Lipid A profiling and metabolomics analysis of paired polymyxin-susceptible and -resistant MDR Klebsiella pneumoniae clinical isolates from the same patients before and after colistin treatment.

BACKGROUND: The increased incidence of polymyxin-resistant MDR Klebsiella pneumoniae has become a major global health concern. OBJECTIVES: To characterize the lipid A profiles and metabolome differences between paired polymyxin-susceptible and -resistant MDR K. pneumoniae clinical isolates. METHODS: Three pairs of K. pneumoniae clinical isolates from the same patients were examined [ATH 7 (polymyxin B MIC 0.25 mg/L) versus ATH 8 (64 mg/L); ATH 15 (0.5 mg/L) versus ATH 16 (32 mg/L); and ATH 17 (0.5 mg/L) versus ATH 18 (64 mg/L)]. Lipid A and metabolomes were analysed using LC-MS and bioinformatic analysis was conducted. RESULTS: The predominant species of lipid A in all three paired isolates were hexa-acylated and 4-amino-4-deoxy-l-arabinose-modified lipid A species were detected in the three polymyxin-resistant isolates. Significant metabolic differences were evident between the paired isolates. Compared with their corresponding polymyxin-susceptible isolates, the levels of metabolites in amino sugar metabolism (UDP-N-acetyl-α-d-glucosamine and UDP-N-α-acetyl-d-mannosaminuronate) and central carbon metabolism (e.g. pentose phosphate pathway and tricarboxylic acid cycle) were significantly reduced in all polymyxin-resistant isolates [fold change (FC) > 1.5, P < 0.05]. Similarly, nucleotides, amino acids and key metabolites in glycerophospholipid metabolism, namely sn-glycerol-3-phosphate and sn-glycero-3-phosphoethanolamine, were significantly reduced across all polymyxin-resistant isolates (FC > 1.5, P < 0.05) compared with polymyxin-susceptible isolates. However, higher glycerophospholipid levels were evident in polymyxin-resistant ATH 8 and ATH 16 (FC > 1.5, P < 0.05) compared with their corresponding susceptible isolates. CONCLUSIONS: To our knowledge, this study is the first to reveal significant metabolic perturbations associated with polymyxin resistance in K. pneumoniae.

Rapid Increase in Carbapenemase-Producing Enterobacteriaceae in Retail Meat Driven by the Spread of the blaNDM-5-Carrying IncX3 Plasmid in China from 2016 to 2018.

The presence and molecular characteristics of carbapenemase-producing Enterobacteriaceae (CPE) among meat products in China were investigated. A total of 110 carbapenem-resistant Enterobacteriaceae (CRE) isolates, including 94 Escherichia coli and 10 Klebsiella pneumoniae isolates, were identified from 105 of 794 (13.2%) samples. The positive rates markedly increased from 2016 (9.4%) to 2018 (22.2%). Only blaNDM genes were detected; 79.1% of blaNDM genes were carried by IncX3 plasmids. Routine monitoring of carbapenemase-producing Enterobacteriaceae in the animal food supply is highly recommended.

First Detection of Colistin-Resistant Klebsiella pneumoniae in Association with NDM-5 Carbapenemase Isolated from Clinical Lebanese Patients.

This study aims to describe the molecular mechanisms of carbapenem and colistin resistance in Klebsiella pneumoniae strains isolated from hospitalized patients in Lebanon. We report in this study the first description of NDM-5 producing carbapenem-resistant K. pneumoniae ST383, as well as the presence of two out of five isolates resistant to colistin due to mutations in the amino acid sequences of proteins (PmrB, PhoQ, and MgrB). Therefore, screening of such isolates may be effective in limiting the spread of these resistant microorganisms in hospitalized patients and within the community.

Cystatins 9 and C as a Novel Immunotherapy Treatment That Protects against Multidrug-Resistant New Delhi Metallo-Beta-Lactamase-1-Producing Klebsiella pneumoniae.

Multidrug-resistant (MDR) bacterial pneumonia can induce dysregulated pulmonary and systemic inflammation leading to morbidity and mortality. Antibiotics to treat MDR pathogens do not function to modulate the extent and intensity of inflammation and can have serious side effects. Here we evaluate the efficacy of two human cysteine proteinase inhibitors, cystatin 9 (CST9) and cystatin C (CSTC), as a novel immunotherapeutic treatment to combat MDR New Delhi metallo-beta-lactamase-1 (NDM-1)-producing Klebsiella pneumoniae Our results showed that mice infected intranasally (i.n.) with a 90% lethal dose (LD90) challenge of NDM-1 K. pneumoniae and then treated with the combination of human recombinant CST9 (rCST9) and rCSTC (rCSTs; 50 pg of each i.n. at 1 h postinfection [p.i.] and/or 500 pg of each intraperitoneally [i.p.] at 3 days p.i.) had significantly improved survival compared to that of infected mice alone or infected mice treated with individual rCSTs (P < 0.05). Results showed that both of our optimal rCST treatment regimens modulated pulmonary and systemic proinflammatory cytokine secretion in the serum, lungs, liver, and spleen in infected mice (P < 0.05). Treatment also significantly decreased the bacterial burden (P < 0.05) while preserving lung integrity, with reduced inflammatory cell accumulation compared to that in infected mice. Further, rCST treatment regimens reduced lipid peroxidation and cell apoptosis in the lungs of infected mice. Additionally, in vitro studies showed that rCSTs (50 or 500 pg of each) directly decreased the viability of NDM-1 K. pneumoniae In conclusion, the data showed that rCST9/rCSTC worked synergistically to modulate host inflammation against MDR NDM-1 K. pneumoniae pneumonia, which significantly improved survival. Therefore, rCST9/rCSTC is a promising therapeutic candidate for the treatment of bacterial pneumonia.

Additivity vs Synergism: Investigation of the Additive Interaction of Cinnamon Bark Oil and Meropenem in Combinatory Therapy.

Combinatory therapies have been commonly applied in the clinical setting to tackle multi-drug resistant bacterial infections and these have frequently proven to be effective. Specifically, combinatory therapies resulting in synergistic interactions between antibiotics and adjuvant have been the main focus due to their effectiveness, sidelining the effects of additivity, which also lowers the minimal effective dosage of either antimicrobial agent. Thus, this study was undertaken to look at the effects of additivity between essential oils and antibiotic, via the use of cinnamon bark essential oil (CBO) and meropenem as a model for additivity. Comparisons between synergistic and additive interaction of CBO were performed in terms of the ability of CBO to disrupt bacterial membrane, via zeta potential measurement, outer membrane permeability assay and scanning electron microscopy. It has been found that the additivity interaction between CBO and meropenem showed similar membrane disruption ability when compared to those synergistic combinations which was previously reported. Hence, results based on our studies strongly suggest that additive interaction acts on a par with synergistic interaction. Therefore, further investigation in additive interaction between antibiotics and adjuvant should be performed for a more in depth understanding of the mechanism and the impacts of such interaction.

Dusuqing granules (DSQ) suppress inflammation in Klebsiella pneumonia rat via NF-κB/MAPK signaling.

BACKGROUND: Dusuqing granules (DSQ) have been used in the treatment of bacterial pneumonia clinically, with remarkable benefits. This study was initiated to explore the effects of DSQ on pulmonary inflammation by regulating nuclear factor (NF)-κB/mitogen-activated protein kinase (MAPK) signaling in bacterial pneumonia rats. METHODS: Rat model was duplicated with Klebsiella pneumonia by a one-time intratracheal injection. Rats were randomized into control, model, DSQ and levofloxacin (LVX) groups. After administrated with appropriate medicines for 7 days, lung tissues were harvested and prepared for pathological analysis, and interleukin (IL)-1, IL-6, monocyte chemotactic protein (MCP)-1and macrophage inflammatory protein (MIP)-2 detections. NF-κB mRNA was measured by real-time qPCR, and the phosphorylation and total proteins of P38MAPK, JNK46/54, ERK42/44 were determined by Western blotting. RESULTS: Marked pathological impairments were observed in model rats, whereas were improved in DSQ group. The cytokines levels, NF-κB mRNA expression and the phosphorylation of P38MAPK, JNK46/54 and ERK42/44 proteins were significantly higher in model group, and were significantly depressed in DSQ group. CONCLUSION: The protective effects of DSQ on Klebsiella pneumonia might be attributed to its inactivative effects of NF-κB/ MAPK pathway.

Metabolic response to Klebsiella pneumoniae infection in an experimental rat model.

Bacteremia, the presence of viable bacteria in the blood stream, is often associated with several clinical conditions. Bacteremia can lead to multiple organ failure if managed incorrectly, which makes providing suitable nutritional support vital for reducing bacteremia-associated mortality. In order to provide such information, we investigated the metabolic consequences of a Klebsiella pneumoniae (K. pneumoniae) infection in vivo by employing a combination of (1)H nuclear magnetic resonance spectroscopy and multivariate data analysis. K. pneumoniae was intravenously infused in rats; urine and plasma samples were collected at different time intervals. We found that K. pneumoniae-induced bacteremia stimulated glycolysis and the tricarboxylic acid cycle and also promoted oxidation of fatty acids and creatine phosphate to facilitate the energy-demanding host response. In addition, K. pneumoniae bacteremia also induced anti-endotoxin, anti-inflammatory and anti-oxidization responses in the host. Furthermore, bacteremia could cause a disturbance in the gut microbiotal functions as suggested by alterations in a range of amines and bacteria-host co-metabolites. Our results suggest that supplementation with glucose and a high-fat and choline-rich diet could ameliorate the burdens associated with bacteremia. Our research provides underlying pathological processes of bacteremia and a better understanding of the clinical and biochemical manifestations of bacteremia.

[Protection and mechanism of Fagopyrum cymosum on lung injury in rats with Klebsiella pneumonia].

OBJECTIVE: To study the mechanism of protective effect of Fagopyrum cymosum on lung injury induced by Klebsiella pneumonia in rats. METHODS: The model of rats with Klebsiella pneumonia was established. The male SD rats were randomly divided into control group, model group, Fagopyrum cymosum (6, 3, 1.5 g/kg) three groups, levofloxacin (25 mg/kg) group. The pathological change of lung was observed. The content of IL-1beta, IL-6, IL-8, TNF-alpha, ICAM-1, INF-gamma in serum were measured by radioimmunoassay and Elisa. TNF-alpha, ICAM-1, NF-kappaB p65 protein expressions were measured by immunohistochemistry. MIP-2mRNA expression was detected by in situ hybridization. RESULTS: The rats of model group had obvious lung injury, but those of Fagopyrum cymosum and levofloxacin groups had less injury. The contents of IL-1beta, IL-6, IL-,8, TNF-alpha, ICAM-1 and INF-gamma in serum and the expressions of TNF-a, ICAM-1, NF-kappaB p65 and MIP--2mRNA of model group were significantly higher than those of the control group (P < 0.05 or P < 0.01), while the indexes of Fagopyrum cymosum and levofloxacin groups were significantly lower than those of model group (P < 0.05 or P < 0.01). CONCLUSION: The lung injury induced by Klebsiella pneumonia is related to TNF-alpha, ICAM-1, NF-kappaB p65 and MIP-2mRNA. To decrease the excessive expression of TNF-alpha, ICAM-1, NF-kappaB p65 and MIP-2mRNA might be the main mechanism of protective effect of Fagopyrum cymosum on lung injury.

[Effect of jinqiaomai on expression of TLR2/4, MyD88 mRNA and IkappaB-alpha in lung tissue of rats with Klebsiella pneumonia].

OBJECTIVE: To study the mechanism of protective effect of Jinqiaomai (JQM) on lung injury induced by Klebsiella pneumonia in rats. METHOD: The model of rats with Klebsiella pneumonia was established. The male SD rats were randomly divided into control group, model group, JQM (6, 3, 1.5 g x kg(-1)) three groups, levofloxacin (25 mg x kg(-1)) group, JQM (3 g x kg(-1)) + levofloxacin (25 mg x kg(-1)) group. The contents of IL-1beta, ICAM-1 and INF-gamma in the lung tissue homogenate were measured by radio-immunoassay and Elisa. TLR2/4 mRNA and MyD88 mRNA expression were detected by RT-PCR. IkappaB-alpha expression was detected by Western Blot. RESULT: The rats of model group had obvious lung injury, but those of JQM, JQM + levofloxacin and levofloxacin groups had less injury. The contents of IL-1beta, ICAM-1 and INF-gamma in lung tissue homogenate and the expressions of TLR2/4 mRNA, MyD88 mRNA and IkappaB-alpha in lung of model group were significantly higher than those in the control group (P < 0.05 or P < 0.01), while IL-1beta, ICAM-1 and INF-gamma of JQM groups were significantly lower than those of model group (P < 0.05 or P < 0.01). The expressions of TLR2/4 mRNA, MyD88 mRNA and IkappaB-alpha of JQM (6.3 g x kg(-1)) groups were significantly lower than those of model group(P <0. 05 or P <0. 01). CONCLUSION: The lung injury induced by Klebsiella pneumonia is related to TLR2/4, MyD88 mRNA and IkappaB-alpha. To decrease the excessive expression of TLR2/4, MyD88 mRNA and IkappaB-alpha might be the main mechanism of protective effect of Jinqiaomai on lung injury.

Zinc supplementation restores PU.1 and Nrf2 nuclear binding in alveolar macrophages and improves redox balance and bacterial clearance in the lungs of alcohol-fed rats.

BACKGROUND: Chronic alcohol abuse causes oxidative stress, impairs alveolar macrophage immune function, and increases the risk of pneumonia and acute lung injury. Recently we determined that chronic alcohol ingestion in rats decreases zinc levels and macrophage function in the alveolar space; provocative findings in that zinc is essential for normal immune and antioxidant defenses. Alveolar macrophage immune function depends on stimulation by granulocyte/monocyte colony-stimulating factor, which signals via the transcription factor PU.1. In parallel, the antioxidant response element signals via the transcription factor Nrf2. However, the role of zinc bioavailability on these signaling pathways within the alveolar space is unknown. METHODS: To determine the efficacy of dietary zinc supplementation on lung bacterial clearance and oxidative stress, we tested 3 different groups of rats: control-fed, alcohol-fed, and alcohol-fed with zinc supplementation. Rats were then inoculated with intratracheal Klebsiella pneumoniae, and lung bacterial clearance was determined 24 hours later. Isolated alveolar macrophages were isolated from uninfected animals and evaluated for oxidative stress and signaling through PU.1 and Nrf2. RESULTS: Alcohol-fed rats had a 5-fold decrease in lung bacterial clearance compared to control-fed rats. Dietary zinc supplementation of alcohol-fed rats normalized bacterial clearance and mitigated oxidative stress in the alveolar space, as reflected by the relative balance of the thiol redox pair cysteine and cystine, and increased nuclear binding of both PU.1 and Nrf2 in alveolar macrophages from alcohol-fed rats. CONCLUSIONS: Dietary zinc supplementation prevents alcohol-induced alveolar macrophage immune dysfunction and oxidative stress in a relevant experimental model, suggesting that such a strategy could decrease the risk of pneumonia and lung injury in individuals with alcohol use disorders.

Curcumin alone and in combination with augmentin protects against pulmonary inflammation and acute lung injury generated during Klebsiella pneumoniae B5055-induced lung infection in BALB/c mice.

Acute lung injuries due to acute lung infections remain a major cause of mortality. Thus a combination of an antibiotic and a compound with immunomodulatory and anti-inflammatory activities can help to overcome acute lung infection-induced injuries. Curcumin derived from the rhizome of turmeric has been used for decades and it exhibits anti-inflammatory, anti-carcinogenic, immunomodulatory properties by downregulation of various inflammatory mediators. Keeping these properties in mind, we investigated the anti-inflammatory properties of curcumin in a mouse model of acute inflammation by introducing Klebsiella pneumoniae B5055 into BALB/c mice via the intranasal route. Intranasal instillation of bacteria in this mouse model of acute pneumonia-induced inflammation resulted in a significant increase in neutrophil infiltration in the lungs along with increased production of various inflammatory mediators [i.e. malondialdehyde (MDA), myeloperoxidase (MPO), nitric oxide (NO), tumour necrosis factor (TNF)-alpha] in the lung tissue. The animals that received curcumin alone orally or in combination with augmentin, 15 days prior to bacterial instillation into the lungs via the intranasal route, showed a significant (P <0.05) decrease in neutrophil influx into the lungs and a significant (P <0.05) decrease in the production of MDA, NO, MPO activity and TNF-alpha levels. Augmentin treatment alone did not decrease the MDA, MPO, NO and TNF-alpha levels significantly (P >0.05) as compared to the control group. We therefore conclude that curcumin ameliorates lung inflammation induced by K. pneumoniae B5055 without significantly (P <0.05) decreasing the bacterial load in the lung tissue whereas augmentin takes care of bacterial proliferation. Hence, curcumin can be used as an adjunct therapy along with antibiotics as an anti-inflammatory or an immunomodulatory agent in the case of acute lung infection.

Efficacy of bacteriophage treatment in murine burn wound infection induced by klebsiella pneumoniae.

In the present study, the therapeutic potential of purified and well-characterized bacteriophages was evaluated in thermally injured mice infected with Klebsiella pneumoniae B5055. The efficacy of five Klebsiella phages (Kpn5, Kpn12, Kpn13, Kpn17, and Kpn22) was evaluated on the basis of survival rate, decrease in bacterial counts in different organs of phage-treated animals, and regeneration of skin cells as observed by histopathological examination of phage-treated skin. Toxicity studies performed with all the phages showed them to be non-toxic, as no signs of morbidity and mortality were observed in phage-treated mice. The results of the study indicate that a single dose of phages, intraperitoneally (i.p.) at an MOI of 1.0, resulted in significant decrease in mortality, and this dose was found to be sufficient to completely cure K. pneumoniae infection in the burn wound model. Maximum decrease in bacterial counts in different organs was observed at 72 h post infection. Histopathological examination of skin of phage-treated mice showed complete recovery of burn infection. Kpn5 phage was found to be highly effective among all the phages and equally effective when compared with a cocktail of all the phages. From these results, it can be concluded that phase therapy may have the potential to be used as stand-alone therapy for K.pneumoniae induces burn wound infection, especially in situations where multiple antibiotic-resistant organisms are encountered.

Cardiac functional and structural alterations induced by endotoxin in rats: importance of platelet-activating factor.

OBJECTIVE: In this study, we evaluated the time course of the alterations in left ventricular (LV) dimensions, LV wall thickness, and LV systolic function in rats with endotoxemia by using echocardiography as well as myocardial histopathologic assessments. Our second goal was to examine whether pretreatment with a platelet-activating factor (PAF) antagonist would ameliorate the lipopolysaccharide (LPS)-induced cardiovascular collapse during the early phase. DESIGN: A prospective, controlled, in vivo animal laboratory study. SETTING: Research laboratory at a university. SUBJECTS: Male, Wistar rats (8-9 wks old; n = 83). INTERVENTIONS: In pentobarbital-anesthetized rats, the right carotid artery was cannulated to measure the arterial blood pressure and to sample blood. The right jugular vein also was catheterized for the administration of drugs. LPS (2 mg/kg) derived from Klebsiella pneumoniae or physiologic saline was administered in the presence or absence of pretreatment with TCV-309, a specific potent PAF antagonist. Echocardiographic studies were performed with an 8- to 13-MHz transducer. MEASUREMENTS AND MAIN RESULTS: LPS administration immediately induced progressive hypotension. The maximal hypotensive response was observed at 10 mins after LPS infusion with mean arterial pressure decreasing from 119 +/- 2 to 56 +/- 3 mm Hg (p < .001). LV end-diastolic internal dimensions decreased from 6.4 +/- 0.1 to 3.1 +/- 0.1 mm (p < .001) at 30 mins after LPS and remained significantly reduced compared with control rats. LV end-systolic dimensions also decreased dramatically from 3.5 +/- 0.2 to 0.5 +/- 0.1 mm (p < .001) at 30 mins after LPS and remained significantly reduced throughout the experiment. LV fractional shortening increased from 45 +/- 1% to 84 +/- 2% (p < .001) at 30 mins after LPS and remained elevated compared with control rats. LV wall thickness increased strikingly from 15 mins until 2 hrs after LPS infusion. Pathologic studies demonstrated marked congestion of capillaries and mild edema in the LV myocardium. The hematocrit increased after the administration of LPS. LPS markedly increased sympathetic tone as demonstrated by the elevation of plasma concentrations of epinephrine and norepinephrine. There was no elevation of concentrations of nitrite and nitrate. Pretreatment with TCV-309, a specific potent PAF antagonist, reduced LPS-induced hypotension and attenuated LV functional and structural changes. TCV-309 administration reduced the LPS-induced adrenergic activation and hemoconcentration. CONCLUSIONS: The hypotension that occurred during the initial phase of LPS-induced shock was accompanied by LV functional and structural alterations. The marked increase in LV wall thickness can be ascribed to the congestion of capillaries and edema in the LV myocardium. Pretreatment with a PAF antagonist reduced LPS-induced alterations. PAF may play a pivotal role during the initial phase of LPS-induced cardiovascular responses.

In vitro and in vivo activities of amikacin, cefepime, amikacin plus cefepime, and imipenem against an SHV-5 extended-spectrum beta-lactamase-producing Klebsiella pneumoniae strain.

The in vitro and in vivo effectiveness of amikacin, cefepime, and imipenem was studied using a high inoculum of an extended-spectrum beta-lactamase-producing Klebsiella pneumoniae strain. An in vitro susceptibility test at the standard inoculum predicted the in vivo outcome of amikacin or imipenem while it did not do so for cefepime due to the inoculum effect.

Evaluation of trovafloxacin in the treatment of Klebsiella pneumoniae lung infection in tumour-bearing mice.

Trovafloxacin, a new trifluoroquinolone, was evaluated for its therapeutic efficacy against Klebsiella pneumoniae lung infection in tumour (P388 murine leukaemia cells)-bearing mice, treated with or without a chemotherapeutic agent, daunorubicin (DNR) and in mice without tumour. Its activity was compared with ciprofloxacin and cephazolin. The effect on therapeutic efficacy of the addition of recombinant granulocyte colony stimulating factor (rGCSF) was also examined. Our study showed that both quinolones successfully cured pneumonia owing to infection with K. pneumoniae in mice without tumours but that all antibiotics failed in tumour-bearing mice if DNR was withheld. Substantial differences were noted in DNR-treated tumour-bearing mice with infection-the cure rate with trovafloxacin was 91% whereas the cure rate with ciprofloxacin or cephazolin was 57%. Addition of rGCSF to ciprofloxacin did not substantially improve its efficacy (when assessed by protection against death owing to infection; the survival rate was 41%). Trovafloxacin cure rates ranged from 80 to 90% whether or not rGCSF was added to the treatment regimen. Our results suggest that prior cancer chemotherapy had no adverse effect on the therapeutic efficacy of trovafloxacin, and that trovafloxacin may be a promising therapeutic agent for treatment of bacterial infections in the presence of leucopenia.

Influence of antimicrobial therapy on kinetics of tumor necrosis factor levels in experimental endocarditis caused by Klebsiella pneumoniae.

The kinetics of tumor necrosis factor (TNF) levels in serum during therapy with cell wall-active agents (ceftriaxone, imipenem) and gentamicin were investigated in rabbits with experimental endocarditis caused by an isogenic pair of Klebsiella pneumoniae strains: a TEM-3 beta-lactamase-producing strain (KpR) or its susceptible variant (KpS). In vitro, KpR was resistant to ceftriaxone and was susceptible to gentamicin and imipenem, while KpS was susceptible to all three antibiotics. Serum TNF levels were determined in control rabbits hourly after bacterial inoculation and then daily; they were determined in treated animals hourly after the first antibiotic injection and then daily during a 4-day therapy with either imipenem (60 mg/kg of body weight four times daily), ceftriaxone (75 mg/kg once daily), or gentamicin (4 mg/kg once daily) alone or in combination with ceftriaxone. After a transient peak (10.2 +/- 3.1 ng/ml) at 90 min following bacterial challenge, serum TNF levels remained low and stable in control animals. The peak in the serum TNF levels occurred 4 h after the first antibiotic injection and with ceftriaxone was significantly higher (P < 0.05) against KpS (1.99 +/- 0.52 ng/ml) than against KpR (1.40 +/- 0.17 ng/ml). Against the KpR strain, the levels observed with ceftriaxone were significantly higher (P < 0.05) than those obtained with the other therapeutic regimens (0.70 to 0.80 ng/ml). On the day of sacrifice, effective regimens were associated with low TNF levels. We concluded that TNF production depends on (i) the antiobiotic's mechanism of action and the susceptibility of the strain at the early phase of therapy, without any effect of the rapidity of bacterial killing, and (ii) the final reduction of the bacterial count at a later stage of therapy.

Efficacy of ceftriaxone and gentamicin in an abscess model.

The therapeutic efficacy of ceftriaxone and gentamicin was investigated in a foreign body induced abscess model in the rat by implanting a dialysis tube contaminated with Klebsiella pneumoniae into the subcutaneous tissue. Animals were treated for four days with ceftriaxone, gentamicin, and their combination starting immediately following or 48 h after the implantation. Peak free ceftriaxone and gentamicin abscess fluid levels were 4.3 and 2.6 mcg/ml, which were 7.3% and 37.5% of peak blood levels respectively. Both agents persisted longer in abscess fluid than in blood. Ceftriaxone inhibited the development of abscess formation when administered shortly after the implantation of the contaminated foreign body whereas gentamicin alone was without beneficial effect. When administered after 48 h ceftriaxone was less effective than immediately after implantation and gentamicin was again without any therapeutic effect. The effect of the combination of ceftriaxone and gentamicin was slightly better than ceftriaxone alone. Low oxygen tension may be an explanation for the lack of bactericidal effect of gentamicin. Ceftriaxone may be more suitable for the therapy of closed space infections caused by susceptible microorganisms than gentamicin.