Expression of β-defensin-3 in lungs of immunocompetent rats with methicillin-resistant Staphylococcus aureus ventilator-associated pneumonia.
BACKGROUND
Despite the rising incidence and high rate of treatment failure of ventilator-associated pneumonia (VAP) due to methicillin-resistant Staphylococcus aureus (MRSA), to date there has been no rat model specifically designed for antimicrobial evaluation. β-Defensin-3 Acronym for β-defensin-3 is correct as (BD-3) is an antimicrobial peptide and mainly expresses in the gastrointestinal and respiratory tract. It demonstrates a broad spectrum of potent antimicrobial activity against many potentially pathogenic microbes, including multi-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus faecium. Therefore, the authors hypothesized that the expression of BD-3 might change in lungs of rats with MRSA VAP, and this change might play an important role in the pathogenesis of VAP.


METHODS
Eighty specific pathogen-free male Sprague-Dawley rats were randomly assigned to the following experimental groups: (1) N (nonventilated pneumonia) group (n=34): rats were infected intrabronchially with 0.2 mL of 10(10) cfu/mL MRSA inoculum; (2)V (ventilator-associated pneumonia) group (n=34): rats were ventilated for 4 h using the protective ventilation settings: 6 mL/kg tidal volume, 5 cm H(2)O of positive end-expiratory pressure (PEEP), 88 breaths/min, and F(i)O(2)=0.21. After ventilation, rats were inoculated intrabronchially with the same amount of MRSA as in N group; (3) P (protective mechanical ventilation) group (n=6): 0.2 mL of normal saline was instilled into lungs of rats after 4 h of ventilation as in V group; (4) C (control) group (n=6): only 0.2 mL of normal saline were instilled into lungs of rats. Rats from both P and C groups were killed 48 h after instillation of normal saline. Rats from other two groups were killed 3, 6, 12, 24, 48 h after inoculation. Pneumonia evaluation was performed by macroscopic, histopathologic, and microbiologic criteria. The expression of BD-3 in lungs was determined by immunohistochemistry staining and Western blot analysis.


RESULTS
Rats inoculated after 4 h of protective mechanical ventilation rapidly developed progressive pneumonia with heterogeneous distribution of lesions and different degrees of histologic evolution predominating in lower lobes. Lung bacterial concentrations in V group at each time point were significantly higher than those of N group. It was 12.2±0.9log(10) cfu/g of tissue at h 48 in V group, and 8.7±0.4 in N group. Bacteremia occurred in nine of 10 rats at h 48 in V group, while two of 10 rats in N group. Both C and P groups showed a very low level of BD-3. Compared with C group, the expression of BD-3 at h 48 in both N and V groups significantly increased. However, the latter was significantly lower than the former.


CONCLUSIONS
Rat model of MRSA VAP was obtained by intrabronchially inoculating rats with 2×10(9) cfu MRSA after 4h of protective mechanical ventilation. VAP was more severe than nonventilated pneumonia in terms of histopathologic and microbiologic criteria, especially systemic spread. This may be associated with the inhibited up-regulation of BD-3 expression by mechanical ventilation.
Wu
Qingping
Q
Department of Anesthesiology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China.
Gui
Ping
P
Yao
Shanglong
S
Zhu
Hongfei
H
Li
Jianrong
J
Li
Yongping
Y
D000818:Animals; D004195:Disease Models, Animal; D007121:Immunocompetence; D008168:Lung / Q000378:metabolism* / Q000473:pathology; D008297:Male; D055624:Methicillin-Resistant Staphylococcus aureus / Q000302:isolation & purification*; D053717:Pneumonia, Ventilator-Associated / Q000378:metabolism* / Q000382:microbiology / Q000473:pathology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012129:Respiratory Function Tests; D013203:Staphylococcal Infections / Q000378:metabolism* / Q000382:microbiology / Q000473:pathology; D012122:Ventilators, Mechanical / Q000382:microbiology; D023083:beta-Defensins / Q000378:metabolism*
D023083:beta-Defensins; C560914:beta-defensin 3, rat