European Journal of Cardiovascular Medicine

Moraxella catarrhalis, formerly called Neisseria catarrhalis or Micrococcus catarrhalis, is a Gram-negative, aerobic, oxidase-positive diplococcus frequently found as a commensal of the upper respiratory tract. Over the last 20–30 years, the bacterium has emerged as a primary pathogen and is now considered an important cause of upper respiratory tract infections in otherwise healthy children and elderly people. Moreover, Moraxella catarrhalis is an important cause of lower respiratory tract infections, particularly in adults with chronic obstructive pulmonary disease (COPD).

In immunocompromised hosts, the bacterium can cause a variety of severe infections, including pneumonia, endocarditis, septicemia, and meningitis. In addition, hospital outbreaks of respiratory disease due to Moraxella catarrhalis have been described [1–3].

In contrast to the upper respiratory tract infections (URTIs) associated with Moraxella catarrhalis in children, infections in adults are mostly associated with lower respiratory tract infections (LRTIs). Chronic obstructive pulmonary disease (COPD) is a major predisposing factor for LRTIs and a considerable public health problem. Published data in the last decade have established that Moraxella catarrhalis is associated with exacerbations of COPD [2–4].

Identification of Moraxella catarrhalis is done by Gram staining, culture, and biochemical tests. Most isolates of Moraxella catarrhalis produce beta-lactamase enzymes, making them resistant to penicillin, ampicillin, and various other antibiotics commonly used to treat respiratory tract infections [1,3].

Moraxella catarrhalis has long been considered a harmless commensal; therefore, relatively little is known about its pathogenic characteristics and virulence factors. However, the emergence of Moraxella catarrhalis as a pathogen in the last decade, together with the increasing prevalence of beta-lactamase-producing strains, has renewed interest in this bacterial species [5].

Aim and Objectives

To study the pathogenic potential of Moraxella catarrhalis in lower respiratory tract infections in terms of its frequency of isolation from respiratory specimens, identification through microscopy, culture, and biochemical tests, incidence in community-acquired and nosocomial infections, antimicrobial susceptibility pattern, and its implications in guiding empirical antibiotic therapy.

Methodology

This was a cross-sectional study conducted in the Department of Microbiology, Kannur Medical College, Anjarakandy, over a period of 18 months. Ethical approval was taken from the institutional ethical committee prior to starting the study. All respiratory specimens reaching the Department of Microbiology were considered for inclusion based on predefined criteria.

Inclusion Criteria:

• Respiratory specimens from patients with lower respiratory tract infections.
• Sputum specimens included in the study were subjected to Bartlett scoring.

Exclusion Criteria:

• Improperly collected or transported samples.
• Non-bacterial causes of lower respiratory tract infections.

A total of 250 respiratory specimens were selected for the study based on the inclusion and exclusion criteria. Only thick mucoid, mucopurulent, or purulent specimens were considered for analysis. Smears were prepared from the specimens and subjected to Gram staining. The number of pus cells and epithelial cells was noted under low power microscopy, and the specimen quality was assessed using Bartlett scoring.

Bartlett Scoring:

Culture and Identification of Isolates:

Respiratory specimens were inoculated on Blood Agar, Chocolate Agar, and MacConkey Agar. An optochin disc was placed over the primary streak line on Blood Agar. The inoculated plates were incubated in carbon dioxide at 37°C for 18-24 hours. Bacterial isolates showing pure, predominant heavy growth consistent with Gram stain findings were considered significant pathogens and included in the study.

Isolates were identified based on:

1. Colony morphology.
2. Gram staining.
3. Biochemical tests for Gram-positive and Gram-negative respiratory pathogens using appropriate controls.

Species identification of Moraxella catarrhalis was performed using Gram stain morphology, culture characteristics, catalase and oxidase tests, nitrate reduction test, rapid carbohydrate utilization test, penicillinase test, tributyrin test, and DNase test.

Antibiotic Susceptibility Testing Antibiotic susceptibility was assessed using the modified Kirby-Bauer disc diffusion method. The tested antibiotics included Ampicillin (30 mcg), Amoxicillin-Clavulanic Acid (30 mcg), Ceftriaxone (10 µg), Cotrimoxazole (25 µg), Ciprofloxacin (5 µg), Azithromycin (15 µg), and Amikacin (30 µg). Susceptibility results were interpreted according to CLSI guidelines (2013).

Data Analysis The collected data were entered into an MS Excel sheet and analyzed using SPSS version 22.0 software. Descriptive variables were presented as frequencies and percentages. Continuous variables were tested for significance using Student’s t-test, while categorical variables were analyzed using the Chi-square test.

Table 1: Age-wise Distribution of Lower Respiratory Tract Infections (LRTIs)

Figure 1: Gram-stained smear of sputum showing M. catarrhalis.

The incidence of LRTIs was higher among individuals aged between 40-70 years. M. catarrhalis infections were most commonly observed in the 6th decade, followed by the 5th, 3rd, and 4th decades.

Table 2: Gender Distribution of Patients

Figure 2: Gram-stained smear of M.catarrhalis colony.

LRTIs were more common in males (67.6%) than in females (32.4%). Among the M. catarrhalis isolates, males accounted for 68% and females 32%.

Table 3: Outpatient (OP) / Inpatient (IP) Distribution of Patients

Figure 3: M. catarrhalis growth on Blood Agar.

The majority of cases were inpatients (68.8%), while outpatients comprised 31.2%. Among the M. catarrhalis isolates, 66% were from inpatients and 34% from outpatients.

Table 4: Specimen Distribution of Isolates

Figure 4: M. catarrhalis growth on Chocolate Agar.

Sputum samples accounted for 82.4% of total respiratory samples, with M. catarrhalis isolated predominantly from sputum (97.36%) and bronchial washing (2.63%).

Table 5: Background Comorbidities of LRTIs

Figure 5: Oxidase Test - Positive.

Diabetes mellitus was the most common comorbidity (32%), followed by COPD (28.4%) and bronchial asthma (16.4%).

Table 6: Microbial Profile of Lower Respiratory Tract Infections

Figure 6: Nitrate Reduction Test - Positive.

Klebsiella pneumoniae (20.8%) was the most commonly isolated pathogen, followed by Streptococcus pneumoniae (17.6%) and Pseudomonas aeruginosa (16.4%). Moraxella catarrhalis accounted for 15.2% of total isolates.

Table 7: Incidence of Moraxella catarrhalis LRTIs

Figure 7: Rapid Carbohydrate Utilization Test

The incidence of Moraxella catarrhalis isolated from patients with lower respiratory tract infections.  Out of 250 isolates obtained during the study, 38 (15.2%) were identified as Moraxella catarrhalis, whereas 212 isolates (84.8%) comprised other organisms. This highlights a significant but relatively lower incidence of Moraxella catarrhalis among the total organisms isolated in LRTIs cases.

Table 8: Comorbidities Associated with LRTIs

Figure 8: Tributyrin Test - Positive.

The distribution of various comorbidities observed among patients with lower respiratory tract infections caused by different bacterial and fungal isolates. Among all isolates, diabetes mellitus was most commonly associated with Klebsiella pneumoniae (31%), followed by chronic obstructive pulmonary disease (COPD), which had the highest association with Moraxella catarrhalis (26%). Bronchial asthma was notably associated with Streptococcus pneumoniae (29%). A significant number of isolates (32.75%) identified as Streptococcus pneumoniae were found among patients without any comorbidity. This table highlights distinct patterns of pathogen association with specific comorbid conditions in patients suffering from LRTIs.

Table 9: Association of Moraxella catarrhalis in LRTIs and COPD

Chi-square test = 9.37, p-value = 0.003

Figure 9: DNase Test - Positive.

The association between Moraxella catarrhalis isolates and chronic obstructive pulmonary disease among patients diagnosed with lower respiratory tract infections. Out of 38 cases with Moraxella catarrhalis infections, an equal number (19 cases each) were observed among COPD and non-COPD patient groups. Among other isolates (212 cases), COPD was present in 54 cases (25.5%). The statistical analysis indicated a significant association between Moraxella catarrhalis infections and COPD (Chi-square = 9.37, p-value = 0.003), highlighting COPD as a notable risk factor for Moraxella catarrhalis-associated LRTIs.

Table 10: Association of Comorbidities and Isolates

Chi-square test = 14.92, p-value = 0.002

Figure 10: Antibiotic Sensitivity Test of M. catarrhalis on Blood Agar.

The association between various comorbid conditions and bacterial isolates identified among participants (N=250). Participants were categorized into four groups: those without comorbidities (n=58), individuals diagnosed with Bronchial Asthma (n=41), Chronic Obstructive Pulmonary Disease (n=71), and Diabetes Mellitus (n=80). Among these groups, isolates were classified into 'Other isolates' and 'Moraxella catarrhalis'. The majority of isolates (212 out of 250) fell into the 'Other isolates' category, whereas 'Moraxella catarrhalis' accounted for 38 isolates. Chi-square testing revealed a statistically significant association between the type of isolate and the presence of comorbid conditions (χ² = 14.92, p = 0.002).

Table 11: Antibiotic Susceptibility Test of    M. catarrhalis

All M. catarrhalis isolates were resistant to Ampicillin. The highest sensitivity was observed for Amoxicillin + Clavulanic Acid and Amikacin (100%), followed by Ceftriaxone (94.7%) and Azithromycin (92.1%).

Table 12: Beta-Lactamase Production in M. catarrhalis

Non-producer      0

All M. catarrhalis isolates (100%) were Beta-lactamase producers.

Moraxella catarrhalis has emerged as a significant respiratory pathogen, particularly in lower respiratory tract infections among individuals with chronic obstructive pulmonary disease and other underlying conditions. Although historically regarded as a commensal organism, recent studies, including findings, support its pathogenic role in exacerbating respiratory illnesses.

In this study, M. catarrhalis was isolated in 15.2% of LRTI cases, with a particularly high prevalence among COPD patients. The findings align with previous studies conducted in different geographical regions, reinforcing its role as a critical respiratory pathogen. The male preponderance observed in this study is consistent with global trends, likely attributed to higher smoking rates and increased exposure to respiratory irritants among males.

Laboratory identification of M. catarrhalis remains crucial, particularly due to its resemblance to commensal Neisseria species. Biochemical tests, including oxidase and catalase positivity, nitrate reduction, tributyrin hydrolysis, and DNase activity, facilitated its accurate differentiation.

Antibiotic susceptibility testing revealed 100% resistance to Ampicillin, consistent with the high beta-lactamase production observed in all isolates. However, the organism exhibited complete sensitivity to Amoxicillin-Clavulanic acid and Amikacin, and high sensitivity to Ceftriaxone (94.7%) and Azithromycin (92.1%). The observed resistance to Ciprofloxacin (42.1%) highlights the emerging challenge of fluoroquinolone resistance in respiratory pathogens.

Given its ability to confer beta-lactamase-mediated protection to co-infecting respiratory pathogens, M. catarrhalis should be considered in the management of polymicrobial respiratory infections. Empirical therapy should prioritize beta-lactamase inhibitor combinations and macrolides to ensure optimal treatment outcomes.

With increasing antibiotic resistance trends, continued surveillance of M. catarrhalis is essential to guide appropriate antimicrobial stewardship strategies. This study underscores the need for accurate laboratory identification, timely diagnosis, and judicious antibiotic use in managing M. catarrhalis-associated respiratory infections.

This study highlights the significant role of Moraxella catarrhalis as a pathogen in lower respiratory tract infections (LRTIs), particularly among individuals with underlying pulmonary conditions such as COPD. The high prevalence of M. catarrhalis in elderly patients and its association with chronic respiratory diseases underscore its clinical importance.

Antibiotic resistance remains a major concern, with all isolates exhibiting 100% resistance to Ampicillin, indicating widespread beta-lactamase production. However, complete sensitivity to Amoxicillin-Clavulanic acid suggests that beta-lactamase inhibitors remain an effective treatment option. This emphasizes the necessity of routine beta-lactamase testing and antibiotic susceptibility profiling to guide appropriate antimicrobial therapy and prevent treatment failures.

The study provides valuable insights into the prevalence and antibiotic resistance patterns of M. catarrhalis, it was limited to phenotypic analyses. Future research employing molecular typing and genetic sequencing is essential to better understand the genetic variations and resistance mechanisms of M. catarrhalis in this region. Further studies are needed to explore its role in mixed infections and its interaction with other respiratory pathogens to optimize patient management and treatment strategies.

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