Drug repurposing strategy: An emerging approach to identify potential therapeutics for treatment of bovine mastitis

Exploring evolutionary perspectives and antibiogram analysis of biofilm-forming Staphylococcus aureus in goat mastitis

Biofilm formation plays a key role in developing antimicrobial resistance in Staphylococcus aureus (S. aureus) and is thus a major virulence factor responsible for persistent intramammary infections and subclinical mastitis in goats. The current study investigated the prevalence and molecular characterization of biofilm-forming S. aureus isolated from goat mastitis, the associated risk factors, and comparative antibiogram profiling. A total of 768 milk samples were conveniently collected from farms dairy goats in three districts of Pakistan Multan, Bahawalpur, and Rahim Yar Khan. The results revealed a molecular prevalence (presence of nuc gene) of 206/426 (48.37%) for S. aureus in milk samples from goats. The risk factors analysis showed that age group, water availability, previous mastitis history, hygienic measures during milking, teat lesion, and veterinary services posed significant associations with S. aureus intramammary infections in goats. The prevalence of biofilm production by phenotypic methods i.e. Congo Red agar and Microtitre plate were recorded to be 36.90% and 27.67% respectively. In comparison, the genotypic confirmation was done by the presence of the icaA gene and was found to be 55.34%. The phylogenetic analysis of the icaA gene revealed high homology between sequences of study isolates and the isolates of other countries like India, Egypt, Japan Kenya, the USA, and China. The S. aureus subjected to the Kirby-Bauer disc diffusion method revealed the highest resistance to cefoxitin and oxytetracycline followed by gentamycin, amikacin, trimethoprim + sulphamethoxazole, and vancomycin. There was a slight variation among the resistant profile of biofilm and non-biofilm producing S. aureus strains against antimicrobial agents. Out of 206, 31.07% (64/206) tested isolates exhibited resistance to three or more antibiotics concurrently, categorizing them as multiple drug resistant (MDR) with multiple antibiotic resistance index greater than 0.2. The study concluded that biofilm-producing S. aureus is prevalent in dairy goats of different breeds, including Beetal, Teddi, Barbari, and Makhi-cheeni, across various lactation stages (early, mid, and late), regardless of milk collection times in Pakistan of Pakistan with risk to the udder health and milk quality. Moreover, the biofilm formation may be associated with multidrug resistance of study isolates.

Molecular epidemiology and antibiotic resistance profiling of Staphylococcus aureus isolates from camel mastitis

Mastitis is considered one of milk-producing animals' most widespread infectious diseases. The present study evaluated the prevalence of antibiotic-resistant isolates of Staphylococcus aureus (S. aureus) including methicillin-resistant S. aureus (MRSA), β-lactam-resistant S. aureus (BRSA), aminoglycoside-resistant S. aureus (ARSA), and tetracycline-resistant S. aureus (TRSA) from the udder of dromedary camels along with the associated risk factors and the antibiogram of resistant isolates. Phylogenetic analysis of antibiotic-resistant genes with NCBI sequences was performed to check their homology. A total of 384 milk samples were collected and subjected to standard microbiological procedures to isolate S. aureus. The results revealed that 177 milk samples were found positive for subclinical mastitis (SCM) out of which 101 milk samples were found positive for S. aureus. The molecular assay found the prevalence of MRSA, BRSA, ARSA, and TRSA as 48.51 %, 46.53 %, 42.57 %, and 39.60 % by targeting the mecA, blaZ, accA-aphD, and tetK genes respectively. The study isolates significant similarities to each other and to previously reported sequences from other countries that were found by in-silico analysis, indicating the possibility of pathogen transboundary transmission. This study also revealed potential risk factors that aid in the spread of mastitis in camels. Among various risk factors, the most significant were farm hygiene, physiological status of animals, type of mastitis, teat injury, use of teat dips, and milk leakage (p < 0.05). The antibiogram of antibiotic-resistant isolates of S. aureus revealed that the highest resistance was observed against penicillin followed by amoxicillin and oxytetracycline while levofloxacin was the most sensitive drug. This study highlights the high prevalence of antimicrobial-resistant S. aureus in camel mastitis. Identified risk factors provide valuable insights into management practices that contribute to disease occurrence, aiding in the development of targeted control strategies. Additionally, antimicrobial susceptibility findings offer guidance for optimizing treatment protocols to effectively manage S. aureus-induced mastitis in camels and mitigate the spread of antimicrobial resistance.

Genetic basis of antibiotic resistance in bovine mastitis and its possible implications for human and ecological health

Bovine mastitis is a mammary gland inflammation that can occur due to infectious pathogens, Staphylococcus aureus and Escherichia coli, which are, respectively, the most prevalent Gram-positive and Gram-negative bacteria associated with this disease. Currently, antibiotic treatment has become more complicated due to the presence of resistant pathogens. This review, therefore, aims to identify the most common resistance genes reported for these strains in the last four years. During the review, it was noted that blaZ, blaSHV, blaTEM, and blaampC are the most reported genes for S. aureus and E. coli, associated with drug inactivation, mainly β-lactamases. They are characterized by generating bacterial resistance to β-lactam antibiotics, the most common treatment in animal and human bacterial treatments (penicillins and cephalosporins, among others). Genes associated with efflux systems were also present in the two strains and included norA, tetA, tetC, and tetK, which generate resistance to macrolide and tetracycline antibiotics. Additionally, the effects of spreading resistance between animals and humans through direct contact (such as consumption of contaminated milk) or indirect contact (through environmental contamination) has been deeply discussed, emphasizing the importance of having adequate sanitation and antibiotic control and administration protocols.

Antimicrobial resistance, virulence profiling, and drug repurposing analysis of Staphylococcus aureus from camel mastitis

Camel mastitis especially caused by Staphylococcus aureus (S. aureus), is a major risk to animal health and milk production. The current investigation evaluated the antibiotic susceptibility and virulence factors of S. aureus isolates from subclinical mastitis in camels. A total of 384 milk samples were collected and submitted to isolate S. aureus. The S. aureus isolates exhibiting resistance to Penicillin and Cefoxitin disc on Kirby-Bauer disc diffusion method were considered as β-lactam resistant S. aureus (BRSA) and methicillin-resistant S. aureus (MRSA) which were further confirmed by PCR targeting blaZ and mecA genes, respectively. The results showed that S. aureus was found in 57.06% of subclinical (SCM) positive camel milk samples. A high molecular prevalence of BRSA and MRSA were found to be 48.51% and 46.53% respectively depicting that treating these infections is challenging due to their high resistance levels. The phylogenetic analysis revealed a significant resemblance of the study isolates with each other and with already reported sequences from different countries which shows the potential for the spread of pathogen. Virulence profiling of antibiotic resistance strains showed the presence of virulence markers (nuc and coag genes), intercellular adhesion genes (icaA, icaD), Panton-Valentine leukocidin (pvl) gene, and enterotoxin-producing genes including sea, seb, sec, and sed. In-vitro antibiotic susceptibility testing revealed that the most resistant antibiotic group was penicillin followed by aminoglycosides and cephalosporins. Drug repurposing analysis of different non-antibiotics for combination therapies with resistant antibiotics was done to combat the S. aureus isolates harboring the mecA and blaZ genes. The results revealed the synergistic effect of amoxicillin, sulfamethoxazole, gentamicin, and doxycycline with ketoprofen, amikacin with flunixin meglumine, and gentamicin with N-acetylcysteine (NAC) against study isolates. The current investigation provides the status of antibiotic-resistant strains and virulence factors of S. aureus in the udder of dromedary camels. The combinational therapy of resistant antibiotics with non-antibiotics provides a potential therapeutic option for the treatment of resistant strains.

Molecular insights into antimicrobial resistant Staphylococcus aureus strains: A potential zoonosis of goat origin

Antimicrobial-resistant (AMR) Staphylococcus aureus (S. aureus) strains have attained global attention due to their life-threatening zoonotic nature. Being a member of ESKAPE group, S. aureus has an ability to escape the biocidal action of antimicrobial drugs. The current study investigated the prevalence and molecular characterization of methicillin-resistant S. aureus (MRSA), β-lactam-resistant S. aureus (BRSA), aminoglycoside-resistant S. aureus (ARSA), tetracycline-resistant S. aureus (TRSA), and fluoroquinolones-resistant S. aureus (FRSA) associated with goat subclinical mastitis (SCM). Furthermore, the antimicrobial resistance and susceptibility profile of various antibiotics and non-antibiotics (NSAIDs, nisin, N-acetylcysteine, vitamin-C) along with their possible role in modulating the antibiotic resistance of MDR isolates was also investigated. A total of 768 goat milk samples were subjected to California mastitis test for SCM followed by bacteriological and molecular characterization of S. aureus. Moreover, in-vitro susceptibility of resistant antibiotics, non-antibiotics, and their combination against MDR S. aureus were conducted through well diffusion and broth microdilution assays. The results depicted that 55.47 % and 26.82 % of milk samples were positive for SCM and S. aureus, respectively. The molecular assay confirmed 35.92 % of isolates as MRSA, 45.63 % as BRSA, 50.49 % as ARSA, and 32.52 % but no isolate was confirmed as FRSA on molecular basis. The multidrug resistance was observed in 62.13 % and 47.09 % isolates, respectively. Molecular characterized MDR S. aureus revealed high homology of study isolates with the isolates of neighboring countries like India, Korea, Iran, and China. Antimicrobial susceptibility trials on well diffusion assay showed higher efficacy of different non-antibiotics with resistant antibiotics as penicillin with ketoprofen and gentamicin with flunixin meglumine while oxytetracycline with N-acetylcystiene. The synergy testing by checkerboard assay revealed synergistic activity of penicillin with ketoprofen, gentamicin with flunixin meglumine, and oxytetracycline with N-acetylcysteine. The current study highlighted the emergence and spread of AMR S. aureus strains from goat SCM and provided insights into possible drug repurposing of various non-antibiotics to modulate the multidrug resistance of S. aureus which will be helpful in devising the therapeutic options and control measures for this pathogen.

Molecular insights into expression and silencing of resistance determinants in Staphylococcus aureus

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.

Repurposing of non-steroidal anti-inflammatory drugs for combination therapies to combat multidrug-resistant S. aureus of bovine reproductive tract origin

Multidrug-resistant bacteria have become the predominant etiology in bovine female reproductive tract infections and thus require effective treatment approaches. The main goal of this study was the molecular detection of mecA, blaZ, tetK, and aacA-aphD genes in Staphylococcus aureus (S. aureus) responsible for methicillin, beta-lactam, tetracycline, and aminoglycoside resistance respectively. Phylogenetic analysis was conducted to check the homology of staphylococcal genes with NCBI sequences. The in-vitro efficacy of non-steroidal anti-inflammatory drugs (NSAIDs) in combination therapies against MDR S. aureus was evaluated using well diffusion assay and checkerboard method. Vaginal swab samples (n = 384) collected from bovines suffering from endometritis, pyometra, and retained placenta were tested for S. aureus. Results showed a 17.96% overall prevalence. Both phenotypic and genotypic resistance was observed among S. aureus isolates with 50.72% and 37.68% isolates being confirmed as methicillin-resistant (MRSA), 36.23% and 18.84% isolates exhibiting beta-lactam, 40.58%, and 27.54% isolates showing tetracycline, and 33.33% and 36.23% isolates showing aminoglycosides resistance based on disc diffusion and gene confirmation, respectively. Phylogenetic analysis indicated homology with previously reported Pakistani isolates suggesting the possibility of MDR S. aureus transmission within and between animals. Synergy testing indicated that combinations of ceftriaxone-ketoprofen (153.77%), ceftriaxone-meloxicam (149.55%), amoxiclav-flunixin meglumine (106.06%), and oxytetracycline-flunixin meglumine (104.47%) showed synergy on well diffusion assay. Based on the fractional inhibitory concentration index by checkerboard method, oxytetracycline-meloxicam and gentamicin-ketoprofen combinations exhibited synergistic interaction. In conclusion, MDR S. aureus resistance was mitigated in-vitro through the combination of antibiotics (oxytetracycline, gentamicin) with NSAIDs (meloxicam, ketoprofen) that could be used to create therapeutic strategies for bovine reproductive issues.

Genotypic insights to Panton-Valentine leukocidin positive methicillin-resistant Staphylococcus aureus isolated from cattle mastitis

In this research communication we investigate the prevalence and antimicrobial susceptibility of S. aureus harboring virulent genes responsible for mastitis in cattle of Punjab, Pakistan. A total of 690 milk samples were collected from commercial dairy farms for analysis of the prevalence of subclinical and clinical mastitis and isolation of S. aureus. Virulence ability and methicillin resistance in S. aureus (MRSA) was determined by targeting the pvl (the gene for Panton-Valentine leukocidin) and mecA genes, respectively. A total of 175 S. aureus isolates exhibiting prevalence of pvl gene (6.28%) and mecA gene (22.28%) were determined. Antimicrobial susceptibility testing of pvl positive and negative MRSA against different classes of antibiotics revealed 100% resistance against β-lactams while 100% sensitivity towards tylosin and linezolid.

First report on genotypic estimation of MRSA load in udder of nomadic sheep flocks affected with subclinical mastitis in Pakistan

Mastitis is one of the highly devastating issues responsible for production and economic losses in all dairy animals including sheep. This study was designed to investigate subclinical mastitis (SCM) associated with S. aureus in lactating nomadic ewes, along with the associated risk factors analysis. Furthermore, molecular characterization and antibiogram profiling of local methicillin-resistant S. aureus (MRSA) isolates of ovine origin were also performed. A total of 384 milk samples (n = 384) were collected from 13 nomadic sheep flocks using a convenient sampling technique. SCM was evaluated using a Surf Field Mastitis test and the S. aureus was isolated using standard microbiological techniques. Kirby-Bauer disc diffusion assay was used for phenotypic identification of MRSA while the mecA gene was tested through PCR. Study results revealed that SCM was prevalent at 34.37% while S. aureus association was recorded at 39.39%. MRSA prevalence was 36.53% and 21.15% using phenotypic and genotypic tests, respectively. The mecA gene sequences of study isolates showed maximum resemblance with already reported sequences from Pakistan, China, and Myanmar. MRSA isolates showed maximum resistance towards penicillin, ceftriaxone sodium, and trimethoprim + sulphamethoxazole while gentamicin, ciprofloxacin, and tylosin showed maximum efficacy. Risk factors analysis revealed that various flock management, housing, and host-related factors positively influenced the incidence of S. aureus-associated SCM. This study is the first report on the prevalence of S. aureus and MRSA associated with SCM in lactating ewes in Pakistan. This study will help to devise effective treatment and control strategies for S. aureus-associated SCM.

On-farm epidemiology, virulence profiling, and molecular characterization of methicillin-resistant Staphylococcus aureus at goat farms

Antimicrobial resistance (AMR) becomes a challenging issue that limits the therapeutic options for both veterinary and public health professionals. The current study aimed to investigate the on-farm epidemiology, antibiotics resisting profiling, virulence analysis, and molecular detection of methicillin-resistant Staphylococcus aureus (MRSA) at the caprine-human interface. A total of 768 goat milk samples and 94 skin swabs from farm personnel were collected from 30 goat flocks and processed for isolation of S. aureus. The study isolates were confirmed as MRSA based on the oxacillin and cefoxitin disc diffusion test and the presence of mecA gene. MRSA isolates of goats and human origin were characterized and further evaluated for the presence of virulence genes responsible for intramammary infections and public health hazards. The results revealed 26.82 % and 27.79 % goat milk samples and human samples positive for S. aureus, respectively. A higher MRSA prevalence of 35.92 % and 10.71 % was found in goat and human isolates respectively. The phylogenetic analysis revealed a lesser extent of homology in mecA gene of S. aureus isolates at the caprine-human interface. Moreover, this study revealed strong evolutionary connection between the study isolates and MRSA isolates of Pakistani cattle and buffalo while the in-silico protein analysis showed that all sequences have the same protein motifs resembling penicillin binding protein 2a. The risk factors analysis revealed that teat length, drainage system, hygienic measures during milking, use of teat dip, teat injury, and veterinary services were significantly associated with subclinical mastitis in goats. A total of 43.24 % of local MRSA isolates showed multi-drug resistance (MDR). The isolates showed higher resistance to oxytetracycline followed by gentamicin and vancomycin while moxifloxacin, and linezolid were among the susceptible antibiotics. Local MRSA isolates carried virulence markers (nuc and coag genes) and biofilm-associated icaA (43.24 %) and icaD (29.73 %) genes which are responsible for the intramammary infection. The local isolates also carried the virulence genes of public health concern including the enterotoxin C (sec) gene (24.3 %), enterotoxins B (seb) gene (5.41 %), and enterotoxin D (sed) gene (2.7 %). Enterotoxins A (sea) and E (see) genes were not detected in any isolate. The study concluded that MRSA is an emerging and prevailing pathogen in dairy goats with a high potential to transmit to associated human beings. The presence of a variety of virulence factors as well as the associated antibiotic resistance makes MRSA a potential threat at animal-human interface and thus demands further research.

Alternatives to antibiotics for treatment of mastitis in dairy cows

Mastitis is considered the costliest disease on dairy farms and also adversely affects animal welfare. As treatment (and to a lesser extent prevention) of mastitis rely heavily on antibiotics, there are increasing concerns in veterinary and human medicine regarding development of antimicrobial resistance. Furthermore, with genes conferring resistance being capable of transfer to heterologous strains, reducing resistance in strains of animal origin should have positive impacts on humans. This article briefly reviews potential roles of non-steroidal anti-inflammatory drugs (NSAIDs), herbal medicines, antimicrobial peptides (AMPs), bacteriophages and their lytic enzymes, vaccination and other emerging therapies for prevention and treatment of mastitis in dairy cows. Although many of these approaches currently lack proven therapeutic efficacy, at least some may gradually replace antibiotics, especially as drug-resistant bacteria are proliferating globally.

Molecular evidence of β-lactam resistant Staphylococcus aureus in equids with respiratory tract infections: Frequency and resistance modulation strategy

The emergence of antimicrobial-resistant strains in Staphylococcus aureus (β-lactam and methicillin-resistant) is an overwhelming issue worldwide. Using the purposive sampling technique, 217 equids samples were collected from district Layyah which were subjected to culturing followed by genotypic identification of mecA and blaZ genes by PCR. This study revealed that by phenotypic methods, a prevalence of 44.24%, 56.25%, and 47.92% was found for S. aureus, MRSA, and β-lactam resistant S. aureus in equids. While genotypically, MRSA was found in 29.63% and β-lactam resistant S. aureus in 28.26% of equids. In-vitro antibiotic susceptibility testing against S. aureus isolates harboring both mecA and blaZ genes showed a high resistance against Gentamicin (75%), followed by Amoxicillin (66.67%) and Trimethoprim+sulfamethoxazole (58.34%). In an attempt to re-sensitize the resistant bacteria to antibiotics, a combination of antibiotics and non-steroidal anti-inflammatory drugs (NSAIDs) was used which revealed synergistic effect of Gentamicin and Trimethoprim+sulfamethoxazole with Phenylbutazone; and Amoxicillin with Flunixin meglumine. Analysis of risk factors revealed significant association with the S. aureus-associated respiratory infection in equids. Phylogenetic analysis of mecA and blaZ genes showed a high resemblance of study isolate's sequences with each other and variable resemblance with already reported isolates obtained from different samples of neighboring countries. This study reports the first molecular characterization and phylogenetic analysis of β-lactam and methicillin resistant S. aureus in equids in Pakistan. Moreover, this study will help in the resistance modulation of resistant antibiotics (Gentamicin, Amoxicillin, Trimethoprim+sulfamethoxazole) and provide a good insight into planning an effective therapeutic regime.

Tea Polyphenols Protect the Mammary Gland of Dairy Cows by Enhancing Antioxidant Capacity and Regulating the TGF-β1/p38/JNK Pathway

Tea polyphenols (TPs) are the main active substances in tea and they have many beneficial effects, such as anti-inflammation, antioxidant, anti-cancer and metabolic regulation effects. The quality of milk is affected by mammary gland diseases and there are substantial economic losses resulting from reduced milk production as a consequence of inflammatory injury of the mammary gland. In this study, transcriptome analysis and molecular biology techniques were used to study the effects of TPs on inflammatory injury of the mammary gland. After intervention with TPs, a total of 2085 differentially expressed genes were identified, including 1189 up-regulated genes and 896 down-regulated genes. GO analysis showed that differentially expressed genes played an important role in proton transmembrane transport, oxidation-reduction reactions and inflammatory response. KEGG enrichment suggested that differential genes were concentrated in the TGF-β pathway and active oxygen metabolism process. Experiments were performed to confirm that TPs increased SOD, CAT, T-AOC and GSH-Px content along with a reduction in MDA. Meanwhile, TPs inhibited the expression of TGF-β1 and reduced the phosphorylation of p38 and JNK. The expression of inflammatory cytokines IL-1β, IL-6 and TNF-α were significantly decreased after intervention with TPs. In summary, all the data indicated that TPs protected the mammary gland by enhancing the antioxidant capacity and down-regulating the TGF-β1/p38/JNK pathway.