Insights on evolution of virulence and resistance from the whole-genome analysis of a predominant methicillin-resistant Staphylococcus aureus clone sequence type 239 in China

Clonal Diversity and Epidemiological Characteristics of ST239-MRSA Strains

Methicillin-resistant Staphylococcus aureus (MRSA) is a major pathogen associated with severe morbidity and mortality and poses a significant threat to public health worldwide. The genetic diversity based on sequence types of MRSA strains was illustrated in previous studies; meanwhile, the diversity along with the predominant sequence type, especially in Egypt, remains unknown. The purpose of the current study was to determine the diversity of the predominant MRSA clone ST239-MRSA (n = 50) isolated from different hosts and clinical samples and to illustrate the correlation between the resistance patterns, toxin genes, and the genetic background in Port-said and El-Sharkia Governorates, Egypt. The ST239-MRSA clone was analyzed by phenotypic antibiotyping and various genotypic assays comprising SCCmec, agr, spa, coa, and coa-RFLP in addition to toxin gene profiles. Most of the analyzed strains (40/50, 80%) were multidrug resistant (MDR), belonged to SCCmec-III, agr-I, and coa genotype I, and harbored sea and pvl genes. A negative correlation between the toxin gene profiles and antimicrobial resistance was recorded. Meanwhile, the correlation between the toxin gene profiles and the genetic background was not observed in this study. Although ST239-MRSA strains belonged to a single sequence type, they exhibited a high degree of phenotypic and genotypic diversity, indicating weak clonality and adaptability. With such diversity, it is assumed that these strains may have undergone different evolutionary processes during transmission events among and/or within a single host or tissue niche.

Characterizations of the endolysin Lys84 and its domains from phage qdsa002 with high activities against Staphylococcus aureus and its biofilms

Staphylococcus aureus (S. aureus), particularly methicillin-resistant S. aureus (MRSA), and its biofilms are great threats in the food industry. Bacteriophage-encoded endolysins are promising tools to inhibit pathogens and to eliminate their biofilms. In this work, a virulent phage qdsa002 against S. aureus ATCC43300 (MRSA) was isolated, and the phage's endolysin (Lys84) and its domains were expressed and purified. Morphological and genome analyses demonstrated that qdsa002 is a Twort-like phage from Myoviridae. Lys84 contains two catalytic domains (CHAP and Amidase_2) and one cell binding domain (SH3b). This endolysin exhibits a strong lytic activity against S. aureus and has a wider bactericidal spectrum than qdsa002. Moreover, Lys84 exceed 10 μM effectively removed around 90 % of the biofilms of S. aureus. Besides, CHAP and Amidase_2 domains remained 61.20 % and 59.46 % of lytic activity as well as 84.31 % and 70.11 % of anti-biofilm activity of Lys84, respectively. The lytic and anti-biofilm activities of the combination of CHAP and Amidase_2 were close to 90 % of those of Lys84. These results indicated that Lys84 and its domains might be alternative antimicrobials for controlling S. aureus and its biofilms.

Molecular Typing of ST239-MRSA-III From Diverse Geographic Locations and the Evolution of the SCCmec III Element During Its Intercontinental Spread

ST239-MRSA-III is probably the oldest truly pandemic MRSA strain, circulating in many countries since the 1970s. It is still frequently isolated in some parts of the world although it has been replaced by other MRSA strains in, e.g., most of Europe. Previous genotyping work (Harris et al., 2010; Castillo-Ramírez et al., 2012) suggested a split in geographically defined clades. In the present study, a collection of 184 ST239-MRSA-III isolates, mainly from countries not covered by the previous studies were characterized using two DNA microarrays (i) targeting an extensive range of typing markers, virulence and resistance genes and (ii) a SCCmec subtyping array. Thirty additional isolates underwent whole-genome sequencing (WGS) and, together with published WGS data for 215 ST239-MRSA-III isolates, were analyzed using in-silico analysis for comparison with the microarray data and with special regard to variation within SCCmec elements. This permitted the assignment of isolates and sequences to 39 different SCCmec III subtypes, and to three major and several minor clades. One clade, characterized by the integration of a transposon into nsaB and by the loss of fnbB and splE was detected among isolates from Turkey, Romania and other Eastern European countries, Russia, Pakistan, and (mainly Northern) China. Another clade, harboring sasX/sesI is widespread in South-East Asia including China/Hong Kong, and surprisingly also in Trinidad & Tobago. A third, related, but sasX/sesI-negative clade occurs not only in Latin America but also in Russia and in the Middle East from where it apparently originated and from where it also was transferred to Ireland. Minor clades exist or existed in Western Europe and Greece, in Portugal, in Australia and New Zealand as well as in the Middle East. Isolates from countries where this strain is not epidemic (such as Germany) frequently are associated with foreign travel and/or hospitalization abroad. The wide dissemination of this strain and the fact that it was able to cause a hospital-borne pandemic that lasted nearly 50 years emphasizes the need for stringent infection prevention and control and admission screening.

Hospital-acquired methicillin-resistant Staphylococcus aureus (MRSA) from Pakistan: molecular characterisation by microarray technology

The prevalence of methicillin-resistant Staphylococcus aureus (MRSA) in Pakistan is known to be high, but very few studies have described the molecular epidemiology of the different MRSA clones circulating in the country. Forty-four MRSA isolates were collected from two tertiary care hospitals of the Rawalpindi district of Pakistan. All strains were identified by a conventional phenotypic method and then subjected to genotyping by microarray hybridisation. Six clonal complexes (CCs) and 19 strains were identified. The most commonly identified strains were: (i) Panton-Valentine leucocidin (PVL)-positive CC772-MRSA-V, "Bengal Bay Clone" (ten isolates; 22.3%), (ii) ST239-MRSA [III + ccrC] (five isolates) and (iii) a CC8-MRSA-IV strain, as well as CC6-MRSA-IV (both with four isolates; 9.1% each). Several of the strains detected indicated epidemiological links to the Middle Eastern/Arabian Gulf region. Further studies are needed to type MRSA from countries with less known epidemiology and to monitor the distribution and spread of strains, as well as possible links to global travel, migration and commerce.

Comparative genomics of methicillin-resistant Staphylococcus aureus ST239: distinct geographical variants in Beijing and Hong Kong

BACKGROUND

The ST239 lineage is a globally disseminated, multiply drug-resistant hospital-associated methicillin-resistant Staphylococcus aureus (HA-MRSA). We performed whole-genome sequencing of representative HA-MRSA isolates of the ST239 lineage from bacteremic patients in hospitals in Hong Kong (HK) and Beijing (BJ) and compared them with three published complete genomes of ST239, namely T0131, TW20 and JKD6008. Orthologous gene group (OGG) analyses of the Hong Kong and Beijing cluster strains were also undertaken.

RESULTS

Homology analysis, based on highest-percentage nucleotide identity, indicated that HK isolates were closely related to TW20, whereas BJ isolates were more closely related to T0131 from Tianjin. Phylogenetic analysis, incorporating a total of 30 isolates from different continents, revealed that strains from HK clustered with TW20 into the 'Asian clade', whereas BJ isolates and T0131 clustered closely with strains of the 'Turkish clade' from Eastern Europe. HK isolates contained the typical φSPβ-like prophage with the SasX gene similar to TW20. In contrast, BJ isolates contained a unique 15 kb PT1028-like prophage but lacked φSPβ-like and φSA1 prophages. Besides distinct mobile genetic elements (MGE) in the two clusters, OGG analyses and whole-genome alignment of these clusters highlighted differences in genes located in the core genome, including the identification of single nucleotide deletions in several genes, resulting in frameshift mutations and the subsequent predicted truncation of encoded proteins involved in metabolism and antimicrobial resistance.

CONCLUSIONS

Comparative genomics, based on de novo assembly and deep sequencing of HK and BJ strains, revealed different origins of the ST239 lineage in northern and southern China and identified differences between the two clades at single nucleotide polymorphism (SNP), core gene and MGE levels. The results suggest that ST239 strains isolated in Hong Kong since the 1990s belong to the Asian clade, present mainly in southern Asia, whereas those that emerged in northern China were of a distinct origin, reflecting the complexity of dissemination and the dynamic evolution of this ST239 lineage.