Isolation and Identification of a Pathogenic Klebsiella pneumoniae Strain from Beef Cattle

Purpose To determine the pathogen causing respiratory diseases and acute death of cattle in a cattle farm.

Method Samples of sick cows nasal fluid were collected and a dominant strain was isolated. The isolated strain was further identified by morphological identification, biochemical identification, 16S rRNA identification, mice inoculation test and drug resistance analysis.

Result The isolated bacteria were gram negative coccobacteria under microscopic examination. Except that arginine double hydrolysis test showed positive, other biochemical characteristics were consistent with Klebsiella pneumoniae. The homology between 16S rRNA sequence and K. pneumoniae strain in GenBank is 99%. Therefore, the isolated bacteria can be identified as K. pneumoniae and named 7Y-1. In the mice inoculation test, eight SPF-KM mice (0.2 mL/mouse) were intraperitoneally injected with 1.01×10⁸ CFU/mL bacterial solution, the mice all (8/8) died within 16-36 h. Section examination of lung, liver, spleen, kidney and other tissues and organs congestion swelling, intestinal gas and fluid, part of intestinal congestion, swelling; histological observation showed lung, liver congestion, spleen congestion hemorrhage and glomerulonephritis changes; the drug sensitivity test results showed that the isolated strains were resistant to carbapenems, imipenem, meropenem, aminoglycoside amikacin and sulfamethoxazole, and were highly sensitive to antibiotics commonly used in veterinary clinic, such as ceftriaxone, cefoxitin, cefazolin, kanamycin, gentamicin and florfenicol.

Conclusion K. pneumoniae was isolated from the infected cattle and was highly lethal to mice, and had special drug resistance, indicating that the bacteria might be the main bacteria or secondary infection bacteria that caused the respiratory infection of the beef cattle, or even death, which should be paid high attention to.