Isolates of AB- During the study period of the 350 AB obtained, 317(90.5%) were carbapenem resistant (CRAB). CRAB isolates were obtained from various samples like - tracheal aspirates (159, 50.2%), blood (66, 20.8%), wound swab (56, 17.7%), pus (20, 6.3%), tissue (11, 3.5%) CSF (3, 0.9%) and urine (2, 0.6%).There were only 69, 21.8% CRAB isolates from different wards while rest were from ICUs. Most of the CRAB samples in the present study were from Burn ICUs (76; 23.9%) which also had the highest percentage of ABCoR (8; 42.1%). Colistin resistant AB (ABCoR) was detected in 19 (5.9%) strains of which 4 (21.1%) were from different wards and rest from various ICUs. (Table-2)
Table-2: Characteristics of the 19 colistin resistant Acinetobacter baumanii isolated
ID
|
MIC
|
Age
|
Sex
|
Sample
|
Site
|
S
|
MS
|
Outcome
|
Resistance genes
|
1
|
16
|
70
|
F
|
Blood
|
NSICU
|
Tgc
|
Le
|
Discharge
|
pmrA, oxa48
|
4
|
16
|
58
|
F
|
Sputum
|
BICU
|
-
|
-
|
Death
|
pmrA, lpxA, ndm
|
7
|
32
|
52
|
F
|
ET
|
MICU
|
Cfs, Ak, Cot, Mi, Tgc
|
Caz
|
Discharge
|
pmrB, oxa48
|
8
|
64
|
65
|
M
|
ET
|
MICU
|
Ak, Cot
|
Tgc
|
Discharge
|
pmrA, oxa48
|
13
|
16
|
25
|
M
|
Tissue
|
BICU
|
-
|
Mi
|
Death
|
lpxA, ndm, oxa48
|
14
|
32
|
29
|
M
|
Pus
|
MICU
|
Mi, Tgc
|
Caz
|
Discharge
|
pmrA, oxa48
|
23
|
16
|
55
|
F
|
ET
|
NSICU
|
Cot
|
Caz, Tgc
|
Discharge
|
pmrA, pmrB, oxa48
|
24
|
32
|
67
|
M
|
Wound swab
|
SICU
|
Caz, Mi, Tgc
|
-
|
Discharge
|
pmrA, pmrB, lpxA, lpxC, kpc, vim, oxa48
|
25
|
8
|
85
|
M
|
Blood
|
Ward
|
Caz, Mi, Le, Mi, Tgc
|
-
|
Discharge
|
pmrB, oxa48
|
26
|
32
|
25
|
M
|
ET
|
NSICU
|
Caz, Ak, Mi, Tgc
|
Cfs
|
Discharge
|
lpxA, vim, oxa 48
|
28
|
16
|
45
|
M
|
Pus
|
BICU
|
-
|
-
|
Death
|
pmrA, oxa48
|
31
|
32
|
25
|
M
|
Wound swab
|
BICU
|
Caz, Cpm, Tic, Cfs, Mi
|
Gen, Cip, Tgc
|
Discharge
|
pmrA, pmrB, oxa48, lpxA
|
35
|
32
|
75
|
F
|
Wound swab
|
BICU
|
-
|
-
|
Death
|
pmrA, pmrB, oxa48
|
40
|
16
|
36
|
M
|
Wound swab
|
BICU
|
-
|
-
|
Death
|
pmrB, oxa48, ndm
|
41
|
64
|
65
|
F
|
Blood
|
BICU
|
Cfs,Ak, Mi, Tgc
|
-
|
Death
|
pmrA, pmrB, vim, oxa48
|
45
|
16
|
53
|
M
|
Wound swab
|
Ward
|
Cot
|
Tgc
|
Death
|
pmrA, ndm, pmrB,oxa48,
|
52
|
32
|
62
|
M
|
Pus
|
Ward
|
-
|
-
|
Death
|
pmrA, oxa48, ndm
|
62
|
32
|
41
|
M
|
Sputum
|
Ward
|
-
|
-
|
Death
|
pmrA, pmrB, lpxA, lpxC, vim, imp, ndm, oxa48
|
67
|
16
|
57
|
F
|
Tissue
|
BICU
|
Caz
|
Tgc, Tic
|
Death
|
pmrA, kpc, oxa48, ndm
|
Caz- Ceftazidime, Cpm-Cefepime, Pit-Piperacillin tazobactam Tic- Ticarcillin clavulanic acid, Cfs- Cefoperzone sulbactam, Ak-amikacin, Gen-Gentamicin, Cip-Ciprofloxacin, Le-Levofloxacin, Mi-Minocycline, Tgc- Tigecycline Cot-Cotrimoxazole
Sensitivity pattern of AB (Fig 1): Of the 19 ABCoR isolates, seven of these isolated had 2 isolate had MIC 64, MIC of 32 and 16 in 8 isolates each,and one isolate had MIC of 8.The results of the antimicrobial susceptibility testing of both colistin intermediate and resistant isolates are showed in Table 3. The strains were found to be highly resistant to almost all the drugs tested. The antibiotics which were most susceptible were tigecycline (65.4% in CI; 31.6% in CR) and minocycline (44.3% in CI; 36.8% in CR). Among the BL agents ceftazidime had the highest susceptibility (29.2%). Cefepime (89.5%), TIC (78.9%), CFS (68.4%) had lower rate of resistance in colistin resistant isolates than the colistin intermediate ones. Similarly levofloxacin and ciprofloxacin had better sensitivity in ABCoR than ABCoI strains.
Clinical characteristics- The 19 ABCoR were taken as cases to determine the clinical status and for analysis of various risk factors three times the cases i.e.57 controls were taken. There was no significant difference in age and gender characteristics of the cases and controls. 73.7% of cases and 78.9% of controls were admitted in ICU respectively.When prior ICU days were considered the mean ICU stay of the patients harboring ABCoR were lesser than those of the controls. The mean duration of getting the colistin-resistant organisms was 5±6.3days of ICU stay. Only 57.9% of ABCoR were hospital-acquired in contrast to 78.9% of controls. There was no significant difference in the development of ABCoR or ABCoI as a result of nosocomial infections or ventilator-associated pneumonia. When preexisting illnesses were considered there was significant difference among cases and controls in terms of Type 2 diabetes mellitus, chronic kidney diseases and COPD. Patients having hypothyroid, COPD, CKD, Pneumonia, Post COVID pneumonia and post surgery patients have higher odds of developing ABCoR infections. Pneumonia patients have the highest likelihood of development of ABCoR infections. Prior colistin regimen was offered to 89.5% of cases and 33.5% of controls. Among the ABCoR harboring cases 10 (52.6%) died. There is a significant difference in mortality of the cases in ABCoR and ABCoI infections. Similarly the duration of ICU stay was prolonged in cases (16.3±13.3 days) than controls (6.8±7.3 days).
Table 3- Comparison of the various clinical characters of the cases and controls
Characteristics
|
Cases
(n=19)
|
Controls
(n=57)
|
p-value
|
OR
|
95% C.I.
|
Lower
|
Upper
|
Age (Mean ± SD)
|
53.16±16.85
|
53.33±16.68
|
0.972
|
0.978
|
0.949
|
1.008
|
Gender
|
|
|
|
|
|
|
Male
|
12(63.2%)
|
34(59.6 % )
|
0.801
|
|
|
|
Female
|
7(36.8%)
|
23(40.4%)
|
|
|
|
ICU admission
|
14 (73.7%)
|
45 (78.9%)
|
0.227
|
|
|
|
Prior ICU days
|
5±6.3d
|
8.7±15.5 d
|
0.316
|
|
|
|
HAI
|
11(57.9)
|
45(78.9)
|
0.071
|
1.333
|
0.381
|
4.661
|
VAP
|
2(10.8)
|
15(26.3)
|
0.153
|
0.230
|
0.071
|
0.740
|
Preexisting illness
|
Type II DM
|
11(57.9)
|
16(28.1)
|
0.019
|
0.450
|
0.153
|
1.323
|
Hypertension
|
5(26.3)
|
12(21.1)
|
0.634
|
0.230
|
0.071
|
0.740
|
Hypothyroidism
|
5(26.3)
|
3(5.3)
|
0.010
|
3.857
|
0.856
|
17.380
|
Maligancy
|
1(5.3)
|
2(3.5)
|
0.734
|
0.000
|
0.000
|
|
CKD
|
1(5.3)
|
17(29.8)
|
0.029
|
1.114
|
0.315
|
3.940
|
COPD
|
6(31.6)
|
5(8.8)
|
0.014
|
2.333
|
0.267
|
20.354
|
CVA
|
3(15.8)
|
5(8.8)
|
0.388
|
0.300
|
0.079
|
1.138
|
Pneumonia
|
3(15.8)
|
4(7)
|
0.252
|
10.769
|
1.876
|
61.807
|
Post-covid pneumonia
|
3(15.8)
|
11(19.3)
|
0.733
|
4.636
|
1.350
|
15.921
|
Surgerywithin 30 days
|
11(57.9)
|
28(49.1)
|
0.508
|
1.071
|
0.372
|
3.086
|
Antibiotic use
|
Prior colistin (iv/ intranasal )use
|
17 (89.5)
|
19 (33.5%)
|
<0.001
|
17
|
3.553
|
81.327
|
Outcome
|
Death
|
10(52.6)
|
8(14.1)
|
<0.001
|
|
|
|
Discharge
|
9 (47.4%)
|
49 (85.9)
|
|
|
|
Days of ICU stay prior to discharge
|
16.3±13.3 d
|
6.8±7.3 d
|
|
|
|
|
The ABCoR patients were treated variously as per the treating physician’s discretion and patient’s clinical profile. Out of the 19 cases, 13 patients received combination therapy of tigecycline and carbapenem, 2 patients received tigecycline with cefoperazone sulbactam and 1 patient received tigecycline with a carbapenem and cefoperazone sulbactam. 3 other patients received combination of colistin with tigecycline. There was no significant difference in the colistin added or sparing therapy when outcome in terms of death or discharge was considered.
PCR Results of Carbapenemase and colistin resistant Genes (Fig-2)
Among the CRAB strains, blaOXA-23 gene was the commonest genetic pattern observed alone in 147(49.3%) strains and in combination with other genes in 54(17.03%) strains. Metallo beta-lactamase genes werepresent in 46.7% strains of CRAB. Among these 24.2 % of strains carried blaNDM-1 followed by 17.4% of strains who had blaVIM and17.7 % of CRABs who had bla IMP. Many strainsi.e.17.02% co-harbored both MBL and non MBL genes in this study. Among the 19 ABCoR strains, 52.6% had bla-OXA genes alone serving as the most common pattern while 42.2% of the stains had multiples genes including Class A, C and D beta-lactamase genes.
pmrA was the commonest 14(73.8%) colistin-resistant gene present in our isolates; 6(31.6%) alone and rest along with other genes. Other genes were pmr B (47.4%), lpxA (31.6%) and lpx C (10.5%). None of the strains possessed any plasmid-mediated mcr 1-5 genes.
Table 4: Various carbapenem and colistin resistant genes detected
Genes
|
Number of isolates from ABCoI n=298
N (% total ABCoI)
|
Number of isolates
ABCoR n=19
N (% total ABCoR)
|
Total
CRAB n=317
N (% total CRAB)
|
Known Carbapenemase genes
|
|
blaKPC alone
|
22 (7.4%)
|
0
|
22 (6.9%)
|
bla OXA-48 alone
|
137 (45.9%)
|
10 (52.6%)
|
147 (49.3%)
|
blaIMP alone
|
17 (5.7%)
|
0
|
17 (5.4%)
|
BlaNDM alone
|
46 (15.4%)
|
1 (5.2%)
|
47 (14.8%)
|
blaVIM alone
|
6 (2.01%)
|
0
|
6 (1.9%)
|
VIM+ IMP
|
24 (8.1%)
|
0
|
24(7.6%)
|
VIM+IMP+OXA48
|
14 (4.7%)
|
0
|
14 (4.4%)
|
VIM+IMP+OXA48+NDM
|
0 (0)
|
1 (5.2%)
|
1 (0.32%)
|
NDM+OXA-48
|
18 (6.04%)
|
3 (15.7%)
|
21 (6.6%)
|
VIM+OXA-48
|
4 (1.3%)
|
2 (10.4%)
|
6 (1.9%)
|
VIM+KPC+OXA48
|
3 (1.0%)
|
1 (5.2%)
|
4 (1.3%)
|
NDM+KPC+OXA48
|
7 (2.3%)
|
1 (5.2%)
|
8 (2.5%)
|
Colistin resistant genes
|
|
|
|
lpx A alone
|
NA
|
2 (10.5%)
|
NA
|
lpxC alone
|
NA
|
0 (0)
|
NA
|
pmrA alone
|
2
|
6 (31.6%)
|
NA
|
pmr B alone
|
1
|
3 (15.8%)
|
NA
|
pmrA+ pmrB
|
2
|
4 (21.1%)
|
NA
|
pmrA+lpxA
|
NA
|
1 (5.3%)
|
NA
|
pmrA+ pmrB+lpxA
|
NA
|
1 (5.3%)
|
NA
|
lpx A+ lpxC+ pmrA+ pmrB
|
NA
|
2 (10.5%)
|
NA
|
mcr 1-5
|
NA
|
0 (0)
|
NA
|