The etiology of neonatal pneumonia,complicated by bronchopulmonary dysplasia

Abstract

BACKGROUND:

The frequency of bronchopulmonary dysplasia (BPD) in preterm infants with a “ventilator-associated” pneumonia (VAP) ranges between 7 to 50%.

OBJECTIVE:

To investigate the features of the etiological structure of neonatal pneumonia complicated by BPD, and to determine the sensitivity of pathogens to antibiotics.

METHODS:

A retrospective chart review of 194 preterm infants with VAP, birth weight from 780 to 2820 g and gestational age from 27 to 37 weeks was conducted. A microbiological study of washings from the respiratory tract was conducted by standard qualitative and quantitative methods.

RESULTS:

Respiratory tract infections caused by E. coli (with hemolytic properties), Enterococcus spp. (with hemolytic properties), Pseudomonas aeruginosa, Stenotrophomonas maltophilia, various types of mycoplasmas, Staphylococcus aureus, and Candida krusei were found 4– 13 times more frequent in preterm infants with BPD than in preterm infants without BPD and more mature infants with or without this complication. BPD developed 7– 11 times more frequent in preterm infants with prolonged VAP and change in pathogens than in preterm infants with VAP without change of agent. BPD developed 5– 7 times more frequent in preterm infants with the association of pathogens than in preterm infants with a monoinfection. Massive colonization of respiratory tract pathogens by 1– 3 days of life (lg4 colony forming units in 1 ml and above) was an unfavorable prognostic factor for the development of VAP, complicated by BPD.

CONCLUSION:

The reduction in the frequency of BPD is might be possible with timeous and adequate antibacterial therapy of VAP.

Keywords

Preterm infants pneumonia bronchopulmonary dysplasia microorganisms antibiotics

1 Introduction

In the last two decades the development of neonatology has made it possible to achieve good results in the treatment of infants, including preterm infants with different birth weight [1]. However, the use of instrumental methods of treatment with the use of hardware and artificial lung ventilation (ALV), nasal and venous catheters, can be accompanied by the development of severe infection. The greatest danger is represented by the “ventilator-associated” pneumonia (VAP) [1, 2]. We keep the following definition of the ventilator-associated pneumonia (VAP): VAP is an infectious inflammation of the lung tissue that occurs not earlier than 48 hours after intubation of the trachea and the beginning of mechanical ventilation of the lungs.

This disease can cause the development of bronchopulmonary dysplasia (BPD), leading to the formation of severe chronic respiratory pathology (emphysema, bronchiectasis, cystic fibrosis, asthma) and disability [3 –6]. We keep the following definition of the BPD. Arising in the perinatal period bronchopulmonary dysplasia is polyetiological chronic disease of morphologically immature lungs, developing in newborns, mainly deeply premature infants, as a result of intensive therapy of respiratory distress syndrome and (or) pneumonia. It flows with the predominant lesion of bronchioles and parenchyma of the lungs, development of emphysema, fibrosis and (or) disruption of alveolar replication; is manifested by dependence on oxygen at the age of 28 days of life and older, bronchial obstructive syndrome and symptoms of respiratory failure; characterized by specific radiographic changes in the first months of life and regression of clinical manifestations as the infant grows. BPD has the code P27.1 in the International Classification of Diseases ICD-10.

According to the literature’ source, the incidence of BPD among preterm infants varies within wide range: from 7 to 50% [3 , 7– 10]. According to our clinic’ source, preterm infants with BPD accounted 10.6% of all infants from 3 months to 2 years old who were observed in the department of catamnesis for preterm infants (125 infants with BPD of 1,179 infants) in 2016.

Given the high incidence of BPD, one of the major complications of neonatal pneumonia, it is interesting to conduct studies on the determination of the possible role of opportunistic microorganisms in the formation of this severe illness. The study question is whether the feature of the etiological structure of VAP influences BPD development or not?

Objective of this study is to investigate the features of the etiological structure of neonatal pneumonia complicated by BPD, and to determine the sensitivity of pathogens to antibiotics.

The current study is retrospective. This study was conducted in accordance with the ethical standards of all applicable national and institutional committees and the World Medical Association’s Helsinki Declaration.

2 Material and methods

A retrospective chart review of about 194 preterm infants with VAP was conducted. All infants were divided into four groups: The first group included 45 very preterm infants with very low birth weight from 780 to 1450 g (1120±30 g), gestational age from 27 to 32 weeks (29.5±0.44 weeks) and development of BPD. The second group included 79 preterm infants with very low birth weight from 850 to 1500 (1198±48 g), gestational age from 28 to 32 weeks (30.2±0.64 weeks) and without development of BPD. The third group included 17 preterm infants with a body weight of birth from 1501 to 2660 (2380±55 g), gestational age from 33 to 37 weeks (34.8±1.3 weeks) and development of BPD. The fourth group included 53 preterm infants with birth weight from 1510 to 2820 g (2430±55 g), gestational age from 32.5 to 37 weeks (34.2±1.6 weeks) and without development of BPD. Criteria for inclusion in the main research groups (the first and the second groups) were preterm infants with VAP, complicated by the development of BPD. Criteria for inclusion in the comparison groups (the third and the fourth groups) were preterm infants with VAP, not complicated by the development of BPD. The criteria for excluding infants from the study were 1) preterm infants with congenital malformations, 2) preterm infants with severe neurologic disorders.

We performed microbial cultures of tracheobronchial aspirates (TBA) in newborns on ALV. Also cultures of the posterior pharyngeal mucus were taken with oral swabs in newborns after extubation in the observation dynamics. The microbiological examination was carried out for 1– 3 days, at the beginning of pneumonia (in 4– 10 days of life) and 1– 3 times in the dynamics of observation with an interval of at least 7 days. This examination was performed by standard quantitative method for all infants for a wide range of nutrient media for the isolation of aerobian and facultative microorganisms [11, 12]. All bacterial cultures were identified by commercial test systems API 20 NE ‘BioMerieux’ (France), E | NE “Crystal” (USA), NEFERM test “Lachema” (Czech Republic) in accordance with the manufacturer’s instructions. The biomaterial was also examined for the content of strict anaerobes [13] and mycoplasma [14, 15]. The number of microorganisms was expressed in the following units: 1) The number of colony forming units in one standard tampon (CFU/t) or one ml of biofluid (TBA) in microbial contamination up to 1000 cells. 2) The decimal logarithm (lg) in microbial load 1000 and higher microbial cell in one tampon or one ml of biofluid. Etiologically significant number of microbial cells believed lg4 and higher CFU/ml for TBA, lg6 and higher CFU/t for the smear the posterior pharyngeal mucus [11]. Sensitivity determination of emphasized strains of bacteria to antibiotic conducted by disk-diffusion method on agar Mueller – Hinton (Mueller Hinton Agar) using standard commercial drive test systems NITSF (Russia) and test systems ATV pse 5 (BioMerieux) [12, 16]. The sensitivity of Bacteroudes fragilis to metronidazole and Prevotella melaninogenic to metronidazole and benzylpenicillin was determined by serial dilution in solid nutrient medium with an estimate of the minimum inhibitory concentration (MIC) [13]. The sensitivity of mycoplasmas to antibiotics was determined by inoculation from two dilutions of pathogens into special liquid nutrient substrate with a MIC score [15]. The indicator of the frequency of occurrence of the characteristic in percent (%) and Pearson consensus criterion χ2 were calculated. The study was conducted in Moscow (Russia) in the City Clinical Hospital No. 13 from November 2010 to December 2015.

3 Results

The results of a comparative study of the features of the VAP’s etiological structure in infants with and without outcome in BPD are presented in Table 1. This table combines the results of both primary crops and studies in the dynamics of VAP with revealing of cases of infection of the pathogen changes. Analyzing the findings, it was found that VAP with some types of microorganisms – pathogens were significantly more frequently in preterm infants who had the development of complication of BPD. Among the most frequent are E. coli (with hemolytic properties), Enterococcus spp. (with hemolytic properties), Pseudomonas aeruginosa (Ps.aeruginosa), Stenotrophomonas maltophilia (Sten. maltophilia) and Mollicutes (Mycoplasma) spp. In addition, in the group of extremely preterm infants with BPD significantly more frequent pathogens were Saphylococcus aureus (S. aureus) and Candida krusei.

Table 1
The etiological structure of VAP in preterm infants with outcome in bronchopulmonary dysplasia and without this complication

No Causative agent Groups of infants with weigh less than 1500g Groups of infants with weigh more than 1500g Significant differences

1 2 3 4 (p)

BPD NO BPD BPD NO BPD p_1,2 p_3,4

(n = 45) n % (n = 79) n % (n = 17) n % (n = 53) n % (^– p < 0,05)

1 Pseudomonas aeruginosa* 27 60 6 8 14 82 11 21 ^* ^*

2 Stenotrophomonas maltophilia 6 13 1 1 4 24 1 2 ^* ^*

3 E.coli (in all) 15 33 25 32 2 12 2 4 – –

4 E.coli (with hemolytic properties) 6 1 0 0 2 12 2 4 ^* –

5 Klebsiella ozenae 4 9 0 0 1 6 0 0 – –

6 Klebsiella pneumoniae 5 11 10 13 2 12 8 15 – –

7 Serracia marcescens 0 0 0 0 2 12 0 0 – –

8 Proteus mirabilis 1 2 0 0 0 0 0 0 – –

9 Enterococcus faecalis 15 33 22 28 3 18 8 15 – –

10 Enterococcus faecium 2 4 4 5 1 6 2 4 – –

11 Streptococcus pneumoniae 4 9 6 8 1 6 6 11 – –

12 Streptococcus group A 3 7 0 0 0 0 0 0 – –

13 Streptococcus group B 1 2 1 1 1 6 1 2 – –

14 Staphylococcus aureus 10 22 4 5 1 6 0 0 ^* –

15 Staphylococcus haemoliticus 5 11 6 8 2 12 7 13 – –

16 Staphylococcus epidermidis 5 11 6 8 2 12 7 13 – –

17 Haemophilus influenzae 4 9 1 1 1 6 0 0 – –

18 Prevotella melaninogenica 3 7 0 0 2 12 0 0 – –

19 Bacteroides fragilis 7 16 3 4 3 18 1 2 – –

20 Mycoplasma pneumoniae 14 31 3 4 6 35 1 2 ^* ^*

21 Mycoplasma hominis 15 33 5 6 7 41 3 6 ^* ^*

22 Ureaplasma urealyticum 15 33 5 6 6 35 2 4 ^* ^*

23 Chlamidia trachomatis 5 11 2 3 1 6 0 0 – –

24 Candida krusei 6 13 0 0 1 6 0 0 ^* –

25 Candida albicans 8 18 15 19 1 6 4 9 – –

26 Fusobacterium spp. 0 0 0 0 1 6 1 2 – –

No	Causative agent	Groups of infants with weigh less than 1500g	Groups of infants with weigh more than 1500g	Significant differences
1	Pseudomonas aeruginosa	27	60	6	8	14	82	11	21	^*	^*
2	Stenotrophomonas maltophilia	6	13	1	1	4	24	1	2	^*	^*
3	E.coli (in all)	15	33	25	32	2	12	2	4	–	–
4	E.coli (with hemolytic properties)	6	1	0	0	2	12	2	4	^*	–
5	Klebsiella ozenae	4	9	0	0	1	6	0	0	–	–
6	Klebsiella pneumoniae	5	11	10	13	2	12	8	15	–	–
7	Serracia marcescens	0	0	0	0	2	12	0	0	–	–
8	Proteus mirabilis	1	2	0	0	0	0	0	0	–	–
9	Enterococcus faecalis	15	33	22	28	3	18	8	15	–	–
10	Enterococcus faecium	2	4	4	5	1	6	2	4	–	–
11	Streptococcus pneumoniae	4	9	6	8	1	6	6	11	–	–
12	Streptococcus group A	3	7	0	0	0	0	0	0	–	–
13	Streptococcus group B	1	2	1	1	1	6	1	2	–	–
14	Staphylococcus aureus	10	22	4	5	1	6	0	0	^*	–
15	Staphylococcus haemoliticus	5	11	6	8	2	12	7	13	–	–
16	Staphylococcus epidermidis	5	11	6	8	2	12	7	13	–	–
17	Haemophilus influenzae	4	9	1	1	1	6	0	0	–	–
18	Prevotella melaninogenica	3	7	0	0	2	12	0	0	–	–
19	Bacteroides fragilis	7	16	3	4	3	18	1	2	–	–
20	Mycoplasma pneumoniae	14	31	3	4	6	35	1	2	^*	^*
21	Mycoplasma hominis	15	33	5	6	7	41	3	6	^*	^*
22	Ureaplasma urealyticum	15	33	5	6	6	35	2	4	^*	^*
23	Chlamidia trachomatis	5	11	2	3	1	6	0	0	–	–
24	Candida krusei	6	13	0	0	1	6	0	0	^*	–
25	Candida albicans	8	18	15	19	1	6	4	9	–	–
26	Fusobacterium spp.	0	0	0	0	1	6	1	2	–	–

1. The percentage of small numbers is given for comparing indicators between groups.

2. p – Significant difference between groups of indicators 1 and 2, as well as 3 and 4 (* – p < 0.05).

As a rule, in the initial planting, the bacteria family of Enterobacteriaceae, Staphylococcus spp., Streptococcus spp., Haemophilus influenzae (H. influenzae), Bacteroides spp., Chlamidia trachomatis, Mycoplasma spp., Fusobacterium comprised 82% strains of pathogens. In the secondary infection (with a change in the pathogen of VAP in preterm infants), they most frequent pathogens were Ps.aeruginosa, Sten. maltophilia, C andida spp. and Enterococcus spp. (75% strains of these types of pathogens).

Almost all strains emphasized isolates from preterm infants with BPD had various pathogenicity factors (haemolysing properties, lecithinase activity, increased proteinase and DNA-ase activity and etc.). These properties determined the ability of microorganisms to cause destructive changes in the lung tissue. The detection of these microorganisms on the 1– 3 days of life in TBA in a significant amount – lg4 and above was accompanied by the development of pneumonia with outcome in BPD in 75% of the extremely preterm infants and in 63% of the more mature preterm infants (hereinafter in the text, the percentage of small numbers is given to compare the indicators in groups). High titers of the causative agent were found in TBA at the same time but much less often in preterm infants with VAP without development of BPD (25% and 37% of groups II and IV, respectively). Thus, massive colonization of the respiratory tract pathogens and VAP in the early days of life are an unfavorable risk factors for development of BPD.

As a whole, the pathogens were in the form of pathogens’ associations in preterm infants with BPD: in all patients of group I, and in 15 preterm infants out of 17 (88%) of group III. In contrast, pneumonia was more often represented as a monoinfection among preterm infants without BPD: in 63 preterm infants (80%) of group II, in 47 preterm infants (88%) of group IV. In addition, a change in the pathogen in preterm infants with BPD was noted quite often, which made the course of VAP more severe and prolonged. Thus, a single change of pathogen was in 30 preterm infants (67%), double change was in 8 preterm infants (18%) of group I, the pathogens changed once in 10 preterm infants (59%), and changed twice in 2 preterm infants (12%) of group III. In contrast, there was no change in the pathogen in most of preterm infants without BPD: in 74 preterm infants (94%) of group II and in 49 preterm infants (92%) of group IV. Rarely there was a single change of pathogen: in 5 preterm infants of group II (6%) and in 4 preterm infants of group IV (8%), and there was no two-time change of pathogens in preterm infants without BPD.

The frequency of associations and changes of the pathogen in preterm infants with BPD and in preterm infants without BPD did not correlate with body weight or gestational age at birth (i.e., between groups I and III p > 0.05, II and IV groups p > 0.05).

Table 2

Sensitivity to antibiotics of the main gram-positive pathogens of pneumonia

No	Antibiotic	Microflora (number of strains)
		S. epidermidis (n = 20)			S.aureus (n = 15)		Streptococcus pneumoniae (n = 17)		Streptococcus A,B (n = 7)
		S	SR	R	S	R	S	R	S
1	Benzylpenicillin	–	–	–	0	15	17	0	7
2	Meticillin	3	0	17	6	9	17	0	7
3	Oxacillin	3	0	17	6	9	17	0	7
4	Ampicillin	3	0	17	6	9	17	0	7
5	Ampicillin+ Sulbactam	3	0	17	6	9	17	0	7
6	Amoxicillin/clavulanic acid	12	0	8	6	9	17	0	7
7	Cefazolin	12	4	4	11	4	17	0	0
8	Ceftazidime	11	2	7	6	9	15	2	7
9	Cefotaxime	9	2	9	6	9	16	1	7
10	Ceftriaxone	6	3	11	6	9	16	1	7
11	Cefoperazone	6	2	12	6	9	17	0	7
12	Gentamycin	10	1	9	6	9	–	–	7
13	Kanamycin	5	0	15	4	11	–	–	–
14	Netilmycin	6	1	13	5	10	–	–	–
15	Amicacyn	14	0	6	6	9	–	–	–
16	Imipenem/cilastatin	15	1	4	6	9	17	0	7
17	Meropenem	15	0	5	6	9	17	0	7
18	Erythromycin	3	0	17	6	9	17	0	7
19	Fusidinum-natrium	18	0	2	4	11	–	–	–
20	Lincomycin	3	0	17	6	9	17	0	7
21	Vancomycin	20	0	0	15	0	17	0	7
22	Linezolid	20	0	0	15	0	17	0	7
23	Rifampicin	15	0	5	4	11	17	0	7
24	Ofloxacin	16	0	4	6	9	12	5	7
25	Ciprofloxacin	16	0	4	6	9	12	5	7

1. S – sensitivity strain, R – resistant strain, SR– strain with an intermediate sensitivity. 2. “-” – the strains sensitivity to the antibiotic was not investigated.

Particular attention should be paid to the role of mycoplasmas in the formation of BPD in preterm infants. So, various kinds of mycoplasmas (M. pneumoniae, M.hominis, U.ureliticum) were found in titers lg4– 8 in 41 extremely preterm infants out of 45 with BPD (92%) and in 15 preterm infants out of 17 more mature infants with this disease (90%). Two types of mycoplasmas were found in 2 preterm infants of group I and 3 preterm infants of group III. At the same time, mycoplasmas were very rare in preterm infants without BPD (in 13 out of 79 preterm infants, 17% and in 6 out of 53 preterm infants, 11%, respectively), their titers were lower by 1– 3 orders, and the pathogens were eliminated faster by 5– 7 days from the body than it was in preterm infants with BPD.

The mycoplasmas were found in associations with other microorganisms (bacteria, Chlamydia spp., phungi) in all preterm infants with BPD. Most frequent, there were associations of mycoplasmas with 1-2 types of gram-negative bacteria – in 37 out of 45 preterm infants (82%) in group I and in 12 out of 17 preterm infants (71%) in group III. It should be noted that as a rule, mycoplasma-bacterial pneumonia had a severe form of flow with an early manifestation of the disease (in the first 3–4 days of life in 80% of preterm infants). In bacterial etiology of pneumonia, on the contrary, late neonatal pneumonia developed later (on the 6– 10th day of life) in 80% of the cases.

The majority of preterm infants with mycoplasma-bacterial pneumonia (in 60 out of 75 preterm infants, 80%) had a severe form of infectious toxicosis with rapid development of anemia (on the 2-3rd week of life with a drop in hemoglobin below 110 g/l.), regardless of their birth weight and the development of complication in the form of BPD, the presence of toxic granularity in neutrophils and short-term (not more than 1 week) and the appearance of myelocytes and metamyelocytes in the peripheral blood. The duration of pneumonia was more than one month.

The development of VAP caused by mycoplasmas was preceded by early respiratory distress syndrome (within the first 4 hours of life). Tracheobronchitis was diagnosed in 60% of preterm infants with pneumonia caused by M. pneumoniae, and only 20% of preterm infants with pneumonia caused by genital mycoplasmas (M. hominis and U. urealyticum). The duration of tracheobronchitis was two and two-three weeks, respectively. Every fourth preterm infant with mycoplasma pneumonia was diagnosed with a general edematous syndrome.

The results of the sensitivity to antibiotics study of the main gram-positive pathogens of VAP are presented in Table 2.

As it seen from the Table 2, all or most strains of Streptococcus pneumoniae and Streptococcus of groups “A” and “B” (from 83 till 100%) with VAP retained sensitivity to vancomycin, linezolid, penicillins, cephalosporins of I and III generations, carbapenems, lincomycin, erythromycin and rifampicin. All Enterococcus spp. were sensitive to vancomycin and linezolid, and 40– 45% to carbapenems, 50% of strains retained intermediate sensitivity to rifampicin, and 20– 35% of strains to ampicillin and fusidine. All strains such as S. epidermidis and S. haemoliticus were sensitive to vancomycin and linezolid, most strains were sensitive to fusidin, rifampicin, amikacin, carbapenem, cephalosporins of the I generation and to a lesser extent the III generation. All strains of S. aureus were sensitive to vancomycin, linezolid and most of them – to cephalosporins of the I generation. The results of the sensitivity of the main gram-negative pathogens of VAP are presented in Table 3.

Table 3

Sensitivity to antibiotics of the main gram-negative pathogens of VAP

No	Antibiotic	Microflora (number of strains)
	E.coli (n = 44)	K.p n eumoniae (n = 25)			Ps.aeruginosa (n = 58)
	S	SR	R	S	SR	R	S	SR	R
1	Azlocillin	38	6	0	21	4	0	28	0	30
2	Ampicillin	16	0	28	0	0	25	0	0	58
3	Ampicillin + Sulbactam	36	8	0	0	0	25	0	0	58
4	Carbenicillin	15	0	29	0	0	25	0	0	58
5	Piperacillin	40	4	0	25	0	0	58	0	0
6	Piperacillin + Tasobactam	44	0	0	25	0	0	58	0	0
7	Ceftazidime	26	0	18	17	0	8	24	3	31
8	Cefotaxime	22	5	17	13	0	12	5	0	53
9	Ceftriaxone	23	1	20	15	2	8	10	6	42
10	Cefoperazone	35	0	9	25	0	0	43	0	15
11	Gentamycin	28	1	15	2	0	23	12	3	43
12	Kanamycin	18	1	25	23	2	0	5	0	53
13	Netilmycinum	31	6	30	13	0	12	5	0	53
14	Amicacin	22	8	16	18	1	6	40	3	15
15	Imipenem/cilastatin	35	1	8	18	3	4	37	12	9
16	Meropenem	34	2	8	18	3	4	36	11	11
17	Rifampicin	24	0	43	8	0	17	5	0	53
18	Ofloxacin	42	2	0	23	2	0	35	19	4
19	Ciprofloxacin	38	6	0	22	3	0	17	5	36
20	Colistin	–	–	–	–	–	–	58	0	0

1. S – sensitivity strain, R – resistant strain, SR– strain with an intermediate sensitivity. 2. “-” – the strains sensitivity to the antibiotic was not investigated.

As it seen from Table 3, among E.coli and Klebsiella pneumoniae prevailed strains, which are sensitive to carbapenems, amikacin, azlocillin, piperacillin, piperacillin+tasobactam, colistin, cephalosporins of the III and IV generations. Representatives of other type genus Enterobacteriaceae (Enterobacter spp., Proteus mirabilis, Serracia marcescens, K. ozenae) were sensitive to the same antibiotics. All strains of Ps. aeruginosa were sensitive to colistin, piperacillin and piperacillin+tasobactam, 48 to 70% of strains to azlocillin, amikacin, carbapenem and cefoperazone, 41% to ceftazidime, significantly less (from 7– 18%) to other antibiotics.

All strains of Sten. maltophilia were sensitive only to ticarcillin+clavulanate. Six (6) strains of Sten.maltophilia were sensitive to ciprofloxacin and chloramphenicol, three (3) strains to ceftazidime, co-trimoxazole, sulfamethoxazole+trimethoprim. The intermediate sensitivity from one to three strains is retained to the same antibiotics. All seven strains of H. influenzae were sensitive to kanamycin, gentamycin, chloramphenicol, rifampicin, as well as to carbapenems and cephalosporins of the III-IV generation. Three strains were sensitive to erythromycin. All isolated strains of Bacteroides fragilis were sensitive to metronidazole (MIC less than 1μg/ml), and Prevotella melaninogenica to benzylpenicillin (MIC 0.1μg/ml) and metronidazole (MIC less than 1μg/ml).

The sensitivity of mycoplasmas to anti-infectives was depended on their species. As a rule, M. pneumoniae strains (80– 100%) were sensitive to erythromycin (MIC 0.015– 0.03μg/ml), clarithromycin (MIC ≤0.08μg/ml), midecamycin (MIC 0.01– 0.07μg/ml), lincomycin – (MIC 0.5– 2μg/ml), less often (30– 45%) to chloramphenicol, gentamycin and amikacin (MIC 2– 5μg/ml). M. hominis and U. urealyticum were sensitive to midecamycin (MIC 0.05– 0.16μg/ml), gentamycin and amikacin (MIC 2μg/ml). In addition, M. hominis strains were sensitive to josamycin (MIC 0.25μg/ml), and U. urealitycum to clarithromycin (MIC 0.4μg/ml).

4 Discussion

According to our research studies, most often BPD as a complication of VAP develops with infection caused by certain etiologic agents in preterm infants. The severe form of VAP with the development of complications is also determined by the biological properties of pathogens. Such pathogens as P. aeruginosae strains have pronounced toxic properties against the infant’s body. Thus, phospholipase C, bacterial elastase, protease IV, alkaline protease, protease staphylolytic (phospholipases C, bacterial elestase, protease IV, alkaline protease, staphylolytic protease) have destructive effects on the respiratory tract tissues and other organs [17, 18]. They contribute to the invasion of the pathogen in the blood and the spread of infection. Moreover, heat-stable and heat-labile hemolysins cause destruction of the red blood cells and disrupt their transport functions [17, 18]. S. aureus strains produce pathogenicity factors such as hemolysins, DNase, proteases, lecithinases [11 –13].

The high incidence of mycoplasma infection in preterm infants with BPD is drawn attention. Mycoplasma spp. have a high tropicity to the lung tissue, especially in preterm infants, the ability to cause cytopathological changes in the lung tissue with the development of an inflammatory reaction [15, 19]. In addition, mycoplasmas as intracellular pathogens are detected with incomplete phagocytosis [15, 19]. This circumstance points to an insufficient anti-infectious protection of the baby’s organism both against mycoplasmas and as well as against other pathogens of the infection, which can lead to a prolonged course of the disease and the development of complications. In this connection, it may be necessary to use immunoglobulin replacement therapy for intravenous administration in patients with severe pneumonia caused by mycoplasma and /or their association with bacteria. However, this question requires further research study.

It can be assumed that the process of destruction of the lung tissue is intensified under conditions of toxic effects of direct oxygen flow and its high concentrations in ALV [4 , 10]. Simultaneously, the formation of connective tissue increases leading to the formation of fibrotic changes [4 , 9]. Apparently, the bacterial microflora also participates in the development of BPD [5]. There are literature data that genital mycoplasmas (M. hominis and U. urealyticum), as well as M. pneumoniae, cope the tissue barriers faster than bacteria, creating favorable conditions for the subsequent invasion of gram-negative microorganisms and their manifestation of the pathogenic properties [15, 19]. Our data also demonstrate synergism of damaging action of mycoplasma association with gram-negative bacteria causing severe pneumonia during the formation of BPD.

Therefore, the results of the study indicated a negative role of opportunistic pathogens as pathogens of nosocomial infection (P. aeruginosa, S. aureus, M. pneumonia) and intrauterine pathogens (M. hominis and U. urealiticum) in the development of VAP and the formation of BPD. To prevent the negative role of these microorganisms, it is necessary to carry out anti-epidemiological measures in the hospital, to monitor the formation of hospital strains and to study their sensitivity to antibiotics along with the examination of pregnant women and preterm infants for intrauterine infection and treatment of birth canals of preterm infants and respiratory tracts upon detection of pathogens. Conducting an adequate antibiotic therapy will reduce the severity of VAP, shorten the duration of rigid modes of mechanical ventilation, especially, the total duration of its conduct, which will help to prevent or mitigate the impact of VAP on the development of BPD.

5 Conclusion

Most often BPD as a complication of VAP in preterm infants develops with infection caused by E. coli strains (with hemolytic properties), Enterococcus spp. (with hemolytic properties), Ps. aeruginosa, Sten. Maltophilia and different types of mycoplasmas. S. aureus, and Candida krusei occurred significantly more frequently in extremely preterm infants with BPD than in extremely preterm infants without BPD and more mature preterm infants as with this complication and without it. BPD developed 7– 11 times more frequent in preterm infants whose VAP was prolonged with a change of the pathogen than in preterm infants with VAP without the change of the pathogen. BPD developed 5– 7 times more frequent in preterm infants whose VAP was caused by pathogens associations than in preterm infants with a monoinfection. Massive colonization of respiratory tract by pathogens by the 1– 3 days of life (lg4 CFU/ml and above) is an unfavorable risk factor for the development of VAP, complicated by BPD. The sensitivity of the pathogens of VAP to antibiotics was very variable and depended on the type of pathogens. These statistics are typical for Moscow and Moscow region. However, the results of the study can be taken into account and used in other regions, since problem microorganisms (VAP pathogens) are prevalent everywhere.

Conflict of interest

There is no conflict of interest.

Financial disclosure statement

The study was carried out with the financial support of Ministry of Healthcare of the Russian Federation.

Human research statement

The current study is retrospective. The examination and treatment of BPD already had been approved by the IRB. This study was conducted in accordance with the ethical standards of all applicable national and institutional committees and the World Medical Association’s Helsinki Declaration.

Footnotes

Acknowledgment

The authors thank the translator Elena Ivleva.

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