Antibiotic Susceptibility and Molecular Detection of Virulent Pseudomonas aeruginosa Isolated from Bovine Mastitis Milk in Egypt

Pseudomonas aeruginosa (P. aeruginosa) is one of the most common causative agents causing mastitis in dairy cattle, which is primarily responsible for the dairy farms' significant economic losses. The purpose of this study was to investigate the prevalence, antimicrobial sensitivity profiling, phenotypic detection of extended-spectrum ß-lactamase (ESBL) producing isolates, molecular identification of major virulence factors (toxA, lasB, and exoS), and biofilm profiles of P. aeruginosa strains isolated from mastitis milk. A total of 200 mastitic milk samples were collected from cows and subjected to bacteriological examination. Suspected colonies were confirmed by PCR targeting the 16S rRNA gene. Positive isolates were genotypically examined to determine the presence of virulence factors (toxA, lasB, and exoS). An antimicrobial susceptibility test was carried out on all positive isolates. The phenotypic detection of ESBL was done using the combination disc test (CDT) and the double disc synergy test (DDST). Finally, biofilm production was accessed through the tube adherent method (TA). Among the total samples, P. aeruginosa was identified in 15% (n = 30) of the retrieved isolates. Virulence genes (toxA, exoS, and lasB) were detected in 100%, 83.3%, and 66.6% of isolates, respectively. Antimicrobial susceptibility testing showed high sensitivity to imipenem, meropenem, ciprofloxacin, colistin, and gentamicin, while all isolates were completely resistant to amoxicillin, penicillin, ceftazidime, ceftriaxone, streptomycin, erythromycin, doxycycline, and spectinomycin. CDT confirmed ESBL production in 15 isolates (50%) and DDST confirmed it in 10 isolates (33.3%). Biofilm formation by the TA method revealed that 33.3% were strong, 33.3% were moderate, 16.6% were weak, and 16.6% were nonadherent isolates. In conclusion, P. aeruginosa strains on dairy farms that harbor virulence genes, produce biofilm, and are resistant to the most popular antimicrobial drug can be hazardous not only to the dairy industry but also for public health.