A rapid,high‐throughput screening method for carriage of methicillin‐resistant Staphylococcus aureus

Rapid screening of methicillin‐resistant Staphylococcus aureus (MRSA) colonization prior to hospital admittance is important to reduce nosocomial infections and health care costs. Molecular detection of mecA and S. aureus specific target genes has become widely established for this purpose. However, there are still limitations in potential for high‐throughput screening in the methods described. We have compared the time aspects and workload of four different DNA preparation platforms, resulting in an automated and simple MRSA screening method which combines two liquid handling systems and a simple lysis buffer. We have further transferred our in‐house dual real‐time PCR to a fast‐PCR protocol, reducing the time and labour spent on these samples to a minimum.     

Clinical and molecular characteristics of community‐acquired methicillin‐resistant Staphylococcus aureus infections in Chinese neonates

This study aims to characterize the clinical features of community‐acquired methicillin‐resistant Staphylococcus aureus (CA‐MRSA) infections in Chinese neonates, as well as the molecular characteristics and expression of key virulence genes of isolates. Clinical information and molecular characteristics of 130 cases were analyzed. Up to 83.8% patients were affected with late‐onset infection. Cesarean delivery was the main delivery route, accounting for 74.6% of the total deliveries. Pneumonia (69, 53.1%) was the most common infection. A total of 38 patients (29.2%) suffered from complications. Moreover, 35 cases (26.9%) were invasive infections, among which 88.6% involved multiple organs and 45.7% suffered from complications. Cesarean section and premature birth were the risk factors for invasive CA‐MRSA infection. ST59‐MRSA‐SCCmecIVa‐t437 (54, 41.5%) was the most predominant CA‐MRSA clone. The hla expression in the ST59 isolates was higher than that in ST910 (p = 0.02) and the hla expression in ST59‐SCCmecV‐t437 was higher than that in ST59‐SCCmecIVa‐t437. Approximately, 46.4% (13/28) of the infections caused by ST59‐SCCmecV were invasive. This value is higher than that of ST59‐SCCmecVa caused infections (14/59, 23.7%) (p = 0.03). This study showed that neonatal CA‐MRSA infections in China readily become invasive, involve multiple organs, and are often accompanied by complications. The SCCmec V clone may be more pathogenic than the SCCmecVIa clone.     

Comparative analysis of the virulence characteristics of epidemic methicillin–resistant Staphylococcus aureus (MRSA) strains isolated from Chinese children: ST59 MRSA highly expresses core gene–encoded toxin

This study aims to investigate the prevalence of a novel cell wall‐anchored protein gene, sasX, and to obtain information on the genetic basis for the pathogenic potential of the MRSA strains isolated from Chinese children. The molecular and virulence characteristics of the clinical strains were analyzed. Twenty‐two sequence types (STs) were obtained, with six epidemic clones ST59, ST239, ST1, ST910, ST88, and ST338 accounting for 35.8, 22, 6.6, 6.6, 5.3, and 4.1% respectively. The expression levels of hla, psmα, and RNAIII were higher in ST59 than in other STs (p < 0.05). The sasX gene was detected in 26 (10.7%) MRSA isolates. ST239‐MRSA‐SCCmecIII‐t037 (61.5%) was the predominant sasX‐positive MRSA clone. The expressions of PSMα and RNAIII were higher in sasX‐positive ST239 isolates than in sasX‐negative ST239 ones (p < 0.01). Notably, the percentage of invasive infection in infections caused by sasX‐positive ST239 MRSA was higher than that by sasX‐negative ST239 MRSA (p = 0.008). This study indicated that ST59 was the predominant clone in the MRSA isolates obtained from Chinese children and might have stronger pathogenic potential. The prevalence of the sasX gene in the MRSA isolates from children was relatively low. Furthermore, the sasX gene might be related to the expressions of PSMα and RNAIII and infection invasiveness.     

Effect of sub‐lethal doses of vancomycin and oxacillin on biofilm formation by vancomycin intermediate resistant Staphylococcus aureus

Biofilms are means of protection to bacteria against antibiotics and antibodies. Catheters and others tube devices used by patients are prone to accumulation of thick layers of biofilms as hiding place for etiologic agents, resulting in substantial morbidity and mortality. Methicillin‐resistant Staphylococcus aureus (MRSA) is a major cause of hospital‐acquired infections. Vancomycin remains the only treatment of choice for MRSA infections. In the present study a vancomycin resistant S. aureus (VRSA) (Labeled as CP2) was isolated from the blood of a post‐operative cardiac patient. It harbors a plasmid which carry vanA gene and exhibited low‐level vancomycin resistance (MIC 16μg/ml), high level of oxacillin/methicillin resistance (MIC 500 μg/ml) and was sensitive to teicoplanin. CP2 also found to carry icaA gene on its chromosome. This strain exhibited resistance to triton‐X100 induced autolysis under sub‐inhibitory concentration of vancomycin and produced some extracellular matrix material that surrounding the cells. These characteristic features have warranted us to study the biofilm formation by CP2 on biomedical indwellings in presence of vancomycin and oxacillin. Our findings suggest that sub‐lethal dose of vancomycin induced the biofilm formation by CP2 on nylon and silicon indwellings whereas oxacillin facilitated the biofilm formation on glass surfaces exclusively. This implicates that not only the antibiotics but also the indwelling material influences biofilm formation. Therefore, these implants serve as potential surfaces for bacterial adhesion that lead to biofilm formation, thus provide hiding places for pathogens from the actions of antimicrobials. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Detection of cross-transmission of multiresistant Gram-negative bacilli and Staphylococcus aureus in adult intensive care units by routine typing of clinical isolates

Objective: To determine the potential of laboratory services in identifying cross-transmission of multiresistant Gram-negative bacilli (MR GNB) and Staphylococcus aureus in adult intensive care units by routine typing of clinical isolates.
Methods: Over a 12-month period, isolates with indistinguishable PCR fingerprints were traced back to the source patients and their epidemiologic relationships were investigated. Possible episodes of cross-transmission were ascertained, and the validity of antibiograms in identifying the same cluster assessed.
Results: Of 3503 specimens received by the microbiological laboratory during 5372 patient days, 1295 cultures showed bacterial growth. Of these, 132 were primary isolates of MR GNB and 92 were primary isolates of S. aureus . Thirty-two MR GNB isolates (24%) shared fingerprints with one or more other isolates. Indistinguishable isolates from epidemiologically related patients suggested 17 episodes of cross-transmission. The positive and negative predictive values of antibiogram-based identification of these episodes were 19% and 72% respectively. S aureus displayed limited genetic diversity. The two most frequent genotypes contained 19 and 16 isolates, of which the majority appeared to be epidemiologically unrelated.
Conclusions: Endemic transmission of MR GNB occurs mainly between two patients and remains unrecognized by conventional laboratory investigation. Rapid genetic typing methods identify patients involved in cross-transmission and give an insight into the population dynamics of MR GNB on adult intensive care units.     

Carbapenem resistant Gram-negative bacteremia in an Indian intensive care unit: A review of the clinical profile and treatment outcome of 50 patients

Background:

Growing antimicrobial resistance and limited therapeutic options to treat carbapenem-resistant bacteremia prompted us to evaluate the clinical outcomes associated with healthcare-associated bacteremia.

Methods:

This was a retrospective observational study of carbapenem-resistant Gram-negative bacteremia performed at a tertiary care facility in Chennai, India between May 2011 and May 2012.

Results:

In our study, patients had mean 11.76 days of intensive care unit (ICU) care and mean time to onset of bacteremia was 6.4 days after admission. The commonest organism was Klebsiella pneumoniae (44%). Patients with combination treatment had lower mortality (44.8%) compared with colistin monotherapy (66.6%); (P = 0.35).

Conclusion:

Carbapenem resistant bacteremia is a late onset infection in patients with antibiotic exposure in the ICU and carries a 30 days mortality of 60%; K. pneumoniae is the most common organism at our center. Two drug combinations appear to carry a lower mortality compared with monotherapy.     

Antibiofilm effect of green engineered silver nanoparticles fabricated from Artemisia scoporia extract on the expression of icaA and icaR genes against multidrug‐resistant Staphylococcus aureus

Silver nanoparticles (AgNPs) are at the forefront of the swiftly developing scope of nanotechnology. In the current study, we investigated the green synthesis of AgNPs using Artemisia scoporia as a reducing and capping agent. The biosynthesized AgNPs were characterized using ultraviolet–visible spectroscopy, X‐ray diffraction, Fourier‐Transform infrared spectroscopy, dispersive absorption spectroscopy, scanning electron microscopy, and transmission electron microscopy. The efficacy of the nanoparticle synthesis was assessed by comparing the antibiofilm activity with commercial AgNPs. The effect of sub‐minimum inhibitory concentrations (MICs) of AgNPs on biofilm formation was determined by microtiter plate assay. The expression level of the icaA and icaR genes was assessed by real‐time polymerase chain reaction assay. The structural and functional aspects of AgNPs were confirmed. The expression levels of icaA and icaR in the isolates exposed to sub‐MIC of both commercial and biosynthetic AgNPs were lower and higher than in the control group, respectively. Our results also indicated that greater reduction and induction in icaA and icaR gene expression were noticed with the sub‐MIC doses of biosynthetic AgNP versus commercial AgNP, respectively. This study suggested the application of AgNPs as a significant therapeutic and clinical option in the future and usage for fabricating medical implants. Nevertheless, further investigation is required for examining the pharmaceutical and medicinal properties of AgNPs.