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Long term surveillance of resistance
in Neisseria gonorrhoeae in the Netherlands
Bert van Klingeren PhD, Mirjam Dessens, Marga van Santen
National Institute of Public Health & Environmental Protection, Bilthoven, Netherlands
Antibiotic resistance in gonococci is monitored in the Netherlands
since the first reports on penicillinase producing strains (PPNG) in 1976 (1). During the period 1977 to 1990 almost
all PPNG isolates in this country were send to our laboratory for quantitative susceptibility testing, auxotyping,
serotyping and plasmid characterisation. The prevalence of PPNG among gonococci was calculated based on data from
annual inquiries among the isolating laboratories.
In the period 1978-79 the PPNG frequency increased from 1% to 3%
followed by a sharp rise in the early eighties. In 1982 11% of the approximately 13000 isolates were PPNG. This
figure stabi-lised around 7 to 8% during the next three years. From 1985 onwards the incidence of gonorrhoea dramatically
decreased but the portion of PPNG increased. This is shown in table 1 in which the number of reported isolates
and PPNG percentages (annual inquiry), as well as the number of cases of gonor-rhoea reported by physicians to
the Ministry of Health (obligatory) are depicted.
This table illustrates that the number of gonococcal isola-tes -
and the virtually identical number of reported cases of gonorrhoea - dropped from roughly 12000 in 1985 to 3000
in 1988 and following years. The PPNG frequency increased in this period from 7% to 30% in 1990 followed by a sharp
decrease to 12% in 1992.
The three major cities Amsterdam, Rotterdam and The Hague contribute
for 70-80% to the total number of gonorrhoea cases in this country. In figure 1 the rise and fall of PPNG in these
centres during the last decade is shown.
Typing of PPNG
To obtain insight in the variety of circulating strains all PPNG isolates were tested for plasmid pattern and auxotype
since the early eighties.(2) Serotyping according to Knapp et al., using a panel of 12 mono-clonal antibodies to
gonococcal outer membrane protein 1 (Syva Co., CA) was introduced in 1987.(3)
Plasmid patterns
Initially two types of penicillinase encoding plasmids were found in PPNG isolates, the 3.2 Mdal and the 4.5 Mdal
plas-mid. Together with the presence or absence of the 24.5 Mdal so cal-led transfer plasmid four patterns were
distinguished. Since 1986 a 2.9 Mdal plasmid was increasingly found, always together with the 24.5 Mdal plasmid.
Moreover a transfer plasmid with a slightly increased molecular weight (25.2 Mdal) appeared, for the first time
in 1985, reaching a peak in 1989. This plasmid encodes for tetracycline resistance by harbouring the tetM determinant
(see below).
In able 2 the prevalence of the different plasmid patterns since
1986 is summarized. Apparently a major shift took place from dominance of the 4.5 Mdal to the smaller penicillinase
plasmids. In the mean time all pen`ase plasmids have been found in tetracycline resistant strains, carrying the
25.2 Mdal plas-mid.
Auxotypes and serovars
Auxanographic typing alone yields very limited data for epide-miological studies since the majority of the strains
belonged to only two auxotypes, i.e. non requiring (NR) and proline requiring (Pro-) strains. However, combination
with serovar pat-terns yields so called A/S classes with significant discri-minatory power. Since 1988 we have
typed 1438 P-PNG isolates in this way; 123 different A/S classes were found. The most predominant types are shown
in table 3. Not-withstan-ding a great diversity of classes, a limited number appeared to dominate, in particular
NR/1B-1 and NR/1B-3. For this reason this typing system has limited value as an epidemiological tool. In special
cases however it has shown its merits as is illustrated with the following examples.
Outbreak of tetracycline resistant PPNG
Plasmid encoded high level resistance to tetracycline in gono-cocci (TRNG) was first described by Morse et al.(4)
This trait was encountered as early as 1985 in a small outbreak of PPNG in the Hague comprising 12 patients. All
TRNG/PPNG isola-tes involved belonged to the same A/S class (Pro-/1B-4).(5) No TRNG were found among 833 PPNG in
1986. In the next year the preva-lence of tetracycline resistant PPNG carrying the 25.2 Mdal plasmid started to
increase going from 2% in 1987 to 9% in 1988 and exploding to 40% (of 689 PPNG) in 1989.(6) During the peak of
this outbreak (first half of that year) nearly 80% of the PPNG in the Rotterdam/the Hague area were TRNG. The distribution
of A/S classes among these TRNG/PPNG is presented in table 4. It presumably illustrates the clonal spread of a
limited number of strains followed by the transfer of the tetM determinant to gonococci belonging to different
A/S classes.
In 1990 the TRNG frequency among PPNG dropped to 12%. A subsequent
epidemiological inquiry revealed that belonging to a particular ethnic community was the most important risk factor
to acquire gonorrhoea caused by these strains.
Molecular studies carried out by Gascoyne et al. showed that the
Dutch TRNG plasmid differed from the American plasmid, indicating at least two evolutional events.(7)
Surveillance after 1990
Since 1991 we monitor the resistance in gono-cocci in the Netherlands by testing all isolates from 5 sentinel centres
in the three major cities during one month quarterly. In table 5 the annual number of isolates and the prevalence
of PPNG, TRNG and TRNG/PPNG among them is depicted. Obviously the frequ-ency of PPNG remains high and actually
doubled last year. High level resistance to tetracycline is fairly constant around 7 to 8% and combined resistance
(TRNG/PPNG) is now found in 3% of all gonococcal isolates. Most of the latter strains belong to a great variety
of A/S classes indicating multiple introductions from abroad or frequent transfer of resistance plasmids between
strains of different A/S classes.
Susceptibility to other antibiotics
Since penicillinase producers are frequently encountered, the newer cefalosporins and the fluoroquinolones are
considered the drugs of choice for treating gonorrhoea. The suscep-tibility of all isolates send to our laboratory
is determined for ceftriaxone and ciprofloxacin. The distribution of MIC values for these drugs among PPNG and
non-PPNG isolated in the period 1992-93 is presented in figure 2. These data indicate that in general PPNG are
less susceptible to both antibiotics than non-PPNG. However, no strains have been found yet that were not inhibited
by 0.03 mg/l ceftriaxone. On the other hand 3%(n=7) of the PPNG isolates and 0.8%(n=8) of the non-PPNG in this
period were not inhibited by 0.03 mg/l ciprofloxacin; the highest MIC was 1 mg/l found for one isolate. Since the
failure rate of ciprofloxacin treatment of gonococcal infec-tions caused by such strains is increased, continuous
monitor-ing is indicated.(8)
References
- Klingeren B van, Embden JDA van, Wijngaarden LJ van.
Sur-veil-lance of penicillinase-producing gonococci in the Netherlands. Cur Chemother Infect Dis, Proceedings of
19th ICAAC, ASM 1980; 2:1258-60.
- Ansink-Schipper MC, Klingeren B van, Huikeshoven MH,
Woudstra RK, Dessens-Kroon M, Wijngaarden LJ van. Epidemiology of PPNG infections in the Netherlands; Analysis
by auxanographic typing and plasmid iden-tification. Br J Vener Dis 1984; 60:141-6.
- Knapp JS, Tam MR, Nowinski RC, Holmes KK, Sandström
EG. Serological classification of Neisseria gonorrhoeae with use of monoclonal antibodies to gonococcal outer membrane
protein I. J of Infect Dis 1984; 150:44-8.
- Morse SAS, Johnson SR, Biddle JW, Roberts MC. High-level
tetracycline resistance in Neisseria gonorrhoeae is result of acquisition of streptococcal tetM determinant. Antimicrob
Agents Chemother 1986; 30:664-70.
- Roberts MC, Wagenvoort JHT, Klingeren B van, Knapp
JS. TetM and ß-lactamase containing Neisseria gonorrhoeae (tetracycline resistant and penicillinase producing)
in the Netherlands. Antimicrob Agents Chemother 1988; 32:158.
- Klingeren B van, Dessens-Kroon M, Verheuvel M. Increased
tetracycline resistance in gonococci in the Netherlands. The Lancet 1989, 1278.
- Gascoyne DM, Heritage J, Hawkey PM, Turner A, Klingeren
B van. Molecular evolution of tetracycline-resistance plasmids carrying TetM found in Neisseria gonorrhoeae from
different countries. J Antimicrob Chemother 1991; 28:173-83.
- Easmon CSF. The changing pattern of antibiotic resistance
of Neisseria gonorrhoeae. Genitourin Med 1990; 65:55-6.
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