Epidemiology of aminoglycoside resistance in a large animal hospital.

This research article explores the resistance to antibiotics, specifically aminoglycosides, in bacteria found in a large animal hospital over a five-year period. It reveals the existence of a significant resistance to gentamicin, one of the aminoglycosides, in certain types of bacteria found in hospitalised horses and presents data on the susceptibility rates to this and another antibiotic, amikacin.

Methodology

• For this study, the researchers examined the antimicrobial susceptibility of 1244 Gram-negative equine isolates obtained over sixty months (5 years) from July 1985 to June 1990.
• The samples for the cultures came from the first medical and surgical treatment submissions from 693 patients suspected of infections. Medical records of 480 out of the 693 cases were available, and 393 of these received antibiotic treatment. The researchers selected 190 cases for examination and conducted an in-vitro antibiotic susceptibility test of the isolates found.
• They analyzed susceptibility to amikacin and gentamicin for the six most frequently isolated Gram-negative pathogens, making up 80% of all Gram-negative genera cultured during the study period.
• Susceptibility testing was done using the Kirby-Bauer technique, and the researchers recorded results as susceptible, intermediate, or resistant. They, however, excluded intermediate susceptibility results from their study data.

Results

• The results of the study showed that a significant number of bacteria, including E. coli, Klebsiella spp., and Enterobacter spp., were more susceptible to amikacin than gentamicin. However, more Pasteurella spp. were susceptible to gentamicin than amikacin. Gentamicin resistance varied significantly among the five Gram-negative genera, with only Pasteurella spp. showing consistent susceptibility.
• Of the microbes isolated during the study, E. coli was the most prevalent, followed by Enterobacter spp., Pseudomonas spp., Klebsiella spp., Pasteurella spp., and Proteus spp.
• The researchers noted a steady increase in resistance of E. coli and Klebsiella spp. to amikacin and a decrease in gentamicin resistance among Pasteurella spp. over the course of study.

Discussion

• The discovery of significant resistance to gentamicin has important clinical implications, essentially suggesting that the use of gentamicin could increase the number of infections caused by resistant strains.
• The main factors leading to aminoglycoside resistance include limited in vivo penetration and the action of enzymes contributed by a plasmid or occasionally by the bacterial chromosome.
• Though resistance to amikacin was relatively low compared to gentamicin, there was a noted increase over the study period. This indicates that while amikacin might be preferred for treating Gram-negative infections, close monitoring of its usage is essential to mitigate rising resistance.