|Year : 2012 | Volume
| Issue : 4 | Page : 189-192
A study of antibacterial and antifungal properties of human cerumen
Sumit Gupta, Rohit Singh, Kranthi Kosaraju, Indira Bairy, Balakrishnan Ramaswamy
Department of ENT HNS and Department of Microbiology, Kasturba Medical College, Manipal University, Karnataka, India
|Date of Web Publication||19-Dec-2012|
Department of ENT HNS, Kasturba Medical College, Manipal University, Karnataka
Source of Support: None, Conflict of Interest: None
Objective: To investigate the effect of human cerumen on the growth of Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa and Candida albicans. Study Design: Prospective study Setting: The study was conducted in the Department of Otolaryngology-Head and neck Surgery and Department of Microbiology, at a tertiary care teaching hospital in southern India. Materials and Methods: Cerumen samples were collected from 120 healthy cases by using sterile Jobson Horn Probe. Sterile samples were taken and further tested. The bacterial strains were cultured on nutrient agar and Candida was grown on SDA. Serial 10 fold dilutions of the test organisms were made using normal saline acting as control and using 3.5% cerumen suspension as test and were incubated at 37°C for 12 hours. Subcultures were performed from test as well as control tubes to assess the inhibitory activity of human cerumen. Results: Of 120 samples, only sterile samples were tested. At dilutions of 1 in 10 3 there was complete inhibition of Escherichia coli and Pseudomonas aeruginosa in all samples, complete inhibition of Staphylococcus aureus in 83.3% samples and Candida albicans in 80% samples. The order of inhibition demonstrated by cerumen in the present study was Escherichia coli > Pseudomonas aeruginosa > Staphylococcus aureus > Candida albicans. Conclusion: Human cerumen has antibacterial and antifungal properties against the commonest bacterial and fungal pathogens. Other than the physical barrier, wax acts as protective coating over the external auditory canal. Hence, routine wax removal/ear cleaning is not mandatory unless impacted wax is leading to earache or conductive hearing loss.
Keywords: Antibacterial, Antifungal, Cerumen
|How to cite this article:|
Gupta S, Singh R, Kosaraju K, Bairy I, Ramaswamy B. A study of antibacterial and antifungal properties of human cerumen. Indian J Otol 2012;18:189-92
| Introduction|| |
Cerumen is produced in the outer third of the cartilaginous portion of the human ear canal. It is composed of desquamated sheets of corneocytes, originating from the deep and superficial external auditory canal, mixed with glandular secretions. It's a mixture of secretions from sebaceous glands and modified apocrine sweat glands.  Sebaceous and cerumenous glands in the auditory canal secrete lipids and peptides, respectively. Hairs in the external third of the canal also produce glandular secretions that contribute to cerumen's composition.  The balance of secretions from the sebaceous and cerumenous glands varies between ethnic groups, which might partly explain the phenotypic differences in cerumen observed in different ethnic groups.  However, whether these phenotypic variations translate into clinically significant differences in the prevalence of impacted cerumen or the treatment outcome is unknown.
There is some evidence of genetic polymorphisms in cerumen phenotypes. Current evidence stratifies cerumen into two phenotypes: wet and dry. Wet cerumen, which is light or dark brown and sticky, is characterized by a relatively high concentration of lipid and pigment granules. Dry cerumen, which is grey or tan and brittle, tends to express lower levels of these components.  For example, dry wax contains around 20% lipid, compared to approximately 50% in wet cerumen. Besides this, the two forms show few other biochemical differences. These two forms are associated with race and are controlled by two autosomal alleles. 
Cerumen production seems to show neither discordance between sexes, nor marked differences over the years. However, the lack of marked differences over the year might offer one strand of circumstantial evidence against cerumen playing a clinically or biologically significant antibacterial role. 
Although, the role of human cerumen is believed to protect the external ear canal against infections there are still controversies on this topic. Some authors have suggested that cerumen is unable to prevent infections and that the rich nutrients of cerumen support abundant growth of bacteria and fungi. Besides providing a physical barrier against infection, it is believed that cerumen has antibacterial and antifungal properties.  Our study aims at evaluating the effect of human cerumen on the growth of Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa and Candida albicans.
| Materials and Methods|| |
Study design and setting
This was a prospective study that was conducted at the Department of Otolaryngology-Head and neck Surgery and Department of Microbiology, at a tertiary care teaching hospital, in southern India.
Healthy subjects, of all age groups, without any external or middle ear pathology, who attended the ENT outpatient clinic of the hospital during five months of the study period.
After Institutional ethics committee clearance (IEC 016/2010/KH, Manipal) cerumen samples were collected from 120 normal, healthy individuals using a sterile Jobson Horn Probe, then emulsified in a solution containing 30 percent glycerol with 5 percent sodium bicarbonate, producing a cerumen suspension of 3.5 percent (weight/volume). The mixture of cerumen and buffer was then emulsified by pumping it back and forth using a sterile syringe. The cerumen suspension was stored at minus 20°C until microbiological testing.
The cerumen suspensions were cultured on nutrient agar plate and incubated at 37°C overnight. Samples that showed any microbiological growth, even the commensals of the external auditory canal, were treated as unsterile and were excluded from further testing. The samples which did not show any growth were preserved for further testing.
Bacterial and fungal strains
The bacterial strains that were tested are Staphylococcus aureus (American Type Culture Collection (ATCC) 25923), Escherichia coli (ATCC 25922), Pseudomonas aeruginosa (ATCC 27853) and the fungi Candida albicans.
Antibacterial and antifungal assays
The three bacterial strains and the fungal strain were cultured on nutrient agar and Sabouroud's dextrose agar (SDA) respectively and incubated at 37°C for 24 hours to obtain fresh cultures. A single isolated colony of each culture was transferred to 10ml nutrient broth and incubated for minimum of 6 hours at 37°C and inoculum was adjusted to 0.5McF (i.e. 1.5 × 10 8 cfu/ml).
In the next step, 10-fold serial dilution ranging from 1 in 10 1 to 1 in 10 5 was prepared by adding 100 μl of the prepared inoculum to tubes containing 900 μl of 3.5% cerumen suspension. The tubes containing various dilutions of the inoculums were incubated at 37°C for 16-18 hrs. After overnight incubation, 10 μl of suspension from each dilution was transferred onto a blood agar plate, streaked and incubated at 37°C for 24 hours to observe for colonies. Growth in the form of colony formation was observed following incubation and the results were recorded.
The growth control for each of the strains was also included to ensure adequate growth of the test bacteria and fungus. Negative control was also included to ensure sterility of all the samples and media used in the test procedure.
| Results|| |
- Total number of cerumen samples collected = 120 (labeled from 1 to 120)
- Total number of sterile samples obtained = 60 (considered for further proceedings in the study)
- Total number of unsterile samples obtained = 60 (rejected, hence not considered for the study)
- The growth control showed adequate growth of the test strains and the negative control showed no growth indicating the validity of the test conditions.
- [Table 1] shows the number of samples in which the growth was inhibited.
From the data obtained, it was seen that sterile human cerumen samples could inhibit,
|Table 1: Depicts the number of samples in which the growth was inhibited|
Click here to view
- Escherichia coli
- Pseudomonas aeruginosa
- Staphylococcus aureus
- Candida albicans in the decreasing order of their list.
| Discussion|| |
Cerumen forms an acidic coat that aids in the prevention of external auditory canal infection. , Absence of cerumen may lead to infection, such that cerumen serves an antimicrobial role by physically protecting the external auditory canal skin, establishing a low pH; thus an inhospitable environment for pathogens and producing antimicrobial compounds such as lysozyme, so that its absence leaves the canal vulnerable to infection.
The traditional view holds that cerumen also protects the middle ear from bacterial and fungal infection. For example, some authorities suggest retaining the cerumen barrier to bolster host defenses against ear infections.  However, the evidence that cerumen plays a biologically or clinically significant role in host defence seems relatively weak. It might be expected, for example, that if cerumen played an important role bolstering host defense systems, its composition would alter in response to an infection. Perhaps exposure to bacteria would induce up-regulation of antibacterial components of cerumen. However, the cerumen of patients with otitis externa does not seem to contain more antibacterial polyunsaturated fatty acids than those without. 
In our study the cerumen inhibited the growth of bacteria and fungi at different concentrations. The study demonstrated that cerumen has antibacterial and antifungal properties, which plays a role in the protection of the external auditory canal. Interestingly, Sololov et al., proved that the cerumen of some mammals possess antistaphylococcal, antimicrococcal and antiherpes activities. 
Our findings on the bactericidal effect of cerumen on E. coli are consistent with Stone and Fulghum, Chai and Chai and Bauman et al., ,, However, Lum et al., and Campos et al., found insignificant bactericidal effect and stated that Escherichia coli is not a normal commensal of the ear canal, and thus may not be recognized by the immune system of the ear canal. ,
Campos et al., showed that an increase in growth occurred much more frequently than a decrease in growth in almost every microorganism tested with wet cerumen, with the mean increase percentage being much higher than the mean decrease percentage, except in the case of S. aureus.  Burtenshaw reported inconsistent bactericidal activity of cerumen against S. aureus.  Megarry et al., Stone and Fulghum reported a significant bactericidal activity similar to our study. ,
Our results agree with Lum et al., and Chai and Chai who demonstrated the bactericidal effect of cerumen on two strains of P. aeruginosa. , However other studies have reported a lack of bactericidal effect of cerumen on P. aeruginosa. ,,
Megarry et al., and Lum et al., studied the mycocidal effect of cerumen consistent with our study. , Interestingly, our study shows that the human cerumen has more antibacterial property as compared to antifungal property. Probably some protective mechanism in the fungus led to less inhibition of their growth as compared to the bacteria.
In our study, the sterile samples were stored at 20°C and then processed after some time. This storage might have affected the antibacterial and antifungal property, which might have otherwise been higher if the tests were conducted immediately.
Indeed, immunohistochemical studies suggest that antibody-mediated immune reactions, rather than cerumen, protect the external auditory canal from infection. The epidermis and dermis surrounding the sebaceous and cerumenous glands, as well as the piliary follicles, express cells capable of activating and sustaining local immune reactions, including IgA and IgG.  However, there is a need for further studies to characterize the nature of host defence in this unique anatomical site.
The conflicting results reported in the literature may be explained by differences in individuals, culture media, micro-organism virulence and methodology. Staphylococcus aureus, P. aeruginosa and C. albicans are common pathogens which cause otitis externa, and the presence of cerumen in the ear canal may reduce the likelihood of infection by such micro-organisms. 
Our study tries to put forward that apart from being a physical barrier, cerumen acts as protective coating over the external auditory canal due to its antibacterial and antifungal properties. Hence, routine wax removal/ear cleaning is not mandatory unless impacted wax is leading to earache or conductive hearing loss.
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