ACINETOBACTER BAUMANNII 4
2.The Development of Antibiotic Resistance in Bacterial Species-Acinetobacter baumannii
GeneralFeatures of The Organism
Acinetobacterbaumannii is an adaptable bacteria commonly found in water and soil.Its ability to resist antibiotics presents a challenge to physiciansto control and treat the associated illnesses. The bacteria canwithstand for long periods in diverse environmental settings. Theassociated antimicrobial resistance of the organism reduces thetreatment options for patients infected with the creature. It is alsolinked to frequent outbreaks within health care settings (Camp &Tatum, 2010).
Someof the associated illnesses include pneumonia, urinary tractinfections, wound contagions, and meningitis. The key risk factors ofthe bacteria include prolonged hospital stays in the intensive careunit, surgery, provision of mechanical ventilation, immunodeficiency,and use of invasive procedures. The bacteria occur due toenvironmental contamination as well as use of respiratory equipment,wound care procedures and use of humidifiers. As a result of itsability to affect severely ill patients, the bacteria are associatedwith 26% to 68% related mortality rates in the ICU (Camp & Tatum,2010).
Undera microscope, the bacteria appear to be short, rod-like, andspherical. The genomic structure of the organism is made of a singlecircular chromosome. The chromosome is made of 3,976,747 base pairs,out of which 3,454 are meant for protein coding. A single strain ofthe bacteria is called AYE, and it contains the largest resistanceislands known to date (Howard et al., 2012).
Islandsare sections in the chromosomes that hold the necessary genesresponsible for resisting antibiotics. The A. baumannii chromosome’sresistance island is 86kb in size and contains 45 resistance genes. Amajor 25 genes are responsible for the bacteria’s survival againstvarious antibiotics such as cotrimoxazole, chloramphemical,tetracycline, and aminoglycosides. The island is not only used forantibiotic resistance, but it also codes for resistance againstmercury and operons. The chromosome contains 14 resistance genes usedin coding for class 1 integrons. The genes have the capability tointegrate, express, and recombine (Broek & Bruin, 2009).
TheAcinetobacter baumannii bacteria are everywhere since they can berecovered from all soil and water samples. The organisms thrive inmoist surfaces, including, mucus tissues, or exposed areas of theskin. It also in temperatures between 25 to 37 degrees, and it canstill grow at 45 degrees Celsius. They also flourish in acidic pH ofbetween 5.5 and 6.0. Consequently, the bacteria can survive byavoiding desiccation. The ability to live in harsh conditionsemanates from the design of its cell wall. The cell wall isnon-static and can change and adapt to harsh environmentalconditions. Various studies have reckoned that when the bacteria areplaced in dry conditions, they increase the thickness of their cellwalls. Besides, they increase the distance between the plasma andouter membranes, as well as change their shape from a rod like tococci by decreasing their art of cell division (Camp & Tatum,2010).
Descriptionof the Health Condition in the Case Study
a.The transfer of drug resistance genes
Thetransfer of drug resistance genes in the A.baumannii are facilitatedby integrons, plasmids, and transponsons. The class 1 integronsconducts the transfer of multiple resistant genes since they arepresent in 88% of biofilm formations. The integrons allow the passageof enzyme codes from cell to cell. The beta-lactamase is a commonenzyme that confers resistance to cephalosporins, carbapenems, andpenicillins. The bacterium can recruit acetyltransferases,nucleotidyltransferases, and phosphotransferases that enhance theresistance created by aminoglycosides and fluoroquinolones. Themutated genes increase the Minimum Inhibitory Concentration (MIC) ofa drug by altering the bacterial targets of antimicrobials. They arealso responsible for outbreak strains in treatment facilities ofmilitants in the United States of America and the United Kingdom(Camp & Tatum, 2010).
b.The Source Of Drug Resistance Genes
TheA. baumannii drug resistance capabilities emanate from its ability torecruit other drug resistance bacteria and conduct gene exchanges.The gene transfer is evident from the sequence of amino acids andother organisms in the bacteria. Some of the drug-resistant bacteriarecruited by the A. baumannii include 44% (39 genes) believed tooriginate from Pseudomonas spp. Additional 34% (30 genes) are thoughtto arise from Salmonella spp. 17% (15 genes) from Escherichia spp.and a minimum 4% ( 4 genes) from other resistant microorganisms(Howard et al., 2012).
Theability to resist various antibiotics emanates from its outermembrane of bacteria that contains porins and efflux channels. Theporins serve as sites of attachment of antibiotics and help in thetransport of molecules across the cell membranes. In contrast tosimilar gram-negative bacteria, the A.baumannii has smaller porins.They are also fewer in number and help in decreasing the cellspermeability as well as increasing its antibiotic resistance byreducing the attachment sites of the antibiotics (Camp & Tatum,2010).
Variousstudies have identified that only less than 5% of molecules arepermeable to the bacteria’s cell membrane. Besides, the relatedimpermeability is contributed by the lack of the carO protein genethat is associated with the 29kDa outer membrane. The carO isresponsible for the importation of antibiotics and its deficiencyfurther limits the transportation of antibiotic proteins within thebacteria cells. Besides, the cell membrane contains efflux pumps thatare used in pumping various chemicals and antibiotics out of thecells. Since A. baumannii bacteria are a non-fermentative glucose,aerobic bacteria and oxidase negative, it contains antibioticresistant strains. The strains produce beta-lactamases that furtherprevent the bacteria from antibiotic functions. The beta-lactamaseshydrolyze various antibiotics such as penicillin, carbapenems andcephalosporins and further reduces their efficacy in eliminating thebacteria (Camp & Tatum, 2010).
The best treatment
Theoptimal treatment for A.baumannii depends on the susceptibility ofthe patient. It also depends on pharmacokinetic principles as well asthe site of infection. The optimal treatment of the bacteria requireshigh doses of tigecycline and cefepime. It is also advisable that thedosage should not be provided by inhalation since it initiates theresistance of the bacteria. Specifically, Minimum InhibitoryConcentrations (MIC) of 16 micrograms/ ML and 2 micrograms/ ML ofboth cefepime and tigecycline have proven vulnerable to the bacteriasince susceptibility occurs when the serum and tissue concentrationsexceed the Minimum Inhibitory Concentrations (MIC). For cefepime, aminimum 2 grams dosage provided intravenously only results in 163micrograms/ ML peak serum levels. The related volume of concentrationis 0.29L/kg, which is too small to eradicate the A.baumannii bacteriain the patient`s respiratory secretions. High intravenous doses oftecycline, such as initial doses of 200 and 100 milligrams daily, areused to achieve the peak concentrations. Such concentrations includeapproximately 0.3 milligrams /ML, which exceeds the bacteria’s MICof 2 micrograms/ ML as well as the high distribution volume of 8liters/ kg that is sufficient to eliminate the bacteria (Camp &Tatum, 2010).
Othertreatments include the use of colistin that fights against the gamnegative bacteria as well as a majority of A.baumannii isolates. Mostof the A. baumannii isolates are susceptible to Colistin within abreaking point of less or equals to2 micrograms/ML. The ClinicalLaboratory Standards Institute (CLSI) endorses the dosage. Besides,the European Committee on Antimicrobial Susceptibility Testing(EUCAST) also recommends the dosage.
Broek,P. V., & Bruin, L. D. (2009). Acinetobacterbaumannii.Leiden: Boerhaave Committee for Postgraduate Medical Education,Leiden University Medical Center.
Camp,C . & Tatum, O. (2010). A review of Acinetobacter baumannii as ahighly successful pathogen in times of war. Lab Med,11 (41), 649-657Retrirved from http://www.medscape.com/viewarticle/732915_5
Howard,A.,Donoghue, M., Feeney, A.& Sleator R.(2012).Acinetobacter baumannii. An emerging opportunistic pathogen.Nationalcentre for Biotechnology Information (NCBI), 3(3) 243-250 Retrievedfrom http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3442836/