Australian Group on Antimicrobial Resistance Enterococcus Surveillance Programme annual report, 2010

In 2010, 15 institutions around Australia participated in the Australian Group on Antimicrobial Resistance (AGAR) period prevalence study of key resistances in Enterococcus species associated with a range of clinical disease amongst in- and outpatients. From this study and the examination of trends over the last 15 years antimicrobial resistance, including vancomycin resistance, has increased significantly in E. faecium isolated in Australia.

Page last updated: 21 February 2014

Geoffrey W Coombs, Julie C Pearson, Keryn Christiansen, Thomas Gottlieb, Jan M Bell, Narelle George, John D Turnidge for the Australian Group on Antimicrobial Resistance

Abstract

In 2010, 15 institutions around Australia conducted a period prevalence study of key resistances in isolates of Enterococcus species associated with a range of clinical disease amongst in- and outpatients. Each institution collected up to 100 consecutive isolates and tested these for susceptibility to commonly used antimicrobials using standardised methods. Vancomycin-resistant Enterococcus faecium and Enterococcus faecalis were characterised by pulsed-field gel electrophoresis. Multilocus sequence typing was performed on representative pulsotypes of E. faecium. Susceptibility results were compared with similar surveys conducted in 1995, 1999, 2003, 2005, 2007 and 2009. In the 2010 survey, E. faecalis (1,201 isolates) and E. faecium (170 isolates) made up 98.9% of the 1,386 isolates tested. Ampicillin resistance was very common (85.3%) in E. faecium and absent in E. faecalis. Non-susceptibility to vancomycin was 36.5% in E. faecium (similar to the 35.2% in 2009 but up from 15.4% in the 2007 survey) and 0.5% in E. faecalis. There were significant differences in the proportion of vancomycin-resistant E. faecium between the states ranging from 0% in Western Australia to 54.4% in South Australia. The vanB gene was detected in 62 E. faecium and 3 E. faecalis isolates. The vanA gene was detected in 1 E. faecium isolate. All vancomycin-resistant E. faecium belonged to clonal complex 17. The most common sequence type (ST) was ST203, which was found in all regions that had reports of vancomycin resistant enterococci. ST341 was detected only in New South Wales/Australian Capital Territory and ST414 only in South Australia and Victoria. High-level resistance to gentamicin was 34.1% in E. faecalis and 66.1% in E. faecium. A subset of isolates was tested against high-level streptomycin, linezolid and quinupristin/dalfopristin. High-level streptomycin resistance was found in 8.2% of E. faecalis isolates and 43.8% of E. faecium isolates. Linezolid non-susceptibility was more common in E. faecalis (5.8%) than E. faecium (0.9%). Overall 9.4% of E. faecium were resistant to quinupristin/dalfopristin (E. faecalis is intrinsically resistant). Commun Dis Intell 2013;37(3):E199–E209.

Keywords: antimicrobial resistance surveillance; Enterococcus faecium, Enterococcus faecalis, vancomycin resistant enterococcus

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Introduction

Enterococci are part of the normal flora of the gastrointestinal tract. They can give rise to endogenous infections such as urinary tract infections outside of hospitals. Enterococci are recognised as significant nosocomial pathogens causing urinary tract, blood stream, sterile site and wound infections. In hospitals, enterococci can be transmitted through poor infection control practices and can give rise to a wide variety of infections usually in patients with co-morbidities. The two main species causing infections in humans are Enterococcus faecalis and Enterococcus faecium with only a very small number of other species being isolated from clinical specimens.

In the 1980s, enterococci were generally susceptible to amoxycillin and vancomycin. Since then E. faecium has become increasingly resistant to ampicillin/amoxycillin making vancomycin the treatment of choice for severe infections caused by this organism. The first vancomycin resistant enterococci (VRE) were described in the United Kingdom and Europe in 19881 and in the United States of America (USA) in the early 1990s.2 The first VRE was reported in Australia in 19943 and a report on the emergence and epidemiology of VRE in Australia was described in 1998 when 69 isolates were documented.4

Multilocus sequence typing (MLST) of E. faecium has revealed that clonal complex (CC) 17 strains have become predominant in hospitals in many countries and are characterised by ampicillin resistance and the presence of several genetic elements (e.g. esp and hyl) not present in colonising variants in humans and animals.5–9 There is some evidence that this additional genomic content assists in adaptation to the hospital environment and the ability to spread, therefore when CC17 strains acquired the vanA or vanB gene encoding vancomycin resistance, they were already primed for transmission in the hospital setting.

Prevalence and incidence rates for VRE in Australian hospitals are not routinely collected although there have been reports of individual hospital outbreaks of VRE infections and associated colonisation of other patients.9–13 The clinical impact of vancomycin resistance in enterococci has been reported to include increases in mortality, length of stay and hospital costs.14,15 Serious infections caused by vancomycin-resistant E. faecium are difficult to treat, and rely on recently introduced antimicrobials such as linezolid, quinupristin-dalfopristin, tigecycline and daptomycin which are not approved for all indications. Further complicating the treatment of infections caused by VRE are reports of isolates that are resistant even to these newer agents.16,17

It is important to have an understanding of the occurrence of enterococcal infection and antibiotic resistance in Australia to guide infection control practices, antibiotic prescribing policies and drug regulatory matters.

The objective of the 2010 surveillance program was to determine the proportion of clinical isolates of Enterococcus species demonstrating antimicrobial resistance with particular emphasis on:

  • assessing susceptibility to ampicillin;
  • assessing susceptibility to glycopeptides; and
  • assessing changes in resistance patterns over time using data collected in previous Australian AGAR surveys,
  • determining which VRE clones are circulating within Australia.

The Australian Group on Antimicrobial Resistance (AGAR) commenced surveillance of antimicrobial resistance in Enterococcus species in 1995. Similar surveys were conducted in 1999, 2003, 2005, 2007 and 2009 (www.agargroup.org).

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Methods

Fifteen laboratories from all mainland Australian states and the Australian Capital Territory participated in the 2010 AGAR survey Enterococcus. To ensure institutional anonymity the New South Wales and the Australian Capital Territory data were combined.

From 1 January to 30 June 2010 each laboratory collected up to 100 consecutive clinically significant isolates of enterococci. Only 1 isolate per patient was tested unless subsequent isolates had a different antibiogram to the original isolate.

Species identification

All isolates were tested for pyrrolidonyl arylamidase with optional testing for growth in 6.5% sodium chloride, esculin hydrolysis in the presence of bile, Group D antigen and growth at 45°C. Isolates were identified to species level by either API® 20S (bioMérieux, Marcy l’Etoile, France), Vitek® 2 (bioMérieux, Marcy l’Etoile, France), Phoenix™ (BD, New Jersey, USA), polymerase chain reaction (PCR), or conventional biochemical tests. If biochemical testing was performed, the minimum tests necessary for identification were: motility, pigment production, methyl-α-D-glucopyranoside, fermentation of 1% raffinose, 1% arabinose, 1% xylose and utilisation of pyruvate.

Susceptibility methodology

Participating laboratories performed antimicrobial susceptibility tests according to each laboratory’s routine standardised methodology (Clinical and Laboratory Standards Institute (CLSI) disc diffusion, Vitek® 2, Phoenix™, agar dilution or Etest® (bioMérieux, Marcy l’Etoile, France)). Ampicillin and vancomycin were tested by all laboratories. Vancomycin resistance was confirmed by PCR. Overall, 1,378 (99.4%) isolates were screened for high level gentamicin resistance, 932 (67.2%) were tested against linezolid, 503 (36.3%) were tested against quinupristin/dalfopristin and 146 (10.5%) were screened for high level streptomycin resistance. CLSI breakpoints were utilised for all antimicrobials.18 Isolates with an intermediate and resistant category have been classified as non-susceptible.

Of the 178 invasive isolates, 116 (65.2%) were tested for ß-lactamase production using a chromogenic cephalosporin nitrocefin.

Epidemiological typing of vancomycin resistant enterococci

Pulsed-field gel electrophoresis (PFGE) of SmaI-digested DNA agarose plugs was performed as previously described on all VRE isolates.19 MLST was performed as previously described on a representative of each PFGE pulsotype of vancomycin resistant E. faecium.20

Statistical analysis

The difference between proportions was tested using Chi-square test with alpha set at the 5% level and Fisher’s exact test for 95% confidence limits (GraphPad® Prism Software).

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Results

Both public (n=13) and private (n=2) laboratories participated in the survey. Participants included New South Wales (n=3), the Australian Capital Territory (n=1), Queensland (n=4), Victoria (n=1), South Australia (n=3), and Western Australia (n=3). In 2010 there were 1,386 isolates from 15 institutions (Table 1). E. faecalis was the most frequently isolated species (86.7%) followed by E. faecium (12.3%) (Table 2).

Table 1: Enterococcus isolates in Australia, 2010, by region
Region Number of institutions Isolates %
NSW/ACT
4
380
27.4
Qld
4
400
28.9
SA
3
207
14.9
Vic
1
100
7.2
WA
3
299
21.6
Total
15
1,386
100.0

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Table 2: Enterococcus species isolated in Australia, 2010, by region
Region E. faecalis E. faecium Other spp. or unspeciated Total
NSW/ACT
334
41
5
380
Qld
381
18
1
400
SA
145
57
5
207
Vic
76
23
1
100
WA
265
31
3
299
Total
1,201 (86.7%)
170 (12.3%)
15 (1.1%)
1,386

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The majority of isolates (70.9%) were from the urinary tract (Table 3). They were predominately E. faecalis (91.3%). Invasive (blood, cerebrospinal fluid (CSF) and sterile body cavity) isolates comprised 12.8% of the total number of isolates collected. E. faecium was disproportionately represented in the invasive group (28.7%). Of the E. faecalis isolates, 9.9% were invasive compared with 30.0% of E. faecium isolates.

Table 3: Enterococcus species isolated in Australia, 2010, by source
Source E. faecalis E. faecium Other spp. or unspeciated Total
CSF Cerebrospinal fluid
* Blood/cerebrospinal fluid/sterile body cavity
Urine
897
82
3
982 (70.9%)
Wound
173
37
4
214 (15.4%)
Blood/CSF
77
34
5
116 (8.4%)
Sterile body cavity
42
17
3
62 (4.5%)
Other
12
0
0
12 (0.9%)
Total
1,201
170
15
1,386
Invasive*
119
51
8
178 (12.8%)
Non-invasive
1,082
119
7
1,208 (87.2%)

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Susceptibility

Resistance to ampicillin was common in the E. faecium isolates (Table 4). Resistance in E. faecium was due to penicillin binding protein changes. No ß-lactamase positive E. faecium were detected amongst the subset (30/51, 59%) of invasive isolates tested. Resistance in invasive isolates was lower than for non-invasive isolates (72.9% and 90.7% respectively, P=0.004). Ampicillin resistance was not detected for E. faecalis and none of the 81 invasive isolates tested for ß-lactamase were positive.

Table 4: Number of ampicillin resistant Enterococcus species isolated in Australia, 2010, by region
  NSW/ACT Qld SA Vic WA Aus
n N % n N % n N % n N % n N % n N %
E. faecalis all
0
334
0.0
0
381
0.0
0
145
0.0
0
76
0.0
0
265
0.0
0
1,201
0.0
Invasive
0
46
0.0
0
14
0.0
0
22
0.0
0
8
0.0
0
18
0.0
0
108
0.0
E. faecium all
34
41
82.9
17
18
94.4
51
57
89.5
19
23
82.6
23
31
77.4
145
170
85.3
Invasive
12
18
66.7
1
2
50.0
17
20
85.0
3
3
100.0
4
8
50.0
37
51
72.5

Trend data for E. faecium show that from 1995 to 1999, there was an increase in ampicillin resistance (P=0.002) with a plateau from 1999 to 2005 (Figure 1). Between 2005 and 2010, resistance has once again increased significantly (P=0.005). The gap between resistance in non-invasive versus invasive isolates narrowed over time, however in 2010 there was a reversal of this trend with rates of resistance in invasive isolates falling significantly (P=0.04) compared to 2009 levels.

Figure 1: Percentage of Enterococcus faecium resistant to ampicillin, by survey year

Percentage of Enterococcus faecium resistant to ampicillin, by survey year . A text description follows.

1995: invasive n=26, non-invasive n= 55, overall n=81.
1999: invasive n=30, non-invasive n= 152, overall n=182.
2003: invasive n=51, non-invasive n= 81, overall n=132.
2005: invasive n=43, non-invasive n= 137, overall n=180.
2007: invasive n=51, non-invasive n= 98, overall n=156.
2009: invasive n=48, non-invasive n= 165, overall n=213.
2010: invasive n=51, non-invasive n= 119, overall n=170

Text version of Figure 1 (TXT 1 KB)

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Vancomycin non-susceptibility was uncommon in E. faecalis (0.5%) (Table 5). Of the 6 non-susceptible E. faecalis, two harboured the vanB gene and four did not possess either vanA or vanB.

Table 5: Number of vancomycin non-susceptible Enterococcus species isolated in Australia, 2010, by region
  NSW/ACT Qld SA Vic WA Aus
n N % n N % n N % n N % n N % n N %
E. faecalis all
2
334
0.6
1
381
0.3
0
145
0.0
2
76
2.6
1
265
0.4
6
1,201
0.5
Invasive
2
41
4.9
0
12
0.0
0
40
0.0
0
5
0.0
1
21
4.8
3
119
2.5
E. faecium all
18
41
43.9
3
18
16.7
31
57
54.4
10
23
43.5
0
31
0.0
62
170
36.5
Invasive
6
18
33.3
0
2
0.0
8
20
40.0
1
3
33.3
0
8
0.0
15
51
29.4

A total of 36.5% of E. faecium were vancomycin non-susceptible; a similar proportion to the 2009 survey (35.2%) but more than double that of the 2007 survey (15.4%, P<0.0001) (Figure 2). Vancomycin non-susceptible E. faecium were detected in all regions except Western Australia. Vancomycin non-susceptibility in the other regions ranged from 16.7% in Queensland to 54.4% in South Australia (Table 5). All of the vancomycin non-susceptible E. faecium were confirmed as VRE by PCR and were predominantly of the vanB genotype (61/62, 98.4%). In 2010, more than one third of urine, wound and blood E. faecium were vancomycin resistant. Trend data for E. faecium show there has been a marked increase in vancomycin resistance since 1995 (Figure 2). Vancomycin resistant E. faecium have occurred in all 5 regions over the 6 survey periods, with all regions except Western Australia showing increases in VRE over time (Figure 3).

Figure 2: Percentage of Enterococcus faecium non-susceptible to vancomycin, by survey year

Percentage of Enterococcus faecium non-susceptible to vancomycin, by survey year . A text description follows.

1995: invasive n=26, non-invasive n= 55, overall n=81.
1999: invasive n=30, non-invasive n= 152, overall n=182.
2003: invasive n=51, non-invasive n= 81, overall n=132.
2005: invasive n=43, non-invasive n= 137, overall n=180.
2007: invasive n=51, non-invasive n= 98, overall n=156.
2009: invasive n=48, non-invasive n= 165, overall n=213.
2010: invasive n=51, non-invasive n= 119, overall n=170

Text version of Figure 2 (TXT 1 KB)

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Figure 3: Regional location of vancomycin-resistant Enterococcus faecium, by survey year

Regional location of vancomycin-resistant Enterococcus faecium, by survey year . A text description follows.

* Tasmania did not contribute isolates in 2009 or 2010.

Text version of Figure 3 (TXT 1 KB)

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High level gentamicin (HLG) resistance was seen in E. faecalis (34.1%) and E. faecium (66.1%) (Table 6). Trend data (Figures 4 and 5) show significant increases for E. faecium from 1995 to 1999 (P<0.001) and again from 2003 to 2010 (P<0.0001). The increase from 2003 to 2010 was driven by resistance in non-invasive isolates as rates of resistance remained stable in invasive isolates during that time period despite year-to-year fluctuations (Figure 4) (P=0.09). HLG resistance in E. faecalis invasive and non-invasive isolates continued to increase until 2005 and then stabilised.

Table 6: Number of high level gentamicin resistant Enterococcus species isolated in Australia, 2010, by region
  NSW/ACT Qld SA Vic WA Aus
  n N % n N % n N % n N % n N % n N %
E. faecalis all
141
334
42.2
150
381
39.4
38
142
26.8
18
76
23.7
62
265
23.4
409
1,198
34.1
Invasive
11
41
26.8
4
12
33.3
15
37
40.5
1
5
20.0
12
21
57.1
43
116
37.1
E. faecium all
30
41
73.2
16
18
88.9
30
52
57.7
16
23
69.6
17
31
54.8
109
165
66.1
Invasive
7
18
38.9
1
2
50.0
10
19
52.6
2
3
66.7
3
8
37.5
23
50
46.0

Figure 4: Percentage of Enterococcus faecium resistant to high-level gentamicin, by survey year

Percentage of Enterococcus faecium resistant to high-level gentamicin, by survey year. A text description follows.

1995: invasive n=23, non-invasive n= 50, overall n=73.
1999: invasive n=30, non-invasive n= 152, overall n=182.
2003: invasive n=51, non-invasive n= 81, overall n=132.
2005: invasive n=43, non-invasive n= 137, overall n=180.
2007: invasive n=51, non-invasive n= 98, overall n=156.
2009: invasive n=48, non-invasive n= 165, overall n=213.
2010: invasive n=50, non-invasive n= 115, overall n=165.

Text version of Figure 4 (TXT 1 KB)

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Figure 5: Percentage of Enterococcus faecalis resistant to high-level gentamicin, by survey year

1995: invasive n=100, non-invasive n= 1109, overall n=1,211.
1999: invasive n=135, non-invasive n= 1,442, overall n=1577.
2003: invasive n=190, non-invasive n=1,432, overall n=1,622.
2005: invasive n=170, non-invasive n= 1,816, overall n=1,986.
2007: invasive n=143, non-invasive n= 1,333, overall n=1,520.
2009: invasive n=107, non-invasive n= 1005, overall n=1,112.
2010: invasive n=116, non-invasive n= 1082, overall n=1,198

Text version of Figure 5 (TXT 1 KB)

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In this survey, high level streptomycin resistance (HLS) was tested only in New South Wales/Australian Capital Territory and South Australia. HLS resistance is more common for E. faecium than E. faecalis (Table 7), similar to HLG resistance. The trend from 1995 to 2010 for E. faecium was for relatively stable resistance despite year to year fluctuations (Figures 6 and 7). In E. faecalis, the HLS decreased significantly from 1995 to 2003 but has been relatively stable since then with lower rates of expression than HLG (Figures 5 and 7).

Table 7: Number of high level streptomycin resistant Enterococcus isolated in Australia, 2010, by region
  NSW/ACT Qld SA Vic WA Aus
  n N %   n N %     n N %
E. faecalis all
6
73
8.2
3
37
8.1
9
110
8.2
Invasive
1
9
11.1
2
28
7.1
3
37
8.1
E. faecium all
2
7
28.6
12
25
48.0
14
32
43.8
Invasive
1
5
20.0
6
17
35.3
7
22
31.8

Figure 6: Percentage of Enterococcus faecium resistant to high-level streptomycin, by survey year

Percentage of Enterococcus faecium resistant to high-level streptomycin, by survey year . A text description follows.

1995: invasive n=19, non-invasive n= 44, overall n=63.
1999: invasive n=18, non-invasive n= 83, overall n=101.
2003: invasive n=30, non-invasive n= 44, overall n=74.
2005: invasive n=22, non-invasive n= 72, overall n=94.
2007: invasive n=25, non-invasive n= 43, overall n=73.
2009: invasive n=19, non-invasive n=53, overall n=72.
2010: invasive n=22, non-invasive n=10, overall n=32

Text version of Figure 6 (TXT 1 KB)

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Figure 7: Percentage of Enterococcus faecalis resistant to high-level streptomycin, by survey year

Percentage of Enterococcus faecalis resistant to high-level streptomycin, by survey year. A text description follows.

1995: invasive n=61, non-invasive n= 916, overall n=979.
1999: invasive n=92, non-invasive n= 916, overall n=1008.
2003: invasive n=102, non-invasive n=715, overall n=817.
2005: invasive n=80, non-invasive n= 1012, overall n=1092.
2007: invasive n=197, non-invasive n= 783, overall n=913.
2009: invasive n=38, non-invasive n= 229, overall n=267.
2010: invasive n=37, non-invasive n= 73, overall n=110.

Text version of Figure 7 (TXT 1 KB)

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Linezolid non-susceptibility was present in 5.8% of E. faecalis (up from 4.0% in 2009) and in 0.9% of E. faecium (down from 2.1% in 2009) (Table 8). Forty-six of the 48 non-susceptible isolates had an minimum inhibitory concentration (MIC) in the intermediate resistant category; only two were classified as resistant (MIC ≥8 mg/L). The 2 resistant isolates were E. faecalis from Queensland.

Table 8: Number of linezolid non-susceptible Enterococcus isolated in Australia, 2010, by region
  NSW/ACT Qld SA Vic WA Aus
  n N % n N % n N %   n N % n N %
E. faecalis all
18
334
5.4
28
341
7.3
1
90
1.1
0
5
0.0
47
810
5.8
Invasive
2
41
4.9
0
12
0.0
1
32
3.1
0
5
0.0
3
90
3.3
E. faecium all
1
41
2.4
0
18
0.0
0
52
0.0
0
2
0.0
1
113
0.9
Invasive
1
18
5.6
0
2
0.0
0
18
0.0
0
1
0.0
1
39
2.6

E. faecalis are intrinsically resistant to quinupristin/dalfopristin. Only 9.4% of the E. faecium were non-susceptible (down from 21.9% in 2009) with four of the five non-susceptible isolates having an MIC in the resistant range (MIC >2 mg/L). All quinupristin/dalfopristin non-susceptible cases were identified in isolates originating in New South Wales/Australian Capital Territory, as was the case in 2007 and 2009 (Table 9).

Table 9: Number of quinupristin/dalfopristin non-susceptible Enterococcus isolated in Australia, 2010, by region
  NSW/ACT Qld SA Vic WA Aus
  n N % n N % n N %   n N % n N %
E. faecalis all
246
258
95.3
154
177
87.0
2
3
66.7
5
5
100.0
407
443
91.9
Invasive
33
34
97.1
6
6
100
0
1
0.0
5
5
100.0
44
46
95.7
E. faecium all
5
33
28.1
0
16
0.0
0
2
0.0
0
2
0.0
5
53
9.4
Invasive
4
15
26.7
0
2
0.0
0
1
0.0
4
18
22.2

Cross resistance to other agents was examined in vancomycin resistant isolates of enterococci (Table 10). Resistance to ampicillin and high levels of gentamicin was more common in vancomycin resistant E. faecium. Resistance to high levels of streptomycin, quinupristin/dalfopristin and linezolid was similar for VRE and non-VRE (P>0.05).

Table 10: Cross resistant Enterococcus isolated in Australia, 2010
    Ampicillin Gentamicin Streptomycin Linezolid Quinupristin/dalfopristin
    n N % n N % n N % n N % n N %
VRE Vancomycin resistant enterococci
E. faecalis
Not VRE
0
1,198
0.0
407
1,195
34.1
9
110
8.2
47
809
5.8
407
443
91.9
VRE
0
3
0.0
2
3
66.7
0
1
0.0
E. faecium
Not VRE
82
107
76.6
58
107
54.2
5
16
31.3
1
62
1.6
4
34
11.8
VRE
63
63
100.0
51
58
87.9
9
16
56.3
0
51
0.0
1
19
5.3

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Vancomycin resistant enterococci characterisation

Three (100%) vanB E. faecalis, 1 (100%) vanA E. faecium and 59/62 (95%) vanB E. faecium isolates were available for molecular typing.

Two of the vanB E. faecalis were classified as pulsotype A and one was classified as pulsotype B (Table 11). The vanA E. faecium was a pulsotype C and sequence type (ST) 117. Six pulsotypes and 4 STs were identified in the vanB E. faecium. ST203 was the most common ST (comprising 81% of vanB E. faecium) and was found in all regions that reported VRE. ST341 was found only in New South Wales/Australian Capital Territory, ST414 only in South Australia and Victoria and ST17 only in Queensland (Figure 8). The E. faecium isolates belonged to CC 17.

Table 11: Molecular characterisation of vancomycin-resistant enterococci isolated in Australia, 2010
van Gene Species PFGE MLST NSW/ACT Qld SA Vic
vanB
E. faecalis
A
n.d.
2
vanB
E. faecalis
B
n.d.
1
vanA
E. faecium
C
ST117
1
vanB
E. faecium
D
ST203
5
1
28
9
vanB
E. faecium
E
ST203
2
1
vanB
E. faecium
F
ST203
2
vanB
E. faecium
G
ST341
8
vanB
E. faecium
H
ST414
1
1
vanB
E. faecium
I
ST17
1
Total
 
18
3
30
12

Figure 8: Distribution of vanB Enterococcus faecium multi-locus sequence types, by region

Distribution of vanB Enterococcus faecium multi-locus sequence types, by region. A text description follows.

Text version of Figure 8 (TXT 1 KB)

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Discussion

It is clear from this study and the examination of trends over the last 15 years that antimicrobial resistance has increased significantly in E. faecium. Treatment options for this species are becoming ever more limited as resistance to ampicillin and other penicillins is now very frequent, and glycopeptide resistance is increasing. In some instances only expensive and/or potentially toxic treatment options such as linezolid, quinupristin-dalfopristin, tigecycline or daptomycin are available.

Ampicillin resistance in E. faecuim is the result of changes in penicillin-binding proteins. This is also true for most isolates of E. faecalis, although ß-lactamase production has been seen rarely (3 known instances in Australia in the last 2 decades).21 This survey has shown that ampicillin resistance is now usual in E. faecium but is rare in E. faecalis. Ampicillin resistance in enterococci presents considerable challenges when infections are serious, as the isolates will not be susceptible to any ß-lactam antibiotic, and the drug of choice becomes vancomycin, which is only slowly bactericidal. Further, for endocarditis the combination of vancomycin with an aminoglycoside creates significant toxicity problems.

Unfortunately vancomycin resistance in enterococci has increased in Australia particularly over the past 5 years. It has been seen in all states and territories although rates in each region vary considerably. It is widely recognised that rates of colonisation far exceed the rates of infection with VRE, and thus the amount of VRE seen in this survey does not truly reflect the size of the VRE reservoir. The survey results are also consistent with the previous Australian experience that the dominant type of resistance is encoded by the vanB complex4,22 in contrast with the situation in Europe and the USA where vanA dominates. Vancomycin-resistant isolates causing serious infection are very challenging to treat. The choices are linezolid, quinupristin-dalfopristin, tigecycline and daptomycin. Each of these agents presents its own challenges for treatment.

High-level resistance to gentamicin has increased in recent years after apparently reaching a plateau in the early 2000s. This greatly compromises the ability to treat enterococcal endocarditis effectively.

Molecular characterisation of the VRE isolates in this study has revealed that E. faecium belonging to CC17 are now established in Australia. CC17, including ST203 and ST414 both found in this study are considered to be hospital-associated clones and have been responsible for outbreaks in several countries including Australia.9,23,24 Containing additional genetic content thought to assist in survival and spread in the hospital environment, CC17 poses a challenge for hospital infection control as standard measures may not be enough to control spread in the long term. Extensive screening of patients, confinement of colonised or infected patients, antimicrobial restrictions and additional cleaning protocols are often required to reduce VRE in the hospital environment.7,10,24,25 In addition, VRE belonging to CC17 are causing severe infections, in particular bacteraemia, in increasing numbers.9,23

The data provided by this survey will be useful in informing microbiologists, infectious diseases physicians and infection control practitioners about the increasing importance of VRE in Australia. It will help to guide prescribers treating presumptive enterococcal infections in empirical choices; e.g. ampicillin/amoxycillin still being active against the vast majority of isolates of E. faecalis when treating infections caused by this organism. Finally, the data will assist regulators and the pharmaceutical industry on the growing importance of VRE in Australia, and guide decision makers about controls that might be required on the prescribing of reserve antibiotics.

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Limitations of the study

The enterococci in this study were tested against a limited range of antimicrobials. In part, this was driven by the presence of intrinsic resistances in this genus. Enterococci are intrinsically resistant to cephalosporins, macrolides, lincosamides and conventional therapeutic levels of aminoglycosides when used alone. Other agents which are usually active against enterococci in urinary tract infection, including fluoroquinolones and nitrofurantoin, were not examined, largely because few clinical treatment problems have been encountered up to now with enterococcal urinary tract infection.

It is likely that the number of wound isolates in this study under-represents the true proportion, as it is common for microbiology laboratories not to proceed with identification or susceptibility testing of enterococci when they are found in mixed cultures from wound infections.

Only a maximum of 100 isolates were collected per institution, therefore only a portion of actual clinical isolates are represented.

There have been changes in participating laboratories in the AGAR Enterococcus surveys over time from 1995 through to 2010 with the more recent inclusion of a number of private pathology laboratories. This may have influenced trend data.

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Acknowledgements

This study was primarily funded by a grant from the Australian Government Department of Health.

We gratefully acknowledge Hui-leen Tan, Lynne Wilson, Yi-Kong Chew and Denise Daley from the Department of Microbiology Infectious Diseases, PathWest Laboratory Medicine – WA Royal Perth Hospital; Tam Le and Ka Yan Wong from the Australian Collaborating Centre for Enterococcus and Staphylococcus Species (ACCESS) Typing and Research; and the WA Genome Resource Centre, Department of Clinical Immunology and Biochemical Genetics, Royal Perth Hospital for the molecular typing of MRSA.

Contributing members of AGAR:

Australian Capital Territory

Peter Collignon and Susan Bradbury, The Canberra Hospital

New South Wales

Tom Gottlieb and Graham Robertson, Concord Hospital

James Branley and Donna Barbaro, Nepean Hospital

Iain Gosbell and Annabelle LeCordier, South West Area Pathology Service

Queensland

Graeme Nimmo and Narelle George, Pathology Queensland

Chris Coulter and Sonali Coulter, Pathology Queensland Prince Charles Hospital

Joan Faoagali and Joel Douglas, Pathology Queensland Princess Alexandra Hospital

Jenny Robson and Georgia Peachey, Sullivan Nicolaides Pathology

South Australia

Kelly Papanoum and Nicholas Wells, SA Pathology, Flinders Medical Centre

Morgyn Warner and Fleur Manno, SA Pathology, Royal Adelaide Hospital

John Turnidge and Jan Bell, SA, Pathology, Women’s and Children’s Hospital

Victoria

Benjamin Howden and Peter Ward, Austin Hospital

Western Australia

Barbara Henderson and Ronan Murray, PathWest Laboratory Medicine, WA Queen Elizabeth II Hospital

Keryn Christiansen and Geoffrey Coombs, PathWest Laboratory Medicine, WA Royal Perth Hospital

Victoria D’Abrera and Sindy Budalich, St John of God Pathology

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Author details

Dr Geoffrey W Coombs1,2

Ms Julie C Pearson1,2

Prof Keryn Christiansen1,2

Associate Professor Thomas Gottlieb3

Ms Jan M Bell4

Ms Narelle George5

Prof John D Turnidge4

  1. Australian Collaborating Centre for Enterococcus and Staphylococcus Species (ACCESS) Typing and Research, School of Biomedical Sciences, Curtin University, Perth, Western Australia
  2. Department of Microbiology and Infectious Diseases, PathWest Laboratory Medicine, WA, Royal Perth Hospital, Perth, Western Australia
  3. Department of Microbiology and Infectious Diseases, Concord, Concord, New South Wales
  4. SA Pathology (Women’s and Children’s Hospital), Department of Microbiology and Infectious Diseases, North Adelaide, South Australia
  5. Division of Microbiology, Pathology Queensland, Herston Hospitals Campus, Herston, Brisbane, Queensland

Corresponding author: Dr Geoffrey Coombs, Australian Collaborating Centre for Enterococcus and Staphylococcus Species (ACCESS) Typing and Research, School of Biomedical Sciences, Curtin University, PERTH WA 8000. Telephone: +61 8 9224 2446. Facsimile: +61 8 9224 1989. Email: Geoff.Coombs@curtin.edu.au

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References

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