Correlation Between the Clinical Severity, Bacterial Load, and Inflammatory Reaction in Children with Mycoplasma Pneumoniae Pneumonia

Exploring high-risk factors for the prediction of severe mycoplasma pneumonia in children

Background

As one of the most common causes of community-acquired pneumonia in children, the prevalence of mycoplasma pneumonia (MPP) has long been underestimated. This study aimed to analyze children's severe MPP (SMPP) by examining laboratory characteristics and identifying high-risk factors.

Methods

Clinical data from 447 hospitalized children with MPP were retrospectively analyzed. Patients were categorized into ordinary MPP and SMPP groups. Initial laboratory results on admission were compared between groups, and risk factors for SMPP were assessed using receiver operating characteristic (ROC) and logistic regression analyses.

Results

Children with SMPP exhibited significantly higher levels of neutrophils, neutrophil/lymphocyte ratio (NLR), C-reactive protein (CRP), interleukin-6 (IL-6), erythrocyte sedimentation rate (ESR), and lactate dehydrogenase (LDH), along with lower lymphocyte, albumin (ALB), and prealbumin (PAB) levels compared to the ordinary MPP group (all P<0.05). SMPP children also had a higher incidence of multiple pathogens (P<0.05). ROC analysis identified cutoff values for ESR, LDH, IL-6, CRP, neutrophil percentage, and NLR, with corresponding areas under the curve (AUCs) indicating their predictive values for SMPP. A combined analysis of these factors yielded an AUC of 0.732 (P<0.05). Multivariate logistic regression confirmed ESR >35.50 mm/h, LDH >360.50 U/L, IL-6 >20.28 pg/mL, and CRP >9.74 mg/L as independent high-risk factors for SMPP (P<0.05).

Conclusions

ESR, LDH, IL-6, CRP, neutrophil percentage, and NLR are valuable predictors for early identification of SMPP in children. These findings provide essential insights for clinical management aimed at assessing and intervening in prognosis.

Enhanced insights into the neutrophil-driven immune mechanisms during Mycoplasma pneumoniae infection

Mycoplasma pneumoniae (MP) infections represent a significant component of community-acquired pneumonia, especially in children, invoking a complex neutrophil-mediated immune response, crucial for host defense. This review consolidates current knowledge on the role of neutrophils in MP infection, focusing on their recruitment, migration and activation, as well as the molecular mechanisms underpinning these processes. Significant findings indicate that specific bacterial components, notably CARDS toxin and lipoproteins, intensify neutrophil recruitment via signaling pathways, including the IL-23/IL-17 axis and G-CSF. Furthermore, neutrophils engage in a series of responses, including phagocytosis, degranulation and NETosis, to combat infection effectively. However, dysregulated neutrophil activity can lead to exacerbated lung injury, highlighting the delicate balance required in neutrophil responses. Age and immunodeficiency also emerge as critical factors influencing the severity of MP infections. This review emphasizes the dual role of neutrophils in both defending against and exacerbating MP infections, suggesting that targeted therapeutic strategies could mitigate the adverse effects while enhancing beneficial neutrophil functions.

Analysis of Mycoplasma pneumoniae pneumonia and viral coinfection in southern Guangzhou after the COVID-19 pandemic

Background

Mycoplasma pneumoniae (MP) has recently become an important pathogen of respiratory infection in both children and adults. The objective of this study was to investigate the detection rate of MP and clinical features of viral coinfection in Mycoplasma pneumoniae pneumonia (MPP) after the coronavirus disease 2019 (COVID-19) pandemic in southern Guangzhou.

Methods

We reviewed 3,094 patients with respiratory infection who visited the respiratory medicine and pediatrics department from October 2023 to January 2024. Patients underwent polymerase chain reaction (PCR) or immunoglobulin M (IgM) serology for MP, influenza virus (IFV), respiratory syncytial virus (RSV), adenovirus (ADV) and enterovirus (EV). We further compared the clinical, laboratory, and imaging findings of the MPP patients with and without viral coinfection. In order to identify the significant association with viral coinfection in MPP, multivariable logistic regression analysis was performed.

Results

MP infection was identified in 746 (36.69%) children and 140 (13.20%) adults, and there were 308 (41.29%) children and 76 (54.29%) adults with MPP. Eighty-four (27.27%) children and 7 (5.0%) adults with MPP had viral coinfection. Viral coinfection including MPP-RSV (4.22%), MPP-ADV (4.22%), MPP-EV (7.14%) and MPP-IFV (11.68%) was identified in children. These patients had a higher frequency of fever, higher white blood cell, higher concentration of C-reactive protein and procalcitonin, and higher proportion of lactate dehydrogenase (LDH) at greater than 250 U/L. Imaging feature of consolidation and air bronchogram sign was observed in both MPP and viral coinfection. Multivariable analysis showed fever (adjusted odds ratio, 3.46; 95% confidence interval, 1.02-11.74; P=0.047) and elevated procalcitonin of greater than 5 ng/mL (adjusted odds ratio, 3.17; 95% confidence interval: 1.50-6.72; P=0.003) as the factors associated with the viral coinfection, suggesting that viral infections could aggravate the primary MP infection or predispose patients to secondary bacterial infection.

Conclusions

Viral coinfection in MPP was common after the COVID-19 pandemic in southern Guangzhou. Increase in procalcitonin should be considered as a possibility of viral coinfection in children with MPP. This finding suggests the need for viral test in children with elevated procalcitonin in MPP, which could help clinicians identify viral coinfection at an early stage and provide timely antiviral intervention.

Impact of the COVID-19 pandemic on epidemiological and clinical characteristics of Mycoplasma pneumoniae pneumonia in children: a multicenter study from Hubei, China

Aims

To investigate the epidemiological and clinical characteristics of children with Mycoplasma pneumoniae pneumonia (MPP) in Hubei, China.

Methods

We retrospectively analyzed inpatients with MPP from 20 hospitals in Hubei, China from January 2021 to December 2022. The co-detected pathogens of Mycoplasma pneumoniae (M. pneumoniae) were investigated using targeted next-generation sequencing (tNGS), and 23S rRNA gene mutations were analyzed to assess the macrolide resistance.

Results

M. pneumoniae infected 20.7% of patients with CAP, with cough (96.59%) and fever (80.28%) being the most prevalent symptoms. The infection rates in children younger than 1, 1-2, 3-6, 7-12, and older than 12 years were 6.17%, 19.98%, 26.97%, 43.93%, and 2.95%, respectively. Among 1,349 patients undergoing tNGS, the overall co-detection rate was 59.45%, with Streptococcus pneumoniae (29.30%), Haemophilus influenzae (23.57%), and Human rhinovirus (17.21%) being the most commonly co-detected pathogens. In 635 patients undergoing the 23S rRNA gene mutation test, 86.30% exhibited positive mutations (A2063G, 98.00%; A2064G, 1.50%; A2067G, 0.50%). Despite a significant age difference (P = 0.037) between macrolide-resistant M. pneumoniae and macrolide-sensitive M. pneumoniae groups, there were no significant differences in symptoms, lab data, or disease severity.

Conclusions

In Hubei Province, the prevalence of exhibited consistent changes during the COVID-19 pandemic. MPP was prevalent year-round, particularly in summer and autumn, with school-age children being more susceptible. Co-detections of viruses and bacteria were frequent in MPP cases, and macrolide resistance exceeded 85%. Ongoing surveillance of M. pneumoniae in children is crucial for understanding the healthcare impact of MPP.

Comparative observation between Roxithromycin and Azithromycin sequential therapy in the treatment of Mycoplasma pneumoniae Pneumonia in Children

Objective

To investigate the clinical efficacy of roxithromycin combined with azithromycin sequential therapy in the treatment of mycoplasma pneumoniae pneumonia in children.

Methods

A retrospective study was conducted on 100 patients with mycoplasma pneumoniae pneumonia admitted to The First Affiliated Hospital of Yangtze University from January 2020 to December 2022. All patients were divided into the observation group (roxithromycin combined with azithromycin sequential therapy) and the control group (azithromycin sequential therapy), with 50 cases in each group. The clinical efficacy, improvement time of clinical symptoms/signs, inflammation indexes, oxidative stress indexes and immune function levels of the two groups were compared. Moreover, the improvement of lung function indexes and the adverse reactions were observed.

Results

The overall response rate of the observation group was 96.00%, which was higher than the control group (84.00%) (p<0.05). The time of clinical symptoms/signs in the observation group were significantly lower than those in the control group(p<0.05). After treatment, significant improvements were seen in the levels of CRP, TNF-ɑ, IL-6, GSH-Px, SOD, MDA, CD3+, CD4+, CD4+/CD8+, IgM, IgG , IgA, FEV1, FEV1%, FVC and FEV1/FVC of the two groups compared with those before treatment (p<0.05), and the improvement in the observation group was more obvious than that in the control group(p<0.05). The overall incidence of adverse reactions in the observation group was 6.00%, which was slightly lower than that in the control group (8.00%) (c²=0.154, P=0.695).

Conclusion

Roxithromycin combined with azithromycin sequential therapy is a safe regimen for the treatment of mycoplasma pneumoniae pneumonia in children.

The relationship between IFN-γ, IL-10, IL-6 cytokines, and severity of the condition with serum zinc and Fe in children infected with Mycoplasma pneumoniae

Objective

To explore the relationship between cytokines such as interferon γ (IFN-γ), interleukin-10 (IL-10), and interleukin-6 (IL-6), as well as the severity of the condition, and serum zinc (Zn) and Fe levels in children with Mycoplasma pneumoniae infection.

Methods

A simple random sampling method was used to select 108 children with Mycoplasma pneumoniae infection admitted to the hospital from January to December 2022 as the study subjects. Collect demographic data such as gender, age, and course of disease from all patients, as well as inflammatory cytokines (InCs) such as IFN-γ, IL-10, and IL-6, the severity of the condition, and serum trace element information such as Zn, Fe, calcium (Ca), and potassium (K) from all patients. Spearman correlation analysis was used to examine the relationship between IFN-γ, IL-10, IL-6, severity of illness, and Zn, Fe, Ca, K in children infected with Mycoplasma pneumoniae. Additionally, receiver operating characteristic (ROC) curve analysis was used to test the predictive efficacy of Zn, Fe, Ca, and K on the severity of the patient's condition.

Results

This study included 108 children infected with Mycoplasma pneumoniae, of whom 6 had clinical data missing >10% and were all excluded. Finally, 102 complete clinical data were collected, with a data recovery efficiency of 94.44%. The differences in IFN-γ, IL-10, IL-6 levels, severity of the condition, as well as Zn, Fe, Ca, K levels among children of different ages, disease courses, body mass, and body temperature showed P < 0. 05. Spearman correlation analysis showed that the levels of IFN-γ, IL-10, IL-6, and severity of the condition in children with Mycoplasma pneumoniae infection were negatively correlated with Zn, Fe, Ca, and K (ρ = -0.319 to -0.827, P < 0.05). The ROC curve analysis results indicate that Zn, Fe, Ca, and K can all be used as indicators to predict the severity of the patient's condition (AUC = 0.710-0.759, P < 0.05).

Conclusion

There is a close relationship between InCs and the severity of the condition in children with Mycoplasma pneumoniae and serum trace elements. Therefore, clinical attention should be paid to monitoring the serum trace element levels of children, and reasonable measures should be taken to regulate them to accelerate the progress of disease treatment.

[Value of calprotectin S100 A8/A9 in predicting the severity of Mycoplasma pneumoniae pneumonia in children]

OBJECTIVES

To investigate the role of calprotectin S100 A8/A9 complex in evaluating the condition of children with severe Mycoplasma pneumoniae pneumonia (SMPP).

METHODS

A prospective study was conducted among 136 children with Mycoplasma pneumoniae pneumonia (MPP) and 30 healthy controls. According to the severity of the condition, the children with MPP were divided into mild subgroup (40 children) and SMPP subgroup (96 children). The levels of S100 A8/A9 complex and related inflammatory factors were compared between the MPP group and the healthy control group, as well as between the two subgroups of MPP. The role of S100 A8/A9 in assessing the severity of MPP was explored.

RESULTS

The MPP group had a significantly higher level of S100 A8/A9 than the healthy control group, with a significantly greater increase in the SMPP subgroup (P<0.05). The multivariate logistic regression analysis showed that the increases in serum C reactive protein (CRP) and S100A8/A9 were closely associated with SMPP (P<0.05). The receiver operating characteristic (ROC) curve analysis showed that the combined measurement of serum S100 A8/A9 and CRP had an area under the ROC curve of 0.904 in predicting SMPP, which was significantly higher than the AUC of S100 A8/A9 or CRP alone (P<0.05), with a specificity of 0.718 and a sensitivity of 0.952.

CONCLUSIONS

S100 A8/A9 is closely associated with the severity of MPP, and the combination of S100 A8/A9 with CRP is more advantageous for assessing the severity of MPP in children.

Efficacy of doxycycline therapy for macrolide-resistant Mycoplasma pneumoniae pneumonia in children at different periods

BACKGROUND

The prevalence of macrolide-resistant Mycoplasma pneumoniae has increased considerably. Treatment in children has become challenging. This study aimed to evaluate the efficacy of doxycycline therapy for macrolide-resistant Mycoplasma pneumoniae pneumonia in children at different periods.

METHODS

We retrospectively analyzed the data of patients with macrolide-resistant Mycoplasma pneumoniae pneumonia hospitalized between May 2019 to August 2022. According to treatment, patients were divided into three groups: oral doxycycline treatment alone (DOX group), changed from intravenous azithromycin to oral doxycycline (ATD group), and intravenous azithromycin treatment alone (AZI group). ATD group cases were separated into two sub-groups: intravenous azithromycin treatment<3 days (ATD1 group) and ≥ 3 days (ATD2 group). Clinical symptoms were compared in each group and adjusted by Propensity score matching (PSM) analysis.

RESULTS

A total of 106 were recruited in this study. 17 (16%) were in DOX group, 58 (55%) in ATD group, and 31(29%) in AZI group. Compared with ATD group and AZI group, the DOX group showed shorter hospitalization duration and fever duration after treatment, while higher rate of chest radiographic improvement. After using PSM analysis, shorter days to hospitalization duration (P = 0.037) and to fever duration after treatment (P = 0.027) in DOX + ATD1 group than in ATD2 group was observed. A higher number of patients in the DOX + ATD1 group achieved defervescence within 72 h (P = 0.031), and fewer children received glucocorticoid adjuvant therapy (P = 0.002). No adverse reactions associated with doxycycline was observed during treatment.

CONCLUSIONS

Children receiving early oral doxycycline had a shorter duration of fever and hospitalization in macrolide-resistant Mycoplasma pneumoniae patients.

Absolute quantification of Mycoplasma pneumoniae in infected patients by droplet digital PCR to track disease severity and treatment efficacy

Mycoplasma pneumoniae is a common causative pathogen of community-acquired pneumonia. An accurate and sensitive detection method is important for evaluating disease severity and treatment efficacy. Digital droplet PCR (ddPCR) is a competent method enabling the absolute quantification of DNA copy number with high precision and sensitivity. We established ddPCR for M. pneumoniae detection, using clinical specimens for validation, and this showed excellent specificity for M. pneumoniae. The limit of detection of ddPCR was 2.9 copies/reaction, while that for real-time PCR was 10.8 copies/reaction. In total, 178 clinical samples were used to evaluate the ddPCR assay, which correctly identified and differentiated 80 positive samples, whereas the real-time PCR tested 79 samples as positive. One sample that tested negative in real-time PCR was positive in ddPCR, with a bacterial load of three copies/test. For samples that tested positive in both methods, the cycle threshold of real-time PCR was highly correlated with the copy number of ddPCR. Bacterial loads in patients with severe M. pneumoniae pneumonia were significantly higher than those in patients with general M. pneumoniae pneumonia. The ddPCR showed that bacterial loads were significantly decreased after macrolide treatment, which could have reflected the treatment efficacy. The proposed ddPCR assay was sensitive and specific for the detection of M. pneumoniae. Quantitative monitoring of bacterial load in clinical samples could help clinicians to evaluate treatment efficacy.

Effect of azithromycin combined with ambroxol in children with Mycoplasma pneumoniae pneumonia

OBJECTIVE

This study was designed to investigate the clinical efficacy of azithromycin combined with ambroxol in children with Mycoplasma pneumoniae pneumonia (MPP).

METHODS

The clinical data of 103 children with MPP treated in Fuyang District Hospital of Traditional Chinese Medicine of Hangzhou from December 2020 to August 2021 were selected and retrospectively analyzed, and these children were divided into a control group (n=51, azithromycin treatment) and a study group (n=52, azithromycin plus ambroxol treatment) according to the different treatment methods. The immunoglobulin level, pulmonary function score, treatment efficacy, serum cytokine level, disappearance time of signs and symptoms, and myocardial enzyme indices were observed and compared between the two groups. Univariate and multivariate analyses were conducted to screen the factors affecting the prognosis of MPP patients.

RESULTS

After treatment, the study group showed significantly lower levels of immunoglobulin E, immunoglobulin G, immunoglobulin M and immunoglobulin A; higher pulmonary function scores, and lower levels of interleukin-6, human interferon-gamma, and monocyte chemoattractant protein-4 compared with the control group (all P < 0.05). The total incidence of adverse reactions such as nausea, diarrhea, abdominal pain, and vomiting was 15.38% in the study group, which was slightly lower than that in the control group (17.65%), exhibiting no significant difference (P > 0.05). The disappearance time of cough and lung rales, time required to restore to a normal body temperature, and hospital stay in the study group were shorter than those in the control group (P < 0.05). After treatment, aspartate aminotransferase, lactate dehydrogenase, creatine kinase, and creatine kinase isoenzyme in the study group were lower than those in the control group (all P < 0.05). The course of disease before admission, C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), anemia, albumin < 30 g/L, drug initiation time, pulmonary consolidation, and complications involving multiple systems were the main factors affecting the efficacy of azithromycin combined with ambroxol in the treatment of MPP.

CONCLUSION

Azithromycin combined with ambroxol can effectively improve the immunoglobulin level and lung function, reduce the level of inflammatory factors, improve the therapeutic effect, shorten the recovery process, and reduce the degree of myocardial damage, which is effective in the treatment of MPP and is worth promoting.

Clinical significance of Mycoplasma pneumoniae specific IgM titer in children hospitalized with Mycoplasma pneumoniae pneumonia

BACKGROUND

The present study aimed to identify the clinical significance of Mycoplasma pneumoniae (MP)-specific immunoglobulin M (IgM) titer, in addition to a diagnosis of MP infection, in children with MP pneumonia.

METHODS

This study was performed in 155 children hospitalized with MP pneumonia. The clinical features and laboratory and radiographic findings on admission in children with positive or negative MP-specific IgM titers were retrospectively reviewed from the electronic medical records.

RESULTS

The mean age of the included children was 6.0 years, and 118 (76.1%) of the children were positive for MP-specific IgM. A longer duration between symptom onset and admission (adjusted odds ratio [aOR] 1.47, 95% confidence interval [CI] 1.24-1.75), longer duration of symptoms during the illness (aOR 1.15, 95% CI 1.02-1.30), and development of extra-pulmonary manifestations (aOR 9.16, 95% CI 1.96-42.81) were significantly associated with a positive MP-specific IgM titer. Serum lactate dehydrogenase levels (aOR 1.00, 95% CI 1.00-1.01) and pneumonic infiltration involving > 50% of the total lung volume on chest radiography (aOR 4.68, 95% CI 1.12-19.55) were associated with positive MP-specific IgM in children with MP pneumonia. A poor response to stepwise treatment for MP pneumonia was more common in children with a positive MP-specific IgM titer than those with a negative MP-specific IgM titer on admission.

CONCLUSIONS

A positive MP-specific IgM titer at diagnosis of MP pneumonia may partially suggest an exaggerated immune response with a higher disease burden compared to children with MP pneumonia with a negative MP-specific IgM titer.

[Detection of drug-resistance genes of Mycoplasma pneumoniae in bronchoalveolar lavage fluid of children with refractory Mycoplasma pneumoniae pneumonia]

OBJECTIVE

To study the drug resistance of Mycoplasma pneumoniae (MP) in the bronchoalveolar lavage fluid (BALF) of children with refractory Mycoplasma pneumoniae pneumonia (RMPP) and the distribution of drug-resistance genes, as well as the association of alleles at 2063 locus of 23SrRNA V region central ring with resistance to antimicrobial drugs.

METHODS

BALF specimens were collected from 245 children with RMPP who were admitted to the Children's Hospital Affiliated to Zhengzhou University from March 2016 to December 2020. A rapid cultured drug sensitivity assay was used to detect the resistance of MP isolates to nine commonly used antimicrobial drugs. The real-time PCR was used to measure MP DNA. The direct sequencing was used to detect gene mutations in MP 23SrRNA V region central ring.

RESULTS

Among the 245 BALF specimens, 207 tested positive for MP DNA, with a positive rate of 84.5%. The results of drug susceptibility test showed that the children with RMPP had a resistance rate of > 70% to macrolide antimicrobial drugs, with the highest resistance rate to clarithromycin, followed by roxithromycin, clindamycin, acetylspiramycin, erythromycin, and azithromycin, and these children had a resistance rate of < 5% to quinolone antimicrobial drugs. Among the 207 MP DNA-positive specimens, 41 (19.8%) had no drug-resistance gene mutations and 166 (80.2%) had drug-resistance gene mutations, among which 154 (74.4%) had an A→G mutation at 2063 locus of 23SrRNA V region central ring, 7 (3.4%) had an A→G mutation at 2064 locus, and 5 (2.4%) had mutations in both 2063 and 2064 loci. Among the 166 specimens with point mutations of the MP 23SrRNA gene, 159 (95.8%) had point mutations at 2063 locus. The A→G point mutation at 2063 locus of 23SrRNA V region central ring had a great impact on resistance to macrolide antimicrobial drugs. There was a significant difference in the distribution of alleles at 2063 locus between the children with resistance to clarithromycin, roxithromycin, clindamycin, acetylspiramycin, erythromycin, and azithromycin (P < 0.05).

CONCLUSIONS

MP in the BALF of children with RMPP has a relatively high resistance rate to macrolide antimicrobial drugs. Resistance to macrolide antimicrobial drugs is closely associated with the A→G point mutation in the 23SrRNA gene, and the point mutation at 2063 locus of 23SrRNA V region central ring may affect the drug-resistance mechanism of MP.

[Detection of drug-resistance genes of Mycoplasma pneumoniae in bronchoalveolar lavage fluid of children with refractory Mycoplasma pneumoniae pneumonia]

OBJECTIVE

To study the drug resistance of Mycoplasma pneumoniae (MP) in the bronchoalveolar lavage fluid (BALF) of children with refractory Mycoplasma pneumoniae pneumonia (RMPP) and the distribution of drug-resistance genes, as well as the association of alleles at 2063 locus of 23SrRNA V region central ring with resistance to antimicrobial drugs.

METHODS

BALF specimens were collected from 245 children with RMPP who were admitted to the Children's Hospital Affiliated to Zhengzhou University from March 2016 to December 2020. A rapid cultured drug sensitivity assay was used to detect the resistance of MP isolates to nine commonly used antimicrobial drugs. The real-time PCR was used to measure MP DNA. The direct sequencing was used to detect gene mutations in MP 23SrRNA V region central ring.

RESULTS

Among the 245 BALF specimens, 207 tested positive for MP DNA, with a positive rate of 84.5%. The results of drug susceptibility test showed that the children with RMPP had a resistance rate of > 70% to macrolide antimicrobial drugs, with the highest resistance rate to clarithromycin, followed by roxithromycin, clindamycin, acetylspiramycin, erythromycin, and azithromycin, and these children had a resistance rate of < 5% to quinolone antimicrobial drugs. Among the 207 MP DNA-positive specimens, 41 (19.8%) had no drug-resistance gene mutations and 166 (80.2%) had drug-resistance gene mutations, among which 154 (74.4%) had an A→G mutation at 2063 locus of 23SrRNA V region central ring, 7 (3.4%) had an A→G mutation at 2064 locus, and 5 (2.4%) had mutations in both 2063 and 2064 loci. Among the 166 specimens with point mutations of the MP 23SrRNA gene, 159 (95.8%) had point mutations at 2063 locus. The A→G point mutation at 2063 locus of 23SrRNA V region central ring had a great impact on resistance to macrolide antimicrobial drugs. There was a significant difference in the distribution of alleles at 2063 locus between the children with resistance to clarithromycin, roxithromycin, clindamycin, acetylspiramycin, erythromycin, and azithromycin (P < 0.05).

CONCLUSIONS

MP in the BALF of children with RMPP has a relatively high resistance rate to macrolide antimicrobial drugs. Resistance to macrolide antimicrobial drugs is closely associated with the A→G point mutation in the 23SrRNA gene, and the point mutation at 2063 locus of 23SrRNA V region central ring may affect the drug-resistance mechanism of MP.