Erika A. Rodriguez

CC8 MRSA Strains Harboring SCCmec Type IVc are Predominant in Colombian Hospitals

Background Recent reports highlight the incursion of community-associated MRSA within healthcare settings. However, knowledge of this phenomenon remains limited in Latin America. The aim of this study was to evaluate the molecular epidemiology of MRSA in three tertiary-care hospitals in Medellín, Colombia. Methods An observational cross-sectional study was conducted from 2008–2010. MRSA infections were classified as either community-associated (CA-MRSA) or healthcare-associated (HA-MRSA), with HA-MRSA further classified as hospital-onset (HAHO-MRSA) or community-onset (HACO-MRSA) according to standard epidemiological definitions established by the U.S. Centers for Disease Control and Prevention (CDC). Genotypic analysis included SCCmec typing, spa typing, PFGE and MLST. Results Out of 538 total MRSA isolates, 68 (12.6%) were defined as CA-MRSA, 243 (45.2%) as HACO-MRSA and 227 (42.2%) as HAHO-MRSA. The majority harbored SCCmec type IVc (306, 58.7%), followed by SCCmec type I (174, 33.4%). The prevalence of type IVc among CA-, HACO- and HAHO-MRSA isolates was 92.4%, 65.1% and 43.6%, respectively. From 2008 to 2010, the prevalence of type IVc-bearing strains increased significantly, from 50.0% to 68.2% (p = 0.004). Strains harboring SCCmec IVc were mainly associated with spa types t1610, t008 and t024 (MLST clonal complex 8), while PFGE confirmed that the t008 and t1610 strains were closely related to the USA300-0114 CA-MRSA clone. Notably, strains belonging to these three spa types exhibited high levels of tetracycline resistance (45.9%). Conclusion CC8 MRSA strains harboring SCCmec type IVc are becoming predominant in Medellín hospitals, displacing previously reported CC5 HA-MRSA clones. Based on shared characteristics including SCCmec IVc, absence of the ACME element and tetracycline resistance, the USA300-related isolates in this study are most likely related to USA300-LV, the recently-described ‘Latin American variant’ of USA300.

Characterisation of virulence genes in methicillin susceptible and resistant Staphylococcus aureus isolates from a paediatric population in a university hospital of Medellín, Colombia

Virulence and antibiotic resistance are significant determinants of the types of infections caused by Staphylococcus aureus and paediatric groups remain among the most commonly affected populations. The goal of this study was to characterise virulence genes of methicillin-susceptible S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA) strains isolated from a paediatric population of a Colombian University Hospital during 2009. Sixty MSSA and MRSA isolates were obtained from paediatric patients between zero-14 years. We identified the genes encoding virulence factors, which included Panton-Valentine leucocidine (PVL), staphylococcal enterotoxins A-E, exfoliative toxins A and B and toxic shock syndrome toxin 1. Typing of the staphylococcal chromosome cassette mec (SCCmec) was performed in MRSA strains. The virulence genes were more diverse and frequent in MSSA than in MRSA isolates (83% vs. 73%). MRSA strains harboured SCCmec types IVc (60%), I (30%), IVa (7%) and V (3%). SCCmec type IVc isolates frequently carried the PVL encoding genes and harboured virulence determinants resembling susceptible strains while SCCmec type I isolates were often negative. PVL was not exclusive to skin and soft tissue infections. As previously suggested, these differences in the distribution of virulence factor genes may be due to the fitness cost associated with methicillin resistance.

A comparison of methicillin-resistant and methicillin-susceptible Staphylococcus aureus reveals no clinical and epidemiological but molecular differences

Most studies on Staphylococcus aureus have focused on the molecular epidemiology of methicillin-resistant S. aureus (MRSA) infections. In contrast, little information is available regarding the molecular epidemiology of currently circulating methicillin-susceptible S. aureus (MSSA) isolates in hospital settings, an epoch when the epidemiology of S. aureus has undergone significant changes. We conducted a cross-sectional study to compare the clinical, epidemiological, and genetic characteristics of MSSA and MRSA isolates at 3 tertiary-care hospitals in Medellín, Colombia, from February 2008 to June 2010. The infections were classified according to the Centers for Disease Control and Prevention (CDC) definitions. Genotypic analysis included spa typing, multilocus sequence typing (MLST) and staphylococcal cassette chromosome (mec) (SCCmec) typing. A total of 810 patients was enrolled. One hundred infections (12.3%) were classified as community-associated (31 CA-MSSA, 69 CA-MRSA), 379 (46.8%) as healthcare-associated community-onset (136 HACO-MSSA, 243 HACO-MRSA), and 331 (40.9%) as healthcare-associated hospital-onset (104 HAHO-MSSA, 227 HAHO-MRSA). Genotype analyses showed a higher diversity and a more varied spa type repertoire in MSSA than in MRSA strains. Most of the clinical-epidemiological characteristics and risk factors evaluated did not allow for discriminating MRSA- from MSSA-infected patients. The lack of equivalence among the genetic backgrounds of the major MSSA and MRSA clones would suggest that the MRSA clones are imported instead of arising from successful MSSA clones. This study emphasizes the importance of local surveillance to create public awareness on the changing S. aureus epidemiology.

Livestock-associated methicillin-susceptible Staphylococcus aureus ST398 infection in woman, Colombia.

To the Editor: Staphylococcus aureus causes health care– and community-associated infections worldwide in humans and animals. It also asymptomatically colonizes a large proportion (20%–60%) of otherwise healthy individuals. In recent years, various countries have reported an increasing number of humans infected with livestock-associated S. aureus multilocus sequence type (ST) 398, which suggests that this strain is emerging in community and health care settings (1). Methicillin-resistant S. aureus (MRSA) ST398 has received particular attention as a causative agent of infection in pigs, dogs, horses, cattle, and poultry. Colonization and infection in humans have also been described in Europe (2), Asia (3), Canada (4), and the United States (5), particularly among persons with frequent exposure to animals, such as farmers, veterinarians, and their household members. However, infections with MRSA ST398 and methicillin-susceptible S. aureus (MSSA) ST398 have recently been described in persons with no history of contact with livestock (6–10). We report infection of a woman with MSSA ST398 in Colombia, South America. On November 3, 2009, this 82-year-old woman was admitted to the emergency unit of the Hospital Universitario San Vicente Fundacion in Medellin, reporting a 15-day history of fever, dyspnea, and pain in her left leg. She lived in a rural area and reported previous contact with dogs and chickens. Her medical history included diabetes mellitus, hypertension, valvular heart disease, and chronic arterial occlusive disease. Four months earlier she had received a femoro–popliteal vascular prosthetic graft in her left leg. At the time of admission, blood culture was requested, and intravenous vancomycin (1 g every 12 hours) and piperacillin/tazobactam (4.5 g every 8 hours) were empirically administered. S. aureus was subsequently isolated from blood culture, and antimicrobial drug susceptibility was assessed in accordance with Clinical Laboratory Standards Institute guidelines by using a Vitek 2 instrument (bioMerieux, Marcy l’Etoile, France). The isolate was susceptible to methicillin, rifampin, and vancomycin but resistant to clindamycin, erythromycin, gentamicin, levofloxacin, minocycline, moxifloxacin, tetracycline, and trimethoprim/sulfamethoxazole. Additional laboratory results showed an elevated leukocyte count with predominant polynuclear neutrophils and increased C-reactive protein levels (21.2 mg/L). Angiography of the left femoro–popliteal segment showed a collection surrounding the entire vascular prosthetic graft, which was presumed to be the bacteremic focus. Accordingly, rifampin (600 mg every 12 hours) was added to the regimen, the femoro-popliteal graft was surgically removed, the collection was drained, and the limb was amputated. After the surgery, cephradine was administered for 14 days, after which clinical signs and symptoms of bacteremia resolved completely, and the patient was discharged from the hospital. The blood culture isolate was subsequently confirmed as S. aureus by PCR with primers directed to the nuc gene. Genes encoding the following virulence factors were also evaluated by PCR, but none were detected: Panton-Valentine leukocidin, arginine catabolic mobile element, staphylococcal enterotoxins A–E, exfoliating toxins A and B, and toxic shock syndrome toxin 1. Genotypic analysis indicated that the isolate belonged to multilocus ST398 (allelic profile 3-35-19-2-20-26-39) and spa type t571 (eGenomics spa type 109); pulsed-field gel electrophoresis with SmaI digestion yielded no results, as described previously for ST398 (1). This report documents the emergence of human infection caused by MSSA spa type t571 ST398 in South America. Despite being about only 1 case, this report nevertheless highlights the changing epidemiology of S. aureus within the region. The study was limited by the inability to sample animals from a surrounding farm to determine the potential for zoonotic spread of S. aureus in domestic environments. Notably, spa type t571 ST398 has been found recently in MSSA carriage isolates from New York City (6), the Dominican Republic (6), and the Amazonian region of French Guiana (9) and in clinical MSSA isolates from the Netherlands (7), People’s Republic of China (8), and France (10). Given the patients’ absence of contact with livestock in most of these reports, transmission of MSSA ST398 spa type t571 may not be limited to animal exposure, suggesting the possibility of person-to-person spread. Accordingly, our finding reinforces the need to heighten awareness of the transmission and virulence potential of MSSA ST398, particularly in developing countries where understanding of S. aureus colonization and transmission dynamics is probably limited. Such information has implications for the design of appropriate control measures to reduce human and animal infections from this emerging pathogen.

Differences in Epidemiological and Molecular Characteristics of Nasal Colonization with Staphylococcus aureus (MSSA-MRSA) in Children from a University Hospital and Day Care Centers

Background Clinical significance of Staphylococcus aureus colonization has been demonstrated in hospital settings; however, studies in the community have shown contrasting results regarding the relevance of colonization in infection by community-associated MRSA (CA-MRSA). In Colombia there are few studies on S. aureus colonization. The aim of this study was to determine the molecular and epidemiological characteristics of nasal colonization by S. aureus (MSSA-MRSA) in children from a university hospital and day care centers (DCCs) of Medellin, Colombia. Methods An observational cross-sectional study was conducted in 400 children (200 in each setting), aged 0 months to 5 years, during 2011. Samples were collected from each nostril and epidemiological information was obtained from the parents. Genotypic analysis included spa typing, PFGE, MLST, SCCmec typing, detection of genes for virulence factors and agr groups. Results Frequency of S. aureus colonization was 39.8% (n = 159) (hospital 44.5% and DCCs 35.0%) and by MRSA, 5.3% (n = 21) (hospital 7.0% and DCCs 3.5%). Most S. aureus colonized children were older than two years (p = 0.005), the majority of them boys (59.1%), shared a bedroom with a large number of people (p = 0.028), with history of β-Lactamase inhibitors usage (p = 0.020). MSSA strains presented the greatest genotypic diversity with 15 clonal complexes (CC). MRSA isolates presented 6 CC, most of them (47.6%) belonged to CC8-SCCmec IVc and were genetically related to previously reported infectious MRSA strains. Conclusion Differences in epidemiological and molecular characteristics between populations may be useful for the understanding of S. aureus nasal colonization dynamics and for the design of strategies to prevent S. aureus infection and dissemination. The finding of colonizing MRSA with similar molecular characteristics of those causing infection demonstrates the dissemination capacity of S. aureus and the risk of infection among the child population.