Regional differences and trends in antimicrobial susceptibility of Acinetobacter baumannii

Highlights

• Acinetobacter baumannii susceptibility varied by geographic region but was low everywhere.

• Resistance increased over time in several regions.

• Multidrug resistance was highest in Europe and the Middle East.

• These patterns can help direct antimicrobial therapy and infection control efforts.

Abstract

Acinetobacter baumannii, although representing a small percentage of Gram-negative bacilli isolates in intra-abdominal infections (IAIs) and urinary tract infections (UTIs), is frequently multidrug-resistant (MDR) and can pose difficult therapeutic challenges. From 2011 to 2014, 2337 A. baumannii were collected from IAIs and UTIs at 453 hospital sites in 48 countries as part of the SMART ongoing surveillance initiative. Current susceptibility and multidrug resistance, defined as resistance to at least three of the tested drug classes, were determined in a subset of 1011 isolates from 2013 to 2014. A. baumannii comprised 0.7–4.6% of all aerobic and facultative Gram-negative bacilli isolated in six global regions. MDR rates were lowest in North America (47%) and highest in Europe and the Middle East (>93%), with higher rates in ICUs than in non-ICU wards in almost all regions. Antimicrobial susceptibility profiles varied by region but resistance was high everywhere, with no drug inhibiting >70% of A. baumannii isolates in any region. Susceptibility to imipenem was highest in North America (64%) and lowest in Europe and the Middle East (≤11%). Amikacin overall was the most active of the studied agents, including against MDR isolates (of which 11–38% were susceptible). Trend analysis of only those countries that contributed isolates in each study year (2011–2014) demonstrated an increasing trend in MDR rates in the Middle East as well as decreasing susceptibility to several single antimicrobial agents in Africa, Europe and the Middle East. These patterns and trends can help direct antimicrobial therapy and infection control efforts.

Introduction

In hospitals worldwide today a host of bacterial pathogens have emerged and evolved that confound the ability to treat efficiently and in a cost-effective manner the infectious processes they cause [1], [2], [3], [4]. Increasingly over the past 10 years these pathogens are Gram-negative bacilli, including multidrug-resistant (MDR) isolates with a multitude of evolving antibiotic resistance mechanisms [5], [6]. Less commonly involved in hospital infections, but with increasing frequency, is a pathogen once considered a commensal but now considered a major hospital-associated pathogen, namely Acinetobacter baumannii [7], [8], [9], [10]. A. baumannii is intrinsically resistant to many classes of antibiotics and is frequently MDR, leaving few effective antimicrobial agents that are clinically beneficial [11], [12]. Although A. baumannii can be isolated from a variety of clinical specimens from hospitalised patients, it is commonly isolated in intensive care units (ICUs) from intubated patients [13], [14]. As A. baumannii can frequently be MDR, it is critical that appropriate susceptibility testing be performed after culture as empirical therapy may be problematic due to resistance. Surveillance programmes to monitor susceptibility can assist in delineating resistance in these isolates over time and across multiple regions globally [15], [16], [17], which may assist in choosing appropriate empirical therapy as needed and better understanding evolving resistance. This report documents the in vitro activity of clinically relevant antibiotics against a global collection of A. baumannii isolated in 48 countries from 2011 to 2014 as part of the Study for Monitoring Antimicrobial Resistance Trends (SMART) ongoing surveillance initiative.