1. Senior Talk Alina Iovleva Content Expert: Dr. Robert A. Bonomo
Combination vs. Monotherapy in treatment of Carbapenem Resistant Acinetobacter baumanii (CRAB) infections
Senior Talk
Alina Iovleva
Content Expert: Dr. Robert A. Bonomo

2. Learning Objectives:
1.Epidemiology and significance 2. Mechanisms of resistance 3. Drugs available to treat Carbapenem Resistant A. baumannii 4. Combination vs Monotherapy in A. baumannii treatment 5. Novel approaches to treatment of XDR infections

3. Case:
57 y.o NH resident, with COPD, HTN, OSA, and obstructive uropathy, presented to the hospital with acute renal failure and respiratory failure requiring intubation. She was found to have pneumonia and was started on Vancomycin/piperacillin-tazobactam. She improved on therapy, extubated and discharged back to NH.
She returns 3 days later with respiratory failure. Sputum growing A. baumanii.

4. Susceptibilities come back and are as above. Looks quite dismal.
Then you go to uptodate and try to figure out what kind of bug it is and how to treat it

5. Acinetobacter spp.
G – coccobacilli, strictly aerobic, non-motile, catalase positive and oxidase negative, glucose non-fermenter
group contains 34 genomic species
Ubiquitous (soil, water, hydrocarbon sludge)
A.baumannii complex found almost exclusively in hospitals

6. Acinetobacter calcoaceticus- baumannii complex
Acinetobacter calcoaceticus, A. baumannii, A.pittii, A. nosocomialis
genetically highly related and difficult to distinguish phenotypically and biochemically
25% Acinetobacter isolates are misidentified as A. baumannii by most commercial methods.
Acinetobacter calcoaceticus – nonpathogenic
Higgins, P.G., et al., A PCR-based method to differentiate between Acinetobacter baumannii and Acinetobacter genomic species 13TU. Clinical Microbiology and Infection, (12): p

7. Risk Factors for CRAB infection:
Recent exposure to antibiotics, esp carbapenems and 3rd generation cephalosporins
Presence of CVC or urinary catheter
Severity of illness
Large hospital size (>500)
Prolonged ICU stay
Lin, M.F. and C.Y. Lan, Antimicrobial resistance in Acinetobacter baumannii: From bench to bedside. World J Clin Cases, (12): p

8. Bad Bugs, No Drugs, No ESKAPE
Enterococcus faecium (VRE) Staphylococcus aureus (MRSA) Klebsiella pneumonia Acinetobacter baumannii Pseudomonas aerugenosa Enterobactereceae
2/3 of nosocomial infections
And present therapeutic challenges due to limited treatment options due to resistance
Boucher, H.W., et al., Bad bugs, no drugs: no ESKAPE! An update from the Infectious Diseases Society of America. Clin Infect Dis, (1): p

9. CDC. Antibiotic Resistance Threats in the United States (2013)

10. Resistance Terminology
MDR – resistant to 1 agent in 3 antimicrobial groups
(ex: R to ceftriaxone, Bactrim, Cipro)
XDR –resistance to 1 agent in all but 2 antimicrobial groups
(ex: only sensitive to tigecycline and colistin)
PDR- resistant to all antimicrobial agents

11. 50-70% of Ab clinical isolates are now extensively Drug Resistant (XDR; i.e. resistant to all antibiotics except colistin or tigecycline), reflecting a >15-fold increase since 2000.
Number of PDR strains of Ab, resistant to tigecycline and colistin are increasing
Perez et al AAC 2007, Talbot and others, 2006, CID; Talbot ERAIT, 2009, Boucher CID 2009

12. Does resistance matter?
BSI by XDR Ab cause >50-60% mortality
In a recent study 13,796 patients in 1,265 ICUs from 75 countries, Ab was one of only two of 19 microorganisms strongly linked (p<0.01) to increased mortality by multivariate analysis;
Odds ratio for death: 1.53
McGowan ICHE 2019, Hoffman et al, ICHE 2010, McGowan AJM 2006 Paterson CID 2006, Perez AAC 2007,
Vincent JAMA 2009, Gordon JAC 2009

13. Mortality: 16-76%
from 8% to 35%, according to strain and type of infection (Falagas & Rafailidis, 2007). Accordingly, different A. baumannii strains could be endowed with different pathogenic potential, as suggested by two studies using the mouse model of pneumonia: an MDR strain isolated from the blood culture of a patient with nosocomial pneumonia showed 80% mortality to mice, in contrast to 13% mortality for a strain causing meningitis (Eveillard et al., 2010), while a strain belonging to international clone 1 (see below) and a sporadic isolate were more virulent than a strain belonging to international clone 3 and the type strain (de Breij et al., 2012). Differences in mortality may be attributable to the expression of specific virulence factors and determinants. For example, two strains with the same PFGE profile, where one was a mucoid isolate from cerebrospinal fluid and the other was a nonmucoid isolate from a ventriculo peritoneal catheter, showed mortality rates of 48% and 19%, respectively, in a mouse model of pneumonia (Eveillard et al., 2010).
Lemos, E.V., et al., Carbapenem resistance and mortality in patients with Acinetobacter baumannii infection: systematic review and meta-analysis. Clin Microbiol Infect, (5): p

14. Evolution of resistance
1970s-> sensitive to amoxicillin and nalidixic acid
1980s-> reports of increasing resistance
1990s -> first reports of imipenem resistance
2010-> 49% resistant to carbapenems
-> horizontal gene transfer
-> genome fluidity

15. Survey of “Resistance genes” in A. baumannii
bla
AMEs
QRDR
RND
Efflux pumps
OMPs
Tet
ADC
aacC1
gyrA
AdeABC
HMP-AB
tetA
OXA
aacC2
parC
AdeM
OmpA
tetB
IMP
aacC3
AdeIJK
33-36 kDa
tetM
VIM, GIM
SIM, SPM, NDM
aacA4
AdeS
CraS
AdeDE
25/29 kDa
CarO
tetX
PER
aphA1
Res Is??
OprD
(43kDA)
PBPs
TEM*
aphA6
AbaR 1-10
OmpW
SHV
aadA1
Col R
pmrAB
44, 47kDa, 22
integrons
CTX-M
rmt*
lpxABC
OMVs

16. “The Resistance Island”
86 Kb, 88 orfs, 82 orfs from another source and 45 resistance genes
The sequence analysis of A. baumannii AYE antibacterial resistance genes indicates that frequent genetic exchanges take place with Pseudomonas spp., Salmonella spp., or Escherichia spp.
This repetition is likely due to a duplication, which suggests a transposition mechanism for the insertion. However, no inverted repeats characteristic of transposons were found at the extremities of the island. The 86-kb region was classified as a genomic island (and designated AbaR1) on the basis of its size (>10 kb), marked G + C content difference from the rest of the chromosomes (52.8% versus 38.8%), the presence of genes associated with genome instability such as integrases, transposases, and insertion sequences, and the diverse phylogenetic origin of the associated ORFs [11]. At the same position, flanked by identical nucleotide sequences and within the homologous ATPase ORF, the A. baumannii strain SDF genome sequence exhibits a genomic island (designated AbaG1), albeit only 19,632 bp in length, with a G + C content of 31.3%
Another unexpected finding was the presence of a similar structure in the genome of susceptible strain SDF, identically inserted in the homologous ATPase-like ORF. This genomic island was found in an “empty” state, exhibiting mobility-associated genes but no resistance markers. This coincidental genetic insertion in the two strains strongly suggests that this ATPase ORF constitutes a specific hotspot of genomic instability in the A. baumannii genome. This prompted us to investigate whether this feature was common to all A. baumannii strains. Using a polymerase chain reaction assay based on the conserved ATPase ORF flanking sequences (Protocol S1), 17 (77%) out of the 22 clinical A. baumannii isolates were found to exhibit an intact ATPase ORF. These 17 isolates included 11 isolates resistant to several antibiotic families, including β-lactams, and six susceptible to β-lactams. Among the five isolates exhibiting an interrupted ATPase ORF, four were resistant to most β-lactams except imipenem, including some that were also resistant to other antibiotic families, and one was susceptible to β-lactams but resistant to cotrimoxazole and rifampin (Protocol S1). The presence of a genomic island within the ATPase ORF is thus not a conserved feature among isolates, and its absence at this location is not predictive of the observed pattern of antibiotic susceptibility.
Finally, our last surprise was the identification of several putative resistance genes in a strain not exhibiting the associated phenotype. This was the case for two putative β-lactamases (present in the AYE and SDF), including the class D β-lactamase blaOXA-69. The expression of OXA-69 in E. coli resulted in low levels of carbapenem resistance [35], and its sequence is 97% identical to the OXA-51 carbapenemase, found associated with full carbapenem resistance [41]. However, the presence of blaOXA-69 in the susceptible AYE strain suggests that it might only be a step away from acquiring this new resistance through subtle changes in expression level or a specific mutation or series of mutations that alter the substrate profile and enhance catalytic activity. Besides the direct acquisition of genetic material from resistant bacterial species, the maintenance of spare copies of “ready-to-optimize” resistance genes in the genome of A. baumannii, perhaps selected by exposure to subinhibitory levels of the drug in the environment, might also play a role in its rapid adaptation to new derivatives of the major antibiotic classes.
AbaRs: complexity is growing!
Fournier et al., PLoS Genet Jan;2(1):e7. Epub 2006 Jan 13.

17. Difficulties in studying A.baumanii
Unreliable identifications tests
Unreliable susceptibility tests
Fluid genome and fast development of resistance

18. Drugs available to treat resistant A.baumannii
Colistin
Tigecycline
Sulbactam
Rifampin
Fosfomycin
Minocyline
Vancomycin

19. Monotherapy vs Combination Therapy

20. Monotherapy(MT) vs combination(CT) therapy for sepsis due to MDR A
Monotherapy(MT) vs combination(CT) therapy for sepsis due to MDR A.baumannii: analysis of a multicenter prospective cohort. Lopez-Cortes et al.
Prospective observational study
28 Spanish hospitals
Primary outcome: 30 day mortality
Secondary outcome: all-cause 14 day mortality
MT -> use of single agent active in vitro
Colistin (46)
Carbapenem(10)
Tigecycline (5)
Sulbactam (5)
Tetracycline (2)
CT-> use of 2 or more active drugs
Bitherapy with carbapenem was considered MT when carbapenem MIC was >32 and CT when it was lower
J Antimicrob Chemother, (11): p

21. Monotherapy(MT) vs combination(CT) therapy for sepsis due to MDR A
Monotherapy(MT) vs combination(CT) therapy for sepsis due to MDR A.baumannii: analysis of a multicenter prospective cohort. Lopez-Cortes et al.
CT therapies:
Colistin+tigecycline (9)
Carbapenem+tigecycline (4)
Colistin+carbapenem(3)
Colistin+sulbactam (2)
Colistin+AG(2)
Colistin +rifampicin(2)
Carbapenem+AG(2)
Tigecycline+rifampicin(2)
Tigecycline+AG(1)
Colistin+tigecycline+carbapenem+AG(3)
Colistin+tigecycline+AG(2)
Tigecycline+carbapenem+rifampicin(1)
J Antimicrob Chemother, (11): p

22. Monotherapy(MT) vs combination(CT) therapy for sepsis due to MDR A
Monotherapy(MT) vs combination(CT) therapy for sepsis due to MDR A.baumannii: analysis of a multicenter prospective cohort. Lopez-Cortes et al.
No mortality benefit from using CT compared with MT
30 day mortality : MT 23.5% vs CT 24.2 % RR CI P=0.94
Multivariate analysis of 30 day survival: also showed no trend towards reduced mortality
Problems with the study:
Low colistin dose
?High rate of inappropriate empirical treatment?
Several types of infection
CT and MT groups made up of multiple agents
Small sample size
Did not look into microbiological eradication

23. Excess Mortality Associated with Colistin-Tigecycline compared with colistin-carbapenem combination therapy for XDR A.baumannii Bacteremia: a multicenter prospective observational study. Cheng et al
Primary outcome: 14 day mortality
Colistin- tigecycline (29 patients)
Colistin-carbapenem (26 patients)
14 day mortality 35% vs 15% (p=0.105)
In hospital mortality 69% vs 50% (p=0.152)
Subgroup analysis of 14 day mortality for Tig MIC >2 showed HR of compared to colistin-carbapenem ( ).
Crit Care Med, (6): p

24. Comparison of colistin-carbapenem, colistin-sulbactam, and colistin plus other antibacterial agents for the treatment of XDR A. baumannii bloodstream infections. Batirel et al.
Retrospective observational multicenter study
27 Turkish tertiary hospitals
Primary outcome: 14 day mortality
Secondary outcome: clinical and microbiologic response
MT: colistin (36)
CT:
Colistin+carbapenem (102)
Colistin+sulbactam (69)
Colistin +other abx (43)
Eur J Clin Microbiol Infect Dis, (8): p

25. Comparison of colistin-carbapenem, colistin-sulbactam, and colistin plus other antibacterial agents for the treatment of XDR A. baumannii bloodstream infections. Batirel et al.
14 day survival: CT 68.2% vs MT 55.5% p=0.14
In-hospital crude mortality CT 52.3% vs MT 72.2% p=
Microbiologic eradication CT 79.9% vs MT 55.6% p=0.001
No significant survival difference was found in clinical and microbiological outcomes and 14 day survival between three combination groups
Weakness:
more late therapy in MT group (but not significantly)
Eur J Clin Microbiol Infect Dis, (8): p

26. Comparison of colistin-carbapenem, colistin-sulbactam, and colistin plus other antibacterial agents for the treatment of XDR A. baumannii bloodstream infections. Batirel et al.
Eur J Clin Microbiol Infect Dis, (8): p

27. Comparison of colistin and colistin/sulbactam for treatment of multidrug resistant Ab VAP. Kalin et al
Retrospective, n=89

28. Colistin and rifampicin compared with colistin alone for treatment of serious infections due to XDR A.baumannii: a multicenter randomized clinical trial. Durante-Mangoni et al
Italy, N=210
Weaknesses:
20.8% patient’s in monotherapy group received adjunctive meropenem or tigecycline, which would lower then expected mortality.
Not blinded
No difference in mortality
Increased microbiologic eradication
Clin Infect Dis, (3): p

29. Colistin vs. the combination of colistin and rifampicin for the treatment of carbapenem-resistant Acinetobacter baumannii ventilator-associated pneumonia. Aydemir et al
Epidemiol Infect, (6): p

30. 94 patients infected with CRAB, col alone or col + fosfo for 7 to 14 days..
Combo better micro response and a trend toward better clinical outcomes and lower mortality than mono

31. Retrospective multicenter study
Clinical Experience of Colistin-Glycopeptide Combination in Critically Ill Patients Infected with Gram-Negative Bacteria Petrosillo, et al
Retrospective multicenter study
Patients in ICU who received colistin for GNB infection (n =184)
VAP (64.5%) and BSI (20%)
Outcomes: 30 day mortality and nephrotoxicity
MDR AB(59.6%), CR Klebsiella (14.5%) MDR Psa (18.7%)
16% had G+ infection. 40% received CGC.
Improved survival no difference in nephrotoxicity.
Antimicrob Agents Chemother, (2): p

32. Clinical Efficacy and Safety of the Combination of Colistin plus Vancomycin for the Treatment of Severe Infections Caused by Carbapenem-Resistant Acinetobacter baumannii Garnacho_Montero et al
retrospective study of VAP or bacteremia by CRAB
N=57
Colistin +Vancomycin (29) vs colistin alone (28).
28 day mortality was 48% vs 50%
Baseline characteristics, clinical cure, microbiological eradication, and mortality were similar in both groups but the rate of acute kidney injury was higher in group I (55.2 vs. 28%; p = 0.04).
Chemotherapy, (3): p

33. Tetracyclines for multidrug-resistant A. baumannii infections
Tetracyclines for multidrug-resistant A.baumannii infections. Falagas et al
10 retrospective studies reviewed of using minocyline/doxycycline alone or in combination with other abx. N=156
Clinical success achieved in 76.9%
Mortality in 20 out of 100 available cases
Unable to extrapolate data for monotherapy vs combination therapy

34. Drugs to Rx Ab Drug Dosing +/- Combination vs Monotherapy Colistin
5 mg/kg/d load followed by 5mg/kg/2-3 doses
Mainstay therapy
Poor lung penetration
Difficulty dosing
Combo> mono
Nephrotoxicty
???
Fosfomycin*
4 grams/q12
Well tolerated
No IV in US
Resistance in mono Rx
Combination tx: no mortality benefit, increased microbiologic eradication
Rifampin
600 mg q12-24
Toxic
Sulbactam
3-9 grams /day
Can’t get alone in US
Increasing rates of resistance

35. Drugs to Rx Ab Drug Dosing +/- Combination vs Monotherapy Tigecycline
100 mg load, 50 mg q12
Bacteriostatic
Low blood levels
?increased mortality if MIC>2
Minocycline*
???
High rates of resistance in US
Seems promising but needs
Prospective/randomized studies
Vancomycin
10-15 mg q12
In vitro synergy
nephrotoxicity
??? (probably no benefit)

36. Monotherapy Vs Combination therapy Studies
Sites of infection
Drugs
Monotherapy Vs
Combination therapy
Studies
Patients
Bugs

37. Summary Evidence is inconclusive and hard to interpret Common issues :
Multiple compared antibiotics and different sites of infections
Heterogeneous organisms and mechanisms of resistance
Small number of patients, few randomized studies
Late therapy
Is monotherapy truly monotherapy? Patients often co-infected with other organisms and receive Abx for it. Ex: Vancomycin, meropenem.
Does microbiologic eradication matter even though there is no mortality difference?
Most authors recommend using combination therapy in severe cases.

38. References:
1. Aydemir, H., et al., Colistin vs. the combination of colistin and rifampicin for the treatment of carbapenem-resistant Acinetobacter baumannii ventilator-associated pneumonia. Epidemiol Infect, (6): p
2. Batirel, A., et al., Comparison of colistin-carbapenem, colistin-sulbactam, and colistin plus other antibacterial agents for the treatment of extremely drug-resistant Acinetobacter baumannii bloodstream infections. Eur J Clin Microbiol Infect Dis, (8): p
3. Cheng, A., et al., Excess Mortality Associated With Colistin-Tigecycline Compared With Colistin-Carbapenem Combination Therapy for Extensively Drug-Resistant Acinetobacter baumannii Bacteremia: A Multicenter Prospective Observational Study. Crit Care Med, (6): p
4. Claeys, K.C., A.D. Fiorvento, and M.J. Rybak, A Review of Novel Combinations of Colistin and Lipopeptide or Glycopeptide Antibiotics for the Treatment of Multidrug- Resistant Acinetobacter baumannii. Infect Dis Ther, 2014.
5. Doi, Y., G.L. Murray, and A.Y. Peleg, Acinetobacter baumannii: evolution of antimicrobial resistance-treatment options. Semin Respir Crit Care Med, (1): p
6. Durante-Mangoni, E., et al., Colistin and rifampicin compared with colistin alone for the treatment of serious infections due to extensively drug-resistant Acinetobacter baumannii: a multicenter, randomized clinical trial. Clin Infect Dis, (3): p
7. Falagas, M.E., et al., Tetracyclines for multidrug-resistant Acinetobacter baumannii infections. Int J Antimicrob Agents, (5): p
8. Garnacho-Montero, J., et al., Clinical efficacy and safety of the combination of colistin plus vancomycin for the treatment of severe infections caused by carbapenem- resistant Acinetobacter baumannii. Chemotherapy, (3): p
9. Imperi, F., et al., The genomics of Acinetobacter baumannii: insights into genome plasticity, antimicrobial resistance and pathogenicity. IUBMB Life, (12): p
10. Kalin, G., et al., Comparison of colistin and colistin/sulbactam for the treatment of multidrug resistant Acinetobacter baumannii ventilator-associated pneumonia. Infection, (1): p
11. Karageorgopoulos, D.E., et al., Tigecycline for the treatment of multidrug-resistant (including carbapenem-resistant) Acinetobacter infections: a review of the scientific evidence. J Antimicrob Chemother, (1): p
12. Khawcharoenporn, T., et al., Colistin-based treatment for extensively drug-resistant Acinetobacter baumannii pneumonia. Int J Antimicrob Agents, (4): p

39. References:
13. Lemos, E.V., et al., Carbapenem resistance and mortality in patients with Acinetobacter baumannii infection: systematic review and meta- analysis. Clin Microbiol Infect, (5): p
14. Lin, M.F. and C.Y. Lan, Antimicrobial resistance in Acinetobacter baumannii: From bench to bedside. World J Clin Cases, (12): p
15. Lopez-Cortes, L.E., et al., Monotherapy versus combination therapy for sepsis due to multidrug-resistant Acinetobacter baumannii: analysis of a multicentre prospective cohort. J Antimicrob Chemother, (11): p
16. Pachon, J. and M.J. McConnell, Considerations for the development of a prophylactic vaccine for Acinetobacter baumannii. Vaccine, (22): p
17. Perez, F. and R.A. Bonomo, Vaccines for Acinetobacter baumannii: thinking "out of the box". Vaccine, (22): p
18. Petrosillo, N., et al., Clinical experience of colistin-glycopeptide combination in critically ill patients infected with Gram-negative bacteria. Antimicrob Agents Chemother, (2): p
19. Poirel, L., R.A. Bonnin, and P. Nordmann, Genetic basis of antibiotic resistance in pathogenic Acinetobacter species. IUBMB Life, (12): p
20. Poulikakos, P., G.S. Tansarli, and M.E. Falagas, Combination antibiotic treatment versus monotherapy for multidrug-resistant, extensively drug-resistant, and pandrug-resistant Acinetobacter infections: a systematic review. Eur J Clin Microbiol Infect Dis, (10): p
21. Shields, R.K., et al., Epidemiology, clinical characteristics and outcomes of extensively drug-resistant Acinetobacter baumannii infections among solid organ transplant recipients. PLoS One, (12): p. e52349.
22. Siontorou, C.G., Nanobodies as novel agents for disease diagnosis and therapy. Int J Nanomedicine, : p
23. Sirijatuphat, R. and V. Thamlikitkul, Preliminary study of colistin versus colistin plus fosfomycin for treatment of carbapenem-resistant Acinetobacter baumannii infections. Antimicrob Agents Chemother, (9): p
24. Viehman, J.A., M.H. Nguyen, and Y. Doi, Treatment options for carbapenem-resistant and extensively drug-resistant Acinetobacter baumannii infections. Drugs, (12): p

41. Big picture:
Regardless, mortality is still high and available treatments are limited!

42. Are we entering post-antibiotic era?

43. CDC. Antibiotic Resistance Threats in the United States (2013)

44. Ways to battle resistance:
Antibiotic Stewardship
Rapid diagnostics
Novel therapies

45. Novel therapies: Vaccination Passive antibody therapy
Antibacterial peptides

46. A.Baumannii vaccine development
Pachon, J. and M.J. McConnell, Considerations for the development of a prophylactic vaccine for Acinetobacter baumannii. Vaccine, (22): p

47. Vaccines: unanswered questions
Who to immunize?
Will critically ill patient able to mount a response to vaccine?
Perez, F. and R.A. Bonomo, Vaccines for Acinetobacter baumannii: thinking "out of the box". Vaccine, (22): p