Staff-to-patient transmission of meticillin-resistant Staphylococcus aureus: do bacterial factors play a role?

Integrated meta-analysis and machine learning approach identifies acyl-CoA thioesterase with other novel genes responsible for biofilm development in Staphylococcus aureus

Biofilm forming Staphylococcus aureus is a major threat to the health-care industry. It is important to understand the differences between planktonic and biofilm growth forms in the pathogen since conventional treatments targeting the planktonic forms are not effective against biofilms. The current study conducts a meta-analysis of three public transcriptomic profiles to examine the differences in gene expression between the planktonic and biofilm states of S. aureus using random-effects modeling. Mean effect sizes were calculated for 2847 genes among which 726 differentially expressed genes were taken for further analysis. Major genes that are discriminatory between the two conditions were mined using supervised learning techniques and validated by high-accuracy classifiers. Ten different feature selection algorithms were applied and used to rank the most important genes in S. aureus biofilms. Finally, an optimal set of 36 genes are presented as candidate genes in biofilm formation or development while throwing light on the novel roles of an acyl-CoA thioesterase enzyme and 10 hypothetical proteins in biofilms. The relevance of the identified gene set was further validated by building five different classification models using SVM, RF, kNN, NB and DT algorithms that were compared with models built from other relevant gene sets and by reviewing the functional role of 25 previously known genes in biofilm development. The study combines meta-analysis of differential expression with supervised machine learning strategies and feature selection for the first time to identify and validate a discriminatory set of genes important in biofilms of S. aureus. The functional roles of the identified genes predicted to be important in biofilms are further scrutinized and can be considered as a signature target list to develop anti-biofilm therapeutics in S. aureus.

Prevention and treatment of Staphylococcus aureus biofilms

S. aureus colonizes both artificial and tissue surfaces in humans causing chronic persistent infections that are difficult to cure. It is a notorious pathogen due to its antibiotic recalcitrance and phenotypic adaptability, both of which are facilitated by its ability to develop biofilms. S. aureus biofilms challenge conventional anti-infective approaches, most notably antibiotic therapy. Therefore there is an unmet need to develop and include parallel approaches that target S. aureus biofilm infections. This review discusses two broad anti-infective strategies: (1) preventative approaches (anti-biofilm surface coatings, the inclusion of biofilm-specific vaccine antigens); and (2) approaches aimed at eradicating established S. aureus biofilms, particularly those associated with implant infections. Advances in understanding the distinct nature of S. aureus biofilm development and pathogenesis have led to growing optimism in S. aureus biofilm targeted anti-infective strategies. Further research is needed however, to see the successful administration and validation of these approaches to the diverse types of infections caused by S. aureus biofilms from multiple clinical strains.

Prolonged outbreak of meticillin-resistant Staphylococcus aureus in a cardiac surgery unit linked to a single colonized healthcare worker

BACKGROUND

In low- as well as in high-prevalence settings, healthcare workers (HCWs) may be a substantial, under-recognized, reservoir of meticillin-resistant Staphylococcus aureus (MRSA) and an important potential source of transmission to patients.

AIM

To report an outbreak of MRSA in a cardiac surgery unit in England over a 10-month period.

METHODS

Cases were defined as patients and staff on the cardiac surgery unit from whom the outbreak strain was newly isolated between 20 May 2011 and 16 March 2012. Representative isolates from all cases were characterized by spa-typing, pulsed-field gel electrophoresis and multi-locus variable-number tandem-repeat analysis (MLVA).

FINDINGS

Four patients appeared to acquire MRSA during their inpatient stay on the cardiac surgery unit. All four patients and one HCW were found to be carrying an identical epidemic (E)MRSA-15 strain (spa t032, pulsotype A, MLVA profile 16-6-3-1-1-17-1-4). No other members of staff were found to be colonized with MRSA. The colonized HCW was thought to be the source of the outbreak and was decolonized using a combination of nasal mupirocin, chlorhexidine body wash and oral rifampicin and doxycycline.

CONCLUSIONS

This report highlights recent changes in the epidemiology of MRSA in England and suggests an important role for colonized HCWs in the transmission of MRSA to patients. Screening HCWs may provide an increasingly valuable strategy in managing linked hospital acquisitions and well-defined outbreaks where initial investigation does not reveal a source.