Surveillance of Antibiotic Resistance of Maltose-Negative Staphylococcus aureus in South African Dairy Herds

Abstract

Antibiotic resistance has been reported since the 1940s in both human and veterinary medicine. Many years of monitoring milk samples in South Africa led to identification of a novel maltose-negative Staphylococcus aureus (S. aureus) strain, which appears to be an emerging pathogen. In this study, the susceptibility of this strain to antibiotics was evaluated over time, during diverse seasons in various provinces and according to somatic cell count (SCC) categories. A data set of 271 maltose-negative S. aureus isolates, from milk samples of 117 dairy herds, was examined using the disk diffusion method, between 2010 and 2017. This study also compared the susceptibility testing of 57 maltose-negative and 57 maltose-positive S. aureus isolated from 38 farms, from three provinces using minimum inhibitory concentration (MIC). The MIC results for the maltose-negative S. aureus isolates showed highest resistance to ampicillin (100%) and penicillin (47.4) and lowest resistance (1.8%) to azithromycin, ciprofloxacin and erythromycin. The maltose-negative S. aureus isolates showed overall significantly increased antibiotic resistance compared to the maltose-positive strains, as well as multidrug resistance. Producers and veterinarians should consider probability of cure of such organisms (seemingly non-chronic) when adapting management and treatment, preventing unnecessary culling.

The spread and antimicrobial resistance of Staphylococcus aureus in South African dairy herds – A review

“…The resistance of the maltosepositive S. aureus observed in a South African study (Karzis et al 2020a) was in agreement with that reported in other studies in Denmark and New Zealand (Salmon et al 1998).…”

“…Staphylococcus aureus resistance in South Africa compared to that of other countries: The resistance of the maltose-positive S. aureus observed in a South African study (Karzis et al 2020a ) was in agreement with that reported in other studies in Denmark and New Zealand (Salmon et al 1998 ). The relatively high resistance rates of S. aureus to penicillin and tetracycline in both the South African studies (Karzis et al 2020a ; Schmidt et al 2015 ) also corresponded with the findings of a recent study in Ethiopia (Kalayu et al 2020 ). Similarly, as in South Africa, most isolates from the United States (New York State), Argentina and Germany showed resistance to spiramycin (Monistero et al 2020 ).…”

“…The relatively high resistance rates of S. aureus to penicillin and tetracycline in both the South African studies (Karzis et al 2020a;Schmidt et al 2015) also corresponded with the findings of a recent study in Ethiopia (Kalayu et al 2020).…”

“…In line with the virulence, the trends in antimicrobial resistance for the maltose-negative S. aureus ST 2992 (Karzis et al 2020b) also showed a closer similarity with the data for non-aureus Staphylococci than for the maltose-positive S. aureus (Karzis et al 2020a). Unexpectedly, the maltose-negative displayed more resistance (p < 0.001) than the maltose-positive S. aureus isolates to most of the antimicrobials tested using the MIC method (Karzis et al 2020a).…”

“…Studies in both animal and human medicine identified pan and multidrug resistance in S. aureus isolates in other countries (Haran et al 2011;Karzis et al 2020a).…”