Iraqi J Pharm Sci, Vol.20(2) 2011                                            Microbial contamination of eye drops 

91 

 

Microbial Contamination of Eye Drops in out Patient in Iraq
# 

Raghad A. Razooki
*,1     

,     Ebtihal N. Saeed
*
     and    Hanan I. Omar Al-Deem

* 

 

*Department of Clinical  Laboratory Science,College of Pharmacy,University of Baghdad, Baghdad, Iraq. 
 

Abstract 
         Acontaminated ophthalmic solutions represent a potential cause of avoidable ocular infection. 

This study aimed to determine the magnitude and pattern of microbial contamination of eye drops in 

out patient at the department of ophthalmology, at Baghdad national hospital, Iraq. Fifty four vials 

from the out patient clinic were obtained for microbial examination after an average use of 2 weeks. 

The dropper tip and the residual eye drop were examined for contamination. The specimens were 

cultured, the number of colonies counted, the organisms identified. Eight (15%)  out of 54 analyzed 

vials were contaminated , most bacteria identified belonged to the normal commensal flora of the eye. 

Isolated contaminants were Staphylococcus auereus, Micrococcus , Neisseria catarrhalis, Gram 

negative Rods, Candida albicans, and Staph epidermidus.The dropper tip was more often contaminated 

(n=5) than the residual solution (n=2) and only one vial showed acontamination of both the drop and 

the tip (n=1) . Our data show acontamination rate of 15%, which is in the medium range of data 

puplished on the contamination of eye drops elsewhere (0.07% to 35.8%). 

Key words : Microbial Contamination, Eye Drops 
 

 الخالصة 
ٚؤد٘ انٗ انؼًٗ احٛاَاً نزنك قذ َّ انسثة انشئٛسٙ فٙ انرٓاب انؼٍٛ. ٔيخاطش رنك ًٚثم ذهٕز قطشاخ انؼٌٕٛ خطشاً كثٛشاً ال         

ٙ نقطشاخ انؼٌٕٛ نهًشضٗ فٙ ػٛادج انشدْح انخاسجٛح نقسى انؼٌٕٛ فٙ تذٓذف ْزِ انذساسح انٗ ذحذٚذ يذٖ ٔيسرٕٖ انرهٕز انًاٚكشٔ

 ا تؼذ يؼذل اسرؼًال اسثٕػٍٛ. ساسٙ نٓتنرهٕز انًاٚكشٔيسرشفٗ تغذاد انؼاو فٙ انؼشاق. استؼح ٔخًسٌٕ قطشج جًؼد ٔذى قٛاس ا

انقطشج ٔتقٛح انًحهٕل انًرثقٙ خضغ نهفحص انًاٚكشَٔٙ ٔتؼذ صسع ٔػذ انًسرؼًشاخ ذى ذحذٚذ إَاع انثكرشٚا انًهٕثح. ثًاَٛح قطشاخ 

انًٕجٕدج فٙ انؼٍٛ أ انجهذ ٔيُٓا  ( قطشج ذحٕ٘ تكرشٚا يهٕثح يؼظًٓا ذؼٕد انٗ انثكرشٚا انطثٛؼٛح15%( يٍ يجًٕع )51ا٘ تًؼذل )

Staphylococcus  aureus,  Micrococcus,  Neisseria  catarrhalis, Gram  negative  rods  and  Candida          

  Staph  epidermidus albicansand  يٍ تقٛح انسائم انًرثقٙ فٙ انقطشج ٔٔاحذ فقظ اظٓش  اً هٕثذانقطشج ٔجذ اٚضاً اكثش  سأس

ٙ نقطشاخ انؼٍٛ يٍ انًؼهٕياخ انًُشٕسج فٙ ت%( ٚؼرثش حذ ٔسظ نهرهٕز انًاٚكش51ٔيسرٕٖ انرهٕز )ٔ سأس انقطشج. ذهٕز انسائم

 . (%81.3-0,00اَحاء انؼانى ْٕٔ يا حذد تـ)

Introduction 
         Contaminated eye drops and ophthalmic 

solutions are a potential cause of ocular 

infection. They can be associated with 

keratitis.
(1) 

and corneal ulcers
(2)

 and carry the 

risk of transmitting opportunistic micro-

organisms, 
(3,4)

as well as pathogenic 

organisms, such as pseudomonas aeruginosa 

and Serratia marcescens.
 (1)

 The published 

contamination rate of in-use ophthalmic 

solutions varies widely in the literature from 

0.07% 
(5)

 to 35.8%.
(3)

 A part from the risk of 

infection, bacterial contamination of eye drops 

may alter the pH of the solution and therefore 

reduce the efficacy of the drug
 (6)

.In order to 

prevent contamination, most preparations 

contain antimicrobial substances, unless the 

solution it self has an antimicrobial effect. 

These substances aim to preventing or 

inhibiting the growth of microorganisms which 

increase the risk of infection or degradation of 

the drug. The self sterilizing effect of eye 

drops caused by the presence of preservatives 

has been discussed controversially
(7)

. 

preservatives must meet several requirements  

(1) to be compatible with other ingredient ,(2) 

to be efficient during the entire duration of use 

of eye drops, and (3) to be non toxic. 

Commonly used preservatives of ophthalmic 

solutions are benzalkonium chloride, which 

also works as a detergent and therefore 

increases the penetration of the active 

ingrediente of the drug, thiomers; 

chlorhexdine; parahydroxy benzoate; 

phenylmercuric nitrate, EDTA, chlorobutanol; 

benzylalcohol; phenylethyl alcohol; and 

parabens
(8,9)

. As preservatives interfere with 

the metabolism and inhibit the growth of 

micro-organisms, they may have similar 

effects on human cells, explaining potential 

cytotoxic effects and inflammatory cell 

responses.
(6)

 The antimicrobial activity is 

important for the rate of infection resulting 

from contamination during the process of 

instillation. Contact with fingers or lids, 

ciliaries conjunctiva and cornea are possible 

causes of contamination even if instilled by 

healthcare professionals. 

 
 

# 
Based on oral presentation in the eighth scientific conference of the College of Pharmacy /University 

of Baghdad held in 23-24 February  2011. 

1Corresponding author E- mail :raghadrazook@yahoo.com  

Received : 7/3/2011 

Accepted : 19/9/2011 



Iraqi J Pharm Sci, Vol.20(2) 2011                                            Microbial contamination of eye drops 

92 

 

Plastic bottles have been reported to be more 

commonly contaminated near the bottle cap. 

this has been attributed to a lack of 

preservative at this area.
(4)

 In a clinical study 

220 in-use medications of 101 patients with 

non-microbial acular surface disorders were 

examined by cultivating the bottle caps. the 

authors concluded that acycle of contamination 

between in-use medications and conjunctiva 

may present an important risk factor for 

microbial keratitis in patients with ocular 

surface disease
(10)

.The occurrence of bacterial 

ocular infection such as keratitis and 

endophthalmitis transmitted by contaminated 

eye droppers has been reported.
(11)

 In a recent 

study the authors noted that some cases of 

bacterial keratitis in Iran are thought to be due 

to contaminated eye drops used on multiple 

patients
 (12)

. Brudieu et al found abig difference 

in contamination rates between vials used by 

ophthalmological patients (17.7%) and vials 

used by medical and gerontological patients 

(35.8%). A positive correlation was also found 

for vial contamianation and the duration of use 

vials containing an antimicrobial agent were 

less likely to be contaminated than vials 

without antimicrobials. However no clinically 

relevant infection through such vial 

contamination was identified
(3)

. In a study 

comparing the contamination rate of drops 

used in an eye department and a nursing home 

no difference was found but the authors stated 

that the residual eye drop is more often 

contaminated than the tip of the bottle. They 

also noticed the presence of. Gram negative 

organisms in the nursing home
 (7)

. Most 

studies, however, found the bottle tips to be 

more often contaminated than the 

solution.
(2,4,13)

 Therefore, topical eye 

medications may present a potential risk of 

infection, aspecially if the ocular epithelial 

barrier is compromised. Minimising the 

contamination of eye drops and the 

transmission of infections is an important issue 

in clinical ophthalmology. Several regulations 

and suggestions have been made in this 

context. We conducted the following cross 

sectional study and analysed (54) ophthalmic 

solutions examining bacterial and fungal 

contamination. This study aimed to determine 

the magnitude and pattern of microbial 

contamination multi dose  of eye drops in out 

patient. 
 

Material and Methods 
         A total of (54) eye drop containers  ( in 

use ) were obtained for microbial examination. 

The microbial analysis was performed on the 

dropper tip and the residual eye drop for each 

containers. The eye drops were obtained and 

cultured according to the following: 

 A sterile cotton tip swab was moistened in 
sterile brain heart infusion (BHI) enriched 

medium before wiping the nozzle tip of the 

eye drop containers and then used to 

inoculate the culture plates
(13)

. 

 The vials were inverted and one drop was 
directly inoculated on each of the media and 

then spread across the plates. 

All media except the sabouraud agar plates 

were incubated at 37 
0
C for 48hrs. and 

evaluated after 24 and 48hrs. the blood agar, 

chocolate blood agar plates were incubated in 

amicroaerophile environment.
(15)

 The 

sabourand agar plates were incubated at 30 
0
C 

for up to 10 days and evaluated for growth on 

days 1, 5 and 10. The BHI broth was also 

incubated at 37 
0
C and subcultured on blood 

agar after 24 hours. All culture media except 

sabouraud dextrose agar (BioMerieux, F) were 

obtained from Biotec Laboratories Ltd, UK. A 

significant growth was considered a growth on 

the main inoculation site or on two or more 

streaks on the plate. The BHI was analysed for 

changes in colour and turbidity of the media. 

The colonies on solid media were counted and 

all organisms identified by microscopy after 

Gram staining and biochemical tests. 

 

Results 
         A total of 54 medications were analysed; 

from the out patient clinic. as shown in table 

(1)  the  used of different preservatives found 

in the analysed specimens. They were grouped 

in four different categories analgesics, 

antihistaminc, antibiotic and steroids. . Over 

all, 8(15%) of the 54 analysed vials were 

contaminated table (2) at the bottle tip alone or 

with additional contamination of the solution 

or solution alone. Within the four categories 

the rate of contamination varied between 0% 

for analgesics and 17% ---> for both 

antibiotics and Steroids.The dropper tip was 

more often contaminated (n=5) than the 

residual solution (n=2). One bottle showed 

contamination of both the dropper tip and the 

medical solution. (n=1) Most of the identified 

organisms were part of the normal skin flora or 

conjunctival flora. Gram positive organisms 

were cultivated from five of the eight 

contaminated medications and two 

contaminated medications grew Gram negative 

organisms and one grew Candida albicans. 

One of the medications grew more than one 

bacterium as shown in table 3 . None of the 

medications were found to be past the expiry 

date.  

 



Iraqi J Pharm Sci, Vol.20(2) 2011                                            Microbial contamination of eye drops 

93 

 

Table 1 : Type of preservatives and number of medications  
 

No. Preservative Number of medications 

1 Benzalkonium chloride0.05% 20 

2 Benzalkonium chloride0.02% 14 

3 Benzalkonium chloride0.01% 8 

4 b.chloride 0.004% 4 

5 Thiomersal 0.005% 4 

6 Phenyl mereuric nitrate 0.001% 4 

 Total 54 

 

 

 Table 2 : Eye medication and contamination  

  *(n= 54 ) total eye drops specimens  

 
 Table 3 : Contaminated medications and preservatives (n=54).  
 

No. Eye medication Preservative Contaminant 

1 Antistin-privin   
Benzalkonium 

chloride 0.02% 

2types of colonies on blood white colonies and 

yellow (Staph aureus) 

2 Antistin-privin 
Benzalkonium 

chloride 0.02% 

2types of colonies on blood white colonies and 

yellow (staph aureus) 

3 Oflox  
Benzalkonium 

chloride 0.05% 

On MSA 

Staph aureus 

4 Oflox  
Benzalkonium 

chloride 0.05% 

On blood agar :Candida albicans  

Staph. aureus  

5 Oflox  
Benzalkonium 

chloride 0.05% 
Neisseria catarrhalis 

6 Oflox  
Benzalkonium 

chloride 0.05% 
Staph aureus 

7 
Dexamethason 

0.1% 

Benzalkonium 

chloride 0.01% 
Micrococcus  

8 
Dexamethasone 

phosphate. 0.1% 

Benzalkonium 

chloride 0.01% 
G- Rods  

  

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Analgesic  4 0(0%)     

Antihistamine  14 2(14%) - - 2(14%) 

Two type colonies  

1-white colonies 

coagulase(-). 

2-Yellow  colonies 

coagulase(+). Staph. 

Aureus 

Antibiotics  24 4(17%) 4(17%) - - 

1-Candida albicans 

2-Staph  aureus  

3-Neisseria catarrhalis 

Steroid  12 2(17%) 1(8%) 1(8%)  
Micrococcus  

Gram negative rods 

Total  54 8(15%) 5(9%) 1(2%) 2(4%)  



Iraqi J Pharm Sci, Vol.20(2) 2011                                            Microbial contamination of eye drops 

94 

 

Discussion 
         We noticed amicrobial contamination of 

8/54(15%) of out use application dispensers. 

The mean contamination rate of preserved eye 

drops described in the literature varies widely 

from 0.07%. 
(5)

 to 35.8%. Six different micro 

organismes were detected. As the containers 

were analysed on the day of collection, our 

results are likely to represent the specific 

clinical situation of that day. Five of eight of 

the identified organisms were Gram positive 

and 2/8 Gram negative and one Candida 

spp.Most of the organisms were part of normal 

commensal flora of the conjunctiva or the skin. 

The resident flora of the conjunctiva and eyelid 

mainly comprises of Gram positive bacteria, 

including coagulase negative Staphylococci, 

Corynebacterium spp. Propionibacterium spp. 

as well as Staphylococcus aureus, Bacillus 

spp. Micrococcus spp. and Enterobacter 

spp.
(17,18) 

This  is  in  accordance  with  several  

 

other published studies.
(7,13,16)

 However, it 

differs from results puplished by Rahman 

etal,
(19)

 who found only a small proportion of 

the microorganisms identified to be post of the 

normal commensals flora when studying the 

contamination of unpreserved eye drops.A 

cycle of contamination between the lids and 

dropper tips was suggested by Schein et al.
(10)

 

The contamination of eye drops and eye drop 

dispenser with the same microorganism, 

especially gram negative, has been described 

by the same group. This represents apotentially 

serious risk for ocular infection, especially in 

cases of compromised corneal epithelium as in 

extensive contact lens wear, ocular trauma or 

the use of topical steroids. In this study 

pathogenic organisms were rare and showed 

limited growth that probably did not represent 

a clinically relevant risk of infection. By using 

t.test we did not find any significant difference 

(p<0.05) in the contamination rate of eye 

drops/dropper tips and the residual volume 

which was left in the bottle. This supports the 

previously described self sterilising effect of 

many eye medications.The design of the 

containers might also influence contamination. 

Only bottles with a tip attached to the bottle 

itself were analysed in this study. The bottle 

tips were more often contaminated (n=5) than 

residual drops (n=2) with contamination of 

both the tip and the residual solution appearing 

in one specimen. These results are similar to 

the ones reported in earlier studies.
(11,13,16)

 One 

reason for this pattern to be considered is the 

antimicrobial activity of preservatives of the 

solution itself. Such antimicrobial effects, 

however, may not act sufficiently on the tip 

itself as the contact time is limited. Further the 

tip provides a large surface for contamination 

from ocular structures or hands. Even dried 

crusts can sometimes be found on the bottle 

tips.The removal of such remnants with a 

sterile swab might further reduce the 

contaminator rate.
(4)

 However the 

contamination of the solution itself has to be 

regarded as clinically more relevant since these 

get in direct contact with the patients eye.Non 

of the examined eye drops is expired and we 

recommend not storing any open bottles in the 

back of drawers or on top shelves but always 

keeping them handy and limited to those 

actually needed. Further more, we recommend 

noting the date of first opening on each 

container, as the duration of use might be 

another and possibly more relevant parameter 

rather than the expiry date
(5)

. 

 

Conclusion 
         Aclear instruction sheet about safe and 

effective used should accompany do when they 

are dispensed to patient. Patients who are 

unable to use eye drops in an aseptic way 

because of age or other physical (for example, 

poor vision) or mental limitations should be 

assisted by competent relatives or caretakers.  

The results of this study support the 

importance of a proper set of rules and the 

correct handling and application of eye 

medications. 

 

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