Incidence of decreased penicillin sensitivity of Streptococcus pneumoniae from clinical isolates

Antibiotic resistance among clinically important gram-positive bacteria in the UK

The resistance of bacteria to antibiotics, particularly those used for first-line therapy, is an increasing cause for concern. In the UK, the prevalence of resistance to methicillin and mupirocin in Staphylococcus aureus, and to penicillin and macrolides in Streptococcus pneumoniae, appear to be increasing. There has also been an increase in the number of hospitals where glycopeptide-resistant enterococci are known to have been isolated. The increases in methicillin-resistant S. aureus and glycopeptide-resistant enterococci are due, in part, to the inter-hospital spread of epidemic strains. Although new quinolones and streptogramins with activity against Gram-positive bacteria (including strains resistant to currently available agents) are under development, there is no reason to believe that resistance to these agents will not emerge. The control of resistance in Gram-positive bacteria will require a multi-faceted approach, including continued and improved surveillance, a reduction in the unnecessary use of antibiotics, and the application of other strategies such as vaccination.

Royal Society of Tropical Medicine and Hygiene Meeting at Manson House, London, 12 December 1996. HIV and pneumococcal infection in Africa. Microbiological aspects

By the 1930s several studies had shown that Streptococcus pneumoniae was an important pathogen in Nairobi (Kenya) and various risk factors for infection were recognized, including seasonally cold conditions, overcrowding and recent arrival in the city. Research into pneumococcal disease declined with the arrival of penicillin but recently interest has been rekindled by recognition of the pneumococcus as a human immunodeficiency virus (HIV)-associated pathogen and by the emergence of antibiotic resistance. The pneumococcus and its association with HIV were studied during the course of the Wellcome Trust/Kenya Medical Research Institute HIV Programme in Nairobi (1988-1993). There were generally high rates of pneumococcal disease. The pneumococcus (with tuberculosis and salmonellosis) was a major HIV-related pathogen. One study showed HIV seropositivity to confer a relative risk of 17.8 for pneumococcal infection. Recurrent infection accounted for a large proportion (25%) of disease episodes in a longitudinally studied cohort of HIV patients. There were higher pneumococcal carriage rates in HIV-positive than in HIV-negative patients (28% vs. 16%, P = 0.003). High rates of resistance were found to penicillin (25%). Molecular characterization of penicillin-resistant strains identified 11 separate clones, showing great genetic diversity in a small sample of isolates, and there was evidence of horizontal spread of penicillin-binding protein genes between separate lineages. Molecular characterization of isolates from patients with recurrent disease suggested that both relapse and reinfection might occur. There was molecular evidence of transfer of capsular genes between clones (serotype switching). The overall spectrum of serotypes resembled those reported elsewhere, most serotypes being included in the 23-valent vaccine. Higher numbered serotypes were associated with respiratory tract source and antibiotic resistance. Various methods were used to show 82% concordance between pernasal and blood isolates in pneumonia cases. HIV-seropositive patients were more prone to infection with penicillin- and tetracycline-resistant organisms than seronegative patients (penicillin, 27% vs. 7%; tetracycline, 40% vs. 17%), a difference reflected by different serotype profiles in the 2 groups. These studies highlight the importance of the pneumococcus as an HIV-related pathogen in one part of Africa. The high rates of antibiotic resistance are a cause of concern. There should be continued monitoring of resistance patterns, and assessments of the significance of pneumococcal disease made elsewhere in Africa are to be encouraged.

Childhood pneumococcal bacteraemia in Riyadh, Saudi Arabia

Forty-nine children with pneumococcal bacteraemia seen during a 5-year period (1 January 1991 to 31 December 1995) at King Khalid University Hospital were studied. The majority (61.2%) were under 2 years of age. The focus of infection was pneumonia, pharyngitis or undetermined in 28.6%, 18.4% and 20.4%, respectively. Diseases that had probably predisposed them to pneumococcal bacteraemia (mainly nephrotic syndrome) were encountered in 24.5% of cases. Forty-five per cent of the cases occurred during the summer season and in 29% the disease was nosocomially acquired. No death was recorded in this series and the reasons for this are discussed. Detection of pneumococcal antigens from blood taken for culture was successful in 96% of cases; this test is important in the diagnosis of pneumococcal bacteraemia in partially treated patients. Antimicrobial susceptibility testing showed 20.4% of the isolates to be relatively penicillin-resistant. Resistance to other antimicrobial agents was also recorded and multiple resistance was noted in 22% of isolates. There was a significant difference between the ceftriaxone MIC of the relatively penicillin-resistant strains compared with penicillin-sensitive strains. The emergence and the steady increase in the numbers of relatively penicillin-resistant pneumococcal strains in Saudi Arabia during the last 10 years are discussed.

Serotypes and antibiotic susceptibilities of Streptococcus pneumoniae in Nairobi, Kenya

Two hundred and sixteen clinically significant isolates of Streptococcus pneumoniae from 138 adult patients attending clinics in Nairobi, Kenya over a 2 year period were characterized by antibiotic sensitivity testing and serotyping. Overall antibiotic resistance rates were: penicillin, 25%; tetracycline, 34%; erythromycin, 0%; chloramphenicol, 0.4%. Minimum inhibitory concentrations (MIC's) of penicillin ranged from < 0.008-0.5 microgram/ml. Determination of penicillin resistance (MIC > or = 0.1 microgram/ml) by oxacillin 1 microgram disc diffusion zone diameter < or = 20 mm was 100% sensitive, 92% specific. Relative resistance to oxacillin (MIC range 0.25-1.0 microgram/ml) accounted for penicillin sensitive isolates determined falsely to be penicillin resistant by oxacillin disc testing. Penicillin resistance was more frequent in sputum isolates at 35% than in blood isolates at 18% (P = 0.013). Serotypes 6, 10, 14, 16, 19 and 23 were associated with penicillin resistance. This study provides information of value for planning management strategies for pneumococcal disease from an area where there are few existing data.

Detecting erythromycin resistance in Streptococcus pyogenes: reliability of the disk diffusion method and the breakpoint susceptibility testing method. Finnish Study Group for Antimicrobial Resistance (FIRE)

Erythromycin susceptibility of clinical Streptococcus pyogenes isolates was determined at 19 Finnish clinical microbiology laboratories by their routine disk diffusion method and by a screening method adapted from the breakpoint susceptibility testing method. Results obtained at 12 laboratories using 4 major variants of the disk method were further evaluated. From these laboratories, 286 consecutive resistant and 349 consecutive susceptible isolates were sent to the Antimicrobial Research Laboratory, Turku where the MIC of erythromycin was determined. 96% and 97% of the disk results were correct, as compared with MIC results, when general and laboratory-specific breakpoints, respectively, were used. The results of the screening method were comparable to those of the disk method.

Incidence of bacterial respiratory pathogens and their susceptibility to common antibacterial agents

Although most respiratory tract infections are caused by viruses, bacterial pathogens are responsible for higher morbidity and mortality. Because virtually nothing is known about the etiology of bacterial respiratory pathogens in Saudi Arabia, this study examined the incidence of these organisms in 5426 patients over a 1-year period. Of the bacterial pathogens isolated from 904 patients, the most common organism was Hemophilus influenzae (31%), followed by pneumococci (22%), Pseudomonas aeruginosa (16%), and others (31%). Because the first two organisms accounted for more than 50% of isolates, their susceptibility to commonly used antibiotics was also reviewed. The results are presented here.

Detection of pneumococci with increased resistance to penicillin and their clinical significance

Streptococcus pneumoniae isolates from blood, CSF, respiratory tract and other clinical specimens from 626 patients were tested for sensitivity to penicillin. The bacteria were collected from patients in different hospitals in Riyadh, Saudi Arabia. Using 1 microg oxacillin disk, 147 (23.5%) of these isolates were found to be relatively resistant to penicillin (RPR). When 358 pneumococcal isolates were tested for RPR using 1 or 10 unit penicillin disks and compared with the MIC or oxacillin disk, as many as 18% were incorrectly designated as sensitive meningitis, septicemia and pneumonia, the significance of determining their correct susceptibility to penicillin cannot be over emphasized.

Prevalence of pneumococci with increased resistance to penicillin in Saudi Arabia

Streptococcus pneumoniae isolated from blood, cerebrospinal fluid, respiratory tract and other clinical specimens from 268 patients were tested for sensitivity to penicillin, using 1 micrograms oxacillin disks. Eighty-four (31%) of these isolates were found to be relatively resistant to penicillin.

Penicillin-resistant pneumococci

Penicillin-resistant pneumococci were first reported in Australia in 1967 and appeared in the UK in 1976. Their prevalence is increasing but varies greatly worldwide. The mechanism of resistance lies in the alteration of penicillin-binding proteins. Penicillin-resistant strains are often also resistant to a variety of non-beta-lactam antibiotics. Many different serotypes have been found to be penicillin resistant, type 23 being the most common resistant serotype in the UK. Use of oxacillin discs is recommended for penicillin sensitivity testing, otherwise resistant isolates may escape detection. Treatment of infected patients depends on several factors including the degree of resistance of the infecting strain, the sensitivity to alternative agents and the achievable concentration of antibiotic at the site of the infection. Carriage of penicillin-resistant pneumococci is more common in children, especially the recently hospitalized and those recently exposed to antibiotics. Outbreaks of infection have occurred and various control measures have been suggested in attempts to limit the spread of resistant strains.

Pneumococcal resistance to antibiotics

The geographic distribution of pneumococci resistant to one or more of the antibiotics penicillin, erythromycin, trimethoprim-sulfamethoxazole, and tetracycline appears to be expanding, and there exist foci of resistance to chloramphenicol and rifampin. Multiply resistant pneumococci are being encountered more commonly and are more often community acquired. Factors associated with infection caused by resistant pneumococci include young age, duration of hospitalization, infection with a pneumococcus of serogroup 6, 19, or 23 or serotype 14, and exposure to antibiotics to which the strain is resistant. At present, the most useful drugs for the management of resistant pneumococcal infections are cefotaxime, ceftriaxone, vancomycin, and rifampin. If the strains are susceptible, chloramphenicol may be useful as an alternative, less expensive agent. Appropriate interventions for the control of resistant pneumococcal outbreaks include investigation of the prevalence of resistant strains, isolation of patients, possible treatment of carriers, and reduction of usage of antibiotics to which the strain is resistant. The molecular mechanisms of penicillin resistance are related to the structure and function of penicillin-binding proteins, and the mechanisms of resistance to other agents involved in multiple resistance are being elucidated. Recognition is increasing of the standard screening procedure for penicillin resistance, using a 1-microgram oxacillin disk.