| ObjectiveTo study the therapeutic effect of ceftazidime(CAZ) on pneumonia in rats caused by Klebsiella pneumoniae producing CTX-M-14 extended-spectrumβ-lactamase(ESBL) which is susceptible to ceftazidime in vitro.MethodsIsolates producing CTX-M-type ESBL were selected from 97 strains of Klebsiella pneumoniae and genotypes of CTX-M-type ESBL were ascertained.There are 30 K. pneumoniae isolates which produce CTX-M-type ESBLs and 15 of the isolates produce CTX-M- 14-type ESBLs.48 Sprague-Dawley(SD) rats which had a specific pathogen-free sanitary status were divided into four groups randomly which were ceftazidime-treated group, piperacillin/tazobactam-treated group,ceftaxime-treated group and the control group. All rats were intranasally inculated with 0.2mL of bacterial suspension of 6×10~8CFU/ml Klebsiella pneumoniae producing CTX-M-14 ESBL and sterile water to produce pneumonia models.Twenty four hours after inculation,one rat was sampled randomly from each group. They were sacrificed humanely and apex lobes of right lungs were obtained and fixed with 10%buffer formalin,dehydrated and embedded in paraffin.Sections were cut and stained with haematoxylin and eosin using a standard staining procedure,then examined under a light microscope.Other rats were intramuscularly administered ceftazidime, piperacillin/tazobactam,ceftaxime,saline,respectively.The temperature,leucocyte count,percentage of neutrophils were detected at three timepoints.(1)before inoculation; (2) 24h after inoculation(prior to treatment);(3) at the end of the 72h treatment.The surviving rats were killed humanely four hours after the last dose.Following death,the lungs were separated.The left lungs were homogenized in lmL of sterile saline,after which viable counts were determined by plating 10μl aliquots of ten-fold dilutions on sheep blood agar plates and incubating for 24h at 37℃.CFU(colony-forming units) in each lung = viable bacterial counts X number of dilution multiple X 100.The apex lobes of right lungs were fixed with 10%buffered formalin,dehydrated and embedded in paraffin.Sections were cut and stained with H&E as described above and examined under a light microscope.ResultsLungs from untreated animals showed acute pneumonia.There are many inflammatory cells in alveolar spaces with hemorrhage.The rat model of pneumonia was made successfully.There was no occurrence of death in the ceftazidime-treated and piperacillin/tazobactam-treated groups during the observation period.One rat in the ceftaxime-treated group died 46h after the bacterial inoculation,and two rats died in the control group 28h and 35h after inoculation,respectively.The leucocyte count,percentage of neutrophil count and common logarithm of the bacterial count in the right lungs of ceftazidime-treated group were(15.43±0.58) ×109/L,(17.32±0.56)%and(4.51±0.29),respectively after the treatment which lasted seventy two hours.The leucocyte counts of piperacillin/tazobactam-treated group, ceftaxime-treated group and the control group were(16.38±0.41)×10~9/L, (16.15±0.40)×10~9/L,(15.08±0.46)×10~9/L,respectively;percentage of neutrophil counts of the above three groups were(18.10±0.60)%,(17.89±0.35)%,(16.99±0.25)%, respectively;common logarithm of the bacterial count in the left lungs of the three groups were(4.72±0.21),(5.79±0.25),(5.65±0.27),respectively.Compared with the ceftaxime-treated group and the control group,the leucocyte counts,percentage of neutrophil counts and common logarithm of the bacterial counts in the left lungs of the ceftazidime-treated group and piperacillin/tazobactam-treated group were significantly lower than those of ceftaxime-treated group and the control group(P＜0.05).There was no difference in the parameters above between the ceftazidime-treated group and piperacillin/tazobactam-treated group(P＞0.05).The level of inflammation was lower in lungs of the ceftazidime-treated and piperacillin/tazobactam-treated groups after their 72h treatment.In contrast,pneumonia was seen clearly in the lungs of the ceftaxime-treated group after the 72h treatment as well as in tthose of the control group after given saline for 72h.ConclusionCTX-M-14 was the mainly epidemic genotypes of the C.TX-M-type ESBL in Hefei. Intranasally inculating bacteria is a suitable method for making models of pneumonia in rats.Ceftazidime showed good therapeutic effect on pneumonia in rats caused by Klebsiella pneumoniae producing CTX-M-14 ESBL which was susceptible to ceftazidime in vitro.
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