• Users Online: 233
  • Print this page
  • Email this page

 Table of Contents  
Year : 2021  |  Volume : 1  |  Issue : 1  |  Page : 93-94

Microbial keratitis due to infection with Citrobacter freundii: A rare entity

1 Department of Ophthalmology, Post Graduate Institute of Medical Education and Research, Chandigarh, India
2 Department of Microbiology, Post Graduate Institute of Medical Education and Research, Chandigarh, India

Date of Submission06-Apr-2020
Date of Acceptance10-Aug-2020
Date of Web Publication31-Dec-2020

Correspondence Address:
Dr. Jagat Ram
Professor and Head, Department of Ophthalmology, Post Graduate Institute of Medical Education and Research, Chandigarh - 160 012
Login to access the Email id

Source of Support: None, Conflict of Interest: None

DOI: 10.4103/ijo.IJO_664_20

Rights and Permissions

We report a unique case of Citrobacter freundii keratitis in a 35-year-old male presented with a paracentral corneal ulcer secondary to injury with a tile particle. Clinically, it seemed like a fungal ulcer. However, the bacterial culture was positive for Citrobacter freundii, which responded to topical amikacin and ceftazidime. Citrobacter freundii is a facultative anaerobic gram-negative bacterium belonging to the family of Enterobacteriaceae being associated with external eye infections; while this is another report of it being associated with microbial keratitis.

Keywords: Bacterial keratitis, corneal ulcer, topical ceftazidime, topical amikacin

How to cite this article:
Balamurugan R, Gupta PC, Raghulnadhan R, Angrup A, Yadav B, Ram J. Microbial keratitis due to infection with Citrobacter freundii: A rare entity. Indian J Ophthalmol Case Rep 2021;1:93-4

How to cite this URL:
Balamurugan R, Gupta PC, Raghulnadhan R, Angrup A, Yadav B, Ram J. Microbial keratitis due to infection with Citrobacter freundii: A rare entity. Indian J Ophthalmol Case Rep [serial online] 2021 [cited 2021 Feb 26];1:93-4. Available from: https://www.ijoreports.in/text.asp?2021/1/1/93/305535

Microbial keratitis is one of the major causes of the preventable form of blindness and morbidity caused by it and is a major health problem worldwide.[1] It is a commonly encountered condition in most ophthalmology clinics. The incidence of microbial keratitis in the developing world is even higher, with estimated incidence rates ranging from 100 to 800 per 100,000 person-years.[2] Gram-negative bacteria causing keratitis include Pseudomonas, Haemophilus, and  Moraxella More Details, seen more commonly in extended wear cosmetic contact lens users.[3] Citrobacter species rarely cause keratitis. A retrospective study by Mela et al. to find out the clinical and microbiological features of corneal ulcers was done among 86 patients, of which 23 patients were contact lens wearers.[4] The study revealed that the most frequently isolated organism was Pseudomonas aeruginosa (60%) out of which two were polymicrobial, namely, P. aeruginosa with Citrobacter freundii and  P.aeruginosa Scientific Name Search  with Proteus mirabilis. Another study by Chen et al. in six eyes with culture-proven C. freundii or C. koseri endophthalmitis post intraocular surgery, as well as post-trauma, showed poor visual outcome despite treatment.[5] Studies reporting the incidence of eye diseases caused by C. freundii are still limited. In this report, we will be discussing the various presentation, signs, and treatment strategies of Citrobacter keratitis.

  Case Report Top

A 35-year-old male, mason by profession, was referred to our tertiary care hospital with a history of trauma to the left eye with a tile particle 20 days back. It was accompanied by watering, redness, and diminution of vision in his left eye. He was diagnosed as having fungal corneal ulcer and started on topical antifungals (natamycin and voriconazole) outside but without any improvement in symptoms. His best-corrected visual acuity was 20/20 and 20/200 in the right and left eye, respectively. On slit-lamp biomicroscopy, 360-degree conjunctival congestion was present. An ulcer measuring 4.7 mm × 5 mm was noticed in the paracentral cornea, partially involving the visual axis lying in the inferotemporal quadrant. The ulcer was grayish white, dry looking, spreading circumferentially with feathery margins, with infiltrates concentrated more in the center as well as the margins, with depth less than one-third of the stroma with surrounding stromal edema without hypopyon, immune ring, or any satellite lesion [Figure 1]a. Intraocular pressure was 18 mmHg in the affected eye. Corneal scrapings of the ulcer were sent for bacterial and fungal cultures. KOH staining of the smears did not reveal any fungal elements. However, rod-shaped gram-negative bacilli were seen on Gram's stain. The corneal scraping was inoculated on 5% sheep blood agar medium and incubation was done overnight at 35°C in 5 to 7% CO2. On blood agar medium, pale grayish-white discrete, low convex colonies were cultured after overnight incubation. The final identification was made by the matrix-assisted laser desorption and ionization time-of-flight mass spectrometry (MALDI-TOF MS) analysis (Microflex LT Biotyper Instrument Bruker Daltonics, Bremen, Germany). For identification by MALDI-TOF MS, a thin film of colonies was smeared over a steel MALDI plate, coated with 1.0 μL of a freshly prepared αcyano-4-hydroxycinnamic acid (HCCA) matrix (saturated in 50% acetonitrile with 2.5% trifluoroacetic acid) and then allowed to dry. AutoFlex MALDI-TOF mass spectrometer was used to acquire the mass spectra. The organism was identified as C. freundii by MALDI-TOF MS with a score of 2.0. Kirby-Bauer's disc diffusion method was employed, and antimicrobial susceptibility testing was done using Mueller-Hinton Agar. The organism was sensitive to amikacin, ceftazidime, meropenem, cefepime, cefoperazone-sulbactam, imipenem, piperacillin-tazobactam, gentamicin, and resistant to ciprofloxacin and levofloxacin. After the report, topical antifungals were stopped, and the patient was started on fortified ceftazidime 5% and amikacin 2.5% eye drops hourly based on culture sensitivity after 5 days of presentation. The patient dramatically responded to the treatment, and after 2 weeks, the best-corrected visual acuity in his left eye improved to 20/40. Size of the stromal infiltrates started reducing, and ulcer healed, leaving a superficial scar [Figure 1]b.
Figure 1: (a) Anterior segment photo of the left eye showing a paracentral ulcer with feathery margins and stromal infiltrates. (b) Anterior segment photo of the left eye 2 weeks post antibiotic treatment demonstrating the healed corneal ulcer with a superficial scar

Click here to view

  Discussion Top

Bacterial ulcers are usually associated with situations in which the corneal defense mechanisms are altered, such as trauma, eyelids dysfunctions, advanced age, poor hygiene, dry eye, and contact lens use. The presence of corneal ulcer with hypopyon and fibrinous exudates are suggestive of bacterial keratitis whereas those with satellite lesions, raised slough, serrated margins, and dry texture and are suggestive of mycotic ulcer.[6] The most commonly isolated bacteria from corneal scrapping in traumatic bacterial keratitis are gram-positive bacteria.[7] C. freundii is a rare bacterium causing microbial keratitis. Studies reporting the incidence of ocular diseases caused by Citrobacter species are still limited. The facultative anaerobic gram-negative bacterium, C. freundii belongs to the genus Citrobacter, within the Enterobacteriaceae family. Among the members of Citrobacter genus, C. freundii and C. koseri are the most important human pathogens which are differentiated based on their biochemical reaction.[8] We had identified this isolate by MALDI-TOF C. freundii is responsible for a broad spectrum of infections involving the urinary tract, respiratory tract, bloodstream, and wounds.[9] Keratitis is mostly associated with a history of trauma. They mostly affect patients with a poor immune system, which signifies that they need an “opportunity” to infect the person.[10] The most feared complication of Citrobacter keratitis is panophthalmitis which is difficult to manage.[11]

Management of Citrobacter keratitis is based upon the sensitivity of the bacteria to antibiotics. In our case, keratitis responded dramatically to fortified ceftazidime and amikacin. In patients with corneal perforation, a tectonic graft may be required.

  Conclusion Top

Bacterial keratitis sometimes mimics features of another microbial keratitis like fungal keratitis. Hence, appropriate laboratory diagnosis of corneal scraping for culture sensitivity is mandatory in all cases of microbial keratitis for guiding the further course of management of the disease.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

Gopinathan U, Garg P, Fernandes M, Sharma S, Athmanathan S, Rao GN. The epidemiological features and laboratory results of fungal keratitis: A 10-year review at a referral eye care center in South India. Cornea 2002;21:555-9.  Back to cited text no. 1
Upadhyay M, Karmacharya P, Koirala S, Shah D, Shakya S, Shrestha J, et al. The Bhaktapur eye study: Ocular trauma and antibiotic prophylaxis for the prevention of corneal ulceration in Nepal. Br J Ophthalmol 2001;85:388-92.  Back to cited text no. 2
Al-Mujaini A, Al-Kharusi N, Thakral A, Wali UK. bacterial keratitis: Perspective on Epidemiology, clinicopathogenesis, diagnosis and treatment. Sultan Qaboos Univ Med J 2009;9:184-95.  Back to cited text no. 3
Mela EK, Giannelou LP, Koliopoulos JX, Gartagnis SP . Ulcerative keratitis in contact lens wearers. Eye Contact Lens 2003;29:207-9.  Back to cited text no. 4
Chen KJ, Sun MH, Hwang YS, Chen TL, Lai CC, Chen YP. Endophthalmitis caused by Citrobacter species. Ocul Immunol Inflamm 2008;16:147-53.  Back to cited text no. 5
Thomas PA, Leck AK, Myatt M. Characteristic clinical features as an aid to the diagnosis of suppurative keratitis caused by filamentous fungi. Br J Ophthalmol 2005;89:1554-8.  Back to cited text no. 6
Stefen C, Nenciu A. Post traumatic bacterial keratitis- A microbiological prospective clinical study. Oftalmologia 2006;50:118-22.  Back to cited text no. 7
Anderson MT, Lindsay AM, Z Lili, Mobley H. Citrobacter freundii fitness during bloodstream infection. Sci Rep 2018;8:11792.  Back to cited text no. 8
Koshy M, Ralph R, Paul K, Abhilash P, Varghese GM. Citrobacter freundii endocarditis. J Med Soc 2016;30:3.  Back to cited text no. 9
  [Full text]  
Goold LA, Warrier SK, Wittles NK, Nathan F. Microbial keratitis secondary to infection with Citrobacter koseri. Cornea 2010;29:479.  Back to cited text no. 10
Barsam A, Heatley CJ, Herbert L. Panophthalmitis secondary to infection with Citrobacter koseri. Eye 2006;20:1468-70.  Back to cited text no. 11


  [Figure 1]


Similar in PUBMED
   Search Pubmed for
   Search in Google Scholar for
 Related articles
Access Statistics
Email Alert *
Add to My List *
* Registration required (free)

  In this article
Case Report
Article Figures

 Article Access Statistics
    PDF Downloaded25    
    Comments [Add]    

Recommend this journal