Genotyping of 353 Staphylococcus aureus bloodstream isolates collected between 2004 and 2009 at a Norwegian university hospital and potential associations with clinical parameters

Staphylococcus aureus Genomic Analysis and Outcomes in Patients with Bone and Joint Infections: A Systematic Review

Many studies have been published assessing the association between the presence of S. aureus genes and outcomes in patients with bone and joint infections (BJI), but it is not known if they have had similar findings. A systematic literature review was performed. All available data on studies in Pubmed between January 2000 to October 2022 reporting the genetic characteristics of S. aureus and the outcomes of BJIs were analyzed. BJI included prosthetic joint infection (PJI), osteomyelitis (OM), diabetic foot infection (DFI), and septic arthritis. Because of the heterogeneity of studies and outcomes, no meta-analysis was performed. With the search strategy, 34 articles were included: 15 articles on children and 19 articles on adults. In children, most BJI studied were OM (n = 13) and septic arthritis (n = 9). Panton Valentine leucocidin (PVL) genes were associated with higher biological inflammatory markers at presentation (n = 4 studies), more febrile days (n = 3), and more complicated/severe infection (n = 4). Other genes were reported anecdotally associated with poor outcomes. In adults, six studies reported outcomes in patients with PJI, 2 with DFI, 3 with OM, and 3 with various BJI. Several genes were associated with a variety of poor outcomes in adults, but studies found contradictory results. Whereas PVL genes were associated with poor outcomes in children, no specific genes were reported similarly in adults. Additional studies with homogenous BJI and larger sample sizes are needed.

Epidemiological and clinical features of Panton-Valentine Leukocidin positive Staphylococcus aureus bacteremia: A case-control study

BACKGROUND

Panton-Valentine Leukocidin (PVL) toxin in Staphylococcus aureus has been associated with both severe pneumonia and skin and soft tissue infections. However, there are only limited data on how this virulence factor may influence the clinical course or complications of bacteremic S. aureus infections.

METHODS

Between September 2016 and March 2018, S. aureus isolates from clinical cultures from hospitals in an academic medical center underwent comprehensive genomic sequencing. Four hundred sixty-nine (29%) of 1681 S. aureus sequenced isolates were identified as containing the genes that encode for PVL. Case patients with one or more positive blood cultures for PVL were randomly matched with control patients having positive blood cultures with lukF/lukS-PV negative (PVL strains from a retrospective chart review).

RESULTS

51 case and 56 control patients were analyzed. Case patients were more likely to have a history of injection drug use, while controls more likely to undergo hemodialysis. Isolates from 78.4% of case patients were methicillin resistant as compared to 28.6% from control patients. Case patients had a higher incidence of pneumonia and skin and soft tissue infection and longer duration of fever without differences in length of bacteremia. Clinical cure or expiration was comparable.

CONCLUSIONS

These results are consistent with prior observations associating the PVL toxin with both community-acquired MRSA strains as well as severe staphylococcal pneumonia. The presence of the PVL toxin does not appear to otherwise influence the natural history of bacteremic S. aureus disease other than in prolonging the duration of fever.

Whole genome sequencing of coagulase positive staphylococci from a dog-and-owner screening survey

BACKGROUND

Staphylococcus aureus and S. pseudintermedius are the two most common coagulase positive staphylococci (CPS). S. aureus is more prevalent among humans, whereas S. pseudintermedius is more commonly isolated from dogs, however, both can cause various community and hospital acquired diseases in humans.

METHODS

In the current study we screened 102 dogs and 84 owners in Hungary. We tested the antibiotic susceptibility of the strains and in order to get a better picture of the clonal relationship of the strains, we used pulsed-field gel electrophoresis. In addition, three pairs of isolates with identical PFGE patterns were whole genome sequenced, MLST and spa types were established.

RESULTS

Carriage rate of S. aureus was 23.8% in humans and 4.9% in dogs and two cases of co-carriage were found among dogs and owners. S. pseudintermedius carriage rate was 2.4% and 34.3%, respectively, with only one co-carriage. The isolates were generally rather susceptible to the tested antibiotics, but high tetracycline resistance of S. pseudintermedius strains was noted. The co-carried isolates shared almost the same resistance genes (including tet(K), bla(Z), norA, mepR, lmrS, fosB) and virulence gene pattern. Apart from the common staphylococcal enzymes and cytotoxins, we found enterotoxins and exfoliative toxins as well. The two S. aureus pairs belonged to ST45-t630, ST45-t671 and ST15-t084, ST15-t084, respectively. The co-carried S. pseudintermedius isolates shared the same housekeeping gene alleles determining a novel sequence type ST1685.

CONCLUSIONS

Based on the genomic data, dog-owner co-carried strains displayed only insignificant differences therefore provided evidence for potential human-to-dog and dog-to-human transmission.

Is increased Staphylococcus aureus colonization during military service caused by specific genotypes? Molecular examination of long-term carriage in a prospective cohort study

A 22% increase in Staphylococcus aureus colonization was observed in Norwegian recruits during first year of military service. The aim was to determine whether specific genotypes caused the increase and to examine carriage status based on genotyping. Characterization of S. aureus from nose, throat and perineum sampled at enrolment and discharge included spa typing, MLVA, detection of PVL genes and antimicrobial susceptibility testing. spa typing demonstrated high and stable genetic diversity. The three most frequent spa types were found in 15% of recruits at enrolment and in 29% at discharge. Only t084 increased significantly (p = 0.02). Subtyping revealed that t084, t065 and t002 consisted of 13, 6 and 11 different MLVA types, respectively, at discharge. The military cohort (n = 265) consisted of S. aureus carriers of identical genotype (n = 99, 38%), carriers of non-identical genotype (n = 52, 20%), intermittent carriers (n = 86, 33%) and non-carriers (n = 27, 10%). Carrier status was indefinable for one recruit due to unavailable isolates for genotyping. Antibiotic resistance towards erythromycin, fusidic acid and clindamycin increased significantly and above national surveillance levels. The observed increase in S. aureus colonization during military service was caused by many different genotypes implying many transmission routes. Genotype did not correlate with colonization niche or carriage status.

Molecular Epidemiology of Staphylococcus aureus Bacteremia: Association of Molecular Factors With the Source of Infection

Staphylococcus aureus bacteremia (SAB) is associated with high morbidity and mortality, which varies depending on the source of infection. Nevertheless, the global molecular epidemiology of SAB and its possible association with specific virulence factors remains unclear. Using DNA microarrays, a total of 833 S. aureus strains (785 SAB and 48 colonizing strains) collected in Spain over a period of 15 years (2002–2017) were characterized to determine clonal complex (CC), agr type and repertoire of resistance and virulence genes in order to provide an epidemiological overview of CCs causing bloodstream infection, and to analyze possible associations between virulence genes and the most common sources of bacteremia. The results were also analyzed by acquisition (healthcare-associated [HA] and community-acquired [CA]), methicillin-resistant (MRSA) and methicillin-susceptible (MSSA) strains, and patient age (adults vs. children). Our results revealed high clonal diversity among SAB strains with up to 28 different CCs. The most prevalent CCs were CC5 (30.8%), CC30 (20.3%), CC45 (8.3%), CC8 (8.4%), CC15 (7.5%), and CC22 (5.9%), which together accounted for 80% of all cases. A higher proportion of CC5 was found among HA strains than CA strains (35.6 vs. 20.2%, p < 0.001). CC5 was associated with methicillin resistance (14.7 vs. 79.4%, p < 0.001), whereas CC30, CC45, and CC15 were correlated with MSSA strains (p < 0.001). Pathogen-related molecular markers significantly associated with a specific source of bacteremia included the presence of sea, undisrupted hlb and isaB genes with catheter-related bacteremia; sed, splE, and fib genes with endocarditis; undisrupted hlb with skin and soft tissue infections; and finally, CC5, msrA resistance gene and hla gene with osteoarticular source. Our study suggests an association between S. aureus genotype and place of acquisition, methicillin resistance and sources of bloodstream infection, and provides a valuable starting point for further research insights into intrinsic pathogenic mechanisms involved in the development of SAB.

Distribution of the Most Prevalent Spa Types among Clinical Isolates of Methicillin-Resistant and -Susceptible Staphylococcus aureus around the World: A Review

Background:Staphylococcus aureus, a leading cause of community-acquired and nosocomial infections, remains a major health problem worldwide. Molecular typing methods, such as spa typing, are vital for the control and, when typing can be made more timely, prevention of S. aureus spread around healthcare settings. The current study aims to review the literature to report the most common clinical spa types around the world, which is important for epidemiological surveys and nosocomial infection control policies.

Methods: A search via PubMed, Google Scholar, Web of Science, Embase, the Cochrane library, and Scopus was conducted for original articles reporting the most prevalent spa types among S. aureus isolates. The search terms were “Staphylococcus aureus, spa typing.”

Results: The most prevalent spa types were t032, t008 and t002 in Europe; t037 and t002 in Asia; t008, t002, and t242 in America; t037, t084, and t064 in Africa; and t020 in Australia. In Europe, all the isolates related to spa type t032 were MRSA. In addition, spa type t037 in Africa and t037and t437 in Australia also consisted exclusively of MRSA isolates. Given the fact that more than 95% of the papers we studied originated in the past decade there was no option to study the dynamics of regional clone emergence.

Conclusion: This review documents the presence of the most prevalent spa types in countries, continents and worldwide and shows big local differences in clonal distribution.

Spa type distribution in MRSA and MSSA bacteremias and association of spa clonal complexes with the clinical characteristics of bacteremia

The genetic distribution of invasive methicillin-susceptible (MSSA) and resistant S. aureus (MRSA) strains has to be addressed in order to target infection control strategies. A large MRSA epidemic caused by a certain MRSA strain (spa type 067) broke out in 2001 in our health district. We wanted to investigate the current spa type distribution in MRSA and MSSA bacteremias and assess the potential association of spa clonal complexes (spaCC) with the clinical characteristics of S. aureus bacteremia. One hundred nine invasive MRSA isolates and 353 invasive MSSA isolates were spa typed and grouped into clonal complexes (spaCC). Spa type distribution was compared to that of colonizing MRSA strains. Spa type and spaCC data linked to clinical information on the course of bacteremic cases was used to search for differences in virulence between strains. Spa type distribution in MRSA is less heterogenic than in MSSA. t067 dominates both in MRSA colonisations and in invasive findings. Among MSSA, no such dominating strains were found. Of spaCCs, mortality was the highest in spaCC 067 (25.6%). SpaCC 008 was more often associated with endocarditis than other CCs (22.7 vs 5.8%, p = 0.013), spaCC 2133 with skin infections (68.4 vs 36.4%, p = 0.007), and spaCC 012 with foreign body infections (25.0 vs 9.3%, p = 0.029) than other clonal complexes. A single successful strain can explain the major proportion of MRSA among S. aureus bacteremias. Certain spaCCs showed association with certain clinical characteristics. These findings suggest that S. aureus strains differ in their virulence and invasiveness.

Molecular Characterization of Community Acquired Staphylococcus aureus Bacteremia in Young Children in Southern Mozambique, 2001-2009

Background: The emergence of community-acquired Staphylococcus aureus infections is increasingly recognized as life threating problem worldwide. In Manhiça district, southern Mozambique, S. aureus is the leading cause of community-acquired bacteremia in neonates. Methods: Eighty-four S. aureus isolates from children less than 5 years admitted to Manhiça District Hospital from 2001 to 2009 were randomly selected and genetically characterized by DNA microarray and spa typing. Antimicrobial susceptibility was determined by VITEK 2. Results: Thirty-eight different spa types and 14 clonal complexes (CC) were identified. Spa-type t084 (n = 10; 12%) was the most predominant while CC8 (n = 18; 21%) and CC15 (n = 14; 16%) were the most frequent CCs. Mortality tended to be higher among children infected with CC45 (33.3%, 1/3) and CC8 (27.8%, 5/18). The majority of isolates possessed the accessory gene regulator I (45%) and belonged to either capsule type 8 (52%) or 5 (47%). Panton valentine leukocidin (PVL) encoding genes were detected in 30%. Antibiotic resistance was high for penicillin (89%), tetracycline (59%) and Trimethoprim Sulfamethoxazole (36%) while MRSA was uncommon (8%). Conclusions: Although MRSA were uncommon, we found high genetic diversity of methicillin susceptible S. aureus causing bacteremia in Mozambican children, associated with high resistance to the most available antibiotics in this community. Some CCs are likely to be more lethal indicating the need for prompt recognition and appropriate treatment.

Low mortality but increasing incidence of Staphylococcus aureus endocarditis in people who inject drugs: Experience from a Swedish referral hospital

Staphylococcus aureus is a leading cause of infective endocarditis in people who inject drugs (PWID). The management of S aureus endocarditis (SAE) in PWID can be problematic. The objective of this retrospective observational study was to assess the epidemiology, clinical characteristics, and mortality of S aureus endocarditis (SAE) in PWID in Stockholm, Sweden.The Department of Infectious Diseases at the Karolinska University Hospital serves as a regional referral center for drug users with severe infections. Patients with active intravenous drug use treated for SAE at the department between January 2004 and December 2013 were retrospectively identified. Clinical and microbiological data were obtained from medical records and the diagnosis verified according to the modified Duke criteria.In total, 120 SAE episodes related to intravenous drug use were identified. Its incidence in Stockholm was 0.76/100,000 adult person-years for the entire period, increasing from 0.52/100,000 person-years in 2004 to 2008 to 0.99 in 2009 to 2013 (P = 0.02). The SAE incidence among PWID specifically was 249 (range 153-649) /100,000 person-years. Forty-two (35%) episodes were left-sided, and multiple valves were involved in 26 (22%). Cardiac valve surgery was performed in 10 (8%) episodes, all left-sided. The in-hospital and 1-year mortality rates were 2.5% (3 deaths) and 8.0% (9 deaths), respectively.We noted a high and increasing incidence over time of SAE related to intravenous drug use in Stockholm. The increased incidence partly reflects a rising number of PWID during the study period. The low mortality noted, despite a substantial proportion with left-sided endocarditis, probably in part reflects the quality of care obtained at a large and specialized referral center for drug users with severe infections.

High frequency of occupied attB regions in Norwegian Staphylococcus aureus isolates supports a two-step MRSA screening algorithm

Rapid nucleic acid amplification tests for methicillin-resistant Staphylococcus aureus (MRSA) diagnostics commonly target the mec resistance gene, genes specific for S. aureus, and the integration site for the SCCmec resistance cassette, orfX. Due to poor specificity when these target genes are used individually, additional culture is required to verify positive results. The combination of these targets is useful, but the optimal algorithm may depend on the presence of the genetic markers in S. aureus isolates, as well as the prevalence of MRSA in a population. The aim of the present study was to identify a rapid, low-cost, and functional screening algorithm in order to reduce the response time for MRSA diagnostics. An in-house orfX-SCCmec polymerase chain reaction (PCR) assay was established and evaluated. The results were compared with an existing mec/nuc PCR assay and traditional culture. Methicillin-sensitive S. aureus (MSSA) that tested false-positive in the orfX-SCCmec PCR assay were further investigated with full genome sequencing using the Ion PGM™ System to verify results and causality. Based on these data, a two-step screening algorithm with initial mec/nuc PCR followed by orfX-SCCmec PCR on positive samples was suggested and tested on 1443 patient samples. 22.5 % of MSSA isolates tested false-positive with the orfX-SCCmec PCR. Full genome sequencing of these isolates identified genetic variation in the attB region of S. aureus, including empty cassette variants and non-mec SCC. The suggested two-step MRSA screening algorithm allowed us to report MRSA results for 95.6 % of all samples and 99 % of MRSA-negative samples after one day.

DNA microarray analysis of Staphylococcus aureus causing bloodstream infection: bacterial genes associated with mortality?

Providing evidence for microbial genetic determinants' impact on outcome in Staphylococcus aureus bloodstream infections (SABSI) is challenging due to the complex and dynamic microbe-host interaction. Our recent population-based prospective study reported an association between the S. aureus clonal complex (CC) 30 genotype and mortality in SABSI patients. This follow-up investigation aimed to examine the genetic profiles of the SABSI isolates and test the hypothesis that specific genetic characteristics in S. aureus are associated with mortality. SABSI isolates (n = 305) and S. aureus CC30 isolates from asymptomatic nasal carriers (n = 38) were characterised by DNA microarray analysis and spa typing. Fisher's exact test, least absolute shrinkage and selection operator (LASSO) and elastic net regressions were performed to discern within four groups defined by patient outcome and characteristics. No specific S. aureus genetic determinants were found to be associated with mortality in SABSI patients. By applying LASSO and elastic net regressions, we found evidence suggesting that agrIII and cna were positively and setC (=selX) and seh were negatively associated with S. aureus CC30 versus non-CC30 isolates. The genes chp and sak, encoding immune evasion molecules, were found in higher frequencies in CC30 SABSI isolates compared to CC30 carrier isolates, indicating a higher virulence potential. In conclusion, no specific S. aureus genes were found to be associated with mortality by DNA microarray analysis and state-of-the-art statistical analyses. The next natural step is to test the hypothesis in larger samples with higher resolution methods, like whole genome sequencing.

Population-based epidemiology of Staphylococcus aureus bloodstream infection: clonal complex 30 genotype is associated with mortality

Staphylococcus aureus bloodstream infections (SABSI) are associated with a high burden of morbidity and mortality. The impact of specific S. aureus genotypes on outcome is unclear. The aim of this study was to evaluate the epidemiology and outcome of SABSI, with a special emphasis on the impact of bacterial clonal lineage on mortality. We conducted a 3-year population-based prospective study between 2011 and 2014, including 303 consecutive adult patients. Clinical data were obtained from interviews and medical records. S. aureus isolates were genotyped using DNA microarrays. The incidence rate of SABSI was 27.6 per 100,000 inhabitants [95 % confidence interval (CI) 24.6-31.0]. The median age of the patients was 71 years (interquartile range 56-81 years) and 61.4 % were male. Most SABSI (70.6 %) occurred in hospitals or associated to healthcare, and 34.1 % of these were associated with intravascular catheters. Only five (1.6 %) SABSI were caused by methicillin-resistant S. aureus (MRSA). The 30-day case fatality rate was 20.8 % (95 % CI 16.6-25.7). S. aureus clonal complex 30 [hazard ratio (HR) 3.9; 95 % CI 1.8-8.5, p = 0.001], unknown focus of infection (HR 4.5; 95 % CI 1.9-10.8, p = 0.001) and respiratory tract infection (HR 12.7; 95 % CI 4.6-34.6, p < 0.001) were independent predictors of mortality in a Cox regression analysis after adjusting for age, sex and underlying conditions. A high proportion of potential preventable SABSI calls for effective infection control measures. S. aureus clonal complex 30 genotype was associated with mortality in patients with bloodstream infections. The genetic basis underlying this association remains to be demonstrated.

Memory Th1 Cells Are Protective in Invasive Staphylococcus aureus Infection

Mechanisms of protective immunity to Staphylococcus aureus infection in humans remain elusive. While the importance of cellular immunity has been shown in mice, T cell responses in humans have not been characterised. Using a murine model of recurrent S. aureus peritonitis, we demonstrated that prior exposure to S. aureus enhanced IFNγ responses upon subsequent infection, while adoptive transfer of S. aureus antigen-specific Th1 cells was protective in naïve mice. Translating these findings, we found that S. aureus antigen-specific Th1 cells were also significantly expanded during human S. aureus bloodstream infection (BSI). These Th1 cells were CD45RO⁺, indicative of a memory phenotype. Thus, exposure to S. aureus induces memory Th1 cells in mice and humans, identifying Th1 cells as potential S. aureus vaccine targets. Consequently, we developed a model vaccine comprising staphylococcal clumping factor A, which we demonstrate to be an effective human T cell antigen, combined with the Th1-driving adjuvant CpG. This novel Th1-inducing vaccine conferred significant protection during S. aureus infection in mice. This study notably advances our understanding of S. aureus cellular immunity, and demonstrates for the first time that a correlate of S. aureus protective immunity identified in mice may be relevant in humans.

Staphylococcus aureus is a leading cause of skin, soft tissue and bone infections and, most seriously, bloodstream infection. When S. aureus does get into the bloodstream, it is more likely to kill than any other bacterial infection, despite all the treatments modern medicine has to offer. It has thus far developed resistance to all antibiotics licensed to treat it. Thus, there is an urgent need to develop a vaccine against S. aureus. However, such a vaccine remains elusive. This is largely due to the fact that we have a very limited understanding of how our immune system fights this infection. Here, we examine how certain T cells of the mouse immune system effectively recognise and respond to S. aureus, and show that transferring these cells to other mice improves their ability to clear infection. We then demonstrate that a vaccine which drives these specific T cells also improves clearance of infection. Until recently, it was not known if human T cells could recognise and respond to S. aureus. Here we show, for the first time, that these cells are expanded in patients with S. aureus bloodstream infection, and suggest that they should be targeted in anti-S. aureus vaccines.

No change in the distribution of types and antibiotic resistance in clinical Staphylococcus aureus isolates from orthopaedic patients during a period of 12 years

Staphylococcus aureus (S. aureus) is the most common cause of bone and joint infections. However, limited information is available on the distribution of S. aureus geno- and phenotypes causing orthopaedic infections. The aim of this study was to identify the dominating types causing infections in orthopaedic patients, investigate if the characteristics of these types changed over time and examine if different types were more often associated with surgical site infection (SSI) than primary infection (non-SSI). All clinical S. aureus isolates collected from orthopaedic patients from 2000 through 2011 at Akershus University Hospital, Norway, were characterised by S. aureus protein A (spa) typing and tested for antibiotic resistance. A total of 548 patients with orthopaedic S. aureus infections were included, of which 326 (59 %) had SSI and 222 (41 %) had non-SSI. The median age was 62 years [range 2-97 years] and 54 % were male. Among the 242 unique spa types, t084 was the most common (7 %). Penicillin resistance was identified in 75 % of the isolates, whereas the resistances to the other antibiotics tested were <5 %. Three isolates (0.5 %) were resistant to methicillin. There was no significant difference in the distribution of geno- and phenotypes over time and there was no difference in types between SSI and non-SSI. In this large collection of S. aureus from orthopaedic patients, the S. aureus infections, regardless of origin, were heterogeneous, mainly resistant to penicillin, stable over time and consisted of similar types as previously found in both carrier and other patient populations.

Low mortality of Staphylococcus aureus bacteremia in Icelandic children: nationwide study on incidence and outcome

BACKGROUND

Staphylococcus aureus is a major cause of blood stream infections, but population-based studies on pediatric S. aureus bacteremia (SAB) are sparse. The objective of the study was to evaluate the incidence and mortality of SAB in Icelandic children over time, and to assess the proportions of nosocomial and health-care-associated infections.

METHODS

Children <18 years with positive blood cultures for S. aureus from January 1995 through December 2011 were identified retrospectively at the clinical microbiology laboratories performing blood cultures in Iceland. Clinical data were collected from medical records.

RESULTS

In total, 140 children had 146 distinct episodes of SAB. Bacteremia-related mortality was 0.7% (1/146), all-cause 30-day mortality, 1.4% (2/146), and 1-year mortality, 3.6% (5/140). The annual incidence of SAB was 10.9/100,000 children, decreasing by 36% from 13.1/100,000 in 1995-2003 to 8.4/100,000 in 2004-2011 (P < 0.001). At the same time the annual number of blood cultures analyzed at the main study site decreased from 1529 to 1143 (25%). SAB incidence was highest in infants (<1 year), 58.8/100,000. Of 146 episodes 50 (34%) were nosocomial, 21 (14%) health-care associated and 75 (51%) community acquired. No methicillin-resistant S. aureus isolate was identified.

CONCLUSIONS

In this nationwide study on pediatric SAB, the case fatality ratio was very low. A decreasing incidence was seen, possibly related to fewer blood cultures being collected. Nosocomial and health-care-associated infections accounted for 50% of the cases. The findings provide useful information on the epidemiology and outcome of SAB in children.

Long term molecular epidemiology of methicillin-susceptible Staphylococcus aureus bacteremia isolates in Sweden

Staphylococcus aureus is one of the major pathogens that causes bacteremia; therefore, it is important to understand the long-term molecular epidemiology of S. aureus bacteremia infections. In particular, little is known about the population structure of methicillin-sensitive S. aureus (MSSA) compared to that of methicillin-resistant S. aureus. We investigated potential changes in the MSSA molecular epidemiology in Örebro County, Sweden, from 1980 through 2010. 400 MSSA bacteremia isolates, the first 100 isolated each decade from 1980 through 2010, were retrospectively identified and analyzed regarding assignment to clonal complexes (CCs), presence of virulence genes and antibiotic resistant determinants with DNA microarray-based genotyping. 24 different CCs were identified. Most isolates (80%) belonged to 6 predominant lineages. Of those, the number of isolates assigned to CC5 and CC15 increased, and those assigned to CC8, CC25, and CC30 decreased. The most prevalent clone, CC45, did not show a significant change in prevalence during the study period. A change in prevalence was observed for some of the virulence genes, mainly attributed with their association to certain CCs. With the exception of the common blaZ gene (encoding penicillinase), antibiotic resistance genes were only sporadically detected. In conclusion, the MSSA population structure was genetically diverse. We observed decadal changes in assignments to five predominant clones, and corresponding changes in the prevalence of some virulence genes linked to CC affiliation. In light of the restrictive antibiotics prescriptions and extensive infection control procedures in Sweden, antibiotic resistance genes were rarely detected and their prevalence unaffected during the study period.

spa typing alone is not sufficient to demonstrate endemic establishment of meticillin-resistant Staphylococcus aureus in a low-prevalence country

BACKGROUND

The prevalence of meticillin-resistant Staphylococcus aureus (MRSA) in Norway is low but increasing. Over the last decade, numerous nursing homes have experienced MRSA outbreaks. One genetic lineage, spa type t304, has been identified at multiple nursing homes and has caused large outbreaks lasting for several years.

AIM

To evaluate whether spa typing is sufficient for the detection of MRSA spread and endemic establishment in a low-prevalence area, using spa type t304 as the test organism.

METHODS

All spa type t304 isolates detected in 1991-2010 in the most densely populated area of Norway were included. Time and place of bacterial sampling were recorded. The isolates were analysed using multi-locus sequence typing, staphylococcal cassette chromosome mec typing, detection of lukS/F-PV and pulsed-field gel electrophoresis (PFGE).

FINDINGS

In total, 181 spa type t304 isolates were identified in three of 23 municipalities. Most (91%) of the isolates could be linked to 13 nursing homes, eight of which experienced outbreaks. PFGE analysis revealed three PFGE types, consisting of 19 PFGE patterns; 95% of the isolates were PFGE type 2. In total, PFGE types 2 and 3 accounted for 99% of all nursing home isolates, and included isolates from different nursing homes, different outbreaks and different time periods. Additional genetic analyses did not further differentiate between the spa type t304 isolates.

CONCLUSION

MRSA spa type t304 appears to have established itself as an endemic genetic lineage in the study area. spa typing does not provide sufficient resolution when investigating the spread of an endemic-like genetic lineage in a low-prevalence area, and should be supplemented by additional typing techniques.

Phenotypes and genotypes of old and contemporary porcine strains indicate a temporal change in the S. aureus population structure in pigs

INTRODUCTION

Staphylococcus aureus sequence type ST398 has recently gained attention due to the spread of methicillin-resistant strains among people exposed to livestock. The aim of this study was to explore temporal changes in the population structure of S. aureus in pigs over the last 40 years with particular reference to the occurrence of ST398.

METHODS

We analysed a unique collection of 91 porcine strains isolated in six countries between 1973 and 2009 using a biotyping scheme described in the 1970's in combination with spa typing and multi-locus sequence typing (MLST). The collection comprised 32 historical isolates from 1973-1974 (n = 19) and from 1991-2003 (n = 13), and 59 contemporary isolates from 2004-2009. The latter isolates represented the most common MLST types (ST1, ST9, ST97 and ST433) and spa types isolated from pigs in Europe.

RESULTS AND DISCUSSION

S. aureus sequence type ST398 was not found among old isolates from the 1970's or from 1991-2003, suggesting that this lineage was absent or present at low frequencies in pigs in the past. This hypothesis is supported by the observed association of ST398 with the ovine ecovar, which was not described in pigs by studies carried out in the 1970's. In addition, various phenotypic and genotypic differences were observed between old and contemporary isolates. Some biotypes commonly reported in pigs in the 1970's were either absent (human ecovar) or rare (biotype A) among contemporary isolates. Nine clonal lineages found among old porcine isolates are occasionally reported in pigs today (ST8, ST30, ST97, ST387, ST1092, ST2468) or have never been described in this animal host (ST12, ST133, ST1343). These results indicate that the population structure of porcine S. aureus has changed over the last 40 years and confirm the current theory that S. aureus ST398 does not originate from pigs.

Molecular typing of MRSA and of clinical Staphylococcus aureus isolates from Iaşi, Romania

Romania is one of the countries with the highest prevalence of methicillin-resistant Staphylococcus aureus (MRSA) in the world. To obtain data on affiliation of MRSA to strains and clonal complexes and on the population of methicillin susceptible S. aureus (MSSA), clinical isolates from bloodstream infections, skin and soft tissue infections as well as from screening swabs were collected at hospitals in Ia?i, a city in the North-Eastern part of Romania. Isolates were characterised by microarray hybridisation. Nearly half of all isolates (47%), and about one third (34%) of bloodstream isolates were MRSA. The prevalence of the Panton-Valentine leukocidin (PVL) was also high (31% among MRSA, 14% among MSSA). The most common MRSA strain was a PVL-negative CC1-MRSA-IV that might have emerged locally, as a related MSSA was also common. PVL-positive CC8-MRSA-IV (“USA300”) and PVL-negative ST239-like MRSA-III were also frequently found while other MRSA strains were only sporadically detected. Among MSSA, PVL-positive CC121 as well as PVL-negative CC1, CC22 and CC45 predominated. Although this study provides only a snapshot of S. aureus/MRSA epidemiology in Romania, it confirms the high burden of MRSA and PVL on Romanian healthcare settings.

A recommendation to perform a blood culture before the administration of intravenous antibiotics increased the detection of Staphylococcus aureus bacteremia

In 2004, the Surviving Sepsis Campaign was launched to increase awareness and improve the outcome of severe sepsis. Accordingly, in Jönköping County, Sweden, a strong recommendation to perform a blood culture before the start of intravenous antibiotic treatment was introduced in 2007. Moreover, a reminder was included in the laboratory report to consult an infectious disease specialist when Staphylococcus aureus was isolated from a blood culture. Retrospectively, patients with at least one blood culture growing S. aureus during 2002 through 2003 (pre intervention n = 58) or during 2008 through 2009 (post intervention n = 100) were included. Medical records were evaluated regarding clinical data and outcome. Blood culture isolates were characterized by antibiotic susceptibility testing (AST) and S. aureus protein A (spa) gene typing. The annual incidence of S. aureus bacteremia (SAB) increased from 28 per 100,000 inhabitants at the pre intervention period to 45 per 100,000 at the post intervention period (p = 0.046). During post intervention, the SAB incidence was significantly higher in men (p = 0.009). The mortality rate during hospital stay was 14 % during pre intervention and 18 % during post intervention (p = 0.47). The most common spa types were t012 and t084. The Surviving Sepsis Campaign resulted in an increased number of detected cases of SAB. The mortality rate was the same before and after the intervention, and no spa type correlated to certain clinical manifestations or mortality.

Genetic characterization of Staphylococcus aureus isolates causing bloodstream infections in Austria

A total of 112 Staphylococcus aureus bloodstream isolates were genetically characterized. Spa typing and DNA microanalysis exhibited high diversity, resulting in 64 different spa types and 9 different SplitsTree clusters. Methicillin-resistant S. aureus (MRSA) were found in 6 cases only, including the first case of life-stock-associated MRSA (MRSA ST398) in bloodstream infection in Austria.

Characterization of PVL-positive MRSA from Norway

Norway is a country in which the Methicillin-resistant Staphylococcus aureus (MRSA) prevalence has been low for the last decades. There are virtually no epidemic, hospital-acquired MRSA because of an emphasis on strict infection control rules and restrictive use of antibiotics. However, community-acquired and/or Panton-Valentine leucocidin (PVL)-positive MRSA need to be monitored as these strains are transmitted outside of healthcare facilities and cannot be contained by healthcare-centred strategies. All 179 non-repetitive isolates of PVL-positive MRSA that were received during 2011 at the regional infection control laboratory at Akershus University Hospital were preserved and spa typed. Seventy isolates were further characterized by DNA microarray hybridization. The most common PVL-MRSA lineages were ST8-MRSA-IV and CC30-MRSA-IV. Further common clones were CC80-MRSA-IV and CC5-MRSA-IV. Other clones were found sporadically. These included ST772-MRSA-V and ST834-MRSA-IV, the latter in patients with epidemiological connections to the Philippines. Small-scale family outbreaks affecting at least 49 individuals were noted, with numbers of known cases per outbreak ranging from two to seven. At least 24 cases were related to foreign travel to Eritrea, India, Iraq, Macedonia, Pakistan, the Philippines, Poland, Singapore, Turkey, the USA and Vietnam. These data show that community-acquired/PVL-positive MRSA are not yet a major public health problem in Southern Norway. Our study corroborates the current practice of mandatory screening of patients and staff with travel histories, admissions or employment in healthcare institutions outside the Scandinavian countries or with known MRSA contacts.

[Cases of MRSA in nursing homes in Oslo 2005-11]

BACKGROUND

The number of infections caused by MRSA has increased substantially in Norway in the past decade. It is an objective to prevent MRSA from becoming established in nursing homes and hospitals. The purpose of the article is to describe the features of the development of MRSA cases found in nursing homes in Oslo.

MATERIALS AND METHOD

We carried out a retrospective study of registered cases of MRSA (both sufferers and carriers) in Oslo in 2005-11. Data were obtained from the City of Oslo municipal health services' MRSA database and from genotyping carried out at Akershus University Hospital.

RESULTS

The annual number of cases of MRSA found in Oslo increased during the period 2005-11 from 92 in 2005 to 268 in 2011, a total of 1198 cases. Of these, 224 cases (19%) were registered in nursing homes, distributed among 22 institutions, 158 residents and 66 staff, with an average of 32 cases annually (14-58 spread). Twenty-eight of 50 nursing homes had no cases of MRSA, while 159 of the cases were related to outbreaks of MRSA. Three of 20 outbreaks affected residents only. The nursing home isolates consisted of 40 different spa types, of which 160 (71%) of the isolates were clustered in three clonal complexes. The most common spa type t304 was found in 116 (52%) of the cases.

INTERPRETATION

Cases of MRSA in Oslo in total increased sharply from 2005 to 2011, while the number of cases in nursing homes was stable. It is, however, uncertain whether this reflects the actual incidence.

Molecular characterization of methicillin-sensitive Staphylococcus aureus isolates from bacteremic patients in a Norwegian University Hospital

Staphylococcus aureus bacteremia is common in both nosocomial and community settings, and the pathogenicity of the microbe depends upon a large repertoire of virulence factors. S. aureus bacteremia isolates (n = 126) were characterized using DNA microarrays. Clonal complexes 5, 8, 15, 30, and 45 accounted for 74.6% of the isolates. We identified geographical differences in dominating clones and toxin gene profiles. One isolate was methicillin resistant. Potential associations between age and genotype were detected.