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Updated: Jun 27, 2025
A Fluorescence-based Method to Study Bacterial Gene Regulation in Infected Tissues
Published on: February 19, 2019
Molecular insights into expression and silencing of resistance determinants in Staphylococcus aureus
Muhammad Ijaz1, Muhammad Jawad Sabir1, Muhammad Umar Javed1
1Department of Veterinary Medicine, University of Veterinary and Animal Sciences, Lahore, Pakistan.
Objective:
This study aimed to investigate the status of antimicrobial-resistant strains of Staphylococcus aureus in Pakistan, their association in terms of co-occurrence with the biofilm-forming genes, resistance profiling and associated discrepancies in diagnostic methods.
Methodology:
A total of 384 milk samples from bovine was collected by using convenient sampling technique and were initially screened for subclinical mastitis, further preceded by isolation and confirmation of S. aureus. The S. aureus isolates were subjected to evaluation of antimicrobial resistance by phenotypic identification using Kirby-Bauer disc diffusion method, while the genotypic estimation was done by polymerase chain reaction to declare isolates as methicillin, beta-lactam, vancomycin, tetracycline, and aminoglycoside resistant S. aureus (MRSA, BRSA, VRSA, TRSA, and ARSA), respectively.
Results:
The current study revealed an overall prevalence of subclinical mastitis and S. aureus to be 59.11% and 46.69%, respectively. On a phenotypic basis, the prevalence of MRSA, BRSA, VRSA, TRSA, and ARSA was found to be 44.33%, 58.49%, 20.75%, 35.84%, and 30.18%, respectively. The results of PCR analysis showed that 46.80% of the tested isolates were declared as MRSA, 37.09% as BRSA, and 36.36% as VRSA, while the occurrence of TRSA and ARSA was observed in 26.31% and 18.75%, respectively. The current study also reported the existence of biofilm-producing genes (icaA and icaD) in 49.06% and 40.57% isolates, respectively. Lastly, this study also reported a high incidence of discrepancies for both genotypic and phenotypic identification methods of resistance evaluation, with the highest discrepancy ratio for the accA-aphD gene, followed by tetK, vanB, blaZ, and mecA genes.
Conclusion:
The study concluded that different antibiotic resistance strains of S. aureus are prevalent in study districts with high potential to transmit between human populations. The study also determined that there are multiple resistance determinants and mechanisms that are responsible for the silencing and expression of antibiotic resistance genes.
Insights
Antimicrobial-resistant Staphylococcus aureus strains, including methicillin-resistant S. aureus (MRSA), are prevalent in Pakistani bovine milk. These resistant strains, associated with biofilm genes, highlight potential transmission risks and diagnostic discrepancies.
Area of Science:
- Veterinary Microbiology
- Antimicrobial Resistance
- Molecular Epidemiology
Background:
- Subclinical mastitis in bovines is a significant concern in Pakistan.
- Staphylococcus aureus is a primary pathogen associated with bovine mastitis.
- Understanding antimicrobial resistance patterns is crucial for public health and animal welfare.
Purpose of the Study:
- To investigate the prevalence of antimicrobial-resistant Staphylococcus aureus in Pakistan.
- To determine the association between biofilm-forming genes and antimicrobial resistance.
- To identify discrepancies between genotypic and phenotypic resistance detection methods.
Main Methods:
- 384 bovine milk samples were collected and screened for subclinical mastitis.
- Staphylococcus aureus isolates were identified and subjected to antimicrobial susceptibility testing using the Kirby-Bauer disc diffusion method.
- Genotypic analysis using Polymerase Chain Reaction (PCR) was performed to detect specific resistance genes (e.g., mecA, blaZ, vanB, tetK, accA-aphD) and biofilm genes (icaA, icaD).
Main Results:
- The prevalence of subclinical mastitis and Staphylococcus aureus was 59.11% and 46.69%, respectively.
- Phenotypic resistance was high for methicillin-resistant S. aureus (MRSA) (44.33%), beta-lactam-resistant S. aureus (BRSA) (58.49%), and others.
- PCR confirmed significant proportions of MRSA (46.80%), BRSA (37.09%), and VRSA (36.36%), with biofilm genes (icaA, icaD) detected in 49.06% and 40.57% of isolates, respectively.
- High discrepancies were observed between genotypic and phenotypic resistance identification, particularly for the accA-aphD gene.
Conclusions:
- Antibiotic-resistant Staphylococcus aureus strains are prevalent in Pakistan, posing a potential risk for transmission to humans.
- Multiple resistance determinants and mechanisms contribute to the expression and silencing of antibiotic resistance genes.
- Discrepancies in diagnostic methods necessitate careful interpretation of resistance profiles.
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