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BMC Infectious Diseases

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Shifting trends in bacteriology and antimicrobial resistance among gastrointestinal fistula patients in China: an eight-year review in a tertiary-care hospital

  • Qinjie Liu1,
  • Jianan Ren1, 2, 3Email author,
  • Xiuwen Wu2,
  • Gefei Wang2,
  • Zhiwei Wang1,
  • Jie Wu2,
  • Jinjian Huang3,
  • Tianyu Lu2 and
  • Jieshou Li2
BMC Infectious DiseasesBMC series – open, inclusive and trusted201717:637

https://doi.org/10.1186/s12879-017-2744-7

©  The Author(s). 2017

Received: 24 January 2017

Accepted: 18 September 2017

Published: 21 September 2017

Open Peer Review reports

Abstract

Background

The purpose of this study was to determine the shifting trends in bacteriology and antimicrobial resistance of infectious specimens isolated from gastrointestinal (GI) fistula patients over eight years in China.

Methods

We retrospectively reviewed the microbial records of intra-abdominal specimens at a teaching hospital from 2008 to 2015. Study period was divided into the first half (2008–2011) and the second half (2012–2015). All isolates underwent antibiotic susceptibility testing by the micro dilution method.

Results

A total of 874 intra-abdominal isolates were consecutively collected from 502 GI fistula patients (mean age, 46.5 years, 71.1% male) during the study period. Patients in the second study period (2012–2015) were older (>65 years) and more likely to have experienced cancer. Over the entire study period, most infections were caused by E. coli (24.2%) and K. pneumonia (14.1%). There was a significant decrease in the proportion E. coli isolates that were extended- spectrum beta-lactamase (ESBL)-positive (P = 0.026). The proportion of E. coli resistant to imipenem increased from 14.3% in 2008–2011 to 25.9% in 2012–2015 (P = 0.037). Imipenem resistance prevalence was higher in ESBL-negative bacteria than ESBL-positive bacteria for both E. coli and K. pneumonia (P < 0.001). In Enterococcus, significant increase in resistance to ampicillin (P = 0.01) and moxifloxacin (P = 0.02) over time were observed. In Staphylococcus and fungi, rates of antibiotic resistance did not significantly change over the study period.

Conclusions

Gram-negative bacteria predominated as causative agents of intra-abdominal infections in GI fistula patients, and there was an increase in levels of resistance to certain antibiotics, particularly carbapenems. Infection control and source control are important tools available to surgeons to prevent the emergence of antibiotic-resistant pathogens.

Keywords

BacteriologyAntibiotic resistanceIntra-abdominal infections

Background

Gastrointestinal (GI) fistula is a complex and challenging problem associated with intra-abdominal infections (IAIs), leading to high morbidity and mortality worldwide [1, 2]. Effective treatment for IAIs patients involves both source control and antimicrobial therapy [3]. Despite improvements in patient care, therapeutic failure remains common [4].

Selection and prompt initiation of the appropriate empiric antimicrobial therapy play an important role in decreasing morbidity and mortality in GI fistula patients with IAIs [5]. The Infectious Diseases Society of America (IDSA) guidelines recommend use of single agents, such as carbapenems, piperacillin/tazobactam, cephalosporins, fluoroquinolones and aminoglycosides combined with metronidazole to treat IAIs in adults [2]. The distribution of pathogens causing IAIs and their drug susceptibility profiles may change over time, particularly with the spread of antibiotic resistance, making it more challenging for surgeons to select appropriate antibiotic therapies [6, 7]. To improve the outcome of GI fistula patients with IAIs, it is essential for surgeons to be aware of the local bacteriology and antimicrobial resistance trends of the causative pathogens [8].

Large-scale antibiotic susceptibility surveillances have been launched over the past decades which have informed surgeons of current trends in the emergence of antibiotic-resistant bacterial strains involved in IAIs [9–11]. However, these short-term surveillances might put up an incomplete facade pattern as the fluctuations of antibiotic resistance appeared in the shorter time period [12]. Therefore, a longitudinal surveillance is critical as guidance for empiric therapy.

Methods

Patients and samples

Microbiology and antibiotic susceptibility of isolates collected at Jinling Hospital between 2008 and 2015 were retrospectively reviewed using the hospital medical record system. Data extracted from the system for each isolate included demographic characteristics of the patient (age, sex), co-morbidities (hypertension, diabetes, cancer, inflammatory bowel disease, lung injury, renal injury) and fistula location. Upper GI fistula was defined as fistula located in the stomach or duodenum and lower GI fistula was defined as fistula located in the jejunum, ileum or colon [13]. Isolates from tissue, fluid or deep wound cultures obtained during operation, abdominal drains, fluid from paracentesis or percutaneous aspiration of abscesses were included, and those from drain bottles, stool, superficial wounds, or perirectal abscess were excluded.

The study protocol was approved by the Institutional Review Board Ethics Committee of Jinling Hospital, and all research work was in compliance with the Helsinki Declaration.

Pathogenic examination and antibiotic susceptibility determination

Samples were collected with sterile cotton swabs (Zhejiang Gongdong Medical Technology Co. Ltd., Taizhou, Zhejiang, China) and then sent to the microbiology laboratory for processing. Bacteria were isolated and then identified by the Vitek and Analytical Profile Index (API) bacterial identification systems or by traditional manual methods (BioMérieux, Hazelwood, MO, USA).

To assess antimicrobial susceptibility, minimum inhibitory concentrations (MICs) for each antimicrobial agent were determined by the agar dilution method, according to each year’s CLSI guidelines (Clinical Laboratory Standards Institute, USA, as annually updated) [14]. Phenotypic identification of extended-spectrum beta-lactamase (ESBL) production of Escherichia. Coli (E. coli), Klebsiella and Enterobacter species were expanded. If MICs of ceftazidime, cefepime, or ceftriaxone were ≥2 mg/L among E. coli, Klebsiella or Enterobacter species, ESBL production was suspected. For these ESBL-suspected isolates, if the MIC of cefepime was at least eightfold more than that of cefepime in the presence of clavulanic acid, ESBL production was identified [15]. Escherichia coli ATCC 25922, Klebsiella pneumonia ATCC 700603 and Pseudomonas aeruginosa ATCC 27853 were used as quality control strains.

Statistical analysis

Descriptive statistics were presented for categorical variables and continuous variables. We divided the study period into two periods for analysis: 2008–2011 and 2012–2015. We use the Mantel–Haenszel linear-by-linear association χ2 test to detect significant differences over time. Continuous variables were analyzed using the student t-test. P < 0.05 was considered statistically significant. All statistical analyses were performed using SPSS software (Version 22 IBM, Armonk, NY).

Results

Patient characteristics

A total of 502 GI fistula patients (mean age 46.5 years, 71.1% male) were included. Demographic characteristics of included patients are shown in Table1. Patients in the second study period (2012–2015) exhibited significant enrichment of clinical factors, including advanced age (P = 0.02), cancer (16.0% VS 6.7%, P = 0.001) and renal injury (16.7% VS 9.2%, P = 0.013) than patients from 2008 to 2011. In addition, the 2012–1015 cohort had a significantly higher percentage of lower GI fistula (P = 0.005) and a lower percentage of intensive care unit (ICU) patients (P < 0.001) (Table 1). We did not find the difference change in mortality rates over time (27.6% VS 28.1%, P = 0.896).
Table 1

Clinical characteristics of patients during 2008 and 2015

 

2008–2012

(n = 239)

2012–2015

(n = 263)

P

Gender

 Male

169 (70.71%)

188 (71.48%)

0.849

Age (years)

44.85 ± 14.99

48.05 ± 15.62

0.020

  ≤ 16

6 (2.51%)

3 (1.14%)

0.248

 17–32

49 (20.50%)

41 (15.59%)

0.152

 33–48

88 (36.82%)

96 (36.50%)

0.941

 49–64

76 (31.80%)

81 (30.80%)

0.809

  ≥ 65

20 (8.37%)

42 (15.97%)

0.010

Patient location

 ICU

150 (62.76%)

123 (46.77%)

<0.001

Fistula location,

 Upper gastrointestinal

107 (45.15%)

98 (37.26%)

0.073

 Lower gastrointestinal

106 (44.35%)

150 (57.03%)

0.005

 Both

19 (7.95%)

15 (5.70%)

0.317

Co-morbidities

 Hypertension

39 (16.32%)

57 (21.67%)

0.128

 Diabetes

20 (8.37%)

30 (11.41%)

0.256

 Cancer

16 (6.69%)

42 (15.97%)

0.001

 IBD

8 (3.35%)

16 (6.08%)

0.151

 Lung Injury

33 (13.81%)

45 (17.11%)

0.308

 Renal Injury

22 (9.21%)

44 (16.73%)

0.013

30-day mortality

66 (27.62%)

74 (28.14%)

0.896

Microbiological profile

During the entire study period, 874 isolates were collected, and the mean number of isolates per year was 109+/−19. Co-infection with multiple microbial strains was identified in 118(49.4%) patients during the first study period and 124(47.2%) during the second period. The distribution of microbial strains, stratified by study period, is shown in Fig. 1. The total number of Gram-negative was 638 (73.0%), which became more common over time (P = 0.024), followed by Gram-positive isolates (188, 25.5%), respectively. Overall, E. coli was the most frequently identified bacterial microorganism (216 isolates, 24.2% of all bacterial growths and 33.9% of Gram-negative isolates), followed by K. pneumonia (123 isolates, 14.1% of all bacterial growths and 19.3% of Gram-negative isolates). A significant decrease in the percentage of E. coli isolates that were ESBL-positive occurred between study periods (P = 0.026), but there was no significant difference in the proportion of K. pneumonia that were ESBL positive between study periods. The common Gram-positive bacteria were Enterococcus and Staphylococcus. (Additional file 1: Table S1).
Figure 1
Fig. 1

Distribution of strain groups identified in the study periods

Enterobacteriaceae antibiotic resistance

Tables 2 and 3 list the in vitro resistance profiles of E. coli and K. pneumonia, respectively, stratified by ESBL-production ability. There were similar patterns of antibiotic resistance for E. coli and K. pneumonia isolates over the study period, with both displaying high levels of resistance to penicillins, cephalosporins and fluoroquinolones. There was a statistically significant decrease in prevalence of resistance to ceftazidime and cefepime in E. coli isolates (P = 0.042, P = 0.035). No significant change in prevalence of resistance to aztreonam and amikacin was observed in both E. coli and K. pneumonia isolates. Resistance to amikacin was relatively low compared with the other antibiotics mentioned above for both E. coli and K. pneumonia isolates.
Table 2

Antimicrobial resistance of Escherichia coli isolates to the tested antibiotics

Resistance rate (%)

Isolate/Antibiotics

2008–2011

2012–2015

Total

P for Trend Test

All Escherichia coli

 AMK

7.78

14.16

11.33

0.154

 AMP

97.92

96.49

97.14

0.537

 SAM

81.97

87.93

85.88

0.279

 TZP

23.47

25.00

24.30

0.795

 CZO

92.55

91.30

91.87

0.742

 CAZ

81.82

69.83

75.35

0.042

 FEP

75.51

62.07

68.22

0.035

 IPM

14.29

25.86

20.56

0.037

 CIP

90.16

79.13

82.95

0.064

ESBL+

 AMK

6.78

12.33

9.85

0.287

 AMP

100.00

100.00

100.00

–

 SAM

77.78

93.15

88.07

0.020

 TZP

20.31

6.85

13.14

0.020

 SXT

84.21

73.61

77.27

0.207

 CZO

100.00

100.00

100.00

–

 CAZ

89.23

68.49

78.26

0.003

 FEP

81.25

60.27

70.07

0.007

 IPM

12.31

8.22

10.14

0.427

 CIP

86.11

80.82

82.57

0.494

ESBL-

 AMK

6.67

16.22

13.46

0.361

 AMP

88.24

89.74

89.29

0.867

 SAM

77.78

77.50

77.55

0.986

 ZP

35.29

57.50

50.88

0.125

 SXT

88.89

67.50

71.43

0.199

 CZO

58.82

74.36

69.64

0.245

 CTT

28.57

70.00

63.83

0.035

 CAZ

52.94

70.00

64.91

0.217

 FEP

52.94

62.50

59.65

0.501

 IPM

43.75

57.50

53.57

0.351

 CIP

88.89

77.50

79.59

0.444

Not all tested antibiotics are listed

AMK Amikacin, AMP Ampicillin, SAM Ampicillin/Sulbactam, CAZ Ceftazidime, efepime, CTT Cefotetan, CZO Cefazolin, IPM Imipenem, TZP Piperacillin-Tazobactam, CIP Ciprofloxacin

Data in boldface reflected p values < 0.05

 
Table 3

Antimicrobial resistance of Klebsiella pneumonia isolates to the tested antibiotics

Resistance rate (%)

Isolate/Antibiotics

2008–2011

2012–2015

Total

P for Trend Test

All Klebsiella pneumonia

 AMK

40.91

36.11

37.93

0.605

 SAM

97.14

85.14

88.99

0.061

 TZP

75.00

58.11

64.75

0.056

 CTT

60.61

54.79

56.60

0.576

 CAZ

89.80

78.38

82.93

0.099

 FEP

75.00

67.57

70.49

0.379

 IPM

65.31

56.76

60.16

0.343

 CIP

74.29

75.68

75.23

0.875

ESBL+

 AMK

33.33

7.41

16.67

0.031

 SAM

100.00

89.29

92.11

0.281

 TZP

55.56

17.86

32.61

0.008

 CTT

12.50

14.81

14.29

0.869

 CAZ

94.44

71.43

80.43

0.055

 FEP

83.33

53.57

65.22

0.039

 IPM

38.89

14.29

23.91

0.056

 CIP

50.00

71.43

65.79

0.220

ESBL-

 AMK

40.91

53.33

49.25

0.339

 SAM

94.44

82.61

85.94

0.221

 TZP

86.36

82.61

83.82

0.694

 CTT

88.89

78.26

81.25

0.327

 CAZ

82.61

82.61

82.61

–

 FEP

72.73

76.09

75.00

0.765

 PM

78.26

82.61

81.16

0.663

 CIP

83.33

78.26

79.69

0.650

Not all tested antibiotics are listed

AMK Amikacin, SAM Ampicillin/Sulbactam, CAZ Ceftazidime, FEP Cefepime, CTT Cefotetan, IPM Imipenem, TZP Piperacillin-Tazobactam, CIP Ciprofloxacin

Data in boldface reflected p values < 0.05

In ESBL-positive E. coli, prevalence of resistance to piperacillin/tazobactam (13.1%) was lower than ampicillin/sulbactam resistance prevalence (88.1%) and both decreased over the study period (P = 0.020). The same resistance trend to piperacillin/tazobactam was also observed in ESBL-positive K. pneumonia (P = 0.008). Imipenem resistance prevalence was higher in K. pneumonia than E. coli. It increased over time in E. coli (14.3% VS 25.9%, P = 0.037) but there was no significant change in K. pneumonia (65.3% VS 56.8%, P = 0.343). Imipenem resistance prevalence was higher in ESBL-negative than ESBL-positive bacteria for both E. coli and K. pneumonia (P < 0.001).

Antimicrobial resistance of non-fermenting bacteria

In A. baumannii isolates, extremely high levels of cephalosporin resistance were observed, which increased to 100% in 2012–2015. In contrast, ceftazidime and cefepime resistance rates were lower in P. aeruginosa isolates (Table 4). Both A. baumannii and P. aeruginosa showed strikingly high resistance rates to imipenem during the study period. Among A. baumannii isolates, imipenem resistance prevalence was 95.6% and did not significantly change during the study period. In contrast, imipenem resistance in P. aeruginosa isolates was much lower. Resistance to fluoroquinolones showed no significant change over time in either pathogen.
Table 4

Antimicrobial resistance of Acinetobacter baumannii and Pseudomonas aeruginosa isolates to the tested antibiotics

Resistance rate (%)

Isolate/Antibiotics

2008–2011

2012–2015

Total

P for Trend Test

Acinetobacter baumannii

 AMP

96.43

100.00

98.55

0.223

 SAM

90.48

100.00

96.77

0.045

 TZP

96.30

95.00

95.52

0.801

 SXT

95.24

73.17

80.65

0.037

 CRO

94.44

100.00

98.31

0.128

 CTX

100.00

100.00

100.00

–

 CAZ

88.89

100.00

95.59

0.029

 FEP

96.30

100.00

98.53

0.214

 IPM

96.30

95.12

95.59

0.818

 LVX

66.67

56.10

60.29

0.383

 CIP

95.24

97.56

96.77

0.624

Pseudomonas aeruginosa

 AMK

31.82

22.22

25.86

0.418

 SAM

100.00

100.00

100.00

–

 TZP

60.87

33.33

44.07

0.038

 ATM

58.82

75.00

61.90

0.549

 SXT

100.00

97.22

98.11

0.488

 CRO

100.00

100.00

100.00

–

 CTX

100.00

100.00

100.00

–

 CAZ

69.57

61.11

64.41

0.508

 FEP

65.22

50.00

55.93

0.251

 IPM

73.91

58.33

64.41

0.223

 LVX

34.78

44.44

40.68

0.461

 CIP

38.89

41.18

40.38

0.873

Not all tested antibiotics are listed

AMK Amikacin, SAM Ampicillin/Sulbactam, TZP piperacillin-tazobactam, ATM Aztreonam, SXT Trimethoprim/Sulfamethoxazole, CRO Ceftriaxone, CTX cefotaxime, CAZ ceftazidime, FEP cefepime, IPM imipenem, LVX levofloxacin, CIP ciprofloxacin

Data in boldface reflected p values < 0.05

Antimicrobial resistance of gram-positive bacteria and fungi

Antibiotic resistance prevalence rates of Gram-positive bacteria are listed in Table 5. In Enterococcus, resistance to ampicillin increased from 72.2% in 2008–2011 to 92.5% in 2012–2015 (P = 0.01). Resistance to moxifloxacin also increased significantly (P = 0.02). No significant changes in resistance to vancomycin (P = 0.311) and linezolid (P = 0.111) over time were observed.
Table 5

Antimicrobial resistance of Enterococcus and Staphylococcus isolates to the tested antibiotics

Resistance rate (%)

Isolate/Antibiotics

2008–2011

2012–2015

Total

P for Trend Test

Enterococcus

 AMP

72.22

92.45

84.27

0.01

 STH

47.06

57.58

52.24

0.389

 GEH

71.74

79.25

75.76

0.385

 ERY

88.57

88.68

88.64

0.988

 CIP

89.29

90.57

90.12

0.854

 CLI

100.00

95.56

95.92

0.667

 MFX

63.64

91.11

85.71

0.02

 PEN

87.23

92.31

89.90

0.403

 TCY

74.29

69.23

71.26

0.609

 VAN

4.26

9.43

7.00

0.311

 LNZ

4.88

0.00

2.17

0.111

 LVX

77.14

90.38

85.06

0.089

Staphylococcus

 OXA

82.69

93.10

86.42

0.190

 SXT

47.62

24.14

38.03

0.045

 ERY

84.62

82.76

83.95

0.827

 CIP

73.68

89.66

83.33

0.147

 CLI

69.57

57.14

64.86

0.278

 MFX

46.34

37.93

42.86

0.484

 PEN

94.34

100.00

96.34

0.192

 GEN

71.15

72.41

71.60

0.904

 TCY

56.82

68.97

61.64

0.296

 VAN

0.00

0.00

0.00

–

 LNZ

0.00

0.00

0.00

–

 LVX

68.89

79.31

72.97

0.324

Not all tested antibiotics are listed

AMP Ampicillin, OXA Oxacillin, STH Streptomycin-High, SXT Trimethoprim/Sulfamethoxazole, ERY erythromycin, GEH gentamicin, CIP ciprofloxacin, CLI Clindamycin, MFX moxifloxacin, PEN penicillin, TCY tetracycline, VAN Vancomycin, LNZ Linezolid, LVX Levofloxacin

Data in boldface reflected p values < 0.05

Methicillin-resistant S. aureus (MRSA) accounted for 94.1% of S. aureus isolates in 2012–2015. There was no significant change in S. aureus resistance to oxacillin over time. All of 51 Staphylococcus were susceptible to vancomycin (Table 5).

Fungi isolates showed lower antibiotic resistance rates than bacteria isolates, and rates did not significantly vary over time (Table 6).
Table 6

Antimicrobial resistance of Fungi isolates to the tested antibiotics

Resistance rate (%)

Antibiotics

2008–2011

2012–2015

Total

P for Trend Test

 FLU

18.18

8.33

11.43

0.395

 VOR

0.00

8.33

5.71

0.324

 ITR

18.18

5.56

10.34

0.279

FLU Fluconazole, VOR Voriconazole, ITR Itraconazole

Discussion

To our knowledge, this is the first study to examine the shifting trends in bacteriology and antimicrobial resistance among GI fistula patients in China. Our findings indicate a significant increase in the percentage of IAIs attributable to Gram-negatives bacteria, with a corresponding decrease in the percentage attributable to Gram-positive isolates. There was a trend for increased resistance prevalence levels to certain antibiotics for Gram-negative bacteria, especially carbapenems.

K. pneumonia and A. baumannii have gained notoriety as important pathogens because of their increasing resistance to antibiotics and a rise in the number of severe infections caused by these micro-organisms in surgical settings [16]. We found an increase in IAIs attributable to K. pneumonia and A. baumannii infection over time, although this increase did not reach statistical significance. Colonization with these bacteria have been described as the reason for high incidence in surgical wards and this could be prevented through effective infection control [17, 18]. Therefore, we must heighten our awareness of the importance of infection control.

ESBL production which can hydrolyze β-lactam antibiotics has been increasingly identified worldwide amongst the Enterobacteriaceae family, particularly E. coli and K. pneumonia [19]. In the present study, the overall prevalence of ESBL-positive strains of E. coli was 63.9%, which decreased significantly over time, and the overall prevalence of ESBL-positive strains of K. pneumonia was 37.3%, which did not significant change over the study periods. These levels are somewhat lower than those reported by SMART research in 2012 and 2013 [10]. Carbapenems and piperacillin-tazobactam are the most potent and reliable antibiotics for the treatment of ESBL-producing infection [20]. In our study, we found that resistance to piperacillin-tazobactam decreased over time both ESBL-producing E. coli (P = 0.02) and K. pneumonia (P = 0.008). It suggests that piperacillin-tazobactam is a suitable treatment option for these infections [21].

Resistance to carbapenems is associated with high mortality and has been an emerging concern worldwide [22, 23]. The overall prevalence of imipenem resistance in E. coli isolates was 20.6%, which significantly increased over time. Prevalence in K. pneumonia was 60.2%, which did not change over time. Both these prevalence levels are higher than previous reports [9, 24–26]. This may be because the majority of our patients have transferred from other hospitals and have been treated with antibiotics for a number of days, which has been shown to be a risk factor for carbapenem resistance [27]. High resistance prevalence has also resulted from its spread in surgical wards and ICUs [12]. Standard infection control practice (basic hand hygiene, active surveillance cultures of patients, staff, and the environment) should be carried out to prevent the colonization and spread of resistant bacteria [8, 28, 29].

The prevalence of multidrug resistance amongst A. baumannii isolates makes carbapenem the most effective treatment [30]. Carbapenem resistance has become a serious problem, with prevalence reaching a remarkable 95.6% of all isolates in our study. Similarly high levels have been reported in blood stream infections [23]. Once carbapenem resistant A. baumannii emerges, the infected patient has little chance of effective treatment [31]. Therefore, we need to pay attention to source control and limiting the spread of carbapenem-resistant bacteria.

P. aeruginosa is another a common Gram-negative non-fermenting pathogen causing IAIs. In this study, the most efficient antimicrobial agent for P. aeruginosa was found to be amikacin, as has been reported elsewhere [32]. However, we rarely treat patients with amikacin because of its renal toxicity. In our study we observed a significant decrease in resistance to piperacillin-tazobactam over time, suggesting that piperacillin- tazobactam could be the first choice treatment option for patients infected by P. aeruginosa, as recommended by several studies [33, 34].

The proportion of Gram-positive bacterial isolates that were Enterococcus increased over time. Antibiotic resistance rates for this group of pathogens also increased. Staphylococcus isolates had high levels of penicillin G, macrolide, and clindamycin resistance, but no resistance to vancomycin or linezolid was observed. Antibiotics resistance levels were lower among Gram-positive than Gram-negative bacteria. we therefore recommend focusing on Gram-negative bacteria with high antibiotic resistance in GI fistula patients.

In an attempt to identify factors that might influence antibiotic resistance emergence, we analyzed the clinical characteristics of patients. We found that patients in the second study period were older (aged >65 years) and were more likely to suffer cancer, both of which have been demonstrated as risk factors for antibiotic resistance [8, 18, 35]. We also found more IAIs caused by lower GI fistula in the second study period. A recent study by Mu et al. reported that antibiotic intervention exerts location-specific effects on antibiotic resistance genes (increased in the lower GI tract) [36]. Most of our patients were transferred from other hospitals, which means they had been previously treated with antibiotics and were therefore at increased risk of antibiotic resistance. Excessive antibiotic use has been linked with the development of resistance, which is a common practice in many developing countries [18]. Combined, these factors at least partly explain the increase in antibiotic resistance that we have observed. We found that smaller ICU patients showed higher antibiotic resistance. And that again underlines the serious antibiotic resistance.

Inappropriate use of antibiotics and inadequate source control were found to be independent predictors of mortality in a previous analysis [37]. High levels of antibiotic resistance have left few treatment options available to surgeons [8]. However, we found no change in mortality rates over time. This could partially be attributable to the effective management of source control. Newer IAI treatment guidelines recommend intravenous antimicrobial agents as a supplement to source control, and source control may be an available option for surgeons to prevent the emergence of antibiotic-resistant microbial strains [38].

There are some limitations to our study. First, it is a retrospective and single-center surveillance study, which may explain the higher resistance levels observed in our study than other reports from China [23]. However, the critically ill patients at our center were transferred from other hospitals throughout the country, so our study may represent the bacteriology and antimicrobial resistance profiles of severely infected GI fistula patients in China more generally. Second, we did not perform polymerase chain reaction (PCR) and DNA sequencing of isolates. Third, we did not use the unified CLSI breakpoints, as annually updated. In fact, our microbiology laboratory updated determinations according to the newest CLSI documents and 2008–2015 isolates were determined by each year’s documents. Change of breakpoints might cause fluctuations of antimicrobial resistance in short-term surveillances [12]. But there is not a large difference between CLSI breakpoints. And a longitudinal surveillance spanning over 8 years is of great significance for monitoring resistance, which may minimize referral bias.

Conclusions

This study illustrates the shifting trends in bacteriology and antimicrobial resistance in GI fistula patients in China over time. Gram-negative bacteria have become a more significant cause of IAIs in these patients. Currently, carbapenem resistances in Gram-negative bacteria is a serious problem in this patient group. Our findings confirm the urgent need to continue surveillance studies that monitor bacteriology and antimicrobial resistance trends. Infection control and source control are important tools for surgeons to use to prevent the emergence of isolated antibiotic-resistant pathogens.

Abbreviations

AMK: 

Amikacin

AMP: 

Ampicillin

ATCC: 

American Type Culture Collection

ATM: 

Aztreonam

CAZ: 

Ceftazidime

CIP: 

Ciprofloxacin

CLI: 

Clindamycin

CLSI: 

Clinical Laboratory Standards Institute

CRO: 

Ceftriaxone

CTT: 

Cefotetan

CTX: 

Cefotaxime

CZO: 

Cefazolin

ERY: 

Erythromycin

ESBL: 

extended-spectrum beta-lactamase

FEP: 

Cefepime

FLU: 

Fluconazole

GEH: 

Gentamicin

GEN: 

Gentamicin

GI fistula: 

gastrointestinal fistula

IAIs: 

intra-abdominal infections

IDSA: 

Infectious Diseases Society of America

IPM: 

Imipenem

ITR: 

Itraconazole

KPC: 

Carbapenem-resistant K. pneumonia

LNZ: 

Linezolid

LVX: 

Levofloxacin

MFX: 

Moxifloxacin

MICs: 

minimum inhibitory concentrations

MRSA: 

Methicillin-resistant S. aureus

OXA: 

Oxacillin

PCR: 

Polymerase chain reaction;

PEN: 

Penicillin G

QDA: 

Quinupristin/Dalfopristin

SAM: 

Ampicillin/Sulbactam

SMART: 

Study for Monitoring Antimicrobial Resistance Trends

STH: 

Streptomycin-High

SXT: 

Trimethoprim/Sulfamethoxazole

TCY: 

Tetracycline

TOB: 

Tobramycin

TZP: 

Piperacillin/Tazobactam

VAN: 

Vancomycin

VOR: 

Voriconazole

Declarations

Acknowledgments

The authors would like to declare that this report is exclusively based on epidemiological findings and we are very thankful to all staff at the Department of Microbiology, Jinling Hospital. We thank Rebecca Baggaley, PhD, from Liwen Bianji, Edanz Editing China (www.liwenbianji.cn/ac), for editing the English text of a draft of this manuscript.

Funding

The work was supported by grants from the Natural Science Foundation of China (81571881) and the Key Project of Jiangsu Social Development (BE2016752).

Availability of data and materials

The data supporting the findings of this study are contained within the manuscript.

Authors’ contributions

Qinjie Liu and Jianan Ren devised and designed the study. Qinjie Liu, Zhiwei Wang, Jie Wu, Tianyu Lu, and Jinjian Huang were responsible for the collection of clinical data and resolved problems by discussion if any occurred. Qinjie Liu was the primary statistician for the study and drafted the manuscript. All authors reviewed the manuscript, which was revised in response to comments by Qinjie Liu and Xiuwen Wu. Gefei Wang monitored the project and Jieshou Li was responsible for the paper as a whole. All authors read and approved the final manuscript.

Ethics approval and consent to participate

The entire study protocol was approved by the Institutional Review Board Ethics Committee of Jinling Hospital, and all research work was conducted in compliance with the Helsinki Declaration.

Consent for publication

Not applicable.

Competing interests

The authors declare that they have no competing interests.

Publisher’s Note

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Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

Authors’ Affiliations

(1)
Department of Surgery, Jinling Hospital, Nanjing Medical University, Nanjing, People’s Republic of China
(2)
Department of Surgery, Jinling Hospital, Medical School of Nanjing University, Nanjing, People’s Republic of China
(3)
Department of Surgery, Jinling Hospital, Medical School of Southeast University, Nanjing, People’s Republic of China

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