression.

The antibacterial efficacy of trovafloxacin against an experimental infection with Listeria monocytogenes in hydrocortisone-treated mice

The efficacy of trovafloxacin in treating Listeria monocytogenes infections in glucocorticosteroid-treated mice was compared with the efficacy of amoxycillin. Swiss mice were treated with daily injections of 2.5 mg hydrocortisone s.c. and then infected i.v. with 1 x 10(7) cfu of L. monocytogenes. Untreated, this level of infection resulted in 100% mortality between day 3 and day 5 after infection. Both s.c. trovafloxacin and amoxycillin were effective in reducing the number of viable L. monocytogenes in the liver and spleen. Although the MIC of amoxycillin for this isolate of L. monocytogenes was lower than that of trovafloxacin (0.063 mg/L versus 0.5 mg/L, respectively), trovafloxacin was more efficacious in vivo after a single dose in the dose range between 12.5 and 100 mg/kg than was amoxycillin. After treatment with trovafloxacin at 100 mg/kg bodyweight od for 3 days, a mean log10 cfu of 1.58 and 2.52 L. monocytogenes could be recovered from the spleens and livers, respectively, whereas after treatment with amoxycillin at 100 mg/kg bodyweight every 8 h for 3 days, the mean 1og10 cfu values were 2.36 and 2.02, respectively. These differences were statistically not significant. Results of the present study show that the antibacterial efficacy of trovafloxacin against L. monocytogenes in our animal model is equivalent to that of amoxycillin.

Clinafloxacin (CL 960) is superior to standard therapeutics in the treatment of murine listeriosis and salmonellosis

Clinafloxacin is a novel fluoroquinolone with a broad spectrum of antibacterial activity against both gramnegative and grampositive bacteria. In this work, the activity against the facultatively intracellular bacteria Listeria monocytogenes and Salmonella typhimurium was examined in vitro, in tissue culture and in animal models of infection. All strains of L. monocytogenes and S. enterica were highly susceptible against clinafloxacin, with minimal inhibitory concentrations (MICs) that were consistently lower than those for ampicillin and ciprofloxacin, respectively. Clinafloxacin was rapidly bactericidal against L. monocytogenes and S. typhimurium since 8 times the MIC killed the bacteria within 2 hours. In contrast to ampicillin and ciprofloxacin, there was a postantibiotic effect (PAE) of 2 hours with 8 x MIC on L. monocytogenes. Clinafloxacin was more effective than ampicillin and ciprofloxacin in tissue culture cells infected with S. typhimurium or L. monocytogenes. In animal models of infection, clinafloxacin was also more potent than the reference substances. In conclusion, clinafloxacin is an excellent candidate substance for the treatment of infections caused by facultatively intracellular grampositive and gramnegative bacteria.

Comparative activities of new fluoroquinolones, alone or in combination with amoxicillin, trimethoprim-sulfamethoxazole, or rifampin, against intracellular Listeria monocytogenes

We studied the activities of the new fluoroquinolones clinafloxacin, levofloxacin, ofloxacin, and sparfloxacin alone or in combination on the intracellular growth of Listeria monocytogenes. Against intracellular growth of the four strains tested, a similar reduction of the bacterial count was obtained with clinafloxacin at the dose of 10 x MIC (delta log10 CFU/ml = -2.19 +/- 0.24), with levofloxacin at 8 x MIC (delta log10 CFU/ml = -2.28 +/- 0.25), and with sparfloxacin at 4 x MIC (delta log10 CFU/ml = -2.16 +/- 0.21) after 24 h of incubation. The combination of the quinolones with trimethoprim-sulfamethoxazole or amoxicillin did not show a substantial increase in activity compared to the fluoroquinolone alone. Antagonism with rifampin was strongly suggested. No modification of the MIC was observed after 20 successive infections of HeLa cells and contact with subinhibitory concentrations of clinafloxacin, levofloxacin, and sparfloxacin for 24 h. We conclude that clinafloxacin, levofloxacin, or sparfloxacin could represent a therapeutic alternative to amoxicillin for the treatment of Listeria infections in adults, especially clinafloxacin, whose MIC is low (0.06 to 0.12 micrograms/ml), and whose best activity against intracellular L. monocytogenes was obtained at a concentration of 1.2 micrograms/ml, which is similar to clinically achievable levels. The results must be confirmed in an experimental model.

Listeria Monocytogenes infections

This article reviews current information regarding human infection with Listeria monocytogenes. Significant advances have occurred in regard to our knowledge of the epidemiology, pathogenesis, immunology, and treatment of this disease which was formerly believed to be of importance mainly to veterinarians. It remains a cause of high mortality in the many different groups of compromised hosts it infects unless diagnosis and treatment are rapidly established.

Bay Y 3118, a new quinolone derivative, rapidly eradicates Listeria monocytogenes from infected mice and L929 cells

Bay Y 3118 is a new quinolone derivative with pronounced activity against gram-positive bacteria including the facultatively intracellular bacterium Listeria monocytogenes. Bay Y 3118 was tested in vitro and in animal models of listeriosis. All strains of L. monocytogenes and other Listeria spp. were highly susceptible in vitro; the MICs for these organisms ranged from 0.062 to 0.25 micrograms/ml. Bay Y 3118 was rapidly bactericidal in vitro, with a postantibiotic effect occurring for 3 h after removal of the antibiotic. L. monocytogenes was eliminated from infected L929 cells treated with Bay Y 3118, suggesting a bactericidal effect on the listeriae in these cells. Immunocompetent mice were rapidly cured by treatment with 4 mg every 12 h. Concomitantly, the levels of interleukin 6 and gamma interferon in mouse sera declined rapidly. In immunocompetent mice, treatment with 2 mg of Bay Y 3118 every 12 h resulted in a greater initial reduction in the listerial counts in the organs than treatment with 2 mg of ampicillin every 12 h. Bay Y 3118 completely eliminated L. monocytogenes from the livers and spleens of chronically infected nude mice. However, some of the bacteria reappeared after the cessation of therapy. In conclusion, Bay Y 3118 is an excellent candidate substance for the therapy of infections caused by facultatively intracellular gram-positive bacteria such as L. monocytogenes.

An improved direct viable count for the enumeration of bacteria in milk

The direct viable count (DVC), a microscopic method for the enumeration of viable bacteria, was modified by replacing nalidixic acid with ciprofloxacin. This modification made it possible to apply this method to a variety of Gram-negative and Gram-positive bacteria which was not previously possible. Of the four antibiotics tested (nalidixic acid, novobiocin, ciprofloxacin and mitomycin C), ciprofloxacin and mitomycin C were the only ones effective for use in the DVC with all of the bacteria tested. In addition, ciprofloxacin could be used at a single concentration (1 microgram/ml) while adjustments were necessary with the other antibiotics when examining bacteria from different genera and, in some instances, from different species. The use of ciprofloxacin in the DVC resulted in viable cells that had elongated by 5-11 times their original length. We conclude that the modified DVC will be useful in growth and survival studies of bacterial pathogens and spoilage organisms in milk and other foods.