Microbes and Anti-Microbial Substances in Pasteurized Milk Sold in Oman

Figures & data

Table 1 Frequency of isolation of major microbial genera from five brands of milk samples

	Frequency of isolation (%) in milk samples
Target microorganisms	IA	IB	LA	LB	LC
Bacillus spp.	39	40	48	36	46
Citrobacter spp.	2	4	6	0	0
Enterobacter spp.	0	4	2	9	0
Escherchia spp.	0	0	30	16	33
Klebsiella spp.	7	4	28	9	3
Pigmented bacteria	4	2	7	4	1
Pseudomonas spp.	2	5	11	13	3

Table 2 Mean microbial counts in milk samples from five producers

	Mean (CFU mL^−1) ± Standard deviation
Type of milk sample	SPC	Total coliforms	Fecal coliforms	S. aureus
IA	108b±74	12b c±12	1b±2	1b±4
IB	168b±133	8c±10	4b±5	2b±6
LA	1,585a±1,084	91a±85	25a±45	76a±109
LB	301b±507	55a b±88	8a b±11	12b±32
LC	74b±43	24b c±19	16a b±13	5b±17

SPC = Standard plate count.

^a,b,cMeans within columns with different superscripts are different (P < 0.05).

Table 3 Percentage of milk samples with anti-microbial activity against S. aureus collected from April 2001 to June 2002 using the standard agar-well diffusion method

	Percentage of samples with positive results (%)
Time	IA	IB	LA	LB	LC
Apr-01	4/4=100	0/4=0	0/3=0	2/4=50	2/4=50
May-01	3/4=75	0/3=0	1/4=25	3/4=75	3/3=100
Jun-01	2/5=40	0/5=0	2/5=40	2/5=40	0/4=0
Jul-01	3/4=75	0/4=0	3/4=75	2/4=50	ND
Aug-01	3/3=100	0/4=0	1/4=25	3/4=75	ND
Sep-01	2/4=50	0/3=0	2/4=50	2/4=50	ND
Oct-01	0/3=0	0/4=0	0/4=0	0/3=0	0/2=0
Nov-01	0/3=0	0/3=0	0/3=0	0/3=0	0/3=0
Dec-01	0/4=0	0/4=0	0/4=0	0/3=0	0/4=0
Jan-02	0/3=0	0/3=0	0/3=0	0/3=0	0/3=0
Feb-02	0/3=0	0/3=0	0/2=0	0/3=0	0/3=0
Mar-02	0/4=0	0/4=0	0/4=0	0/4=0	0/3=0
Apr-02	4/5=80	1/5=20	3/5=60	2/5=40	4/4=100
May-02	2/3=67	0/3=0	0/3=0	3/3=100	3/3=100
Jun-02	2/3=67	0/3=0	0/3=0	1/3=33	1/3=33
Overall frequency	25/55=45a	1/55=2b	12/55=22a	20/55=36a	13/39=33a

ND = Not done due to no production during summer.

^a,bOverall frequency within the row with different superscripts are different (P < 0.05).

Table 4 Mean zones of inhibition against S. aureus by milk samples collected from April 2001 to June 2002 using the standard agar-well diffusion method and the presence (+) of S. aureus in these milk samples

	Mean (mm) ± Standard deviation (SD)
Time	IA	IB	LA	LB	LC
Apr-01	19	0	0	24	24
May-01	24	0 (+)	15 (+)	27	24
Jun-01	11	0	23	10	0
Jul-01	15	0	15	16	ND
Aug-01	18	0	20 (+)	15	ND
Sep-01	15	0	13	10 (+)	ND
Oct-01	0	0	0 (+)	0	0
Nov-01	0	0	0 (+)	0 (+)	0 (+)
Dec-01	0	0 (+)	0	0 (+)	0
Jan-02	0	0	0 (+)	0 (+)	0
Feb-02	0	0	0	0	0 (+)
Mar-02	0	0	0 (+)	0	0
Apr-02	10 (+)	10	10 (+)	14 (+)	16
May-02	10 (+)	0	0	10	12
Jun-02	8	0	0 (+)	8	7
Mean ± SD	9a ± 8	1b ± 3	6a ± 9	9a ± 9	7a ± 10

ND = Not done due to no production during summer.

^a,bMeans within the row with different superscripts are different (P < 0.05).

Table 5 Percentage of occurrence of antibiotic residues of the beta-lactam group in milk samples tested from April to June 2002 by the Snap rapid antibiotic screening test

	Percentage of samples with positive results (%)
Time	IA	IB	LA	LB	LC
Apr-02	3/4 = 75	0/1 = 0	3/3 = 100	2/2 = 100	2/4 = 50
May-02	1/2 = 50	0/0 = 0a	0/0 = 0a	3/3 = 100	3/3 = 67
Jun-02	1/2 = 50	0/0 = 0a	0/0 = 0a	1/1 = 100	1/1 = 100

^aTest was not done because the results were negative for the growth of the control strain of S. aureus using the standard agar-well diffusion method (Table 3).