Clonality of clinical methicillin-resistant Staphylococcus epidermidis isolates in a neonatal intensive care unit

The complexity of Staphylococcus epidermidis molecular epidemiology in neonatal intensive care units (NICU) as revealed by genomic approaches

Bloodstream infections caused by Staphylococcus epidermidis are among the most frequent and serious infections in neonatal intensive care units (NICU), being responsible for high rates of morbidity and mortality. However, how S. epidermidis prevails, disseminates and evolves to cause outbreaks in NICU is poorly understood. We aimed to understand what is the genomic basis of S. epidermidis outbreaks in NICU to provide guidelines for a better infection control. We collected all S. epidermidis isolated from newborn blood cultures admitted to a hospital NICU in Brazil over one-year and compared their genomes. The S. epidermidis infection incidence rate was 1.17 per baby-year. 83.64% of S. epidermidis were resistant to methicillin (MRSE) and 84.5% belonged to sequence type 2 (ST2) or related, carrying the staphylococcal cassette chromosome mec (SCCmec) type III or IVa. Single nucleotide polymorphisms (SNPs) analysis showed that S. epidermidis infections resulted from the co-existence of three ST2 transmission chains originating from distinct endemic sources (<50 SNPs). Each transmission chain was characterized by specific antibiotic resistance and virulence profile and content in staphylococcal cassette chromosome elements (SCCmec, SCC non-mec and ACME). During transmission, other mobile genetic elements were acquired/lost and mutations emerged in genes involved in adhesion, signal transduction, general metabolism, replication, recombination and repair. Tracking S. epidermidis transmission chains in the NICU will require a deep genomic analysis, combining bacterial genetic background and accessory genome. This study highlighted the need for the integration of whole genome sequencing as a key surveillance tool for infection control in NICUs.

Topical antimicrobials for burn wound infections

Throughout most of history, serious burns occupying a large percentage of body surface area were an almost certain death sentence because of subsequent infection. A number of factors such as disruption of the skin barrier, ready availability of bacterial nutrients in the burn milieu, destruction of the vascular supply to the burned skin, and systemic disturbances lead to immunosuppression combined together to make burns particularly susceptible to infection. In the 20th century the introduction of antibiotic and antifungal drugs, the use of topical antimicrobials that could be applied to burns, and widespread adoption of early excision and grafting all helped to dramatically increase survival. However the relentless increase in microbial resistance to antibiotics and other antimicrobials has led to a renewed search for alternative approaches to prevent and combat burn infections. This review will cover patented strategies that have been issued or filed with regard to new topical agents, preparations, and methods of combating burn infections. Animal models that are used in preclinical studies are discussed. Various silver preparations (nanocrystalline and slow release) are the mainstay of many approaches but antimicrobial peptides, topical photodynamic therapy, chitosan preparations, new iodine delivery formulations, phage therapy and natural products such as honey and essential oils have all been tested. This active area of research will continue to provide new topical antimicrobials for burns that will battle against growing multidrug resistance.

Proof of principle for successful characterization of methicillin-resistant coagulase-negative staphylococci isolated from skin by use of Raman spectroscopy and pulsed-field gel electrophoresis

Coagulase-negative staphylococci (CNS) are among the most frequently isolated bacterial species in clinical microbiology, and most CNS-related infections are hospital acquired. Distinguishing between these frequently multiple-antibiotic-resistant isolates is important for both treatment and transmission control. In this study we used isolates of methicillin-resistant coagulase-negative staphylococci (MR-CNS) that were selected from a large surveillance study of the direct spread of MR-CNS. This strain collection was used to evaluate (i) Raman spectroscopy as a typing tool for MR-CNS isolates and (ii) diversity between colonies with identical and different morphologies. Reproducibility was high, with 215 of 216 (99.5%) of the replicate samples for 72 isolates ending up in the same cluster. The concordance with pulsed-field gel electrophoresis (PFGE)-based clusters was 94.4%. We also confirm that the skin of patients can be colonized with multiple MR-CNS types at the same time. Morphological differences between colonies from a single patient sample correlated with differences in Raman and PFGE types. Some morphologically indistinguishable colonies revealed different Raman and PFGE types. This indicates that multiple MR-CNS colonies should be examined to obtain a complete insight into the prevalence of different types and to be able to perform an accurate transmission analysis. Here we show that Raman spectroscopy is a reproducible typing system for MR-CNS isolates. It is a tool for screening variability within a collection of isolates. Because of the high throughput, it enables the analysis of multiple colonies per patient, which will enhance the quality of clinical and epidemiological studies.

Epidemiology and characterization ofStaphylococcus epidermidisisolates from humans, raw bovine milk and a dairy plant

Geographically relatedStaphylococcus epidermidisisolates from human patients (n=30), dairy farms (farmers and individual raw milk from cattle,n=36) and a dairy plant (n=55) were examined for epidemiological relatedness by pulsed-field gel electrophoresis and, usingin vitromethods, for the ability to produce biofilm and antimicrobial resistance. Methicillin-resistant isolates (MRSE) were also identified and characterized. Isolates from farmers and dairy cattle were found to be genetically related, while isolates from human patients were highly diverse. Some dairy plant isolates (18·2%) were closely related to those from dairy farms. Biofilm production and resistance to antimicrobial agents were most typical for isolates from human patients, of which 76·7% were MRSE. Methicillin resistance was also widespread in farm-related isolates (61·1%). This study indicates the possible transmission ofS. epidermidisbetween cattle and farmers. Dairy products were not proven to be an important source of either human infections or methicillin-resistant strains.

A three-year surveillance of nosocomial infections by methicillin-resistant Staphylococcus haemolyticus in newborns reveals the disinfectant as a possible reservoir

OBJECTIVE

Study of the clonality of methicillin-resistant Staphylococcus haemolyticus responsible of epidemic infections in a neonatal intensive care unit.

PATIENTS AND METHODS

Methicillin-resistant Staphylococcus haemolyticus isolates were collected during the period from March 2004 to November 2006, from newborns, the clean hands of nurses and from disinfectant bottles used in the unit. Molecular typing by pulsed-field gel electrophoresis (PFGE) was achieved for all isolates.

RESULTS

Forty-six isolates of S. haemolyticus resistant to methicillin were collected from 42 newborns, the hand of two nurses and from two disinfectant bottles used in the unit. PFGE analysis revealed five types (A, B, C, D and E) among newborns isolates. Types A and B were predominant. Nurses' isolates revealed PFGE types similar to types A and B. Disinfectant isolates were of type B. qacA/B PCR analysis revealed that the majority of type B isolates contain the disinfectant resistance gene qacA/B. No isolate of type A possessed this gene.

CONCLUSION

These results suggest that MRSH neonatal infections are caused by a limited number of clones. Clone B was able to survive in disinfectant bottles and to conserve its ability to infect newborns. We therefore conclude that the disinfectant can serve as a reservoir for MRSH and point out the need to control all disinfectants used in a neonatal intensive care unit.

Clonality of Providencia stuartii isolates involved in outbreak that occurred in a burn unit

In order to investigate an outbreak of multidrug-resistant Providencia stuartii that occurred in a burn unit, we analyzed by pulsed-field gel electrophoresis (PFGE) all isolates of P. stuartii collected during 4 months of 2005 from patients and from a tracheal aspirator. Seventeen clinical isolates of P. stuartii, extended-spectrum beta-lactamase (ESBL) producing, were collected from 17 patients. All these isolates were nosocomially acquired. Three other isolates were collected from the aspirator probe, the aspirator reservoir and from the aspirator tube. Three different antibiotypes were identified without correlation with the genotype. Two PFGE types were obtained (types A and B) with predominance of one (type A) that was observed for 15 isolates. P. stuartii isolates collected from different components of the aspirator (probe, reservoir and tube) yielded PFGE type A. This study suggests the bi-clonality of the outbreak and that transmission of epidemic P. stuartii isolates was through a common source. The aspirator probe, contaminated from aspirator that functioned as a reservoir of bacteria, seems to be the route of transmission of P. stuartii. Furthermore, this study shows the utility of PFGE in typing for the purpose of understanding the epidemiological behaviour of P. stuartii and as a basis for the development of rational control strategies.