[The vicissitude of pathogenic bacteria isolated from critically ill patients in an intensive care unit during a period of using antibiotics].

OBJECTIVE: To observe the changing spectrum of the pathogenic bacteria during seven-day antibiotics targeted therapy in an intensive care unit (ICU).

METHODS: In a group of 100 patients of hospital-acquired pneumonia (HAP) with identified pathogenic bacteria undergoing antibiotic treatment according to susceptibility test, the changes in the species of the pathogens and their ratio in their sputum specimens were studied, and the relationship were analyzed the characteristic between the changes and the age, the time of medication and the length of stay.

RESULTS: Among all the bacterial isolates (n=295) in ICU, the percentage of Gram-negative bacillus was 62.4% (184/295). The prevalent causative microorganisms isolated were Pseudomonas aeruginosa 22.4% (66/295), MRSA/MRSE 20.7% (61/295) and Acinetobacter spp. 10.5% (31/295). When one or more than one potent antibiotic in accord with the result of sensitivity test, change in ratio of pathogens occurred in 160, and change in species in 126. When the use of antibiotics was prolonged, the change in the former became less often. The change in ratio was less in 3-5 days than that of 6-7 days, the ratio was 72.7%, 62.5%, 60.0% (P<0.01) respectively on the 3rd day, the 4th day and the 5th day, showing that susceptible pathogenic bacteria became less gradually, indicating that the treatment was effective . However, the change in species of pathogenic bacteria began more obvious, and it was more predominant on the 6th day and the 7th day, which was 66.0%, 77.1% (P<0.01) respectively, showing emergence of new non-susceptible pathogenic bacteria. With increase in the use of different antibiotics, the species of pathogenic bacteria showed to increase an increasing tendency of change. When Gram-negative bacillus infection was treated, antibiotic resistant bacteria such as Candida albicans and MRSA usually appeared. But when Gram-positive bacillus infections were treated, Candida albicans, Pseudomonas aeruginosa and Enterobacter cloacae readily appeared. There was relationship between the change in pathogenic bacteria and age, and the length of stay of the patients. The more older in age and the longer the length of stay, the change in pathogenic bacteria was more predominant.

CONCLUSION: New antibiotic resistant pathogenic bacteria appears after seven-day antibiotic-targeted therapy in ICU. The change of species of pathogenic bacteria is related to the duration and type of using antibiotic, and also the age and length of stay. The longer time of use and the more different types of antibiotic used, the older in age and the longer in length of stay, the change in species of pathogenic bacteria is more predominant. Monitoring the dynamic change of pathogenic bacteria, adjusting the antibiotic promptly and rational use of antibiotics are very important to decrease the change in species and antibiotic resistance of the bacteria.