Role of Streptococcus pneumoniae and Haemophilus influenzae in the development of acute otitis media and otitis media with effusion in a gerbil model

Gerbils

The gerbil is usually nonaggressive and is one of the easiest rodents to maintain and handle. Its disposition, curious nature, relative freedom from naturally occurring infectious diseases, and adaptability to its environment have contributed to its popularity as a laboratory animal. Gerbils are found in deserts and semiarid geographical regions of the world. The Mongolian gerbils that are available today originated from 20 pairs of captured animals that were maintained in 1935 in a closed, random-bred colony at the Kitasato Institute in Japan. Gerbils have several unique anatomical and physiological features. Mature gerbils are smaller than rats, but larger than mice. Mongolian gerbils are attracted to saliva and use salivary cues to discriminate between siblings and nonsiblings, and females use oral cues in the selection of sociosexual partners. Gerbils have been used as experimental models in a number of areas of biomedical research. Gerbils are excellent subjects for laboratory animal research as they are susceptible to bacterial, viral, and parasitic pathogens that affect humans and other species. Gerbils may have spontaneous seizures secondary to stress such as handling, cage change, abrupt noises, or changes in the environment. Cystic ovaries are seen commonly in female gerbils over 1 year of age. Gerbils have unique characteristics, which make them appropriate for a number of animal models. Classically, gerbils have been used in research involving stroke, parasitology, infectious diseases, epilepsy, brain development and behavior, and hearing.

Evaluation and improvement of real-time PCR assays targeting lytA, ply, and psaA genes for detection of pneumococcal DNA

The accurate diagnosis of pneumococcal disease has frequently been hampered not only by the difficulties in obtaining isolates of the organism from patient specimens but also by the misidentification of pneumococcus-like viridans group streptococci (P-LVS) as Streptococcus pneumoniae. This is especially critical when the specimen comes from the respiratory tract. In this study, three novel real-time PCR assays designed for the detection of specific sequence regions of the lytA, ply, and psaA genes were developed (lytA-CDC, ply-CDC, and psaA, respectively). These assays showed high sensitivity (<10 copies for lytA-CDC and ply-CDC and an approximately twofold less sensitivity for psaA). Two additional real-time PCR assays for lytA and ply described previously for pneumococcal DNA detection were also evaluated. A panel of isolates consisting of 67 S. pneumoniae isolates (44 different serotypes and 3 nonencapsulated S. pneumoniae isolates from conjunctivitis outbreaks) and 104 nonpneumococcal isolates was used. The 67 S. pneumoniae isolates were reactive in all five assays. The new real-time detection assays targeting the lytA and psaA genes were the most specific for the detection of isolates confirmed to be S. pneumoniae, with lytA-CDC showing the greatest specificity. Both ply PCRs were positive for all isolates of S. pseudopneumoniae, along with 13 other isolates of other P-LVS isolates confirmed to be non-S. pneumoniae by DNA-DNA reassociation. Thus, the use of the ply gene for the detection of pneumococci can lead to false-positive reactions in the presence of P-LVS. The five assays were applied to 15 culture-positive cerebrospinal fluid specimens with 100% sensitivity; and serum and ear fluid specimens were also evaluated. Both the lytA-CDC and psaA assays, particularly the lytA-CDC assay, have improved specificities compared with those of currently available assays and should therefore be considered the assays of choice for the detection of pneumococcal DNA, particularly when upper respiratory P-LVS might be present in the clinical specimen.

Tracing of gastric reflux into the middle ear in a mongolian gerbil model

OBJECTIVES

The purpose of this study was to trace induced gastric reflux and to examine whether it reaches the middle ear in a Mongolian gerbil model.

BACKGROUND

Otitis media with effusion is the most frequent middle ear disease in childhood. Gastroesophageal reflux is suspected to be a possible factor in its pathogenesis.

METHODS

Seventeen Mongolian gerbils were assigned to three groups: the control (phosphate-buffered saline application to the lower esophageal sphincter) and two experimental groups (Aquo-Trinitrosan [Merck, Darmstadt, Germany] application to the lower esophageal sphincter, low gastric pressure and Aquo-Trinitrosan application, higher gastric pressure). We injected Chinese ink into the stomach to trace the path of a potential gastroesophageal reflux in all three groups. The traces of ink were investigated by ear and larynx endoscopy and histology.

RESULTS

There were no signs of gastroesophageal reflux based on the data obtained from the control group. In animals with traceable laryngeal reflux, the ink was also shown to advance through the eustachian tube and reach the middle ear. In addition, we found that when reflux reaches the middle ear on one side, it also reaches the contralateral middle ear in most cases.

CONCLUSION

Gastroesophageal reflux induced by relaxation of the lower esophageal sphincter was shown to reach the middle ear in our Mongolian gerbil model. These results support recent hypotheses linking gastroesophageal reflux to the development of otitis media with effusion.

Effect of erythromycin treatment delay on therapeutic outcome of experimental acute otitis media caused by Streptococcus pneumoniae

OBJECTIVE

To evaluate the effect of delayed administration of erythromycin in the course of acute otitis media caused by an erythromycin-susceptible Streptococcus pneumoniae strain in the gerbil model.

METHODS

The bacterium was inoculated by transbullar challenge in the middle ear (ME) and antibiotic treatment at different doses was administered at various times thereafter.

RESULTS

When 2.5 mg/kg of erythromycin was administered as a single dose 2, 5, 18 or 21 h post-inoculation (pi) the bacterial eradication rate was 55, 40, 0 and 0%, respectively. A higher dose (5 mg/kg) administered also as a single dose 2, 5, 18 and 21 h pi achieved bacterial eradication rates of 62.5, 43.8, 0 and 0%, respectively. Using a very high dose (50 mg/kg) repeated three times at 3 h intervals (total dose 150 mg/kg) and starting the treatment 21 h pi only achieved bacterial eradication in 25% of cases. The concentration of erythromycin achieved in the ME 90 min after administration of 5 mg/kg 5 or 21 h pi was very similar (0.74 and 0.79 mg/L) but the ME half-life was longer (98.2 min) with the early administration as compared with the delayed form (47.5 min), which could partially explain the different results. Further experiments showed that the failures observed with the delayed administration were not related to the time elapsed from antibiotic administration to ME sampling or selection of antibiotic-resistant mutants.

CONCLUSION

Bacteriological and clinical efficacies were significantly diminished if antibiotic administration was delayed.

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.

Does acetaminophen interfere in the antibiotic treatment of acute otitis media caused by a penicillin-resistant pneumococcus strain? A gerbil model

The possible interference of acetaminophen, combined with antibiotics, in the treatment of acute otitis media (AOM) caused by a penicillin-resistant (minimal inhibitory concentration [MIC], 2 microg/mL), amoxicillin/clavulanic acid- and erythromycin-sensitive pneumococcus was evaluated in a gerbil model. Animals were challenged with approximately 5 x 106 bacteria in each ear through transbullar instillation. Acetaminophen was administered s.c. at 50 mg/kg 30 min before each antibiotic dose. Amoxicillin/clavulanic acid and erythromycin (2.5 and 10 mg/kg) were administered s.c. at 2, 10, and 18 h after inoculation. Samples were obtained from the middle ear (ME) on day 2 after inoculation for bacterial count. The overall results showed no difference between animals that received acetaminophen, with or without antibiotics, and those that did not receive acetaminophen. The antibiotic concentrations in the ME were practically identical in both groups of animals, so acetaminophen did not interfere with the pharmacokinetics of antibiotics in the ME. However, both antibiotics significantly reduced the number of culture-positive and the bacterial concentration in ME samples when compared with antibiotic-untreated animals. Both antibiotics, whether combined with acetaminophen or not, lowered the number of AOM to <25%, but >75% of animals presented otitis media with effusion, and no differences were shown between groups. A high rate of bacterial eradication from the ME correlated with antibiotic serum concentrations being over the MIC of the infecting organism for only >15% of the dose interval and with an ME concentration exceeding the MIC by a factor of 1.7. In this experimental model, acetaminophen had neither a synergistic nor an antagonistic effect on the antibiotics tested.

Efficacy and pharmacodynamics of gemifloxacin versus levofloxacin in guinea pig pneumococcal pneumonia induced by strains with decreased ciprofloxacin susceptibility

Quinolone in vivo bactericidal activity was investigated in a guinea pig pneumonia model using three Streptococcus pneumoniae strains with decreasing susceptibility to ciprofloxacin. Treatment regimens resulted in values of AUC(0-24 h) and C(30 min) similar to those of standard oral regimens in human serum. Efficacy was defined as a significant difference in number of viable bacteria in the lungs compared with the control. Ciprofloxacin, levofloxacin and gemifloxacin were effective against the levofloxacin-susceptible strain. Only gemifloxacin achieved a >/=99.9% reduction versus control against the levofloxacin intermediate-resistant strain. Gemifloxacin achieved a 99.69% reduction and was the only quinolone significantly different from the control (P<0.05) against the levofloxacin-resistant strain. Gemifloxacin offers in vivo activity against ciprofloxacin- to levofloxacin-resistant pneumococci.

Optimal dose of amoxicillin in treatment of otitis media caused by a penicillin-resistant pneumococcus strain in the gerbil model

Amoxicillin at doses of 0.2 to 5 mg/kg of body weight was administered for the treatment of pneumococcal otitis media in a gerbil model. Doses greater than or equal to 2.5 mg/kg, which resulted in concentrations in middle ear fluid of > or = 1.4 microg/ml and concentrations in serum higher than the MIC (1 microg/ml) for > or = 14% of the dosing interval, were both clinically and bacteriologically effective.