Experimental otitis media with Moraxella (Branhamella) catarrhalis

Experimental study of vibrations of gerbil tympanic membrane with closed middle ear cavity

The purpose of the present work is to investigate the spatial vibration pattern of the gerbil tympanic membrane (TM) as a function of frequency. In vivo vibration measurements were done at several locations on the pars flaccida and pars tensa, and along the manubrium, on surgically exposed gerbil TMs with closed middle ear cavities. A laser Doppler vibrometer was used to measure motions in response to audio frequency sine sweeps in the ear canal. Data are presented for two different pars flaccida conditions: naturally flat and retracted into the middle ear cavity. Resonance of the flat pars flaccida causes a minimum and a shallow maximum in the displacement magnitude of the manubrium and pars tensa at low frequencies. Compared with a flat pars flaccida, a retracted pars flaccida has much lower displacement magnitudes at low frequencies and does not affect the responses of the other points. All manubrial and pars tensa points show a broad resonance in the range of 1.6 to 2 kHz. Above this resonance, the displacement magnitudes of manubrial points, including the umbo, roll off with substantial irregularities. The manubrial points show an increasing displacement magnitude from the lateral process toward the umbo. Above 5 kHz, phase differences between points along the manubrium start to become more evident, which may indicate flexing of the tip of the manubrium or a change in the vibration mode of the malleus. At low frequencies, points on the posterior side of the pars tensa tend to show larger displacements than those on the anterior side. The simple low-frequency vibration pattern of the pars tensa becomes more complex at higher frequencies, with the breakup occurring at between 1.8 and 2.8 kHz. These observations will be important for the development and validation of middle ear finite-element models for the gerbil.

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.

Indirect pathogenicity of Haemophilus influenzae and Moraxella catarrhalis in polymicrobial otitis media occurs via interspecies quorum signaling

Otitis media (OM) is among the leading diseases of childhood and is caused by opportunists that reside within the nasopharynx, such as Haemophilus influenzae and Moraxella catarrhalis. As with most airway infections, it is now clear that OM infections involve multiple organisms. This study addresses the hypothesis that polymicrobial infection alters the course, severity, and/or treatability of OM disease. The results clearly show that coinfection with H. influenzae and M. catarrhalis promotes the increased resistance of biofilms to antibiotics and host clearance. Using H. influenzae mutants with known biofilm defects, these phenotypes were shown to relate to biofilm maturation and autoinducer-2 (AI-2) quorum signaling. In support of the latter mechanism, chemically synthesized AI-2 (dihydroxypentanedione [DPD]) promoted increased M. catarrhalis biofilm formation and resistance to antibiotics. In the chinchilla infection model of OM, polymicrobial infection promoted M. catarrhalis persistence beyond the levels seen in animals infected with M. catarrhalis alone. Notably, no such enhancement of M. catarrhalis persistence was observed in animals infected with M. catarrhalis and a quorum signaling-deficient H. influenzae luxS mutant strain. We thus conclude that H. influenzae promotes M. catarrhalis persistence within polymicrobial biofilms via interspecies quorum signaling. AI-2 may therefore represent an ideal target for disruption of chronic polymicrobial infections. Moreover, these results strongly imply that successful vaccination against the unencapsulated H. influenzae strains that cause airway infections may also significantly impact chronic M. catarrhalis disease by removing a reservoir of the AI-2 signal that promotes M. catarrhalis persistence within biofilm.

Development of a non-invasive murine infection model for acute otitis media

Otitis media (OM) is one of the most frequent diseases in childhood, and Streptococcus pneumoniae is among the main causative bacterial agents. Since current experimental models used to study the bacterial pathogenesis of OM have several limitations, such as the invasiveness of the experimental procedures, we developed a non-invasive murine OM model. In our model, adapted from a previously developed rat OM model, a pressure cabin is used in which a 40 kPa pressure increase is applied to translocate pneumococci from the nasopharyngeal cavity into both mouse middle ears. Wild-type pneumococci were found to persist in the middle ear cavity for 144 h after infection, with a maximum bacterial load at 96 h. Inflammation was confirmed at 96 and 144 h post-infection by IL-1beta and TNF-alpha cytokine analysis and histopathology. Subsequently, we investigated the contribution of two surface-associated pneumococcal proteins, the streptococcal lipoprotein rotamase A (SlrA) and the putative proteinase maturation protein A (PpmA), to experimental OM in our model. Pneumococci lacking the slrA gene, but not those lacking the ppmA gene, were significantly reduced in virulence in the OM model. Importantly, pneumococci lacking both genes were significantly more attenuated than the DeltaslrA single mutant. This additive effect suggests that SlrA and PpmA exert complementary functions during experimental OM. In conclusion, we have developed a highly reproducible and non-invasive murine infection model for pneumococcal OM using a pressure cabin, which is very suitable to study pneumococcal pathogenesis and virulence in vivo.

Ionic binding of C3 to the human pathogen Moraxella catarrhalis is a unique mechanism for combating innate immunity

Moraxella catarrhalis ubiquitous surface proteins A1 and A2 (UspA1/A2) interfere with the classical pathway of the complement system by binding C4b-binding protein. In this study we demonstrate that M. catarrhalis UspA1 and A2 noncovalently and in a dose-dependent manner bind both the third component of complement (C3) from EDTA-treated serum and methylamine-treated C3. In contrast, related Moraxella subspecies (n = 13) or other human pathogenic bacteria (n = 13) do not bind C3 or methylamine-treated C3. Experiments with recombinant proteins and M. catarrhalis mutants devoid of UspA1/A2 revealed that UspA1/A2 exert their actions by absorbing and neutralizing C3 from serum and restrain complement activation. UspA2 was responsible for most of the effect, and the Moraxella mutant lacking UspA2 was more sensitive to the lytic effect of human serum compared with the wild type. Interestingly, among the large number of bacteria analyzed, only M. catarrhalis has this unique ability to interfere with the innate immune system of complement by binding C3.

Thickness of the gerbil tympanic membrane measured with confocal microscopy

Thickness data for the gerbil tympanic membrane, an extremely thin biological membrane, are presented. Thickness measurements were performed on fresh material using fluorescence images taken perpendicular through the membrane with a commercial confocal microscope. Thickness varies strongly across the membrane. Similar thickness distributions in all samples (pars tensa n = 11; pars flaccida n = 3) were observed. The pars tensa has a rather constant thickness of about 7 microm in the central region curving as a horse shoe upwards around the manubrium. In the most superior parts of the pars tensa thickness becomes gradually twice as large. Thickness increases also steeply from the central region towards the edges (about 35 microm near the annulus and 20 microm near the manubrium). A pronounced, local thickening of about 30 microm is present close to the edge and extends as a ring along the entire annular periphery of the pars tensa. Overall, the pars flaccida is thicker than the pars tensa and has a rugged surface. Its central region has a mean thickness of about 24 microm with a mean variation of about 4 microm. The average thickness in the inferior region is slightly larger than in the superior region. The pars flaccida thickens steeply, up to about 80 microm, near the edges.

Bacterial otitis media: a new non-invasive rat model

This study describes the development of a physiological rat model for otitis media. The model is based on the assumption that bacteria, intranasally introduced into the nasopharynx, will be transferred into the middle ear cavity during swallowing provided that the ambient air pressure is higher than the middle ear pressure. This model demonstrates that small pressure changes, generated in a pressure cabin under controlled conditions, can be used as driving force for the transfer of bacteria into the middle ear cavity resulting in bilateral otitis media. Because invasive techniques or biochemical agents are not applied, this model is suited to investigate immunological aspects of otitis media, including the effects of vaccination.

Moraxella catarrhalis: a review of an important human mucosal pathogen

Moraxella catarrhalis has again been recognized as a significant pathogen. The past decade has witnessed an increased amount of research and understanding of the pathogenesis of the organism. This review will summarize the research pertaining to the epidemiology and components of pathogenesis in M. catarrhalis.

Purified streptococcal cell wall (PG-APS) causes experimental otitis media

Purified peptidoglycan-polysaccharide from Group A Streptococcus pyogenes cell wall (PG-APS) was prepared under sterile, pyrogen-free conditions and injected percutaneously into the middle ear cavities (MEC) of groups of gerbils. Each group was observed otoscopically at 1, 2, 5, 7, 9, 12 and 14 days. Histologic specimens were obtained from each group at 2, 5, 7, 9 and 14 days. Histologically, PG-APS produced mild, acute inflammation during the first 3 days and mild to moderate inflammation with features of both acute and chronic pathology from days 5 through 9. An early response by plasma cells and macrophages was seen. Most animals had recovered with minor sequelae by day 14. Challenge intraperitoneally with 20 micrograms of PG-APS at 14 days following MEC injection of PG-APS did not exacerbate the middle ear inflammation. Five chinchillas, tested for comparison, responded similarly to PG-APS.