A longitudinal study of antimicrobial resistant faecal bacteria in sediments collected from a hospital wastewater system

Figures & data

Fig. 1.  Sampling arrangement in a sewage line at Kalmar county hospital. The sampling equipment was installed in a manhole. Wastewater was pumped from a sump placed with the bottom lower than the main furrow in the manhole to ensure the continuous presence of water in the sump. In the tank, settled particles were collected in tubes

Table 1. Breakpoints for sensitive (S), intermediate (I) and resistant (R) categorisation by the paper disc method and minimum inhibitory concentration (MIC) breakpoints for resistance categorisation by the spread plate method

Antimicrobial	Paper disc concentration (µg)	Zone diameter breakpoints (mm)		MIC breakpoints (mg l^−1 agar)
		Coliforms	Enterococci	Coliforms	Enterococci
Ampicillin	10	–	20/16	–	8
Imipenem	10	23/16	20/16	8	8
Vancomycin	5	–	11/9	–	4
Ciprofloxacin	5	24/17	32/12	1	2
Trimetroprim–Sulphamethoxasol	25	17/13	–	32	–

Zone breakpoints 23/16, i.e. clear zone with a diameter: S ≥ 23 mm, R ≤ 16 mm and 16 < I<23. MIC breakpoint 8: R can grow in antimicrobial concentration > 8 mg l⁻¹ 18.

Table 2. Resistant coliform bacterial isolates (/total isolates) by the disc diffusion method on PDM agar and percentage resistant coliform bacteria as determined by the ratio CFU ml⁻¹ on LES endoagar with and without antimicrobials (%) in concentrations corresponding to Table 1

Antimicrobial	Ciprofloxacin		Imipenem		Trimetroprim–Sulphamethoxazole
Medium	PDM	LES	PDM	LES	PDM	LES
Sampling date
13 December 2000	0/44	1.4	0/44	<0.1	0/44	0.7
15 February 2001	2/43	<0.1	1/43	<0.1	0/43	0.2
17 April 2001	0/58	1.1	3/58	<0.1	0/58	3.4
07 June 2001	0/16	ND	0/16	ND	0/16	ND
30 August 2001	0/46	ND	0/46	ND	0/46	ND
24 October 2001	0/34	<0.1	1/29	<0.1	1/29	5.4
24 January 2002	1/37	<0.1	1/37	0.1	5/37	3.8
	3/273		6/273		6/273

Table 3. Resistant intestinal enterococci isolates (/total isolates) by the disc diffusion method on PDM agar and percentage resistant enterococci as determined by the ratio CFU ml⁻¹ on ES agar with and without antimicrobials (%) in concentrations corresponding to Table 1

Antimicrobial	Ciprofloxacin		Imipenem		Ampicillin		Vancomycin
Medium	PDM	ES	PDM	ES	PDM	ES	PDM	ES
Sampling date
13 December 2000	2/12	0.2	2/12	0.2	2/12	0.1	2/12	<0.1
15 February 2001	0/24	3.5^a	0/24	<0.1	0/24	<0.1	0/24	<0.1
17 April 2001	2/24	4.0^a	0/24	1.0	1/24	<0.1	0/24	<0.1
07 June 2001	0/20	ND	0/20	ND	0/20	ND	0/20	ND
30 August 2001	9/24^a	ND	0/24	ND	0/20	ND	0/20	ND
24 October 2001	8/30^a	0.4	0/30	0.3	0/30	<0.1	0/30	<0.1
24 January 2002	0/24	<0.1	0/24	<0.1	0/24	<0.1	0/24	<0.1
	21/158		2/158		3/158		0/158

^a(P<0.05).

Fig. 2.  Dendrogram from PhP-typing of ciprofloxacin-resistant faecal enterococci at sample dates

Table 4. Generation and lag-phase times (±standard deviation) (min) for nine independent intestinal enterococci isolates from three CIP resistance classes in different ciprofloxacin concentrations (µg l⁻¹)

CIP resistance class	0 (µg l^−1)		100 (µg l^−1)		500 (µg l^−1)		1000 (µg l^−1)		4000 (µg l^−1)
	Generation time (min)	Lag-phase time (min)	Generation time (min)	Lag-phase time (min)	Generation time (min)	Lag-phase time (min)	Generation time (min)	Lag-phase time (min)	Generation time (min)	Lag-phase time (min)
Resistant	39.8±0.2	127±12	39.8±0.1	127±12	40.2±0.4^b’	130±17	46.6±3.9^b,c’	138±19	52.8±6.6	150±17
Intermediate	40.4±11	133±21	40.4±0.1	133±21	43.9±0.3^b’	133±7.6	109±18	120±20	–	–
Sensitive	40.4±11	97±6^a	42.1±14	97±6^a	61.2±9.6	90±10^b	175±21	90±10^a’	–	–

^aStatistically shorter time (P<0.05).

^a’Statistically shorter time than the longer of the other two (P<0.05).

^bStatistically shorter time (P<0.01).

^b'Statistically shorter time than the longer of the other two (P<0.01).

^c’Statistically shorter time than the longer of the other two (P<0.001).

Olsson-Liljequist B, Larsson P, Walder M, Miorner H. Antimicrobial susceptibility testing in Sweden. III. Methodology for susceptibility testing. Scand J Infect Dis. 1997; 105(Suppl): 13–23.

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