Microbiology

Microbiology

Using traditional culture techniques pathogenic microorganisms are isolated in 2/3 to ¾ of patients with bronchiectasis, although we now know from modern molecular techniques sequencing the 16s bacterial ribosomal RNA gene (16s rRNA) that a large and diverse bacterial community is present in the bronchiectasis airway even in patients without detectable bacteria on routine culture.[51,52] Bacterial infection drives the “vicious cycle” of bronchiectasis consisting of bacterial infection, airway inflammation and airway damage.[53] The most frequently isolated organisms in patients with non-CF bronchiectasis are Haemophilus influenzae, Pseudomonas aeruginosa, Moraxella catarrhalis, Streptococcus pneumoniae and Staphylococcus aureus.[12,37,54] Less frequently isolated pathogens include Aspergillus species, enteric gram negative organsisms, methicillin resistant Staphylococcus aureus and non-tuberculous mycobacteria as discussed previously. The frequency of pathogens isolated in selected studies of adults with bronchiectasis is shown in Table 3.

Author

Year

Country

N

Age

Method

Hi

PA

Sa

Sp

Mc

Asp

Myco

NP

Nicotra (55)

1995

USA

123

57

Sputum

30

31

7

11

2

5

23

23

Evans (56)

1996

UK

135

-

Sputum

ND

12

ND

ND

ND

ND

ND

ND

Cabello (57)

1997

Spain

17

57

BAL

35

5

-

-

-

-

ND

60

Wilson (58)

1997

UK

87

54

Sputum

20

25

-

-

-

-

-

38

Pasteur (59)

2000

UK

150

53

Sputum

35

31

14

13

20

2

ND

5

Angrill (60)

2001

Spain

49

57

BAL

26

20

-

2

-

-

ND

28

Palwatwichai (61)

2002

Thailand

50

58

Sputum

14

20

-

6

4

-

6

36

Angrill (54)

2002

Spain

42

58

Sputum

26

9

-

14

5

2

0

60

Angrill (54)

2002

Spain

59

58

BAL

32

10

3

7

-

-

0

32

Kelly (62)

2003

UK

100

57

Sputum

54

21

8

16

20

ND

ND

-

Tsang (63)

2005

Hong Kong

86

58

Sputum

11

27

-

-

-

-

-

60

King (64)

2007

Australia

89

57

Sputum

47

12

4

7

8

2

2

21

Martinez-Garcia (15)

2007

Spain

76

70

Sputum

18

20

-

-

-

-

-

-

O’Connell (65)

2010

USA

230

-

Sputum

-

31

9

-

-

-

35

87

Wong (66)

2012

N.Zealand

141

60

Sputum

28

12

3

3

4

-

-

-

Goeminne (17)

2012

Belgium

479

67

Sputum

31

30

23

20

15

20

-

-

King (9)

2012

Australia

178

58

Sputum

35

23

-

-

-

-

-

28

Chalmers (67)

2013

UK

470

65

Sputum

30

15

9

6

12

ND

ND

23

Tunney (52)

2013

UK

40

65

Sputum

30

25

70

45

3

-

-

0

 

Table 2. Reported frequency of bacterial isolates in adult patients using culture based techniques in non-CF bronchiectasis. ND= not done. Dashes indicate data not reported. Some percentages may add up to more than 100% as frequently patients culture more than one organism.

Hi= Haemophilus influenzae, PA= Pseudomonas aeruginosa, Sa= Staphylococcus aureus, Sp= Streptococcus pneumonia, Mc= Moraxella catarrhalis, ASP= Aspergillus species, Myco= Mycobacterium , NP= no pathogens isolated.

Bacteria in the airway are the primary drivers of the neutrophil mediated airway inflammation that is characteristic of bronchiectasis. Neutrophils are by far the most numerous immune cell type found in the airway lumen. While neutrophils are required to control bacteria in the lung, their response also contributes directly and indirectly to lung damage.[42] Large numbers of neutrophils and evidence of neutrophil degranulation can be detected in patients with clinically stable bronchiectasis, [37,68] while numbers further increase during exacerbation. Activated neutrophils release large amounts of proteinases and toxic granule products including elastase into the airways.[37] Proteolytic damage is an important contributing factor in airway remodelling and overall progression of the disease and also contributes indirectly to bacterial infection by disabling neutrophil functions and other innate immune mechanisms.[42]