require_once('DBConnection.php');
define("DB_HOST", "localhost");
define("DB_USER", "placidojrc");
define("DB_PASS", "");
define("DB_NAME", "proyecto_fitness");
$app->get('/usuarios', function () {

$response = array();
$dbc = new DBConnection();
$sql="SELECT 'nombre' FROM usuarios";
$rs=$dbc->getQuery($sql);
$profile=$rs->fetch();
echoResponse(200, $response);
});

<?php

class DBConnection{

    private $host = DB_HOST;
    private $db = DB_NAME;
    private $user = DB_USER;
    private $pass = DB_PASS;
    private $dbh;
    private $error=null;


    public function __construct(){
        $options = array(
            PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION
        );
        $dsn="mysql:host=" . $this->host . ";dbname=" . $this->db . ";";

        try{
            $this->dbh=new PDO($dsn, $this->user, $this->pass, $options);
        }
        catch(PDOException $ex){
            $this->error=$ex->getMessage();
        }

    }

    public function __toString(){
        return $this->error;
    }

    public function __destruct(){
        $dbh=null;
    }

    public function getError(){
        return $this->error;
    }

    public function runQuery($query){
        try{
            return $this->dbh->exec($query);
        }
        catch(PDOException $ex){
            $this->error=$ex->getMessage();
            return "Error";
        }
    }

    public function getQuery($query){
        try{
            $sentencia = $this->dbh->query($query);
            $sentencia->setFetchMode(PDO::FETCH_ASSOC);
            return $sentencia;
        }
        catch(PDOException $ex){
            $this->error=$ex->getMessage();
            return "Error";
        }
    }


}?>