Antimicrobial Drug Usage Research Articles

Antimicrobial resistance in commensal Escherichia coli in veal calves is associated with antimicrobial drug use.

The aim of this study was to determine the association between farm management factors, including antimicrobial drug usage, and resistance in commensal Escherichia coli isolates from the faeces of white veal calves. Ninety E. coli isolates from one pooled sample per farm (n = 48) were tested for their phenotypical resistance against amoxicillin, tetracycline, cefotaxime, ciprofloxacin and trimethoprim/sulfamethoxazole (TMP/SMX). Logistic regression analysis revealed the following risk factors (P < 0·05); farmer wearing the same work clothes for several days [ciprofloxacin, odds ratio (OR) 2·6; tetracycline, OR 2·4], administration of trimethoprim-sulfonamide combinations (TMP/SMX, OR 3·0; amoxicillin, OR 3·1; tetracycline, OR 2·6), ⩾0·3 animal daily dosage per production cycle (ADD/pc), quinolones (ciprofloxacin, OR 2·8), ⩾1·3 ADD/pc, penicillins (ciprofloxacin, OR 3·3; tetracycline, OR 3·4), 20-40 ADD/pc, tetracyclines (tetracycline, OR 3·2) and >40 ADD/pc, tetracyclines (tetracycline, OR 13·1; amoxicillin, OR 6·5). In this study antimicrobial resistance in commensal E. coli was mainly associated with antimicrobial drug use.

Genome Sequences of Mannheimia haemolytica Serotype A1 Strains D153 and D193 from Bovine Pneumonia

Here we report two genome sequences, one complete and one draft, from virulent bovine strains of Mannheimia haemolytica serotype A1 recovered prior to the field usage of modern antimicrobial drugs.

Application value of procalcitonin and immune inflammatory factors for prediction of bacteraemia in patients with hematologic malignancy combined with febrile neutropenia

This study was purposed to evaluate the diagnostic value of procalcitonin (PCT), C-reactive protein, interleukin-6 (IL-6), serum amyloid A (SAA) for bacteremia in patients with hematologic malignancy combined with febrile neutropenia. The total of 297 patients with hematologic malignancy combined with febrile neutropenia were analyzed retrospectively from 1253 patients admitted to West China hospital of Sichuan University from March 2011 to October 2012. They were divided into sepsis group (n = 95) and non-sepsis group (n = 202) according to blood culture. The results showed that the levels of PCT, CRP, IL-6 and SAA in sepsis group were higher than those in non-sepsis group, and there was statistically significant difference between these two groups (P < 0.05). The PCT had an AUC value of 0.974 (P < 0.05), and obviously higher than that of CRP (AUC = 0.681, P < 0.05), IL-6 (AUC = 0.661, P < 0.05) and SAA (AUC = 0.605, P < 0.05). When PCT had cut-off value of 1.06 ng/ml, sensitivity of 95.8%, specificity of 92.1%, and the Youden indicator of 0.879, the negative and positive predictive values were 97.8% and 85.0% respectively, the negative and positive likelihood ratios were 0.05 and 12.5 respectively, and all significantly higher than that of CRP, IL-6 and SAA. It is concluded that for patients with hematologic malignancy combined with febrile neutropenia and bacterial infection, the diagnostic value of serum PCT is superior to that of immune inflammatory factors (CRP, IL-6 and SAA), the PCT can predict the bacterium infection, provide laboratory evidence for rational antimicrobial drug usage and mortality reduction.

Impact of the Implementation of Clinical Pathway on Postoperative Infection Rate

Objectives. To study the impact of the implementation of clinical pathway (CP) on the control of nosocomial infection and to provide an evidence for the management of infection. Methods. We compared and analyzed the average length of stay (LOS), antimicrobial drug usage, catheter and infection rate before and after the implementation of CP, by surveying the conditions of general surgical patients who underwent radical gastrectomy, radical resection of rectal carcinoma and modified radical mastectomy, without the implementation of CP, in 2009, and with the implementation of CP, in 2010. Results. The average LOS of the three categories of surgical patients after the implementation of the CP was significantly shortened, the average LOS of patients who underwent radical gastrectomy was shortened by 6.1 days, the average LOS of patients who underwent radical resection of rectal carcinoma was shortened by 6.29 days, and the average LOS of the patients who underwent modified radical mastectomy was shortened by 6.3 days. The antimicrobial drug usage was significantly reduced, wherein the usage of one antibacterial drug was increased by 25.05%, and the usage of a combination of two antimicrobial drugs was decreased by 19.26%; the usage of a combination of three antibiotics was decreased by 4.5%, while the usage of a combination of four antimicrobial drugs was decreased by 2.13%. The rate of nosocomial infection was decreased from 5.64% to 3.28%. The average number of days of requirement of a urinary catheter and deep vein catheterization was decreased significantly. It was statistically significant (P<0.001). Conclusions. The CP regulates the behavior of medical care staff, strengthens the execution of infection control measures, reduces the risk factors for infection, and effectively reduces the infection rates.

RAPID REAL TIME PCR BASED DETECTION OF CELL COUNT IN CASE OF URINARY TRACT INFECTION

Microbial identification and antimicrobial suscepti bility testing methods currently used in clinical microbiology laboratories require at least two to t hree days because they rely on the growth and isola tion of micro-organisms. This long, but necessary, delay ha s enormous consequences on prophylactic usage of antimicrobial drugs. This study was an attempt to r educe this detection time span. Taq Man Real Time PCR has been used as an important tool in the different iation of Gram nature of bacteria present in UTI pa tients that allows detection of spiked bacterial 16S rDNA from urine samples within a short span of 5h and al so gives us the corresponding cell count of both/eithe r Gram positive and negative organisms present. A standard curve was generated which was used to determine the cell count of control as well as patient samples. Detection could be done in the range of 10 3 to 10 6 cells/mL Patient samples screened clustered either in the allele 1 or allele 2 axes, depending on majority concentration of Gram nature of the mic roorganisms. The cell counts for control individuals were scattered within 0 to 10 2 , while very few in the range of 10 4 . The case was just reverse for patient group, wher e most of the points were scattered within 10 4 to 10 8 . Thus the optimal selection of appropriate antimic robials (depending on the gram nature) by clinicians, will be gradually improved as an increa sing number of rapid molecular diagnostic tools for the detection, identification and characterization of i nfectious agents become commercially available.

Modified Hodge test: A useful and the low-cost phenotypic method for detection of carbapenemase producers in Enterobacteriaceae members

Background:The global spread of antimicrobial resistance has acquired greater significance in the public health perspective. Drug resistance has posed a threat for the management of various hospital-acquired infections (HAI). For bacteria producing extended spectrum ß lactamase, carbapenems are the drug of choice. However, treatment failures are still a cause of concern due to carbapenemase producers.Aim:Various phenotypic and genotypic methods are available for the detection of carbapenemase producers. Studies thus far have mostly concentrated on comparing various methods for detection of carbapenemase producers. We used low-cost and the easily performed modified Hodge test (MHT) for detecting the carbapenemase producers in Enterobacteriaceae members isolated from various clinical specimens.Material and Methods:The study included 1072 clinical isolates of Enterobacteriaceae collected in India between April 2008 and February 2010. MHT was performed on all the isolates in accordance with CDC and CLSI guidelines.Results:The carbapenemase activity was detected in 35.9% (385/1072) of the isolates. Klebsiella spp. 28.7% (80/278), Citrobacter spp. 20.4% (25/122), 11.3% (38/334) in E. coli, 20.3% (45/221) in Enterobacter spp., and 16.2% (9/117) in Proteus spp. revealed variable resistance activities against carbapenems.Conclusion:Enterobacteriaceae members are among the most common and easily transferable bacterial species responsible for severe HAI. This study revealed a high percentage of Enterobacteriaceae clinical isolates producing carbapenemases in India. Detection of such bacteria, formulating hospital antibiogram, and monitoring the usage of antimicrobial drugs is recommended.

Short communication: Streptococcus species isolated from mastitis milk samples in Germany and their resistance to antimicrobial agents

Mastitis is one of the most frequent infectious diseases in dairy cattle and is a reason for antimicrobial drug usage in dairy cows. The bacteria involved in bovine mastitis are mainly Streptococcus spp., Staphylococcus spp., and coliforms. The aim of this study was to determine antimicrobial resistance among Streptococcus spp. isolated from bovine mastitis milk. Antimicrobial resistance in Strep. uberis (n=227), Strep. dysgalactiae (n=49), and Strep. agalactiae (n=3) was determined for 9 antimicrobial agents using the broth microdilution method in accordance with Clinical and Laboratory Standards Institute recommendations. Of all Streptococcus spp., 13% were multidrug resistant. The rate of multidrug resistance was higher among Strep. uberis (15%) than among Strep. dysgalactiae (6%) and Strep. agalactiae (0%). Resistance to tetracycline was the most common, followed by resistance to erythromycin, pirlimycin, and gentamicin. Resistance rates were higher on farms with more than 80 cows compared with those with fewer than 20 cows. β-Lactams should remain the drugs of choice in the treatment of streptococcal mastitis. The slightly elevated minimum inhibitory concentrations determined for these antibiotics may indicate, however, the emergence of resistant streptococci. To identify such changes in susceptibility as early as possible, antimicrobial resistance in streptococci should be surveyed regularly.

Antimicrobial resistance of thermotolerant Campylobacter spp. as a food safety issue

Antimicrobial resistance is a daunting public health threat impacting both human and animal health and it is a cause for concern wherever antimicrobial agents are in use. The usage of antimicrobial drugs in food producing animals could results in significant food safety issue - antimicrobial resistance among zoonotic bacteria in these animals. Resistance monitoring program still does not exist in Serbia, so we made a pilot program to screen the situation in our abattoirs. We found similar situation like the one in EU. The resistance to one or more antimicrobial drugs was found in 40.00% and 75.32% Campylobacter spp. strains isolated from poultry and pig carcasses, respectively. Fluoroquinolones are anitmicrobial drugs which, beside beta-lactams, are most often used in poultry breeding. Fluoroquinolones are also very important for treatment of some human diseases. We examined relationship between presence of fluoroquinolone resistant C. jejuni in poultry carcasses and fluoroquinolone treatment of poultry. Treatment with one of this antimicrobials - enrofloxacine selects resistant strains in chickens carcasses, C. jejuni strains resistant to enrofloxacine were isolated from all livers (100%) and 70% carcasses. The resistant bacteria may then be transmitted to humans through food supply and increase the risk of treatment failures. Resistant zoonotic pathogens in food have to be controlled through a complete, continuous farm-to-fork system.

Evaluating the efficacy of antimicrobial cycling programmes and patient isolation on dual resistance in hospitals

Antibiotic-resistant bacteria cause a number of infections in hospitals and are considered a threat to public health. A strategy suggested to curb the development of resistant hospital-acquired infections is antimicrobial cycling, in which antibiotic classes are alternated over time. This can be compared with a mixing programme in which, when given two drugs, half of the physicians prescribe one drug over the other. A mathematical model of antimicrobial cycling in a hospital population setting is developed to evaluate the efficacy of a cycling programme with an emphasis on reducing the emergence and significance of dual resistance. The model also considers the effects of physician compliance and isolating patients harbouring dual-resistant bacteria. Simulation results show that the optimal antimicrobial drug usage programme in hospital populations depends upon the type of resistance being targeted for treatment; a cycling programme is more effective against dual resistance compared with mixing. Patient isolation and high compliance to a cycling programme is also shown to dramatically decrease dual resistance in hospitalized populations. Ultimately, the exclusive use of antimicrobials in fighting nosocomial infection does not solve the problem but just slows down what appears to be a losing battle against drug resistance. We hope that this paper serves to instigate discussion on the many dimensions of the complex problem of drug resistance in hospital settings.

Antimicrobial use in food and companion animals

The vast literature on antimicrobial drug use in animals has expanded considerably recently as the antimicrobial resistance (AMR) crisis in human medicine leads to questions about all usage of antimicrobial drugs, including long-term usage in intensively managed food animals for growth promotion and disease prevention. Attention is also increasingly focusing on antimicrobial use and on bacterial resistance in companion animals, which are in intimate contact with the human population. They may share resistant bacteria with their owners, amplify resistant bacteria acquired from their owners, and act as a reservoir for human infection. Considerable effort is being made to describe the basis of AMR in bacterial pathogens of animals. Documentation of many aspects of use of antimicrobials in animals is, however, generally less developed and only a few countries can describe quantities of drugs used in animals to kg levels annually. In recent years, many national veterinary associations have produced 'prudent use guidelines' to try to improve antimicrobial drug use and decrease resistance, but the impact of guidelines is unknown. Within the evolving global movement for 'antimicrobial stewardship', there is considerable scope to improve many aspects of antimicrobial use in animals, including infection control and reduction of use, with a view to reducing resistance and its spread, and to preserving antimicrobial drugs for the future.

Impact of antimicrobial drug usage measures on the identification of heavy users, patterns of usage of the different antimicrobial classes and time‐trends evolution

Several measurement units are available to quantify antimicrobial usage in veterinary medicine, to obtain diverse measures such as the weight of active substance used, the live weight (LW) treated, the fraction of animals exposed, the number of treatments recorded or the cost represented. These measures can be applied to study practices variability between farms, to characterize patterns of usage of the different antimicrobial classes or to follow evolution of antimicrobial usage with time. An investigation was carried out to specifically explore the influence of measurement units on the conclusions obtained from such studies. Antimicrobial exposure was explored in a sample of turkey and chicken broiler flocks, using six different units [kg of active compound, treatments, days of administration, kg of LW treated, animal daily dose to treat 1 kg of LW (ADD(kg)) and euros] to compare flocks usage variability and patterns of use of the different antimicrobial classes. Time-trends evolutions of macrolides usage in turkey broilers, characterized by percentage of flocks exposed and LW treated, were also compared. In all analyses, the measure gave different results without equivalences, highlighting the necessity for care in choosing the measurement unit and caution in interpreting the figures obtained.

Contemporary food safety trends: Antimicrobial resistance in zoonotic pathogens

Antimicrobial resistance is a daunting public health threat affecting both human and animal health and it is a cause for concern wherever antimicrobial agents are in use. The usage of antimicrobial drugs in food producing animals could result in a significant food safety issue - antimicrobial resistance among zoonotic bacteria in these animals. The resistant bacteria may then be transmitted to humans through the food supply and increase risk of treatment failures. Campylobacter spp. and Salmonella spp. are two examples of food borne pathogens in which increasing resistance gives rise to concern. No monitoring program has been applied in Serbia. Therefore, the Veterinary Directorate of the Ministry of Agriculture financed three projects of the Scientific Veterinary Institute 'Novi Sad' to screen the spread of resistant food borne pathogens. The examinations have shown a similar situation as in the EU. Resistance to one or more antimicrobial drugs was found in 25-40.58% Salmonella spp. and 40-75.32% Campylobacter spp. isolates from poultry and pig carcasses. Zoonotic pathogens in food have to be controlled through a complete, continuous farm-to-fork system. Application of prophylactic and sanitary measures in farm breeding, slaughtering, food distribution and preparation of food in the kitchen may considerably reduce risk from the incidence of resistant zoonotic pathogens.

PREVALENCE OF ANTIMICROBIAL RESIDUES IN MILK AND DAIRY PRODUCTS IN THE STATE OF KUWAIT

ABSTRACT Approximately, 1,000 locally produced and imported milk and dairy product samples were collected at different seasonal periods from different farms and retail outlets in Kuwait, and screened for the presence of four antimicrobial residues (beta‐lactams, tetracyclines sulfonamides and chloramphenicol) using Charm II system. Results indicated that 29.1% of the analyzed local fresh milk samples were above the maximum residue level (MRL) for tested residues with tetracycline as predominant residue. The prevalence of antimicrobial residues in imported pasteurized milk samples (5.4%) was higher than that of local pasteurized milk samples (3.4%). No residues were detected in powdered and condensed milk samples imported from the European Union (EU) countries with the exception of tetracyclines. Results also showed that 9.4% of the analyzed imported cheese samples were above the MRL for tested residues, while tested ice cream samples were negative for antimicrobial residues. The significant presence of antimicrobial residues, particularly chloramphenicol, in raw and pasteurized milk, clearly implies the misuse of antimicrobial drugs in animal farms in Kuwait and neighboring countries, and implies the need for stricter regulations on antimicrobial drug usage in the dairy industry. PRACTICAL APPLICATIONSThis article addresses the generation of a baseline data on the current presence of four antimicrobial residues in locally produced and imported milk and dairy products in the state of Kuwait. The outcome of this study will provide valuable baseline information for local governmental authorities for effective monitoring for the use and misuse of agricultural antimicrobial drugs. Such data will also be important for other Gulf Cooperation Council countries, because such countries share similar farming practices and import comparable foodstuffs.

Prescription of antimicrobial drugs in Norwegian aquaculture with an emphasis on “new” fish species

The usage of antimicrobial (AM) drugs in farmed fish in Norwegian aquaculture for the period 2000–2005 was investigated by using prescription data. These data were validated against national sales data of AM drugs sold for use in farmed fish and were found to be highly valid. The defined course dose (DCD) was applied as the unit of measurement to correct for the variations in the dosages between different AM drugs. The DCD kg was the amount of an AM drug recommended for the treatment of a 1-kg fish. The calculated number of prescribed DCD kgs is an estimate of the biomass of farmed fish that can be treated with a certain amount AM drug. In the present study, the number of prescriptions issued (i.e., numbers of initiated treatments), weight of active substance prescribed and biomass treated were applied to describe the usage. An increase, although modest, in the AM drug usage in Norwegian aquaculture was observed from 2002 to 2005. This increase was accounted for by new-farmed fish species (other than Atlantic salmon and rainbow trout), especially Atlantic cod. The increased usage of AM drugs in cod in the study period was significantly positively correlated to the biomass produced; even so from 2001 to 2005 the number of prescriptions for cod relative to the produced biomass declined. The AM drug usage in Atlantic halibut as well as the production varied during the study period. For other species such as turbot, coalfish and wolffish the usage of AM drugs was found to be negligible. “Mono-therapy” with quinolones may present a selective pressure in regard to development of quinolone resistance.

Treatment Practices and Quantification of Antimicrobial Drug Usage in Conventional and Organic Dairy Farms in Wisconsin

The objective of this study was to develop a method to quantify antimicrobial drug usage and treatment practices on conventional and organic dairy farms that had been recruited to represent a broad spectrum of potential exposure to antimicrobial drugs. Data on disease prevalence and treatment practices of organic (n=20) and conventional (n=20) farms were obtained during a farm visit using a survey instrument. A standardized estimate of antimicrobial drug usage was developed using a defined daily dose (DDD) of selected compounds. Density of antimicrobial drug usage was expressed as the number of DDD per adult cow per year. Differences in prevalence and management of selected diseases between conventional and organic farms were identified. The overall estimated prevalence of selected diseases was greater for conventional farms compared with organic farms. Organic farmers reported use of a variety of nonantimicrobial compounds for treatment and prevention of disease. Conventional farmers reported that penicillin was the compound most commonly used for dry cow therapy and cephapirin was most commonly used for treatment of clinical mastitis. On conventional farms, the estimated overall exposure to antimicrobial drugs was 5.43 DDD per cow per year composed of 3.58 and 1.85 DDD of intramammary and parenteral antimicrobial drugs, respectively. Of total intramammary antimicrobial drug usage, treatment of clinical mastitis contributed 2.02 DDD compared with 1.56 DDD attributed to the use of dry cow therapy. Of total parenteral treatments, the distribution of exposure was 0.52 (dry cow therapy), 1.43 (clinical mastitis treatment), 0.39 (treatment of foot disease), 0.14 (treatment of respiratory disease), and 0.32 (treatment of metritis) DDD. For treatments of foot infections (0.33 DDD), respiratory infections (0.07 DDD), and metritis (0.19 DDD), the mean density of ceftiofur usage was significantly greater compared with other compounds.

Relationship Between Antimicrobial Drug Usage and Antimicrobial Susceptibility of Gram-Positive Mastitis Pathogens

The objective of this study was to analyze relationships between usage of antimicrobial drugs on dairy farms and results of antimicrobial susceptibility testing of mastitis pathogens. Exposure to selected antimicrobial drugs (n=10) was standardized by calculation of the number of defined daily doses used per cow. Farms (n=40) were categorized based on amount of antimicrobial exposure: organic (no usage); conventional–low usage (conventional farms not using or using less than or equal to the first quartile of use of each compound); and conventional–high usage (conventional farms using more than the first quartile of a particular compound). The minimum inhibitory concentration (MIC) of selected antimicrobial drugs was determined using a commercial microbroth dilution system for isolates of Staphylococcus aureus (n=137), coagulase-negative staphylococci (CNS, n=294), and Streptococcus spp. (n=95) obtained from subclinical mastitis infections. Most isolates were inhibited at the lowest dilution tested of most antimicrobial drugs. Survival curves for Staph. aureus and CNS demonstrated heterogeneity in MIC based on the amount of exposure to penicillin and pirlimycin. For CNS, farm type was associated with the MIC of ampicillin and tetracycline. For Streptococcus spp., farm type was associated with MIC of pirlimycin and tetracycline. For all mastitis pathogens studied, the MIC of pirlimycin increased with increasing exposure to defined daily doses of pirlimycin. The level of exposure to most other antimicrobial drugs was not associated with MIC of mastitis pathogens. A dose–response effect between antimicrobial exposure and susceptibility was observed for some pathogen–antimicrobial combinations, but exposure to other antimicrobial drugs commonly used for prevention and treatment of mastitis was not associated with resistance.

抗菌剤使用における薬剤師の能動的介入の評価

Anti-microbial drugs are used for both the treatment and prevention of microbial infections. Though they are used under the guidelines issued by various academic societies, physicians play an active role in the selection of anti-microbial drugs and determination of their dosages. Pharmacists should therefore actively participate in the design of prescriptions for anti-microbial drugs. We studied the effect of pharmacists' interventions in the use of injective anti-microbial drugs by comparing their use in in-patients before and after intervention.When pharmacists intervened, no aggravation of patients' conditions or anti-microbial resistance occurred, leading to a significant decrease in anti-microbial drug usage and duration of their administration. During the time of our study, our hospital's Infectious Committee established a system for the appropriate use of anti-microbial drugs suggesting that the interventions by pharmacists in the treatment of patients had been seen as important.

Community Case of Methicillin-resistantStaphylococcus aureusInfection

Community Case of Methicillin-resistant<i>Staphylococcus aureus</i>Infection

Comment on: Surveillance of the overall use of antimicrobial drugs in humans over a 5 year period (1997–2001) in Kenya

Sir, The baseline 5 year data on antimicrobial drug usage in Kenya as procured from the Kenyan national licensing authority for all drugs is interesting. The quantities of antimicrobial agents available for bacteria, including mycobacteria, were procured from the Pharmacy and Poisons Control Board responsible for approval of the import licenses. The cooperation of the manufacturers in obtaining this data is commendable. Certainly, this could address any irrational and indiscriminate usage of antimicrobials in Kenya. However, no information was supplied about antimicrobial storage practices at manufacturers’ warehouses. The results could be depressing. The quality of 33 formulations of antimicrobial and antimalarial drugs (namely amoxicillin capsules, metronidazole tablets, sulfamethoxazole/32#trimethoprim tablets, quinine tablets and sulfadoxine/pyrimethamine tablets) marketed in Rwanda and Tanzania was assessed, and the influence of tropical storage conditions on potency and in vitro dissolution addressed. In both countries, essential drug formulations met pharmacopoeial potency requirements, but some had poor in vitro drug release profiles. Some of the formulations tested were not stable upon storage under simulated tropical conditions. In Nigeria, five samples of ampicillin capsules with a label claim of 250 mg were purchased from different dispensing points in a small town. The pharmaceutical quality of the products and a sample from a batch produced by a local manufacturer was evaluated, and five of the capsule samples were examined in an in vivo bioavailability study. Three of the five capsule samples from dispensing points were found to be of lower quality than the officially prescribed standard of pharmaceutical quality. Unfortunately, these substandard capsules were being dispensed from authorized and unauthorized sources. Recently, a serious threat to public health was identified. The prevalence of counterfeit antimalarial drugs in Southeast Asian pharmacies and shops selling antimalarial drugs in Myanmar (Burma), Lao PDR, Vietnam, Cambodia and Thailand was found to be widespread. Of the 188 tablet packs labelled as artesunate, 53% did not contain any artesunate. Of the 44 mefloquine samples, 9% contained ,10% of the expected amount of active ingredient. Efforts to procure fundamental data regarding the consumption of antimicrobials consumed in developing countries should therefore take into account evidence of potency and appropriate storage conditions. Funding sources should also be identified to facilitate this process from a worldwide perspective.

Prevalence of Multidrug Resistant Staphylococcus aureus in Milk from Large- and Small-Scale Producers in Kenya

This study evaluated the prevalence of multidrug resistant Staphylococcus aureus in Kenyan milk and investigated any differences in antimicrobial resistance between large- (>200 L/d) and small- (<50 L/d) scale producers. Susceptibility profiles for penicillin G, tetracycline, erythromycin, trimethoprim/sulfamethazine, and chloramphenicol were determined for Staph. aureus (n = 402) isolated from cows with subclinical mastitis. There was a significant difference in the overall mean resistance profile between large- (7.1%) and small-scale farm (14.7%) isolates. The overall prevalence of multidrug resistance (≥2 antibiotics) differed significantly between isolates from small farms (34.3%) and those from large farms (18.0%). Additionally, the producers were interviewed about their usage of antimicrobial drugs and their attitudes toward education in related fields. There was an evident difference between the producer types in their documentation of the use of antimicrobial drugs. Small-scale farms were less inclined to documentation, and treatment records were available from 22% of small-scale farms, compared with 73% of large-scale farms. Farmers expressed a need for more information in 5 areas, ranking preventive management highest (34.0%); followed by affordable tests to control residues in milk (22.8%); preparation of antimicrobial drugs (20.0%); public health concerns (11.2%); disposal of surplus antimicrobial drugs (7.8%); and antimicrobial drug residue persistence in milk (4.2%). It was concluded that herd size might be an indirect risk factor in the development of antimicrobial resistance in Staph. aureus within the region.