Variability of SCCmec in the Zurich area

Microbiological findings in burn patients treated in a general versus a designated intensive care unit: Effect on length of stay

BACKGROUND

Infection is one of the most common causes of mortality and morbidity in burn patients. The incidence and frequency of microbiological micro-organisms are known to vary across different models of intensive care units. To date, no study has attempted to describe the different findings in burn patients treated in an open, general intensive care unit (GICU) versus a dedicated burns intensive care unit (BICU). Only limited data is available on the effect of these microbiological micro-organisms on patients' length of stay.

AIM

To characterize and compare the microbiological flora and antibiotic resistance patterns encountered in two different models of burn intensive care and to determine the effect of specific microbiological types on length of intensive care unit (ICU) and overall stay.

METHODS

A retrospective case-control study of 209 burn patients treated in two highly specialized, Western burn referral centres between September 2009 and March 2014.

RESULTS

9710 culture results were analysed, of which 2590 (26.7%) yielded positive results (1537 in the GICU and 1050 in the BICU). Gram-positive cultures were more frequently found in the GICU, whereas Gram-negative and yeast cultures were more prevalent in the BICU. The most frequently encountered micro-organisms in both units were similar and included Staphylococcus aureus, Pseudomonas aeruginosa, coagulase-negative staphylococci (CoNS) and Candida albicans. Significantly more resistant bacteria were detected in the BICU. Testing positive across all types of microbiological isolates, as well as for both Gram-positive and -negative bacteria significantly prolonged patient length of stay. This effect was even more pronounced if the micro-organisms were resistant to antimicrobial therapy.

CONCLUSION

There are notable differences in the microbiological isolate and antibiotic resistance patterns between burn patients treated in a GICU compared to a designated BICU. In both units, testing positive for resistant microbiological micro-organisms is significantly associated with longer hospital stay.

Clonality and antimicrobial susceptibility of methicillin-resistant Staphylococcus aureus at the University Hospital Zurich, Switzerland between 2012 and 2014

Background

Methicillin-resistant Staphylococcus aureus (MRSA) is a global epidemic threat. The aim of this study was to determine which globally known MRSA lineages are currently present at our tertiary care hospital in Switzerland, a hospital with low MRSA prevalence. In light of the increasing prevalence of multi drug resistance including vancomycin resistance we also assessed antibiotic susceptibilities.

Methods

The 146 MRSA strains collected over two years (March 2012 until February 2014) at the University Hospital Zurich, Switzerland, were analyzed by PFGE analysis of SmaI digests in combination with spa-typing. In addition, representative isolates were analyzed by multi locus sequence typing (MLST). Susceptibilities to eight antibiotics were assessed using the Kirby-Bauer disc diffusion method.

Results

Isolates showed resistance to erythromycin (48%), ciprofloxacin (43%), clindamycin (31%), tetracycline (22%), and gentamicin (16%). All isolates were susceptible to vancomycin, 95% were susceptible to sulfamethoxazole/trimethoprim and rifampicin, respectively. PFGE analysis revealed 22 different patterns, with four major patterns that accounted for 53.4% of all MRSA isolates, and seven sporadic patterns. Spa typing revealed 50 different spa types with the predominant types being t008 (14%), t002 (10%), and t127 (9%). 82% of the MRSA isolates could be assigned to six clonal complexes (CCs) namely CC1 (10%), CC5 (23%), CC8 (18%), CC22 (17%), CC30 (11%), and CC45 (3%) based on spa-types, PFGE patterns, and MLST. Two isolates could not be typed by either PFGE analysis or spa-typing and three isolates had spa-types that have not yet been described.

Conclusions

The combination of the two typing methods was more discriminatory as compared to the use of a single method. Several of the lineages that are predominant in Europe are present in our hospital. Resistances to antibiotics have decreased in comparison to a study conducted between 2004 and 2006.

Electronic supplementary material

The online version of this article (doi:10.1186/s12941-015-0075-3) contains supplementary material, which is available to authorized users.

USA300 methicillin-resistant Staphylococcus aureus in Zurich, Switzerland between 2001 and 2013

USA300 methicillin-resistant Staphylococcus aureus (MRSA) is the most prevalent MRSA in the United States of America (USA) and a global epidemic threat. We investigated the prevalence of USA300 at a tertiary care hospital in Zurich, Switzerland, where all MRSA strains have been collected and PFGE typed since 1992. These strains were retrospectively compared to the PFGE pattern of USA300 strain JE2. Isolates with a respective PFGE pattern were spa-typed and tested for the presence of the arginine catabolic mobile element (ACME) arc gene cluster and Panton-Valentine Leucocidin (PVL) genes. The first MRSA strain with a USA300 PFGE pattern was isolated in 2001 from a patient visiting from the USA. USA300 strains represented between 0% (in 2002) and 9.2% (in 2012) of all MRSA isolates in our hospital. We identified various USA300 subtypes based on either the PFGE pattern, the spa-type or absence of either the PVL genes or ACME arc gene cluster. All the USA300 strains including the variants (n=47) accounted for 5.6% of all MRSA isolates typed between 2001 and 2013 and reached a maximum of 14.5% in 2009. They predominantly caused skin and soft tissue infections (74.4%). In conclusion, even though USA300 has been present in our hospital for over twelve years it has not become the predominant MRSA clone like in the USA. However, in light of the global burden of USA300, care must be taken to further contain the spread of this lineage and of MRSA in general in our hospital.

Diversity of staphylococcal cassette chromosome mec elements in predominant methicillin-resistant Staphylococcus aureus clones in a small geographic area

Recent population genetic studies suggest that staphylococcal cassette chromosome mec (SCCmec) was acquired much more frequently than previously thought. In the present study, we aimed to investigate the diversity of SCCmec elements in a local methicillin-resistant Staphylococcus aureus (MRSA) population. Each MRSA isolate (one per patient) recovered in the Vaud canton of Switzerland from January 2005 to December 2008 was analyzed by the double-locus sequence typing (DLST) method and SCCmec typing. DLST analysis indicated that 1,884/2,036 isolates (92.5%) belong to four predominant clones. As expected from the local spread of a clone, most isolates within clones harbored an identical SCCmec type. However, three to seven SCCmec types have been recovered in every predominant DLST clone, suggesting that some of these elements might have been acquired locally. This pattern could also be explained by distinct importations of related isolates into the study region. The addition of a third highly variable locus to further increase the discriminatory power of typing as well as epidemiological data suggested that most ambiguous situations were explained by the second hypothesis. In conclusion, our study showed that even if the acquisition of new SCCmec elements at a local level likely occurs, it does not explain all the diversity observed in the study region.

Molecular picture of community- and healthcare-associated methicillin-resistant Staphylococcus aureus circulating in a teaching hospital in Milan

The epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) has dramatically changed over the past 10 y with the emergence of community-associated MRSA (CA-MRSA). Recent studies have reported a frequent association of these strains with hospital outbreaks, and an incidence varying over time and by region. In order to evaluate the MRSA lineages circulating in our area of Italy, we performed a molecular characterization of CA-MRSA isolates prospectively collected from April 2006 to July 2007 at the San Paolo Hospital of Milan. We investigated the protein A-encoding gene (spa-typing), the staphylococcal chromosomal cassette SCCmec, the presence of Panton-Valentine leukocidin (PVL), and 3 adhesin genes. Twenty-five CA-MRSA isolates cultured from 25 patients were collected; an equal number of healthcare-associated (HA)-MRSA strains, from 25 patients hospitalized in various wards, were collected for comparison purposes. SCCmec type IV emerged as the most frequent genotype in both CA- and HA-MRSA. Seventeen different spa types were identified: t515 was the most common (36%), followed by t008 (20%). We detected 3 PVL-positive strains, only among the CA-MRSA. On the whole, our local MRSA epidemiology appears to be heterogeneous, with a predominant t515 spa type, only recently considered to belong to clonal EMRSA-15.

GeneXpert captures unstable methicillin-resistant Staphylococcus aureus prone to rapidly losing the mecA gene

A cefoxitin-susceptible Staphylococcus aureus strain was identified by the Cepheid GeneXpert as methicillin-resistant S. aureus (MRSA). This strain was highly unstable and rapidly lost SCCmec upon subculturing in vitro, indicating that unstable MRSA is best detected by gene amplification-based methods.