Conjunctivitis due to Neisseria sicca: a case report.

We report the first case, in Medline-based literature, of conjunctivitis caused by gram negative diplococcus, Neisseria sicca. Although it is not widely accepted as such, isolation from cultures of repeated eye swab samples suggests that N. sicca may be a pathogen in conjunctival infections. Positive culture for this organism should not be readily dismissed. Such conjunctivitis responded favorably to treatment with netilmicin eye drops.

Acute conjunctivitis accounts for approximately 1% of all conditions treated in primary eye care. Staphylococcus aureus, Staphylococcus epidermidis, Haemophilus influenzae, Streptococcus pneumoniae, Viridans streptococci and Moraxella catarrhalis are the most common pathogens isolated from acute bacterial conjunctivitis cases. Neisseria gonorrhoeae is the most common cause of hyperacute bacterial conjunctivitis. Other bacterial pathogens are rarely reported.[1]

A variety of nonpathogenic neisseriae are common commensals of the upper respiratory tract and are rarely implicated as pathogens in eyes.[2] We report the first case, in Medline-based literature, of conjunctivitis caused by a gram negative diplococcus, Neisseria sicca. Although it is not widely accepted as such,[3] isolation from cultures of repeated eye swab samples suggests that N. sicca may be a pathogen for conjunctival infections. This report will aid clinicians to diagnose and treat such a rare occurrence. The organism was repeatedly grown in culture and case were treated successfully with netilmicin.

Case Report

A 79-year-old woman presented with complaints of redness and purulent discharge in the left eye for the previous 2 days. She had no history of trauma or surgery. On slit-lamp examination, a mucopurulent discharge and severe crusting of the eye were noted. Samples were taken from the inferior fornix for microbiological examination using two separate conjunctival swabs. The cultures were then inoculated onto blood and chocolate agar, incubated at 36°C for 48 hours and evaluated with a Neisseria–Haemophilus identification (NH) card on a Vitek2 compact system (bioMerieux, Marcy, I’Etoile, France).

The patient was empirically put on fucidic acid (Fucithalmic gel 1%) therapy four times daily, but did not respond to this treatment. On the third day, treatment was changed to ofloxacin (Exocin 0.3%, Allergan) four times daily with fluorometholon (Efemoline 1%, Novartis) four times daily added in spite of the fact that usage of corticosteroids is controversial as it may contribute to progression of the infection by inhibiting the immune response.[4] Then, a second sample was taken. In the first sample, gram stain revealed large numbers of polymorphonuclear leukocytes and gram variable diplococci [Fig. 1]. On sheep blood agar and chocolate agar plates, small, pale colonies grew [Fig. 2]. The same organism grew in the culture of the sample taken at the second visit. The isolated organism was gram negative diplococci. The identification of the organism was accomplished by standard biochemical tests and with a NH card on Vitek2 compact system. The organism was oxidase positive, DNase negative, catalase positive, nitrate reduction positive and produced acid from glucose, fructose, maltose, and sucrose. Using the Vitek2 system, the organism was identified as N. sicca with a bionumber of 0632400000 and 98% probability. There are no accepted criteria for evaluation of the antimicrobial susceptibility of this organism according to the Clinical and Laboratory Standards Institute (CLSI).[5] Furthermore, in vitro susceptibility testing of the isolated bacteria cannot always guide the therapy of conjunctival infections, while susceptibility interpretations of minimum inhibitory concentration (MIC) values are based on serum concentrations.[1] MIC values of ceftriaxone (0.125 μg/ml), benzylpenicillin (2 μg/ml), tetracycline (1 μg/ml) and netilmicin (1 μg/ml) were determined using Etest (AB BIODISK, Solna, Sweden) on Muller Hinton agar with 5% sheep blood agar. As the patient did not respond to the previous treatments and slit-lamp examination findings remained the same, she was given netilmicin (Netira® SIFI, SpA, Catania, Italy) drops four times daily. Three days later, there was no evidence for conjunctivitis and the patient's complaint resolved.

Figure 1

Gram stain of Neisseria sicca

Figure 2

Colonies of Neisseria sicca grown on chocolate agar

Discussion

Any organism cultured from conjunctival samples needs to be interpreted within the context of the clinical case and other supportive laboratory evidence. If clinical suspicion is high and many polymorphonuclear leukocytes and organisms are seen in gram stains of samples, even unusual or environmentally isolated organisms should be reported to avoid false-negative reporting. The isolated microorganism, N. sicca, did not respond to wide spectrum antibiotics such as fucidic acid and ofloxacin, but responded to netilmicin. This fact implies that netilmicin may be used empirically in future conjunctival infections caused by this organism.

As the patient was not known to be immunocompromised or diabetic, and had no history of using any eye drops on a chronic basis which might change the conjunctival flora, N. sicca was considered as the causative agent for her conjunctivitis. Although there was no history of trauma mentioned, as she was a farm worker she might have been unaware of a minor trauma which might have caused unilateral conjunctivitis. One conjecture for the source of the bacteria might be the oropharyngeal flora as some Neisseria species are found in the oropharnyx. Following a Medline search incorporating keywords Neisseria sicca and conjunctivitis, to the best of our knowledge, conjunctivitis caused by this organism has not been previously reported. N. sicca has been implicated in cases of meningitis, pneumonia, endocarditis, peritonitis and urethritis.[678910]

When microbiological examination is considered in conjunctivitis cases, the best practice is to obtain two swab samples from each eye. One swab can be used for gram stain and the other for culture procedures. This procedure helps the laboratory to define the causative organism and consider the pathogenicity of the isolated bacteria.

This case confirmed the potential pathogenicity of N. sicca in conjunctiva and emphasizes that positive cultures for this organism should not be readily dismissed; netilmicin proved an effective treatment in such cases.