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Year : 2018  |  Volume : 14  |  Issue : 1  |  Page : 68-71

Increasing rates of Acinetobacter baumannii infection and resistance in an oncology department

1 Clinical Pharmacology Base, Xinqiao Hospital, The Third Military Medical University, Chongqing, China
2 Department of Oncology, Southwest Hospital, The Third Military Medical University, Chongqing, China
3 Department of Pharmacy, Xinqiao Hospital, The Third Military Medical University, Chongqing, China
4 Department of Outpatient, Chinese PLA August First Film Studio, Beijing, China

Date of Web Publication8-Mar-2018

Correspondence Address:
Dr. Shiwen Zhou
Clinical Pharmacology Base, Xinqiao Hospital, The Third Military Medical University, Chongqing
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jcrt.JCRT_737_17

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 > Abstract 

Objective: Acinetobacter baumannii is an opportunistic pathogen found in immunocompromised patients, especially cancer patients. This study was to investigate the clinical characteristics of cancer patients and the antimicrobial resistance of A.baumannii isolates.
Materials and Methods: Clinical isolates were collected from the oncology department of a general teaching hospital, and the clinical and demographic information of patients was obtained from the hospital's information system. Antimicrobial susceptibility was examined using the agar dilution method. Carbapenemase-encoding genes were amplified by polymerase chain reaction, and sequence types were determined by multilocus sequence typing.
Results: The isolation rate of A.baumannii increased annually in the oncology department. Multivariate analysis showed that only prior antibiotic use was an independent risk factor for A.baumannii infection. The use of antibiotics in A.baumannii-infected patients was significantly more frequent than in non-A.baumannii-infected patients. A.baumannii isolates were highly resistant to most tested antibiotics. The IMP-4 and VIM-2 genes were present in 6 and 2 isolates, respectively. Sixty isolates had 12 genotypes, and ST208 was the most common genotype.
Conclusion: Our results suggest that the use of antibiotics and hospital environmental pollution may be the main causes of A. baumannii infection.

Keywords: Acinetobacter baumannii, antibiotic use, nosocomial infection, resistance

How to cite this article:
Fan L, Wang Z, Wang Q, Xiong Z, Xu Y, Li D, Zhou S. Increasing rates of Acinetobacter baumannii infection and resistance in an oncology department. J Can Res Ther 2018;14:68-71

How to cite this URL:
Fan L, Wang Z, Wang Q, Xiong Z, Xu Y, Li D, Zhou S. Increasing rates of Acinetobacter baumannii infection and resistance in an oncology department. J Can Res Ther [serial online] 2018 [cited 2022 Nov 26];14:68-71. Available from: https://www.cancerjournal.net/text.asp?2018/14/1/68/226758

 > Introduction Top

Acinetobacter baumannii is becoming the most common pathogenic bacterium of clinical isolates, especially for nosocomial infections.[1],[2] Moreover, A. baumannii is an opportunistic pathogen and can live in the hospital environment for a month.[3],[4]

A. baumannii easily infects immunocompromised and antibiotic-therapy patients, especially cancer patients.[5],[6] However, there has been little research on A. baumannii infections in Oncology Departments. Therefore, we analyzed the characteristics of cancer patients and the antimicrobial resistances of clinically isolated A. baumannii. The objective of the current study was to determine the relationship between A. baumannii infections in patients and antibiotic use as well as other risk factors.

 > Materials and Methods Top

Bacterial isolates

A. baumannii isolates were retrospectively collected from cancer patients with nosocomial infections at the oncology department of a general teaching hospital in Chongqing, China from January 2010 to December 2015. Nosocomial infection was defined according to the guideline of Centers for Disease Control.[7] All A. baumannii samples of cancer patients were collected at 48 h after admission, and only one strain was isolated from the same patient. Patients recently colonized with A. baumannii who did not have any overt signs of infection were excluded from the study. In the clinical laboratory, these strains were first identified using the API 20-NE system. Further identification at the species level was carried out by detection of the species-specific blaOXA-51 gene and 16S rRNA gene sequencing. The demographic and clinical characteristics of the cancer patients, including gender, age, hematologic malignancy, radiation, hospitalization time, operation, and prior antibiotic use, were obtained from the hospital's information systems.

Antimicrobial susceptibility

The determination of minimal inhibitory concentrations was carried out by the agar dilution procedure according to the guidelines of Clinical and Laboratory Standards Institute (2014). Twelve antibiotics were tested, including piperacillin, ceftazidime, cefepime, gentamicin, tobramycin, ciprofloxacin, levofloxacin, amikacin, imipenem, meropenem, aztreonam and sulfamethoxazole. Pseudomonas aeruginosa ATCC27853 and Escherichia coli ATCC25922 were used as control strains. The resistance rate of A. baumannii isolates was calculated as the number of resistant strains divided by the total number of strains.

Detection of the carbapenemase genes

The amplification of carbapenemase genes was performed with primers as described previously.[8] Total genomic DNA of A. baumannii isolates was extracted using a DNeasy kit (Qiagen, Germany). The polymerase chain reaction (PCR) products were purified and sequenced using an Applied Biosystems ABI 3730 Analyzer (Applied Biosystems, Inc., USA). The sequence results were aligned using the software available on the NCBI website (https://blast.ncbi.nlm.nih.gov/Blast.cgi).

Multilocus sequence typing (MLST) analysis

The multilocus sequence typing (MLST) analysis of A. baumannii isolates was carried out as previously described.[9] The fragments of seven house-keeping genes, including cpn60, fusA, pyrG, gltA, rplB, recA, and rpoB, were determined by PCR amplification. A final 50-μl volume containing 25 μl of 2×Es Taq MasterMix, 1 μl of 10 μM each primers, and 2 μl of 10 ng/μl DNA was amplified in the GeneAmp PCR system 9700. PCR amplification conditions included an initial melt at 94°C for 2 min, followed by 35 cycles (94°C, 30 s; 50°C, 30 s; 72°C, 30 s), and ended at 72°C for 5 min. The PCR products of seven genes were purified using the QIAquick PCR purification kit (Qiagen, Germany) and then sequenced by the ABI 3730 automated DNA sequencer. The sequence types were generated using the software available on the MLST website (http://pubmlst.org/abaumannii/).

Statistical analysis

Multivariate analysis with binary logistic regression was conducted to examine the associations of risk factors with A. baumannii infection with control for potential confounders using the SPSS 17.0 software package (IBM, USA). Differences among groups were statistically analyzed using the Chi-square test. P < 0.05 was considered to be statistically significant.

 > Results Top

There were 6,154 cancer inpatients during the study, and the infection rate was 9.9% (610). The distribution of common pathogenic bacteria in cancer patients from 2010 to 2015 is shown in [Figure 1]. Gram-negative bacteria were the major pathogens infecting tumors (59.7%), followed by Gram-positive bacteria (22.8%), and fungi (18.2%). The five most common pathogenic bacteria were E. coli (22.8%), Klebsiella pneumoniae (16.7%), Staphylococcus aureus (13.6%), A. baumannii (9.8%), and P. aeruginosa (8.7%). The A. baumannii isolation rate increased annually from 2010 to 2015 whereas S. aureus decreased annually. The isolation rates of other common pathogenic bacteria remained stable and showed no clear trend of change. Multivariate analysis of risk factors for A. baumannii infection showed that only prior antibiotic use was an independent risk factor [Table 1]. A comparison of antibiotic use between A. baumannii-infected and non-A. baumannii-infected patients are shown in [Table 2]. Among A. baumannii-infected patients, 58.3% (35) used antibiotics as a treatment, whereas there was only 26.2% (144) non-A. baumannii-infected patients who used antibiotics; this difference in the two groups was significant (P< 0.01). Among A. baumannii-infected patients, lung cancer patients were particularly vulnerable to nosocomial infection, accounting for 66.7% of these infections [Table 3]. The resistance of A. baumannii isolates to antibiotics is shown in [Table 4]. During the study, the rates of resistance increased annually. Bacterial strains were resistant to most of the antimicrobial agents tested. However, they had a relatively high susceptibility to sulfamethoxazole and levofloxacin.
Figure 1: The distribution of common pathogenic bacteria in tumor patients from 2010 to 2015

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Table 1: Multivariate analysis of risk factors for Acinetobacter baumannii infection

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Table 2: Comparison of antibiotic use between Acinetobacter baumannii-infected and non-Acinetobacter baumannii-infected patients

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Table 3: The relationship and composition ratio between tumor types and nosocomial infections

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Table 4: The resistance of Acinetobacter baumannii isolates to antibiotics

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Amplification of the carbapenemase genes revealed that the IMP gene was present in six clinical isolates and that the VIM gene was present in two isolates. There were no other carbapenemase genes presented in the isolates. Sequence analyses revealed that the amplified positive genes were IMP-4 and VIM-2. All eight MBL-producing strains were isolated from the past 3 years. The MLST results showed that the 60 isolated strains comprised of 12 genotypes. ST208 was the most common genotype with 28 strains, followed by ST92 (9 strains), and ST195 (7 strains). In addition, five strains were genotype ST22, two strains were ST25, ST191, and ST90, and one strain each was ST75, ST218, ST368, ST365, and ST172. Five IMP-4 positive strains were genotype ST208, and one was ST368. Two VIM-2- positive were genotype ST191.

 > Discussion Top

A. baumannii is an opportunistic pathogen, frequently isolated from immunocompromised patients, including cancer patients.[10],[11] Most studies have focused on resistant A. baumannii infections in clinical treatments. Little research has been performed on the spectrum of pathogens in oncology departments because of the small sample sizes. In our study, we found that A. baumannii was one of the most isolated pathogens in the oncology department. Moreover, the rates of isolation and antimicrobial resistance were increasing.[12],[13] No clear changes in the isolation rates of other pathogens were observed during the study. E. coli, K. pneumoniae, S. aureus and P. aeruginosa, were the most common pathogenic bacteria in a previous study,[14],[15] which is similar to results from 2010 to 2014. The increasing isolation rate of A. baumannii was considered a highly resistant rate, which was confirmed in the risk factor analysis.

In the multivariate analysis of A. baumannii infection risk factors, we found that only prior antibiotic use was a risk factor of A. baumannii infection. Although risk factors differed among different studies, most found that antibiotic use was mainly associated with infections.[6],[10],[16] Then, we further analyzed the differences in antibacterial drug use among different pathogenic bacterial infections. More than 50% patients of A. baumannii infection were using antibiotics, which is more than the non-A. baumannii-infected patients. The result suggests the prior antibiotic use was the important reason of A. baumannii infection.

Among 60 isolated A. baumannii strains, 28 were ST208, and 5 IMP-positive isolates were ST208. The results of ST gene typing and antimicrobial resistance gene analysis suggested that there was small-scale outbreak of A. baumannii in the oncology department. The source of the A. baumannii infection may be hospital environmental pollution or A. baumannii-infected inpatients. A. baumannii MLST types have differed in different reports,[17],[18],[19] which may be due to the inconstancy of the A. baumannii genome. It can survive in hospital settings for a long time and potentially cause serious hospital outbreaks.[20]

 > Conclusion Top

A. baumannii has now become the most common pathogenic bacterium in the hospital, and antibiotic use and hospital environmental pollution may be the main cause. To reduce the rate of A. baumannii infection, establishing more pertinent and reasonable infection control measures is necessary. Bacterial spectrum analysis and resistance surveillance like those used in this study will be a good approach.

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Conflicts of interest

There are no conflicts of interest.

 > References Top

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  [Figure 1]

  [Table 1], [Table 2], [Table 3], [Table 4]

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