Antimicrobial susceptibility pattern of Acinetobacter isolates from patients in Kenyatta National Hospital, Nairobi, Kenya

Introduction Infection due to multidrug-resistant microorganisms is a growing threat in healthcare settings. Acinetobacter species specifically A. baumannii is increasingly becoming resistant to most antimicrobial agents recommended for treatment. This study aimed to determine the antimicrobial susceptibility pattern of Acinetobacter species isolated from patients in Kenyatta National Hospital. Methods We conducted a retrospective study based on VITEK 2 (BioMérieux) electronic records capturing identification and antimicrobial susceptibility of Acinetobacter isolates from patient samples analyzed between 2013 and 2015 at Kenyatta National Hospital microbiology laboratory. Generated data were analyzed using WHONET and SPSS. Results A total of 590 Acinetobacter isolates were analyzed. 85% of the isolates tested were multi-drug resistant (MDR). Among the 590 isolates, 273 (46%) were from tracheal aspirates and 285 (48%) from the critical care unit. A. baumannii was the most frequently isolated species with high susceptibility to amikacin (77%) and poor susceptibility to ciprofloxacin (69-76%), tobramycin (37%) and meropenem (27%). Both A. lwoffii and A. haemolyticus had high susceptibility to amikacin (80-100%) and meropenem (75-100%). Conclusion A. baumannii is resistant to commonly administered antibiotics. There is need for continuous antimicrobial resistance surveillance especially in health care facilities and strengthening of antibiotic stewardship programmes which will contribute to enhancement of infection control policies.


Introduction
The genus Acinetobacter comprises of non-motile gram-negative coccobacilli bacteria. The colonies are 1 to 2mm, non-hemolytic, mucoid, smooth and round on sheep's blood agar after 24 hours of incubation at 37ºC (Figure 1) [1][2][3]. Most species in this genus have emerged as common pathogens causing community as well as hospital-acquired infections [4,5]. Hospital-acquired infections are common among patients admitted in the intensive care unit (ICU) and those patients not admitted in the ICU but are immunocompromised.
Infections linked to these species include wound infections, urinary tract infections, pneumonia and bacteremia subsequent to trauma, urinary catheters, mechanical ventilators and central venous access catheters respectively. These infections increase the length of hospital stay and risk of hospital death [6]. As a health concern, Acinetobacter associated infections are difficult to treat due to the natural tendency of acquisition and spread of multidrug-resistant strains among hospitalized patients and the organisms' different mechanism of antimicrobial resistance [7,8]. This has contributed to the high morbidity and mortality rate ranging from 27% and 91% especially in immunocompromised patients in the last three decades [9]. Globally, the occurrence of MDR Acinetobacter, particularly A. baumannii has been reported through several epidemiological studies [10] with a documentation of 10-15% prevalence of Acinetobacter resistance to carbapenem, penicillins and fluoroquinolones [11,12]. Acinetobacter species have relatively high resistance to carbapenems, even in countries with high level of awareness and vibrant national nosocomial infection surveillance with an overall low antibiotic resistance [11][12][13].
However, carbapenems remain the treatment of choice for Acinetobacter infections [14]. In two separate studies conducted in Kenya, one study noted that 10% of community-acquired bacteremia was associated with Acinetobacter species [13]

Methods
This was a retrospective study. We analyzed electronic laboratory records of Acinetobacter isolates from clinical specimens analyzed between 2013 and 2015 at KNH microbiology laboratory. Identification and antimicrobial susceptibility data were retrieved from the VITEK-2 antimicrobial susceptibility system and exported to WHONET through BACLINK. Analysis was done using WHONET version 5.6 and IBM SPSS Statistics version 21. Identification of Acinetobacter isolates was done using VITEK-2 Gram Negative identification card (GN83). Clinical specimens were mainly tracheal aspirates, pus, and urine and were

Discussion
In this study, we recorded 95% of Acinetobacter baumannii from all the samples analyzed. Other species were detected in low numbers and included Acinetobacter lwoffii ( A. baumannii and A. lwoffii were the predominant species. The predominance of Acinetobacter baumannii is most likely due to its ability to survive for a long period in the hospital environment, the potential to respond to selective environment pressure and its nonfastidious nature. Based on hospital units and specimen type, majority of the isolates were obtained from samples collected from the critical care unit (48%) and tracheal aspirates (46%) respectively.
Consequently, high level of resistance (71-86%) to the commonly used antibiotics was noted in isolates from these units. Acinetobacter species. In our study, A. baumannii was resistant to meropenem (72%), compared to A. lwoffii and A. haemolyticus which recorded a high susceptibility of 100% and 75% respectively. Studies in other countries have however reported a slightly higher rate of resistance to meropenem (80-87%) in A. baumannii [28,35,36].

Conclusion
We report a high proportion of Acinetobacter isolates from samples obtained from critical care unit (48%) and tracheal aspirates (46%).

What is known about this topic
• Acinetobacter is a non-motile, gram-negative coccobacillus that is found in the environment and colonizes the human body; • Acinetobacter is a nosocomial pathogen associated with high mortality and morbidity especially among the immunocompromised patients; • It's known for its intrinsic antibiotic resistance mechanism and the ability to rapidly acquire resistance genes.

What this study adds
• Acinetobacter baumannii was the most frequently isolated species and demonstrated high susceptibility to amikacin; • Other species isolated were A. lwoffii and A. haemolyticus.
Both had high susceptibility to amikacin, meropenem, ciprofloxacin and gentamicin, but showed poor susceptibility to cephalosporins; • Critical care units and tracheal aspirate had the highest proportion of A. baumannii isolates and recorded high resistance to commonly used antibiotics such as penicillins, fluoroquinolones, cephalosporins and meropenem.

Competing interests
The authors declare no competing interests.

Authors' contributions
All the authors were involved in designing, data interpretation, and manuscript preparation. Victor Musyoki, Moses Masika and Gitau Wilfred also participated in data retrieval and data analysis. All the authors read and approved the final manuscript.