Pathogen Distribution and Antibiotic Sensitivity in Ocular Bacterial Infections

Table of Content

Introduction

Ocular infections are potentially blinding diseases, and bacteria are the most frequently encountered pathogens affecting ocular structures.

Aim

To provide statistical evidence for the use of antibiotics in ophthalmology by assessing the distribution and antibiotic sensitivity of bacterial isolates from ocular specimens with suspected microbial infections.

Patients Profile

Clinical specimens were obtained from conjunctiva, cornea, aqueous humor, vitreous body, eyelid margin, lacrimal passage, orbital contents, and other ocular sites in the Inpatient Wards and Outpatient Clinics

Methods

  • Retrospective analysis
  • 11 530 ocular specimens with suspected microbial infections were submitted for microbiological evaluation
  • The parameters assessed mainly included
    • distribution of isolated bacteria  
    • results of susceptibility tests for antibiotics.
  • In the analysis of antibiotic sensitivities, the bacteria were divided into four groups according to gram staining, and statistical methods were used to compare their antibiotic sensitivities.

Results

  • Among a total of 11 530 specimens
    • 3625 (31.44%) showed bacterial growth, and 3690 bacterial strains were isolated
  • Among 3625 bacterial specimens
  • 2849 (78.59%) were obtained from the conjunctiva
  •  569 (15.70%) from the cornea
  •  111 (3.06%) from the aqueous humor or vitreous body
  • 96 (2.65%) from the lacrimal passage, eyelid margin, orbital contents and other ocular sites
  • A total of 3690 bacterial strains (32 genera and 140 species) were isolated           
  • G+C (82.30%) were prominent in the total bacterial isolates (Figure 1)
  • Staphylococcus epidermidis (54.39%) was the predominant bacterial isolate followed by Staphylococcus aureus (7.05%), C. xerosis (4.34%), Staphylococcus hominis (3.39%), Staphylococcus haemolyticus (3.12%), and P. aeruginosa (2.09%). (Table 1).
Figure 1: Percentage (%) distribution of organisms isolated

Table 1: Distribution of bacteria isolated from different ocular sites between 2013 and 2017

Bacterial isolates from

different ocular sites

Number of isolates

(n=3690)

%

Conjunctiva

2892

78.37

Staphylococcus epidermidis

1661

45.01

Staphylococcus aureus

213

5.77

Corynebacterium xerose

130

3.52

Staphylococcus hominis

97

2.63

Staphylococcus haemolyticus

97

2.63

Staphylococcus lentus

57

1.54

Enterococcus faecalis

44

1.19

Streptococcus mitis

27

0.73

Pseudomonas aeruginosa

27

0.73

Others

539

14.61

Cornea

579

15.69

Staphylococcus epidermidis

256

6.94

Pseudomonas aeruginosa

39

1.06

Staphylococcus aureus

34

0.92

Corynebacterium xerose

24

0.65

Staphylococcus hominis

19

0.51

Staphylococcus haemolyticus

16

0.43

Micrococcus luteus

13

0.35

Streptococcus mitis

11

0.30

Others

167

4.53

Aqueous humor or vitreous body

118

3.20

Staphylococcus epidermidis

42

1.14

Staphylococcus aureus

9

0.24

Staphylococcus hominis

6

0.16

Bacillus subtilis

6

0.16

Pseudomonas aeruginosa

5

0.14

Bacillus cereus

5

0.14

Others

45

1.22

Other ocular sites

101

2.74

Staphylococcus epidermidis

47

1.27

Pseudomonas aeruginosa

6

0.16

Escherichia coli

4

0.11

Staphylococcus aureus

4

0.11

Others

40

1.08

Total

3690

100

 

 

  • The sensitivity rate of the total isolates to gatifloxacin was up to 90.01%, with G+C, G+B, G-C, and G-B being all highly sensitive
    • These finding indicated that gatifloxacin is a broad-spectrum antibiotic with high sensitivity and is suitable for topical prophylactic use in ophthalmology
  • The sensitivity rate of the total isolates to levofloxacin was low (51.91%), whereas that of G-B was high (83.66%)
  • The sensitivity rates of G+C and G+B to vancomycin were significantly higher than those of G-C and G-B (P<0.05)
Table 2: Sensitivities of the antibiotics

Antibiotics

Total

G+C

G+B

G-C

G-B

Tigecycline

99.59

99.59

100.00

-

100.00

Vancomycin

97.15

97.95

97.54

70.59

68.57

Rifampicin

94.48

94.90

90.84

90.00

76.92

Gatifloxacin

90.01

92.69

91.12

81.48

71.17

Cefuroxime

89.28

94.35

87.74

89.29

57.28

Fusidic acid

85.40

89.83

73.37

52.63

29.83

Ceftazidime

81.99

84.41

69.62

90.91

78.79

Amikacin

81.61

5.00

100.00

100.00

90.00

Moxifloxacin

80.30

81.21

32.00

100.00

100.00

Ofloxacin

67.40

66.63

64.22

78.57

73.39

Gentamicin

66.59

65.96

64.95

56.52

72.57

Tobramycin

64.13

63.50

62.87

75.00

68.64

Levofloxacin

51.91

46.28

71.30

60.87

83.66

Ciprofloxacin

44.61

43.36

26.86

60.00

74.46

  • For fusidic acid, the sensitivity rates of G+C (89.83%) and G+B (73.37%) were significantly higher than that of G-B (29.83%; P<0.05)
  • The gram-negative bacteria’s sensitivity rate to cefuroxime was as low as 59.25%, but only G-B was less sensitive to cefuroxime (57.28%), while G-C was still highly sensitive (89.29%)
  • The sensitivity rate of gram-positive bacteria to moxifloxacin was as high as 80.28%, but only G+C was highly sensitive to moxifloxacin (81.21%), while G+B was still less sensitive (32.00%)
Table 3 Sensitivity ranking results of the antibiotics

Stains

Sensitivity ranking (P<0.05)

Total

TGC>VAN>RIF>GAT, CXM>FDA>CAZ, AMK, MFX>OFX, GEN>TOB>LVX>CIP

G+C

TGC>VAN>RIF, CXM>GAT>FDA>CAZ>MFX>OFX, GEN>TOB>LVX>CIP

G+B

VAN>GAT, RIF, CXM>FDA, LVX, CAZ, GEN, OFX, TOB>MFX, CIP (FDA>TOB)

G-C

CAZ>LVX, CIP, GEN, FDA

G-B

AMK>LVX, CAZ, RIF, CIP, OFX, GEN, GAT, TOB, VAN, CXM>FDA (LVX>CIP>CXM)

Any sensitivity rate with a denominator number less than 15 was not included in this statistical analysis. TGC: Tigecycline; VAN: Vancomycin; RIF: Rifampicin; GAT: Gatifloxacin; CXM: Cefuroxime; FDA: Fusidic acid; CAZ: Ceftazidime; AMK: Amikacin; MFX: Moxifloxacin; OFX: Ofloxacin; GEN: Gentamicin; TOB: Tobramycin; LVX: Levofloxacin; CIP: Ciprofloxacin. “A>B, C” means the sensitivity of A was significantly higher than that of B and C (P<0.05), and no statistically significant difference was noted in the sensitivity of B and C (P>0.05).

Conclusion

  • This 5-year study found that S. epidermidis was the main isolate of all ocular specimens with bacteria
  • As a broad-spectrum antibiotic with high sensitivity, gatifloxacin is more suitable than levofloxacin for topical prophylactic use in ophthalmology, and levofloxacin is an effective drug for treating G-B
  • Vancomycin and fusidic acid both have better effects on gram-positive bacteria than gram-negative bacteria
  • These findings may help ophthalmologists make more appropriate decisions for the treatment of ocular bacterial infections

Reference

Int J Ophthalmol 2020;13(1):54-60