الفهرس 
TItle pageOnly 14 pages are availabe for public view
 |  | from | 16 |  |  |
| | | from | 16 | | |
Abstract
Acinetobacter baumannii is non fermentative, strictly aerobic, gram-negative bacteria. The combination of its environmental resilience and its wide range of resistance determinants renders it a successful nosocomial pathogen. (23) MDR A. baumannii infections tend to occur in those subjected to invasive procedures and treated with broad-spectrum antibiotics, in immuno-suppressed patients and in patients with serious underlying diseases. (54)
Infections caused by A. baumannii are frequently found in ICUs, where they are implicated as the leading cause of ventilator-associated pneumonia, urinary tract infections, and bacteremia. A. baumannii also causes complicated skin and soft tissue, abdominal, and central nervous system infections, that is why A. baumannii has emerged as one of the most problematic nosocomial pathogens. (1)
The current study included (150) MDR A. baumannii clinical isolates from patients admitted to ICU of Alexandria main university hospital. Duplicate isolates from the same patients were excluded from analysis. The majority of A. baumannii clinical isolates (91; 60.67%) were collected from respiratory tract, followed by skin and soft tissues; (41; 27.34%), urine; (9; 6%), blood; (5; 3.34%) and indwelling device; (3; 2%). Only one isolate (0.67%) was collected from cerebrospinal fluid.
The management of A. baumannii infections can be difficult, due to the increasing number of isolates exhibiting resistance to multiple classes of antibacterial agents. β-lactam antibiotics are the most widely used group of antibiotics which are indicated for the prophylaxis and treatment of bacterial infections caused by susceptible organisms. (145)
In the present study all recovered isolates were resistant to the tested β-lactams including Cephalosporins (Cefotaxime, Ceftazidime, Cefepime and Ceftriaxone), β-lactams-β-lactamase inhibitors (Amoxicillin / Clavulanic acid Cefoperazone / Sulbactam and Piperacillin / Tazobactam) and Monobactams (Aztreonam) and resistant to both tested Quinolones (Ciprofloxacin and Levofloxacin).
Trimethoprim/Sulfamethoxazole or Co-trimoxazole is an antifolate antibiotic that inhibits both de novo folate biosynthesis and metabolism. Trimethoprim and Sulfamethoxazole have a synergistic effect when given together than when given separately. (175) In the present study, (67.33%) of the recovered MDR A. baumannii clinical isolates were resistant to Trimethoprim/ Sulfamethoxazole compared to only (32.67%) sensitive isolates.
Aminoglycosides are bactericidal agents that inhibit protein synthesis in aerobic gram-negative, gram-positive bacteria and Mycobacteria. (167) In the present study three Aminoglycosides were tested: Amikacin, Gentamicin and Tobramycin. Amikacin showed the highest susceptibility pattern as (43%) A. baumannii isolate were sensitive to it followed by Tobramicin (31%). Gentamicin had the least susceptibility pattern as only (26%) of recovered isolates were sensitive to it.
Carbapenems remained as last resort and drugs of choice for the treatment of A. baumannii infection yet, Carbapenem-resistant A. baumannii isolates are becoming increasingly prevalent worldwide. (7) In the present study, the majority of A. baumannii isolates (93.34%) were resistant to all tested Carbapenems, while (6.67%) of isolates were sensitive to Imipenem compared to only (2%) isolates sensitive to Meropenem.
Out of the 150 A. baumannii tested clinical isolates in the present study 80 (53.33%) isolates were positive for carbapenemase production by Hodge test while 70 (46.67%) isolates were negative. On the other hand 120 (80%) isolates were positive for metallo-β-lactamase production by EDS-test compared to 30 (20%) isolates which were found to be negative. EDTA disk synergy test seems to be a better method for MBL detection than modified Hodge test.
In the present study, the in vitro activity of Tigecycline against MDR A. baumannii in ICU was evaluated. Tigecycline showed very good in vitro activity against MDR A. baumannii as (67.34%) of our isolates were sensitive to Tigecycline. It should also be mentioned that the determination of the microbiological activity of Tigecycline may vary with the use of different antimicrobial susceptibility methods. The use of the disc diffusion method has been associated with lower susceptibility rates of A. baumannii isolates to Tigecycline when compared with the broth microdilution method or the E-test.
Since no interpretive criteria have been approved for Tigecycline against Acinetobacter species, breakpoints for Tigecycline susceptibility were interpreted according to the US Food and Drug Administration standards for Enterobacteriacea, which is (S≥19 mm; I=15–18 mm; R≤14 mm) for disc diffusion method & (S≤2, R≥4) for broth microdilution method, (189) also according to criteria recommended by Jones, et al. (S≥16 mm; I=13-15 mm; R≤12 mm). (248)
In the present study the percentages of susceptible and resistant isolates determined by the broth microdilution method were (67.34%) and (32.67%), respectively. The rates of susceptible and resistant isolates by the disk diffusion method using the criteria of Jones et al. were the same as microdilution method while using the US FDA criteria were (54%) and (46%), respectively. The total error rate of the disk diffusion method in comparison with the broth microdilution method was 13.34% (20/150).
In the present study, all recovered MDR A. baumannii isolates were sensitive to Colistin. MDR A. baumannii strains remain generally susceptible to Polymyxins (Colistin and Polymyxin B), a fact that has contributed to the reconsideration and re-introduction of this practically abandoned for decades class of antibacterials into clinical practice. (251, 252)