Distribution of CRISPR in Escherichia coli Isolated from Bulk Tank Milk and Its Potential Relationship with Virulence

Staphylococcus aureus, Escherichia coli, and Klebsiella spp. prevalence in bulk tank milk of Colombian herds and associated milking practices

Background and Aim

Bovine mastitis is one of the most costly and prevalent diseases in dairy herds, which can be prevented and controlled through proper milking practices, diagnosis, and elimination of chronic animals, among others. Contagious pathogens such as Staphylococcus aureus and environmental pathogens such as Escherichia coli and Klebsiella spp. can affect cows and milk for human consumption, generating a public health risk. This study aimed to estimate the prevalence of herds with somatic cell count (SCC) ≥200,000 cells/mL, S. aureus, E. coli, and Klebsiella spp., in bulk tank milk (BTM) and its associated risk factors in Colombian dairy cow herds.

Materials and Methods

A cross-sectional probabilistic study was carried out in 150 dairy herds located in the north of the Antioquia province. A single visit per herd was conducted, during which three BTM samples were aseptically collected. General data and milking practices were collected through an epidemiological survey applied in each herd.

Results

The prevalence of S. aureus, E. coli, and Klebsiella spp. were 14% (21/150), 2% (3/150), and 8% (12/150), respectively. Moreover, 95% of the herds presented an SCC of ≥200,000 cells/mL. Practices such as in-paddock milking, change of milker during the last month, use of disposable gloves, and hand disinfection were associated with increased prevalence of S. aureus, whereas proper dipping was a protective factor. Proper washing and disinfection of the milking machine, use of chlorinated disinfectants for hand hygiene, and use of disposable gloves decreased the prevalence of E. coli and Klebsiella spp. Bulk tank SCC increased in herds with 30-60 milking cows, herds with >60 milking cows, and herds with a change of milker during the last month. Hand disinfection and dipping decreased the SCC.

Conclusion

Staphylococcus aureus, E. coli, and Klebsiella spp. were prevalent in BTM from dairy cow herds. The risk of S. aureus isolation was higher in herds with an in-paddock milking system. The risk of E. coli and Klebsiella spp. isolation were higher in herds with >60 milking cows, with a change of milker during the last month. Processes such as avoiding changing the milker and greater control in medium and large herds could improve the SCC in BTM.

Genetic characterization of third- or fourth-generation cephalosporin-resistant avian pathogenic Escherichia coli isolated from broilers

The third- or fourth-generation cephalosporins (3GC or 4 GC) are classified as "critically important antimicrobials for human medicine" by WHO, but resistance to these drugs is increasing rapidly in avian pathogenic E. coli (APEC). This study investigated the distribution and genetic characteristics of 3GC- or 4 GC-resistant APEC isolates from five major integrated broiler operations in Korea. The prevalence of 3GC- or 4GC-resistant APEC isolates in 1-week-old broilers was the highest in farms of operation C (53.3%); however, the highest prevalence of these isolates in 4-week-old broilers was the highest on the farms of operation A (60.0%), followed by operations E (50.0%) and C (35.7%). All 49 3GC- or 4GC-resistant APEC isolates had at least one β-lactamase-encoding gene. The most common β-lactamase-encoding genes was extended-spectrum β-lactamase gene, bla _CTX-M-15, detected in 24 isolates (49.0%), followed by bla _TEM-1 (32.7%). Sixteen isolates (32.7%) harbored class 1 integrons, and four isolates (8.2%) showed different gene cassette-arrangements. However, only 1 of 26 isolates harboring class 2 integrons carried a gene cassette. Furthermore, both CRISPR 1 and 2 arrays were detected in most isolates (36 isolates; 73.5%), followed by CRISPR 2 (18.4%) and CRISPR 1 (4.1%). Interestingly, CRISPR 2 was significantly more prevalent in multidrug resistant (MDR)-APEC isolates than in non-MDR APEC isolates, whereas CRISPR 3 and 4 were significantly more prevalent in non-MDR APEC isolates (each 11.1%; p < 0.05). None of the protospacers of CRISPR arrays were directly associated with antimicrobial resistance. Our findings indicate that the distribution and characteristics of 3GC or 4GC-resistant APEC isolates differed among the integrated broiler operations; moreover, improved management protocols are needed to control the horizontal transmission of 3GC or 4GC-resistant APEC isolates.