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Drug-resistant Streptococcus pneumoniae: the beginning of the end for many antibiotics?

Peter J Collignon, Jan M Bell and the AGAR
Med J Aust 1996; 164 (2): 64-67.
Published online: 15 January 1996

Drug-resistant Streptococcus pneumoniae: the beginning of the end for many antibiotics?

Peter J Collignon and Jan M Bell, on behalf of the Australian Group on Antimicrobial Resistance (AGAR)*

Abstract - Introduction - Methods - Antibiotic sensitivity testing - Statistical analysis - Results - Discussion - Acknowledgements - References - Authors' details

- ©MJA1997


 

Abstract

Objective: To determine the levels of antibiotic resistance in Streptococcus pneumoniae in Australia.
Design: Prospective, Australia-wide, laboratory-based survey.
Setting: 27 hospital and private laboratories around Australia, from January 1994 to August 1995.
Subjects: First 100 patients with clinically significant isolates of S. pneumoniae at each laboratory.
Outcome measures: Resistance to penicillin (determined from penicillin minimum inhibitory concentration [MIC] measured by the Etest), erythromycin, trimethoprim-sulfamethoxazole, tetracycline, chloramphenicol, cefotaxime and ceftriaxone.
Results: A total of 2396 isolates were tested (including 537 invasive isolates and 740 from children). Penicillin resistance was seen in 161 isolates (6.7%), including 17 with high level resistance. Penicillin resistance rates were significantly lower in invasive than in non-invasive strains (3.7% versus 7.6%; odds ratio [OR], 0.47; 95% confidence interval [CI], 0.28-0.77; P = 0.001). There was no significant difference in penicillin resistance rates between children ( < 15 years) and adults (7.3% versus 6.5%; OR, 1.14; 95% CI, 0.80-1.63; P = 0.47). Resistance rates were higher for most other antibiotics than for penicillin (chloramphenicol, 6%; erythromycin, 11%; tetracycline, 15%; and trimethoprim-sulfamethoxazole, 42%). No high level resistance was seen to third generation cephalosporins, but 17 of 109 penicillin-resistant isolates tested (16%) displayed intermediate resistance to cefotaxime. Rates of antibiotic resistance varied between States, with the lowest rates in Tasmania.
Conclusions: Antibiotic resistance levels in S. pneumoniae are increasing in Australia and high level penicillin resistance is being encountered for the first time (including in invasive strains). This will lead to an increasing number of therapeutic dilemmas and possible therapeutic failures, especially important in meningitis.

MJA 1996; 164: 64  

Introduction

The pneumococcus (Streptococcus pneumoniae) continues to be a common cause of serious and life-threatening infections, including pneumonia, bacteraemia and meningitis. It is also a frequent cause of respiratory tract infections, such as otitis media and sinusitis.1-4 A major advance was made in the treatment of these infections with the introduction of penicillin 50 years ago. Until relatively recently, pneumococci were considered so uniformly sensitive to penicillin (with minimum inhibitory concentrations [MICs] < 0.02 mg/L) that sensitivity tests were usually not performed.

It was from Australia in 1967 that the first clinically significant isolate of a penicillin-resistant pneumococcus was reported.5 However, penicillin resistance was not a major clinical problem in this country, although it caused major problems elsewhere, particularly in Papua New Guinea and South Africa.1-3 In the late 1970s and the 1980s, rates of resistance (including multiple resistance) increased in Western countries, particularly in Spain (with resistance levels of 50%).1,2,3 A recent United States study found 25% of invasive S. pneumoniae isolates were penicillin-resistant.6 Resistance rates are usually higher in children, and the distribution of resistance varies within countries and population groups.1,2,3,6

In an Australia-wide study of over 1800 isolates of S. pneumoniae in 1989, we found that only 1% were penicillin-resistant,7 a lower rate than in most other Western countries. However, some communities (especially Australian Aboriginals) have relatively high rates of resistance.8

Because of the worldwide increase in resistance to many antibiotics and the implications of penicillin resistance in S. pneumoniae for treatment of life-threatening conditions (particularly meningitis), we undertook a further study of resistance to penicillin and other commonly used antibiotics in clinically significant S. pneumoniae isolates from both the community and hospitals.  

Methods

Twenty-seven hospital and private laboratories from around Australia parti cipated. From January 1994, each laboratory tested the first 100 consecutive clinically significant isolates. The rate of collection varied from 5 to 20 months, with all laboratories filling their quota in August 1995.

Patients' sex, age, specimen site and inpatient or outpatient status were recorded prospectively.

Clinically significant isolates were defined as those isolated either from normally sterile sites (e.g., cerebrospinal fluid and blood [invasive isolates]) or from specimens that made contact with mucosal surfaces (e.g., sputum) if they were associated with an increased white cell count on gram staining and would normally have been reported as clinically significant. Throat or surveillance swabs were excluded, as were duplicates of clinically significant isolates.

S. pneumoniae was identified by colonial morphology, a -haemolysis on blood agar plates, susceptibility to optochin and/or bile solubility.  

Antibiotic sensitivity testing

Isolates were tested for susceptibility to penicillin, erythromycin, trimethoprim-sulfamethoxazole, tetracycline and chloramphenicol by the standardised routine method of each laboratory. Methods included disc diffusion with either National Committee for Clinical Laboratory Standards (NCCLS)9 (14 laboratories) or Calibrated Dichotomous Sensitivity (CDS)10,11 (7 laboratories); agar dilution12 with either Isosensitest agar (Oxoid) (2 labora tories) or Mueller-Hinton agar (3 lab oratories); and the ATB system (BioMerieux sa , Marcy-l'Etoile, France) (1 laboratory).

The MIC of penicillin was also determined for each isolate by the Etest on Mueller-Hinton agar supplemented with 5% blood;13,14 plates were incubated at 35¡C in 5% CO 2 for 20-24 hours. 14 The interpretive criteria of the NCCLS15 were used for susceptibility categorisation of Etest values (susceptible, MIC < 0.06 mg/L; intermediate resistance, MIC = 0.125-1 mg/L; and high level resistance, MIC > > 2 mg/L).

For the study, antibiotic resistance was defined as decreased susceptibility (both intermediate and high level resistance),6,12 and multidrug resistance as decreased susceptibility to two or more of the antibiotic agents tested.

Isolates from normally sterile sites and those that appeared resistant to penicillin or chloramphenicol by routine susceptibility testing or had penicillin MICs > > 0.047 mg/L were forwarded to Monash Medical Centre for further susceptibility testing: Etest strips were used to determine cefotaxime and ceftriaxone MICs.  

Statistical analysis

Fisher's two-tailed exact test was used to calculate P values. Calculations were performed with True Epistat software.16  

Results

A total of 2396 isolates from different patients were tested. The average age of the patients was 41.6 years (range, < 1 day to 98 years); 32% were children ( < 15 years) and 60% were male.

The percentage of penicillin-resistant isolates from each specimen site is shown in Box 1; the overall rate of penicillin resistance was 6.7%, with rates in individual laboratories ranging from 0 to 13%. High level resistance was seen in 17 isolates, including two from normally sterile sites.


The rate of penicillin resistance was significantly lower among invasive isolates than among non-invasive isolates (3.7% versus 7.6%; odds ratio [OR], 0.47; 95% confidence interval [CI], 0.28-0.77; P = 0.001) (Box 2). The rate of penicillin resistance was slightly higher among children ( < 15 years) than among adults, but the difference was not statistically significant (7.3% versus 6.5%; OR, 1.14; 95% CI, 0.8-1.63; P = 0.47).


Resistance to antibiotics other than penicillin was common (Boxes 2 and 3). Rates varied around Australia, with the lowest rates for nearly all antibiotics in Tasmania and the highest in the eastern States, particularly Queensland and New South Wales. The rate of penicillin resistance was highest in South Australia. Very high levels of resistance were seen for trimethoprim-sulfamethoxazole (29%-52%).


All five antibiotics were tested on 1895 isolates; 267 (14%) were multi resistant, with 159 (8%) resistant to three or more antibiotics and 31 (1.6%) to all five (Box 3). Of 124 penicillin-resistant isolates tested, 72 (58%) were resistant to three or more non--lactam agents; 40% were resistant to chloramphenicol; 52% to erythromycin; 64% to tetracycline; and 78% to trimethoprim-sulfamethoxazole. Of the 1771 pencillin-susceptible isolates, 101 (6%) were resistant to three or more non--lactam agents; 3% to chloramphenicol; 8% to erythromycin; 12% to tetracycline; and 39% to trimethoprim- sulfamethoxazole .

Of 109 penicillin-resistant isolates tested with cefotaxime, 17 (16%) had intermediate resistance (MIC, 1 mg/L). These comprised 12 of 13 isolates with high-level penicillin resistance and 5 of 96 with intermediate penicillin resistance. Only three of the 109 isolates had intermediate resistance to ceftriaxone (all with high-level penicillin resistance).  

Discussion

We found that the level of penicillin resistance among S. pneumoniae isolates was six times higher than that found in 1989 in the only other large multicentre Australian study,7 but fortunately it was still lower than in most other countries. Penicillin resistance rates are very high in Third World countries, and in some areas of Western Europe and the USA.1-3 However, the rate of rise in resistance in Australia appears very similar to that seen in the early 1980s in countries such as Spain1-3 and in the early 1990s in the United States;6 there, only 0.02% of isolates nationally were penicillin-resistant in the early 1980s and still only 1.3% in 1992,6 but a recent study found a rate of 25%, with much higher rates in some subgroups (e.g., 40% in white children). Of equal concern was that 3% of isolates had high level resistance to both penicillin and third generation cephalosporins.6 Over the next few years, we are likely to see similar rates of resistance developing in Australia.

The finding of high level penicillin resistance among S. pneumoniae isolates in Australia is of particular concern; in meningitis caused by organisms with any level of penicillin resistance, penicillin treatment is likely to fail.1-3,17,18 Penicillin resistance has consequences for other related drugs, as in S. pneumoniae it is not due to -lactamase production (as in Staphylococcus aureus ), but to changes in the target for penicillin (the penicillin-binding proteins).1,2,19 This change increases the MICs for all -lactams, including the third generation cephalosporins.1,2,19 However, the levels of third generation cephalosporins achieved in cerebrospinal fluid are still high enough to eradicate organisms with intermediate penicillin resistance.1-3,18 Alternative regimens include combination therapy with vancomycin, third generation cephalosporins and rifampicin, as well as newer agents such as meropenem, teicoplanin and quinolones (under investigation),1 but none has been adequately evaluated.

Of even greater concern are the implications of the rapid rise in resistance to third generation cephalosporins noted in the United States. Primary resistance to these drugs is less frequent than to penicillin, but requires less genetic change.1,19 In some areas up to 27% of penicillin-resistant pneumococci have high level resistance to cefotaxime.1 This leads to therapeutic failure of these agents, yet they are the main treatment for the increasingly common intermediate penicillin-resistant strains. No high level cefotaxime-resistant strains were seen in our study or have been reported in Australia, to our knowledge. However, given the worldwide spread of resistant pneumococci in the recent past, they will inevitably be seen soon in Australia and leave us with major therapeutic dilemmas in the treatment of meningitis.

In life-threatening situations other than meningitis (e.g., bacteraemia), high dose intravenous penicillin appears sufficient to eradicate organisms with intermediate resistance, as drug levels achievable in serum are still much higher than the MIC.1,2,3 There is, however, controversy, and many recommend use of either cefotaxime or ceftriaxone.1,3 For organisms with high level resistance, the most appropriate agent is unclear. However, we would favour vancomycin.

In non-life-threatening infections with penicillin-resistant pneumococci, the most appropriate antibiotics are less clear. In otitis media, amoxycillin still appears the best choice,20,21 as drug levels achieved in the middle ear can still exceed the MICs of strains with intermediate resistance (although higher doses may be needed). Other oral agents available in Australia for use in children (cefaclor, trimethoprim, erythromycin and cefpodoxime) do not reach adequate levels to eradicate resistant isolates.20,21 Third generation cephalosporins, such as ceftriaxone, are active, but their parenteral route is likely to preclude their use. Combining clavulanic acid with amoxycillin is no advantage, as the resistance is not due to -lactamase. For high level penicillin-resistant isolates there does not appear to be a satisfactory oral agent.

The reasons for the increasing resistance in S. pneumoniae worldwide are not completely understood, although antibiotic pressure appears to be a major factor.1 A few resistant clones were shown to have spread from one continent to others (e.g., from Spain to the United States and Iceland) and then through the local population, undergoing minor genetic changes in the process.1,3,19 The pneumococcus can acquire DNA molecules from other bacteria that probably include viridans group streptococci (e.g., Streptococcus mitis), which form part of the normal flora of the nasopharynx.1,19 While it would probably be impossible to eradicate carriage of these resistant organisms from the population, it may be possible to reduce the rate of increase in resistance by minimising the prescription of unnecessary antibiotics.

Other strategies, such as vaccination, may be necessary. Unfortunately, the currently available vaccine is a polysaccharide and therefore a poor immunogen, especially in young children. Studies are under way to assess a conjugated pneumococcal vaccine (i.e., a carbohydrate with protein carrier), but vaccine development is difficult as there are over 80 serotypes of pneumococci (compared with only one commonly invasive serotype of Haemophilus influenzae -- type b). However, at present most of the resistant organisms belong to relatively few serotypes.1,2,3 A vaccine containing most of these might not only decrease life-threatening disease, but might also decrease carriage of the organisms, as was found for the H. influenzae type b (Hib) vaccine.1 However, as the pneumococcus can acquire DNA from other organisms,1,19 the number of resistant serotypes is likely to increase.

Our study was one of the largest in the world where all organisms were clinically significant and all were assessed for MIC for penicillin. It is valuable not only for showing the rate of resistance (both intermediate and high level), but also for providing a baseline to assess future changes in resistance and to differentiate subtle shifts in resistance in the whole population of pneumococci from the introduction of resistant clones.

In the past, determining MICs was time-consuming, laborious and not routine. The recent development of the Etest (which consists of a strip of paper impregnated with increasing concentrations of antibiotic from one end to the other) has simplified the procedure. This technological advance, along with the willingness of so many laboratories around Australia to participate in the project, has allowed us to obtain information essential for guiding us in making appropriate antibiotic choices and designing empiric therapy for these emerging threats.  

Acknowledgements

We wish to thank the many doctors, scientists and technicians at the participating laboratories who donated their time and resources to carry out this project. The penicillin Etest strips were supplied by Australian Laboratory Services Pty Ltd at cost price. Eli Lilly provided funding for many of the participants to meet at the twice-yearly AGAR meeting. Cefotaxime and ceftriaxone Etest strips were donated by AB Biodisk (Sweden).  

References

  1. Lister PD. Multiply-resistant pneumococcus: therapeutic problems in the management of serious infection. Eur J Clin Microbiol Infect Dis 1995; 14 Supp 1: 18-25.
  2. Klugman K. Pneumococcal resistance to antibiotics. Clin Microbiol Rev 1990; 3: 171-196.
  3. Schreiber J, Jacobs M. Antibiotic-resistant pneumococci. Pediatr Clin North Am 1995; 42: 519-537.
  4. Collignon P. Penicillin-resistant pneumococci: will the recent Olympics bring back to Australia more than gold? Med J Aust 1992; 157: 655-657.
  5. Hansman D, Bullen M. A resistant pneumococcus. Lancet 1967; 2: 264-265.
  6. Hofmann J, Cetron M, Farley M, et al. The prevalence of drug resistant Streptococcus pneumoniae in Atlanta. N Engl J Med 1995; 333: 481-486.
  7. Collignon P, Bell J, on behalf of AGAR. Streptococcus pneumoniae : how common is penicillin resistance in Australia? Aust N Z J Med 1992; 22: 473-476.
  8. Hansman D, Morris S, Gregory M, McDonald B. Pneumococcal carriage amongst Australian aborigines in Alice Springs, Northern Territory. J Hyg (Camb) 1985; 95: 677-684.
  9. National Committee for Clinical Laboratory Standards. Performance standards for antimicrobial disk susceptibility tests. 5th ed. Approved standard. Document M2-A5. Villanova, Pa: NCCLS, 1993.
  10. Bell SM, Gatus BJ, Pham JN, et al. CDS users group newsletter No. 6. Sydney: The Prince of Wales Hospital, 1993.
  11. Bell SM. Additions and modifications to the range of antibiotics tested by the CDS method of antibiotic sensitivity testing. Pathology 1988; 20: 303-304.
  12. National Committee for Clinical Laboratory Standards. Methods for dilution antimicrobial susceptibility tests for bacteria that grow aerobically. 3rd ed. Approved standard. Document M7-A3. Villanova, Pa: NCCLS, 1993.
  13. Jorgensen JH, Ferraro MJ, McElmeel ML, et al. Detection of penicillin and extended spectrum cephalosporin resistance among Streptococcus pneumoniae clinical isolates by use of the Etest. J Clin Microbiol 1994; 32: 159-163.
  14. AB Biodisk . Etest Technical Guide 5B. Solna, Sweden: AB Biodisk , 1995.
  15. National Committee for Clinical Laboratory Standards. Performance standards for antimicrobial susceptibility testing. 5th informational supplement. Document M100-S5. Villanova, Pa: NCCLS, 1994.
  16. True Epistat [computer program]. Version 5.0. Richardson, TX: Epistat Services, 1994.
  17. Collignon P, Bell J, Hufton I, Mitchell D. Meningitis caused by a penicillin- and chloramphenicol-resistant Streptococcus pneumoniae . Med J Aust 1988; 149: 497-498.
  18. Friedland I, McCracken G. Management of infections caused by antibiotic-resistant Streptococcus pneumoniae . N Engl J Med 1994; 331: 377-382.
  19. Tomasz A. The pneumococcus at the gates. N Engl J Med 1995; 333: 514-515.
  20. Barnett E, Klein J. The problem of resistant bacteria for the management of acute otitis media. Pediatr Clin North Am 1995; 42: 509-517.
  21. Nelson C, Mason E, Kaplan S. Activity of oral antibiotics in middle ear and sinus infections caused by penicillin-resistant Streptococcus pneumoniae : implications for treatment. Pediatr Infect Dis J 1994; 13: 585-589.

(Accepted 30 Nov 1995)  


Authors' details

Infectious Diseases Unit, Woden Valley Hospital, Canberra, ACT.
Peter J Collignon, FRACP, FRCPA, Head of Unit, Microbiologist and Infectious Diseases Physician.
Department of Microbiology and Infectious Diseases, Monash Medical Centre, Melbourne, VIC.
Jan M Bell, BSc(Hons), BA, Scientist.

* Australian Group on Antimicrobial Resistance (AGAR).
For this study AGAR consisted of the microbiology laboratories at:
ACT: Woden Valley Hospital (Peter Collignon, Linda Halliday).
NSW: Concord Hospital (Joan Yap, Tom Gottlieb, Glenn Funnell); Illawarra Regional Hospital (Keith Wise, Rodney Jones); Liverpool Hospital (Denise Daley, Rosemary Munro); Prince of Wales Hospital (Jeanette Pham, Barrie Gatus, Sydney Bell); Royal North Shore Hospital (Clarence Fernandes); Royal Prince Alfred Hospital (Richard Benn, Barbara Yan, Alison Vickery).
QLD: Mater Misericordiae Hospital, Brisbane (Martyn Tilse, Janet Montgomery); Princess Alexandra Hospital (Graeme Nimmo, Jacqueline Schooneveldt); Royal Brisbane Hospital (Narelle George, Joan Faoagali); Sullivan, Nicolaides and Partners (Jenny Robson, Sylvia van der Valk); Toowoomba Base Hospital (David Farrell).
SA: Flinders Medical Centre (Hendrik Pruul); Institute of Medical and Veterinary Science (Irene Lim, Richard Lumb); Queen Elizabeth Hospital (Peter Lawson, David Grove).
TAS: Diagnostic Pathology (which includes Hobart Pathology and Launceston Pathology) (Barbara Henderson, Danny McColl, Gary Fenton); Launceston General Hospital (Erika Cox, Veronica Lyons); Royal Hobart Hospital (Keith Ott, Rob Peterson).
VIC: Alfred Hospital (John Spicer, J Clare Franklin); Dorevitch Pathology (Liz Snashall); Heidelberg Repatriation Hospital (Barrie Mayall, Angie Chan, Vicki Moritz); Melbourne Pathology (Christine Hargreaves); Monash Medical Centre (Dianne Olden, Jan Bell, John Turnidge); Royal Children's Hospital and Microbiological Diagnostic Unit (Geoff Hogg, Marion Easton, Janet Strachan).
WA: Fremantle Hospital (David McGechie, Neil Stingemore, Graham Francis); Royal Perth Hospital (Keryn Christiansen, Claire Khinsoe, Geoff Coombs).

Reprints: Dr P J Collignon, Infectious Diseases Unit, Woden Valley Hospital, PO Box 11, Woden, ACT 2606.

©MJA 1997

<URL: http://www.mja.com.au/> © 1997 Medical Journal of Australia.

Received 22 November 2018, accepted 22 November 2018

  • Peter J Collignon
  • Jan M Bell
  • the AGAR


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