|Iranian Journal of Pharmaceutical Research
((2008), 7 (4): 305-309
Received: March 2008
Accepted: July 2008
Copyright ? 2008 by School of Pharmacy
Prevalence of Microorganisms Causing
and Determination of Antimicrobial Resistance
in Intensive Care Unit
Yunes Panahia*, Mojtaba Mojtahedzadehb, Fatemeh
Marzeyeh Pazookid and Yashar Moharamzada
aResearch Center of Chemical Injuries, Baqiyatallah Medical Sciences University, Tehran, Iran. bPharmaceutical Research Center, Faculty of Pharmacy, Tehran University of Medical Sciences, Tehran, Iran. cNephrology and Urology Research Center, Baqiyatallah Medical Sciences University, Tehran, Iran. dICU of Sina Hospital, Tehran University of Medical Sciences, Tehran, Iran.
The objective of this study was to determine the frequency of microorganisms isolated from blood samples of patients admitted to Intensive Care Unit (ICU), and the rate of their resistance to common administered antibiotics in an Iranian ICU. One-hundred patients with Systemic Inflammatory Response Syndromes (SIRS), hospitalized in ICU of Sina Hospital, Tehran, Iran, were entered to this cross-sectional study from March 2005 to March 2006. Blood samples were taken from these patients and transferred to culture medium. After detecting the type of microorganism, minimum density for inhibition of growth of microorganisms by antibiotics, using minimum inhibitors concentration (MIC) method, was determined for ceftazidime, ceftriaxone, amikacin, ciprofloxacin, meropenem and cefepime. Culture results of 38 patients were positive (38%). Klebsiella (14 patients, 37%), coagulase negative Staphylococcus (9 patients, 23.6%), Pseudomonas and Acinetobacter (each of them recovered in 6 patients, 15.8%), Staphylococcus aureus (one patient, 2.6%) and gram positive bacilli (2 patients, 5.2%) were detected microorganism. Only Staphylococcus aureus was resistant to all studied antibiotics. Gram-negative bacilli showed resistance to all antibiotics except for amikacin and meropenem.
The rate of septicemia detected was higher in comparison to developed countries. Clinical suspicion with appropriate microbiological tests is essential for early diagnosis to prevent adverse outcomes in patients admitted to ICU.
Systemic Inflammatory Response Syndrome (SIRS) includes infectious (local and general) and non-infectious causes (trauma, thermal injuries, etc) which would raise high inflammatory response of the host with systemic manifestations (1). Presence of evidences of infection together with systemic responses to this infection like fever, hypothermia, tachycardia, etc is described as sepsis (2). Sepsis is one of the prevalent infections among patients admitted to Intensive Care Units (ICUs), with a significant morbidity, and the rate of its mortality is estimated to be from 25% to 80% (3, 4). Almost 751,000 persons with sepsis have been detected in US in 1995, resulting in 215,000 deaths. The average cost per case of sepsis was $22,100 with total costs of $16.7 billion nationally (5).
ICU-associated infections are mostly due to Staphylococcus aureus and coagulase negative Staphylococcus (like Staphylococcus epidermidis) and usually because of contaminated intra vascular devices like artificial heart valves, intravenous and intra-arterial catheters (6).
Administration of antibiotics to control infection, prescription of proper amounts of liquid, oxygen and vasoconstrictor medications are the basic treatments of sepsis syndrome (7).
Before accurate diagnosis by specific culture media is made, different antibiotics are prescribed for septic patients in ICUs. Selection of appropriate antibiotics that can cover both positive and gram negative microorganisms, at this phase is usually empiric. This selection is depending on factors like epidemiological evidences, antibiotic resistance patterns and probable infective causes (8). Prevalence of microorganisms causing septicemia in ICUs depends on environmental and geographical locations. In developing countries, many hospitals are not equipped with isolation facilities (9), and it is of high probability that prevalent microorganisms in hospitals of these countries may be different from those in developed countries. Apart from different prevalence, these microorganisms show various degrees of resistance to antibiotics. The aim of this study was to determine the prevalence of microorganisms extracted from blood samples of patients admitted to ICU of a university general hospital in Tehran, the capital of Iran and to recognize degree resistance of the micro organisms to commonly used antibiotics.
In this observational study which conducted from March 2005 to March 2006, 100 septic patients hospitalized in ICU of Sina Hospital were included. The inclusion criteria were age older than 18 years, and presence of SIRS. This syndrome was defined as presence of at least two of the following criteria (2): fever or hypothermia (38?C<T<36?C), leukocytosis or leucopenia (12000/mm3<white blood cell count<4000/mm3 or Band cell>10%), tachypnea (RR>20/min or PCO2<32 mmHg), and tachycardia (HR>90 beat/min). The score on the Acute Physiology and Chronic Health Evaluation (APACHE) II (10) at admission was also calculated.
Blood samples were taken from patients? veins using sterile syringes. Five milliliters of the sample was transferred to aerobic and anaerobic culture media. This sample was then taken to the laboratory and cultured in nutrient agar environment using four-zone method. It was kept in incubator for 24 h and then taken to the microbiology laboratory. After appearance of bacteria colonies, each colony would be cultured separately in order to get pure bacterial colonies. Type of microorganism identification (bacillus, coccus or yeast) in singel colony was done by microscope after gram staining and for accurate recognition, it was cultured in selectiv medium as follow:
1. Cetrimide agar culture medium for Pseudomonas, that existence of Pseudomonas would cause green mucoid colony. Existence of cetrimide would prevent growth of confounding bacteria.
2. EMB (Eosin Methylene Blue) and TSI (Triple Sugar Iron Agar) culture media for Klebsiella, which would cause red colored colony in EMB medium and in TSI medium would change into Acid/Acid with yellow color.
3. In order to detect Staphylococcus aureus, manitol salt agar private culture medium was used on which turns color of the medium to yellow.
4. EMB culture medium for Acinetobacter that causes red colored colony.
Other materials used in this study were Mueller-Hinton agar & broth, nutrient agar, casein-peptone soymeal-peptone agar (CASO Agar), soybean casein digest agar (SCDA), Salmonella, Shigella, EMB and manitol salt culture medium, which were purchased from Merck Co., Germany.
Minimum inhibitory density of growth of microorganisms was determined by MIC (Minimum Inhibitory Concentration) method. MIC is the minimum density of antibiotic (?g/ml) that can prevent visible growth of microorganisms. In this study, broth micro dilution method (a common method in microbiology laboratories) was used for MIC test. Antibiotics used in this study included cefepime, ceftazidime, amikacin, ciprofloxacin, meropenem, and ceftriaxone. Antibiotics dilution was done by two fold (1/2) method with maximum and minimum density of 64 and 0.5 (?g/ml), respectively. In order to evaluate MIC results, NCCLS (National Committee for Clinical Laboratory Standards) recommendations were used (11).
For statistical analyses, descriptive indices like frequency, percentage, mean, and standard deviation (?SD) were used to express data. Comparisons were done using the chi-square and student t-tests, and linear correlation coefficient and Pearson correlation tests. All statistical analyses were done by statistical software SPSS (Ver. 13.0, Chicago, IL).
One hundred patients (36 females, and 64 males) were enrolled. The mean (?SD) age of patients were 55.6 (?19.9). Mean (?SD) duration of hospitalization was 18.8 (?15.9) days. Sixty four percent of patients showed SIRS, that 28 cases (43.7%) were progressed to sepsis. Prevalence of bacteremia was 38% that 28 patients of them (73.7%) had sepsis. Table 1 shows demographics, APACHE II scores, serum glucose level, and mean arterial pressure of patients with septicemia and those without septicemia.
Among the positive culture results (38 patients), Klebsiella was the most common pathogen recovered (14 patients, 36.8%). Table 2 presents the frequency of detected microorganisms in 38 patients with septicemia.
Antimicrobial resistance status of microorganisms isolated is shown in Table 3. Various densities of these microorganisms were exposed to antibiotics in order to detect the resistance limit of them to common antibiotics. As shown, only Staphylococcus aureus was resistant to all studied antibiotics. Gram-negative bacilli showed resistance to all antibiotics except for amikacin and meropenem.
According to obtained results, prevalence of septicemia was 38%, which is a higher percentage comparing to previous studies. For example, prevalence of bloodstream infections has been reported 18.2% in a Turkish university hospital (12). In another report from 17 ICUs of European countries, septicemia has been reported to be 12% (13). Central venous catheter, hyperglycemia, urinary tract infections (UTI), pneumonia, use of sedative drugs and surgery are among risk factors of bacteremia (12).
Another study which was performed by Brun-Buisson et al. showed that prevalence of SIRS in ICU patients was more than 80% while one-third of them (26.7%) had sepsis (1).
As body systems do not function individually, infection spreads to cause SIRS or sepsis when it defeats defending mechanisms of body. In advanced cases, while SIRS or sepsis occurs, we can detect the origin of infection, consider proper therapy and control infection in ICU based on type of bacteria detected in blood samples.
From the results obtained,it can be deduced that the highest rate of microbial resistance was to ceftriaxone, and the lowest rate to amikacin. Klebsiella, the most prevalent microorganism detected in this study, showed the lowest resistance to amikacin. The selected antibiotic for Acinetobacter microorganism is meropenem as no microbial resistance to meropenem was observed. Studies performed in European and American countries, revealed a resistance rate of 13.6% of Acinetobacter infection to meropenem (14), although one study reported the resistance percentage as 3.5% (15).
In the current study, septic group had higher levels of mean arterial pressure and lower blood glucose in comparison with non septic group. It should be mentioned that sepsis has the criteria to be considered as SIRS, for which a microbial etiology has been proven or suspected. However, severe sepsis is the situation accompanied by one or more signs of organ dysfunction and mean arterial pressure≤70 mmHg that respond to administration to of intravenous fluid (16, 17). Regarding this definition, the blood pressure is not a diagnostic criteria of sepsis but, in fact is one of the criteria of severe sepsis, responded to fluid resuscitation which in turn may lead to blood pressure normalization. This may explain the normal mean arterial pressure of this group, it has been shown that blood glucose decreases with insulin therapy in critically ill patients.It also results in less mortality (18) and morbidity (19). Blood glucose levels less than 8-9 mmol/lit (144-162 mg/dl) (20) or less than 145-150 mg/dl (21, 22) are ideal in these patients. It was shown that blood glucose decreasing with insulin therapy in critically ill patients, results in less mortality (18) and morbidity (19), and blood glucose levels less than 8-9 mmol/l (144-162 mg/dl) (20) or less than 145-150 mg/dl (21, 22) were more favorable.
Vancomycin is the drug of choice for infection caused by methicillin resistant Staphylococcus aureus and Staphylococcus epidermidis (22, 23). In conclusion, the hospitalized patients in ICU of a general university hospital in Iran are at high risk of developing septicemia. High clinical suspicion with appropriate microbiological tests is essential for early diagnosis and proper administration of antimicrobial treatments to reduce mortality rate.
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