Abstract:
The objectives of this study were to examine the
diversity of Staphylococcus spp. recovered from bovine
intramammary infections and humans working in close
contact with the animals and to evaluate the susceptibility
of the staphylococcal isolates to different antimicrobials.
A total of 3,387 milk samples and 79 human
nasal swabs were collected from 13 sampling sites in
the KwaZulu-Natal province of South Africa. In total,
146 Staph. aureus isolates and 102 coagulase-negative
staphylococci (CNS) were recovered from clinical and
subclinical milk samples. Staphylococcus aureus was
isolated from 12 (15.2%) of the human nasal swabs and
95 representative CNS were recovered for further characterization.
The CNS were identified using multiplex-
PCR assays, matrix-assisted laser desorption/ionization
time-of-flight mass spectrometry (MALDI-TOF
MS), and tuf gene sequencing. Seven Staphylococcus
spp. were identified among the CNS of bovine origin,
with Staph. chromogenes (78.4%) predominating. The
predominant CNS species recovered from the human
nasal swabs was Staph. epidermidis (80%) followed by
Staph. chromogenes (6.3%). The antimicrobial susceptibility
of all staphylococcal isolates was evaluated using
disk diffusion and was supplemented by screening for
specific antimicrobial resistance genes. Ninety-eight
(67.1%) Staph. aureus isolates of bovine origin were
pansusceptible; 39 (26.7%) isolates were resistant to
a single class, and 7 (4.8%) isolates were resistant to
2 classes of antimicrobials. Two Staph. aureus (1.4%)
isolates were multidrug-resistant. Resistance to penicillin
was common, with 28.8% of the bovine and 75% of
the human Staph. aureus isolates exhibiting resistance.
A similar observation was made with the CNS, where
37.3% of the bovine and 89.5% of the human isolates
were resistant to penicillin. Multidrug-resistance was
common among the human CNS, with 39% of the
isolates exhibiting resistance to 3 or more classes of antimicrobials. The antimicrobial susceptibility results
suggest that resistance among staphylococci causing
bovine intramammary infections in South Africa is uncommon
and not a significant cause for concern. In contrast,
antimicrobial resistance was frequently observed
in staphylococcal isolates of human origin, highlighting
a possible reservoir of resistance genes. Continued
monitoring of staphylococcal isolates is warranted to
monitor changes in the susceptibility of isolates to different
classes of antimicrobials.
