- Email: [email protected]
Antibiotic susceptibility patterns from Irish equines
Viewpoint Antibiotic Susceptibility Patterns From Irish Equines A longitudinal, retrospective investigation was carried out of antimicrobial resistance in bacterial isolates (n = 1060) from horses in Ireland over the period 1990 through 2000. Bacterial isolates that were collected from clinical cases of equine infection from throughout Ireland in 1990 (n = 394), 1996 (n = 323), and 2000 (n = 343), were recultured from archived isolates. Standard antibiotic disk susceptibility tests were performed against the following antibiotics (disk concentration): penicillin, ampicillin, amoxicillin, amoxicillin/clavulanic acid, gentamicin, sulfamethoxazole/trimethoprim, erythromycin, and ceftiofur. In all cases, plates were incubated at 35°C for 18 hours before results were read. Antibiotic resistance rates are shown in the Table (opposite page). Using r2 test for trend, statistically significant rising trends (P < .05) were identified in the resistance of (1) Escherichia coli and gentamicin, (2) hemolytic streptococci and penicillin, (3) hemolytic streptococci and penicillin, (4) hemolytic streptococci, (5) hemolytic streptococci and ampicillin, and (6) hemolytic streptococci and erythromycin. No significant trends were apparent for any of the other organism/drug interactions examined. To date, there has been relatively limited data in the literature regarding antibiotic resistance patterns in horses, and the current study is the first formal report of resistance patterns in horses from Ireland. Ensink et al1 suggested that quantitative antibiotic susceptibility testing of bacterial pathogens in equine infection may serve as a useful means to optimize antibiotic management in the patient. National monitoring of antibiotic resistance patterns in horses is important for several reasons, including (1) optimum employment of licensed anti-infectives for therapeutic purposes, (2) development of a longterm anti-infective strategy between equine veterinarians and the pharmaceutical industry, and (3) examining the potential interaction with human clinical medicine.
136
Currently there has been growing concern over antimicrobial resistance in pathogenic bacterial populations in both human and clinical medicine and a recent report has demonstrated the nosocomial transmission of methicillin-resistant Staphylococcus aureus from humans to horses in a surgical unit in a veterinary teaching hospital.2 The emphasis of antimicrobial resistance in equines differs from other large animals, in that antimicrobials are not used as growth promoters nor is the zoonotic link with humans as strong, given that consumption of horse meat in the British Isles is not common. In conclusion, the main findings of this study were rising trends in resistance by the majority of the isolates tested. Significant differences in resistance levels were found in at least one antimicrobial in each organism isolated. Prospective investigations are needed to identify selection pressures on the development of antimicrobial resistance in bacterial isolates from horses, so that control measures can be put in place to minimize future increases in resistance. Regular surveillance should therefore be encouraged to monitor resistance patterns in healthy, as well as sick, equines. Nicola Fletcher,a,b Thomas Buckley,a and John E. Moorec aIrish Equine Centre, Johnstown, NAAS, Co. Kildare, Ireland, bDepartment of Equine Studies, University of Limerick, Co. Limerick, Ireland, cNorthern Ireland Public Health Laboratory, Department of Bacteriology, Belfast City Hospital, Belfast BT9 7AD, Northern Ireland. 0737-0806/$ - see front matter © 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.jevs.2004.03.007
REFERENCES 1. 2.
Ensink JM, van Klingeren B, Houwers DJ, Klein WR, Vulto AG. Invitro susceptibility to antimicrobial drugs of bacterial isolates from horses in The Netherlands. Equine Vet J 1993;25:309-13. Seguin JC, Walker RD, Caron JP, Kloos WE, George CG, Hollis RJ, et al. Methicillin-resistant Staphylococcus aureus outbreak in a veterinary teaching hospital: potential human-to-animal transmission. J Clin Microbiol 1999;37:1459-63.
Journal of Equine Veterinary Science
April 2004
Volume 24, Number 4
137
Hemolytic streptococci Hemolytic streptococci Escherichia coli Staphylococcus aureus Proteus sp. Pseudomonas aeruginosa
Organism
(c) 2000
Hemolytic streptococci Hemolytic streptococci Escherichia coli Staphylococcus aureus Proteus sp. Pseudomonas aeruginosa Salmonella spp. Klebsiella pneumoniae Rhodococcus equi
Organism
(b) 1996
Hemolytic streptococci Hemolytic streptococci Escherichia coli Staphylococcus aureus Proteus sp. Pseudomonas aeruginosa Salmonella spp.
14 8 98 63 89 100 100
Penicillin
16 5 97 62 83 100 100 100 0
10 2 57 47 67 100 71 100 50
0 5 59 28 78 100 86
Amoxycillin
10 2 12 8 0 67 0 0 0
87 100 26 26 67 0 14 0 0
Amoxycillin/ Clavulanic acid Gentamicin
90 97 66 63 83 100 43
79 29 173 41 16 5
37 17 94 73 94 100
28 10 65 63 94 100
42 41 32 29 56 80
87 97 47 39 25 0
62 28 59 54 88 100
24 10 86 33 100 100 100
Sulfamethoxazole/ Trimethoprim Erythromycin
63 49 58 40 83 67 71 0 0
90 97 62 52 83 100 43 100 100
87 93 65 66 75 100
71 62 65 56 56 80
37 12 92 39 100 100 100 100 0
61 69 47 46 50 0
46 21 73 54 67 80
Enrofloxacin Erythromycin
42 65 80 48 83 100 100 100 100
SulfamethOxytetraoxazole/ cycline Trimethoprim Ceftiofur Erythromycin
Percentage (%) isolates resistant
13 2 56 47 67 100 86 100 0
Amoxycillin
74 92 8 17 11 0 14
Gentamicin
Percentage (%) isolates resistant
0 3 65 32 78 100 71
Ampicillin
Total No. Amoxycillin/ Sulfamethisolates Clavulanic Oxytetraoxazole/ examined Penicillin Ampicillin acid Gentamicin cycline Trimethoprim Ceftiofur
62 65 90 87 6 3 7 1 2
Total no. isolates examined Penicillin Ampicillin
42 88 93 141 18 5 7
Total No. isolates examined
Percentage (%) isolates resistant
In vitro antibiotic susceptibility of equine bacterial isolates to a range of antimicrobials
Organism
(a) 1990
Table
136
Currently there has been growing concern over antimicrobial resistance in pathogenic bacterial populations in both human and clinical medicine and a recent report has demonstrated the nosocomial transmission of methicillin-resistant Staphylococcus aureus from humans to horses in a surgical unit in a veterinary teaching hospital.2 The emphasis of antimicrobial resistance in equines differs from other large animals, in that antimicrobials are not used as growth promoters nor is the zoonotic link with humans as strong, given that consumption of horse meat in the British Isles is not common. In conclusion, the main findings of this study were rising trends in resistance by the majority of the isolates tested. Significant differences in resistance levels were found in at least one antimicrobial in each organism isolated. Prospective investigations are needed to identify selection pressures on the development of antimicrobial resistance in bacterial isolates from horses, so that control measures can be put in place to minimize future increases in resistance. Regular surveillance should therefore be encouraged to monitor resistance patterns in healthy, as well as sick, equines. Nicola Fletcher,a,b Thomas Buckley,a and John E. Moorec aIrish Equine Centre, Johnstown, NAAS, Co. Kildare, Ireland, bDepartment of Equine Studies, University of Limerick, Co. Limerick, Ireland, cNorthern Ireland Public Health Laboratory, Department of Bacteriology, Belfast City Hospital, Belfast BT9 7AD, Northern Ireland. 0737-0806/$ - see front matter © 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.jevs.2004.03.007
REFERENCES 1. 2.
Ensink JM, van Klingeren B, Houwers DJ, Klein WR, Vulto AG. Invitro susceptibility to antimicrobial drugs of bacterial isolates from horses in The Netherlands. Equine Vet J 1993;25:309-13. Seguin JC, Walker RD, Caron JP, Kloos WE, George CG, Hollis RJ, et al. Methicillin-resistant Staphylococcus aureus outbreak in a veterinary teaching hospital: potential human-to-animal transmission. J Clin Microbiol 1999;37:1459-63.
Journal of Equine Veterinary Science
April 2004
Volume 24, Number 4
137
Hemolytic streptococci Hemolytic streptococci Escherichia coli Staphylococcus aureus Proteus sp. Pseudomonas aeruginosa
Organism
(c) 2000
Hemolytic streptococci Hemolytic streptococci Escherichia coli Staphylococcus aureus Proteus sp. Pseudomonas aeruginosa Salmonella spp. Klebsiella pneumoniae Rhodococcus equi
Organism
(b) 1996
Hemolytic streptococci Hemolytic streptococci Escherichia coli Staphylococcus aureus Proteus sp. Pseudomonas aeruginosa Salmonella spp.
14 8 98 63 89 100 100
Penicillin
16 5 97 62 83 100 100 100 0
10 2 57 47 67 100 71 100 50
0 5 59 28 78 100 86
Amoxycillin
10 2 12 8 0 67 0 0 0
87 100 26 26 67 0 14 0 0
Amoxycillin/ Clavulanic acid Gentamicin
90 97 66 63 83 100 43
79 29 173 41 16 5
37 17 94 73 94 100
28 10 65 63 94 100
42 41 32 29 56 80
87 97 47 39 25 0
62 28 59 54 88 100
24 10 86 33 100 100 100
Sulfamethoxazole/ Trimethoprim Erythromycin
63 49 58 40 83 67 71 0 0
90 97 62 52 83 100 43 100 100
87 93 65 66 75 100
71 62 65 56 56 80
37 12 92 39 100 100 100 100 0
61 69 47 46 50 0
46 21 73 54 67 80
Enrofloxacin Erythromycin
42 65 80 48 83 100 100 100 100
SulfamethOxytetraoxazole/ cycline Trimethoprim Ceftiofur Erythromycin
Percentage (%) isolates resistant
13 2 56 47 67 100 86 100 0
Amoxycillin
74 92 8 17 11 0 14
Gentamicin
Percentage (%) isolates resistant
0 3 65 32 78 100 71
Ampicillin
Total No. Amoxycillin/ Sulfamethisolates Clavulanic Oxytetraoxazole/ examined Penicillin Ampicillin acid Gentamicin cycline Trimethoprim Ceftiofur
62 65 90 87 6 3 7 1 2
Total no. isolates examined Penicillin Ampicillin
42 88 93 141 18 5 7
Total No. isolates examined
Percentage (%) isolates resistant
In vitro antibiotic susceptibility of equine bacterial isolates to a range of antimicrobials
Organism
(a) 1990
Table