Efficacy of single-dose ceftriaxone in experimental otitis media induced by penicillin- and cephalosporin-resistant Streptococcus pneumoniae

Can Helicobacter pylori cause inflammation in the middle ear?

OBJECTIVES

To investigate whether Helicobacter pylori causes inflammation in the normal middle ear and in the middle ear with effusion.

METHODS

Sixteen adult New Zealand white rabbits were divided into two gropus equally. Group I was representing histamine-induced middle ear inflammation and Group II was representing normal middle ear. While H. pylori was inoculated in the right ears, physiologic saline was inoculated in the left ears of the rabbits in both groups. Results were evaluated clinically, histopathologically and microbiologically. Fisher's exact test was used for statistical analysis.

RESULTS

In Group I, clinical scores of the inflammation in the right ears were higher than the left ears scores at the 7th day. Histopathological scores of the inflammation in the right ears were higher than the left ears scores at the 7th day. Also, H. pylori was isolated in 6 of the 8 right ears of the rabbits. In Group II, while clinical scores of the inflammation in the right ears scores were higher than the left ears scores at the 7th day, histopathological scores were not significantly different between both ears. Also, no H. pylori was isolated in right ears of the rabbits.

CONCLUSIONS

Effusion in the middle ear induced by histamine is an appropriate medium for H. pylori reproduction and it also aggravates the inflammation process. In contrary, H. pylori did not cause inflammation in the normal middle ear. We suggest that H. pylori does not play a role in the etiology of otitis media with effusion alone, but it contributes to the inflammation process in the presence of an effusion.

Use of Carbapenems against clinical, nontyphoid Salmonella isolates: results from in vitro and in vivo animal studies

The emergence of multidrug-resistant Salmonella isolates has created the need for new therapeutic agents. We evaluated the intracellular activity of four carbapenem compounds against clinical nontyphoid Salmonella (NTS) isolates in vitro and ex vivo. Subsequently, the efficacy of carbapenem treatment against selected Salmonella isolates in vivo was assessed using a murine peritonitis model. The MIC(50) and MIC(90) for doripenem, ertapenem, imipenem, and meropenem against 126 NTS isolates were found to be 0.062 and 0.062, 0.015 and 0.015, 0.5 and 1, and 0.031 and 0.031 μg/ml, respectively. The intracellular killing effect of ertapenem was sustained for 24 h and was superior to that of imipenem, meropenem, and doripenem; its effect was comparable to that of ceftriaxone. Ertapenem demonstrated an excellent pharmacokinetic profile with a percent time above the MIC of 75.5% and an area under the concentration-time curve/MIC ratio of 20,733. When peritoneal exudate cells were examined directly ex vivo from mice with Salmonella-induced peritonitis, cells from mice treated with ertapenem and ceftriaxone had intracellular and extracellular bacterial counts reduced 10(2)- to 10(4)-fold and exhibited killing effects similar to each other. The survival rates of mice inoculated with 1 × 10(5) and 10(6) CFU of a ceftriaxone-susceptible Salmonella isolate that were subsequently treated with ertapenem or ceftriaxone were 100% and 90%, respectively. When mice were inoculated with 5 × 10(4) and 10(5) CFU of a ceftriaxone-resistant and ciprofloxacin-resistant Salmonella isolate, mice treated with ertapenem had a higher survival rate than mice treated with ceftriaxone (70% versus 0% and 50% versus 0%, respectively; P < 0.001). Our results suggest that ertapenem is at least as effective as ceftriaxone in treating murine Salmonella infections and show that further clinical investigations on the potential use of ertapenem in treatment of human Salmonella infections are warranted.

The effects of caspofungin and voriconazole in an experimental fungal infection of the ear due to Aspergillus

The purpose of the study was to evaluate the effectiveness of caspofungin and voriconazole in the treatment of experimental Aspergillus otitis media in an experimental rabbit model. A total of 30 New Zealand white rabbits were divided into four treatment groups and one control group. The rabbits were immunosuppressed by cyclophosphamide and triamcinolone acetonide. The right ear of each rabbit was infected by an injection of the inoculum of 0.1 ml (8.6 x 103 CFU/0.1 ml) of Aspergillus fumigatus into the middle ear cavity. At 72 h after the inoculation, amphotericin B 1 mg/kg per day (n = 6), itraconazole 10 mg/kg per day (n = 6), voriconazole 10 mg/kg per day (n = 6) and caspofungin 5 mg/kg per day (n = 6) were injected to each treatment group. No antifungal drug was administered to the control group (n = 6). Clinical and histopathological examination scores and microbiological analysis of middle ear mucosa were compared.There was statistically significant difference in the clinical scores, histopathological scores, and mean CFU/g between the treatment and control groups (P < 0.05). There was no statistically significant difference among the treatment groups in the clinical and histopathological scores, whereas there was statistically significant difference in the mean CFU/g (P < 0.05). The mean CFU/g of amphotericin B and caspofungin groups were similar and both were lower than the itraconazole and voriconazole groups. Also, the mean CFU/g of voriconazole group was lower than the itraconazole group (P < 0.05). Caspofungin and voriconazole were demonstrated at least as effective as amphotericin B and itraconazole. We suggest that caspofungin and voriconazole may be considered for the treatment of fungal infection of the ear.

Animal models of Streptococcus pneumoniae disease

SUMMARY

Streptococcus pneumoniae is a colonizer of human nasopharynx, but it is also an important pathogen responsible for high morbidity, high mortality, numerous disabilities, and high health costs throughout the world. Major diseases caused by S. pneumoniae are otitis media, pneumonia, sepsis, and meningitis. Despite the availability of antibiotics and vaccines, pneumococcal infections still have high mortality rates, especially in risk groups. For this reason, there is an exceptionally extensive research effort worldwide to better understand the diseases caused by the pneumococcus, with the aim of developing improved therapeutics and vaccines. Animal experimentation is an essential tool to study the pathogenesis of infectious diseases and test novel drugs and vaccines. This article reviews both historical and innovative laboratory pneumococcal animal models that have vastly added to knowledge of (i) mechanisms of infection, pathogenesis, and immunity; (ii) efficacies of antimicrobials; and (iii) screening of vaccine candidates. A comprehensive description of the techniques applied to induce disease is provided, the advantages and limitations of mouse, rat, and rabbit models used to mimic pneumonia, sepsis, and meningitis are discussed, and a section on otitis media models is also included. The choice of appropriate animal models for in vivo studies is a key element for improved understanding of pneumococcal disease.

Effect of antibiotic treatment delay on therapeutic outcome of experimental acute otitis media caused by Streptococcus pneumoniae strains with different susceptibilities to amoxicillin

The effect of delayed administration of amoxicillin on the course of acute otitis media (AOM) caused by two Streptococcus pneumoniae strains with different susceptibilities to amoxicillin (MICs of 0.016 and 1 microg/ml for strains A and B, respectively) was evaluated in the gerbil model. The organisms were inoculated by transbullar challenge into the middle ear, and antibiotic treatment was administered at various times thereafter. The bacteriological and clinical efficacies of treatment diminished significantly with the delay of antibiotic administration. The bacterial eradication rates when antibiotic treatment was started at 2, 5, 8, 18, and 21 h post-bacterial inoculation were different for both strains (95, 95, 90, 55, and 55% for strain A and 95, 95, 65, 10, and 0% for strain B). Results of further experiments using strain B with higher antibiotic doses and numbers of administrations and different follow-up times indicate that the failures observed with the delayed administration were not related to the bacterial burden, selection of antibiotic-resistant mutants, or inadequate pharmacodynamic parameters. Such failures may be related to the metabolic bacterial status. The delayed amoxicillin treatment of AOM caused by S. pneumoniae may lead to therapeutic failures, mainly when organisms with diminished antibiotic susceptibility are involved.

Therapeutic effects of parenteral beta-lactam antibiotics on experimental otitis media caused by penicillin-resistant Streptococcus pneumoniae in guinea-pigs

The therapeutic effects of parenteral beta-lactam antibiotics were evaluated in experimental acute otitis media caused by penicillin-resistant Streptococcus pneumoniae (PRSP) in guinea-pigs. Cefotaxime, ceftriaxone and piperacillin significantly reduced viable cell counts of PRSP in the middle ear at a dose of 50 mg/kg bd for 3 days (P < 0.01 compared with control). The therapeutic effects of cefotaxime, ceftriaxone and piperacillin were superior to those of cefotiam and ceftazidime. These therapeutic effects reflected both in vitro activity and pharmacokinetic properties of the drugs.

Antimicrobial treatment of an experimental otitis media caused by a beta-lactamase positive isolate of Haemophilus influenzae

A gerbil model of otitis media induced by a beta-lactamase producing and non-serotypeable isolate of Haemophilus influenzae was used to assess the in-vivo efficacy of co-amoxiclav and cefuroxime at low (5 mg/kg) and high (20 mg/kg) doses. The MIC of the antibiotics tested against the pathogen was 1 mg/L (1/0.5 mg/L for co-amoxiclav). The organism was inoculated (+/-10(6) cfu) by transbullar challenge directly in the middle ear and antibiotic treatment was commenced 2 h post-inoculation and continued at 8 h intervals for three doses. Only high dose co-amoxiclav significantly reduced the number of culture-positive specimens as compared with untreated animals or with other treatment groups (91.7% as compared with 36.7% for high dose cefuroxime). The results obtained in any treatment group were related to middle ear antibiotic level/MIC. Antibiotic concentrations in the middle ear 90 min after administration were about 10% of serum levels at 15 min, probably related to a slight inflammatory response. Only after high dose co-amoxiclav did the concentration in the middle ear exceed the MIC by a factor of four. In otitis media with effusion, if indicated, antibiotics active in vitro should be administered in high doses and, to avoid side effects, probably in short courses.

Management of infections due to antibiotic-resistant Streptococcus pneumoniae

Antibiotic-resistant strains of Streptococcus pneumoniae are becoming more prevalent throughout the world; this has resulted in modifications of treatment approaches. Management of bacterial meningitis has the greatest consensus. Strategies for treating other systemic infections such as pneumonia, bacteremia, and musculoskeletal infections are evolving, in part related to the availability of new antibiotics which are active in vitro against isolates resistant to penicillin and the extended-spectrum cephalosporins. However, there are currently very limited data related to the clinical efficacy of these new agents. The studies upon which current recommendations are based are reviewed. Otitis media represents the single most common infection due to S. pneumoniae. Recommendations for treatment of acute otitis media due to drug-resistant strains and the rationale for these recommendations are discussed.

In vivo efficacies of amoxicillin and cefuroxime against penicillin-resistant Streptococcus pneumoniae in a gerbil model of acute otitis media

The comparative efficacies of amoxicillin and cefuroxime against acute otitis media caused by a penicillin-resistant (MIC, 2 micrograms/ml) Streptococcus pneumoniae strain were assessed in a gerbil model by challenging each ear with 10(7) bacteria through transbullar instillation. Each antibiotic was tested at two doses (5 and 20 mg/kg of body weight) administered at 2, 10, and 18 h postinoculation. Samples were obtained from the middle ear (ME) on days 3 and 7 postinoculation for determination of bacterial counts. Only amoxicillin, at both doses, was able to significantly halt the weight loss in animals, reducing both the number of culture-positive animals and the bacterial concentration in ME samples versus the values for untreated animals. Comparison of the efficacies between the antibiotics, determined by their ability to achieve culture-negative ME specimens, showed that amoxicillin at 5 mg/kg was significantly more active than cefuroxime at the same dose. The use of higher doses of either amoxicillin or cefuroxime did not produce significantly better results than those obtained with the lower dose but caused a greater inflammatory response. The more favorable results obtained with amoxicillin compared with those obtained with cefuroxime could be related to the antimicrobial susceptibility of the pneumococcal strain (MICs and minimum bactericidal concentrations of 1 and 1 microgram/ml and 4 and 4 micrograms/ml for amoxicillin and cefuroxime, respectively) as well as to the better pharmacokinetic parameters obtained with amoxicillin.