Ajay Kumar Vijay

Pseudomonas aeruginosa causes ocular and other infections and quickly acquires antimicrobial resistance. Polymyxin B and colistin are last-line agents against resistant P. aeruginosa, yet even resistance to these is increasing. Antimicrobial peptides (AMPs) are also being developed as new antibiotics, but resistant mechanisms to polymyxins might also cause resistance to these AMPs. This study evaluated whether isolates with differing polymyxin resistances also showed elevated minimum inhibitory concentrations (MICs) to the human cathelicidin LL-37 and a synthetic AMP, Mel4. Forty isolates of P. aeruginosa, mostly collected in India and Australia, were assessed for minimum inhibitory concentrations (MICs) by broth microdilution in cation-adjusted Mueller–Hinton broth. Whole genome sequences were analyzed using NCBI BLAST (version 2.17.0). SNPs vs. MIC associations were evaluated with Fisher’s exact test. Sixty-five percent of isolates were resistant to polymyxin B, and 80% to colistin. Polymyxin B MICs ranged from 0.5 to 512 µg/mL, with 32.5% showing intermediate resistance and 22.5% being highly resistant (MIC ≥ 256 µg/mL). MICs for polymyxin B and colistin were strongly correlated with each other (Spearman’s R ≥ 0.6; n = 40; p ≤ 0.001). LL-37 showed moderate correlations with polymyxin B, colistin, and Mel4, whereas Mel4 showed weaker correlations with polymyxin B or colistin (R < 0.4). Genomic analysis identified SNPs in mipB (V469M, G441S) as being associated with the MICs to all the antimicrobials. Strains with MICs between 64 and 512 µg/mL were significantly more likely to harbor nalC (E153Q/D) or the mipB variants (p < 0.05). Higher polymyxin MICs were associated with elevated MICs to LL-37 and, to a lesser extent, Mel4, suggesting partial shared resistance among membrane active peptides. Defining the effect of the SNPs and clinical relevance of AMP cross-resistance may inform future therapies and safer contact lenses.

The ongoing battle against viral pandemics continues, with the possibility of future outbreaks. The search for effective antiviral compounds that can combat a diverse range of viruses continues to be a focal point of research. This study investigated the efficacy of two natural antimicrobial peptides (AMPs) (lactoferricin and LL-37), two synthetic AMPs (melimine and Mel4), and nine AMP mimics (758, 1091, 1096, 1083, 610, NAPL, 3-BIPL, 4-BIPL, and Sau-22) against influenza A virus strains H1N1 and H3N2, human adenovirus 5 (HAdV-5), and murine norovirus 1 (MNV-1). These compounds were tested using virus pre-treatment, cell pre-treatment, or post-cell entry treatment assays, electron microscopy, and circular dichroism (CD), alongside evaluations of cytotoxicity against the host cells. After virus pre-treatment, the AMP mimics 610 and Sau-22 had relatively low IC₅₀ values for influenza strains H1N1 (2.35 and 6.93 µM, respectively) and H3N2 (3.7 and 5.34 µM, respectively). Conversely, natural and synthetic AMPs were not active against these strains. For the non-enveloped viruses, the AMP Mel4 and mimic 1083 had moderate activity against HAdV-5 (Mel4 IC₅₀ = 47.4 µM; 1083 IC₅₀ = 47.2 µM), whereas all AMPs, but none of the mimics, were active against norovirus (LL-37 IC₅₀ = 4.2 µM; lactoferricin IC₅₀ = 23.18 µM; melimine IC₅₀ = 4.8 µM; Mel4 IC₅₀ = 8.6 µM). Transmission electron microscopy demonstrated that the mimics targeted the outer envelope of influenza viruses, while the AMPs targeted the capsid of non-enveloped viruses. CD showed that Mel4 adopted an α-helical structure in a membrane mimetic environment, but mimic 758 remained unstructured. The diverse activity against different virus groups is probably influenced by charge, hydrophobicity, size, and, in the case of natural and synthetic AMPs, their secondary structure. These findings underscore the potential of peptides and mimics as promising candidates for antiviral therapeutics against both enveloped and non-enveloped viruses.

The development of potent antiviral agents is of utmost importance to combat the global burden of viral infections. Traditional antiviral drug development involves targeting specific viral proteins, which may lead to the emergence of resistant strains. To explore alternative strategies, we investigated the antiviral potential of antimicrobial peptidomimetic compounds. In this study, we evaluated the antiviral potential of 17 short anthranilamide-based peptidomimetic compounds against two viruses: Murine hepatitis virus 1 (MHV-1) which is a surrogate of human coronaviruses and herpes simplex virus 1 (HSV-1). The half-maximal inhibitory concentration (IC₅₀) values of these compounds were determined in vitro to assess their potency as antiviral agents. Compounds 11 and 14 displayed the most potent inhibitory effects with IC₅₀ values of 2.38 μM, and 6.3 μM against MHV-1 while compounds 9 and 14 showed IC₅₀ values of 14.8 μM and 13 μM against HSV-1. Multiple antiviral assessments and microscopic images obtained through transmission electron microscopy (TEM) collectively demonstrated that these compounds exert a direct influence on the viral envelope. Based on this outcome, it can be concluded that peptidomimetic compounds could offer a new approach for the development of potent antiviral agents.

The development of potent antiviral agents is of utmost importance to combat the global burden of viral infections. Traditional antiviral drug development involves targeting specific viral proteins, which may lead to the emergence of resistant strains. To explore alternative strategies, we investigated the antiviral potential of antimicrobial peptidomimetic compounds. In this study, we evaluated the antiviral potential of short anthranilamide-based peptidomimetic compounds 1-17 against two viruses: Murine Hepatitis Virus 1 (MHV-1-single stranded RNA virus) which is a surrogate of human coronaviruses and Herpes Simplex Virus 1 (HSV-1-double stranded DNA virus). The half-maximal inhibitory concentration (IC50) values of these compounds were determined in vitro to assess their potency as antiviral agents. Compounds 11 and 14 displayed the most potent inhibitory effect with IC50 values of 2.38μM, and 6.3μM against MHV-1 while compounds 9 and 14 showed IC50 values of 14.8μM and 13μM, against HSV-1. Multiple antiviral assessments and microscopic images obtained through transmission electron microscopy (TEM) collectively demonstrated that these compounds exert a direct influence on the viral envelope. Based on this outcome, it can be concluded that peptidomimetic compounds could offer a new approach for the development of potent antiviral agents.

Staphylococcus aureus (S. aureus) is a frequent cause of eye infections with some isolates exhibiting increased antimicrobial resistance to commonly prescribed antibiotics. The increasing resistance of ocular S. aureus to ciprofloxacin is a serious concern as it is a commonly used as a first line antibiotic to treat S. aureus keratitis. This study aimed to analyse genetic mutations in the genomes of 25 S. aureus isolates from infections or non-infectious ocular conditions from the USA and Australia and their relationship to ciprofloxacin resistance. Overall, 14/25 isolates were phenotypically resistant to ciprofloxacin. All isolates were analyzed for mutations in their quinolone resistance-determining regions (QRDRs) and efflux pump genes. Of the fourteen resistant isolates, 9/14 had ciprofloxacin resistance mutations within their QRDRs, at codons 80 or 84 within the parC subunit and codon 84 within the gyrA subunit of DNA gyrase. The highest resistance (MIC = 2560 μg/mL) was associated with two SNPs in both gyrA and parC. Other resistant isolates (3/14) had mutations within norB. Mutations in genes of other efflux pumps and their regulator (norA, norC, mepA, mdeA, sepA, sdrM, mepR, arlR, and arlS) or the DNA mismatch repair (MMR) system (mutL and mutS) were not associated with increased resistance to ciprofloxacin. The functional mutations associated with ciprofloxacin resistance in QRDRs (gyrA and parC) and norB suggests that these are the most common reasons for ciprofloxacin resistance in ocular isolates. Novel SNPs of gyrA Glu-88-Leu, Asn-860-Thr and Thr-845-Ala and IIe-855-Met, identified in this study, need further gene knock out/in studies to better understand their effect on ciprofloxacin resistance.

Staphylococcus aureus is a major cause of ocular infectious (corneal infection or microbial keratitis (MK) and conjunctivitis) and non-infectious corneal infiltrative events (niCIE). Despite the significant morbidity associated with these conditions, there is very little data about specific virulence factors associated with the pathogenicity of ocular isolates. A set of 25 S. aureus infectious and niCIEs strains isolated from USA and Australia were selected for whole genome sequencing. Sequence types and clonal complexes of S. aureus strains were identified by using multi-locus sequence type (MLST). The presence or absence of 128 virulence genes was determined by using the virulence finder database (VFDB). Differences between infectious (MK + conjunctivitis) and niCIE isolates from USA and Australia for possession of virulence genes were assessed using the chi-square test. The most common sequence types found among ocular isolates were ST5, ST8 while the clonal complexes were CC30 and CC1. Virulence genes involved in adhesion (ebh, clfA, clfB, cna, sdrD, sdrE), immune evasion (chp, esaD, esaE, esxB, esxC, esxD), and serine protease enzymes (splA, splD, splE, splF) were more commonly observed in infectious strains (MK + conjunctivitis) than niCIE strains (p = 0.004). Toxin genes were present in half of infectious (49%, 25/51) and niCIE (51%, 26/51) strains. USA infectious isolates were significantly more likely to possess splC, yent1, set9, set11, set36, set38, set40, lukF-PV, and lukS-PV (p < 0.05) than Australian infectious isolates. MK USA strains were more likely to possesses yent1, set9, set11 than USA conjunctivitis strains (p = 0.04). Conversely USA conjunctivitis strains were more likely to possess set36 set38, set40, lukF-PV, lukS-PV (p = 0.03) than MK USA strains. The ocular strain set was then compared to 10 fully sequenced non-ocular S. aureus strains to identify differences between ocular and non-ocular isolates. Ocular isolates were significantly more likely to possess cna (p = 0.03), icaR (p = 0.01), sea (p = 0.001), set16 (p = 0.01), and set19 (p = 0.03). In contrast non-ocular isolates were more likely to possess icaD (p = 0.007), lukF-PV, lukS-PV (p = 0.01), selq (p = 0.01), set30 (p = 0.01), set32 (p = 0.02), and set36 (p = 0.02). The clones ST5, ST8, CC30, and CC1 among ocular isolates generally reflect circulating non-ocular pathogenic S. aureus strains. The higher rates of genes in infectious and ocular isolates suggest a potential role of these virulence factors in ocular diseases.