is one of the most common pathogens of humans and animals, where it frequently colonizes skin and mucosal membranes. It is of major clinical importance as a nosocomial pathogen and causative agent of a wide array of diseases. Multidrug-resistant strains have become increasingly prevalent and represent a leading cause of morbidity and mortality. For this reason, novel strategies to combat multidrug-resistant pathogens are urgently needed. Bacteriophage-derived enzymes, so-called endolysins, and other peptidoglycan hydrolases with the ability to disrupt cell walls represent possible alternatives to conventional antibiotics. These lytic enzymes confer a high degree of host specificity and could potentially replace or be utilized in combination with antibiotics, with the aim to specifically treat infections caused by Gram-positive drug-resistant bacterial pathogens such as methicillin-resistant . LysK is one of the best-characterized endolysins with activity against multiple staphylococcal species. Various approaches to further enhance the antibacterial efficacy and applicability of endolysins have been demonstrated. These approaches include the construction of recombinant endolysin derivatives and the development of novel delivery strategies for various applications, such as the production of endolysins in lactic acid bacteria and their conjugation to nanoparticles. These novel strategies are a major focus of this review.

Background:Acinetobacter spp. is characterized as an important nosocomial pathogen and increasing antimicrobial resistance. Our aim was to evaluate antimicrobial susceptibility and aminoglycosides resistance genes of Acinetobacter spp. isolated from hospitalized patients.Methods:Sixty isolates were identified as Acinetobacter species. The isolates were tested for antibiotic resistance by disc diffusion method for 12 antimicrobials. The presence of aphA6, aacC1 aadA1, and aadB genes were detected using PCR.Results:From the isolated Acinetobacter spp. the highest resistance rate showed against amikacin, tobramycin, and ceftazidim, respectively; while isolated bacteria were more sensitive to ampicillic/subactam. More than 66% of the isolates were resistant to at least three classes of antibiotics, and 27.5% of MDR strains were resistant to all seven tested classes of antimicrobials. The higher MDR rate presented in bacteria isolated from the ICU and blood samples. More than 60% of the MDR bacteria were resistance to amikacin, ceftazidim, ciprofloxacin, piperacillin/tazobactam, doxycycline, tobramycin and levofloxacin. Also, more than 60% of the isolates contained phosphotransferase aphA6, and acetyltransferase genes aacC1, but adenylyltransferase genes aadA1 (41.7%), and aadB (3.3%) were less prominent. 21.7% of the strains contain three aminoglycoside resistance genes (aphA6, aacC1 and aadA1).Conclusion:The rising trend of resistance to aminoglycosides poses an alarming threat to treatment of such infections. The findings showed that clinical isolates of Acinetobacter spp. in our hospital carrying various kinds of aminoglycoside resistance genes.

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Cysteine/histidine-dependent amidohydrolase/peptidase (CHAP) and amidase are known as catalytic domains of the bacteriophage-derived endolysin LysK and were previously reported to show lytic activity against methicillin-resistant Staphylococcus aureus (MRSA). In the current study, the in silico design and analysis of chimeric CHAP-amidase model was applied to enhance the stability and solubility of protein, which was achieved through improving the properties of primary, secondary and tertiary structures. The coding gene sequence of the chimeric CHAP-amidase was synthesized and subcloned into the pET-22(+) expression vector, and the recombinant protein was expressed in E. coli BL21 (DE3) strain. Subsequent affinity-based purification yielded ~12 mg soluble protein per liter of E. coli culture. Statistical analysis indicated that concentrations of ≥1 μg/mL of the purified protein have significant antibacterial activity against S. aureus MRSA252 cells. The engineered chimeric CHAP-amidase exhibited 3.2 log reduction of MRSA252 cell counts at the concentration of 10 μg/mL. A synergistic interaction between CHAP-amidase and vancomycin was detected by using checkerboard assay and calculating the fractional inhibitory concentration (FIC) index. This synergistic effect was shown by 8-fold reduction in the minimum inhibitory concentration of vancomycin. The chimeric CHAP-amidase displayed strong antibacterial activity against S. aureus, S. epidermidis, and enterococcus. However, it did not indicate any significant antibacterial activity against E. coli and Lactococcus lactis. Taken together, these findings suggest that our chimeric CHAP-amidase might represent potential to be used for the development of efficient antibacterial therapies targeting MRSA and certain Gram-positive bacteria.

Background: Nasal colonization of healthy children with Staphylococcus aureus is an important risk factor for different infections. Detection of colonized individuals with methicillin resistant S. aureus (MRSA) and its eradication is the proper prevention strategy for infection spread in the community and health-care centers. Objectives: The aim of this study was to determine the prevalence, associated risk factors and antibiotic resistance pattern among healthy children who were nasal carriers of S. aureus. Patients and Methods:This cross-sectional study was conducted on 350 one month to 14-year-old healthy children living in Kashan/Iran. The nasal specimens were cultured in blood agar medium for S. aureus. Positive cultures were evaluated for cephalothin, co-trimoxazole, clindamycin, ciprofloxacin, oxacillin and vancomycin susceptibility by the disc diffusion method and E-test. Risk factors for nasal carriage of S. aureus and MRSA were evaluated. Results: Frequency of S. aureus nasal carriage was 92 from 350 cases (26.2%), amongst which 33 (35.9%) were MRSA. Isolates indicated an overall resistance of 52.2% to cephalothin, 33.7% to co-trimoxazol, 26.1% to ciprofloxacin, 26.1% to clindamycin, 35.9% to oxacillin and 4.3% to vancomycin. Factors associated with MRSA nasal carriage included gender (P value 0.001), age of less than four years (P value 0.016), number of individuals in the family (P value < 0.001), antibiotic use (P value < 0.001) and admission (P value < 0.001) during the previous three months, parental smoking (P value < 0.001) and sleeping with parents (P value 0.022). Conclusions: Age of less than four years, male sex, family size being more than four, antibiotic use and admission during the previous three months, parental smoking and sleeping with parents were independent risk factors for nasal colonization with MRSA.