Prevalence, Molecular Identification and Antimicrobial Resistance Profiles of Klebsiella pneumoniae Isolated from Mastitic Cattle and Buffaloes, Menofia Governorate, Egypt

Background: Bovine mastitis remains a primary global challenge for the dairy sector, representing one of the most economically taxing diseases. Bacterial-induced intramammary infections, in particular, result in significant financial deficits driven by diminished milk yields, compromised milk quality, escalating healthcare expenditures, and the involuntary culling of livestock. This study investigated the prevalence, molecular characteristics, and antimicrobial resistance of K. pneumoniae. Methodology: The study included 400 milk samples (250 clinical; 150 subclinical) from mastitic cows and buffaloes. Isolates were identified using bacteriological and molecular methods, followed by comprehensive susceptibility testing using Kirby Bauer disc diffusion method per CLSI guidelines to establish resistance profiles. Results: K. pneumoniae was isolated from 8.75% (35/400) of the total samples. Isolation rates for clinical mastitis were 6.5% (13/200) in cattle and 6% (3/50) in buffaloes, while subclinical mastitis showed higher prevalence at 11.5% (15/130) and 20% (4/20), respectively. Antimicrobial susceptibility testing of 35 K. pneumoniae isolates showed 100% sensitivity Carbapenems (Imipenem/Meropenem), third-generation Cephalosporins (Ceftiofur/Cefotaxime), Aminoglycosides (Kanamycin/Gentamicin), and Marbofloxacin. Conversely, high resistance rates were identified in older-generation drugs, including Nalidixic acid (100%), Norfloxacin (88.5%), Amoxicillin (74.3%). Moreover, Erythromycin encountered total resistance (100%) and Tetracycline showed moderate efficacy (60%). The most frequent resistance profile was E, NA, AMX, NX (Erythromycin, Nalidixic Acid, Amoxicillin, Norfloxacin), which was observed in 25.7% (9/35) of the isolates. This was closely followed by the profile E, NA, AMX, NX, found in 22.8% (8/35) of the samples. All isolates (100%) surpassed the MAR index threshold of 0.2, which statistically indicates a "high-risk" source of contamination where antibiotics are frequently used or misused. PCR amplification targeting the gyrA gene successfully confirmed the molecular identity of all 35 K. pneumoniae isolates. Conclusion: The presence of K. pneumoniae in dairy herds highlights a significant epidemiological threat and a rise in drug-resistant strains. To combat this, it is vital to implement strict surveillance, promote the responsible use of antimicrobials, and develop proactive prevention strategies to protect herd health.