Containing antimicrobial resistance is crucial to mitigate against a post-antimicrobial era given the current limited production of novel antimicrobial drugs. Surveillance of antimicrobial use and resistance is a critical component of antimicrobial resistance containment strategies because it provides the background information needed to guide decisions regarding policy changes and therapeutic regimes. A substantial percentage of the livestock in South Africa are reared by communal farmers yet there is a paucity of published research on antimicrobial use practices and antimicrobial resistance profiles in communal farming systems. Given the substantial contribution of communal livestock to the national herd, it is vital to include them in any surveillance work including antimicrobial resistance surveillance.
The aim of this study was to determine the resistance of the indicator bacteria, Escherichia coli and Enterococcus species, isolated from communal cattle, and to determine the knowledge on and use practices of antimicrobial drugs by farmers in the Mnisi community Ward B1 in Mpumalanga province of South Africa. Seventy farmers were interviewed at five dip tanks on antibiotics they have used and where they source the drugs; observation of withdrawal periods; disposal of expired antibiotics and knowledge on antimicrobial resistance. Rectal swabs were collected from cattle (n=100) belonging to the interviewed farmers for culture of E. coli and enterococci on MacConkey (without crystal violet) and sheep blood agar. The bacterial isolates were presumptively identified using primary biochemical tests, while confirmatory identification was done using API 10S for E. coli, and a streptococcal grouping kit and differential substrate utilisation for the Enterococcus species. Susceptibility of the isolates to selected antimicrobial drugs belonging to different classes was determined using a broth micro-dilution method.
The farmers indicated that they source their drugs from the local animal clinic (60%) and from an agricultural retailer (34%) in the nearby town. Among the various listed antibiotics, farmers (87%) indicated having used tetracyclines yet worryingly nearly all of them (99%) neither know what an antimicrobial drug is nor understand the concept of antimicrobial resistance. Only 1% of the farmers adhere to the recommended treatment duration while 29% keep treatment records. Forty five percent of the farmers indicated that observation of withdrawal periods was necessary because drug residues in treated animals can affect humans.
In total, 150 (79 E. coli and 71 Enterococcus species) bacterial isolates were obtained. The enterococci species isolated were E. faecium (46%, 33/71), E. faecalis (4%, 3/71), E. durans (4%, 3/71), E. avium (4%, 3/71) and non-specified Enterococcus species (41%, 29/71). The Enterococcus isolates were resistant to amoxycillin (3%, 2/71) and enrofloxacin (55%, 39/71), intermediate to erythromycin (38%), and completely susceptible to chlortetracycline and vancomycin. E.coli isolates exhibited resistance to colistin (16%, 13/79), amoxycillin (8%, 6/79), chlortetracycline (8%, 6/79) and enrofloxacin (3%, 2/79), and complete susceptibility (100%, 79/79) to gentamicin. The level of colistin resistance detected was an unexpected finding considering that the study focused on a rural communal farming area. It is thus suspected that technical limitations in performing minimum inhibitory concentration tests for polymixins, may be contributory to the high resistance levels. Antimicrobial resistance in the indicator bacteria was generally low. However, given that colistin is a last resort drug for the treatment of multidrug resistant Gram-negative infections, the detection of colistin resistance warrants further research. A critical outcome of this study is the identification of the need for tailor made farmer education to raise awareness on antimicrobial resistance and to promote prudent use of antimicrobial drugs in the community. The findings of this study can be compared with follow up studies in this community to assess the impact of implemented awareness programs.