Table 3.
Distribution and prevalence of Enterobacteriaceae (n = 27), Staphylococcus aureus (n = 23), Streptococcus spp. (n = 30), non-aureus staphylococci (n = 66), Bacillus spp. (n = 27) Other (n = 21), and their antimicrobial resistance to one (R = 1), two (R = 2) and greater than two antimicrobial classes (R > 2).
| Bacterial group | Isolates (n) | Percentages |
R = 1 AM§ [n (%)] |
R = 2 AM [n (%)] |
R = >2 AM [n (%)] |
|---|---|---|---|---|---|
| Enterobacteriaceae | 27 | 100 | 14 (51) | 3 (11) | 13 (48) |
| Escherichia coli | 11 | 40 | 7 (64) | 2 (18) | 2 (18) |
| Enterobacter cloacae | 7 | 25 | 4 (57) | 0 (0) | 3 (43) |
| Serratia marcescens | 5 | 18 | 0 (0) | 0 (0) | 5 (100) |
| Enterobacter asburiae | 1 | 3 | 0 (0) | 0 (0) | 1 (100) |
| Citrobacter species | 2 | 7 | 2 (100) | 0 (0) | 0 (0) |
| Pantoea eucrina | 1 | 3 | 1 (100) | 0 (0) | 0 (0) |
| Staphylococcus aureus | 23 | 100 | 6 (26) | 0 (0) | 0 (0) |
| Streptococcus spp. | 30 | 100 | 14 (47) | 7 (23) | 0 (0) |
| Streptococcus uberis | 18 | 60 | 7 (39) | 6 (33) | 0 (0) |
| Streptococcus agalactiae | 7 | 23 | 7 (100) | 0 (0) | 0 (0) |
| Streptococcus dysgalactiae | 1 | 3 | 0 (0) | 0 (0) | 0 (0) |
| Streptococcus species | 4 | 13 | 0 (0) | 1 (25) | 0 (0) |
| Non-aureus staphylococci | 66 | 100 | 10 (15) | 1 (2) | 0 (0) |
| Staphylococcus chromogenes | 40 | 61 | 7 (18) | 1 (3) | 0 (0) |
| Staphylococcus haemolyticus | 16 | 24 | 3 (19) | 0 (0) | 0 (0) |
| Staphylococcus warneri | 2 | 3 | 0 (0) | 0 (0) | 0 (0) |
| Staphylococcus sciuri | 2 | 3 | 0 (0) | 0 (0) | 0 (0) |
| Staphylococcus simulans | 2 | 3 | 0 (0) | 0 (0) | 0 (0) |
| Staphylococcus equorum | 1 | 2 | 0 (0) | 0 (0) | 0 (0) |
| Staphylococcus hominis | 1 | 2 | 0 (0) | 0 (0) | 0 (0) |
| Staphylococcus hyicus | 1 | 2 | 0 (0) | 0 (0) | 0 (0) |
| Staphylococcus xylosus | 1 | 2 | 0 (0) | 0 (0) | 0 (0) |
| Bacillus spp. | 27 | 100 | 10 (37) | 1 (4) | 1 (4) |
| Bacillus megaterium | 10 | 20 | 8 (80) | 0 (0) | 0 (0) |
| Bacillus pumilus | 6 | 12 | 0 (0) | 0 (0) | 0 (0) |
| Bacillus cereus | 2 | 4 | 0 (0) | 1 (50) | 1 (50) |
| Bacillus licheniformis | 1 | 2 | 1 (100) | 0 (0) | 0 (0) |
| Bacillus subtilis | 1 | 2 | 0 (0) | 0 (0) | 0 (0) |
| Bacillus species | 7 | 14 | 1 (14) | 0 (0) | 2 (29) |
| Others | 21 | 100 | 13 (62) | 1 (5) | 9 (43) |
| Acinetobacter venetianus | 2 | 4 | 0 (0) | 0 (0) | 2 (100) |
| Aerococcus species | 1 | 2 | 1 (100) | 0 (0) | 0 (0) |
| Aerococcus viridans | 5 | 10 | 1 (20) | 0 (0) | 0 (0) |
| Enterococcus faecium | 3 | 6 | 0 (0) | 1 (33) | 2 (67) |
| Exiguobacterium sp[3] | 1 | 2 | 0 (0) | 0 (0) | 0 (0) |
| Lactococcus garvieae | 1 | 2 | 0 (0) | 0 (0) | 1 (100) |
| Pasteurella multocida | 2 | 4 | 0 (0) | 0 (0) | 0 (0) |
| Pseudomonas aeruginosa | 1 | 2 | 0 (0) | 0 (0) | 1 (100) |
| Pseudomonas species | 1 | 2 | 0 (0) | 0 (0) | 1 (100) |
| Pseudomonas stutzeri | 1 | 2 | 0 (0) | 0 (0) | 1 (100) |
| Rothia terrae | 3 | 6 | 1 (33) | 0 (0) | 0 (0) |
| Total | 194 | 100 | 57 (29) | 12 (6) | 22 (11) |
Bacterial species were cultured from milk samples collected from 151 clinical mastitis quarters and 268 apparently healthy control quarters from 18 dairy herds located in Northern Queensland, Southeast Queensland, and Victoria between March and June 2019.
§
Antimicrobial; Corynebacterium auriscanis, C. bovis, C. falsenii, C. xerosis, and Corynebacterium species were excluded from this analysis (11 isolates in total).