Aeromonas diversity
Phylogenetic tree based on housekeeping gene gyrB exhibited that all 58 isolates were divided into 5 different species, with the predominant specie being A. dhakensis (26/58). Besides, 13 isolates of Aeromonas veronii, 10 isolates of Aeromonas caviae, 7 isolates of A.s hydrophila and 2 isolates of Aeromonas jandaei were identified to the species level (Fig. 1). Vitek 2 Compact system and the MALDI-TOF MS system showed poor coincidence with housekeeping gene sequencing analysis at the species level. A. dhakensis was incorrectly identified as A. hydrophila by Vitek 2 Compact system or MALDI-TOF MS. Moreover, two A. jandaei strains were misidentified as A. hydrophila and Aeromonas veronii, respectively.
Characteristics Of Investigated Patients
During the investigated period, 58 patients were detected with positive blood culture of Aeromonas. 16 patients had poor prognosis (death or therapy failure), where A. dhakensis (12/26) to be predominant, followed by A. veronii (2/13), A. caviae (1/10), A. hydrophila (1/7) and A. jandaei (0/2). The mean age was 61.1 ± 16.7 and the percentage of male patients were up to 70% (40/58). Polymicrobial infections were detected in nine cases, which co-infected with Klebsiella pneumoniae (3 cases), Escherichia coli (3 cases). Proteus vulgaris (1 case), Klebsiella oxytoca (1 case) and Enterobacter cloacae (1 case). The exact characteristics of patients were listed in the Table 1. Logistic regression analysis showed that poor prognosis was only significantly associated with community-acquired infections (OR = 11.027, 95% confidence interval (CI), 1.646–73.867, P < 0.05), and liver cirrhosis (OR = 16.854, 95% CI, 1.755-161.844, P < 0.05). Age, Gender, monomicrobial or polymicrobial infection, antimicrobial susceptibility and other underlying diseases didn’t have the predictive ability of bacteremia-related prognosis. Length of hospital stay of community-acquired infections with poor prognosis range from 1 to 7 days (median 2 days), which indicated that the progression of bacteremia caused by Aeromonas was extremely fast. The outcomes of A. dhakensis bacteremia were worsen than other species (p < 0.05).
Table 1
Clinical characteristics of 58 patients with bacteremia caused by Aeromonas species
Clinical characteristic
|
No (%) of all patients
(n = 58)
|
Prognosis
|
p
|
Poor (n = 16)
|
Well (n = 42)
|
Gender
|
|
|
|
|
Male
|
40 (70.0%)
|
12 (75.0%)
|
28 (66.7%)
|
o.752
|
Female
|
18 (30.0%)
|
4 (25.0%)
|
14 (33.3%)
|
Age, years (means ± SD)
|
61.1 ± 16.7
|
56.56 ± 14.45
|
62.76 ± 17.30
|
0.208
|
Age
|
|
|
|
|
༜65
|
30 (51.7%)
|
10 (62.5%)
|
20 (47.6%)
|
0.311
|
≥ 65
|
28 (48.3%)
|
6 (37.5%)
|
22 (52.4%)
|
Microbial findings
|
|
|
|
|
Monomicrobial
|
49 (84.5%)
|
16 (100.0%)
|
33 (78.6%)
|
0.051
|
Polymicrobial
|
9 (15.5%)
|
0 (0.0%)
|
9 (21.4%)
|
Antimicrobial susceptibility
|
|
|
|
|
MDR
|
9 (15.5%)
|
4 (25.0%)
|
5 (11.9%)
|
0.243
|
Non MDR
|
49 (84.5%)
|
12 (75.0%)
|
37 (88.1%)
|
Source of infection
|
|
|
|
|
Community acquired
|
34 (58.6%)
|
13 (81.3%)
|
21 (50%)
|
0.031*
|
Nosocomial infection
|
24 (41.4%)
|
3 (18.8%)
|
21 (50%)
|
Underlying disease
|
|
|
|
|
liver cirrhosis
|
26 (44.8%)
|
11 (68.8%)
|
15 (35.7%)
|
0.024*
|
Diabetes mellitus
|
7 (12.1%)
|
2 (12.5%)
|
5 (11.9%)
|
1.000
|
Malignancy
|
18 (31.0%)
|
6 (37.5%)
|
12 (28.6%)
|
0.538
|
Leukemia
|
8 (13.8%)
|
3 (18.8%)
|
5 (1.9%)
|
0.672
|
Clinical outcomes
|
|
|
|
|
Length of stay in hospital, days
|
17 (6-24.75)
|
2.5 (1–6)
|
19 (11.25-30)
|
0.000*
|
Values are presented as No. (%), mean ± SD or median (25th − 75th percentile) of patients. Poor prognosis cases include in-hospital deaths and deaths after discharge from hospital without treatment. * significant. |
Distribution Of Virulence Determinants
Virulence encoding genes, including aer, lip, hlyA, alt, ast, and act, were detected at ratios of 24.1% (14/58), 62.1% (36/58), 65.5% (38/58), 58.6% (34/58), 15.5% (9/58) and 65.5% (38/58), respectively. Virulence genes profile of 58 Aeromonas isolates was showed in Fig. 2. At least one virulence determinants were found in all 58 isolates. The gene hlyA and act were most prevalent in these isolates. Single virulence gene was detected in 12.1% (7/58) of isolates, and more than two virulence genes were found in remaining strains. There was no significant difference in virulence genes between strains isolated from patients with poor prognosis and well prognosis. Additionally, no statistical significance was observed in the prevalence of all the studied virulence genes between isolates separated from community acquired and nosocomial infection. We found 27 different combination patterns (PTs) of six examined genes. The two most prevalent PT (n ≥ 5) were PT1 (lip/hlyA/alt/act, n = 6) and PT2 (lip/alt, n = 5). Only one isolate of A. hydrophila carried all the investigated virulence genes, and the patient was cured after 32 days of hospitalization. Notably, 4 of 6 isolates grouped into PT1 were A. hydrophila, among which 3 lead to poor prognosis.
Antimicrobial Susceptibility
Antimicrobials susceptibility test exhibited that the majority of 58 isolates maintained susceptible to aminoglycosides, fluoroquinolones and furantoin (Table 2). Resistance to ceftazidime, cefotetan, ceftriaxone, cefepime, piperacillin/tazobactam, aztreonam were 10.3%, 13.8%, 15.5%, 1.7%, 10.3% and 5.2%, respectively. No significant increase in resistance during six years was observed. 9 out of 58 isolates was identified as multi-drug resistant (MDR) organism, including four isolates of A. dhakensis, 3 A. hydrophila, 1 A. veronii, and 1 A. caviae. Among which, six MDR strains were isolated in 2017 and 2018. The first MDR strain was recovered from a 78-years old woman with community-acquired infection in 2013. 24.1% (14/58) isolates were non-susceptible to imipenem.
Table 2
Antimicrobial susceptibility patterns of 58 Aeromonads separated from bacteremia.
Antimicrobial agent
|
CLSI breakpoint interpretation (%)
|
MIC50
|
MIC range
|
S
|
I
|
R
|
ceftazidime
|
88
|
1.7
|
10.3
|
≤ 1
|
≤ 1 ~ ≥ 64
|
cefotetan
|
86.2
|
0
|
13.8
|
≤ 4
|
≤ 4 ~ ≥ 64
|
ceftriaxone
|
79.3
|
5.2
|
15.5
|
≤ 1
|
≤ 1 ~ ≥ 64
|
cefepime
|
98.3
|
0
|
1.7
|
≤ 1
|
≤ 1 ~ 32
|
piperacillin/tazobactam
|
88
|
1.7
|
10.3
|
≤ 4
|
≤ 4 ~ ≥ 128
|
aztreonam
|
91.4
|
3.4
|
5.2
|
≤ 1
|
≤ 1 ~ ≥ 64
|
imipenem
|
75.9
|
10.3
|
13.8
|
≤ 1
|
≤ 1 ~ ≥ 16
|
levofloxacin
|
96.6
|
1.7
|
1.7
|
≤ 0.25
|
≤ 0.25 ~ ≥ 8
|
ciprofloxacin
|
96.6
|
0
|
3.4
|
≤ 0.25
|
≤ 0.25 ~ ≥ 4
|
Trimethoprim/sulfamethoxazole
|
87.9
|
0
|
12.1
|
≤ 20
|
≤ 20 ~ ≥ 320
|
amikacin
|
100
|
0
|
0
|
≤ 2
|
≤ 2
|
gentamicin
|
100
|
0
|
0
|
≤ 1
|
≤ 1
|
tobramycin
|
93.1
|
5.2
|
1.7
|
≤ 1
|
≤ 1 ~ ≥ 16
|
furantoin
|
100
|
0
|
0
|
≤ 16
|
≤ 16
|