llamando a funciones de contrato inteligente desde app.js

Implementé un contrato inteligente en la red de ganache usando trufa de la cuenta 1. El código del contrato inteligente es el siguiente.

pragma solidity ^0.4.0;

import "./strings.sol";
import "./safemath.sol";
contract PublishService {

    using strings for *;
    using SafeMath for uint;
    struct ServiceListStruct {
        string cloudID;
        address gatewayID;
        string serviceProducerID;
        mapping (string => string) serviceProducerMetadata;
        string serviceConsumerMetaAttr;
        string accessControlModel;
    }

    ServiceListStruct[] public BCServiceList;

    uint BCServiceListIndex;

    function PublishService() {
        BCServiceListIndex = 0;
    }

    modifier onlyServiceProducerOwner(address _gatewayID) {
        require(msg.sender == _gatewayID);
        _;
    }

    ServiceListStruct sls;
    uint public maxParams = 0;


    function addEntry(string _cloudID, address _gatewayID, string _serviceProducerID, string _serviceProducerMetadata, string _serviceConsumerMetaAttr, string _accessControlModel) public onlyServiceProducerOwner(_gatewayID) returns (uint) {
        sls.cloudID = _cloudID;
        sls.gatewayID = _gatewayID;
        sls.serviceProducerID = _serviceProducerID;
        sls.serviceConsumerMetaAttr = _serviceConsumerMetaAttr;
        sls.accessControlModel = _accessControlModel;
        BCServiceList.push(sls);
        //
        string memory s1;
        string memory s2 = _serviceProducerMetadata;
        string memory s3;
        bytes memory s2bytes = bytes(_serviceProducerMetadata);
        uint paramCount = 0;
        while(s2bytes.length != 0) {
            (s1,s2) = splitString(s2,";");
            (s1,s3) = splitString(s1,":");
            BCServiceList[BCServiceListIndex].serviceProducerMetadata[s1] = s3;
            paramCount = paramCount.add(1);
            s2bytes = bytes(s2);
        }
        if(maxParams < paramCount) {
            maxParams = paramCount;
        }
        BCServiceListIndex = BCServiceListIndex.add(1);
        return 1;
    }

    function deleteEntry(string _cloudID, address _gatewayID, string _serviceProducerID) public onlyServiceProducerOwner(_gatewayID) returns (uint) {
        require(msg.sender == _gatewayID);
        int pos = -1;
        for(uint index = 0; index < BCServiceList.length; index++) {
            if(compareStringsbyBytes(_cloudID, BCServiceList[index].cloudID)) {
                if(_gatewayID == BCServiceList[index].gatewayID) {
                    if(compareStringsbyBytes(_serviceProducerID, BCServiceList[index].serviceProducerID)) {
                        pos = int(index);
                    }
                }
            }
        }
        if(pos > -1) {
             BCServiceList[index] = BCServiceList[BCServiceList.length -1];
             delete BCServiceList[BCServiceList.length - 1];
             BCServiceList.length--;
             return 1;
        }
        else
            return 0;
    }

    function compareStringsbyBytes(string s1, string s2) internal pure returns(bool) {
        bytes memory s1bytes = bytes(s1);
        bytes memory s2bytes = bytes(s2);
        if(s1bytes.length!=s2bytes.length) {
            return false;
        }
        else {
            for(uint i = 0; i < s1bytes.length; i++) {
                if(s1bytes[i] != s2bytes[i])
                return false;
            }
            return true;
        }
    }

    function splitString(string _s, string _seperator) internal returns(string, string) {
        var s_slice = _s.toSlice();
        var seperator_slice = _seperator.toSlice();
        string memory result = "";
        var result_slice = result.toSlice();
        result_slice = s_slice.split(seperator_slice);
        return (result_slice.toString(), s_slice.toString());
    }
}

Ahora creé un archivo app.js como se muestra a continuación, donde intento llamar a una función de ese contrato inteligente usando PublishService.addEntry (...).

var Web3 = require('web3');
var web3Provider = null;
var PublishService;
var contract = require('./PublishService_abi.js');

function init() {
  //initializing web3 to access blockchain
  initweb3();
}

function initweb3() {
  //To make sure not to overwrite the already set provider when in mist, check first if the web3 is available
  if (typeof web3 !== 'undefined') {
    web3 = new Web3(web3.currentProvider);
  } else {
    // create an instance of web3 using the HTTP provider
    web3 = new Web3(new Web3.providers.HttpProvider("http://localhost:7545"));
  }
  web3.eth.defaultAccount = web3.eth.accounts[1];
  var PublishServiceContractAddress = "0x6c68d153b9709283e3900e944f1c6677273987c5";
  var PublishServiceContract = new web3.eth.Contract(contract,PublishServiceContractAddress ); 
  PublishService.addEntry("LC1", web3.eth.defaultAccount, "SP1", "location:inside;reading:degree", "scattr", "ngac");
}

init();

Pero esto da un error

TypeError: no se puede leer la propiedad 'addEntry' de undefined

Seguí muchos tutoriales y sugirieron lo mismo, pero no entiendo el motivo del fracaso en mi caso.

¡Gracias!