Bacillus oleronius and Demodex mite infestation in patients with chronic blepharitis

Authors


Corresponding author: A. Szkaradkiewicz, Department of Medical Microbiology, University of Medical Sciences in Poznan, Wieniawskiego 3, str., 61-712 Poznan, Poland
E-mail: szkaradkiewicza@poczta.onet.pl

Abstract

Clin Microbiol Infect 2012; 18: 1020–1025

Abstract

To better recognize the pathogenicity of ocular Demodex mites, we analysed Bacillus oleronius infection in patients with Demodex-related chronic blepharitis. The studies were conducted on 68 adult patients, in whom ophthalmological and parasitological tests permitted the distinction of a group of 38 patients with a diagnosis of Demodex-related chronic blepharitis (group 1, including a subgroup 1a with moderate blepharitis and a subgroup 1b with severe blepharitis) and a group of 30 healthy individuals (group 2). In every person studied six eyelashes were epilated from each eye and the number of Demodex per eyelash was scored. In parallel, bacterial culture and isolation allowed their phenotypic and molecular identification. The drug sensitivity of the isolates was tested using E-tests. Intensity of Demodex infestation showed no significant differences between subgroups 1a and 1b. From the epilated eyelashes 23 bacterial isolates were obtained, identified as being B. oleronius. All the studied strains were sensitive to ciprofloxacin, doxycycline and gentamicin. The Demodex mite represents an independent aetiopathogenetic factor in blepharitis. In parallel, the parasite may act as a carrier of B. oleronius bacteria, which most probably function as a co-pathogen in the development of severe forms of blepharitis.

Introduction

Blepharitis is an inflammation of the eyelid margins, resulting in extremely irritating ocular discomfort in patients, pruritus, palpebral reddening and a decline in visual function persisting in the patients [1]. An aetiological role of Demodex mites is recognized, particularly Demodex folliculorum, in causing chronic blepharitis [2,3]. Nevertheless, the pathogenicity of Demodex remains unclear and Demodex infestations can also be found in asymptomatic individuals [4,5]. Studies indicate that Demodex is a non-pathogenic parasite and induces morbid signs/symptoms only in individuals with immune deficits [5–7]. New data related to the pathogenicity of the parasite were introduced by Lacey et al. [8], demonstrating the presence of Bacillus oleronius inside Demodex mites from patient with papulopustular rosacea. Bacillus oleronius is a non-motile, Gram-negative, rod-shaped endospore-forming bacterium, which was first isolated from the hindgut of the termite Reticulitermes santonensis by Kuhnigk et al. [9]. The pathogenic role of Demodex infestation may therefore be associated with B. oleronius.

To better understand the pathogenicity of ocular Demodex mites, we analysed the signs of B. oleronius infection in patients with Demodex-related chronic blepharitis.

Materials and Methods

Patient population

Studies were performed in 68 selected adults who visited the Department of Ophthalmology (111 Military Hospital in Poznan, Poland) for ophthalmic examinations between 1 September 2010 and 30 June 2011. All patients underwent complete ophthalmic examination under a slit-lamp biomicroscope. Examinations for the detection of ocular symptoms were performed on the eyelids, conjunctiva and cornea. The ocular surface blepharitis signs (lid debris, eyelid margin erythema, plugging of the meibomian glands and secretions expressed from the meibomian glands) were assessed and their severity was scored on a scale from 0 to 4, according to Werdich et al. [10]. In parallel, in every patient 12 eyelashes were isolated (three from the upper eyelid and three from the lower eyelid for both eyes) for microbiological tests. We tried to epilate the lashes with cylindrical dandruff around the root of the lash as deeply as possible. Finally, the patients replied to a questionnaire relating to frequency and severity of five common symptoms (eyelid itching, foreign body sensation, ocular dryness, ocular burning or pain, and swollen/heavy eyelids). The patients’ replies were scored on a scale from 0 to 4, according to Werdich et al. [10]. Total symptom and sign scores were calculated and normalized to a scale of 0–10. Severity of symptoms and signs were categorized as normal (0), mild (0.1–3.3), moderate (3.4–6.6) and severe (6.7–10), according to criteria suggested by Werdich et al. [10]. For at least 2 weeks before examination none of the patients used local or systemic antibiotic/chemotherapeutic agents. Moreover, in dermatological examinations none of the patients demonstrated any signs of inflammatory dermatosis on facial skin and dental examinations failed to find any potential infection foci in the oral cavity.

Detection and counting of Demodex mites on epilated lashes

Eight of the isolated eyelashes (the four remaining eyelashes were used for bacteriological tests) were placed separately at each end of glass slides. A coverslip was mounted on each lash before slowly pipetting 20 μL 10% potassium hydroxide solution at the edge of the coverslip to surround the eyelash [11]. Under the microscope (at magnifications of ×100 and ×400), a positive result involved the presence of adult mites, nymphs, larvae or Demodex eggs in the studied material. In parallel, the number of Demodex was counted in a conventional manner. For evaluation of Demodex infestation intensity the Demodex count for the eight eyelashes was divided by eight to obtain an average number of Demodex per eyelash.

Isolation of bacteria from eyelashes and phenotyphic identification

Each of four epilated eyelashes was incubated separately in nutrient broth (Difco, Franklin Lakes, NJ, USA) at 37°C for 24 h. Then, the growing bacteria were transferred to tryptic soy agar (Difco) and sheep blood agar, incubated at 37°C for 24–48 h. The grown colonies were evaluated macroscopically and under a microscope (Gram-stained). The bacterial isolates were identified as B. oleronius if they were aerobic, endospore-forming (detected under phase microscopy), Gram-negative, medium-sized rods, non-motile (they manifested no movement in a hanging drop and demonstrated no flagella, employing BD Flagella Stain Droppers; BD, Franklin Lakes, NJ, USA). The isolate identification was finally confirmed using PCR.

Purification of DNA

DNA was isolated from the obtained isolates preliminarily identified as belonging to B. oleronius species. For isolation of DNA, Sherlock AX (A&A Biotechnology, Gdynia, Poland) kits were used. The kit is based on the use of DNA-binding ion-exchange membranes, which trap DNA with 99% efficiency. In the kits, a precipitation amplifier is used, which increases precipitation efficacy and stains blue the obtained DNA precipitate. Isolation of DNA was conducted as recommended by the manufacturer. The purified DNA was stored at −20°C until further analyses were performed.

Target sequence and primers

To determine the target sequence the studies took advantage of a gene fragment for 16S ribosomal RNA of B. oleronius, available in the NCBI Nucleotide database (AY988598.1, GI:62546254). Detection of the above target sequence enabled the following primers to be designed for PCR:

BO1: 5′-AACGGCTCACCAAGGCGACG-3′ (20 nucleotides)

BO2: 5′-TCCGGACAACGCTTGCCACC-3′ (20 nucleotides).

The primers were designed using NCBI PrimerBLAST software and analysis of sequence specificity in the product took advantage of BLAST software [12]. The B. oleronius gene sequence for 16S rRNA analysis shows a close relation with two other species: Bacillus licheniformis and Bacillus sporothermodurans. However, strains of the last two species represent Gram-positive rods so in our study the identification involved exclusively DNA of B. oleronius. The primers were synthesized by DNA Gdansk company (Gdansk, Poland).

PCR assay

The control DNA was obtained from the standard strain of B. oleronius Kuhnigk et al. (ATCC 700005) purchased from the American Type Culture Collection (Manassas, VA, USA). In cases of positive control, 2 μL control DNA was added.

The PCR was performed in a Mastercycler gradient (Eppendorf Poland, Warsaw, Poland), in the following conditions of amplification:

  •  2 min at 94°C (preliminary denaturation)
  •  30 s at 94°C (denaturation)
  •  60 s at 60°C (primer annealing)
  •  60 s at 72°C (elongation)
  •  5 min at 72°C (terminal elongation)

The number of PCR cycles was 35. The PCR product was subjected to electrophoresis in a 2% agarose gel and the result was read after staining with ethidium bromide. The positive result involved the presence of a PCR product of 299 base pairs.

Antimicrobial susceptibility testing

Sensitivity to ampicillin, benzylpenicillin, ciprofloxacin, clindamycin, doxycycline and gentamicin was established on Mueller–Hinton agar (bioMérieux, Marcy L’Etoile, France) using E-test in accordance with the E-test technical guide (AB Biodisk, Solna, Sweden). CLSI and the European Committee on Antimicrobial Susceptibility Testing do not define MIC interpretative criteria for B. oleronius. Therefore, the following CLSI interpretative criteria were used as breakpoints for Bacillus spp. resistance: ampicillin 0.5 mg/L, benzylpenicillin 0.25 mg/L, ciprofloxacin 4 mg/L, clindamycin 4 mg/L, tetracycline 16 mg/L and gentamicin 16 mg/L [13]. Results were presented in the form of MIC50 and MIC90 values (minimum concentration of the antibiotic required to induce growth inhibition in 50% and 90% of strains, respectively).

Data analysis

The results were expressed as the mean ± standard deviation (SD) and median. Differences in distributions of B. oleronius in studied patients were compared using Fisher’s exact test. Differences in the intensity of Demodex invasion were compared with Mann–Whitney U test. A p-value greater than 0.05 was considered non-significant.

Results

The ophthalmological and parasitological studies conducted on 68 adult patients permitted the distinction of two research groups. Group 1 comprised 38 patients (23 women and 15 men) with a diagnosis of Demodex-related chronic blepharitis. Within this group, a subgroup 1a was distinguished, of 15 patients (mean age of 50 ± 7.9 years; median age 48 years) with a diagnosis of moderate blepharitis (clinical score of 4.1–6.2) and a subgroup 1b, including 23 patients (mean age of 56.3 ± 9.2 years; median age 57 years) with a diagnosis of severe blepharitis (clinical score ranged between 6.9 and 8.1). Group 2 included 30 healthy individuals (16 women and 14 men; mean age of 48.5 ± 7.8 years; median age: 48 years) and provided a control group (clinical score of 0).

Analysing the relationship between severity of blepharitis and intensity of ocular mite infestation, a mean number of Demodex per eyelash was evaluated in the two subgroups of group 1 patients. The number of parasites per eyelash was 0.125–1 in subgroup 1a. The same range of parasites per eyelash was found in 18 patients of subgroup 1b (i.e. 0.125–1). In the remaining five patients of subgroup 1b a heavier infestation with Demodex was disclosed, with number of parasites per eyelash ranging from 1.125 and 1.75. There was no significant difference between the two subgroups (p 0.0554). Results are presented in Table 1.

Table 1.  Intensity of Demodex infestation and detection of Bacillus oleronius in the groups of patients examined
Examined groupSubgroupsMean ± SD number of Demodex per eyelash (range in parentheses) [median]No. of patients Bacillus oleronius detectionSignificant difference
  1. *Significant difference as compared with the control group.

Group 1 (patients with Demodex blepharitis)Subgroup 1a (moderate blepharitis)0.69 ± 0.24 (0.125–1) [0.750]152 
Subgroup 1b (severe blepharitis)0.75 ± 0.25 (0.125–1) [0.8125]181216*
1.33 ± 0.26 (1.125–1.75) [1.250]54
Group 2 (control group)0305 

Using the epilated eyelashes, culture permitted the isolation of 23 strains of bacteria, originating from 18 patients of group 1 (two strains were isolated from patients of subgroup 1a and 16 strains were isolated from patients of subgroup 1b) and from five patients of group 2. The difference in the frequency of B. oleronius detection in patients of subgroup 1b and healthy people (group 2) was significant (p 0.0190). All the obtained bacterial isolates were aerobic, non-motile, endospore-forming, Gram-negative, medium-sized rods (Fig. 1). None of the cultures showed the presence of other bacteria. In parallel, the DNA of the isolates obtained gave a PCR product of 299 bp, which confirmed the diagnosis of B. oleronius species (Fig. 2).

Figure 1.

 Optical micrograph (magnification, ×1000) of Gram-negative, medium-sized rods isolated from eyelashes of studied patients and finally identified (PCR assay) as Bacillus oleronius species.

Figure 2.

 Polymerase chain reaction detection of Bacillus oleronius. Ethidium bromide-stained agarose gel. M—100 bp molecular weight standard. C(−), negative control; C(+), positive control; 1–9, positive patients.

Antibiotic sensitivity testing showed that all of the examined strains were sensitive to ciprofloxacin (MIC50 and MIC90 values 0.094 and 0.125 mg/L, respectively), doxycycline (MIC50 and MIC90 values 1.5 and 2 mg/L, respectively) and gentamicin (MIC50 and MIC90 values 0.25 and 0.5 mg/L, respectively). Only 12 strains (75%) were sensitive to clindamycin (MIC50 and MIC90 values 1.5 and 16 mg/L, respectively). In contrast, all the strains showed resistance to ampicillin (MIC50 and MIC90 values amounted to 32 and 256 mg/L, respectively) and benzylpenicillin (MIC50 and MIC90 values amounted to 64 and 256 mg/L, respectively). The results of the E-tests are presented in Table 2.

Table 2.  Antimicrobial susceptibilities of 16 Bacillus oleronius isolates
Antimicrobial drugMICs (mg/L)
RangeMIC50MIC90
Ampicillin4–25632256
Benzylpenicillin6–25664256
Ciprofloxacin0.064–0.1250.0940.125
Clindamycin0.25–161.516
Doxycycline0.125–21.52
Gentamicin0.125–10.250.5

Discussion

Demodex mites are the most common parasite in humans, with a life-cycle lasting about 14–18 days [14]. There are many species of Demodex, but only D. folliculorum and D. brevis are found in the human body [3]. Demodex folliculorum inhabits the hair follicles of eyelashes while D. brevis lives deep in the meibomian glands and the sebaceous glands of the lash [5]. These parasites live also on the skin of the face, where their principal habitat involves nose skin. Their intradermal residence (near the skin surface), and possible direct interactions, modulating the effects of mites and their products on immune reactivity, apparently allows Demodex to avoid the immune responses of the host and to survive in the human body. In parallel, Demodex mites consume epithelial cells and induce micro-abrasions, which can result in epithelial hyperplasia and reactive hyperkeratinization around the base of the lashes, forming cylindrical dandruff [5]. As a result, Demodex mites can cause chronic blepharitis, conjunctival inflammation and meibomian gland dysfunction. In addition, in penetrating the dermis, they can cause dermatological diseases, such as acne, rosacea and folliculitis [3,15,16]. In this study we investigated two groups of patients, evaluating ocular symptoms and clinical signs, and calculating total scores on a scale of 0–10 [10]. These scores allowed the objective distinction among the group of patients with Demodex-induced chronic blepharitis of a subgroup of patients with a moderate form and another subgroup with severe blepharitis. In both subgroups the number of parasites per eyelash amounted to 0.125–1, except for five patients with severe blepharitis, in whom a more intense infestation with Demodex was recorded. We detected and counted Demodex using 10% potassium hydroxide solution, which effectively dissolved the cylindrical dandruff, unmasking the embedded Demodex. Another method that effectively unmasks Demodex mites involves the use of fluorescein solution [17]. Recently, Lee et al. [18] showed a positive correlation between the number of Demodex and the severity of ocular discomfort. However, the ocular discomfort was evaluated on a scale from 0 to 100 points in all the patients with or without blepharitis. In addition, the presented data indicate that intensity of ocular surface discomfort was not exclusively related to an increase in Demodex [18]. Hence, the results can only in part be related to our results, which were conducted in strictly clinically defined subgroups of patients with distinct severity of blepharitis symptoms and signs. In our study we demonstrated that in most of the patients with severe blepharitis, infestation with Demodex was accompanied by B. oleronius infection, which might determine the development of infection in the eyelid margins and, therefore, a more severe course of the disease. This conclusion is supported by the studies of Lacey et al. [8], who isolated B. oleronius from D. folliculorum mite extracted from the face of a patient with papulopustular rosacea. In parallel, the authors found that two specific antigenic proteins (62 and 83 kDa) produced by the bacteria may stimulate an inflammatory response in the infected patients [8]. Moreover, Li et al. [19] presented a positive correlation between ocular Demodex infestation and serum immunoreactivity to both 62-kDa and 83-kDa B. oleronius proteins. Nevertheless, our demonstration of B. oleronius in eyelash cultures from five healthy individuals may argue against a pathogenic role of these bacteria in the development of blepharitis. On the other hand, it is well known that certain species of Bacillus are closely associated with insect guts, including some B. cereus strains, characterized by filamentous growth in the intestines of healthy arthropods [20,21]. Moreover, it is suggested that in Africa, B. anthracis may be disseminated via ingestion and excretion by Tabanid flies [21]. In the context of the data it may be assumed that B. oleronius strains as the symbiotic bacteria grow in Demodex intestines and are excreted by the parasite into their habitat in humans, with pathogenic sequelae for the humans.

In the absence of Demodex mites, B. oleronius probably persists in a dormant stage, in the form of endospores. Like many species of Bacillus and Clostridium, B. oleronius can manifest itself in two distinct cellular morphologies, the vegetative cell and the endospore [9]. Considering this, we suggest that in the five healthy people the B. oleronius was in a dormant stage, in the form of endospores, which in the nutrient broth rapidly germinated to vegetative forms, that were then detected in a laboratory culture. In turn, our demonstration of B. oleronius strain presence in only two patients with moderate blepharitis seems to indicate low pathogenicity of the strains.

Drug resistance was evaluated for 16 B. oleronius strains isolated from patients with severe blepharitis. All the strains were sensitive to ciprofloxacin, doxycycline and gentamicin and most strains showed sensitivity to clindamycin. However, the above antibiotics do not kill the mites, and could be helpful only in reducing the progression of blepharitis.

Our results indicate that Demodex mites represent an independent aetiopathogenic factor in blepharitis. The data show also that the parasite may be a carrier of B. oleronius bacteria, most probably acting as a co-pathogen in the development of severe forms of blepharitis.

Conflict of interest

Nothing to declare.

Transparency Declaration

The authors have no conflicts of interest to disclose or any financial support.

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