Abstract
This study analyzed clinical and microbiological characteristics of heteroresistant (hVISA) and vancomycin-intermediate Staphylococcus aureus (VISA) from bloodstream infections (BSI) in a Brazilian teaching hospital, between 2011 and 2013. Minimum inhibitory concentrations (MIC) of antimicrobials were determined by broth microdilution method and SCCmec was detected by PCR. Isolates with a vancomycin MIC ≥ 2mg/L were cultured on BHI agar with 3, 4 or 6 mg/L (BHIa3, BHIa4 or BHIa6) of vancomycin and BHIa4 with casein (BHIa4ca). Macromethod Etest® and Etest® Glicopeptides Resistance Detection were also used. VISA and hVISA isolates were confirmed by the population analysis profile then typed by pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing. Medical data from the patients were obtained from their medical records. Among 110 consecutive isolates, 31 (28%) were MRSA and carried the SCCmec type II (15 isolates) or IV (16 isolates). Vancomycin MIC50 and MIC90 were 1 and 2 mg/L, respectively. MRSA isolates had increased non-susceptibility to daptomycin (p = 0.0003). Six (5%) isolates were VISA, four of which were MRSA, three SCCmec type II/USA100/ST5 and one type IV/USA800/ST3192. One MRSA SCCmec II isolate grew on agar BHIa3, BHIa4 and BHIa4ca, and it was confirmed as hVISA. Among the six VISA isolates, five (83%) grew on BHIa3 and three (50%) on BHI4ca. Four of the six VISA isolates and the one hVISA isolate were from patients who had undergone dialysis. Thus, a possible dissemination of the SCCmec II/USA100/ST5 lineage may have occurred in the hospital comprising the VISA, hVISA and daptomycin non-susceptible S. aureus Brazilian isolates from health care associated bloodstream infections.
Highlights
Staphylococcus aureus continues to be an important human pathogen, and represents a challenge for public health due to its virulence and ability to develop resistance to antimicrobials [1]
Our results showed that vancomycin-intermediate resistant (VISA) and hVISA isolates were from healthcare-associated bloodstream infections (BSI) and were predominantly from staphylococcal cassette chromosome mec (SCCmec) type II/USA100/ST5 lineage
Previous reports from the United States have shown the emergence of VISA-type resistance in type II USA100/ST5/CC5 isolates [30], [31], which corresponds to the prevalent VISA clone in the present study
Summary
Staphylococcus aureus continues to be an important human pathogen, and represents a challenge for public health due to its virulence and ability to develop resistance to antimicrobials [1]. Methicillin-resistant S. aureus (MRSA) isolates harbor the mecA gene, which is located into the staphylococcal cassette chromosome mec (SCCmec). Hospital-acquired MRSA (HA-MRSA) isolates traditionally carry SCCmec types II and III, while type IV is often found in community-acquired MRSA [3]. These boundaries have become blurred with epidemiological studies showing a change in circulating lineages within hospitals [3], [4]. There are several options for the treatment of MRSA infections including such as linezolid, tigecycline, daptomycin and ceftaroline, being the last one the active metabolite of ceftaroline fosamil. Vancomycin has continued to be the primary treatment for the last fifty years [5]. There has been reports of isolates with reduced susceptibility to vancomycin, including both vancomycin-intermediate resistant (VISA) and heteroresistant S. aureus (hVISA)[6]
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