Case 1 A-79-yr-old man was admitted to hospital due to weakness of both upper limbs. He had history of alzheimer disease, hypertension and type 2 diabetes for many years. One day after admission, the patient´s body temperature rose to 38.5℃, white bloodcell (WBC) count, 11.8×109/L (3.5-9.5×109/L, 77.97% segmented neutrophils); C-reactive protein (CRP) level was 9.06mg/L (0-4mg/L) and chest CT showed fibrosis of the upper right lung with pleural adhesions. These suggested that he might have lung infection. The patient had many diseases with a long medical history. His immunity was low, so the treatment measures were mainly based on symptomatic treatment, while empiric antimicrobial treatment was used. Continuous of empiric antimicrobial treatment with ceftriaxone, meropenem and moxifloxacin. Pseudomonas aeruginosa was isolated from the sputum cultures, antibiotics were changed to tigecycline, imipenem and cilastatin combined with fluconazole. However, the patient´s fever persisted and the infection had not resolved. He was transferred to intensive care unit (ICU) due to respiratory failure. Deep venous catheters and tracheotomy were used to meet treatment needs. But chest CT showed his lung infection got worse and CRP level was 43.76mg/L (0-4mg/L). Two samples of blood cultures were positive for bacterial growth, and L lactis was identified using the VITEK 2 (bioMérieux, Marcy I´Etoile, France) system. Imipenem and cilastatin combined with linezolid were used according to blood culture results. After a period of treatment, the patient´s infection symptoms were controlled.
Case 2 A-88-yr-old man, with a previous diagnosis of hypertension and lung cancer. This time he was admitted to hospital in ICU for coma after trauma. Brain CT showed bleeding skulls which was the direct cause of his coma. Taking into account the patient´s condition, hemostasis and other symptomatic treatment measures were used after admission. Pseudomonas aeruginosa was isolated in the sputum cultures. According to the results of drug sensitivity test, cefepime, imipenem and cilastatin combined with teicoplanin were used to treat infection until cultures from sputum had no isolates. Since the patient had been in a coma, multiple organ failures started after one month in hospital, tracheotomy and deep venous catheters were used to meet treatment needs. The day after the surgery of venous catheterization, the patient presented a serious infection. His body temperature rose to 39℃, WBC count, 19.2×109/L (89.06% segmented neutrophils); CRP level was 63mg/L (0-4mg/L); procalcitonin level was 1.28ng/ml (<0.5ng/ml). Blood cultures yielded Leuconostoc spp. The pathogen was gram-positive cocci and was identified as L lactis. Due to L lactis resistant to vancomycin, piperacillin was used instead of teicoplanin. Then, three blood cultures were taken at different times and all yielded L lactis. Bacteremia caused by L lactis existed persistently. The patient died finally three months after confirmation of L lactis infection.
Two additional sets of blood cultures were collected to obtain microbiological diagnosis of the two patients, repectively. Bacterium growing in all cultures were catalase-negative, alpha-hemolytic gram-positive cocci. The colonies were white, small and raised on blood agar (Figure 1). The bacteria was identified as
Leuconostoc spp. by VITEK 2 system. The VITEK MS system (bioMérieux, Marcy I´Etoile, France) was used to identified this clinical bacterial isolate as L lactis quickly and reliably. To obtain more reliable phenotypic data and species identification, the 16S rRNA genes of the isolates of these two patient´s blood were sequenced. All sequences were analyzed by BLAST (basic local alignment search tool) and ribosomal database project. The sequence showed 99% similarity to that of L lactis. Antimicrobial susceptibility tests were detected by diffusion disk method. The microorganism was susceptible to levofloxacin, penicillin, piperacillin-tazobactam, cefoperazone-sulbactam, clindamycin, erythromycin, cefepime and imipenem, but resistant to compound trimethoprim, cefoxitin vancomycin and teicoplanin.