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Fig. 1.

Genetic similarity of tested Listeria monocytogenes strains.
Genetic similarity of tested Listeria monocytogenes strains.

Fig. 2.

Electrophoregram presenting the occurrence of virulence genes among the strains tested (M – marker, K+ – positive control (IW41), line 4, 143, 185, 199, 344, 267, 112, 317, 368 – L. monocytogenes strains from milk, K (−) – negative control).
Electrophoregram presenting the occurrence of virulence genes among the strains tested (M – marker, K+ – positive control (IW41), line 4, 143, 185, 199, 344, 267, 112, 317, 368 – L. monocytogenes strains from milk, K (−) – negative control).

Fig. 3.

Prevalence of virulence genes among L. monocytogenes strains isolated from milk and blood.
Prevalence of virulence genes among L. monocytogenes strains isolated from milk and blood.

Fig. 4.

Differences in biofilm formation among clinical L. monocytogenes strains and the strains isolated from milk.
Differences in biofilm formation among clinical L. monocytogenes strains and the strains isolated from milk.

Fig. 5.

The intensity of biofilm formation by the selected L. monocytogenes strains.A – weak biofilm, B – moderate biofilm, C – strong biofilm, green – live cells, red – death cells.
The intensity of biofilm formation by the selected L. monocytogenes strains.A – weak biofilm, B – moderate biofilm, C – strong biofilm, green – live cells, red – death cells.

Fig. 6.

Multiple correlations between the intensity of biofilm formation, the number of virulence genes, and the drug resistance of L. monocytogenes strains isolated from milk.
Multiple correlations between the intensity of biofilm formation, the number of virulence genes, and the drug resistance of L. monocytogenes strains isolated from milk.

Fig. 7.

Multiple correlations between the intensity of biofilm formation, the number of virulence genes, and the drug resistance of the clinical L. monocytogenes strains.
Multiple correlations between the intensity of biofilm formation, the number of virulence genes, and the drug resistance of the clinical L. monocytogenes strains.

The profiles of drug resistance/susceptibility of strains of L. monocytogenes isolated from milk and the blood.

ProfileDrug resistance/susceptibilityNumber of strainsTotal (n = 28)
Strains from milk (n = 18) (the strain identification number)Strains from the blood (n = 10) (the strain identification number)
AR: -S: P, AM, MEM, E, SXT8 (44.44%)(7, 29, 63, 199, 231, 282, 317)4 (40.0%)(3, 4, 8, 10)12 (42.86%)
BR: PS: AM, MEM, E, SXT3 (16.67%)(76, 185, 251)0 (0.0%)3 (10.71%)
CR: ES: P, AM, MEM, SXT1 (5.56%)(267)4 (40.0%)(1, 2, 7, 9 )5 (17.86%)
DR: P, ES: AM, MEM, SXT1 (5.56%)(143)0 (0.0%)1 (3.57%)
ER: E, SXTS: P, AM, MEM1 (5.56%)(344)0 (0.0%)1 (3.57%)
FR: P, AM, MEM, SXTS: E1 (5.56%)(368)0 (0.0%)1 (3.57%)
GR: P, AM, MEM, E, SXTS: - - -3 (16.67%)(112, 372, 375)0 (0.0%)3 (10.71%)
HR: MEM, ES: P, AM, SXT0 (0. 0%)2 (20.0%)(5, 6)2 (7.14%)

The intensity of biofilm formation by L. monocytogenes strains derived from cow’s milk and the blood.

Strains originThe strain identification numberMean number of bacteria [log CFU/cm−2]STD
Milk3726.87± 6.12*
Milk3756.79± 6.09
Milk1126.71± 6.13
Milk3686.64± 6.17
Milk3446.05± 5.21
Milk1435.95± 4.99
Milk2675.81± 5.07
Milk2515.18± 4.80
Milk1854.99± 4.06
Milk7m4.94± 4.00
Milk1994.94± 3.76
Milk3174.89± 3.78
Milk4m4.85± 3.67
Milk2824.81± 3.81
Milk764.77± 3.65
Milk294.76± 3.74
Milk2314.74± 3.96
Milk634.64± 3.72
ATCC191115.80± 5.04
Blood55.70± 4.87
Blood65.67± 4.76
Blood34.18± 3.83
Blood14.01± 2.87
Blood84.00± 3.27
Blood23.97± 3.61
Blood93.92± 3.83
Blood73.72± 3.63
Blood103.71± 3.72
Blood43.61± 3.71

Listeria spp. transmission system: udder skin – silicone teat cup – udder skin.

StrainNumber of re-isolated L. monocytogenes [log CFU/cm2]
Silicone teat cupUdder skinUdder skin
Sample 1Sample 2Sample 3Sample 4Sample 5Sample 6Recovery of bacteria (12 h/25°C)
M3725.91*±5.81**3.81±3.613.77±3.733,. 0±2.853.00±2.852.81±2.652.81±2.651.92±1.822.83±2.53
M3755.84±5.633.68±3.453.61±3.832.68±2.502.68±2.501.87±1.931.87±1.93n.d.***1.66±1.76
M2315.57±5.603.71±3.233.66±3.542.68±2.722.68±2.722.00±1.902.00±1.901.11±1.162.37±2.48
M635.52±5.343.543.633.47±3.551.47±1.661.47±1.661.00±1.691.00±1.69n.d1.26±1.03
ATCC 191115.66±5.543.76±3.573.72±3.272.74±1.992.74±1.992.26±1.982.26±1.981.64±1.472.57±2.32
B55.71±5.613.62±3.203.56±3.472.57±2.422.57±2.421.84±1.031.84±1.03n.d.1.46±1.58
B65.69±5.453.79±3.863.73±3.702.91±2.782.91±2.782.72±2.642.72±2.641.811.712.72±2.63
B105.32±5.683.59±3.023.53±3.371.62±1.481.62±1.481.11±1.461.11±1.46n.d.1.20±1.68
B45.13±5.403.58±3.503.51±3.581.52±1.611.52±1.610.90±0.860.90±0.86n.d.1.08±1.71

Primers used for identification of L. monocytogenes.

Primer Primer sequence (5' - 3')Size of PCR product (bp)Amplification conditions
L1 CAG CAG CCG CGG TAA TAC938Initial denaturation - 94°C/2 min 30 cycles: denaturation - 94°C/30 s annealing, - 50°C/30 s elongation - 72°C/1 min final elongation - 72°C/5 min
L2 CTC CAT AAA GGT GAC CCT
LM1 CCT AAG ACG CCA ATC GAA750
LM2 AAG CAC TTG CAA CTG CTC

Transmission of L. monocytogenes from a biofilm on silicone teat cups to milk.

StrainNumber of re-isolated L. monocytogenes
Silicone teat cup[log CFU/cm2]Milk[log CFU/ml]
M3726.87*±6.12**3.37±3.03
M3756.79±6.093.29±3.37
M2314.74±3.962.75±2.62
M634.64±3.722.71±2.52
ATCC 191115.80±5.042.972.85
B55.70±4.872.94±2.74
B65.67±4.762.84±2.32
B103.71±3.722.63±2.51
B43.61±3.712.57±2.32

The profiles of virulence genes in strains of L. monocytogenes isolated from milk and from the blood.

ProfileVirulence genesNumber of strainsThe strain identification number
Strains isolated from milk
 IhlyA, plcB24, 63
  IIhlyA, iap, plcB27, 29
 IIIhlyA, inlB, plcB2199, 231
 IVactA, hlyA, plcB2282, 317
 VactA, hlyA, plcB, prfA276, 185
  VIactA, hlyA, iap, plcB, prfA2143,368
 VIIactA, hlyA, iap, inlA, inlB, plcA, plcB, prfA2372, 375
VIIIactA, hlyA, inlA, plcB1267
  IXactA, hlyA, inlA, plcA, plcB1344
 XactA, hlyA, plcA, plcB, prfA1251
  XIactA, hlyA, inlA, inlB, plcA, plcB, prfA1112
Strains isolated from the blood
 IactA, hlyA, iap, inlA, inlB, plcA, plcB, prfA51, 2, 5, 6, 9
  IIactA, hlyA, iap14
 IIIactA, hlyA, iap, prfA110
  IVhlyA, inlA, plcA, plcB, prfA13
 VhlyA, inlA, inlB, plcA, plcB, prfA18
  VIactA, hlyA, inlA, inlB, plcA, plcB, prfA17

Transmission of L. monocytogenes from a biofilm on silicone teat cups to the cow’s udder skin.

StrainNumber of re-isolated L. monocytogenes strains [log CFU/cm2]
Silicone teat cupUdder skin
Sample 1Sample 2Sample 3Sample 4Sample 5Sample 6Sample 7Sample 8Regrowth on first negative or last positive sample (12 h/25°C)
M3726.87*±6.12**4.33±3.983.88±3.773.71±3.343.45±2.882.92±2.712.66±2.352.09±2.311.85±1.842.92±2.74
M3756.79±6.094.54±4.373.99±3.823.65±3.633.10±3.452.83±2.692.51±1.961.92±1.821.61±1.312.79±2.62
M2314.74±3.963.87±3.723.76±3.793.47±3.552.79±2.712.52±2.331.93±1.201.67±1.471.08±1.541.99±1.85
M634.64±3.723.96±3.823.80±3.333.34±3.622.70±2.582.33±2.321.86±1.781.59±1.48n.d.1.87±1.51
ATCC 191115.80±5.043.64±3.673.02±3.512.79±2.392.62±2.442.14±2.481.79±1.511.53±1.63n.d.2.01±2.31
B55.70±4.873.56±3.712.85±2.702.63±2.202.48±2.231.96±1.861.76±1.611.43±1.01n.d.1.81±1.20
B65.67±4.763.47±3.172.91±2.762.76±1.992.39±2.611.92±1.651.64±1.711.26±1.33n.d.1.72±1.80
B103.71±3.722.85±2.582.57±2.201.88±1.571.49±1.04n.d.***n.d.n.d.n.d.1.63±1.41
B43.61±3.712.92±2.882.73±2.531.84±1611.20±1.35n.d.n.d.n.d.n.d.1.38±1.50

Primers used for the detection of virulence genes in Listeria monocytogenes strains (Franciosa et al. 2005; Rawool et al. 2007).

PrimerPrimer sequence (5’ - 3’)Size of PCR product (bp)
actA - FCGC CGC GGA AAT TAA AAA AAG A    839
actA - RACG AAG GAA CCG GGC TGC TAG
hlyA - FGCA GTT GCA AGC GCT TGG AGT GAA    456
hlyA - RGCA ACG TAT CCT CCA GAG TGA TCG
iap - FACA AGC TGC ACC TGT TGC AG    131
iap - RTGA CAG CGT GTG TAG TAG CA
inlA - FCAG GCA GCT ACA ATT ACA CA    2 341
inlA - RATA TAG TCC GAA AAC CAC ATC T
inlB - FAGG AGA GGA TAG TGT GAA    1 905
inlB - RTTA TTT CTG TGC CCT TAA
plcA - FCTG CTT GAG CGT TCA TGT CTC ATC CCC C    1 484
plcA - RATG GGT TTC ACT CTC CTT CTA C
plcB - FGCA AGT GTT CTA GTC TTT CCG G    794
plcB - RACC TGC CAA AGT TTG CTG TGA
prfA - FCAT GAA CGC TCA AGC AGA AG    706
prfA - RAAT TTT CCC AAG TAG CAG GA
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