Clinico-epidemiological nature and antibiotic susceptibility profile of Acinetobacter species.

OBJECTIVES
Acinetobacter spp. has emerged as an important opportunistic pathogen responsible for nosocomial infections in many health-care settings worldwide. The study describes the clinico-epidemiology and antimicrobial susceptibility of Acinetobacter spp. in a tertiary health-care institution. Methodology : Acinetobacter spp. were isolated from 141 specimens of the patients who reported to Universiti Kebangsaan Medical Centre (UKMMC). The sources of specimens were wound, skin and soft tissue, respiratory and urinary tract from patients in various wards. Clinio-epidemiological features of patients infected with Acinetobacter spp. were recorded. Standard bacteriological techniques with API 20NE kits and disk diffusion method were followed for identification and antibiotic sensitivity of the organisms.


RESULTS
One hundred and forty one patients with positive culture for Acinetobacter spp. were identified. Soft tissue/wound and respiratory tract were among the commonest sites of Acinetobacter spp. isolation. The isolates were most frequently obtained from ICU. All isolates were multi-drug resistant and had a resistance rate of more than 70% to most antibiotics, except polymyxin B.


CONCLUSION
High prevalence of multi-drug resistance Acinetobacter spp. provides essential information on judicious antibiotic selection for empirical therapy in our health-care institution.

Bacterial isolates: From October 2010 to April 2011, non-duplicate isolates of Acinetobacter spp. grown from all clinical specimens of hospitalized patients were analyzed. The sources of isolates included blood, sputum, tracheal aspirate, bronchoalveolar lavage, pus, sterile body fluid and urine. In this study, nosocomial isolate was defined as isolate grown from specimen that was sampled after 48 hours of hospitalization. Non-nosocomial isolate was defined as isolate grown from specimen sampled within 48 hours of hospitalization. Colonizer was defined as isolate that had microscopy smear showing 0 to 1 pus cell/high power field. Isolate showing more than 1 pus cell/high power field was regarded as significant isolate. Patient data: Medical and demographic data of hospitalized patients with culture-positive Acinetobacter spp. were retrieved from patients' medical records. Data that were recorded include age, gender, ward location, date of hospitalization, transfer and discharge, date of specimen sampling, specimen site, ICU stay and antibiotic usage. Laboratory identification: Microbiological data were obtained from laboratory records. Bacterial colonies grown on MacConkey plates were identified by its colonial morphology, Gram-staining and oxidase test. Genus identification was performed using conventional biochemical tests. For blood and sterile body fluid specimens, speciation was performed using API 20NE system, based on manufacturer's instruction (bioMérieux, France). Antimicrobial susceptibility test: The antimicrobial susceptibility testing was assessed by disk diffusion method, according to the guidelines of Clinical and Laboratory Standards Institute (CLSI). 4

RESULTS
A total of 141 non-duplicate isolates of Acinetobacter spp. grown from all clinical specimens were included in this study. Distribution for the 141 isolates was as shown in Fig.1. The isolates were most frequently derived from ICU, followed by medical, orthopedics and surgery wards. Soft tissue/wound (43.3%) and respiratory tract (31.2%) were among the commonest sites of isolation (Table-I). The isolates were predominantly colonizers (53.2%). Only 66/141 (46.8%) isolates were regarded as significant based on the presence of pus cells in Gram stain smear.
The demographic characteristics and clinical epidemiology profile of hospitalized patients with culture-positive Acinetobacter spp. are shown in Table-II. Bacterial isolates were mostly from males 85 (60.3%). The median age of patients was 54 (IQR In this study, 93/141 patients (66.0%) received antibiotics before the isolation of Acinetobacter spp. Thirty-seven of them (39.8%) had one course of antibiotic therapy. Thirty out of ninety-three (32.3%) patients had 2 courses of antibiotic therapy and 26/93 (28.0%) patients had three or more courses of antibiotic therapy prior to Acinetobacter spp. isolation. The most common antibiotic used was meropenem (22.5%), followed by ceftriaxone (17.6%), piperacillin-tazobactam (13.4%) and amoxicillin-clavulanate (12.0%).
The MIC90 was 2 mcg/mL. Comparison of the rate of antibiotic resistance between ICU and non-ICU isolates did not show any significant difference (p>0.05).

DISCUSSION
In the past two decades, Acinetobacter spp. have been considered as important opportunistic pathogens responsible for nosocomial infections, especially among patients in intensive care units (ICUs). 5 The data in this study showed that most of these isolates were obtained from soft tissue and wound followed by respiratory tract. Most of them were isolated from the intensive care unit (ICU), which suggests that seriously ill patients in ICUs have a greater chance of becoming colonized or infected by Acinetobacter spp. especially through the soft tissue/wound and respiratory tract. Similarly Falagas et al 6 reported that infections caused by Acinetobacter spp. are more common in the ICUs in Asian and European hospitals and are lower in the United States hospitals, also Carlet et al 7 and Peleg et al 8 mentioned the prevalence of hospital-acquired infections could be as high as 25% in an ICU and there is a problem with nosocomial infection which is only one third of hospital-acquired infections that are avoidable.
Our data show that the median age of patients is 54 (31-66) which indicates the infection by Acinetobacter spp. occurs in elderly patients. One study documented the distribution of MDR-Acinetobacter was greatest in the >65 age group and long term care facilities. 9 Also, duration of stay in hospital effected to acquire Acinetobacter infections, as in our data point out that this duration is from 3 days to 78 days. In several studies which examined nosocomial, blood stream, and burn infections explained antibiotic-resistance Acinetobacter infections are associated with longer hospital stays. 10,11 The present study showed that most patients (75.2%) exposed to Acinetobacter infection after 48 hours during hospitalization are considered as nosocomial patients. Reports of Chang et al 12 and Enoch et al 13 mentioned that Acinetobacter spp. emerged as a crucial pathogen in health care -associated and nosocomial infections with high mortality, and was difficult to treat efficiently. Munoz-Price 5 also reported that hospital acquired Acinetobacter is often multidrug resistance and widespread.
In the present study, the isolates were predominantly colonizers (53.2%). Thus, Acinetobacter spp. colonization of the hospital environmental may lead to infection because they survive on both moist and dry surfaces for long periods in the hospital environment. 14 This feature of Acinetobacter is helpful to survive in hospital environments and cause infection and eliminating Acinetobacter spp. from clinical materials is difficult. 15 In this study, the frequency of patients who received antibiotics before the isolation of Acinetobacter spp. is 66.0%. The most common antibiotics that patients received before the diagnosis of Acinetobacter spp. were meropenem (22.5%), followed by ceftriaxone (17.6%), piperacillin-tazobactam (13.4%). Other studies 16,17 have reported that prior exposure to antibiotics as one of the risk factors for acquisition of Acinetobacter infections. Besides prior exposure to antibiotics 18 , other factors include long stay in hospital 19 , ICU admission, using tubes and catheter 18 and furthermore, transmission between colonized or infected patients directly from hospital equipment or through the hands of health care workers, were also reported as risk factors for acquisition of Acinetobacter spp. 20 In general, treatment options for Acinetobacter infections are limited and there are not any controlled trials to show therapeutic choices. Also, carbapenems and colistin are the options of choice for the most drug-resistant infections. 1 In view of increasing resistance of Acinetobacter to carbapenem, polymyxins have been considered an option for the treatment of multidrug resistant Acinetobacter spp. infections. 6 In this study for 28 isolates, polymyxin B was tested and all were sensitive to the drug. A study from University Malaya Medical Center also found that all 185 Acinetobacter baumannii isolates from their ICU were sensitive to polymyxin B. 2 However; there are reports of polymyxin-resistant Acinetobacter in Korea 21 and some countries in South America. 22 In our study, except for polymyxin B, tigecycline had high sensitivity rates to Acinetobacter isolates. Therefore, this new glycylcycline agent has bacteriostatic activity against multidrug Acinetobacter spp. to is the appropriate agent for skin and soft tissue infection caused by MDR Acinetobacter spp. 23 However; there are some reports of high level resistance to tigecycline among MDR Acinetobacter spp. 23 In conclusion, the present study provided some information about the patients that are prone to Acinetobacter infections based on their clinicepidemiological features. It also showed that there were high resistant rates of Acinetobacter isolates to common antibiotics except for polymyxin B which becomes emerging problem in combating nosocomial infections in Malaysia. The current findings might be helpful to strategize infection control measures and guidance for prudent use of antibiotic against Acinetobacter infections.