Journal Article

Virulence genes and antibiotic resistance profiling of staphylococcus species isolated from mastitic dairy cows in and around Bahir dar, Ethiopia

Abebe, Laikemariam Teshome, Tarekegn, Habtamu Tassew, Belete, Mequanint Addisu, Tessema, Tesfaye Sisay, Azene, Bizuneh Tsehayneh, Getahun, Dessie Debeb

2025

Overview

Background Mastitis is one of the primary causes of economic and production losses in the dairy cattle industry. Bacterial infections are the most significant contributors to bovine mastitis, with Staphylococcus species among the most prevalent and challenging pathogens. This issue is especially severe in low- and middle-income countries, including Ethiopia, where a comprehensive understanding of Staphylococcus species in clinical and subclinical mastitis remains poorly understood. This is particularly true in the regions surrounding Bahir Dar, where comprehensive data on the genetic determinants of virulence and resistance in Staphylococcus species causing bovine mastitis are notably lacking. The lack of such molecular insights hampers the development of targeted therapeutic and preventive strategies for managing mastitis in the region. Therefore, the present study aimed to investigate the virulence gene profiles and antimicrobial resistance (AMR) patterns of Staphylococcus species isolated from mastitic dairy cows in and around Bahir Dar, Ethiopia. Methodology A cross-sectional study was conducted from March 2023 to December 2023 to investigate the molecular characteristics of Staphylococcus species and their antimicrobial resistance profiles in dairy cows with mastitis. A total of 150 lactating cows from 21 farms were included in the study, with 600 milk samples collected from the four-quarters of each cow. The samples were screened via the California mastitis test and physical examination. Staphylococcus species isolates were identified and single-plex PCR was used to detect virulence genes. The antimicrobial resistance profile of the isolates was determined via the Kary–Bauer disk diffusion method. Results The overall quarter-level mastitis incidence was 19.83% (119/600). Among 119 mastitis-positive samples, 80 samples were bacteriologically confirmed to harbor  Staphylococcus species with eight different Staphylococcus species, of which  Staphylococcus chromogenes  was the most prevalent isolate (19%), followed by  S. aureus, S. hyicus  and  S . epidermidis  (15%) , S. hemolyticus  (11%) ,   S. simulans  and  S. xylosus  (10%), and  S. intermedius  (5%). Seven distinct virulence genes were identified with varying frequencies :  Coa (35%), seb (33.33%), mecA (31.67%), icaD (31.67%), Hla (20%), Hlb (10%), and sea (8.3%). The icaD and seb genes were observed in all 8 species with respective percentages ( S. hemolyticus (62.5, 37.5), S. aureus ( 44.44, 55.55),  S. hyicus (44.44, 44.44), S. epidermidis 2 (22.22, 44.44), chromogenes (9.1, 9.1), S. intermidius (33.33, 33.33), S. simulance (16.67, 16.67) and S. xylosus (16.67, 16.67). Both the Hla and Hlb genes were detected in the same three distinct species, with percentages of S. aureus (44.44; 22.22%), S. hemolyticus (42.5; 25%) and S. hyicus (55.55; 22.22). S. aureus exhibited the highest proportion of mecA-positive isolates, with 6 out of 9 isolates (66.67%) carrying the gene. All the isolated Staphylococcus species were 100% resistant to penicillin, and except for S. chromogenes and S. xylosus,  the remaining 6 species of Staphylococcus also exhibited 100% resistance to tetracycline. Among all MDR isolates, 6/9 (66.7%)  S. aureus,  (5/8; 62.5%)  S. hemolyticus,  and (6/9; 66.7%)  S. hyicus  were resistant to up to seven classes of antibiotics. A lower frequency of MDR isolates was detected among  S. simulans and S. xylosus (both at 2/6; 33.33%), resistant to up to five antibiotics. Conclusions Among the identified Staphylococcus species, S. chromogenes emerged as the dominant isolate. All eight isolated species harbored two or more virulence genes, with nearly one-third of the isolates carrying the mecA gene, underscoring their pathogenic potential in causing bovine mastitis. Furthermore, all the Staphylococcus isolates in this study were resistant to penicillin and were multidrug resistant.

• Publisher: BioMed Central,BioMed Central Ltd,Springer Nature B.V,BMC
• Subject: Animal lactation / Animals / Anti-Bacterial Agents - pharmacology / Antibiotic resistance / Antibiotics / Antimicrobial agents / Antimicrobial resistance / Bacterial diseases / Biological Microscopy / Biomedical and Life Sciences / Bovine mastitis / California mastitis test / Cattle / Causes of / Cross-Sectional Studies / Dairy cattle / Dairy farming / Dairy farms / Dairy industry / Diseases / Drug resistance / Drug resistance in microorganisms / Drug Resistance, Bacterial - genetics / Ethiopia - epidemiology / Female / Genes / Genetic aspects / Histocompatibility antigen HLA / Identification and classification / Life Sciences / Mastitis / Mastitis, Bovine - epidemiology / Mastitis, Bovine - microbiology / MDR / MecA protein / Microbial Sensitivity Tests / Microbiology / Milk / Milk - microbiology / Milk production / Multidrug resistance / Mycology / Parasitology / Pathogens / Penicillin / Risk factors / Species / Staphylococcal infections / Staphylococcal Infections - microbiology / Staphylococcal Infections - veterinary / Staphylococcus / Staphylococcus - drug effects / Staphylococcus - genetics / Staphylococcus - isolation & purification / Staphylococcus - pathogenicity / Staphylococcus species / Toxins / Virology / Virulence / Virulence (Microbiology) / Virulence - genetics / Virulence Factors - genetics / Virulence genes