Identification of microorganisms present in blood cultures of patients in intensive care units and evaluation of coagulase-negative Staphylococcus

Author(s)

Aydir Cecília Marinho Monteiro

• Document type: Doctoral Thesis
• Press: Botucatu. 2016-11-04.
• Institution: Universidade Estadual Paulista (Unesp). Instituto de Biociências. Botucatu
• Defense date: 2016-10-27
• Advisor: Maria de Lourdes Ribeiro de Souza Cunha; Carlos Magno Castelo Branco Fortaleza

Abstract

The rapid and accurate identification of microorganisms which cause bloodstream infections is one of the major roles of the clinical microbiology laboratory. Aiming at reducing the time spent in identifying such microorganisms, several devices have been developed, including the VITEK® 2 system, which is routinely used in a number of clinical microbiology laboratories for identifying isolates from clinical specimens. A lot of microorganisms are isolated from blood cultures; bacteria belonging to the group of aerobic Gram-positive cocci are the main etiological agents of bloodstream infections, especially in patients kept in intensive care units (ICUs). The objectives of this study were to compare the performance of (manual and automated) species identification systems for microorganisms isolated from blood cultures by evaluating the performance of VITEK® 2 system and also to conduct a cohort study of patients who had blood cultures positive for Coagulase-negative staphylococci (CoNS) in order to address two outcomes: isolation of CoNS in more than one blood culture as opposed to a single blood culture and the factors associated with patient prognosis. Four hundred microorganisms isolated from blood cultures were identified: 5 Gram-positive bacilli, 15 yeasts, 165 Gram-negative bacilli, and 215 Gram-positive cocci. This identification was carried out by the VITEK® 2 system and the results were compared with those obtained from conventional phenotypic tests and genotypic methods. Patients with blood cultures positive for CoNS were followed during their stay in hospital with collecting the clinical data from their medical records. The automated VITEK® 2 system accurately identified 94.7% of the specimens. The YST and GN ID cards had 100% accurate identifications of the yeasts and the Gram-negative bacilli respectively, whereas the GP ID card accurately identified 92.6% of the Gram-positive cocci. The susceptibility of the VITEK® 2 system and the statistical analysis allow the conclusion that this instrument is a viable option in the routine of clinical microbiology laboratories for microorganism identification. The multivariate analysis for death as the outcome in the cohort study of patients with CoNS positive blood culture revealed positive associations with AIDS and with blood culture positive for S. hominis, while the use of meropenem showed a negative association. In analyzing the outcome of multiple blood cultures positive for CoNS, a positive association was observed in patients with shock (requiring vasoactive drugs). It suggests that the sepsis (shock) severity is a predictor of CoNS clinical significance with the isolation in more than one blood culture, which is one of the most commonly used criteria for clinical recovery of the microorganisms when isolated from the bloodstream. The analysis of the survival curve of patients included in the cohort revealed that patients with blood cultures positive for S. hominis species showed lower survival compared to patients with blood cultures for other species of CoNS, which indicates the importance of this species in the severity of bloodstream infections. (AU)

• FAPESP's process: 12/15366-8 - PHENOTIPIC AND GENOTIPIC IDENTIFICATION OF MICRO-ORGANISMS IN BLOOD CULTURES OF PATIENTS IN INTENSIVE CARE UNIT: IMPLICATIONS AND PROFILE PATHOGENIC COAGULASE-NEGATIVE Staphylococcus.
• Grantee: Aydir Cecilia Marinho Monteiro
• Support Opportunities: Scholarships in Brazil - Doctorate