Automated systems in the identification and determination of methicillin resistance among coagulase negative staphylococci

Abstract

Coagulase-negative staphylococci (CoNS) (accuracy of 96.8 vs 78.8%, respectively); isolates from the following species had no precise identification: Staphylococcus haemolyticus, S. simulans, and S. capitis. Both systems were similar in the characterization of methicillin resistance. The higher discrepancies for gene mec detection were observed among species other than S. epidermidis (S. hominis, S. saprophyticus, S. sciuri, S. haemolyticus, S. warneri, S. cohnii), and those with borderline MICs.Key words: coagulase-negative staphylococci -methicillin -automated systems Coagulase-negative staphylococci (CoNS) become important nosocomial pathogens, being, in many institutions, among the main etiological agents of nosocomial bacteremias (Cockerill et al. 1997, Hussain et al. 1998, Petinaki et al. 2001. Many clinical laboratories do not identify CoNS in species level when these microrganisms are detected in blood or in cerebrospinal fluid. However, as the significance of CoNS as pathogens has been increased, it has become more important to know the epidemiology and the pathogenic potential of species, individually. This might be particularly important considering blood culture isolates, since it is often difficult to determine the clinical significance of an individual isolate. There are numerous commercial systems and kits available nowadays for the identification of CoNS species (Kloos & Bannerman 1999).Resistance to methicillin among these microrganisms is a matter of concern because of the high and increasing levels detected. In Brazil, a multicenter study showed that methicillin resistance was observed in 87.7% of CoNS isolated from bloodstream infections (Sader et al. 1999). The accurate detection of methicillin resistance among CoNS isolates in the clinical laboratory is important to guide therapy and to promote the correct use of glycopeptides (Hussain et al. 1998, Yamazumi et al. 2001.This work was performed to evaluate the accuracy of two automated systems in the identification of species and determination of methicillin resistance, considering as gold standard the conventional biochemical tests and the characterization of mecA gene by polymerase chain reaction (PCR), respectively. MATERIALS AND METHODSBacterial samples -Ninety-four consecutive CoNS isolates were included in the study, coming from blood cultures of patients hospitalized in the Complexo Hospitalar Irmandade Santa Casa de Misericórdia in Porto Alegre. The isolates were kept at -20 o C in skim milk (Difco), plus 20% glycerol. The quality control of the tests was done using the Staphylococcus hominis ATCC 27844, S. epidermidis ATCC 12228, S. saprophyticus CCM 883, S. haemolyticus CCM 2737, and S. aureus ATCC 33591. Identification of bacterial isolates by conventional biochemical tests -The isolates were identified by conventional biochemical tests based on Manual for Clinical Microbiology (Bannerman 2003). The following test were used: catalase test, coagulase test, clumping factor, urease activity, ornitine decarboxilation, PYRase activi...

Bacteremias por Staphylococcus coagulase negativos oxacilina resistentes em um hospital escola na cidade de Santa Maria, Estado do Rio Grande do Sul

“…Esta resistência está relacionada à presença do gene cromossômico mecA, o qual codifica a produção de proteínas ligadoras de penicilina (PBP) alteradas, denominadas PBP2a ou PBP2', com baixa afinidade por antibióticos β-lactâmicos 4,11 . Nos últimos anos, o aumento substancial nos índices de resistência à oxacilina em SCN, tem gerado maior preocupação acerca de diagnósticos laboratoriais precisos, visto que são fundamentais para orientar a terapêutica e promover o uso racional de antimicrobianos glicopeptídeos 12 .…”

Comparison phenotypic and genotypic identification of Staphylococcus species isolated from bovine mastitis

“…The significance of S. aureus was well recognized not only to to animal health as well to human health. It is also imperative to point out the relevance of those other species to public health in view of the fact that S. epidermidis frequency among human isolates ranged from 43% to 92%, depending on the geographical region where the study was conducted (Ieven et al 1995, Couto et al 2001, Vuong & Otto 2002, De Paulis et al 2003, Spanu et al 2003, Cunha et al 2004, Caierão et al 2006. Among hospitalized Brazilian patients Pereira (2014) studying 300 CoNS isolated by blood cultures from verified that S. epidermidis was the most frequent identified specie (74.3%) and followed by S. haemolyticus 27 (9.0%), S. hominis 22 (7.3%), S. warneri 14 (4.7%), S. lugdunensis 9 (3.0%) e S. capitis 5 (1.7%).…”

Expert Systems in Clinical Microbiology

“…Results for the Automicrobic, Vitek Legacy, and Vitek 2 (3,12,40,54,66,83,91,105,106,112,115,116,123,129,131,140,141,146,148,165,168,169,186,205,213,219,230,249,250,264,278,294,297,298,300,301); Phoenix (44,111,129,172,204,238,249), and autoScan/MicroScan (4,28,39,40,54,69,104,116,…”