World-wide development of antibiotic resistance in pneumococci

Nasopharyngeal carriage of penicillin-resistant Streptococcus pneumoniae in children with sickle cell disease

OBJECTIVE

We studied the prevalence of nasopharyngeal (NP) carriage, antimicrobial susceptibilities, and serotypes of Streptococcus pneumoniae (SP) in children with sickle cell disease (SCD) in the Mid-South. In addition, we examined risk factors for NP carriage of penicillin-resistant SP (PRSP).

STUDY DESIGN

Between July 1994 and December 1995, we obtained NP cultures from 312 children with SCD followed at the Mid-South Sickle Cell Center, 208 (67%) of whom were receiving penicillin prophylaxis.

RESULTS

Among the 312 patients, colonization with SP occurred in 42 (13%), 30 (71%) of whom were receiving penicillin prophylaxis. Twenty-three of the 42 SP isolates (55%) were resistant to penicillin; 5 of the 23 (22%) were highly resistant. PRSP organisms were also resistant to cefotaxime (43%), trimethoprim-sulfamethoxazole (57%), and erythromycin (22%). Serotypes 6A, 6B, 14, 19A, and 23F accounted for 19 (90%) of 21 resistant strains. Children who were treated with antibiotics during the preceding month were more likely to carry PRSP than children who were not treated.

CONCLUSIONS

There is a high prevalence of NP carriage of PRSP in children with SCD in the Mid-South, which raises concerns regarding the continued effectiveness of penicillin prophylaxis in these children. Further studies on the antimicrobial susceptibilities of resistant organisms and the relationship between NP carriage of SP and invasive disease are needed before developing new recommendations for prophylaxis and treatment.

Role of oral antibiotics in treatment of community-acquired lower respiratory tract infections

Amoxicillin/clavulanic acid has been one of the first choice treatments for community-acquired lower respiratory tract infection since its introduction nearly 15 years ago. Since then, it has become the "gold standard" against which most new oral antimicrobials are compared, but none of these newer agents has demonstrated a superior efficacy. To the contrary, two recent studies comparing amoxicillin/clavulanic acid with azithromycin, cefixime, or ciprofloxacin in the treatment of acute exacerbations of chronic bronchitis have demonstrated a higher efficacy rate for amoxicillin/clavulanic acid.

Efficacies of cefotaxime and ceftriaxone in a mouse model of pneumonia induced by two penicillin- and cephalosporin-resistant strains of Streptococcus pneumoniae

We previously demonstrated the efficacy of ceftriaxone (CRO), at 50 mg/kg of body weight every 12 h, against a highly penicillin-resistant (MIC, 4 micrograms/ml) Streptococcus pneumoniae strain with low-level resistance to CRO (MIC, 0.5 microgram/ml) in a leukopenic-mouse pneumonia model (P. Moine, E. Vallée, E. Azoulay-Dupuis, P. Bourget, J.-P. Bédos, J. Bauchet, and J.-J. Pocidalo, Antimicrob. Agents Chemother. 38:1953-1958, 1994). In the present study, we assessed the activity of CRO versus those of cefotaxime (CTX) and amoxicillin (AMO) against two highly penicillin- and cephalosporin-resistant S. pneumoniae strains (P40422 and P40984) (MICs of 2 and 8 for penicillin, 2 and 4 for AMO, and 4 and 8 for CRO or CTX, respectively). Against both strains, a greater than an 80% cumulative survival rate was observed with CRO at a dose of 100 or 200 mg/kg every 12 h (dose/MIC ratio, 25). With CTX, a high dosage of 400 mg/kg (dose/MIC ratio, 100 or 50) administered every 8 h (TID) was needed to protect 66 and 75% of the animals, respectively, with no statistically significant differences versus CRO. Against the P40422 strain, CRO (100 mg/kg) produced the greatest bactericidal effect, from the 8th to the 24th hour after a single injection (1.8-log-unit reduction over 24 h), and the fastest bacterial pulmonary clearance during treatment; with CTX, only multiple injections at a high dosage, i.e., 400 mg/kg TID, demonstrated a significant bactericidal effect. AMO in a high dosage, 400 mg/kg (dose/MIC ratio, 200) TID, showed good activity only against the P40422 strain. Despite the identical MICs of CTX and CRO, the longer time (3.6 to 4.6 h) that serum CRO concentrations remained above the MICs for the pathogens at a dose of 100 mg/kg resulted in greater efficacy versus CTX against highly penicillin- and cephalosporin-resistant S. pneumoniae strains.

Discrepancies between results by E-test and standard microbroth dilution testing of Streptococcus pneumoniae for susceptibility to vancomycin

Vancomycin susceptibility testing of Streptococcus pneumoniae by the E-test consistently resulted in MICs that were at the upper limit of the 1-microgram/ml susceptible category defined by current National Committee for Clinical Laboratory Standards guidelines and were always higher than MICs obtained by microbroth dilution. Three of five E-test results for S. pneumoniae ATCC 49619 were higher than the acceptable limits.

Levofloxacin in vitro activity against bacteremic isolates of Streptococcus pneumoniae. Franklin County Pneumonia Study Group

Levofloxacin had excellent activity in vitro against bacteremic isolates of Streptococcus pneumoniae with 495 (99.2%) of 499 isolates being susceptible. A total of 38 (97.4%) of 39 isolates with minimal inhibitory concentrations > or = 0.12 micrograms/ml of penicillin were susceptible to levofloxacin. There was excellent correlation between the disk diffusion and broth microdilution methods for determining susceptibility. Resistant isolates belonged to four different serotypes. There was no increase in proportion of isolates of S. pneumoniae resistant between 1991 and 1994.

Relationship of MICs to efficacy of cefotaxime in treatment of Streptococcus pneumoniae infections

In June 1993, the National Committee for Clinical Laboratory Standards (NCCLS) recommended stringent new interpretive guidelines for antibiotics indicated for Streptococcus pneumoniae meningitis. To assess the predictive values of the recommended breakpoints, retrospective data were collected from patients who had S. pneumoniae infections and were treated with cefotaxime monotherapy. Susceptibilities based on the NCCLS interpretative categories were compared with clinical and bacteriologic outcomes. In 76 evaluable patients, the most common infections were bacteremia-septicemia (n = 49), meningitis (n = 37), and lower respiratory tract infection (n = 14). Under the NCCLS breakpoints proposed in 1993, 55 isolates would have been classed as susceptible to cefotaxime (MIC, < or = 0.25 microgram/ml), 18 would have been classed as intermediate (MIC, 0.5 to 1.0 microgram/ml), and 2 would have been classed as resistant (MIC, > or = 2 micrograms/ml). Of 75 cefotaxime-treated patients for whom cefotaxime MICs were recorded, 73 were clinically cured or improved (37 of 37 with meningitis and 36 of 38 with other infections). One case of bacteremia and one case of bone-and-joint infection were scored as therapeutic failures because initial monotherapy had to be modified because of an adverse drug reaction. Excluding these patients, there were 18 patients infected with S. pneumoniae that would have been classed as not fully susceptible (i.e., MICs > or = 0.5 microgram/ml); all of these patients were cured or improved. The results of this analysis demonstrate that successful treatment with cefotaxime did not correlate well with the guidelines for the susceptibility of pneumococcal isolates to either penicillin or cefotaxime established by the 1993 NCCLS breakpoint recommendations. Because of this study and other similar findings, the NCCLS adopted more clinically relevant guidelines in 1994.

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.

Trends in antimicrobial susceptibility of bacterial pathogens of the respiratory tract

Rates of antimicrobial resistance have been increasing in bacteria responsible for community-acquired lower respiratory tract infections in the United States. Nearly 100% of clinical isolates of Moraxella catarrhalis now produce beta-lactamase, an enzyme that renders this pathogen resistant to such agents as penicillin, ampicillin, and amoxicillin. However, this organism remains nearly uniformly susceptible to alternative oral antimicrobials, such as cephalosporins, macrolides, tetracyclines, beta-lactamase inhibitor combinations, and the combination of trimethoprim/sulfamethoxazole. The susceptibility of M. catarrhalis to these agents is not expected to change markedly in the next few years. A linear increase in the prevalence of beta-lactamase-mediated ampicillin resistance has been evident among isolates of nontypeable Haemophilus influenzae during the past decade in the United States. By the year 2000, 45-50% of isolates are likely to produce beta-lactamase. Although the susceptibility of this organism to alternative oral antimicrobials varies, rates of resistance to cefuroxime axetil, cefpodoxime, cefixime, azithromycin, and perhaps clarithromycin remain < 1%. The rate of penicillin resistance among isolates of Streptococcus pneumoniae, which has increased steadily in recent years, currently stands at approximately 25% in the United States and will likely reach 40-50% during the next 5-10 years. Because of cross-resistance, in general all beta-lactam antimicrobials have reduced activity against penicillin-resistant strains of S. pneumoniae. A 1994-1995 survey found that 3.4% of S. pneumoniae isolates were highly resistant to cefotaxime, and 4-8% were resistant to chloramphenicol, tetracycline, and the macrolides. Resistance to these antimicrobials has usually followed the emergence of penicillin resistance in other countries. Therefore, S. pneumoniae resistance to these drugs is expected to increase markedly during the next few years in the United States.

Bacterial pneumonia in adult patients with HIV infection

Patients with HIV infection are at increased risk for community-acquired bacterial pneumonias, due in part to their defects in B-cell function. Streptococcus pneumoniae is the commonest cause of community-acquired pneumonia, with the second most common bacterial agent being Haemophilus influenzae. These two organisms account for about two-thirds of community-acquired bacterial pneumonias. Frequently bacterial pneumonias appear difficult to distinguish from Pneumocystis carinii pneumonia or other opportunistic lung infections, because of their atypical clinical and radiologic presentations. Community-acquired pneumonias may be recurrent but have low fatality rates. In comparison, nosocomial pneumonias occur primarily in patients with AIDS and are usually due to Staphylococcus aureus, Pseudomonas aeruginosa and other aerobic gram-negative bacilli. Nosocomial pneumonias have high fatality rates. S.aureus is an important cause of morbidity and mortality in patients with AIDS and has emerged as a secondary opportunist in lungs of patients with opportunistic diseases. While appropriate laboratory study is being done, empiric antibiotic therapy should be directed against the microorganisms above described.

Antimicrobial agents for community-acquired respiratory tract infections

Chemotherapy of community-acquired respiratory tract infections was reviewed from a microbiological perspective. The current worldwide spread of penicillin-resistant Streptococcus pneumoniae and of ampicillin-resistant Haemophilus influenzae has required a reassessment of the antimicrobial agents being used for empiric therapy. In vitro data with different orally administered antibiotics were reviewed in order to identify any deficiencies in their spectra of activity against four common respiratory tract pathogens. Cefixime, cefuroxime axetil, cefprozil, amoxicillin-clavulanic acid and trimethoprim-sulfamethoxazole were active against all four species other than penicillin-resistant pneumococci.

Prevalence of antimicrobial resistance of Streptococcus pneumoniae in southwest Germany as determined by the E test

We have studied the prevalence of anti-microbial resistance of Streptococcus pneumoniae in Southwest Germany. One hundred seventy-four clinical isolates of pneumococci collected from hospitalized patients between October 1992 and April 1994 were used for MIC determinations. MICs for penicillin, ceftriaxone, erythromycin, and rifampicin were assessed by the E test. Eleven of the 174 strains (6.3%) were intermediately resistant to penicillin (MIC between 0.1 and 1.0 microgram/ml) and four of the 174 strains (2.3%) were intermediately resistant to ceftriaxone (MIC between 0.1 and 1.0 microgram/ml). All four isolates with a reduced susceptibility to ceftriaxone also demonstrated intermediate resistance to penicillin. Six of the 174 strains (3.5%) were highly resistant (MIC > or = 8 micrograms/ml) to erythromycin. Resistance to rifampicin was not observed. Our results demonstrate that pneumococcal resistance to penicillin and erythromycin has increased markedly in Germany over the last decade. Our findings underline the need for continuous surveillance of antimicrobial resistance of Streptococcus pneumoniae.

New aspects of old pathogens of pneumonia

Changes in the microorganism or in the host have resulted in exciting new aspects of several old pathogens of pneumonia. Penicillin-resistant Streptococcus pneumoniae, methicillin-resistant Staphylococcus aureus, and "toxic strep" are examples of changes in the microorganisms. Host changes have resulted in Mycoplasma pneumoniae now emerging as a cause of pneumonia in the elderly.

Immune responses of young mice to pneumococcal type 9V polysaccharide-tetanus toxoid conjugate

Pneumococcal type 9V polysaccharide (PS), contained in the current pneumococcal vaccine, induces only a weak antibody response in young children and therefore is not an effective vaccine for young children. To increase its immunogenicity, a conjugate of PS to a protein carrier, tetanus toxoid (TT), was prepared. To quantify the immune response, mouse anti-9V PS immunoglobulin G (IgG) and IgM reference standards were established. Young mice immunized at 2 weeks of age produced IgM antibody in response to 9V PS alone or 9V PS conjugated to TT. However, only the 9V PS-TT conjugate induced an IgG antibody response and an anamnestic effect. Thus, a covalent linkage between TT and 9V PS was required for isotype switching from IgM to IgG. 9V PS-TT adsorbed with aluminum hydroxide adjuvant resulted in a fivefold or greater increase in the IgG antibody level. We also studied the effect of maternal immunization on the immune response of young mice to 9V PS-TT. Maternal immunization before mating or before mating and during gestation primed 2-week-old progeny given two injections of 9V PS-TT to produce more IgM antibody than progeny from unimmunized mothers. The IgG antibody level of neonates at birth was similar to that observed in the mothers and was probably passive antibody. These results indicate that maternal immunization with an optimum dose of a PS-protein conjugate before and/or during pregnancy, followed by immunization of the offspring with the conjugate, could provide young children with an enhanced IgM antibody response to pneumococcal PSs.

Development of o.a.s.i.s., a new automated blood culture system in which detection is based on measurement of bottle headspace pressure changes

o.a.s.i.s. (Unipath Ltd., Basingstoke, United Kingdom) is a new automated blood culture system. The metabolism of microorganisms is detected by measuring changes in the pressure of the headspace of blood culture bottles. These changes are measured by monitoring the position of a flexible sealing septum, every 5 min, with a scanning laser sensor. This noninvasive system can detect both gas absorption and production and does not rely solely on measuring increasing carbon dioxide levels. A research prototype instrument was used to carry out an evaluation of the media, the detection system, and its associated detection algorithm. In simulated blood cultures, o.a.s.i.s. supported growth and detected a range of clinical isolates. Times to positivity were significantly shorter in o.a.s.i.s. than in the BACTEC 460 system. Results of a clinical feasibility study, with a manual blood culture system as a control, confirmed that o.a.s.i.s. was able to support the growth and detection of a variety of clinically significant organisms. On the basis of these findings, full-scale comparative clinical trials of o.a.s.i.s. with other automated blood culture systems are warranted.

Treatment of experimental endocarditis due to penicillin-resistant Streptococcus pneumoniae

Using two strains of pneumococci for which MICs of penicillin were 1 and 4 micrograms/ml, those of cefotaxime were 0.01 and 0.5 micrograms/ml, and those of teicoplanin were 0.01 and 0.1 micrograms/ml, we studied the efficacy of different dosages of penicillin, cefotaxime, and teicoplanin in the treatment of experimental pneumococcal endocarditis in rabbits. Animals treated with dosages of penicillin G procaine needed to achieve levels in serum near the MIC for pneumococci showed a significant reduction in log10 CFU per gram of vegetation, as compared with the control (P < 0.001), although only 20% of the animals showed sterile vegetations. When levels of penicillin in serum were in the range of three- to fourfold the MIC, a greater reduction in log10 CFU per gram of vegetation was seen, and 88% of the animals showed sterile vegetations. Only the regimen of penicillin that provided concentrations in serum above the MIC throughout the interval between two doses provided constant sterilization of the cardiac vegetations. Dosages of cefotaxime and teicoplanin selected to achieve concentrations in serum equivalent to that obtained in humans during treatment resulted in levels of antimicrobial agents in serum hundreds or thousands of times higher than the MICs for the infecting strains. In terms of antimicrobial efficacy, cefotaxime and teicoplanin were equivalent to regimens with high dosages of penicillin.

The use of antimicrobial drugs in Nagpur, India. A window on medical care in a developing country

The objective of the study was to determine the patterns of use of antimicrobial drugs in the general population of the large, industrial city of Nagpur, India. Interviews of pharmacists and clients were carried out in a stratified, random sample of 34 pharmacies to determine beliefs and practices in prescribing and self-prescribing of antibiotics by complaint, choice of drug, dose, duration, cost, age and sex of the consumers. The study showed that drugs were dispensed without prescription despite prohibition by the Indian Pharmaceutical Act. Sales of antimicrobial drugs accounted for 17.5% of 511 purchases and 23.3% of expenditures for drugs. Proprietary brands of penicillins, co-trimoxazole and tetracyclines were dispensed most often (64.8%). The most common indications were upper respiratory, gastrointestinal and nonspecific complaints. The median number of units obtained was 5.0 (95% range 1-20), at a median cost of $0.50 per purchase, usually taken for less than five days. Repeat purchases were made without consulting a physician. Almost two thirds of purchases (63.9%) were for males, mainly under the age of ten years. Clients had poor knowledge of the indications, side effects, adverse reactions and appropriate duration of therapy. The dispenser viewed himself as a businessman rather than a professional and rarely offered unsolicited advice. Co-prescribing of 'tonics' added to costs and decreased the purchasing power for antimicrobial drugs. Most purchases of antimicrobial drugs in community pharmacies in Nagpur were for minor indications and were limited by the purchasing power of the consumers. It is doubtful that the choice of drug and the short duration of therapy would be effective for serious infections.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of E test with standard broth microdilution for determining antibiotic susceptibilities of penicillin-resistant strains of Streptococcus pneumoniae

We compared the E test (AB Biodisk North America, Inc., Culver City, Calif.) with the National Committee for Clinical Laboratory Standards broth microdilution method for the determination of MICs of penicillin and cefotaxime for 108 isolates of Streptococcus pneumoniae. The E test was performed following manufacturer's recommendations with Mueller-Hinton blood agar, and the broth microdilution procedure was performed with lysed horse blood-supplemented Mueller-Hinton broth. The microdilution method classified 26 isolates as highly penicillin resistant (MIC, > or = 2 micrograms/ml), 33 as intermediately resistant to penicillin (MIC, > or = 0.1 < 2.0 micrograms/ml), and 49 as susceptible to penicillin (MIC, < 0.1 micrograms/ml). Discordant results obtained with the E test for penicillin susceptibility testing compared with broth microdilution occurred for 19 of the 108 isolates tested. Cefotaxime MICs for 90% of isolates found highly resistant, intermediately resistant, and susceptible to penicillin by broth microdilution were 2.0, 0.5, and 0.06 micrograms/ml, respectively. There were 16 susceptibility category changes when the E test was used to determine cefotaxime MICs. All of the discrepancies in the penicillin and cefotaxime MICs determined by the E test occurred at the susceptibility category breakpoints, and all represented differences of only one twofold dilution factor. Properly performed and controlled, the E test should be a reliable quantitative procedure for more accurately predicting the susceptibility of S. pneumoniae to several antibiotics.

Genetics of oxacillin resistance in clinical isolates of Streptococcus pneumoniae that are oxacillin resistant and penicillin susceptible

It has recently been reported that penicillin-sensitive pneumococci may exhibit reduced susceptibility to oxacillin, resulting in their misclassification as being penicillin resistant by oxacillin disk testing. Intermediate oxacillin resistance (MIC, 1.0 microgram/ml) in three of these apparently unrelated penicillin-susceptible clinical isolates of Streptococcus pneumoniae isolated in the United Kingdom and in four Spanish isolates was shown to be solely due to the acquisition of a gene encoding an altered penicillin-binding protein (PBP), PBP2X. PBP2X genes cloned from typical penicillin-resistant isolates of S. pneumoniae that possessed high-level oxacillin resistance were shown to be able to transform susceptible isolates of S. pneumoniae to intermediate oxacillin resistance. In all instances, the intermediately oxacillin-resistant PBP2X transformants retained susceptibility to penicillin (MIC, 0.06 microgram/ml). Under appropriate selective pressure, the acquisition of a low-affinity PBP2X by penicillin-susceptible pneumococci could result in an increasing number of false positives for penicillin resistance among isolates of S. pneumoniae screened with oxacillin. Additionally, these intermediately oxacillin-resistant isolates showed reduced susceptibility to cefotaxime, an agent likely to be prescribed in place of penicillin for the treatment of serious infections due to these apparently penicillin-resistant organisms.

Antimicrobial susceptibility and serotype distribution of Streptococcus pneumoniae from Rwanda, 1984-1990

A total of 383 clinical isolates of Streptococcus pneumoniae, obtained from an equal number of patients in Kigali, Rwanda, was tested for resistance to penicillin G with a 1 microgram oxacillin disc. Of these isolates, 99 (25.8%) showed reduced zones of inhibition. By means of an agar dilution method, 21% all isolates were confirmed as relatively resistant (MIC > or = 0.12- < or = 1.0 mg/l) strains of Streptococcus pneumoniae (RRSP). A high degree of resistance to penicillin G (MIC > or = 2 mg/l) was not observed. Resistance to chloramphenicol (MIC > or = 8 mg/l) was found in 31% RRSP and in 6% penicillin susceptible strains (PSSP). Doxycycline resistance was common in both RRSP and PSSP strains. All isolates remained fully susceptible to erythromycin. Children more often harboured a strain giving a reduced inhibition zone than did adults (74/230 versus 25/153; P = 0.0005). A total of 32 serotypes or serogroups were identified, seven of them relating to 64.8% all isolates typed. Of all the isolates 84% belonged to a serotype represented in the 23-valent vaccine or to a cross-reacting serotype. Serotype 25, not included in the vaccine, accounted for 10.7% typed isolates from adults but only for 2.0% typed isolates from children. Results of susceptibility testing and clinical experience suggest that penicillin G, ampicillin and chloramphenicol should not be used alone as empirical treatment for pneumococcal meningitis in patients in Rwanda.

A comparative study of clarithromycin and amoxycillin suspensions in the treatment of pediatric patients with acute otitis media

This phase III, single-blind, randomized, multicentre clinical trial compared the safety and efficacy of clarithromycin and amoxycillin in the treatment of otitis media in pediatric patients. Two hundred and fifty-nine patients aged 1-12 were prescribed suspensions of clarithromycin (132 patients) or amoxycillin (127 patients). Both suspensions were prescribed at a dose of 125 mg for children weighing less that 25 kg or at 250 mg for children weighing more than 25 kg, but three doses of amoxycillin per day were given, while only two doses clarithromycin per day were required. Each drug was administered for approximately 5 days. Clinical evaluations were performed pre-treatment (Study Day 1), at the end of treatment (Study Days 6-9), and post-treatment (Study Days 28-32). At the end of treatment, 91 out of 114 evaluable patients (80%) had clinical cures with clarithromycin, while 71 out of 105 evaluable patients (68%) had clinical cures with amoxycillin (p = 0.057). Clinical success rates were 96% for both treatments (110/114, clarithromycin; 101/105 amoxycillin). Adverse events related to the study medications occurred in four of 132 patients receiving clarithromycin (3%) and eight out of 127 subjects receiving amoxycillin (6%). Three patients discontinued treatment due to adverse events, all three receiving amoxycillin. At the doses administered, clarithromycin given twice-daily was as safe and effective as given three-times-daily in the treatment of acute otitis media in pediatric patients.

Aerobic and anaerobic microbiology of empyema. A retrospective review in two military hospitals

The microbiology and clinical features of empyema were studied retrospectively in 197 patients whose specimens yielded bacterial growth after inoculation for aerobic and anaerobic bacteria. Three hundred forty-three organisms (216 aerobic or facultative and 127 anaerobic organisms) were isolated. Aerobic bacteria were isolated in 127 (64 percent) patients, anaerobic bacteria in 25 (13 percent), and mixed aerobic and anaerobic bacteria in 45 (23 percent). The predominant aerobic or facultative organisms were Streptococcus pneumoniae (70 isolates), Staphylococcus aureus (58), Escherichia coli (17), Klebsiella pneumoniae (16), and Haemophilus influenzae (12). The predominant anaerobes were pigmented Prevotella and Porphyromonas species (24), Bacteroides fragilis group (22), anaerobic cocci (36), and Fusobacterium species (20). beta-Lactamase-producing organisms were recovered in 49 (38 percent) of 128 tested specimens. These included all 42 tested S aureus and 15 B fragilis group, 4 of 9 K pneumoniae, 3 of 9 H influenzae, 3 of 8 pigmented Prevotella and Porphyromonas species, and 2 of 6 E coli. Most patients from whom S pneumoniae and H influenzae were recovered had pneumonia, and most patients with S aureus had pneumonia, aspiration pneumonia, and lung abscesses. The recovery of anaerobic bacteria was mostly associated with the concomitant diagnosis of aspiration pneumonia, and lung, subdiaphragmatic, dental, and oropharyngeal abscesses. These data highlight the importance of anaerobic bacteria in selected cases of empyema.

The role of penicillin-binding protein 3 (PBP 3) in cefotaxime resistance in Streptococcus pneumoniae

A pneumococcal strain, with a reduced amount of penicillin-binding protein 3 (PBP 3), permitted an analysis of the role of this protein in cefotaxime resistance. We observed that reduced amounts of PBP 3 sensitize the bacteria to high temperature, to excess glycine and to some D-amino acids. These phenotypes suggest that the amount of PBP 3 may influence the membrane properties of the bacteria. The strain with reduced PBP 3 was transformed to cefotaxime resistance. We show that the PBP 3 mutation, in certain genetic backgrounds, decreases the level of resistance to cefotaxime by a factor of 2. Models are presented to explain this result.

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

Streptococcus pneumoniae isolates resistant to penicillin, chloramphenicol, tetracycline and sulfamethoxazole-trimethroprim are being recovered with increasing frequency in the United States. We analyzed the penicillin-binding proteins (PBPs), multilocus enzyme electrophoresis (MLEE) genotypes, and ribotypes of 22 multiresistant serotype 23F isolates of S. pneumoniae from the United States and 1 isolate each from Spain and South Africa. Also included were seven multiresistant isolates of other serotypes, three penicillin-resistant but chloramphenicol-susceptible serotype 23F isolates, and two penicillin-susceptible isolates (one penicillin-susceptible isolate was serotype 23F). Fifteen of the 22 multiresistant isolates from the United States and the isolates from Spain and South Africa had identical PBP patterns, MLEE profiles, and ribotypes. Six of the remaining seven multiresistant isolates were related by PBP pattern, but demonstrated slightly different MLEE and/or ribotype profiles, possibly because of acquisition of additional resistance markers (four of the six isolates were also resistant to erythromycin). The remaining multiresistant serotype 23F isolate had a unique PBP pattern and ribotype and was only distantly related to the other pneumococcal isolates by MLEE analysis. The PBP patterns, MLEE profiles, and ribotypes of the multiresistant serotype 23F isolates were easily distinguished from those of six multiresistant isolates of other serotypes; three other penicillin-resistant, chloramphenicol-susceptible, serotype 23F isolates; and two penicillin-susceptible isolates. One exception was a multiresistant serotype 19A isolate that was highly related to the clonal group by PBP pattern and MLEE analysis and that had a ribotype similar to those of the other erythromycin-resistant serotype 23F isolates. MLEE analysis and ribotyping were more discriminating than were the PBP patterns in discerning strain differences. These data strongly suggest that a multiresistant clone of S. pneumoniae serotype 23F that is related to multiresistant isolates from Spain and South Africa has become disseminated in the United States. Clinicians should be alerted to the spread of these multiresistant strains in the United States.

Increased rate of isolation of penicillin-resistant Streptococcus pneumoniae in a children's hospital and in vitro susceptibilities to antibiotics of potential therapeutic use

The isolation of Streptococcus pneumoniae with both high and intermediate resistance to penicillin has increased in our institution since 1989 to an average of 12.1% of all isolates. We determined the susceptibilities of 95 isolates (34 susceptible to penicillin, 42 intermediate in resistance to penicillin, and 19 resistant to penicillin) to 16 antimicrobial agents of potential use in the treatment of disease caused by S. pneumoniae. Susceptibility to penicillin was determined by broth macrodilution with Mueller-Hinton broth supplemented with 5% lysed horse blood. Isolates were classified as highly resistant when the MIC was greater than or equal to 2.0 micrograms/ml, intermediate in resistance when the MIC was between 0.1 and 1.0 microgram/ml, and susceptible when the MIC was less than 0.1 microgram/ml. Fifteen of 19 isolates found to be highly resistant to penicillin were recovered from the middle ear of children. None of the isolates recovered from cerebrospinal fluid was highly resistant to penicillin. Fifteen of these isolates highly resistant to penicillin were found to be serogroup 6. Susceptibilities to other antibiotics were determined by the agar dilution method with Mueller-Hinton agar containing 5% lysed horse blood and an inoculum of 10(4) CFU per spot delivered by a replicator device. The MIC for 90% of isolates increased with increasing penicillin resistance for all antibiotics tested, except chloramphenicol, ciprofloxacin, rifampin, and vancomycin. Regardless of the classification of penicillin resistance, all isolates were classified as susceptible to cefotaxime, cefpirome, cefpodoxime, clarithromycin, imipenem, rifampin, and vancomycin on the basis of National Committee for Clinical Laboratory Standards interpretive guidelines. Interpretation of susceptibilities on the basis of currently available guidelines is difficult in that susceptibility guidelines applicable specifically to S. pneumoniae are not available.

Bacteremic pneumonia caused by penicillin-resistant pneumococci: Case report and review with a Canadian perspective

A Canadian adult with bacteremic pneumonia caused by a relatively penicillin-resistant (minimal inhibitory concentration 0.25 μg/mL) Streptococcus pneumoniae is reported, and the published literature regarding penicillin-resistant pneumococci in Canada reviewed. Although penicillin resistance has been reported infrequently to date, this case emphasizes the need for routine antimicrobial sensitivity testing of all pneumococci isolated from normally sterile sites, and for ongoing systematic surveillance for penicillin and other antibiotic resistance in Canada.

Evaluation of the E-Test for susceptibility testing of pneumococci

The E-Test (AB Biodisk, Sweden) is an antibiotic gradient strip that is applied to an inoculated agar plate and results in an elliptical zone of inhibition that intercepts the graded strip, producing a quantitative (microgram per milliliter) result. Pneumococci (100) were used in this study, 38 penicillin-susceptible [minimal inhibitory concentrations (MICs), less than or equal to 0.12 micrograms/ml], 42 intermediately resistant (MICs, 0.12-1.0 micrograms/ml), and 20 resistant (MICs, greater than 1 microgram/ml). E-Test strips were evaluated on Mueller-Hinton agar plates with 5% sheep blood. Agar dilution MICs were determined by the National Committee for Clinical Laboratory Standards (NCCLS) method. Penicillin MICs for the E-Test tended to be slightly lower (one log2 dilution) than reference MICs due to the continuous scale from which E-Test MICs were read. All but two penicillin-susceptible isolates were correctly categorized by the E-Test method. Of the 62 penicillin-resistant strains, 59 had E-Test MICs of greater than or equal to 0.12 micrograms/ml, with 88% of these strains having E-Test MICs within one doubling dilution of the reference MICs. However, using the current NCCLS breakpoint MICs, many of the penicillin-resistant strains with reference MICs of 2 micrograms/ml were categorized as intermediate by the E-Test, with MICs of 0.38-1 microgram/ml. For chloramphenicol, erythromycin, and tetracycline, correlation of the two methods was excellent. E-Test chloramphenicol MICs provided clearer separation of susceptible and resistant strains than did the reference method. We conclude that the E-Test is a reliable method for determination of MICs of the antibiotics evaluated for pneumococci.

Susceptibilities of penicillin-susceptible and -resistant strains of Streptococcus pneumoniae to RP 59500, vancomycin, erythromycin, PD 131628, sparfloxacin, temafloxacin, win 57273, ofloxacin, and ciprofloxacin

The MICs of four new quinolones, sparfloxacin (AT-4140, CI-978), PD 131628 (the active form of the prodrug CI-990), temafloxacin, and Win 57273, compared with those of ciprofloxacin and ofloxacin were tested against 53 penicillin-susceptible, 35 penicillin intermediate-resistant, and 51 penicillin-resistant pneumococci. Susceptibility to RP 59500, a new streptogramin, was also tested and compared with those to the quinolones, erythromycin, and vancomycin. All MICs were determined by a standardized agar dilution method by using Mueller-Hinton agar supplemented with sheep blood. Quinolone, vancomycin, and RP 59500 susceptibilities were not affected by susceptibility or resistance to penicillin. For Win 57273, the MICs for 50% (MIC50) and 90% (MIC90) of strains tested were 0.015 and 0.03 micrograms/ml, respectively. MIC50S of both sparfloxacin and PD 131628 were 0.25 micrograms/ml, and MIC90S were 0.5 micrograms/ml. The MIC50 of temafloxacin was 0.5 micrograms/ml, and the MIC90 was 1.0 micrograms/ml. By comparison, ofloxacin and ciprofloxacin both yielded MIC50S of 1.0 micrograms/ml and MIC90s of 2.0 micrograms/ml. RP 59500 yielded an MIC50 of 0.5 microgram/ml and an MIC90 of 1.0 microgram/ml and was only 1 doubling dilution less active against 17 erythromycin-resistant strains. Vancomycin was active against all strains (MIC50, 0.25 microgram/ml; MIC90, 0.5 microgram/ml). All four experimental quinolones as well as RP 59500 show promise for therapy of infections with penicillin-resistant and -susceptible pneumococci.

Evaluation of vancomycin for therapy of adult pneumococcal meningitis

The emergence of pneumococci resistant to penicillin and other agents prompted us to evaluate intravenous vancomycin for the therapy of pneumococcal meningitis, which has an overall mortality of 30%. Eleven consecutive adult patients with cerebrospinal fluid (CSF)-culture-proven pneumococcal meningitis and positive initial CSF Gram stain were given intravenous vancomycin (usual dosage, 7.5 mg/kg every 6 h for 10 days). The MBCs of vancomycin ranged from 0.25 to 0.5 micrograms/ml. Early adjunctive therapy with intravenous dexamethasone, mannitol, and sodium phenytoin was also instituted. After 48 h of therapy, all 11 patients showed a satisfactory clinical response, although the CSF culture remained positive in one case; median trough CSF and serum vancomycin levels were 2 and 5.1 micrograms/ml, respectively, and trough CSF bactericidal titers ranged from less than 1:2 to 1:16. On day 3, one patient died of acute heart failure. Four patients had clinical failure at on days 4 (two patients), 7 (one), and 8 (one) of therapy; they all immediately responded to a change in antibiotic therapy. The remaining six patients were cured after 10 days of vancomycin therapy. At this point, median peak CSF and serum vancomycin levels were 1.9 and 18.5 micrograms/ml, respectively. A transient alteration of renal function occurred in two patients, and persistent slight hypoacusia occurred in three patients. In summary, 11 adults with pneumococcal meningitis were treated with vancomycin and early adjunctive therapy including dexamethasone. All patients initially improved, and 10 were ultimately cured of the infection. However, four patients experienced a therapeutic failure, which led to a change in vancomycin therapy.

Vancomycin

Vancomycin is a glycopeptide antibiotic that is active against staphylococci, streptococci, and other gram-positive bacteria. It is the drug of choice for the treatment of infections due to methicillin-resistant staphylococci, Corynebacterium jeikeium, and multiply resistant strains of Streptococcus pneumoniae. Vancomycin is an alternative treatment for serious staphylococcal and streptococcal infections, including endocarditis, when allergy precludes the use of penicillins and cephalosporins. Vancomycin is bactericidal against most strains of staphylococci and nonenterococcal streptococci. Although rare strains of staphylococci and enterococci that are resistant to vancomycin have been reported, bacterial resistance has thus far not emerged as a major clinical problem despite widespread use of vancomycin. When therapy is monitored by periodic determinations of serum concentrations of the drug and rapid infusion rates are avoided, vancomycin is rarely associated with serious toxicity.

Acute Therapy of Bacterial Meningitis

Antimicrobial therapy for bacterial meningitis has markedly reduced mortality rates from this disorder. The efficacy of an antibiotic in meningitis depends on many factors, including its penetration into cerebrospinal fluid (CSF), the bactericidal efficacy of the antibiotic within purulent CSF, and the need for bactericidal activity in CSF because bacterial meningitis represents an infection in an area of impaired host defense. Penicillin G and ampicillin are equally efficacious for meningitis caused by Streptococcus pneumoniae or Neisseria meningitidis. This recommendation may change, however, with the emergence of strains of pneumococci or meningococci that are relatively or highly resistant to penicillin; a third-generation cephalosporin (cefotaxime or ceftriaxone) should be used for meningitis due to relatively resistant strains and vancomycin for pneumococcal meningitis caused by strains that are highly resistant to penicillin. With the high percentage of strains of Haemopbilus influenzae type b that produce β-lactamase, empiric therapy when this organism is suspected should consist of a third-generation cephalosporin; these agents are also used for meningitis caused by enteric gram-negative bacilli, and one agent, ceftazidime, is effective against Pseudomonas aeruginosa meningitis. Despite the availability of effective bactericidal antibiotics, morbidity and mortality from bacterial meningitis remains unacceptably high. Recent studies using animal models of infection have demonstrated the beneficial effect of antiinflammatory agents in attenuating the CSF inflammatory response that may lessen many of the pathophysiological consequences of meningitis. Studies of adjunctive dexamethasone therapy suggest that these agents may reduce morbidity (specifically sensorineural hearing loss) and mortality (due to S. pneumoniae) in patients with bacterial meningitis. Controversy remains, however, concerning the use of dexamethasone in all patients with bacterial meningitis and further studies are necessary. In critically ill patients with bacterial meningitis, control of increased intracranial pressure and seizures may be useful and necessary in improving outcome.