Prevalence, antimicrobial susceptibility profiles and resistant gene identification of bovine subclinical mastitis pathogens in Bangladesh

TNFRSF1A and NCF1 May Act as Hub Genes in Mastitis

BACKGROUND

Bovine mastitis (BM) is a major source of morbidity among cattle, imposing a significant burden on the dairy industry. Understanding the molecular mechanisms that confer susceptibility to bovine mastitis offers potential for therapeutic targeting, but these mechanisms remain complex and incompletely understood.

OBJECTIVES

This study aims to identify key molecular players and regulatory networks involved in bovine mastitis by integrating multiple expression datasets and applying network analysis.

METHODS

We integrated data from three BM expression datasets and applied weighted gene co-expression network analysis (WGCNA) to identify specific modules and hub genes related to BM. Within the module that best correlated with mastitis, we constructed a network of mRNA-miRNA and protein-protein interactions.

RESULTS

Our analysis revealed that TNFRSF1A and NCF1 are implicated as hub genes in the host's immune response to BM. Additionally, we identified bta-mir-2881 as a potential regulator of both TNFRSF1A and NCF1. These genes are crucial in regulating the immune response and defence against bacterial infections, highlighting their importance in mastitis susceptibility.

CONCLUSION

Identifying miRNAs like bta-mir-2881 that may target key genes involved in mastitis susceptibility can shed light on the molecular mechanisms underlying the disease. This provides new targets for BM prevention and treatment, potentially alleviating the significant burden of the disease on the dairy industry.

Subclinical Mastitis in Small-Holder Dairy Herds of Gansu Province, Northwest China: Prevalence, Bacterial Pathogens, Antimicrobial Susceptibility, and Risk Factor Analysis

This cross-sectional study assessed the prevalence, bacterial distribution, antimicrobial susceptibility, and potential risk factors associated with subclinical mastitis (SCM) in small-holder dairy herds in Gansu Province, Northwest China. Forty small-holder cow farms were randomly selected from eight cities/counties in six districts of Gansu Province, and a total of n = 530 lactating cows were included in this study. SCM prevalence was noted at 38.87% and 9.72% at the cow and quarter levels, respectively, based on the California Mastitis Test (CMT). The prevalence of the recovered bacterial species was noted as follows: S. agalactiae (36.02%), S. aureus (19.43%), coagulase-negative staphylococci (CNS) (16.11%), S. dysgalactiae (12.80%), E. coli (9.00%), and S. uberis (6.64%). All isolated bacteria were 100% multi-drug-resistant (MDR) except S. aureus (87.8% MDR). Antimicrobial susceptibility profiles revealed the increased resistance (>85%) of these pathogens to penicillin, streptomycin, trimethoprim-sulfamethoxazole, vancomycin, and erythromycin. However, these pathogens showed increased susceptibility to ampicillin, amoxicillin-sulbactam, ceftazidime, neomycin, kanamycin, spectinomycin, norfloxacin, ciprofloxacin, and doxycycline. The multivariate regression analysis demonstrated that old age, high parity, late lactation, lesions on teats, previous history of clinical mastitis, higher milk yield, and milking training were found to be potential risk factors (p < 0.001) associated with developing SCM in small-holder dairy cows in Gansu Province, China. These findings highlight the need for routine surveillance, antimicrobial stewardship, and effective preventive strategies to mitigate SCM in small-holder dairy production and their possible impacts, i.e., increased antimicrobial resistance and infection, on public health.

A novel diagnostic technique for diagnosis of Staphylococcus aureus subclinical mastitis using gold nanoparticle-based ELISA

Background

Bovine subclinical mastitis (SCM) is a significant cause of economic losses in dairy farms, primarily due to its asymptomatic nature and difficulty in early detection. The enzyme-linked immunosorbent assay (ELISA) is a widely used diagnostic tool in bioscience, facilitating antigen detection through antibody binding.

Aim

The present study designed a gold nanoparticle (AuNPs)-based ELISA, to enhance the sensitivity of conventional ELISA by improving the binding efficiency of capture antibodies to purified antigens. This modified ELISA could enable more accurate detection of bovine SCM.

Methods

A total of 200 milk samples from apparently healthy cows were screened for SCM using the California Mastitis Test (CMT). Positive samples were then subjected to bacteriological culture, biochemical testing, and polymerase chain reaction targeting the Nuc2 gene for confirmation of S. aureus. The purified fraction antigen of all 78 confirmed S. aureus isolates was extracted using sepharose 4B affinity column chromatography, described by SDS-polyacrylamide gel electrophoresis, and assessed for its sensitivity in S. aureus mastitis diagnosis compared with crude antigen and purified fraction antigen-conjugated gold nanoparticles within an indirect ELISA. Immunoglobulins (IGs) from positive cow serum were extracted and purified from all confirmed S. aureus. Gold nanoparticle-based indirect ELISA was used on 400 samples (200 milk and 200 serum) from the same cows.

Results

Using CMT, out of 200 examined milk samples from apparently normal cows, 65% (130/200) were sub-clinically infected. Out of these 130 positive milk samples, 60% (78/130) were confirmed to be infected with S. aureus. Purified fraction antigen-conjugated gold nanoparticles achieved the highest sensitivity to ELISA at 97%, 94%, and 92% immediately before storage, 6 months at -20°C, and 1 year at -20°C, respectively. Gold nanoparticle-based indirect ELISA detected specific IgG antibodies in 97% (76/78) sera and milk samples related to confirmed S. aureus isolates.

Conclusion

The utilization of purified fraction antigen with gold nanoparticles enhances the sensitivity of ELISA, increasing it from 83.3% to 97% (p < 0.01; CI: 99%). The current study establishes a valuable way for S. aureus mastitis diagnosis within the use of purified fraction antigen-conjugated gold nanoparticles instead of the classical way to improve the sensitivity and specificity of ELISA.

Isolation and antimicrobial resistance patterns of Staphylococcus aureus and Escherichia coli from caprine respiratory tract infections: A hospital-based clinical study

Objective

Staphylococcus aureus and Escherichia coli are the most common opportunistic pathogens frequently associated with respiratory tract infection (RTI) in different animals. This cross-sectional study aimed to identify the occurrence of S. aureus and E. coli in goats with RTI, analyze the antimicrobial resistance patterns, and explore potential risk factors contributing to RTI.

Materials and Methods

A total of 120 nasal swab samples were collected from goats, and standard classical bacteriological methods were performed to isolate and identify S. aureus and E. coli. Subsequently, the disc diffusion method was employed to evaluate the antimicrobial sensitivity test. A logistic regression model was used to analyze the factors associated with RTI.

Results

About 13.3% (N = 16; N = 120) isolates were confirmed as S. aureus, and 6.67% (N = 8; N = 120) isolates were confirmed as E. coli. All S. aureus isolates were resistant to ampicillin, and all E. coli isolates were resistant to amoxicillin and penicillin. Among the isolated organisms, 43.7% (N = 7; N = 16) S. aureus and 62.5% (N = 5; N = 8) E. coli isolates were found to be multidrug-resistant (resistant to ≥3 classes of antimicrobials). Multivariable logistic regression analysis revealed that female goats [(odds ratio) OR: 4.2; 95% confidence intervals (CI): 0.8-20.8; p = 0.074] and goats in poor health condition (OR: 3.8; 95% CI: 0.7-19.3; p = 0.100) were more prone to RTI caused by S. aureus. Besides, goats that were not dewormed (OR: 4.8; 95% CI: 1-23.6; p = 0.051) and those reared in semi-intensive conditions (OR: 2.7; 95% CI: 0.8-8.7; p = 0.092) were found to be at higher risk of S. aureus-mediated RTI.

Conclusion

The findings highlight the importance of implementing improved farm management practices and efficient antimicrobial resistance control approaches to minimize respiratory infections and reduce the burden of antibiotic resistance in goats.

Prevalence, Risk Factors, and Antimicrobial Resistance of Staphylococcus and Streptococcus Species Isolated from Subclinical Bovine Mastitis

Subclinical mastitis (SCM) is a prevalent serious disease among dairy cows worldwide. It poses a significant challenge to the dairy industry, animal welfare, and a threat to public health. The present study aimed to investigate the molecular detection, prevalence, and antimicrobial resistance of Staphylococcus spp. and Streptococcus spp. isolated from raw composite milk samples obtained from SCM dairy cattle in Bangladesh. A total of 612 quarters milk samples obtained from 153 cows were analyzed for SCM using the California Mastitis Test. Bacterial isolation and identification were carried out and bacterial species were confirmed using molecular polymerase chain reaction methods. Antimicrobial susceptibility testing was performed using disc diffusion method. The findings revealed that the prevalence of SCM was 70.3% (26/37), 35.95% (55/153), and 23.04% (141/612) in the herd, cow, and quarter levels, respectively. Among the positive samples, 92.7% (51/55) were Staphylococcus spp. (S. aureus, S. chromogenes, and S. simulans) and the remaining isolates were 7.3% (4/55) Streptococcus spp. (Streptococcus agalactiae and Streptococcus dysgalactiae). The most prevalent species was S. chromogenes, accounting for 67.3% (37/55). Antimicrobial susceptibility testing showed that 65.5% of isolates were susceptible to cefoxitin, whereas, 89.1% were resistant to penicillin. Overall, 12 isolates (21.8%) out of 55 were resistant to more than three classes of antimicrobials and were defined as multidrug-resistant isolates. Methicillin-resistance gene was detected in 61.1% of the cefoxitin-resistant isolates. A multivariate logistic regression analysis identified five potential risk factors including the lack of post-milking teat disinfection (OR: 3.06), absence of immediate feeding after milking (OR: 9.81), poor udder hygiene (OR: 7.83), tick infestation (OR: 13.76), and absence of dry cow therapy (OR: 3.31). The findings of the current study underscore the urgent requirement for targeted interventions, considering the identified factors to effectively manage and control SCM in dairy cows.

Molecular Epidemiology and Antimicrobial Resistance of Extended-Spectrum β-Lactamase (ESBL)-Producing Klebsiella pneumoniae in Retail Cattle Meat

Enterobacteriaceae that produce extended-spectrum β-lactamases (ESBLs) can result in severe human infections, contributing to the development of complex diseases. Klebsiella pneumoniae is one of the ESBL-producing pathogens that helps to set antimicrobial resistance as a major public health problem worldwide. The current study aimed to isolate, identify, and characterize ESBL-producing K. pneumoniae and their antimicrobial resistance pattern in retail cattle meat samples. A comprehensive set of 225 cattle meat samples was gathered from 13 upazilas within the Sylhet district of Bangladesh. The bacterial isolates were obtained through biochemical and cultural techniques, and the identification of K. pneumoniae was accomplished using polymerase chain reactions (PCRs). Antimicrobial susceptibilities were assessed using disk diffusion in accordance with the Clinical and Laboratory Standards Institute (CLSI, 2020) guidelines. Genes encoding ESBL enzymes were detected by the double-disk synergy test (DDST) and multiplex PCR. The overall prevalence of Klebsiella spp. was 28.89% (65/225), whereas the positive percentage of K. pneumoniae was 59.2% (29/49) confirmed by PCR. Antimicrobial resistance was observed against 12 antibiotics. According to the phenotypic resistance pattern determined through the disk diffusion method, all isolates (100%) were resistant to ampicillin, amoxicillin, cefuroxime, cefotaxime, and colistin. On the other hand, the highest susceptibility was observed towards gentamicin (97.95%), followed by ciprofloxacin (85.71%), tetracycline (83.67%), and trimethoprim-sulfamethoxazole (81.63%). Out of the total K. pneumoniae isolates analyzed, ESBL genes were present, and the highest percentage, 82.8% (24/29), tested positive for bla TEM genes. Interestingly, among the nine ESBL genes, six were identified in K. pneumoniae isolates, except for bla OXA, bla CTX-M-grp2, and MultiCase DHA. The study's results reveal the presence of extended-spectrum β-lactamase (ESBL)-producing multidrug-resistant (MDR) K. pneumoniae in retail cattle meat samples posing a substantial public health threat.