1. health and fitness
2. disease

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Nocardia keratitis
Prajna Lalitha
Aravind Eye Hospital and Postgraduate Institute of
Ophthalmology, No.1 Anna Nagar, Madurai, Tamil
Nadu 625020, India
Correspondence to Dr Prajna Lalitha, MD, DNB, Head,
Department of Ocular Microbiology, Aravind Eye
Hospital and Postgraduate Institute of Ophthalmology,
No.1 Anna Nagar, Madurai, Tamil Nadu 625 020 India
Tel: +91 452 4356100; fax: +91 452 2530984;
e-mail: [email protected]
Current Opinion in Ophthalmology 2009,
20:000–000
Purpose of review
Nocardia keratitis is a rarity in most parts of the world. If the diagnosis is timely, and
appropriate treatment started, then the visual outcome is good. The purpose of this
review is to discuss the recently published literature in relation to the epidemiology,
cause, diagnosis, and therapy of Nocardia keratitis.
Recent findings
The incidence of Nocardia keratitis, although not well established, appears to be
increasing with new species identified with newer molecular methods. The different
species causing keratitis are Nocardia. arthritidis, N. neocaledoniensis, N. asiatica,
N. asteroids type IV, N. brasiliensis, N. pseudobrasiliensis, N. cyriacigeorgica,
N. farcinica, N. otitidiscaviarum, and N. transvalensis. Current therapies with fortified
amikacin and newer fluoroquinolones are effective, provided the diagnosis has
been made in good time. Ongoing research toward rapid diagnosis using various
molecular techniques seems to be promising. Diagnostic microbiology laboratories
need to be familiar with these organisms especially in endemic areas, and it is important
for the clinician to notify the suspicion of such cases.
Summary
The current recommended treatment is amikacin, and with appropriate therapy,
Nocardia keratitis resolves with scarring, with or without vascularization, resulting in
good visual outcome.
Keywords
amikacin, antibiotics, clinical appearance, Nocardia keratitis, species
Curr Opin Ophthalmol 20:000–000
ß 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins
1040-8738
Introduction
Nocardia are aerobic, branching, beaded filamentous
bacilli with Gram stain variability and are often acid-fast
positive. Although relatively uncommon, Nocardia are an
important cause of keratitis [1,2,3,4,5]. A delay in diagnosis may occur because of its rarity and unfamiliarity.
Microbiology of Nocardia
The taxonomic history of the genus Nocardia is fraught
with confusion and controversy. Edmond Nocard, a
French veterinarian, was the first to isolate a filamentous
aerobic organism from cattle with farcy in 1888. In 1889,
the genus Nocardia was created by Trevisan, and the
organism described by Nocard was named Nocardia farcinica.
However, 80 years later, Nocard’s original isolate
revealed two different filamentous organisms, one of
which was Mycobacterium and the other was Nocardia.
The cause of bovine farcy has been subsequently attributed to a Mycobacterium sp., not a Nocardia sp. It is
probable that the original isolate was Mycobacterium farcinogenes. Nocardia asteroids is now accepted as the type
1040-8738 ß 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins
species of the genus Nocardia, and recently several investigations have contributed to the formation of a homogeneous group of Nocardia [6].
Brown-Elliott et al. [7] have recently reviewed the clinical
and laboratory features of the Nocardia spp. based on
current molecular taxonomy and found that there are
currently more than 30 species of Nocardia of human
clinical significance, with the majority of isolates being
N. nova complex, N. abscessus, N. transvalensis complex,
N. farcinica, N. asteroids type VI (N. cyriacigeorgica), and
N. brasiliensis. These species cause a wide variety of
diseases and have variable drug susceptibilities [7].
Identification
Determination of the various species of Nocardia may be
helpful to define the spectra of disease caused by the
different species. Traditionally, Nocardia were identified
to species by using a battery of biochemical tests,
which included hydrolysis of adenine, casein, tyrosine,
xanthine, and hypoxanthine [8]. Conventional methods
of identification appear to be unreliable for species level
identification of many species of Nocardia because of the
small number of discriminatory tests available and the
DOI:10.1097/ICU.0b013e32832c3bcc
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2 Corneal and external disorders
expertise needed to interpret these tests. Compared with
these methods, molecular testing by hsp65 PCR and 16S
restriction enzyme analysis (PCR-restriction enzyme
analysis) appears to be an improvement and recognizes
more than 90% of currently recognized clinical species
[9–11].
Epidemiology
There have been sporadic reports in the literature about
the incidence of Nocardia keratitis. Upadhyay et al. [12]
from Nepal reported that Nocardia constituted 0.3% of
all bacterial isolates from cases of keratitis. A study [13]
from Hyderabad in South India revealed that among
689 bacterial isolates from cases of keratitis examined
between January 1991 and December 1998, Nocardia
species constituted 1.7%.
An earlier study [14] from our Institution reported that
Nocardia constituted 4.2% of all culture positive bacterial
cultures. Recently, in a review of culture-positive
samples from bacterial keratitis, it was found that Nocardia was isolated from 8.34% of cases (95 cases out of 1139
in the years 2006–2008; unpublished data). This may
indicate that the incidence may be increasing in this part
of the world.
Predisposing factors
The usual predisposing factors are trauma, surgery, corticosteroid use, and contact lens wear. In a series of 16
cases from India, trauma was the inciting factor in 25% of
cases [2]. The nature of traumatizing agents reported
includes vegetative material, dirt, stone, gravel, and nail
injury. Bharathi et al. [15] in their study from South India
found that the majority of the patients had a history of
trauma related to agricultural work.
Yin et al. [19] assessed the hsp65 gene sequencing for
detection and species identification of genus Nocardia
from ocular isolates and found N. arthritidis, N. neocaledoniensis, N. asiatica, N. asteroids type IV, N. brasiliensis,
and N. pseudobrasiliensis, and concluded that N. arthritidis
is the most important causal species that causes Nocardia
keratitis. In the study [3] published from our Institute, of
32 isolates the species identified were N. cyriacigeorgica
(n ¼ 11, 34.37%), N. asteroids (n ¼ 9, 28%), N. farcinica
(n ¼ 7, 22%), and N. otitidiscaviarum (n ¼ 5, 16%;).
Recently, other species found to be associated with
keratitis include N. transvalensis, which was reported to
be resistant to amikacin [20].
Clinical features
Nocardia keratitis generally runs a prolonged course. The
usual presenting symptoms are pain, photophobia,
blepharospasm, and lid swelling. The amount of pain
may be out of proportion to the clinical findings [21].
The ulcer often has a gray, sloughing base and undermining overhanging necrotic edges [22].
Keratitis may be in the form of nonspecific punctate
epitheliopathy or an ulcer with margins studded with
yellow white discrete pinhead-sized superficial infiltration (Fig. 1) [23]. The infiltrates may be arranged in a
ring-like fashion, forming the characteristic ‘wreath’ pattern (Fig. 2). Patchy infiltrates (Fig. 3), which are predominantly anterior stromal with associated involvement
of epithelium and subepithelial tissues, are pathognomonic of Nocardia keratitis [2]. Satellite lesions may be
associated [24,25]. The infiltrates are usually situated
in the midperiphery of the cornea [2,26]. Usually, there
Figure 1 Nocardia keratitis with superficial stromal infiltrates,
with pinhead-like lesions but may also be mistaken for satellite
lesions of mycotic keratitis
N. asteroids keratitis has also been diagnosed following
surgical trauma. Nascimento et al. [16] reported a case of
N. asteroids keratitis following an uncomplicated myopic
keratomileusis. Similarly, Perez-Santonja et al. [17] isolated Nocardia in a case presented as central interface
nodule following uncomplicated laser-assisted in-situ
keratomileusis retreatment for residual myopia. One
case has been described following penetrating keratoplasty for Salzmann nodular degeneration [18].
Most Common causal agents
Until recently, N. asteroids were the common species to
be isolated from cases of keratitis. However, in recent
times, advances in newer molecular techniques, including PCR restriction enzyme analysis and 16S ribosomal
RNA sequencing, have shown that other species of
Nocardia are more common.
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Nocardia keratitis Lalitha 3
Figure 2 Nocardia keratitis with typical wreath pattern infiltrates
found to have an indistinct fluffy or feather-like appearance with radiating projections. Nocardia keratitis may be
associated with complications, which include progressive
thinning leading to perforation, endophthalmitis, and
extension to adjoining sclera [6].
Laboratory diagnosis
Staining with modified acid-fast stains, and especially
Gram stains, are important to provide rapid presumptive
diagnosis while awaiting the results of the culture [28].
is an overlying epithelial defect. The surrounding stroma
is usually clear [21]. Keratic precipitates and endothelial
ring deposits seen on the endothelium are reported [27].
Anterior chamber reaction and hypopyon are usually
associated [2,23]. Peripheral deep neovascularization
extending to the cornea may be seen. The superficial
granular infiltrates with time may coalesce into a white
plaque and corneal ulceration may result. These classic
presentations are manifest only when the patient present
relatively early (within 2 weeks) [3].
The typical clinical appearance of Nocardia keratitis may
prompt the clinician to the diagnosis. Even in situations
in which the clinician either is not familiar with the
clinical appearance or the presentation is atypical, microbiological investigations helps confirm the diagnosis. As
treatment may be prolonged, it is important to have an
exact diagnosis. Good communication between the treating physician and microbiologist is of utmost importance,
especially to establish methods for obtaining and maintaining standard materials for collection, transport, and
processing of samples.
Routine laboratory diagnostic methods that are employed
are very effective in identifying Nocardia organism.
Bharathi et al. [15] found the sensitivity of KOH wet
mount to be superior (100%) in the detection of Nocardia
than that of Gram-stained smears (87%).
Clinically, Nocardia keratitis may resemble mycotic keratitis or keratitis caused by atypical mycobacteria, which
should be considered in the differential diagnosis [26].
Although mycotic keratitis is characterized by feathery
edges, satellite lesions, and posterior cornel abscess,
Nontuberculous Mycobacteria infections cause slowly progressive corneal infection and that infiltrate typically is
Scraping from the corneal lesion is collected with the
help of spatula or blade. Repeated scrapings need to be
collected to make at least three smears and inoculate
several culture media. The choice of media should
encompass a wide range, allowing for the growth of all
types of bacteria (aerobic, facultative anaerobic, and
anaerobic), fungi, and Acanthamoeba [6].
Figure 3 Nocardia keratitis with patchy stromal infiltrates and
larger hypopyon
Processing of corneal scrapings
Microscopic evaluation and culture are done on the
corneal scrapping. Microscopic evaluation is a sensitive
technique for the detection of Nocardia filaments
Microscopic evaluation
Smears are collected and usually stained by Gram stain,
Giemsa stain, and KOH with calcofluor white stain and
acid-fast stain using 1% sulfuric acid (modified Kinyoun’s
method) and 10% KOH wet mount. Branching thin
filaments can be seen in 10% KOH wet mount
(Fig. 4). A corneal scraping smear that is positive for
beaded Gram-positive, branching filaments (Fig. 5) and
the presence of partially acid-fast branching filaments is
highly suggestive of Nocardia sp. (Fig. 6). Branching at
right angles is most often suggestive of N. asteroids.
Demonstrating decolorization with 20% sulfuric acid
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4 Corneal and external disorders
Figure 4 Ten percent potassium hydroxide from direct smear of
Nocardia keratitis showing filamentous fungi and Nocardia
[Nocardia in italics] filaments in the same patient (x 450 magnification)
Figure 6 Corneal scrapping stained with 1% acid-fast stain from
an eye with Nocardia keratitis showing acid fast filaments
Polymorphonuclear cells are also present.
can differentiate it from mycobacteria. The cellular reaction observed in corneal scrapings is predominantly polymorphonuclear cells. Demonstration of typical filaments
of Nocardia in corneal scrapings is sufficient indication
for the initiation of specific antimicrobial therapy for
Nocardia keratitis, especially in the presence of typical
clinical features.
Culture
In culture, Nocardia organisms are not fastidious and grow
aerobically in a variety of media without antibiotics.
However, they tend to grow slowly. Dry colonies, usually
Figure 5 Corneal scrapping stained with Gram’s stain from an
eye with Nocardia keratitis showing Gram-positive, beaded,
branching filaments (x 1250 magnification)
tiny and white grow in 48–72 h on blood agar, chocolate
agar, and Sabouraud’s Dextrose agar (without antibiotics). With prolonged incubation, they may appear
waxy and hard or rough, with a velvety surface caused
by rudimentary aerial mycelia. Colony coloration may
vary from chalky white (Fig. 7), tan, buff, or yellow to
orange. By 2–3 weeks, they may attain a size of 5–10 mm.
Although the growth usually appears within 7 days, at
least 2 weeks of inoculation may be required. Growth
even on one medium is considered significant, especially
with corresponding smear results and clinical picture. As
Nocardia sp. is not a common contaminant of the external
ocular surface or laboratory environment, their isolation is
usually considered significant [6].
Smears from growth on laboratory media show coccoid
and bacillary elements, which are Gram positive and
resist decolorization by 1% sulfuric acid. Branching
may or may not be seen. Clinical microbiology laboratories may not always be geared up to perform all tests for
the species identification of Nocardia organisms. However, with regard to the treatment, speciation is not a
critical requirement as a routine; only in rare instances, in
which the ulcer is not responding to treatment.
Antibiotic susceptibility tests
In 2003, the Clinical and Laboratory Standards Institute
published the first approved recommendations for antimicrobial susceptibility testing of aerobic actinomycetes,
including Nocardia [29]. Although antibiotic susceptibility testing has been carried out routinely for Nocardia
isolates from clinical samples, some factors that must be
kept in mind are the relatively slow growth of the
organism, difficulty in obtaining a smooth suspension
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Nocardia keratitis Lalitha 5
Figure 7 Blood agar inoculated with corneal scrappings and
incubated at 37{deg sign}C for 5 days showing heavy growth of
small white dry colonies
much lower than the sulphonamides when used to treat
ocular nocardial infections [1]. Ever since, amikacin in
the concentration of 2–2.5% is the treatment of choice in
the monotherapy of Nocardia keratitis [24]. This concentration needs to be prepared from parenteral preparations of the drug.
A case of Nocardia keratitis resistant to amikacin has been
reported in literature [20]. It was treated successfully by
adding 0.3% ciprofloxacin to the regimen. Many fluoroquinolones have emerged after the launch of ciprofloxacin.
Third generation fluoroquinolones such as gatifloxacin and
moxifloxacin have a spectrum of activity against most of
the common ocular pathogens, including Nocardia [35].
Prajna et al. [36] have reported a case of nocardial
sclerokeratitis that healed well with 0.02% polyhexamethylene biguanide, a swimming pool disinfectant used
to treat Acanthamoeba keratitis.
of the inoculum, pH, and type of agar used. Antibiotic
susceptibility can be assessed by disc diffusion, broth
dilution, and Epsilometer or E test methods. Different
Nocardia strains vary in antibiotic sensitivity. Most
Nocardia isolates are sensitive to sulfonamides such
as sulfamethoxazole, trimethoprim–sulfamethoxazole,
doxycycline, and amikacin.
Newer diagnostic tools
Reports have described the use of confocal laser microscopy as an in-vivo diagnostic tool. Vaddavalli et al. [30]
examined three patients with microbiologically proven
Nocardia keratitis with confocal microscopy and concluded that Nocardia, a filamentous bacterium, produces
a distinct image on confocal microscopy. This in-vivo
examination technique may be useful in cases of deepseated infiltrates in which routine microbiology workup
does not yield positive result [30]. Molecular diagnosticbased methods such as the PCR are proving useful
for both detection of Nocardia from the infected tissues
as well as for species determination. PCR and PCR–
restriction fragment length polymorphism molecular
analysis (PRA, DNA sequencing, pyrosequencing, and
ribotyping) [31,32]. Galor et al. [33] reported one case in
which the new technology using pyrosequencing was used
for the rapid species determination of Nocardia keratitis.
The role of addition of systemic antibiotics is not very
clear from the evidence in the literature. On the basis of
the experience of treating our patients, systemic antibiotics really do not add any extra benefit in the outcome
of Nocardia keratitis.
Nocardia keratitis is quite amenable to medical treatment
if the diagnosis is correct and treatment has been started
early. In the study by Lalitha et al. [3] that correlated
clinical presentation and treatment outcome of Nocardia
keratitis with the time to diagnosis, different species and
with the drug sensitivity pattern, it was found that the
patients with Nocardia keratitis who presented within a
15-day period after the onset of the infection showed the
highest recovery rate. It was also further found clinically
that the ulcers were found to have a faster healing
response in patients presenting early and combined with
2% amikacin treatment. In this series, only one patient
needed therapeutic keratoplasty, and in one patient, the
eye was enucleated. Ulcers healed in the majority of
patients without vascularization. The surgical options
are therapeutic lamellar keratectomy, penetrating keratoplasty, and conjunctival flap. Reports of surgically treated
Nocardia keratitis are few and the outcome of surgical
treatment was reported to be good in all these cases [3].
Conclusion
Treatment of Nocardia keratitis
Treatment of Nocardia keratitis is very prolonged. Since
their discovery, sulphonamides were widely used to treat
Nocardia in the early years. Sulphacetamide, sulphamethoxazole, and trimethoprim were considered to be
the treatment of choice [34], until it was discovered that
the minimum inhibitory concentrations of amikacin was
The clinical presentation of Nocardia keratitis in the
majority of instances is consistent with the typical
description in the literature and is with patchy anterior
stromal infiltrates and wreath pattern infiltrates in a
patient with a history of ocular trauma. It is very important to alert the laboratory to look for the presence of
Nocardia filaments in direct microscopy. Identification
of thin, Gram-positive branching filaments, which are
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6 Corneal and external disorders
also 1% acid-fast staining positive is highly suggestive of
Nocardia and treatment can be started. Treatment of
choice in the current scenario is with topical fortified
amikacin. Even though the treatment is prolonged, the
infection responds well to treatment and resolves, forming a corneal scar. A high degree of suspicion, especially
in areas endemic for Nocardia, aids in early diagnosis
and initiation of treatment, which will decrease ocular
morbidity.
References and recommended reading
Papers of particular interest, published within the annual period of review, have
been highlighted as:
of special interest
of outstanding interest
Additional references related to this topic can also be found in the Current
World Literature section in this issue (pp. 000–000).
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