Feline upper respiratory tract disease (URTD) includes a wide range of clinical signs and is not a specific disease. It is defined as a syndrome with clinical signs, such as nasal and ocular exudates, sneezing, conjunctivitis, cough, fever, lack of energy, and loss of appetite. The causes of feline URTD are divided into infectious and non-infectious causes. First, as for infectious causes, viruses such as feline herpesvirus (FHV) and feline calicivirus (FCV); primary bacteria such as Bordetella bronchiseptica (B. bronchiseptica), Chlamydia felis (C. felis), and Mycoplasma felis (M. felis); and secondary bacteria such as Pasteurella multocida (P. multocida) are suggested as major pathogens (Holst et al, 2010; Sykes, 2014; Litster et al, 2015). M. felis may be part of the normal bacterial flora in the feline upper respiratory tract but is mainly found in cats with respiratory signs or healthy cats living with infected cats. Recently, it has been considered a major pathogen in feline URTD (Holst et al, 2010; Hong et al, 2015; Lobova et al, 2019). However, a vaccine against M. felis infection has not yet been developed. Therefore, cats infected with M. felis are managed with adjuvant therapy to improve immunity along with long-term antibiotic administration (Lappin et al, 2017). P. multocida is a gram-negative bacterium classified into five serogroups (A, B, D, E, and F) based on capsule composition and somatic serotype (Kuhnert and Christensen, 2008