Efficacy of cefmenoxime in experimental Escherichia coli bacteremia and meningitis.

Cefmenoxime, a new semisynthetic cephalosporin structurally similar to cefotaxime, was evaluated for its activities in vitro and in vivo against a K1 Escherichia coli strain in comparison with activities of cefotaxime and ampicillin. In vitro the MICs and MBCs of both cefmenoxime and cefotaxime were the same, 1/16th and 1/32nd those of ampicillin, respectively. The efficacies of cefmenoxime and cefotaxime against experimentally induced E. coli bacteremia and meningitis in newborn rats were similar and significantly better than that of ampicillin as judged by bactericidal titers of blood and cerebrospinal fluid, rapidity of clearance of bacteria from blood and cerebrospinal fluid, and incidence of meningitis in animals with bacteremias. The efficacy of cefmenoxime or cefotaxime measured by impact on mortality was influenced by the size of bacterial populations. The mortality was significantly greater in rats with bacterial counts before therapy of greater than or equal to 10(6) CFU/ml of blood than in animals with lower counts. Overall, the in vivo efficacy of cefmenoxime was similar to that of cefotaxime; thus it could be useful in the therapy of neonatal E. coli infection.     

Role of the eaeA gene in experimental enteropathogenic Escherichia coli infection.

Enteropathogenic Escherichia coli (EPEC) infections are a leading cause of infant diarrhea in developing countries. Recently eaeA, a gene necessary for the characteristic intimate attachment of EPEC to epithelial cells in tissue culture, was described. We conducted a randomized, double-blind study to determine the role of the eaeA gene in human EPEC infection. 11 adult volunteers ingested 2 x 10(10) colony-forming units of O127:H6 EPEC strain E2348/69, and an equal number received the same dose of an isogenic eaeA deletion mutant constructed from E2348/69. Volunteers were monitored for the development of diarrhea, fever, and systemic and gastrointestinal complaints. Diarrhea developed in all 11 volunteers who received E2348/69 and in 4 of 11 who received the mutant (P = 0.002). Fever was more common in recipients of the wild-type strain (P = 0.024). Stool volumes were lower in recipients of the mutant. All volunteers seroconverted to E2348/69 LPS, but the geometric mean peak titers of serum IgG and IgA in recipients of the mutant were lower than those of recipients of the wild-type strain. IgA against LPS was detected in the jejunal fluid of six of six recipients of E2348/69 and 5/6 recipients of the mutant. This study unambiguously assigns a role for eaeA as an EPEC virulence gene, but the residual diarrhea seen in recipients of the mutant indicates that other factors are involved.     

Treatment of experimental Escherichia coli infection with recombinant bacteriophage-derived capsule depolymerase

OBJECTIVES: The aim of this study was to investigate the effect of single doses of the capsule depolymerizing enzyme endosialidase E (endoE) on the course of systemic infection due to Escherichia coli K1 strains in neonatal rats. We also determined the capacity of the enzyme to increase the sensitivity of K1 strains to rat peritoneal macrophages. METHODS: Bacteraemia was established in Wistar rats by induction of gastrointestinal colonization with the virulent K1 strain A192PP; colonization preceded a lethal bacteraemia. Decreasing single doses of endoE were administered intraperitoneally. Macrophage engulfment of K1 strain A192PP was evaluated by staining and microscopy in the presence and absence of endoE. RESULTS: A192PP colonized the gastrointestinal tract of all 2-day-old animals and produced bacteraemia in over 90%. A single endoE dose of 0.25 microg curtailed bacteraemia and prevented death in at least 80% of infected animals. Older animals (up to 5 days of age) were less susceptible to systemic infection following intestinal colonization. EndoE-mediated removal of K1 capsular polysaccharide led to increased ingestion by macrophages. CONCLUSIONS: A small single dose of capsule-depolymerizing enzyme has therapeutic utility in lethal systemic infection in a non-invasive model that has characteristics of the infectious process in humans. We propose that the enzyme reduces the virulence of E. coli K1 by rapid removal of the protective capsular polysaccharide, sensitizing the pathogen to host defences such as phagocytosis by macrophages. Thus, whilst endoE-mediated therapy may not be a viable approach to the treatment of systemic infection in humans, it does support the concept that alteration of the cell wall phenotype is a valid therapeutic strategy.     

Appearance of a new trimethoprim resistance gene, dhfrIX, in Escherichia coli from swine.

A new gene, dhfrIX, coding for a trimethoprim-resistant dihydrofolate reductase (DHFR), was found in porcine isolates of Escherichia coli. The new enzyme, DHFR IX, containing 178 amino acids, showed an amino acid similarity of about 26% with DHFR I and the chromosomal DHFR of E. coli K-12. The dhfrIX gene was observed to occur on two distinctly different transferable plasmids, although a fragment of about 2.9 kb, including dhfrIX, had an identical restriction enzyme digestion map in each case. The new plasmid-borne dhfrIX gene mediates resistance to a drug level of only about 250 micrograms/ml, as compared with more than 1,000 micrograms/ml for the more frequently encountered dhfrI gene. The new plasmid-borne trimethoprim resistance gene could have been selected and spread as a consequence of the extensive use of trimethoprim in veterinary practice in Sweden. It will be important to try to follow its possible occurrence in human pathogens as well.     

Local cytokine production in a murine model of Escherichia coli pyelonephritis.

Cytokines may play an important role in the regulation of host defense against local bacterial infections. We have evaluated the local production of cytokines in a BALB/c mouse model of Escherichia coli pyelonephritis. Kidneys, draining lymph nodes, and spleens, were harvested at specific time intervals after bladder inoculation with E. coli corresponding to the stages of renal infection, infiltration, and bacterial clearance seen in this model. The presence of messenger RNA for specific cytokines (interleukins 1 through 6, chemotactic factors, granulocyte and granulocyte macrophage-colony stimulating factor (GM-CSF), tumor necrosis factor (TNF alpha) and beta, IFN gamma, transforming growth factor (TGF beta), and cytokine synthesis inhibitory factor (CSIF)/IL-10) was determined by polymerase chain reaction (PCR) amplification of reverse transcribed RNA. We have demonstrated mRNA encoding IL-1, IL-6, G-CSF, GM-CSF, TNF alpha, H400 (a protein homologous to a family of chemotactic factors and identical to MIP-1 beta), and CSIF/IL-10 in the kidney at 12 h and 1, 2, and 3 d after bacterial challenge. No signal was seen in normal animals or in mice after 5 d. This pattern of cytokine expression was observed only in renal tissues suggesting a localized response. IL-6 was present in the urine at 4 h with rapid resolution to baseline levels by 24 to 48 h. In contrast, IL-6 was not usually detectable in the serum. TNF alpha was not detectable in the serum or urine during the course of the infection. By immunohistochemical staining of kidney sections we have shown that IL-6 is produced predominantly by mesangial cells rather than by the inflammatory infiltrate. This study provides additional evidence utilizing novel techniques that specific cytokines are produced locally in response to bacterial infections. The time course of production demonstrated in this model supports the important role of cytokines in natural host resistance to local infection.     

Evaluation of pefloxacin in experimental Escherichia coli meningitis.

The therapeutic efficacy of the fluoroquinolone pefloxacin mesylate was compared with those of cefotaxime and chloramphenicol in a rabbit model of Escherichia coli meningitis. The mean percent penetration (+/- the standard deviation) of pefloxacin (range, 1 to 30 mg/kg per h) into cerebrospinal fluid of infected rabbits was 51.3 +/- 14.0 compared with 11.1 +/- 1.0 for cefotaxime (100 mg/kg per h) and 22.3 +/- 1.5 for chloramphenicol (60 mg/kg per h). The rate of bacterial killing (delta log10 CFU/ml per h) did not change over a dosage range of 1 to 15 mg/kg per h (-0.37 +/- 0.15, 20% sterile). At 30 mg/kg per h, the rate achieved (-0.77 +/- 0.18, 100% sterile) was comparable to that of cefotaxime (-0.88 +/- 0.23, 100% sterile) and superior to that of chloramphenicol (-0.10 +/- 0.14, 0% sterile).     

Efficacy of posaconazole in murine experimental sporotrichosis

We developed a murine model of systemic sporotrichosis by using three strains of each of the two commonest species causing sporotrichosis, i.e., Sporothrix schenckii sensu stricto and Sporothrix brasiliensis, in order to evaluate the efficacy of posaconazole (PSC). The drug was administered at a dose of 2.5 or 5 mg/kg of body weight twice a day by gavage, and one group was treated with amphotericin B (AMB) as a control treatment. Posaconazole, especially at 5 mg/kg, showed good efficacy against all the strains tested, regardless of their MICs, as measured by prolonged survival, tissue burden reduction, and histopathology.     

Trimethoprim-sulfamethoxazole therapy of experimental Escherichia coli meningitis in rabbits.

We used two strains of ampicillin-susceptible Escherichia coli to produce meningitis in rabbits and utilized these models (i) to compare the killing effects of parenteral trimethoprim-sulfamethoxazole (TMP-SMZ) and ampicillin on E. coli in cerebrospinal fluid after 8 h of treatment and (ii) to measure the penetration of TMP-SMZ and ampicillin into cerebrospinal fluid and the brain. At 16 h after intracisternal inoculation with a test strain, rabbits were treated with TMP (6 mg/kg per h) and SMZ (30 mg/kg per h), ampicillin (40 mg/kg per h), or saline intravenously for 8 h. TMP-SMZ levels were measured by high-pressure liquid chromatography, and ampicillin levels were measured by microbiological assay. Mean +/- standard deviation concentrations of TMP, SMZ, and ampicillin in cerebrospinal fluid (mean percent penetration) at the completion of 8 h of therapy were 0.80 +/- 0.41 (18%), 15.7 +/- 21.1 (27.2%), and 2.6 +/- 1.7 (8.9%) microgram/ml, respectively. TMP, SMZ, and ampicillin levels in brain homogenate after 8 h of therapy were 0.23 +/- 0.07 (6.6%), 3.31 +/- 3.3 (5.5%), and 0.6 +/- 4.53 (1.9%) microgram/g, respectively. TMP-SMZ infusion for 8 h produced a significant reduction in mean bacterial counts in cerebrospinal fluid in both models of meningitis compared with saline controls. The decrease in mean bacterial counts with TMP-SMZ therapy was equivalent to that produced by ampicillin.     

Antimicrobial activity of intraurethrally administered probiotic Lactobacillus casei in a murine model of Escherichia coli urinary tract infection

The antimicrobial activity of the intraurethrally administered probiotic Lactobacillus casei strain Shirota against Escherichia coli in a murine urinary tract infection (UTI) model was examined. UTI was induced by intraurethral administration of Escherichia coli strain HU-1 (a clinical isolate from a UTI patient, positive for type 1 and P fimbriae), at a dose of 1 x 10(6) to 2 x 10(6) CFU in 20 microl of saline, into a C3H/HeN mouse bladder which had been traumatized with 0.1 N HCl followed immediately by neutralization with 0.1 N NaOH 24 h before the challenge infection. Chronic infection with the pathogen at 10(6) CFU in the urinary tract (bladder and kidneys) was maintained for more than 3 weeks after the challenge, and the number of polymorphonuclear leukocytes and myeloperoxidase activity in the urine were markedly elevated during the infection period. A single administration of L. casei Shirota at a dose of 10(8) CFU 24 h before the challenge infection dramatically inhibited E. coli growth and inflammatory responses in the urinary tract. Multiple daily treatments with L. casei Shirota during the postinfection period also showed antimicrobial activity in this UTI model. A heat-killed preparation of L. casei Shirota exerted significant antimicrobial effects not only with a single pretreatment (100 microg/mouse) but also with multiple daily treatments during the postinfection period. The other Lactobacillus strains tested, i.e., L. fermentum ATCC 14931(T), L. jensenii ATCC 25258(T), L. plantarum ATCC 14917(T), and L. reuteri JCM 1112(T), had no significant antimicrobial activity. Taken together, these results suggest that the probiotic L. casei strain Shirota is a potent therapeutic agent for UTI.     

Efficacy of BMY-28142 in experimental bacteremia and meningitis caused by Escherichia coli and group B streptococci.

We evaluated the activity of BMY-28142 against a K1 E. coli strain and a type III group B streptococcal strain in vitro and in vivo and compared the results with those of cefotaxime and penicillin G, respectively. In vitro, the MICs and MBCs of BMY-28142 were close to those of cefotaxime (less than or equal to 2-fold difference) for E. coli and fourfold less than those of penicillin G for group B streptococci. In vivo studies with an experimental bacteremia and meningitis model in newborn rats revealed that the mean penetration of BMY-28142 into the cerebrospinal fluid was 15% that of concomitant levels in serum and that significantly greater bactericidal titers were achieved in blood and cerebrospinal fluid for both test organisms with BMY-28142 than with cefotaxime and penicillin G. However, the overall efficacy of BMY-28142 was similar to that of cefotaxime for the E. coli infection and that of penicillin G for the group B streptococcal infection. This was shown by similar rates of bacterial clearance from blood and cerebrospinal fluid and similar mortality rates. These findings indicate that the activity of BMY-28142 is bactericidal in vitro and in vivo against E. coli and group B streptococci, suggesting that this agent may be a suitable alternative for the therapy of E. coli and group B streptococcal bacteremia and meningitis.     

Bactericidal activity of trimethoprim alone and in combination with sulfamethoxazole on susceptible and resistant Escherichia coli K-12.

The combined effects of trimethoprim and sulfamethoxazole on the viability of Escherichia coli K-12 and resistant strains possessing resistance plasmids were examined in minimal medium. When methionine, glycine, and adenine were present, sulfamethoxazole could enhance trimethoprim activity against E. coli K-12 so that the combination was bactericidal. However, this enhancement occurred over a narrow range of trimethoprim concentrations (0.04 to 0.2 mg liter-1) and only when the sulfamethoxazole concentration was more than 10 times that of trimethoprim. Under certain conditions, sulfamethoxazole enhanced trimethoprim bactericidal activity against E. coli K-12 carrying plasmid R1 at concentrations of sulfamethoxazole far below those required to inhibit the organism, but there was no such enhancement with the same host containing the SSu plasmid. Similar differences were found with strains possessing trimethoprim resistance plasmids R483 and R751. Sulfamethoxazole can promote a bactericidal response with trimethoprim in E. coli K-12 and some of its resistant derivatives, but only under a narrow range of concentrations.     

Efficacy of amoxycillin/clavulanic acid in experimental Bacteroides fragilis/Escherichia coli mixed infections

The efficacy of amoxycillin/clavulanic acid was compared with those of metronidazole, cefuroxime, metronidazole/ampicillin, metronidazole/gentamicin and metronidazole/cefuroxime, in experimental mixed infections produced in mice by subcutaneous inoculation of amoxycillin-resistant strains of Bacteroides fragilis and Escherichia coli. The combination of metronidazole/ampicillin failed to inhibit the growth of E. coli, and exerted only a transient effect on the numbers of Bact. fragilis in the groin abscesses. In contrast, amoxycillin/clavulanic acid prevented the development of the infection, eliminating both organisms. Metronidazole and cefuroxime, alone and in combination, were less effective than amoxycillin/clavulanic acid in inhibiting the growth of the infecting organisms. These results demonstrate the clinical potential of amoxycillin/clavulanic acid in prophylaxis, or in the therapy of mixed aerobe/anaerobe infections.     

Occurrence of transposable trimethoprim resistance in clinical isolates of Escherichia coli devoid of self-transmissible resistance plasmids.

Fifty trimethoprim-resistant clinical isolates of Escherichia coli, devoid of self transmissible trimethoprim resistance plasmids, were examined for the presence of trimethoprim resistance transposons. Trimethoprim resistance was mobilized from 12 strains by transposition onto plasmid RP4. The trimethoprim resistance transposons isolated comprised two groups: those with and without linked streptomycin resistance.     

Efficacy of Gatifloxacin in Experimental Escherichia coli Meningitis

The effectiveness of gatifloxacin therapy (15 mg/kg every 5 h [q5h]) was compared with that of meropenem (75 mg/kg q5h) and cefotaxime (75 mg/kg q5h) therapy in experimental meningitis caused by a beta-lactamase-producing strain of Escherichia coli. Gatifloxacin therapy was more rapidly bactericidal than cefotaxime but similar to meropenem therapy (bacterial killing rates at 5 h, 0.83 +/- 0.26, 0. 46 +/- 0.3, and 0.73 +/- 0.17 CFU/ml/h, respectively; P = 0.03 for gatifloxacin versus cefotaxime). At 10 h, seven of eight animals treated with gatifloxacin had <10 CFU/ml in their cerebrospinal fluid, compared with one of seven treated with cefotaxime therapy (P = 0.01). Gatifloxacin was at least as effective as currently available antibiotics in this model of E. coli meningitis.     

Comparative methods for detection of thymidine kinase-deficient herpes simplex virus type 1 strains.

Four methods for analyzing viral susceptibility to antiviral substances were compared. In two methods viral products were measured: late viral proteins were measured by an enzyme-linked immunosorbent assay and viral DNA was measured by DNA hybridization. Infectious virus was quantified in the other two assays as the number of plaques and the yield of virus. The enzyme-linked immunosorbent assay procedure in our hands detected the smallest amounts (lowest proportions) of thymidine kinase-deficient herpes simplex virus type 1 mixed with wild-type virus. The thymidine kinase-deficient proportion of the herpes simplex virus type 1 isolate increased rapidly in the presence of acyclovir in cell culture.