Principles and Practice of Clinical Bacteriology Second Edition - Free

36 ORAL AND OTHER NON-β-HAEMOLYTIC STREPTOCOCCI
isolates, 5 of which were found to be resistant to cefpirome and 12 to
cefepime. How widespread this phenomenon of penicillin resistance
was is difficult to ascertain, since a study from the opposite side of the
Iberian Peninsula (Lugo), although admittedly based on a small
collection of anginosus group bacteraemic strains (1988–1994), found
all to be sensitive to penicillin and erythromycin (Casariego et al.,
1996). More recent evidence from central Spain (Madrid) also
reported a high proportion of non-β-haemolytic streptococci isolated
from blood culture between 1998 and 2001 to be to erythromycin
(42%), tetracycline (35%) and clindamycin (25%) resistant
(Rodriguez-Avial et al., 2003). Researchers also found evidence of
cross-resistance between erythromycin and tetracycline, with resistance
to one agent being associated with the occurrence of the other. Also of
note is that 3 of the 111 isolates tested by Rodriguez-Avial et al.
(2003) were found to be resistant to the streptogramin quinupristin/
dalfopristin.
National surveillance data from England and Wales also point to
a similar increase in resistant phenotypes (PHLS, 2001, 2002; HPA,
2003a). The numbers of bacteraemic strains reported through routine
surveillance as having reduced susceptibility to penicillin increased
between 2000 and 2002 for all non-β-haemolytic streptococcal
groups, with yearly increases for S. mitis group being particularly
pronounced, stepping from 9 reports in 2000 to 33 in 2001 to 73 in
2003. Of the multitude of species that constitute the non-β-haemolytic
streptococci, S. mitis, S. sanguis and S. oralis, have been described as
most frequently exhibiting reduced susceptibility to penicillin
(Alcaide et al., 1995; Mouton et al., 1997; de Azavedo et al., 1999;
Wisplinghoff etal., 1999; Gershon etal., 2002). Analysis of streptococcal
isolates submitted to the UK national reference laboratories between
1996 and 2000, originating from patients with endocarditis, found one
in four of S. mitis isolates to have reduced susceptibility to penicillin
(MIC >0.125 mg/l), with one in seven of S. sanguis and one in eight
of S. oralis isolates also showing reduced penicillin susceptibility
(Johnson et al., 2001). Tetracycline and erythromycin resistance
similarly increased over this period, with S. mitis group showing highest
frequency of erythromycin resistance and S. bovis group showing the
highest frequency of tetracycline resistance (HPA, 2003a). In the light
of the common target of activity for streptogramins and macrolides,
studies have found evidence of cross-resistance between erythromycin
and quinupristin/dalfopristin (Mouton et al., 1997).
Similarly worrying reports of antibiotic resistance in non-β-haemolytic
streptococci causing bacteraemia and/or endocarditis emerged from
other parts of Europe during this period. Although frequently based on
small collections of strains, studies in France, Germany, Sweden and
Denmark documented substantial proportions of non-β-haemolytic
streptococcal strains as having decreased sensitivity to erythromycin
and/or penicillin (Wisplinghoff et al., 1999; Lefort et al., 2002; Westling
et al., 2002). Pooled data for 1997–1998 from European countries
participating in the SENTRY Antimicrobial Surveillance Programme
found 39% of non-β-haemolytic streptococci to be nonsusceptible to
penicillin, whereas 30% exhibited reduced susceptibility to erythromycin
(Fluit et al., 2000).
Interestingly, two studies from the Far East both showed high levels
of macrolide resistance in bacteraemic isolates. Sixty-three per cent of
non-β-haemolytic streptococcal strains collection from Taiwan were
reported as having reduced susceptibility to erythromycin and
clarithromycin, although all strains were sensitive to penicillin,
cefotaxime, imipenem, vancomycin and teicoplanin (Teng et al.,
2001). Similarly, in Hong Kong, characterization of bacteraemic
S. bovis isolates showed all to be sensitive to penicillin, cephalothin
and vancomycin, whereas 65% had reduced susceptibility to erythromycin.
Forty-one per cent also showed reduced susceptibility to
clindamycin (Lee et al., 2003). Subsequent reports from participants
in the Asia-Pacific region SENTRY Antimicrobial Surveillance
Programme, which includes Hong Kong and Taiwan, documented a
frequency of penicillin and erythromycin resistance in non-β-haemolytic
streptococci more akin to that documented in Europe and the Americas,
possibly due to the effect of pooling data from many countries,
including Australia and South Africa (Gordon et al., 2002).
Research from North America began to show a similar pattern of
emerging penicillin resistance as that seen in Europe among nonβ-haemolytic
streptococci. Studies conducted in the United States
during the mid-1990s began to report levels of penicillin tolerance
(nonsusceptibility) at between 39% and 44% of isolates (Doern et al.,
1996; Pfaller et al., 1997). Cases of quinupristin/dalfopristin-resistant
S. mitis have also been uncovered in the United States through the
SENTRY Antimicrobial Surveillance Programme (Kugler et al., 2000).
Similarly, research from the Canadian Bacterial Surveillance Network
found levels of penicillin resistance increasing from the mid-1990s
(28% of blood culture isolates) to 2000 (37%) (de Azavedo et al.,
1999; Gershon et al., 2002). Bigger increases still were seen in the
frequency of isolates nonsusceptible to erythromycin, from 29% to
42%, with frequency of reduced clindamycin susceptibility also
increasing from 4% to 10%.
Following the mottled array of reports describing the emergence of
resistant phenotypes over 1990s, more recent descriptions from the
SENTRY global antimicrobial surveillance network suggest that some
degree of uniformity of antibiotic resistance may now exist among
non-β-haemolytic streptococci causing blood stream infection
(Gordon et al., 2002). The increase in resistance in these important
pathogens presents a challenge to the treatment and control of infections
and warrants further vigilance, especially in the light of the first
description of a naturally occurring vancomycin-resistant S. bovis
strain (Poyart et al., 1997).
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