Letters

Prevalence of antibiotic resistance in pneumococci

EDITOR,--Alan P Johnson and colleagues report that the prevalence of intermediate or full resistance to penicillin was 3.9% in England and Wales in 1995 and that the prevalence of resistance to erythromycin was 8.6%.¹ We have examined the prevalence of resistance of Streptococcus pneumoniae to common antimicrobial agents in two consecutive periods in east London.

In our first study we determined the antimicrobial susceptibilities of sequential clinical isolates of pneumococci obtained during January to September 1994. Seven (12%) of 60 isolates had reduced susceptibility to penicillin (either intermediate resistance (minimum inhibitory concentration 0.1-1 mg/l) or high resistance (minimum inhibitory concentration >/=2 mg/l)). In view of this high prevalence we then collected all isolates from October 1994 until April 1995 and established the minimum inhibitory concentrations for a range of antimicrobial agents and the serological type.² Seventy five isolates were obtained during this period, of which nine (12%) had reduced susceptibility to penicillin. We believe that this is the highest reported prevalence of pneumococci with reduced susceptibility to penicillin in Britain. All strains were typable and are represented in the vaccine that is currently used.

During the overall study period 16 pneumococcal strains of reduced susceptibility (12% of the 135 isolates) were collected from 16 patients. Two isolates had minimum inhibitory concentrations of penicillin of >1 mg/l but were sensitive to erythromycin. Four isolates were also resistant to at least two of the three agents commonly tested in vitro--namely, tetracycline, erythromycin, and chloramphenicol. Nine (7%) of the 135 isolates were resistant to erythromycin. The sources of the samples were predominantly sputum or respiratory samples (65 isolates), blood cultures (38), and eye (15) and ear swabs (9). Two patients yielded multiple isolates.

Our results confirm that the prevalence of resistant strains of pneumococci varies considerably in Britain and that continued monitoring of antimicrobial resistance at a local level is essential for the continuing optimal management of infections due to this organism. Many pneumococcal infections, even when caused by an organism with reduced susceptibility to penicillin, will respond to penicillin as long as adequate doses are used.³ This does not, however, apply to pneumococcal meningitis, as adequate concentrations of penicillin in the cerebrospinal fluid may not be achieved. The increasing prevalence of resistance to penicillin means that this drug will no longer be useful for empirical treatment of this condition, and it is vital that the individual susceptibilities of the causative organism are determined for each patient.

PETER WILSON Consultant microbiologist

D LEWIS Registrar in microbiology

Newham District Microbiology Laboratories, St Andrew's Hospital, London E3 3NT

PETER JENKS Lecturer in microbiology

S HOQUE Lecturer in microbiology

Microbiology Laboratories, Royals Hospital Trust, London E1 1BB

Peter Wilson, D Lewis, Peter Jenks, S Hoque 

1. Johnson AP, Speller DCE, George RC, Warner M, Domingue G, Efstratiou A. Prevalence of antibiotic resistance and serotypes in pneumococci in England and Wales: results of observational surveys in 1990 and 1995. BMJ 1996;312:1454-6. (8 June.) [Abstract/Free Full Text]
2. Sorensen UBS. Typing of pneumococci by using 12 pooled antisera. J Clin Microbiol 1993;31:2097-100. [Abstract/Free Full Text]
3. Friedland IR, McCracken H. Management of infections caused by antibiotic resistant Streptococcus pneumoniae. N Engl J Med 1994;331:377-82. [Free Full Text]