21-08-2012, 12:24 PM
Acinetobacter Emerging as a Nosocomial pathogen
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INTRODUCTION
The Genus Acinetobacter belongs to the family Moraxellaceae, within the gamma subdivision of proteobacteria. they are gram negative bacteria, strictly aerobic, non-motile coccobacilli that are oxidase negative and catalase positive. The bacteria are ubiquitous and can be isolated from soil and water. they are commonly associated with skin colonization of hospitalized patients and have been associated with serious infections. Over the recent decades, the acinetobacter species has increasingly been implicated in outbreaks of nosocomial infections causing Pneumonia, bacteraemia, urinary tract infections, wound infections and meningitis worldwide.
There are over 20 species of Acinetobacter, through the species Acinetobacter Baumanii accounts for more than 80% of isolates causing Human disease. previously , all were named Acinetobacter Calcoaceticus.they are now divided into 7 species:A.Johnsonii,A.Junii,A.Levoffi and A.Radioresistans.the capsule that surrounds most strains may inhibit phagocytosis and has been speculated to predispose persons with selective complement component deficiencies to infections.
The lack of characteristics (no color, non-motile, unable to reduce nitrates, oxidase negative and non-ferment ting) has led Acinetobacter to be constantly reclassified. First discovered in 1908, as Diplococcus mucosus, it has successively been named Micrococcus (small), mimic (mimics), Achromobacter (colorless), Acinetobacter (motionless) and anitratus (nitrate no reducing).
Presently, atleast 24 genomic species have been described within the genus Acinetobacter. Strains belonging to some of the genomic species are very similar that identification by phenotypic characterization is difficult. It has been reported that most of the isolates of clinical origin are closely related to the Acinetobacter Calcoaceticus, A.Baumanii, genospecies 3, TU13,”close to TU13 and between 1 and 3 with the exception of the genomic species 1, which has been regarded as an environmental species, each genomic species within the Acb complex has been shown to be associated with outbreaks of nosocomial infections .
Material and Method
Methods’: perform a review of 15 patients admitted to a hospital and identified 8 patients with acinetobacter baumanii.
Result:8 cases of acinetobacter were associated with trauma wounds.the median age of the patients was 28 years.
The strains were origanlly isolated from different clinical and environmental specimens .eg:blood,cerebrospinal fluid,sputum,urine,soil,E-T secretion,wound swab,bronchial wash and E-T tip. They were preserved in nutrient broth at 37 degree Celsius. Most isolates have been recovered from cases of community acquired and nosocomial pneumonia. Most patients suffer from respiratory compromise patients on respirators are at risk of infections. Organism have also been recovered from cases of UTI, Septicemia, and wound contaminated by soil and water.
Characteristics
It grows well on Macconkey agar. Colonies are circular, entire, opaque and slightly smaller than standard enteric colonies. Most isolates grow on macconkey agar as colorless colonies that may turn slightly pink due to oxidation of lactose. Two species are mostly encountered in the clinical setting. A.Baumanii and A.Calcoaceticus.they can utilize citrate as a carbon source, oxidizes glucose (ofo +) growth at 42c .
Culture on macconkey agar and blood agar: firstly we inoculate the sample on macconkey agar and blood agar and keep the plates in an incubator at 37 degree Celsius. Next day we observe a growth on the plates. Colorless colonies grow on the plate that means it is non lactose ferment.
Biochemical test
Oxidative-fermentative test (of test):
The oxidation-fermentation test was developed by Hugh and Leif son in 1953.during this time microbiologist has observed that some bacteria produce acid from carbohydrates only under aerobic and anaerobic conditions. Production of acid from the metabolism of carbohydrates in aerobic and anaerobic metabolism was at this time defined as fermentation. Hugh and Leifson were the first to refer to the production of acid from carbohydrates under aerobic conditions only, as oxidative. Hugh and Leifson developed OF media to differentiate these two populations of bacteria. OF test is used to determine if gram negative bacteria metabolize carbohydrates oxidative by fermentation or are non sacchrolytic and therefore have no ability to use the carbohydrate in the media.