The study examined 45 raw cow milk samples from Uasin Gishu County for contamination by Staphylococcus aureus, finding a 60% prevalence. Most isolates showed high resistance to ampicillin and co-trimoxazole, while being susceptible to gentamycin and sulfamethoxazole; multidrug resistance was also observed. The findings highlight the urgent need for effective preventive measures against mastitis and vigilant antibiotic stewardship.

1. Otin, J1., Loye, C2., and Oduori DO.1
Materials & Methods
Forty-five milk samples, were sourced from dairy cows located in
different farms within Uasin Gishu County. They were collected
using sterilized tubes, transported to a laboratory and incubated at
37°C for 2 hours, cultured in 5% sheep blood agar, and MSA by
spreading method. Pure culture of S. aureus was obtained based
on Beta-hemolysis on blood agar, gram staining, biochemical
characteristics, catalase tests as per the procedures by
Cheesbrough (1985).
Sensitivity test was done as per (CLSI, 2012). Discs impregnated
with Amplicillin (Amp), Co-Trimoxazole (CoT), Gentamycin
(Gen), Sulfamethoxazole (Sx), Streptomycin (S), Kanamycin (K),
Tetracycline (Te), Chloramphenicol (C) were used.
Results
27/45, 60% of the milk samples were positive for
S. aureus (Fig. 1). Most of the isolates had high
resistance to Ampicillin 66.7%, and Co-
Trimoxazole 63%, but susceptible to Gentamycin
74%, and Sulfamethoxazole 51.9%. Intermediate
resistance was observed for all antibiotics tested &
ranged from (7.4-40.7%) (Fig. 2).
Resistance to multiple antibiotics was as follows:
1(14.8%), 2(18.5%), 3(25.9%), 4(22.2%),
5(11.1%) antibiotics. Resistance to 6 and 8
antibiotics was (3.7%).
Occurrence of multidrug resistant Staphylococcus aureus in bovine milk, a pilot
study conducted at Veterinary Investigation Laboratory-Eldoret, Kenya
Abstract
Antibiotic resistance is a threat to human and animal health. Staphylococcus aureus is an important reservoir for
antibiotic resistance determinants. Forty-five raw cow milk samples were examined for bacterial contamination by S.
aureus and the prevalence was 60%. Most of the isolates had high resistance to Ampicillin and Co-Trimoxazole but
were susceptible to Gentamycin and Sulfamethoxazole. Resistance to multiple antibiotics was observed
.
Introduction
Antibiotic resistance occurs when microbes evolve mechanisms
protecting them from effects of antimicrobials. As a result, standard
treatment become ineffective, infection persist and may spread to others.
The objective of this study was to detect S. aureus contamination in raw
bovine milk and its antimicrobial resistance profile.
0.00%
10.00%
20.00%
30.00%
40.00%
50.00%
60.00%
70.00%
80.00%
Amp Te CoT S Ken Gen Sx C
Sensitivity
R= Resistant, I= Intermediate resistance, S= Susceptible
Graph of antimicrobial susceptibility of Staph. aureus isolates from
raw milk
R I S
One Health Relevance
S. aureus has the capacity to colonize various parts of the human body
and dairy cows leading to a diverse array of diseases. Mastitis is the
common result of infection in animals leading to significant economic
loss. Consumption of milk from infected animals by a human can lead to
infections or intoxications. The zoonotic potential of the pathogen
suggests that effective control can be achieved via a One-Health
approach.
Albeit the limitations in statistical strength, the study intimates an urgent
need for effective preventive measures against mastitis in cattle and
vigilance in antibiotic stewardship.
References
Alexander, T. W., Yanke, L. J., Topp, E., Olson, M. E., Read, R. R., Morck, D.
W., & McAllister, T. A. (2008). Effect of subtherapeutic administration of
antibiotics on the prevalence of antibiotic-resistant Escherichia coli bacteria in
feedlot cattle. Applied and environmental microbiology, 74(14), 4405–4416.
https://doi.org/10.1128/AEM.00489-08
CLSI (2012) Performance standards for antimicrobial susceptibility testing.
Twenty second informational supplement. CLSI document M100-S22. Wayne,
PA: Clinical and Laboratory Standard Institute. Available at
https://clsi.org/media/2663/m100ed29_sample.pdf
1. Maasai Mara University, Narok Kenya, P.O. Box 861 - 20500, Narok, Kenya.
2. Veterinary Investigation Laboratory, Eldoret , Kenya
Fig. 2: The antimicrobial susceptibility profile for 27 isolates of S. aureus
against 8 different antibiotics.
Fig. 1: Prevalence of S. aureus in bovine milk, reported/staggered
over 30 days
70.0
80.0
62.5
37.5 40.0
66.7
60
1-5 6-10 11-15 16-20 21-25 26-30 1-30
Prevalence
(%)
Timeline in days
Prevalence of S. aureus reported during study timeline
n=10
n= 5
n= 8
n= 8 n=5
n=9
n= 45