Moraxella catarrhalis is a gram-negative aerobic
diplococcus that belongs to the Neisseraceae family.
It has been known as Micrococcus catarrhalis, Niesseria
catarrhalis, and Branhamella catarrhalis. It commonly
inhabits the upper respiratory tract. For many years, it was considered
a nonpathogenic member of the resident flora of the nasopharynx.
Over the past 25 to 30 years, it has been recognized as a genuine mucosal
pathogen and is now considered an important cause of otitis media
and sinusitis in healthy children and adults. It also causes lower
respiratory tract infections and exacerbation of bronchitis in adults
with chronic lung disease. Occasionally, it can cause a variety
of severe infections, including septicemia, pneumonia, and meningitis,
especially in the immunocompromised hosts.
M catarrhalis is a normal inhabitant of the
upper respiratory tract. Nasopharyngeal colonization rate is highest
during infancy and early childhood and lowest in adulthood. Colonization
rates of as high as 36% to 50% in infants and
young children,1 and 1% to 3% in
adults,2 have been reported. In one study of a
large cohort of infants who were followed prospectively from birth
to 2 years of age, 66% became colonized with M
catarrhalis by 1 year and 77.5% by 2 years of
age. In the same group, nasopharyngeal colonization increased from
27% during healthy visits to 63% on visits associated
with otitis media.3 Other studies have shown that
colonization of children varies with the season and is more common
in fall and winter (46%) than in spring and summer (9%).4 Overall,
colonization was higher in children with upper respiratory tract
infection (36%) than in children without (18%),
and was more common in children ages 24 months (32%) than
in children older than 24 months (14%). Colonization with M
catarrhalis is reported to be more common in asthmatic
children than in normal children.
Factors influencing colonization and elimination are not fully
understood, but adhesion to mucosal receptors and immune responses are
implicated in addition to bacterial colonization dynamics. In general,
potential pathogens are more likely to colonize the nasopharynx
of children prone to recurrent otitis media, where impaired local
immunity and repeated exposure to respiratory pathogens are additional
risk factors.5Colonization appears to be an ongoing
process with an elimination-colonization turnover of various strains.
The mode of transmission of the organism is presumed to be direct
contact with contaminated respiratory tract secretions and/or
M catarrhalis is an aerobic gram-negative diplococcus
that has a striking resemblance to meningococcus and gonococcus,
except that it is unencapsulated. It grows well on blood and chocolate
agars, forming small, opaque, gray-white nonhemolytic colonies.
Recovery of the organism from the mixed flora of mucosal surfaces
can be enhanced by using selective culture media such as modified
Thayer-Martin or TV broth (Mueller-Hinton broth supplemented with
trimethoprim and vancomycin).
After the nasopharynx ...