Single-cell transcriptomics reveals pathogen-specific monocyte heterogeneity and potential biomarkers in gram-positive versus gram-negative bloodstream infections

doi:10.5847/wjem.j.1920-8642.2026.035

Abstract

Abstract:

BACKGROUND: Bloodstream infections (BSIs) caused by gram-positive cocci (GPC) and gram-negative bacilli (GNB) are major causes of sepsis. However, their distinct effects on host responses remain poorly characterized at the single-cell level. This study used single-cell transcriptomics to define pathogen-specific monocyte heterogeneity in BSIs to identify the mechanisms underlying clinical differences.

METHODS: Single-cell RNA sequencing (scRNA-seq) was performed on peripheral blood mononuclear cells obtained from healthy volunteers, two patients with GNB-BSI sepsis, and two patients with GPC-BSI sepsis. Differential gene expression, particularly in monocytes, was analyzed. The key findings were validated with clinical characteristics and outcomes of 45 patients with GNB-BSI sepsis and 40 patients with GPC-BSI sepsis. The distinguishing performances of identified biomarkers were evaluated via receiver operating characteristic (ROC) curve.

RESULTS: In pathogen-specific transcriptomes, 54 identified genes were significantly associated with GNB-BSI (upregulated genes enriched in inflammatory pathways and downregulated genes enriched in oxidative phosphorylation). Twenty-one identified genes were associated with GPC-BSI (downregulated genes associated with cell adhesion molecules and upregulated genes involved in PI3K-Akt signaling). Nineteen genes were common to both groups, with distinct pathogen sensitivities. Patients with GNB-BSI presented with significantly greater disease severity, systemic inflammation and lymphopenia than patients with GPC-BSI. Conversely, patients with GPC-BSI had higher S100A12 and globulin levels and platelet counts. The combination of S100A12^high and procalcitonin (PCT)^low discriminated GPC-BSI from GNB-BSI (area under the curve=0.882, sensitivity 75%, specificity 91%; cutoff value 0.56).

CONCLUSION: ScRNA-seq reveals the heterogeneity of GPC-BSI and GNB-BSI. Compared with GPC-BSI, GNB-BSI causes severe inflammation and metabolic suppression, which are associated with poor outcomes. The S100A12^high+PCT^low combination may have potential to discriminate among the major causes of BSI.

Key words: Sepsis, Single-cell RNA sequencing, Monocytes, S100A12, Procalcitonin

Jinlan Ma, Li Peng, Hongming Yu, Jianfeng Xie, Ying Tang, Shenglin Su, Libing Ma, Xiaojun Yang. Single-cell transcriptomics reveals pathogen-specific monocyte heterogeneity and potential biomarkers in gram-positive versus gram-negative bloodstream infections[J]. World Journal of Emergency Medicine, 2026, 17(2): 162-171.

Figures/Tables 5

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Variables	GNB-BSI (n=45)	GPC-BSI (n=40)	χ²/t/Z	P-value
Male, n (%)	18 (40)	24 (60)	3.389	0.066
Age, years, mean±SD	64.91±13.31	58.22±15.51	2.138	0.035
Underlying diseases, n (%)
Cardiovascular and cerebrovascular diseases	16 (35.6)	7 (17.5)	3.498	0.061
Diabetes mellitus	8 (17.8)	11 (27.5)	1.153	0.283
Cancer	5 (11.1)	2 (5.0)	0.394	0.530
Infection sites, n (%)
Skin and soft tissue	0 (0)	16 (40.0)	22.174	<0.001
Abdominal cavity	25 (55.6)	7 (17.5)	13.065	<0.001
Urinary tract	16 (35.6)	6 (15.0)	4.664	0.031
Lung	4 (8.9)	10 (25.0)	3.995	0.046
Others	0 (0)	1 (2.5)	13.805	<0.001
APACHE Ⅱ score, median (IQR)	15 (12.25-17.25)	10 (8.5-11.5)	-6.870	<0.001
SOFA score, mean±SD	12.43±1.62	5.83±1.56	19.095	<0.001
Mechanical ventilation time, h, mean±SD	121.74±25.76	16.77±6.13	3.756	<0.001
Hospitalization duration, d, mean±SD	15.49±2.30	13.05±1.97	0.795	0.429
Total hospitalization costs, yuan, mean±SD	84139.4±15166.9	45267.9±8015.5	2.186	0.032
28-day mortality, n (%)	21 (46.7)	9 (22.5)	5.416	0.020

Parameter	GNB-BSI (n=45)	GPC-BSI (n=40)	t/Z	P-value
Lactate (mmol/L)	6.30 (4.55-9.17)	2.80 (1.18-4.42)	-4.935	<0.001
Total bilirubin (μmol/L)	38.50 (20.65-99.50)	19.90 (14.20-31.25)	-3.584	<0.001
Creatinine (μmol/L)	119.00 (88.55-228.92)	83.60 (56.15-148.90)	-3.153	0.002
Albumin (g/L)	23.75 (21.07-24.85)	32.30 (28.05-36.65)	-6.249	<0.001
Globulin (g/L)	22.32±6.18	29.68±6.58	-5.321	<0.001
Albumin/globulin	1.00 (0.90-1.18)	1.10 (0.90-1.40)	-1.265	0.206
D-dimer (DDU)	8.89 (5.67-20.28)	2.82 (1.41-8.13)	-4.208	<0.001
Prothrombin activity (%)	44.93±15.26	79.15±20.35	-8.806	<0.001
Platelet counts (×10⁹/L)	33.00 (16.00-45.75)	195.00 (154.50-250.00)	-7.516	<0.001
White blood cell counts (×10⁹/L)	13.41 (7.81-25.64)	12.21 (7.199-18.38)	-1.086	0.277
Neutrophil percentage (%)	93.15 (88.15-94.27)	88.20 (83.25-93.90)	-1.728	0.084
Interleukin-6 (pg/mL)	2350.00 (442.75-5000.00)	167.00 (43.10-2452.00)	-3.452	0.001
Procalcitonin (ng/mL)	56.50 (32.50-100.00)	6.10 (0.71-30.50)	-5.417	<0.001
Lymphocyte percentage (%)	5.9 (2.6-10.0)	3.4 (2.3-4.5)	2.626	0.009