Table 3.

Multivariable Cox proportional hazard regression model of susceptibility of Escherichia coli isolates from urinary and non-urinary origin to different antimicrobials in this study, in canine clinical infections at the Cornell University Animal Health Diagnostic Center (AHDC), 2007–2020.

	Hazard ratio	Probability of lower MIC^¶	P-value	adj. P-value^§	95% CI

*Ampicillin (N = 6724 isolates)*
Urinary tract ^a
Intestinal	0.57	0.36	< 0.001	< 0.001	0.49–0.67
Invasive	0.78	0.44	0.007	0.015	0.65–0.93
Unspecified site	0.74	0.43	0.009	0.017	0.59–0.93
Reproductive system	1.07		0.222	0.278	0.96–1.19
Skin and soft tissues	0.83	0.45	0.002	0.004	0.73–0.93
Isolation date (2007–2010) ^a
Isolation date (2011–2014)	1.09		0.095	0.122	0.99–1.20
Isolation date (2015–2017)	1.05		0.304	0.358	0.96–1.15
Isolation date (2018–2020)	0.98		0.608	0.657	0.90–1.06
*Amoxicillin-clavulanate (N = 6721 isolates)*
Urinary tract ^a
Intestinal	0.67	0.40	< 0.001	< 0.001	0.59–0.76
Invasive	0.75	0.43	< 0.001	0.001	0.65–0.88
Unspecified site	0.84		0.095	0.122	0.69–1.03
Reproductive system	1.16	0.54	0.016	0.026	1.03–1.30
Skin and soft tissues	0.90		0.077	0.110	0.80–1.01
Isolation date (2007–2010) ^a
Isolation date (2011–2014)	1.11		0.071	0.109	0.99–1.24
Isolation date (2015–2017)	1.05		0.347	0.397	0.95–1.16
Isolation date (2018–2020)	1.02		0.637	0.671	0.94–1.11
*Ceftiofur (N = 5526 isolates)*
Urinary tract ^a
Intestinal	0.82	0.45	0.012	0.022	0.70–0.96
Invasive	0.81	0.45	0.009	0.017	0.69–0.95
Unspecified site	0.84		0.089	0.122	0.70–1.03
Reproductive system	1.09		0.076	0.110	0.99–1.21
Skin and soft tissues	0.81	0.45	< 0.001	< 0.001	0.73–0.89
Isolation date (2007–2010) ^a
Isolation date (2011–2014)	1.09		0.034	0.054	1.01–1.18
Isolation date (2015–2017)	1.02		0.729	0.748	0.93–1.11
Isolation date (2018–2020)	1.02		0.777	0.777	0.92–1.12
*Enrofloxacin (N = 6723 isolates)*
Urinary tract ^a
Intestinal	0.54	0.35	< 0.001	< 0.001	0.48–0.60
Invasive	0.80	0.44	0.001	0.003	0.70–0.92
Unspecified site	0.91		0.270	0.327	0.76–1.08
Reproductive system	1.29	0.56	< 0.001	< 0.001	1.18–1.41
Skin and soft tissues	0.79	0.44	< 0.001	< 0.001	0.72–0.86
Isolation date (2007–2010) ^a
Isolation date (2011–2014)	1.18	0.54	< 0.001	0.001	1.08–1.28
Isolation date (2015–2017)	1.12	0.53	0.009	0.017	1.03–1.23
Isolation date (2018–2020)	1.04		0.367	0.408	0.96–1.13
*Trimethoprim -sulfamethoxazole (N = 6741 isolates)*
Urinary tract ^a
Intestinal	0.63	0.39	< 0.001	< 0.001	0.56–0.70
Invasive	0.83	0.45	0.006	0.014	0.73–0.95
Unspecified site	0.67	0.40	< 0.001	< 0.001	0.57–0.79
Reproductive system	1.15	0.53	0.005	0.014	1.04–1.26
Skin and soft tissues	0.88	0.47	0.006	0.014	0.81–0.97
Isolation date (2007–2010) ^a
Isolation date (2011–2014)	1.19	0.54	< 0.001	< 0.001	1.09–1.29
Isolation date (2015–2017)	1.23	0.55	< 0.001	< 0.001	1.12–1.35
Isolation date (2018–2020)	1.17	0.54	< 0.001	0.001	1.07–1.28

Reference group

^¶

Probability = HR/(1 + HR) − calculated if P-value< 0.05 (e.g., a hazard ratio of 2 corresponds to a 0.67 chance of an isolate at this condition having a lower MIC value compared to an isolate in the reference group).

^§

P-values were adjusted according to (Benjamini and Hochberg, 1995).