Analysis of multiply antimicrobial-resistant isolates of Streptococcus pneumoniae from the United States

Serotype 19A variants of the Spanish serotype 23F multiresistant clone of Streptococcus pneumoniae

Multiply-antibiotic-resistant isolates of serogroup 19 Streptococcus pneumoniae, possessing altered penicillin-binding protein (PBP) 1A, 2B, and 2X genes that are indistinguishable from those of the Spanish multiresistant serogroup 23F clone, are now commonly encountered in Spain. Those isolates that have been serotyped express type 19F capsular polysaccharide. Serotyping of further isolates, and hybridization using a serotype 19F-specific probe, has shown that some of them are serotype 19A, rather than 19F. The Spanish multiresistant serotype 19A, 19F, and 23F multiresistant strains were all shown to be very closely related in overall genotype, as they were indistinguishable by REP-PCR and by the sequencing of internal fragments of three house-keeping genes. The serotype 19A multiresistant strains, like the serotype 19F multiresistant strains, therefore appear to be a serotype variant of the Spanish multiresistant serotype 23F clone, which presumably has arisen by recombination at the capsular locus.

High incidence of multidrug-resistant Streptococcus pneumoniae in South Korea

Streptococcus pneumoniae was isolated from patients with bacteremia, meningitis, pneumonia, and otitis media and used to determine susceptibility to various antibiotics. Of 105 isolates, 51% to 83% were resistant to 6 antibiotics (i.e., the percentages of resistance to penicillin, ampicillin, cephalothin, chloramphenicol, tetracycline, and erythromycin were 78%, 67%, 51%, 56%, 83%, and 58%, respectively). Also, 66 of the 105 isolates were multidrug resistant. Seventy-eight percent of multidrug-resistant strains were highly resistant to tetracycline (minimum inhibitory concentration [MIC] > or = 50 micrograms/ml), and 39% of multidrug-resistant strains were also highly resistant to erythromycin (MIC > or = 128 micrograms/ml). However, only 4% of the 105 isolates were resistant to cefotaxime.

Antipneumococcal activities of gemifloxacin compared to those of nine other agents

The activities of gemifloxacin compared to those of nine other agents was tested against a range of penicillin-susceptible and -resistant pneumococci by agar dilution, microdilution, time-kill, and post-antibiotic effect (PAE) methods. Against 64 penicillin-susceptible, 68 penicillin-intermediate, and 75 penicillin-resistant pneumococci (all quinolone susceptible), agar dilution MIC(50)s (MICs at which 50% of isolates are inhibited)/MIC(90)s (in micrograms per milliliter) were as follows: gemifloxacin, 0.03/0.06; ciprofloxacin, 1.0/4.0; levofloxacin, 1.0/2. 0; sparfloxacin, 0.5/1.0; grepafloxacin, 0.125/0.5; trovafloxacin, 0. 125/0.25; amoxicillin, 0.016/0.06 (penicillin-susceptible isolates), 0.125/1.0 (penicillin-intermediate isolates), and 2.0/4.0 (penicillin-resistant isolates); cefuroxime, 0.03/0.25 (penicillin-susceptible isolates), 0.5/2.0 (penicillin-intermediate isolates), and 8.0/16.0 (penicillin-resistant isolates); azithromycin, 0.125/0.5 (penicillin-susceptible isolates), 0. 125/>128.0 (penicillin-intermediate isolates), and 4.0/>128.0 (penicillin-resistant isolates); and clarithromycin, 0.03/0.06 (penicillin-susceptible isolates), 0.03/32.0 (penicillin-intermediate isolates), and 2.0/>128.0 (penicillin-resistant isolates). Against 28 strains with ciprofloxacin MICs of >/=8 microg/ml, gemifloxacin had the lowest MICs (0.03 to 1.0 microg/ml; MIC(90), 0.5 microg/ml), compared with MICs ranging between 0.25 and >32.0 microg/ml (MIC(90)s of 4.0 to >32.0 microg/ml) for other quinolones. Resistance in these 28 strains was associated with mutations in parC, gyrA, parE, and/or gyrB or efflux, with some strains having multiple resistance mechanisms. For 12 penicillin-susceptible and -resistant pneumococcal strains (2 quinolone resistant), time-kill results showed that levofloxacin at the MIC, gemifloxacin and sparfloxacin at two times the MIC, and ciprofloxacin, grepafloxacin, and trovafloxacin at four times the MIC were bactericidal for all strains after 24 h. Gemifloxacin was uniformly bactericidal after 24 h at </=0.5 microg/ml. Various degrees of 90 and 99% killing by all quinolones were detected after 3 h. Gemifloxacin and trovafloxacin were both bactericidal at two times the MIC for the two quinolone-resistant pneumococci. Amoxicillin at two times the MIC and cefuroxime at four times the MIC were uniformly bactericidal after 24 h, with some degree of killing at earlier time points. Macrolides gave slower killing against the seven susceptible strains tested, with 99.9% killing of all strains at two to four times the MIC after 24 h. PAEs for five quinolone-susceptible strains were similar (0.3 to 3.0 h) for all quinolones, and significant quinolone PAEs were found for the quinolone-resistant strain.

Bacteremic pneumonia caused by a single clone of Streptococcus pneumoniae with different optochin susceptibilities

Two isolates of Streptococcus pneumoniae having different optochin susceptibilities were recovered from a blood sample of a 2-year-old boy with community-acquired pneumonia. The two isolates were documented to belong to a single clone on the basis of the isolates' identical serotype (23F), antibiograms by the E-test, random amplified polymorphic DNA patterns generated by arbitrarily primed PCR, pulsed-field gel electrophoresis, and restriction fragment length polymorphism of the penicillin-binding protein genes pbp2b and pbp2x.

Population biology of Streptococcus pneumoniae isolated from oropharyngeal carriage and invasive disease

The population structure of Streptococcus pneumoniae in a sample of 134 carried antibiotic-susceptible isolates, and 53 resistant and susceptible invasive isolates, was examined using a DNA-based version of multilocus enzyme electrophoresis: multilocus restriction typing (MLRT). This involved RFLP analysis of PCR products generated from nine loci of housekeeping genes located around the pneumococcal chromosome. The combination of alleles at each of the nine loci gave an allelic profile or restriction type (RT). All carried (throat or nasopharyngeal) isolates from children or adults in Oxford and Manchester, UK, and from an HIV-seropositive cohort in Nairobi, Kenya, showed an epidemic population structure. Twelve carried clonal groups, each with different serotypes, were identified at both locations within the UK. Almost all of the carried clones examined (16/17) were found to possess identical RTs or sequence types (STs) to invasive isolates, indicating that frequently carried clones are also associated with cases of invasive disease. As expected from previous studies, the population of 53 invasive, mainly penicillin-resistant, isolates was also found to be at linkage equilibrium. Serotype switching was identified among 14% of RTs that possessed two or more members, or 5.7% of individual isolates within these RTs. In support of a population structure in which there is frequent recombination, there is also clear evidence that the trpA/B locus within pneumococci has evolved by horizontal gene transfer. A non-serotypable isolate from an HIV-seropositive patient in Kenya was clearly genetically distinct from other strains studied, with unique alleles at eight out of nine loci examined. However, it was initially identified as a pneumococcus by a 16S RNA gene probe (Gen-Probe), optochin susceptibility and the presence of pneumolysin and autolysin.

Antibiotic therapy for community-acquired pneumonia

This article takes a broad perspective of community-acquired pneumonia (CAP). The arguments and data that support or refute the current approaches to initial antimicrobial treatment of CAP as outlined in the American Thoracic Society and Infectious Disease Society of America documents are provided. The complex issues involved in the decision of how to properly treat CAP are addressed.

Antimicrobial resistance among clinical isolates of Streptococcus pneumoniae in North America

From a historical perspective, the development of antibiotic resistance among Streptococcus pneumoniae isolates can be traced over the past 3 decades. In North America, penicillin-resistant pneumococci are now found in nearly all medical centers, but the prevalence of such strains varies by region and time period. In the United States, only approximately 75% of all pneumococci are fully susceptible to penicillin, 15% are intermediately susceptible, and approximately 10% are highly resistant. The latter are often multiply resistant to other unrelated drugs, which leaves few effective chemotherapeutic agents with which to treat serious infections caused by such strains. New approaches to therapy are needed to avoid further selection of antibiotic-resistant mutants; these include discontinuing inappropriate or unnecessary use of antibiotics.

Dissemination of a chloramphenicol- and tetracycline-resistant but penicillin-susceptible invasive clone of serotype 5 Streptococcus pneumoniae in Colombia

A national surveillance conducted in Colombia between 1994 and 1996 identified serotype 5 Streptococcus pneumoniae as the second most frequent cause of invasive disease in children younger than 5 years of age. All 43 serotype 5 isolates collected during this period were shown to be susceptible to penicillin, erythromycin, cefotaxime, and vancomycin, but most (38 of 43, or 88%) were highly resistant to chloramphenicol. In order to clarify a possible genetic relatedness among these isolates, additional microbiological and molecular characterizations were performed. Most (40 of 43, or 93%) of the isolates were found to be resistant to tetracycline. Pulsed-field gel electrophoresis (PFGE) patterns of chromosomal DNAs revealed that all the 43 isolates were closely related and that 38 of the 43 isolates were representatives of a "Colombian clone" of S. pneumoniae isolates which were recovered throughout the 3-year surveillance period from patients in 13 hospitals located in five Colombian cities. Isolates belonging to this Colombian clone were resistant to chloramphenicol and tetracycline, hybridized with the cat and tetM DNA probes in the same 340-kb SmaI fragment, and had identical PFGE patterns after both SmaI and ApaI digestions.

Nasopharyngeal carriage of penicillin-resistant Streptococcus pneumoniae among children with acute respiratory tract infections in Thailand: a molecular epidemiological survey

The prevalence of penicillin-resistant Streptococcus pneumoniae in Thailand has dramatically increased over the last decade. During a national survey, which was conducted from 1992 to 1994, 37.2% of the pneumococci isolated from the nasopharynges of children with acute respiratory tract infections were penicillin resistant (MIC, >/=0.1 microg/ml). In order to investigate the prevalence and clonal relatedness of nasopharyngeal carriage of penicillin-resistant S. pneumoniae in Thailand, a molecular epidemiological survey was undertaken. To this end, 53 penicillin-resistant pneumococcal isolates from children who suffered from acute respiratory tract infections and who originated from five distinct regions of the country were characterized in detail. DNA fingerprint analysis demonstrated 13 clusters, i.e., genotypes shared by two or more strains, and 14 unique genotypes. The cluster size varied from 2 (nine clusters) to 11 strains (one cluster). Six of the 13 restriction fragment end labeling clusters consisted of two or more distinct serotypes, indicating frequent horizontal transfer of capsular genes. Geographical distribution of the genotypes among the five regions of Thailand demonstrated that only four genetic clusters were restricted to single areas of the country, whereas the other nine clusters represented isolates collected in two or more districts. These observations demonstrate that the majority of the genetic clusters are spread throughout the country. The most predominant genetic cluster, representing 21% of the isolates, was identical to the Spanish pandemic clone 23F. In addition, the second largest cluster matched the Spanish-French international clone 9V. These data indicate that the genetic clones 23F and 9V, which are widely spread throughout the world, are the most predominant multidrug-resistant pneumococcal clones in Thailand. Therefore, we conclude that these pandemic clones are primarily responsible for the increase in the prevalence of pneumococcal penicillin resistance in Thailand.

Multidrug-resistant Streptococcus pneumoniae in Poland: identification of emerging clones

Penicillin resistance among Streptococcus pneumoniae isolates has rapidly emerged in Poland during the last decade and has reached prevalence levels of up to 14.4% in 1997. In order to investigate the nature of this increase, a molecular epidemiological analysis of non-penicillin-susceptible multidrug-resistant pneumococci isolated in 1995 and 1996 was conducted. Thirty-seven patients who suffered mainly from upper respiratory tract infections and pneumococcal pneumonia were enrolled in this study. The medical centers to which the patients were admitted were located in 16 Polish towns across the country. Eight distinct BOX PCR types were observed, representing 14 subtypes. Restriction fragment end labeling (RFEL) analysis divided the pneumococcal strains into 16 distinct types. By combining the BOX PCR and RFEL data, four genetically distinct clusters of strains were identified. Two clusters represented the genetic clones 23F and 9V, which have recently emerged all over the world. The two other genetic clusters, which represented serotypes 23F and 6B, clearly predominated in the analyzed collection of Polish non-penicillin-susceptible pneumococcal strains. Since the latter clusters did not match any of the 133 RFEL types of non-penicillin-susceptible pneumococci collected in 15 other countries, their Polish clonal origin is most likely.

In-vitro activity of 29 antimicrobial agents against penicillin-resistant and -intermediate isolates of Streptococcus pneumoniae

Antibiotic resistance among isolates of Streptococcus pneumoniae is increasing worldwide. Optimal therapy, though unknown, should be guided by in-vitro susceptibility testing. Currently, vancomycin is the only approved antibiotic that is universally active against multiresistant S. pneumoniae. In-vitro activities were determined for 29 antimicrobial agents against 22 penicillin-intermediate S. pneumoniae (PISP) and 16 penicillin-resistant S. pneumoniae (PRSP) isolates. MICs were determined in cation-adjusted Mueller-Hinton broth with 3% lysed horse blood in microtitre trays. Antimicrobial classes tested included cephalosporins, penicillin, aminopenicillins, macrolides, quinolones, carbapenems and other antimicrobial agents. Among the classes of antimicrobial agents tested, wide differences in susceptibility were demonstrated for both PISP and PRSP. Of the cephalosporins, ceftriaxone and cefotaxime demonstrated the best in-vitro activity for both PISP and PRSP. Of the quinolones, clinafloxacin and trovafloxacin showed the greatest in-vitro activity. Rifampicin and teicoplanin demonstrated excellent in-vitro activity. Promising in-vitro results of newer agents, such as quinupristin/dalfopristin, ramoplanin, teicoplanin and linezolid may justify further evaluation of these agents in clinical trials.

Dissemination of high-level penicillin-, extended-spectrum cephalosporin-, and erythromycin-resistant Streptococcus pneumoniae clones in Taiwan

Sixty-seven clinical isolates of Streptococcus pneumoniae (40 of serotype 23F, 19 of serotype 19F, and 8 of serotype 6B) with decreased susceptibilities to penicillin and erythromycin were characterized by antimicrobial susceptibility patterns; DNA restriction endonuclease cleavage profiles of the penicillin-binding protein genes pbp1a, pbp2b, and pbp2x; random amplified polymorphic DNA (RAPD) patterns generated by arbitrarily primed PCR; and chromosomal macrorestriction profiles based on pulsed-field gel electrophoresis. A total of 22 clones (identical or closely related pulsotypes and identical RAPD patterns) were identified; 14 clones of 23F, 6 of 19F, and 2 of 6B. Three 23F clones (26 isolates) and one 19F clone (9 isolates) expressed high-level resistance to penicillin, cefotaxime, and erythromycin (MICs >/= 256 microg/ml). These data strongly suggest that multiple high-level penicillin-, extended-spectrum cephalosporin-, and macrolide-resistant clones of S. pneumoniae have been disseminated in Taiwan.

Antipneumococcal activities of levofloxacin and clarithromycin as determined by agar dilution, microdilution, E-test, and disk diffusion methodologies

The activities of levofloxacin and clarithromycin against 199 penicillin- and macrolide-susceptible and -resistant pneumococci were tested by agar and microdilution methods in air and by disk diffusion and E-test methods in air and CO2. For levofloxacin, >/=99. 0% of strains were susceptible at /=17 mm, regardless of incubation in air or CO2. Although zone sizes were smaller and E-test MICs were higher for clarithromycin in CO2 than those in air, category differences were minor, and susceptibility rates for clarithromycin were similar to those obtained by agar and microdilution in air (range, 76.9 to 80.9% by all methods). For clarithromycin, adjustment of breakpoints based upon distribution of results resulted in susceptibility rates which were similar by all methods (75.8 to 76.9% susceptible, 0 to 1.5% intermediate, 22.6 to 23.1% resistant). Minor discrepancies were obtained with levofloxacin for one strain (0.5%) by microdilution and two strains (1.0%) by disk diffusion in CO2. For clarithromycin, minor discrepancies were found in three strains (1.5%) by microdilution, seven strains (3.5%) by agar dilution, four strains (2.0%) by E-test in air, six strains (3.0%) by disk diffusion in air, and five strains (2.5%) by disk diffusion in CO2. Major discrepancies occurred with levofloxacin in one strain (0.5%) by microdilution but were not found with clarithromycin. Very major discrepancies were not seen with levofloxacin, but occurred with clarithromycin in five strains (2.5%) by microdilution, three strains (1.5%) by agar dilution, two strains (1.0%) by E-test in air, eight strains (4.0%) by disk diffusion in air, and one strain (0.5%) by disk diffusion in CO2.

A multilocus sequence typing scheme for Streptococcus pneumoniae: identification of clones associated with serious invasive disease

The population biology of Streptococcus pneumoniae is poorly understood. Most of the important issues could be addressed by the molecular characterization of large, well sampled populations from carriage and from the different manifestations of pneumococcal disease. The authors have therefore developed a pneumococcal multilocus sequence typing scheme and database by sequencing approximately 450 bp fragments of seven housekeeping loci from 295 isolates. The combination of alleles at the seven loci provided an allelic profile, or sequence type (ST), and the relatedness between isolates was obtained by constructing a dendrogram from the matrix of pairwise differences between STs. The typing scheme was validated using pneumococci of known genetic relatedness and could resolve >6 billion STs. Among 274 isolates from recent cases of invasive pneumococcal disease in eight countries, 143 STs were resolved, but 12 STs contained at least five isolates (range 5-21 isolates). The repeated recovery of indistinguishable isolates from invasive disease in different countries implies that these STs define strains with an increased capacity to cause invasive disease. The relationship between STs and serotypes suggested that, in the longer term, capsular genes have been distributed horizontally within the pneumococcal population, but in the short term, expansion of clones occurs with only occasional changes of serotype. The multilocus sequence typing scheme provides a powerful new approach to the characterization of pneumococci, since it provides molecular typing data that are electronically portable between laboratories, and which can be used to probe aspects of the population and evolutionary biology of these organisms. A Web site for the molecular characterization of pneumococci by MLST is available (http ://mlst.zoo.ox.ac.uk).

Molecular epidemiology of penicillin-resistant Streptococcus pneumoniae isolates recovered in Italy from 1993 to 1996

Thirty-nine penicillin-resistant Streptococcus pneumoniae isolates recovered among the approximately 700 pneumococcal strains collected from 1993 to 1996 in central and northern Italy were analyzed for several characteristics, including serotype, antibiotic susceptibility profile, chromosomal relatedness (by using pulsed-field gel electrophoresis [PFGE]), restriction fragment length polymorphism (RFLP) of the penicillin-binding protein (PBP) genes 1A, 2X, and 2B, and the presence of a variety of antibiotic resistance genes (determined by hybridization with appropriate DNA probes). The MICs of penicillin for most of the isolates (30 of 39) were high, in the range of 1 microgram/ml or higher, and these 30 isolates carried additional resistance traits to two or more drugs (erythromycin, chloramphenicol, co-trimoxazole, and tetracycline) and expressed serotypes 9, 19, and 23 and three distinct PFGE patterns. More than half (22 of 30) of the isolates for which MICs were high were identified as representatives of two widespread international epidemic clones of S. pneumoniae. The first one of these clones (seven isolates) expressed serotype 23F and possessed all properties characteristic of the widespread Spanish/USA international clone. Seven additional strains with serotype 19 also had the same PFGE pattern, PBP gene, and RFLP polymorphisms, and other properties typical of the serotype 23 Spanish/USA clone, suggesting that these strains were the products of a capsular transformation event (from serotype 23F to serotype 19) in which the Spanish/USA clone was the recipient. The second international clone was represented by eight serotype 9 isolates which were resistant to penicillin and trimethoprim-sulfamethoxazole and had the molecular properties of the French/Spanish epidemic clone. The remaining eight isolates for which penicillin MICs were high appeared to represent a hitherto-undescribed "Italian" clone; they had a novel PFGE type, unique RFLPs for the PBP genes, and resistance to tetracycline, trimethoprim-sulfamethoxazole, and erythromycin, and the penicillin MICs for these isolates were 2 to 4 microgram/ml.

Detection of Tn917-like sequences within a Tn916-like conjugative transposon (Tn3872) in erythromycin-resistant isolates of Streptococcus pneumoniae

A series of macrolide-lincosamide-streptogramin B (MLS)-resistant pneumococcal isolates of a variety of serotypes was examined and was found to contain Tn917-like elements by DNA-DNA hybridization. Like Tn1545, Tn917 also encodes an ermAM gene but does not mediate resistance to other antimicrobial agents. Furthermore, nucleotide sequence analyses of the DNAs flanking three of the Tn917-like elements revealed that they were inserted into orf9 of a Tn916-like element in a composite transposon-like structure (Tn3872). Other MLS-resistant strains appeared to contain Tn1545-like elements that had suffered a deletion of sequences including the aphA-3 sequences responsible for kanamycin resistance. Thus, the MLS resistance phenotype in pneumococci appears to be mediated by the ermAM present on a much wider variety of genetic elements than was previously appreciated.

Molecular analysis by pulsed-field gel electrophoresis and antibiogram of Streptococcus pneumoniae serotype 6B isolates from selected areas within the United States

Fifty-eight clinical isolates of Streptococcus pneumoniae serotype 6B, including 16 from Alaska, 14 from Arizona, 11 from Washington, and 17 from seven additional states, were analyzed. The antibiograms of these isolates were assigned to 10 antibiotic profiles based on their susceptibilities to penicillin, erythromycin, tetracycline, and trimethoprim-sulfamethoxazole. Thirty-two (55%) of these isolates were penicillin nonsusceptible, while 21 (36%) were intermediate or resistant to three or more antibiotics. The restriction endonucleases ApaI and SmaI were used to digest intact chromosomes, and the fragments were resolved by pulsed-field gel electrophoresis (PFGE). The ApaI and SmaI PFGE patterns were combined, and 13 of the 16 Alaskan isolates showed indistinguishable PFGE patterns. One other isolate exhibited highly related ApaI and SmaI PFGE patterns, differing by only one band after restriction with ApaI. Among the 14 isolates from Arizona, 1 was indistinguishable from the predominant ApaI and SmaI PFGE patterns seen in the Alaskan isolates; 5 others were highly related (+/-1 band after cutting with either enzyme) to the Alaskan isolates, suggesting a common ancestral origin. Of the remaining eight isolates, six additional ApaI plus SmaI PFGE patterns were observed. The 28 isolates from the various contiguous states had 22 ApaI plus SmaI PFGE patterns. No correlations were found between specific PFGE patterns, antibiograms, dates of isolation, or geography. The serotype 6B isolates across the contiguous United States were genetically diverse, while the 6B isolates from Alaska appeared to be much less diverse.

Extremely high prevalence of nasopharyngeal carriage of penicillin-resistant Streptococcus pneumoniae among children in Kaohsiung, Taiwan

Resistance (intermediate and high) to penicillin among Streptococcus pneumoniae strains is an emerging problem worldwide. From 1995 to 1997, isolates of S. pneumoniae not susceptible to penicillin were seen with increasing frequency from blood, cerebrospinal fluid, pleural fluid, and middle ear fluid from pediatric patients at the Veterans General Hospital-Kaohsiung. To determine the prevalence of carriage of these penicillin-nonsusceptible S. pneumoniae isolates, we obtained nasopharyngeal swab specimens from 2,905 children (ages, 2 months to 7 years) attending day-care centers or kindergartens or seen in our outpatient clinic. S. pneumoniae was isolated from 611 children, and 584 strains were available for analysis. The oxacillin disc test was used as a screening test to evaluate penicillin susceptibility. The MICs of 11 antibiotics (penicillin, cefaclor, cefuroxime, ceftriaxone, cefotaxime, imipenem, chloramphenicol, clarithromycin, rifampin, vancomycin, and teicoplanin) were determined by the E-test. Only 169 (29%) of the strains were susceptible to penicillin; 175 (30%) strains were intermediately resistant and 240 (41%) were highly resistant. The isolates also demonstrated high rates of resistance to other beta-lactams (46% were resistant to cefaclor, 45% were resistant to cefuroxime, 45% were resistant to ceftriaxone, 31% were resistant to cefotaxime, and 46% were resistant to imipenem). The rate of resistance to macrolide antimicrobial agents was strikingly high; 95% of the isolates were not susceptible to clarithromycin. However, 97% were susceptible to rifampin and 100% were susceptible to the two glycopeptides (vancomycin and teicoplanin). While reports of penicillin-resistant S. pneumoniae increased worldwide through the 1980s, the high prevalence (71%) of resistance reported here is astonishing. Surveillance of nasopharyngeal swab specimen cultures may provide useful information on the prevalence of nonsusceptible strains causing invasive disease. Such information could be used to guide therapy of pneumococcal infections.

Entry of sanfetrinem into human polymorphonuclear granulocytes and its cell-associated activity against intracellular, penicillin-resistant Streptococcus pneumoniae

The entry of antibiotics into phagocytes is necessary for activity against intracellular pathogens. The ability of sanfetrinem, the first member of a new class of antibiotics, to penetrate human polymorphonuclear granulocytes and its consequences upon subsequent phagocytosis and killing of ingested penicillin-resistant Streptococcus pneumoniae have been evaluated. Sanfetrinem penetrated into human polymorphonuclear leukocytes (PMNs) at all concentrations tested, with cellular concentration/extracellular concentration ratios of 6.6 to 5.03 and 4.21 when sanfetrinem was used at 0.25 to 0.5 and 1 microgram/ml, respectively, within 30 min of incubation. The uptake was complete within 5 min and was not energy dependent, since it was not affected by cell viability, environmental temperature, or the addition of a metabolic inhibitor. At a concentration of one-half the MIC, sanfetrinem significantly enhanced human PMN phagocytosis and increased intracellular bactericidal activity against penicillin-resistant S. pneumoniae. Following preexposure of PMNs to a concentration of one-half the MIC of sanfetrinem, there was a significant increase in both phagocytosis and killing compared with that for the controls, indicating the ability of sanfetrinem to interact with biological membranes and remain active within PMNs. Preexposure of streptococci to sanfetrinem made penicillin-resistant S. pneumoniae more susceptible to the bactericidal mechanisms of human PMNs than untreated organisms.

An outbreak of multidrug-resistant pneumococcal pneumonia and bacteremia among unvaccinated nursing home residents

BACKGROUND

Outbreaks of pneumococcal disease are uncommon and have occurred mainly in institutional settings. Epidemic, invasive, drug-resistant pneumococcal disease has not been seen among adults in the United States. In February 1996, there was an outbreak of multidrug-resistant pneumococcal pneumonia among the residents of a nursing home in rural Oklahoma.

METHODS

We obtained nasopharyngeal swabs for culture from residents and employees. Streptococcus pneumoniae isolates were serotyped and compared by pulsed-field gel electrophoresis. A retrospective cohort study was conducted to identify factors associated with colonization and disease.

RESULTS

Pneumonia developed in 11 of 84 residents (13 percent), 3 of whom died. Multidrug-resistant S. pneumoniae, serotype 23F, was isolated from blood and sputum from 7 of the 11 residents with pneumonia (64 percent) and from nasopharygeal specimens from 17 of the 74 residents tested (23 percent) and 2 of the 69 employees tested (3 percent). All the serotype 23F isolates were identical according to pulsed-field gel electrophoresis. Recent use of antibiotics was associated with both colonization (relative risk, 2.3; 95 percent confidence interval, 1.3 to 4.2) and disease (relative risk, 3.6; 95 percent confidence interval, 1.2 to 10.8). Only three residents (4 percent) had undergone pneumococcal vaccination. After residents received pneumococcal vaccine and prophylactic antibiotics, there were no additional cases of pneumonia, and the rates of carriage decreased substantially.

CONCLUSIONS

In this outbreak a single pneumococcal strain was disseminated among the residents and employees of a nursing home. The high prevalence of colonization with a virulent organism in an unvaccinated population contributed to the high attack rate. Clusters of pneumococcal disease may be underrecognized in nursing homes, and wider use of pneumococcal vaccine is important to prevent institutional outbreaks of drug-resistant S. pneumoniae infection.

Application of molecular typing to the epidemiology of Streptococcus pneumoniae

The spread of antibiotic resistance and the development of new vaccines have focused attention on the epidemiology of Streptococcus pneumoniae over recent years. While serotyping and the determination of antibiotic resistance remain primary methods for characterising pneumococci, molecular typing can add greater discrimination and complementary information. Methods based on restriction fragment length polymorphism within total DNA or non-specific polymerase chain reaction provide information representative of the whole genome and can be used to recognise closely related isolates from different sources, whether in the investigation of possible cross infection at the local level or in the investigation of national or international spread of antibiotic resistant strains. Fingerprinting of penicillin binding protein genes adds further information in the analysis of penicillin resistant isolates. The use of a combination of typing methods to analyse both the genome as a whole and specific loci has led to the realisation that pneumococci undergo horizontal gene transfer much more often than most other bacterial species. In particular the spread of penicillin resistance has been characterised by a combination of the spread of epidemic strains, transfer of chromosomal resistance genes from such strains into other genetic backgrounds, and transfer of capsule genes resulting in the switch of serotypes within strains. In the future molecular typing will have an important role in discovering whether widespread vaccination leads to genetic modification of the pneumococcal population causing invasive disease.

Introduction: Evolving needs in respiratory tract infections

Two issues that have become clinically relevant to the treatment of pneumonia over the past few years are the development of antibiotic resistance among respiratory pathogens and the increasing importance of the atypical respiratory pathogens---Mycoplasma pneumoniae, Chlamydia pneumoniae and Legionella spp. Resistance has become an important issue in Streptococcus pneumoniae, methicillin-resistant Staphylococcus aureus and Gram-negative rods. The ways by which bacteria become resistant to antibiotics include production of antibiotic-modifying enzymes, reduced access to target sites, efflux of antibiotic, change in the bacterial target site and the bypassing of inhibited pathways. In Streptococcus pneumoniae that are penicillin resistant, the mechanism is through alteration of the target site for penicillins (penicillin-binding proteins) and this may also confer resistance to some cephalosporins. Multidrug resistance has also been reported in some strains of pneumococci. Of particular concern is resistance to macrolides mediated by the ermAM gene, which also confers resistance to lincosamides and streptogramin-B drugs. In Staphylococcus aureus, resistance to virtually all beta-lactam drugs is mediated by acquisition of the mecA gene, which codes for the drug-resistant beta-lactam target PBP2a. Antimicrobials are now needed that have enhanced activity against aerobic Gram-negative rods, atypical respiratory pathogens and Gram-positive cocci.

Recombinational exchanges at the capsular polysaccharide biosynthetic locus lead to frequent serotype changes among natural isolates of Streptococcus pneumoniae

Serotype 19F variants of the major Spanish multiresistant serotype 23F clone of Streptococcus pneumoniae have been proposed to have arisen by recombinational exchanges at the capsular biosynthetic locus. Members of the Spanish multiresistant serotype 23F clone and the serotype 19F variants were confirmed to be essentially identical in overall genotype, as they were indistinguishable by REP-PCR, and had identical sequences at three polymorphic housekeeping genes. Eight serotype 19F variants were studied and all had large recombinational replacements at the capsular biosynthetic locus. In all cases, one of the recombinational cross-over points appeared to be upstream of dexB, which flanks one end of the capsular locus, and in six of the variants the other cross-over point was downstream of aliA, which flanks the other end of the locus. In two strains a recombinational cross-over point between the introduced serotype 19F capsular region and that of the Spanish serotype 23F clone could be clearly identified, within cpsN in one strain and within cpsM in the other. The differences in the recombinational junctions and sequence polymorphisms within the introduced capsular genes, suggested that the eight serotype 19F variants emerged on at least four separate occasions. Changes in capsular type by recombination may therefore be relatively frequent in pneumococci and this has implications for the long-term efficacy of conjugate pneumococcal vaccines that will protect against only a limited number of serotypes.

Antipneumococcal activity of BAY 12-8039, a new quinolone, compared with activities of three other quinolones and four oral beta-lactams

Activities of BAY 12-8039 against 205 pneumococci were tested by agar dilution. MICs (in micrograms per milliliter) at which 50 and 90% of the isolates are inhibited (MIC50s and MIC90s, respectively) were 0.125 and 0.25 (BAY 12-8039), 2.0 and 4.0 (ciprofloxacin and ofloxacin), and 0.25 and 0.5 (sparfloxacin). Beta-lactam MIC50s and MIC90s for penicillin-susceptible, -intermediate, and -resistant strains, in that order, were 0.016 and 0.03, 0.25 and 2.0, and 2.0 and 4.0 (amoxicillin); 0.03 and 0.06, 0.25 and 4.0, and 4.0 and 8.0 (ampicillin); 0.03 and 0.06, 0.5 and 4.0, and 4.0 and 8.0 (cefuroxime); and 0.03 and 0.125, 0.25 and 2.0, and 4.0 and 8.0 (cefpodoxime). At two times their MICs after 24 h, BAY 12-8039, ciprofloxacin, ampicillin, and cefuroxime were uniformly bactericidal (99.9% killing) against 12 strains; other compounds were bactericidal at four times their MICs.

Susceptibility of twenty penicillin-susceptible and -resistant pneumococci to levofloxacin, ciprofloxacin, ofloxacin, erythromycin, azithromycin, and clarithromycin by MIC and time-kill

This study uses MIC and time-kill methodology to examine the antipneumococcal activity of levofloxacin, ciprofloxacin, ofloxacin, erythromycin, azithromycin, and clarithromycin against 20 pneumococci. Ten strains had levofloxacin MICs of 1.0 microgram/ml, and ten levofloxacin MICs of 2.0 micrograms/ml. Five strains in each group were macrolide susceptible, and five were macrolide resistant. MICs for ciprofloxacin and ofloxacin ranged from 0.5 to 4.0 micrograms/ml and 1.0 to 8.0 micrograms/ml, respectively. MICs of erythromycin, azithromycin, and clarithromycin were similar for macrolide susceptible strains, ranging between 0.004 to 0.06 microgram/ml, and were > or = 128.0 micrograms/ml for macrolide resistant strains. The three quinolones were bactericidal (99.9% killing) for all macrolide-susceptible strains at 2 x MIC at 24 h. The three quinolones yielded 99% killing of all strains after 12 h at 2 x MIC, and 90% killing of all strains after 6 h at the MIC of levofloxacin and ciprofloxacin and 2 x MIC for ofloxacin. Levofloxacin yielded 90% killing of all strains after 4 h at 2 x MIC and ofloxacin at 4 x MIC. For macrolide-susceptible strains, erythromycin and clarithromycin were bactericidal for 9 of 10 strains after 24 h at 4 x and 2 x MIC, respectively, and azithromycin was bactericidal after 24 h at 2 x MIC for 8 of 10 strains. All three macrolides were bactericidal after 12 h only, while 90% killing occurred in 9 of 10 strains at 8 x MIC after 6 h. Quinolone kill kinetics were similar for the 10 macrolide-resistant strains. For macrolide-resistant strains, at 64 to 128.0 micrograms/ml, virtually no decrease in count was seen, with no bactericidal effect.

Oxazolidinones: new antibacterial agents

The oxazolidinones are a new chemical class of synthetic antibacterial agents that are active orally or intravenously against multidrug-resistant Gram-positive bacteria. Their unique mechanism of action and activity against bacteria that pose therapeutic problems in hospital and community treatments make them promising candidates for antimicrobial agents.

Determination of penicillin susceptibility of Streptococcus pneumoniae using the polymerase chain reaction

AIM

To develop a polymerase chain reaction (PCR) based method to detect penicillin susceptibility in isolates of Streptococcus pneumoniae (SP).

METHOD

PCR primers were designed to amplify differential nucleotide sequences of the penicillin-binding protein (PBP) genes 2b, 2x, and 1a in penicillin susceptible and resistant strains of SP. Primers derived from the PBP 2x and 2b genes were designed to amplify products from penicillin susceptible S pneumoniae (PSSP), whereas primers derived from the PBP 1a gene were designed to amplify gene sequences of penicillin resistant S pneumoniae (PRSP).

RESULTS

Two hundred and thirty clinical isolates of SP from the USA, UK, Kenya, Romania, and the Kingdom of Saudi Arabia were tested. Of the isolates, 116 were penicillin susceptible, 65 were intermediately resistant, and 49 were highly resistant. PCR identified 108 (93%) of 116 of PSSP isolates, 55 (85%) of 65 intermediately resistant isolates, and all of the 49 highly resistant isolates of SP. The susceptibility of 16 (7%) isolates could not be determined using PCR. All of these 16 isolates had a minimum inhibitory concentration (MIC) of penicillin < 1 mg/l. None of the highly resistant isolates was identified as penicillin susceptible by PCR, although two of the isolates with intermediate resistance (MIC = 0.125 mg/l) were.

CONCLUSION

Using primers that differentially identify the genotypes of susceptible and resistant strains of SP, PCR provides a rapid method for determining the penicillin susceptibility of SP isolates and could potentially be used for testing clinical samples.

Clonal distribution of penicillin-resistant Streptococcus pneumoniae 23F in France

We studied the clonality of clinical isolates of Streptococcus pneumoniae 23F, the serotype most often associated with penicillin resistance in France. Clinical isolates obtained between November 1992 and April 1993 from nasopharyngeal samples from children with acute otitis media from different regions of the country were analyzed. The genetic polymorphism of penicillin-susceptible and -resistant 23F isolates (MIC, 2 mg/liter) was studied by pulsed-field gel electrophoresis. The resistant isolates were closely related, whereas the susceptible isolates were genetically heterogeneous. PCR amplification and restriction of the genes encoding penicillin-binding proteins (PBPs) 1A, 2B, and 2X also showed that the 24 resistant isolates had similar patterns which were very different from those of the susceptible isolates. All resistant isolates gave the same PBP pattern, with low affinities of PBPs for penicillin. Our results indicate that, in contrast to penicillin-susceptible 23F isolates, the penicillin-resistant 23F isolates have a single clonal origin, suggesting the rapid clonal spread of a resistant epidemic strain throughout the country.

MIC and time-kill study of antipneumococcal activities of RPR 106972 (a new oral streptogramin), RP 59500 (quinupristin-dalfopristin), pyostacine (RP 7293), penicillin G, cefotaxime, erythromycin, and clarithromycin against 10 penicillin-susceptible and -resistant pneumococci

Broth MICs and time-kill studies were used to test the activity of RP 59500 (quinupristin-dalfopristin), RPR 106972, pyostacine (RP 7293), erythromycin, clarithromycin, and cefotaxime for four penicillin-susceptible (MICs of 0.008 to 0.03 microgram/ml), two penicillin-intermediate (MIC of 0.25 microgram/ml), and four penicillin-resistant (MIC of 2.0 to 4.0 micrograms/ml) strains of pneumococci: 6 of 10 strains were resistant to macrolides (MICs of > or = 0.5 microgram/ml). MICs of RP 59500 (0.5 to 1.0 microgram/ml), RPR 106972 (0.125 to 0.25 microgram/ml), and pyostacine (0.125 to 0.25 microgram/ml) did not alter with the strain's penicillin or macrolide susceptibility status. Three penicillin-susceptible strains and one penicillin-intermediate strain were susceptible to macrolides (MICs of < or = 0.25 microgram/ml); the macrolide MICs for the remaining strains were > or = 4.0 micrograms/ml. Cefotaxime MICs rose with those of penicillin G, but all strains were inhibited at MICs of < or = 2.0 micrograms/ml. RP 59500 was bactericidal for all strains after 24 h at 2 x MIC and yielded 90% killing of all strains at 6 h at 2 x MIC; at 8 x MIC, RP 59500 showed 90% killing of six strains within 10 min (approximately 0.2 h). In comparison, RPR 106972 was bactericidal for 9 of 10 strains at 2 x MIC after 24 h and yielded 90% killing of all strains at 2 x MIC after 6 h; 90% killing of six strains was found at 8 x MIC at 0.2 h. Results for pyostacine were similar to those of RPR 106972. Erythromycin and clarithromycin were bactericidal for three of four macrolide-susceptible strains after 24 h at 4 x MIC. Clarithromycin yielded 90% killing of three strains at 8 x MIC after 12 h. Cefotaxime was bactericidal for all strains after 24 h at 4 x MIC, yielding 90% killing of all strains after 6 h at 4 x MIC. All three streptogramins yielded rapid killing of penicillin- and erythromycin-susceptible and -resistant pneumococci and were the only compounds which killed significant numbers of strains at 0.2 h.

Antipneumococcal activities of cefpirome and cefotaxime, alone and in combination with vancomycin and teicoplanin, determined by checkerboard and time-kill methods

The checkerboard titration method was used to test the synergy of cefpirome and cefotaxime with teicoplanin or vancomycin against 35 penicillin-susceptible, 34 penicillin-intermediate, and 31 penicillin-resistant pneumococci. The MICs at which 50 and 90% of isolates are inhibited (MIC50s and MIC90s, respectively) of both cefpirome and cefotaxime were 0.016 and 0.06 microgram/ml, respectively, for penicillin-susceptible strains and 0.125 and 0.5 microgram/ml, respectively, for penicillin-intermediate strains. The MIC50s and MIC90s of cefotaxime for penicillin-resistant strains were 1.0 and 2.0 micrograms/ml, respectively, and those of cefpirome were 0.5 and 1.0 microgram/ml, respectively. All pneumococci were inhibited by cefpirome at MICs of < or = 1.0 microgram/ml. The MIC50s and MIC90s of vancomycin and teicoplanin (0.25 and 0.25 microgram/ml and 0.03 and 0.03 microgram/ml, respectively) did not differ for the three groups. Checkerboard synergy studies showed that cefpirome and vancomycin showed synergy for 31 strains (fractional inhibitory concentration [FIC] indices, < or = 0.5) cefpirome and teicoplanin showed synergy for 18 strains, cefotaxime and vancomycin showed synergy for 51 strains, and cefotaxime and teicoplanin showed synergy for 27 strains. Cefpirome and vancomycin had FIC indices indicating indifference (2.0) for two strains, and cefotaxime and vancomycin had FIC indices indicating indifference for one strain. All other FIC indices indicating indifference or additivity were > 0.5 to 1.0. No FIC indices indicating antagonism (> 4.0) were found. Synergy between beta-lactams and glycopeptides for three susceptible, three intermediate, and three resistant strains were tested by the time-kill assay, and all combinations were synergistic by this method. Synergy between cephalosporins and glycopeptides can be demonstrated and may be useful for the treatment of pneumococcal infections, especially meningitis.

Colonization with penicillin-nonsusceptible Streptococcus pneumoniae in urban and rural child-care centers

OBJECTIVES

To determine the prevalence of penicillin-nonsusceptible Streptococcus pneumoniae (NS-SP) at 12 child-care centers (CCC) in urban and rural Nebraska and to evaluate the genetic diversity of pneumococcal strains present in the CCC environment.

METHODS

Nasopharyngeal cultures for S. pneumoniae were obtained from children 2 to 24 months old. Capsular serotyping, pulsed field gel electrophoresis (PFGE) and microbroth dilution MICs were performed for all S. pneumoniae. Antibiotic exposure was also evaluated as a potential risk factor for colonization with NS-SP.

RESULTS

Nasopharyngeal colonization with S. pneumoniae was present in 121 (56%) of 215 children. The MICs of penicillin were 0.12 to 1.0 microgram/ml for 57 (47%) and > 1.0 microgram/ml for 10 (8%) isolates. Clindamycin MICs of > 0.5 microgram/ml were found in 6 isolates (5%). MICs of ceftriaxone were 0.5 microgram/ml in 28% of S. pneumoniae and 1.0 microgram/ml in 7%. PFGE and capsular serotyping demonstrated multiple strains that were penicillin-nonsusceptible in both the urban and rural CCC. PFGE and capsular serotype defined shared strains within each CCC, but some PFGE "types" could be found in multiple serotypes. Antibiotic exposure during the 2 months before nasopharyngeal culture was not a statistically significant risk factor for nasopharyngeal colonization with NS-SP.

CONCLUSIONS

NS-SP are highly prevalent in urban and rural Nebraska. PFGE similarities between serotypes may reflect "serotype switching" but may also reflect genetic similarity between S. pneumoniae strains.

Molecular epidemiological characteristics of pneumococcal meningitis in children

The molecular epidemiological characteristics of pneumococcal meningitis in children were studied. Pneumococcal isolates were characterized by serotyping and two genotyping methods, BOX fingerprinting and restriction fragment end labeling, to evaluate whether clonal strains were present within the serotypes or serogroups. During a 17-year period, 68 children admitted to the Sophia Children's Hospital were diagnosed with meningitis due to Streptococcus pneumoniae. Pneumococcal isolates from 44 patients were still available for analysis. All strains were susceptible to penicillin. Serotypes/ serogroups 14, 19, 6, and 18 represented 56% of all isolates. The results of the molecular typing methods demonstrate the absence of clonal relatedness between isolates from patients with pneumococcal meningitis.

Genetic relatedness within and between serotypes of Streptococcus pneumoniae from the United Kingdom: analysis of multilocus enzyme electrophoresis, pulsed-field gel electrophoresis, and antimicrobial resistance patterns

A collection of 54 isolates of invasive Streptococcus pneumoniae of serotypes 3 and 14 and serogroups 6, 9, 19, and 23 was investigated. Multilocus enzyme electrophoresis and pulsed-field gel electrophoresis suggested that two clones were represented in the collection, one of serotype 14 isolates, most of which were resistant to erythromycin, and one of serotype 9V isolates, in which resistance to penicillin (MIC, 1 microgram/ml), cefotaxime, and co-trimoxazole was common. Among other isolates there were only a limited correlation between genetic relatedness measured by multilocus enzyme electrophoresis and expression of the same capsule type. However, isolates with highly related pulsed-field gel electrophoresis patterns always shared the same serotype and highly related allele profiles. Calculation of the index of association suggests a freely recombining population structure with epidemic spread of successful clones.

MIC and time-kill study of activities of DU-6859a, ciprofloxacin, levofloxacin, sparfloxacin, cefotaxime, imipenem, and vancomycin against nine penicillin-susceptible and -resistant pneumococci

MIC and time-kill methods were used to test the activities of DU-6859a, ciprofloxacin, levofloxacin, sparfloxacin, cefotaxime, imipenem, and vancomycin against nine penicillin-susceptible, -intermediate, and -resistant pneumococci. The MIC of penicillin for penicillin-susceptible strains was 0.016 micrograms/ml, those for intermediate strains were 0.25 to 1.0 microgram/ml, and those for resistant strains were 2.0 to 4.0 micrograms/ml. Of the four quinolones tested, DU-6859a had the lowest MIC (0.064 micrograms/ml), followed by sparfloxacin (0.25 to 0.5 micrograms/ml) and levofloxacin and ciprofloxacin (both 1.0 to 4.0 micrograms/ml). Vancomycin inhibited all strains at MICs of 0.25 to 0.5 micrograms/ml. The MICs of imipenem and cefotaxime for penicillin-susceptible, -intermediate, and -resistant strains were 0.004 to 0.008, 0.008 to 0.032, and 0.25 micrograms/ml and 0.016, 0.125 to 0.5, and 2.0 micrograms/ml, respectively. DU-6859a was bactericidal at eight times the MICs (0.5 micrograms/ml) for seven of the nine strains after 4 h and bactericidal for all nine strains after 6 h at eight times the MICs and after 12 h at two times the MICs. By comparison, sparfloxacin, the next most active quinolone, was uniformly bactericidal at two times the MICs only after 24 h, with little activity after 2 h. Levofloxacin and ciprofloxacin were bactericidal against all strains after 12 h at eight times the MICs and against all strains at 24 h at four times the MICs. Imipenem was bactericidal against all strains, at concentrations exceeding the MICs, after 24 h. Cefotaxime was also uniformly bactericidal only after 24 h of incubation at two times the MICs. Vancomycin, despite having uniformly low MICs for all strains irrespective of their penicillin susceptibility, was uniformly bactericidal only at two times the MICs after 24 h.

Rapid emergence of penicillin-resistant pneumococci in Hong Kong

The prevalence of penicillin resistance in Streptococcus pneumoniae isolated at the Prince of Wales Hospital, Hong Kong, rose from 6.6% of sputum isolates in the first quarter of 1993 to 55.8% of isolates in the second quarter of 1995. Most of the isolates were also resistant to co-trimoxazole, tetracycline, choramphenicol and erythromycin. Type 19F was the most common capsular type in 1993-1994, comprising 40.0% of typed isolates in this period. Type 23F emerged in 1995 as the predominant type, making up 62.2% of typed isolates in the first 2 quarters of 1995. A high population density and excessive community use of antibiotics are likely to be factors promoting the rapid emergence of multiply-resistant pneumococci in Hong Kong.

Molecular population genetic analysis of emerged bacterial pathogens: selected insights

Research in bacterial population genetics has increased in the last 10 years. Population genetic theory and tools and related strategies have been used to investigate bacterial pathogens that have contributed to recent episodes of temporal variation in disease frequency and severity. A common theme demonstrated by these analyses is that distinct bacterial clones are responsible for disease outbreaks and increases in infection frequency. Many of these clones are characterized by unique combinations of virulence genes or alleles of virulence genes. Because substantial interclonal variance exists in relative virulence, molecular population genetic studies have led to the concept that the unit of bacterial pathogenicity is the clone or cell line. Continued new insights into host parasite interactions at the molecular level will be achieved by combining clonal analysis of bacterial pathogens with large-scale comparative sequencing of virulence genes.

Reasons for the emergence of antibiotic resistance

The ability of many different species of bacteria, including those that cause diseases in humans, to resist the inhibitory action of antimicrobial agents has become a global problem. Resistance continues to spread not only in nosocomial pathogens but in several key community-acquired organisms as well. Appropriate control measures for such resistant organisms depend in part on the pathways by which resistance has arisen. Unfortunately, these pathways differ greatly from organism to organism and setting to setting. In addition, although the epidemiology of resistant organisms sometimes is similar to that of susceptible organisms of the same kind, in some situations it may be quite different. In this article, the authors highlight some of the pathways leading to the development of resistance in bacteria, the importance of antimicrobial use, and the relevance of these mechanisms to measures for the control of resistant bacteria in hospital and community settings.

Evaluation of commercial methods for determining antimicrobial susceptibility of Streptococcus pneumoniae

Seven commercial systems for antimicrobial susceptibility testing of Streptococcus pneumoniae were evaluated by using a challenge set of 55 pneumococcal isolates with a variety of resistance phenotypes and genotypes. Overall, the results produced by the Pasco and Etest methods were found to be acceptable for all drugs tested except for trimethoprim-sulfamethoxazole testing by the Etest. The Just One system for penicillin MIC testing was also judged to be acceptable (minor error rate, 5.5%). Although the Sensititre and MicroTech methods both produced 12.7% minor errors with penicillin, the Sensititre method classified penicillin-intermediate strains as resistant or vice versa, while four of MicroTech's errors were among intermediate strains that were classified as susceptible. The MicroMedia (minor error rate, 16.4%) and MicroScan Rapid (minor error rate, 63.6%) methods produced unacceptably high levels of errors when testing penicillin. Minor error rates for cefotaxime and ceftriaxone ranged from a low of 12.7% (Etest and Sensititre) to a high of 28% (MicroMedia). Error rates were low for erythromycin, tetracycline, and chloramphenicol by most methods with the exception of the MicroScan method, which had a high very major error rate for erythromycin (34.6%). For testing of beta-lactam drugs, the Pasco, Etest, and Just One tests for penicillin are the most accurate methods; the Sensititre method also provided acceptable results.

Bacterial meningitis. Practical guidelines for management

The therapy of bacterial meningitis has evolved over the past century. Initially, antimeningococcal antiserum was used to treat patients with meningococcal meningitis. During the 1930s, sulphonamides were the first antibiotics used in the treatment of bacterial meningitis. The use of other antibiotics followed in later decades. Insights into the pathophysiology of meningitis have led to the use of prophylaxis against infection, as well as adjunctive therapy aimed at attenuating the harmful sequelae, should infection occur. This article outlines the basic principles important in the selection of appropriate antimicrobials. the emergence of resistant organisms, specifically Streptococcus pneumoniae and Haemophilus influenzae, has necessitated changes in previously effective antimicrobial regimens. The availability of third generation cephalosporins has increased the survival rate for meningitis caused by Gram-negative bacilli. Research into the use of adjunctive steroids has led to the recommendation that these agents be used in the paediatric population, which traditionally has had a high prevalence of H. influenzae meningitis. The high efficacy of H. influenzae type b conjugate vaccine and the observation that steroids, by decreasing inflammation, also decrease CNS penetration of some drugs, has led to reconsideration of routine steroid use. Effective chemoprophylactic regimens for contacts of patients with either H. influenzae or Neisseria meningitidis can diminish the spread of infection. Vaccination for both immunocompetent and immunodeficient patients protects against disease caused by some of the more common meningeal pathogens.