Myanmar Health Sciences Research Journal
Original Articles :
Myanamr Health Research Registration 2020; 32(2): 132-138.
DOI: DOI: https://doi.org/10.34299/mhsrj.00993

Antibiotic Susceptibility Patterns of Conjunctival Bacterial Isolates Among Patients Undergoing Cataract Surgery

Nann Shwe Aung, Khin Thawtar Shein, Khin Nwe Nwe Oo, Cho Cho Oo

Myanmar Health Sciences Research Journal, 2020; 32(2): 132-138

ABSTRACT

Conjunctiva harbors a population of microorganisms known as normal flora and sometimes potential pathogens may constitute. However, these microorganisms are not harmful to the host until the epithelial surface of eye is breached by surgery or trauma. Post-operative ocular infection is one of the complications after cataract surgery that interfere to get full vision and may lead to permanent loss of vision. Conjunctival bacterial isolates are responsible for post-operative infections. This study was performed from January 1,2018 to September30, 2018. The aim of this study was to identify the conjunctival bacterial isolates from patients undergoing cataract surgery, and to determine their antibiotic susceptibility patterns.Conjunctival swabs were collected from 150 patients according to inclusion and exclusion criteria and then culture and sensitivity tests were done using conventional method. In collected 150 specimens, positive bacterial culture was seen in 67 specimens (44.7%). Out of 76 isolates, coagulase-negative staphylococci were shown as the most commonly isolated bacteria (48.7%) followed by Staphylo-coccusaureus (25.0%), Pseudomonas species (10.5%) and Klebsiellaspecies (10.5%), Escherichia coli (4.0%) and Citrobacter species (1.3%). Among isolated coagulase-negative staphylococci, sensitivity to moxifloxacin and clindamycin were higher than other drugs (89.2% each) followed by vancomycin (73.0%). Out of total 37 isolates,methicillin resistance was seen in 16 isolates (43.2%). Isolated Staphylococcus aureus were highly sensitive to vancomycin (89.4%) followed by clindamycin (84.2%) and moxifloxacin (78.9%). Some 36.8% were found as methicillin resistant. This information will be helpful to eye surgeons in choosing pre-and post-operative antibiotics against the conjunctival flora to reduce post-operative ocular infection rate.


RESULT
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One-hundred and fifty patients, 49 male patients and 101 female patients were included in the present study and the age of patients ranges from 20 years to 87 years where the most common age group was 61-70 years age group. Out of 150 specimens, 67 specimens (44.7%) showed positive bacterial growth and 83 specimens (55.3%) showed no growth. Among 67 positive bacterial growth, there were single bacterial growth in 58 specimens and mixed growth with two bacterial isolates in nine specimens A total of 76 bacterial isolates which include 56 isolates (73.7%) of gram-positive cocci and 20 isolates (26.3%) of gram-negative bacilli were identified from 67 specimens of positive culture plates. Among them, the commonest isolated bacteria were coagulase-negative staphylococci (48.7%) followed by Staphylococcus aureus (25.0%), Entero-bacteriaceae (15.8%) and Pseudomonas species (10.5%) (Table 1). Among mixed bacterial isolates, the most common combination of bacteria was CoNS and Pseudomonas species (55.6%).

Table 1. Distribution of isolated bacteria from conjunctiva of patients undergoing cataract surgery

 

Isolated bacteria

No. of

isolates

%

Gram-positive bacteria

 

Coagulase-negative

staphylococci

37

48.7

Staphylococcus aureus

19

25.0

Gram-negative bacteria

 

Pseudomonas species

8

10.5

Klebsiella species

8

10.5

Escherichia coli

3

4.0

Citrobacter species

1

1.3

Total

76

100

Table 2.Antibiotic susceptibility patterns of isolated coagulase-negative staphylococci (n=37)

Antibiotics

Sensitive

Intermediate

Resistant

Total

N(%)

N(%)

N(%)

N(%)

Azithromycin

16(43.2)

0(0.0)

21(56.8)

37

(100)

Cefoxitin

19(51.4)

2(5.4)

16(43.2)

(MRCoNS)

37

(100)

Clindamycin

33(89.2)

2(5.4)

2(5.4)

37

(100)

Moxifloxacin

33(89.2)

1(2.7)

3(8.1)

37

(100)

Oxacillin

12(32.4)

1(2.7)

24(64.9)

37

(100)

Vancomycin

27(73.0)

8(21.6)

2(5.4)

37

(100)

MRCoNS=Methicillin-resistant,coagulase-negativestaphylococci

Table 3.    Antibiotic susceptibility patterns of isolated Staphylococcus aureus (n=19)

Antibiotics

Sensitive

Intermediate

Resistant

Total

N(%)

N(%)

N(%)

N(%)

Azithromycin

10(52.6)

0(0.0)

9(47.4)

19

(100)

Cefoxitin

11(57.9)

1(5.3)

7(36.8)

(MRSA)

19

(100)

Clindamycin

16(84.2)

1(5.3)

2(10.5)

19

(100)

Moxifloxacin

15(78.9)

1(5.3)

3(15.8)

19

(100)

Oxacillin

7(36.8)

0(0.0)

12(63.2)

19

(100)

Vancomycin

17(89.4)

15.3

1(5.3)

19

(100)

MRSA=Methicillin-resistant, Staphylococcus aureus

In concerning with the antibiotic susceptibility patterns of all isolated Staphylococcus species,

clindamycin and moxifloxacin were found to be the most sensitive drugs and oxacillin was the least sensitive drug. Among isolated Staphylococcus species, 43.2% of CoNS and 36.8% of Staphylococcus aureus had been found as methicillin resistant (Table 2 &3).


Fig.1.Antibiotic susceptibility patterns of isolated Enterobacteriaceae (n=12)


Fig. 2. Antibiotic susceptibility patterns of isolated Pseudomonas species (n=8)

All isolated Enterobacteriaceae were sensitive to moxifloxacin and nearly 100% were resistant to amoxicillin-clavulanic acid and cefazolin (Figure 1). Isolated Pseudomonas species were totally sensitive to levofloxacin and ceftazidime. But they were totally resistant to neomycin. Only 37.5% of Pseudomonas species were sensitive to moxifloxacin (Figure 2).


INTRODUCTION
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Cataract is the leading cause of blindness and the second cause of moderate and severe vision impairment Moderate and severe vision impairment (MSVI) according to the Global Burden of Disease, Injuries and Risk Factors Study (GBD).1 It is also common in Asia and has been documented in rural Myanmar2 which was the single most common cause of severe visual impairment and blindness (SVI/BL)with 288 cases (54.2%).3Although there have been tremendous advances in the efficiency and outcomes of cataract surgery over the last 3 decades, cataract is still the leading cause of vision loss worldwide3 which was accounted for 54%of blindness and 71% of MSVI in 2010.4 It is suggested that the bacterial flora in apparently healthy conjunctiva might be the commonest source of post-operative infection.5 External ocular flora from patient may gain entrance into the posterior chamber of eye during surgery. About 90% of isolates were gram-positive and 10% were gram- negative bacteria.6

In many countries, cataract surgery remains one of the most commonly performed procedures, offering significant improvements to the quality of life for patients of all ages1. But there may be complications of cataract surgery including posterior capsule opacity, intraocular lens dislocation, post-operative infections, light sensitivity, macular oedema, ptosis and increased intraocular pressure. Therefore, an infection after this elective procedure is especially devastating since it can lead to permanent vision loss and loss of the eye in severe cases.7In Korea, Kim, et al.8 found that Staphylococcus epidermidiswas the most common organism in post-operative ocular infections.In reports from India, Pseudomonas species and fungi were the common organisms associated with post-operative ocular infections.9, 10

In Myanmar, Pseudomonas species and Staphylococcus species were common organisms in post-operative infections after cataract surgery.11The ophthalmologists use many pre- and post-operative methods to prevent post-operative infections including installation of topical antibacterial eye drops, subconjunctival injections or intracameral injections of anti-bacterials, installation of 5-10% povidone-iodine7. Topical anti-bacterials are commonly used for the prophylaxis of endophthalmitis following cataract surgery12, despite the fact that the clinical evidence for their efficacy is limited.7 Use of prophylactic antibiotics in cataract surgery reduces the number of organisms in the conjunctiva and eyelids and thus, reduces the risk of post-operative infections.13 However, whether antibiotic prophylaxis pre-and post-surgery reduces the risk of endophthalmitis remains controversial. There also are no standard guidelines on the type of antibiotic to be utilized.14

The normal flora of the eye and their sensitivity pattern to antibiotics can vary in different parts of the world. The late-generation fluroquinolones is the antibiotics used widely in current practice as they penetrate the cornea well and achieve measurable concentrations in the anterior chamber aqueous fluid.7It is suggested that there are bacterial flora in apparently healthy conjunctiva and lid margin which can cause post-operative infections after cataract surgery. To effectively prescribe empiric antibiotics, a profile of potential pathogens in a local community is required because the choice for the prophylactic topical antibiotic is influenced by the spectrum of bacteria covered. Therefore, understanding the spec-trum of the ocular flora and their antibiotic susceptibility patterns in local geographic area can assist eye surgeons in optimizing prophylactic antibiotic treatments and this study was conducted to determine the antibiotic susceptibility patterns of conjunctival bacterial isolates.

 


SUPPLEMENTARY MATERIAL
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This hospital-based, cross-sectional descriptive  study was conducted with 150 cataract patients at eye units of Eye, Ear, Nose and Throat Hospital, Mandalay from January 1, 2018 to September 30, 2018.

Sample collection

The conjunctival swabs were collected from patients undergoing cataract surgery at eye units of Eye, Ear, Nose and Throat Hospital, Mandalay. Patients were selected according to inclusion and exclusion criteria. All patients who were undergoing cataract surgery before giving any antibiotic treatment from hospital were included in this study and patients with any active ocular infection were excluded. Specimens were collected from 2 persons per day and three days a week at the day of operating morning by simple random sampling method. Before collecting the specimens, the informed consent was taken. Conjunctival swab from eye undergoing cataract surgery was taken by the help of eye surgeon after installation of 0.5% proparacaine hydrochloride eye drop. Then, conjunctival swab was collected  by gently rubbing the conjunctiva with a sterilized cotton wool swab stick. The specimen was placed in a Stuart’s transport medium tube and transported immediately to Department of Microbiology, University of Medicine, Mandalay, for plating on Blood agar, Chocolate agar, MacConkey agar and Mannitol salt agar.

Isolation and identification of bacteria

Cultures were incubated at 37°C overnight. After overnight incubation, examination of culture plates was done. The obtained organisms were identified by their cultural characters, by Gram’s stain and by using specific biochemical tests for each organism using the Cowen and Steel’s manual.

Antibiotic susceptibility testing of isolated bacteria

For performing antibiotic susceptibility testing of positive cultures, a 0.5 MacFarland solution of growth was prepared and modified Kirby-Bauer disc diffusion method on Mueller-Hinton agar was done. The Clinical and Laboratory Standards Institute (CLSI) zone size interpretation was used to identify the sensitive and resistant isolates.

Tested antibiotic discs for the isolated microorganisms were chosen carefully appropriate for each group of microorganisms that is gram-positive bacteria and gram-negative bacteria. Besides, antibiotics discs were selected according to the ophthalmologists’ usage of topical and oral antibiotics in which most of them were commonly used in daily practice of  EENT hospital, Mandalay.

Antibiotic susceptibility test for the isolated Staphylococcus species was done by using six antibiotics including azithromycin (15 µg), cefoxitin (30 µg), clindamycin (2µg), moxifloxacin (5µg), oxacillin (1µg) andvancomycin (30µg). Antibiotic discs using for susceptibility of the isolated Entero- bacteriaceae were amoxicillin-clavulanic acid (20+10 µg), cefazolin (30µg), cefixime (5µg), moxifloxacin (5µg), tetracycline (30µg) and tobramycin (10µg). Antibiotic susceptibility test for the isolated Pseudomonas species was done by using amikacin (30µg), ceftazidime (30µg), levofloxacin (5µg),moxifloxacin (5µg), neomycin (30µg) and tobramycin (10µg). All antibiotic discs were from TM media. Screening of methicillin-resistant Staphylococcus species was performed by using a cefoxitin disc according to the Clinical and Laboratory Standards Institute (CLSI) guideline (2017).

Data processing and analysis

Data was collected by using pro forma for completeness, consistency and correctness. The collected data was checked manually by researcher. After checking the data and code, data entry was done in Microsoft Excel 2010. The result was shown in frequency distributary tables, bar diagrams and pie diagrams.

Ethical consideration

This study was approved by the Ethical Review Committee of University of Medicine, Mandalay.



DISCUSSION
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Post-operative infection after cataract surgery is one of the most feared compli- cations and these infections are usually caused by patients’ own conjunctival flora. Same as other microorganisms, antimicrobial resistance among conjunctival flora are increased and become worldwide concern including multidrug-resistant bacteria.

Infections caused by multidrug-resistant bacteria are not only threatened to get the full vision but also difficult to treat. Thus, to reduce the rate of post-operative infections, proper use of antimicrobial drugs is necessary. The prevalence of antibiotic used may vary in different regions, which can cause different susceptibility patterns of the isolates. Therefore, local epidemiological information about common conjunctival flora and ocular pathogens, and their antibiotic susceptibility patterns is required.

In this study, bacterial growth occurred in 44.7% (67/150) of specimens and no growth in 55.3% (83/150). Similarly, bacterial growthrates were found 47.6% in a study by Jyoti, et al.5 from North India and 45.8% in a study by Mshangila, et al.15 from Uganda. However, the present study detected a lower incidence of conjunctival flora than the finding of Cham, Valenton&Lim14 ,who observed that the positive bacterial culture was 90%. Isolation rate of bacterial growth from conjunctiva of patients varies widely. The bacteria growth rate from conjunctiva and different results of culture may be greatly attributed to various factors such as environment, demography, climate, race and use of eye drops. Furthermore, the use of local anesthetic might be contributory factor to this result. Because local anesthetic eye drop, 0.5% proparacaine used in this study, has antibacterial property also.

Out of the 67 culture-positive specimens, a total of 76 different bacterial isolates were identified in this study. Of 76 isolates, gram- positive cocci were found to be the most commonly identified bacteria (73.7%) and 26.3% of all isolates were gram-negative bacilli. As in this study, a study by Suto et al.16 also identified that the most commonly isolated organism was gram- positive cocci accounting for 67.0% of all isolates. Similarly, Mshangila, et al.15 and PyaePhyo Aung17 showed that gram-positive cocci were most commonly identified which was 92.7% and 84.0% of all isolates, respectively. The growth rate of gram- positive cocci in the present study was harmonious with the results of the studies from other countries.

Sometimes, more than one type of bacterial isolates may be identified from one eye of patients. In the present study, 9(13.43%) out of 67 culture-positive specimens showed mixed growth with two isolates. Similarly, a study in Japan by Sutoet al.16 revealed  that two isolates were detected in 39 eyes (17.2%), three isolates in eight eyes (3.5%), and four isolates in one eye (0.4%). A study in Philippine by Cham, Valenton & Lim14 also found that more than one type of bacteria were isolated from 16 eyes (33.3%) while Sharma et al18 observed that 17.5% of specimens showed more than one isolates. These results were consistent with the present study.

In the present study, coagulase-negative staphylococci were identified as the most frequently isolated bacteria among the conjunctival microbial flora (48.7%) which was agreed with many others studies including Mshangliaet al.15 and PyaePhyo Aung17. Therefore, antibiotic susceptibility patterns of CoNS were important to know to reduce the rate of post-operative infection. Coagulase-negative staphylococci isolated from this study were more susceptible to clindamycin (89.2%), moxifloxacin (89.2%)and vancomycin (73.0%) but lesssusceptible to azithromycin (42.3%) and oxacillin (32.4%) but moxifloxacin showed 100% sensitivity to CoNS in the study of PyaePhyo Aung17 and it may be due to the widely used of quinolones in ophthalmology units nowadays.

Staphylococcus aureuswas the second most common bacteria isolated from the conjunctiva in this study which was consistent with many others studies including PyaePhyo Aung17 and Mshangila, et al.15 They can cause severe post-operative ocular infection that run aggressive course leading to sight loss. According to this study, clindamycin, moxifloxacin and vancomycin showed good activity against Staph. aureusand can effectively reduce Staph. aureuscolonization.

Among isolated Staphylococcus species, 43.2% of CoNS and 36.8% of Staphylo-coccusaureus were resistant to methicillin. Methicillin-resistant Staphylococcus species are not only resistant to methicillin, but also to all betalactam antibiotics. Furthermore, methicillin-resistant Staphylococcus was more likely to be concurrently resistant to another drug class when compared with methicillin-sensitive Staphylococcus species,which may limit treatment options. Moreover, infections caused by methicillin-resistant Staphylococcus species are difficult to treat and can lead to loss of vision and becomes a major concern for global public health infections.Therefore, identification of patients with a high risk of developing methicillin-resistant Staphylococcus aureusinfections may be helpful inpreventing severe complications from cataract surgery.

As a normal flora from the healthy eye, isolation rate of gram-negative bacteria was less than that of gram-positive bacteria. In the present study, total 15.8% of Entero-bacteriaceae were identified which was approximately similar to the finding of Cham, Valenton& Lim14 who observed 12% of Enterobacteriaceae from patients under-going cataract surgery. All isolated Entero-bacteriaceae were sensitive to moxifloxacin which was much different from a study done by Pyae PhyoAung17in which only 50.0% of Enterobacteriaceae were sensitive to moxifloxacin.

Pseudomonas species were also isolated from the eyes of patients undergoing cataract surgery and it may be normal flora or contamination of eye from environment  as Pseudomonas species are widely distributed in surrounding environment. In the present study, eight isolates (10.52%) of Pseudomonas species were identified which was similar to the study of Pyae Phyo Aung 9 who observed that the isolation rate of Pseudomonas species was 9%. According to the result of this study, levofloxacin showed good sensitivity against Pseudomonas species but neomycin and tobramycin cannot effectively reduce the Pseudomonas species colonization.

Moxifloxacin is the most empiric and prophylactic antibiotic in ophthalmology units and commonly used in daily practice. According to this study, moxifloxacin showed good activity against coagulase- negative staphylococci, Staphylococcus aureus and Enterobacteriaceae but it has  less sensitivity to Pseudomonas species. Therefore, it should be noticed that only one class of eye drop will not besufficient to effectively control the colonization of mixed conjunctival bacteria,

Conclusion

The findings from this study can give
the better knowledge about the common organism and its sensitivity. It can be taken into account in choice of antibiotics for those who plan to use pre-operative topical antibiotics and should try to give combined antibiotics for mixed organism coverage.


ACKNOWLEDGMENT
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We would like to express our heartfelt thanks to Professor Yee Yee Aung, Department of Ophthalmology, for her guidance and giving permission to obtain the specimens, and all consultants and their team members for their help in collection of the specimens. We also give our gratitude to Director-General and the External Grant Committee of Department of Medical Research for awarding grant to perform this research.


CONFLICT OF INTEREST
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The authors declare that they have no competing interests.

 


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