Characterization of Nasal and Blood Culture Isolates of Methicillin-Resistant Staphylococcus aureus from Patients in United States Hospitals

Abstract

A total of 299 nares and 194 blood isolates of methicillin-resistant Staphylococcus aureus (MRSA), each recovered from a unique patient, were collected from 23 U.S. hospitals from May 2009 to March 2010. All isolates underwent spa and staphylococcal cassette chromosome mec element (SCCmec) typing and antimicrobial susceptibility testing; a subset of 84 isolates was typed by pulsed-field gel electrophoresis (PFGE) using SmaI. Seventy-six spa types were observed among the isolates. Overall, for nasal isolates, spa type t002-SCCmec type II (USA100) was the most common strain type (37% of isolates), while among blood isolates, spa type t008-SCCmec type IV (USA300) was the most common (39%). However, the proportion of all USA100 and USA300 isolates varied by United States census region. Nasal isolates were more resistant to tobramycin and clindamycin than blood isolates (55.9% and 48.8% of isolates versus 36.6% and 39.7%, respectively; for both, P < 0.05). The USA300 isolates were largely resistant to fluoroquinolones. High-level mupirocin resistance was low among all spa types (<5%). SCCmec types III and VIII, which are rare in the United States, were observed along with several unusual PFGE types, including CMRSA9, EMRSA15, and the PFGE profile associated with sequence type 239 (ST239) isolates. Typing data from this convenience sample suggest that in U.S. hospitalized patients, USA100 isolates of multiple spa types, while still common in the nares, have been replaced by USA300 isolates as the predominant MRSA strain type in positive blood cultures.

Changing Susceptibility of Staphylococcus aureus in a US Pediatric Population

“…15,30,31 Other reports include clindamycin resistance exceeding 30% to 50%. 11,12 It is difficult to make direct comparisons between these studies due to significant variability in study dates, target populations, and methodology.…”

“…8 Although typically preferred over tetracyclines and trimethoprim/sulfamethoxazole (TMP/SMX), rates of resistance to clindamycin in S aureus infections vary widely, whereas resistance to tetracycline and TMP/SMX is uncommon. 11,12 A recent study comparing TMP/SMX to clindamycin in uncomplicated skin infections found these drugs comparable. 13 Several clinical and demographic factors may be associated with antibiotic susceptibility trends.…”

Genomic insights into the emergence and spread of international clones of healthcare-, community- and livestock-associated meticillin-resistant Staphylococcus aureus : Blurring of the traditional definitions

“…However, these MRSA failed to become established in hospitals in the UK and Denmark [20]. isolates are increasingly recognised as a cause of hospital-associated bacteraemia [35][36][37]. Indeed, the USA300 epidemic peaked in 2004 leading to the mathematical Page 13 of 34 A c c e p t e d M a n u s c r i p t 13 predictions that the USA300 CA-MRSA strains will eventually displace the HA-MRSA strains owing to the survival advantage of the former as a result of smaller and fewer genes leading to enhanced fitness [38].…”

Deep sternal wound infection after cardiac surgery: Evidences and controversies

“…The Society of Thoracic Surgeons practice guidelines upon antimicrobial prophylaxis recommend routine 5-d mupirocin 2% nasal administration for all patients undergoing cardiac surgery in the absence of a documented negative testing for staphylococcal colonization [41] . However, concerns still remain about the extensive use of mupirocin because of lack of efficacy, risk of widespread high-level resistance, and costs [42][43][44] . A systematic review of the literature and meta-analysis by Kallen et al [45] demonstrated a 45% reduction in surgical site infections (SSIs) caused by Staphylococcus aureus with the use of preoperative mupirocin among cardiac surgery patients known to be colonized with Staphylococcus aureus.…”