Comparison of Staphylococcus Phage K with Close Phage Relatives Commonly Employed in Phage Therapeutics.

The increase in antibiotic resistance in pathogenic bacteria is a public health danger requiring alternative treatment options, and this has led to renewed interest in phage therapy. In this respect, we describe the distinct host ranges of Staphylococcus phage K, and two other K-like phages against 23 isolates, including 21 methicillin-resistant S. aureus (MRSA) representative sequence types representing the Irish National MRSA Reference Laboratory collection. The two K-like phages were isolated from the Fersisi therapeutic phage mix from the Tbilisi Eliava Institute, and were designated B1 (vB_SauM_B1) and JA1 (vB_SauM_JA1). The sequence relatedness of B1 and JA1 to phage K was observed to be 95% and 94% respectively. In terms of host range on the 23 Staphylococcus isolates, B1 and JA1 infected 73.9% and 78.2% respectively, whereas K infected only 43.5%. Eleven open reading frames (ORFs) present in both phages B1 and JA1 but absent in phage K were identified by comparative genomic analysis. These ORFs were also found to be present in the genomes of phages (Team 1, vB_SauM-fRuSau02, Sb_1 and ISP) that are components of several commercial phage mixtures with reported wide host ranges. This is the first comparative study of therapeutic staphylococcal phages within the recently described genus Kayvirus.

Characterisation of clinical meticillin-resistant Staphylococcus epidermidis demonstrating high levels of linezolid resistance (>256 µg/ml) resulting from transmissible and mutational mechanisms.

Staphylococcus epidermidis (S. epidermidis), one of the leading etiological agents of nosocomial infections poses a significant economic burden globally. Introduced in 2000, linezolid (LZD) has become an important antibiotic, used in nearly seventy countries worldwide to treat infections caused by Gram-positive pathogens such as meticillin-resistant Staphylococcus and Streptococcus species along with vancomycin-resistant enterococci. Resistance to LZD in clinical settings remains rare. Here, we report the emergence of meticillin resistant S. epidermidis (MRSE) clinical isolates from two voluntary general acute hospitals exhibiting higher than typically reported levels of LZD resistance (MIC>256 µg/ml). The MRSE ST-2 clone isolated from eight patients (2010-2011) not only possessed resistance-conferring mutations such as G2576T in domain V of 23S rRNA gene (as determined by HRM-PCR analysis) and R172C substitution in the ribosomal protein L3, but also carried the cfr gene (the only known transmissible mechanism of LZD resistance). All isolates possessed several key biofilm-associated genes (such as icaA, icaD, aap and atlE) and resistance to multiple clinically significant antibiotics was recorded. This study reports the earliest incidence (2010) of clinical MRSE in the Republic of Ireland demonstrating multiple LZD resistance mechanisms both mutational and potentially transmissible, and characterises this emerging resistance from a molecular perspective.

High-resolution melting analysis for rapid detection of linezolid resistance (mediated by G2576T mutation) in Staphylococcus epidermidis.

We describe a novel HRM-PCR (high-resolution melting) assay capable of the accurate identification of the G2576T point mutation in domain V of the 23S rRNA genes attributed to linezolid resistance in Staphylococcus epidermidis. This rapid method demonstrated 100% correlation with the previously established NheI restriction digest assay.