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MICROBIOLOGY LEGEND

CYCLE 44 ORGANISM 1

Moraxella catarrhalis

Moraxella catarrhalis is a fastidious, nonmotile, Gram-negative, aerobic, oxidase-positive that can cause of the , middle ear, eye, central nervous system, and of humans. It causes the of the by sticking to the host cell using trimeric autotransporter adhesins. M. catarrhalis was previously placed in a separate named . The rationale for this was that other members of the genus Moraxella are rod-shaped and rarely caused infections in humans. However, results from DNA hybridization studies and 16S rRNA sequence comparisons were used to justify inclusion of the species M. catarrhalis in the genus Moraxella. As a consequence, the name Moraxella catarrhalis is currently preferred for these . Nevertheless, some in the medical field continue to call these bacteria Branhamella catarrhalis.

Clinical significance

These bacteria are known to cause , , , and . Elderly patients and long-term heavy smokers with chronic pulmonary disease should be aware that M. catarrhalis is associated with , as well as exacerbations of existing chronic obstructive pulmonary disease (COPD). The peak rate of colonisation by M. catarrhalis appears to occur at approximately 2 years of age, with a striking difference in colonization rates between children and adults (very high to very low).

M. catarrhalis has recently been gaining attention as an emerging human pathogen. It has been identified as an important cause in broncho-pulmonary infection, causing infection through in the upper pulmonary tract. Additionally, it causes bacterial , especially in adults with a compromised . It has also been known to cause infective exacerbations in adults with chronic disease, and it is an important cause in acute sinusitis, maxillary sinusitis, bacteremia, , conjunctivitis, acute purulent irritation of chronic bronchitis, , septicaemia (although this is rare), (which is also a rare occurrence), as well as acute laryngitis in adults and acute otitis media in children. M. catarrhalis is an opportunistic pulmonary invader, and causes harm especially in patients who have compromised immune systems or any underlying chronic disease.

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Figure 1: sensitivity test: This shows resistance to because it produces the enzyme β-lactamase. This is confirmed by the disc labelled β turning red

Treatment

M. catarrhalis can be treated with , but it is commonly resistant to , ampicillin, and . Treatment options include antibiotic therapy or a so-called "watchful waiting" approach. The great majority of clinical isolates of this organism produce beta-lactamases and are resistant to penicillin. Resistance to , trimethoprim- sulfamethoxazole (TMP-SMX), , and have been reported. It is susceptible to fluoroquinolones, most second and third generation , , and amoxicillin-clavulanate. Adults can also take tetracycline and fluoroquinolone antibiotics.

Prognosis

The prognosis of M. catarrhalis infection is poor in hospitalized patients with underlying conditions, especially the following:  Patients hospitalized for prolonged periods  Patients in pulmonary units or paediatric intensive care units  Patients of advanced age The most significant infections caused by M. catarrhalis are upper infections (URTIs) such as otitis media and sinusitis in children and lower respiratory tract infections (LRTIs) in adults. Infections with M. catarrhalis in adults are more common if underlying conditions are present, especially if the patient is elderly.

Risk Factors

Persons with chronic obstructive pulmonary disease (COPD), chronic bronchitis, or bronchiectasis are generally more susceptible to infection, as well as those with acquired immunodeficiency disease. Additionally, those who work in cold weather are generally at a higher risk.

Prevention

Because of the high colonization rate and lack of , it is very difficult to completely prevent infections. Proper hygiene such as hand washing is useful in deterring infection. However, this can be very nearly impossible in young children as many will develop otitis media, however not necessarily from M. catarrhalis.

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References

1. http://emedicine.medscape.com/article/222320 2. http://en.wikipedia.org/wiki/Moraxella_catarrhalis 3. https://microbewiki.kenyon.edu/index.php/Moraxella_catarrhalis_pathogenesis

Questions

1. Discuss the morphological characteristics of M. catarrhalis. 2. Discuss the prognosis of M. catarrhalis. 3. Discuss the clinical significance of M. catarrhalis.

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