mec-A-mediated Resistance in Staphylococcus aureus in a Referral Hospital, Tehran, Iran

DNA Nanoflower Eye Drops with Antibiotic-Resistant Gene Regulation Ability for MRSA Keratitis Target Treatment

Methicillin-resistant Staphylococcus aureus (MRSA) biofilm-associated bacterial keratitis is highly intractable, with strong resistance to β-lactam antibiotics. Inhibiting the MRSA resistance gene mecR1 to downregulate penicillin-binding protein PBP2a has been implicated in the sensitization of β-lactam antibiotics to MRSA. However, oligonucleotide gene regulators struggle to penetrate dense biofilms, let alone achieve efficient gene regulation inside bacteria cells. Herein, an eye-drop system capable of penetrating biofilms and targeting bacteria for chemo-gene therapy in MRSA-caused bacterial keratitis is developed. This system employed rolling circle amplification to prepare DNA nanoflowers (DNFs) encoding MRSA-specific aptamers and mecR1 deoxyribozymes (DNAzymes). Subsequently, β-lactam antibiotic ampicillin (Amp) and zinc oxide (ZnO) nanoparticles are sequentially loaded into the DNFs (ZnO/Amp@DNFs). Upon application, ZnO on the surface of the nanosystem disrupts the dense structure of biofilm and fully exposes free bacteria. Later, bearing encoded aptamer, the nanoflower system is intensively endocytosed by bacteria, and releases DNAzyme under acidic conditions to cleave the mecR1 gene for PBP2a down-regulation, and ampicillin for efficient MRSA elimination. In vivo tests showed that the system effectively cleared bacterial and biofilm in the cornea, suppressed proinflammatory cytokines interleukin 1β （IL-1β） and tumor neocrosis factor-alpha （TNF-α）, and is safe for corneal epithelial cells. Overall, this design offers a promising approach for treating MRSA-induced keratitis.

Evidence and Molecular Characterization of Multidrug Resistant Staphylococcus aureus Isolated From Equines in Pakistan

The purpose of the current study was to investigate the nasal colonization and drug resistance profile of Staphylococcus aureus, methicillin-resistant S. aureus (MRSA), and vancomycin-resistant S. aureus (VRSA) in donkeys (n =63), mules (n = 42), and horses (n = 98). MRSA and VRSA were confirmed based on phenotypic and molecular methods, followed by phylogenetic analysis. Furthermore, the association of various animal and management-based risk factors with S. aureus colonization was also evaluated. The presence of nuc gene on polymerase chain reaction showed an overall prevalence of 42.86% of S. aureus in equines. Based on Kirby-Bauer disc diffusion test, 26.44% of isolates showed resistance to vancomycin. Further, mecA and vanB genes were targeted which showed an overall 14.94% and 13.79% prevalence of methicillin and vancomycin-resistant isolates, respectively. The phylogenetic analysis revealed a significant variation of the study isolates with each other and with already reported sequences of mecA and vanB genes. Risk factor analysis revealed that raising purpose (P = .011), work intensity (P < .001), stocking density (P = .006), presence of other livestock animals in surroundings (P = .043), and common drinking water source (P = .023) as significant. Antimicrobial susceptibility testing of MRSA and VRSA isolates showed high resistance to various commonly used antibiotics. Furthermore, all the tested isolates showing resistance to three or more than three antibiotics were considered multiple drug-resistant. The current study manifests the molecular evidence of MRSA and VRSA isolated from equines in Pakistan which will help to address the emerging issue of multidrug resistance in S. aureus in equines and emphasizes the need for possible measures to tackle this issue.

Phenotypic and genotypic characterization of methicillin-resistant Staphylococcus aureus from bovine mastitis

Aim:

This study was conducted to determine the occurrence of methicillin-sensitive and Staphylococcus aureus (MSSA) methicillin-resistant S. aureus (MRSA) from bovine mastitis and to characterize them with respect to antibiotic resistance gene mecA.

Materials and Methods:

A total of 160 mastitic milk samples were screened for the presence of S. aureus. The presumptive positive isolates were confirmed using nuc and 23S rRNA gene-based polymerase chain reaction. All the confirmed isolates were subjected to in vitro antibiogram using a number of antibiotics. Isolates which showed resistance against methicillin were characterized for the presence of mecA gene.

Results:

Out of the total 160 milk samples, 36 (22.5%) samples yielded S. aureus. The in vitro antibiogram revealed that 16.6% S. aureus isolates were resistant to all antibiotics screened for and 5.5% isolates were sensitive to all of them. Furthermore, the study found 94.4%, 83.3%, 77.7%, 66.6%, 50%, and 27.7% of S. aureus isolates resistant to penicillin, ampicillin, amoxicillin-sulbactam, enrofloxacin, ceftriaxone, and methicillin, respectively. Out of the 36 S. aureus isolates, only 6 (16.6%) isolates were confirmed as MRSA while rest were MSSA.

Conclusion:

The higher occurrence of S. aureus-mediated mastitis was concluded due to improper hygienic and poor farm management. The multiple drug resistance reveals the indiscriminate use of drugs and presence of methicillin resistance gene determinant is an alarming situation as such infections are difficult to treat.