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Journal of Integrative Agriculture  2023, Vol. 22 Issue (5): 1514-1528    DOI: 10.1016/j.jia.2022.10.004
Animal Science · Veterinary Medicine Advanced Online Publication | Current Issue | Archive | Adv Search |
Molecular epidemiology, characterization of virulence factors and antibiotic-resistance profile of Streptococcus agalactiae isolated from dairy farms in China and Pakistan

Ambreen LEGHARI1, Shakeel Ahmed LAKHO2, Faiz Muhammad KHAND2, Khaliq ur Rehman BHUTTO3, Sameen Qayoom LONE1, Muhammad Tahir ALEEM1, Iqra BANO2, Muhammad Ali CHANDIO2, Jan Muhammad SHAH2, LIN Hui-xing1, FAN Hong-jie1, 4#

1 MOE Joint International Research Laboratory of Animal Health and Food Safety, College of Veterinary Medicine, Nanjing Agricultural University, Nanjing 210095, P.R.China

2 Shaheed Benazir Bhutto University of Veterinary and Animal Sciences, Sakrand 67210, Pakistan

3 Central Veterinary Diagnostic Laboratory, Tando Jam 70050, Pakistan

4 Jiangsu Co-innovation Center for the Prevention and Control of Important Animal Infectious Diseases and Zoonoses, Yangzhou University, Yangzhou 225009, P.R.China

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Streptococcus agalactiae is one of the most common pathogens that cause bovine mastitis worldwide. Identifying pathogen prevalence and virulence factors is critical for developing prevention and control approaches. Herein, 1161 milk samples from various dairy farms in China (n=558) and Pakistan (n=603) were collected between 2019-2021 and were subjected to S. agalactiae isolation. Prevalence, serotyping, virulence genes, and antibiotic-resistant genes of S. agalactiae were evaluated by PCR assay. All isolates were characterized for haemolysis, biofilm production, cytotoxicity, adhesion, and invasion on bovine mammary epithelial cells. The prevalence of S. agalactiae-induced mastitis in cattle was found to be considerably higher in Pakistan than in China. Jiangsu and Sindh provinces had the highest area-wise prevalence in China and Pakistan, respectively. Serotypes Ia and II were prevalent in both countries, whereas serotype III was found only in Pakistan. Moreover, all isolates tested positive for PI-2b gene but negative for PI-1 and PI-2a genes. All isolates harboured cfb, cylE, hylB, and fbsB virulent genes, whereas many of them lacked bibA, rib and bca. However, the absence of bac and scp genes in Chinese isolates and cspA in Pakistani isolates was noted, while spb1 and lmb were not detected in isolates of both countries. Pakistani isolates, particularly serotype Ia-positive, had a considerably higher ability to produce biofilm, haemolysis, cytotoxicity, adhesion, and invasion than Chinese isolates. Most of the isolates were phenotypically resistant to tetracycline, erythromycin, and clindamycin and genotypic resistance was confirmed by the presence of ermA, ermB, tetM and tetO genes. Our study highlights the antimicrobial resistance profile and virulence-related factors contributing to the epidemiological spread of mastitis-causing S. agalactiae in China and Pakistan. The findings may facilitate future studies designed to develop improved treatment and control strategies against this pathogen. 

Keywords:  Streptococcus agalactiae         mastitis       epidemiology       virulence characterization       antibiotic resistance  
Received: 18 April 2022   Accepted: 09 September 2022

This study was supported by the National Key Research and Development Program of China (2021YFD1800400), the National Natural Science Foundation of China (31872480), the Jiangsu Agriculture Science and Technology Innovation Fund (CX(19)2020), and the Priority Academic Program Development of Jiangsu Higher Education Institutions, China (PAPD).

About author:  Ambreen LEGHARI, E-mail:; #Correspondence FAN Hong-jie, E-mail:

Cite this article: 

Ambreen LEGHARI, Shakeel Ahmed LAKHO, Faiz Muhammad KHAND, Khaliq ur Rehman BHUTTO, Sameen Qayoom LONE, Muhammad Tahir ALEEM, Iqra BANO, Muhammad Ali CHANDIO, Jan Muhammad SHAH, LIN Hui-xing, FAN Hong-jie. 2023. Molecular epidemiology, characterization of virulence factors and antibiotic-resistance profile of Streptococcus agalactiae isolated from dairy farms in China and Pakistan. Journal of Integrative Agriculture, 22(5): 1514-1528.

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