Evaluation of the E-Test for susceptibility testing of pneumococci

Analysis of Susceptibility or Resistance to Antimicrobial Agents

Here were described the main three methods being used for analysis of antibiotic susceptibility or resistance of Streptococcus suis clinical isolates to antimicrobial agents: the Kirby-Bauer disk diffusion, the epsilometer test (E test), and the broth microdilution test. In each case, procedures, results, and interpretation are described, as well as their advantages or limitations when proceeds.

A Rapid Antimicrobial Susceptibility Test for Determining Yersinia pestis Susceptibility to Doxycycline by RT-PCR Quantification of RNA Markers

Great efforts are being made to develop new rapid antibiotic susceptibility tests to meet the demand for clinical relevance versus disease progression. This is important especially in diseases caused by bacteria such as Yersinia pestis, the causative agent of plague, which grows rapidly in vivo but relatively slow in vitro. This compromises the ability to use standard growth-based susceptibility tests to obtain rapid and proper antibiotic treatment guidance. Using our previously described platform of quantifying antibiotic-specific transcriptional changes, we developed a molecular test based on changes in expression levels of doxycycline response-dependent marker genes that we identified by transcriptomic analysis. This enabled us to determine the minimal inhibitory concentration of doxycycline within 7 h compared to the 24 h required by the standard CLSI test. This assay was validated with various Y. pestis strains. Moreover, we demonstrated the applicability of the molecular test, combined with a new rapid bacterial isolation step from blood cultures, and show its relevance as a rapid test in clinical settings.

Effect of Vaccination on Pneumococci Isolated from the Nasopharynx of Healthy Children and the Middle Ear of Children with Otitis Media in Iceland

Vaccination with pneumococcal conjugate vaccines (PCVs) disrupts the pneumococcal population. Our aim was to determine the impact of the 10-valent PCV on the serotypes, genetic lineages, and antimicrobial susceptibility of pneumococci isolated from children in Iceland.

Vaccination with pneumococcal conjugate vaccines (PCVs) disrupts the pneumococcal population. Our aim was to determine the impact of the 10-valent PCV on the serotypes, genetic lineages, and antimicrobial susceptibility of pneumococci isolated from children in Iceland. Pneumococci were collected between 2009 and 2017 from the nasopharynges of healthy children attending 15 day care centers and from the middle ears (MEs) of children with acute otitis media from the greater Reykjavik capital area. Isolates were serotyped and tested for antimicrobial susceptibility. Whole-genome sequencing (WGS) was performed on alternate isolates from 2009 to 2014, and serotypes and multilocus sequence types (STs) were extracted from the WGS data. Two study periods were defined: 2009 to 2011 (PreVac) and 2012 to 2017 (PostVac). The overall nasopharyngeal carriage rate was similar between the two periods (67.3% PreVac and 61.5% PostVac, P = 0.090). Vaccine-type (VT) pneumococci decreased and nonvaccine-type (NVT) pneumococci (serotypes 6C, 15A, 15B/C, 21, 22F, 23A, 23B, 35F, and 35B) significantly increased in different age strata post-PCV introduction. The total number of pneumococci recovered from ME samples significantly decreased as did the proportion that were VTs, although NVT pneumococci (6C, 15B/C, 23A, and 23B) increased significantly. Most serotype 6C pneumococci were multidrug resistant (MDR). Serotype 19F was the predominant serotype associated with MEs, and it significantly decreased post-PCV introduction: these isolates were predominantly MDR and of the Taiwan^19F-14 PMEN lineage. Overall, the nasopharyngeal carriage rate remained constant and the number of ME-associated pneumococci decreased significantly post-PCV introduction; however, there was a concomitant and statistically significant shift from VTs to NVTs in both collections of pneumococci.

Rapid Antibiotic Susceptibility Determination for Yersinia pestis Using Flow Cytometry Spectral Intensity Ratio (SIR) Fluorescence Analysis

Rapid antimicrobial susceptibility tests (ASTs) are essential tool for proper treatment of patients infected by Yersinia pestis (Y. pestis), the causative agent of plague, or for post-exposure prophylaxis of a population exposed to a naturally acquired or deliberately prepared resistant variant. The standard AST of Y. pestis is based on bacterial growth and requires 24–48 h of incubation in addition to the time required for prior isolation of a bacterial culture from the clinical or environmental sample, which may take an additional 24–48 h. In this study, we present a new and rapid AST method based on a fluorescence determination of the minimum inhibitory concentration (MIC). Our method includes the incubation of bacteria with an antibiotic, followed by staining of the bacteria with oxonol dye (SynaptoGreen C4/FM1–43), which enables the rapid detection of an antibiotic’s effect on bacterial viability. We show that stained, non-viable bacteria exhibit a spectral redshift and an increase in fluorescence intensity compared to intact control bacteria. Based on these criteria, we developed a rapid flow cytometer measurement procedure and a unique spectral intensity ratio (SIR) analysis that enables determination of antibiotic susceptibility for Y. pestis within 6 h instead of the 24 to 48 h required for the standard AST. This new rapid determination of antibiotic susceptibility could be crucial for reducing mortality and preventing the spread of disease.

Risk factors for carriage of Streptococcus pneumoniae in children

Background

During the past decades Streptococcus pneumoniae has developed significant resistance to many classes of antimicrobial drugs. Potential risk factors for colonization of the nasopharynx by Streptococcus pneumoniae in children and for carriage of drug resistant strains were examined.

Methods

Between 2007 and 2008 nasopharyngeal swabs were collected from 402 children 6 months to 5 years old visiting the public sector immunization centers and outpatient departments as well as offices of paediatricians from private practice in Nicosia district in Cyprus. Information on demographic characteristics and potential risk factors of participating children were collected using a standardized questionnaire distributed to parents.

Results

In multivariable analyses we found that attendance at day care center, having siblings in the family and having both parents originating from Cyprus, statistically increased the risk of pneumococcal colonization. Full immunization with PCV7 appears to be a protective factor against colonization by pneumococcus. Previous administration of antimicrobials during the last month prior to specimen collection appeared to be the most consistent risk factor for carrying a non susceptible strain of Streptococcus pneumoniae to either penicillin or erythromycin. Factors such as age, nationality, previous or current breastfeeding, passive exposure to cigarette smoke and attendance in a day care center do not appear as independent risk factors for colonization by non susceptible strains.

Conclusions

Prudent use of antibiotics especially for upper respiratory tract infections in children as well as increased vaccination coverage by the pneumococcal conjugate vaccines could prove effective in reducing levels of colonization by drug resistant pneumococcal strains.

Serotype coverage of invasive and mucosal pneumococcal disease in Israeli children younger than 3 years by various pneumococcal conjugate vaccines

BACKGROUND

: Since the introduction of the 7-valent pneumococcal conjugate vaccine (PCV7) in the United States, the need for additional serotype coverage has become clear. Our objective was to assess the potential serotype coverage of PCV7 and of the 2 experimental conjugate vaccines, 10-valent (PCV10) and 13-valent (PCV13), against invasive pneumococcal disease (IPD), acute otitis media (AOM), acute conjunctivitis (AC), and pneumococcal carriage in southern Israel, where PCV7 had not yet been introduced at the time of the study.

METHODS

: Data on isolates were obtained prospectively from children <36 months during 2000-2004. The potential coverage of the PCVs was calculated and analyzed separately for antibiotic-resistant strains.

RESULTS

: A total of 5497 isolates were collected: 189 from blood or cerebrospinal fluid, 3197 from middle ear fluid, 348 from the conjunctiva, and 1763 from the nasopharynx of healthy children. The serotype coverage of PCV7 for IPD, AOM, AC, and carriage was 44%, 54%, 37%, and 46%, respectively. Serotypes included in PCV7 caused 47 IPD cases per 100,000 children <3 years (54 per 100,000 if serotype 6A is included). PCV10 extended mainly the coverage of IPD, while addition of serotypes 6A and 19A to PCV13 increased the coverage substantially in all entities (84%, 79%, 54%, and 67% in IPD, AOM, AC, and carriage, respectively). PCV13 could prevent >90% of penicillin-, macrolide-, and multidrug-resistant strains associated with IPD and AOM.

CONCLUSIONS

: PCV7 can substantially decrease pneumococcal disease and carriage in Israel, but PCV10 and PCV13 have a significant added benefit. Moreover, PCV13 has an important potential added benefit over PCV7 and PCV10 in reducing disease by drug-resistant Streptococcus pneumoniae.

The association between antibiotic use in the community and nasopharyngeal carriage of antibiotic-resistant Streptococcus pneumoniae in Bedouin children

BACKGROUND

The objective of the study was to evaluate whether the increase in antibiotic-resistant Streptococcus pneumoniae carriage was associated with antibiotic use in the community in children in Southern Israel.

METHODS

All the prescriptions given to Bedouin children <5 years old enlisted in 2 sentinel primary pediatric clinics treating approximately 20% of the Bedouin pediatric population of this age range were recorded, from 1998 to 2005. Nasopharyngeal pneumococcal isolates obtained during the same period from healthy children <5 years old were collected and antibiotic susceptibility was determined.

RESULTS

A total of 1488 of 1927 (77.7%) cultures were positive for S. pneumoniae. The proportion of S. pneumoniae with penicillin minimal inhibitory concentration > or = 1.0 microg/mL increased from 8% to 21% (P < 0.01); resistance to clindamycin from 9% to 22%; resistance to erythromycin from 13% to 30%; resistance to tetracycline from 13% to 31%; and multidrug resistance from 16% to 30%. The total annual antibiotic prescription rates decreased by 19%, from 3867 to 3191 prescriptions per 1000 children (P < 0.001). This was mainly the result of a reduction in amoxicillin +/- clavulanate prescriptions (from 3046 to 2582; P < 0.001). Oral cephalosporin, erythromycin and penicillin prescription rates decreased significantly as well (P < 0.001) whereas azithromycin prescription rates increased significantly (P < 0.001).

CONCLUSIONS

We suggest that the increased carriage of S. pneumoniae resistant to multiple antibiotics is possibly associated to the increased azithromycin consumption. Reduction of total antibiotic use may not be sufficient as long as antibiotics with high potential to promote multidrug resistance, given their pharmacokinetics and pharmacodynamics characteristics, are widely used.

An international serotype 3 clone causing pediatric noninvasive infections in Israel, Costa Rica, and Lithuania

BACKGROUND

Serotype 3 is known for its ability to cause invasive diseases worldwide. In the United States, after introduction of the 7-valent pneumococcal conjugate vaccine (PCV7), the prevalence of a serotype 3 clone (Netherlands-31/ST180) increased. The present study was aimed to evaluate the importance of serotype 3 clones in noninvasive infections in Israel, Costa Rica, and Lithuania.

METHODS

Molecular typing and antibiotic resistance were performed on 77 serotype 3 strains recovered from pediatric noninvasive infections during 2003-2005, and on 50 carried strains from healthy carriers.

RESULTS

Serotype 3 ranked second among isolates from noninvasive infections in Costa Rica and Lithuania, and seventh among the Israeli isolates. Pulsed field gel electrophoresis (PFGE) analysis revealed the presence of 1 major cluster (64/77, 83%); this cluster comprised 60/64 fully susceptible strains that corresponded to the Netherlands-31/ST180 clone, and 4/64 multidrug-resistant strains, all from Lithuania, that corresponded to ST505, a double locus variant of ST180. Two additional fully susceptible clones, ST458 (11/77, 14%) and ST1116 (2/77, 3%), were found among the Israeli and Costa Rican strains, respectively. The same PFGE clusters identified among noninvasive infections were found among 50 isolates from carriers, with the same molecular characteristics.

CONCLUSIONS

Serotype 3 accounts for a large proportion of mucosal disease in children, even before the introduction of PCV7. The data presented here describe for the first time the importance of a multidrug-resistant serotype 3 clone, ST505, in noninvasive infections.

Cellulitis in childhood invasive pneumococcal disease: a population-based study

AIM

There are few detailed data on the age-specific incidence and clinical pattern of pneumococcal cellulitis in children. We conducted a retrospective review of cellulitis as a subset of prospectively collected laboratory-identified invasive pneumococcal disease (IPD) and performed a systematic review of published literature.

METHODS

Prospective laboratory surveillance in urban regions of New South Wales, Australia, 1 June 1997-31 December 2001. Medical notes reviewed for each identified case and defined literature search strategy applied.

RESULTS

There were 1067 cases of IPD in children aged 0-17 years; 38 (3.3%) were cellulitis (32 periorbital, 6 buccal). Compared with other types of IPD, a greater proportion of cellulitis cases occur in children<2 years (30/38, 79% vs. 617/1029, 60.0%; P=0.004) in whom underlying illness was less common (0/30, 0% vs. 53/590, 9%; P=0.06). Initially, another diagnosis was made in 13 (34%) of cases; only five had a lumbar puncture, all normal. Of the 239 cases of pneumococcal cellulitis documented in the literature, 28 (11.7%) had the diagnosis made by means other than positive blood culture and 95% were facial or orbital with underlying illness (6%) and associated meningitis (1.9%) uncommon.

CONCLUSION

Cellulitis is an uncommon focus in IPD in children, and is almost always facial. Most cases occur under 2 years of age, are seldom associated with meningitis or other complications, and are frequently not recognised on admission.

Penicillin-Resistant Pneumococci in Sweden 1997–2003: Increased Multiresistance Despite Stable Prevalence and Decreased Antibiotic Use

Antimicrobial resistance patterns and capsular groups of penicillin-resistant Streptococcus pneumoniae (PRP; MIC penicillin G > or = 0.5 mg/ml) in Sweden between 1997 and 2003 were described, and trends in resistance and antibiotic sales during the same period were compared. The most common serogroups were in descending order 9, 19, 14, 23, and 6. Despite a low and stable annual PRP rate (proportion of PRP out of all pneumococci) of around 2% during the study period, the proportion of PRP resistant to other antibiotics increased. Of all tested PRP isolates, 82% were also resistant to trimethoprim/sulfamethoxazole, 32% had additional resistance to tetracycline, and 26% to erythromycin. Antibiotic sales figures for all studied antibiotic subgroups decreased during the same period. Little correlation was found between antibiotic sales and PRP resistance rates, indicating that there are still other poorly defined factors contributing to the reported resistance levels in the population. However, although PRP strains in Sweden are becoming more commonly resistant to antibiotics other than beta-lactams, the low and further reduced antibiotic sales still might have delayed the development and rapid spread of PRP in the population.

Antibiotic susceptibility and serotype distribution in Streptococcus pneumoniae circulating in Italy: results of the SEMPRE surveillance study (2000-2002)

During 2000-2002, 20 clinical microbiology centres collected 1623 Streptococcus pneumoniae isolates. Susceptibility to penicillin, amoxicillin, amoxicillin/clavulanic acid, cefaclor, cefuroxime, cefotaxime, clarithromycin, ciprofloxacin, levofloxacin, rifampicin and teicoplanin was determined locally by the Etest and/or by the microdilution method by three co-ordinating centres. Total resistance to penicillin increased from 15.2% to 16.1% and macrolide resistance increased from 37.9% to 43.7%. Overall, the most effective drugs (>99% susceptible strains) were amoxicillin, amoxicillin/clavulanic acid, levofloxacin and rifampicin. The most frequent serotypes were: 23F (15.8%), 3 (10.8%) 14 (9.1%), 19F (9.1%), 6B (7.2%), 19A (6.9%) and 6A (4.8%). In conclusion, penicillin and macrolide resistance is increasing in Italy, whilst fluoroquinolone currently remains active. The most common serotypes circulating are included in the heptavalent conjugate vaccine, with the exception of type 3.

Clinical and bacterial characteristics of acute bacterial conjunctivitis in children in the antibiotic resistance era

BACKGROUND

Acute conjunctivitis is the most common eye disorder in young children. Bacteria are responsible for 54-73% of all cases. The goals of the study were to identify the rates of Haemophilus influenzae, Streptococcus pneumoniae and Moraxella catarrhalis in cases of bacterial conjunctivitis in children and to define antibiotic resistance rates.

METHODS

During a 2-year study period, conjunctival swabs of children 2-36 months old were collected prospectively. Nontypable H. influenzae, S. pneumoniae and M. catarrhalis were defined as the study pathogens. Analyzed variables included demography, clinical presentation, bacteriologic results and susceptibility patterns.

RESULTS

There were 428 patients enrolled. Of all cultures, 55% (237 of 428) yielded at least 1 of the study pathogens. H. influenzae and S. pneumoniae were isolated from 29 and 20% of cultures, respectively. beta-Lactamase production was found in 29% of H. influenzae isolates, and penicillin nonsusceptibility was observed in 60% of S. pneumoniae isolates. The most common S. pneumoniae serotypes were: 19F (14%); 6A and 14 (11% each). Nontypable S. pneumoniae was found in 12%. The 7-valent pneumococcal conjugate vaccine (PCV-7) could potentially cover 44% of all isolates. Conjunctivitis-otitis syndrome was found in 32% of patients, of whom 82% of cultures yielded H. influenzae.

CONCLUSIONS

Antibiotic resistance rates are alarmingly high. Conjunctivitis-otitis syndrome, predominantly caused by H. influenzae, is quite common. The potential coverage of the PCV-7 in conjunctivitis is relatively lower than that reported in other pneumococcal infections. Our findings should alert physicians on the choice of appropriate antibiotic treatment, on the frequent copresence of acute otitis media and on the potential role of conjunctivitis in the spread of antibiotic-resistant pathogens.

Community prescribing and resistant Streptococcus pneumoniae

We investigated the association between prescribing antimicrobial agents and antimicrobial resistance of Streptococcus pneumoniae among children with acute otitis media in southern Israel. During a 6-year period, all prescriptions of a sample of ≈20% of Jewish and Bedouin children <5 years of age were recorded and all pneumococcal isolates from middle ear fluid were collected. Although antimicrobial drug use was significantly higher in Bedouin children, the proportion of S. pneumoniae isolates with penicillin MIC ≥1.0 μg/mL was significantly higher in Jewish children. In both populations, antimicrobial prescriptions were markedly reduced over time, especially for penicillins and erythromycin. In contrast, azithromycin prescriptions increased from 1998 to 2001 with a parallel increase in macrolide and multidrug resistance. Penicillin resistance was associated with macrolide resistance. These findings strongly suggest that azithromycin affects increased antimicrobial resistance, including multidrug resistance, in S. pneumoniae.

Antimicrobial susceptibility and serotype distribution of Streptococcus pneumoniae causing meningitis in Egypt, 1998–2003

OBJECTIVES

To determine the antimicrobial susceptibility and serotype distribution of 205 isolates of Streptococcus pneumoniae, collected from the CSF of meningitis patients identified between 1998-2003, during sentinel meningitis surveillance in Egypt.

METHODS

Antimicrobial susceptibility was evaluated against six antibiotics using disc diffusion and Etest methods. Serotyping was performed by latex agglutination and the Quellung test.

RESULTS

Forty-nine percent of all isolates were found to be non-susceptible to penicillin (46% intermediate, MIC range 0.12-1.0 mg/L; 3% resistant, MIC = 2.0 mg/L), and 6% of the isolates were non-susceptible to ceftriaxone (5% intermediate, MIC = 1.0 mg/L; 1.3% resistant, MIC >/= 2 mg/L). Resistance rates for tetracycline and trimethoprim/sulfamethoxazole were high (52 and 59.7%, respectively), but those for erythromycin and chloramphenicol were lower (11 and 9%, respectively). Five serotypes (6B, 1, 19A, 23F and 6A) accounted for 37% of the total isolates. Ten isolates (5%) were non-typeable. Overall, 29 and 42% of serotypes were represented in the 7- and 11-valent conjugate vaccines, respectively. However, vaccine coverage for children <2 years was 38 and 56% for the 7- and 11-valent, respectively.

CONCLUSIONS

Resistance to penicillin may be increasing among S. pneumoniae strains causing meningitis in Egypt, and a moderate proportion of these strains are not covered by current pneumococcal conjugate vaccines. In addition to intensifying education efforts about judicious use of antibiotics, laboratory-based surveillance for other forms of invasive pneumococcal disease, especially pneumonia, is needed before decisions can be made regarding the most effective vaccines for control of this disease in Egypt.

Effect of the 7-valent pneumococcal conjugate vaccine on nasopharyngeal colonization by Streptococcus pneumoniae in the first 2 years of life

BACKGROUND

Studies suggest that the 7-valent pneumococcal conjugate vaccine (PCV7) reduces carriage of vaccine-type (VT) Streptococcus pneumoniae (SP). We studied the effect of PCV7 on carriage of VT- and non-VT (NVT) SP, by studying the effect of PCV7 on nasopharyngeal (NP) colonization by VT and NVT SP during early childhood.

METHODS

At 2 months of age, 278 infants were enrolled in this study. To determine carriage of SP, NP samples were obtained before each PCV7 dose, at 9 months of age, and 2-3 months after the booster dose of vaccine.

RESULTS

The carriage of SP increased slightly, from 12% (95% confidence interval [CI], 8%-16%) of subjects at 2 months of age to 18% (95% CI, 13%-23%) at 4 months of age (P<.05). Carriage of SP remained in 24%-30% of subjects during subsequent months. Between the 12- and 18-month visits, the carriage rate of VT SP decreased significantly, from 18% (95% CI, 13%-23%) to 9% (95% CI, 5%-13%) of subjects (P=.001). The trend of a decrease in carriage of penicillin-nonsusceptible SP, from 16% of subjects (95% CI, 11%-21%) at the 12-15-month visit to 9% (95% CI, 5%-13%) at the 15-18-month visit, was found after the booster dose of vaccine.

CONCLUSION

The reduction of VT-SP colonization and replacement by NVT SP after the booster dose of vaccine suggests the possibility that widespread vaccination will result in replacement of pneumococci mainly by antibiotic-susceptible NVT SP.

Antibiotic-resistant invasive pediatric Streptococcus pneumoniae clones in Israel

Antibiotic-resistant international clones of Streptococcus pneumoniae are increasingly reported in different parts of the world. We investigated the spread of these clones through an active surveillance performed at the Israeli Streptococcal National Center during 1998 and 1999. Isolates were tested for antibiotic susceptibility, serotyped, and genotyped by random amplified polymorphic DNA analysis and pulsed-field gel electrophoresis. Of 437 isolates, 276 (63.4%) were antibiotic resistant and 156 (35%) were penicillin nonsusceptible (PNS). The PNS isolates were less frequently encountered in southern Israel (27 of 136 [20%]) than in other regions (127 of 301 [42%]). Among 276 antibiotic-resistant isolates, 43 fingerprint patterns were observed. The most common clones were 9V/14-a (19.2%), 5-a (17.8%), and 1-a (10%). The 9V/14-a clone was less common, while the 1-a clone was more frequent in the south than in other regions. The 5-a clone was more common in Jerusalem than in other regions. Among the Jewish and Arab populations the most frequent clones were 9V/14-a (20%) and 1-a (25%), respectively. Three international clones, 9V/14-a-Spain(9V)-3, 6B-a-Spain(6B)-2, and 5-a-Colombia(5)-19, comprised 40% of all antibiotic-resistant isolates and 56% of all PNS isolates. The seven-valent conjugate vaccine covers 58% of the most common clones, all highly PNS clones, and 94% of the multidrug-resistant clones in Israel, while the nine-valent vaccine covers all of them. The most common antibiotic-resistant invasive pediatric S. pneumoniae clones-mainly the three international ones-contribute significantly to increases in antibiotic resistance. Their geographic distribution varies within the country and between the different populations.

Microbiology of otitis media in Costa Rican children, 1999 through 2001

BACKGROUND

Because of the increasing number of resistant middle ear pathogens and the impact of the new conjugate Streptococcus pneumoniae vaccine, an active surveillance of the microbiology and susceptibility pattern of middle ear pathogens is required.

OBJECTIVE

To study the microbiology and susceptibility pattern of middle ear pathogens obtained from Costa Rican children with acute otitis media (AOM), recurrent otitis media (ROM) and therapeutic failure otitis media (FOM).

METHODS

Between 1999 and 2001 middle ear fluid (MEF) was collected from 276 Costa Rican patients. S. pneumoniae serotyping and pulsed field gel electrophoresis analysis was done on available strains.

RESULTS

Among the total study population, 102 were AOM patients, 98 were ROM patients and 76 were FOM patients. Overall S. pneumoniae (88 strains) was the most common pathogen isolated followed by Haemophilus influenzae (41 strains) and Streptococcus pyogenes (10 strains). H. influenzae was the most common agent in FOM patients (P = 0.015). Beta-lactamase production was observed in 3 of 41 (7%) H. influenzae strains and 3 of 3 (100%) Moraxella catarrhalis strains. Penicillin-nonsusceptible S. pneumoniae strains were more common in FOM (64%) and ROM (63%) patients than in AOM (42%) patients (P = 0.05). S. pneumoniae serotype 19F was the most prevalent serotype, mainly within one distinct clone.

CONCLUSIONS

Overall S. pneumoniae serotype 19F was the most common isolate from the middle ear fluid of Costa Rican children. Beta-lactamase-negative H. influenzae was the most prevalent in the subpopulation of patients with FOM. S. pyogenes was the third most common isolate and M. catarrhalis was uncommon.

Vaccination of day-care center attendees reduces carriage of Streptococcus pneumoniae among their younger siblings

AIM

We conducted a study to determine whether administration of a pneumococcal conjugate vaccine to toddlers attending day-care centers (DCCs) could prevent acquisition of Streptococcus pneumoniae of the vaccine serotypes (VT) by their younger siblings.

METHODS

In a double blind study, 262 DCC attendees ages 12 to 35 months were randomized to receive a 9-valent pneumococcal conjugate vaccine (PnCRM9; n = 132), or a control vaccine (meningococcus C vaccine; n = 130). It was planned to follow the groups for 2 years with monthly nasopharyngeal pneumococcal cultures during the first follow-up year and every 2 months during the second year. Forty-six younger siblings of the above described children, age <18 months (23 siblings of the PnCRM9 recipients and 23 of the controls), were also enrolled, and nasopharyngeal cultures were obtained monthly until the children reached the age of 18 months or started to attend DCC, if before the age of 18 months. Pneumococcal isolates were serotyped and tested for antibiotic susceptibility.

RESULTS

Of the 3748 cultures obtained from the DCC attendees, 2450 (65%) were positive for S. pneumoniae. Of 306 cultures obtained from the younger siblings, 151 (49%) were positive. Among the PnCRM9 recipients, cultures were significantly less frequently positive for the VT S. pneumoniae than among the controls (13% vs. 21%, respectively; P < 0.001). The same pattern was seen in the younger siblings of PnCRM9 recipients vs. the siblings of controls (21% vs. 34%, respectively; P = 0.017). The reverse trend was seen for non-VT strains in both the DCC attendees (44% vs. 34%, respectively; P < 0.001) and their younger siblings (19% vs. 13%, respectively; P = 0.15). There was a significant decrease in the carriage rate of antibiotic-resistant S. pneumoniae in both the PnCRM9 recipients and their younger siblings. The relative risks (and 95% confidence intervals) to carry S. pneumoniae penicillin-nonsusceptible, resistant to > or =1, > or =2 and > or =3 antibiotic categories among younger siblings of PnCRM9 recipients vs. siblings of controls were 0.47 (0.31 to 0.70), 0.49 (0.33 to 0.71), 0.46 (0.30 to 0.73) and 0.49 (0.21 to 1.17), respectively. When acquired, VT and antibiotic-resistant S. pneumoniae were carried for a significantly shorter period of time among siblings of PnCRM9 recipients than in siblings of controls.

CONCLUSION

The marked effect of PnCRM9 administration to DCC attendees on carriage of VT and antibiotic-resistant S. pneumoniae among their younger household close contacts demonstrates a herd effect of the vaccine.

Effect of a nonavalent conjugate vaccine on carriage of antibiotic-resistant Streptococcus pneumoniae in day-care centers

BACKGROUND

In the developed societies, day-care centers (DCCs) play an important role in the spread of antibiotic-resistant pneumococci both within the facility and from the facility to the community. This study was conducted to determine the effect of a nonavalent pneumococcal conjugate vaccine (PCV-9) on the carriage of antibiotic-resistant pneumococci in the DCC.

SUBJECTS AND METHODS

Healthy DCC attendees ages 12 to 35 months were randomized to receive either PCV-9 or a control vaccine (conjugate meningococcus C vaccine) in a double blinded manner. Nasopharyngeal Streptococcus pneumoniae cultures were obtained from each subject before vaccination, monthly during the first year of follow-up and every 2 to 3 months during the second year of follow-up. For each isolate the serotype and antibiotic susceptibility were determined.

RESULTS

A total of 132 and 130 evaluable toddlers received either PCV-9 or the control vaccine, respectively. In total 3748 cultures were obtained, of which 2450 (65%) were positive for S. pneumoniae. The resistance rates to penicillin, trimethoprim-sulfamethoxazole and erythromycin were 36, 35 and 16%, respectively. Resistance rates to > or =1 and > or =3 antibiotic categories were 52 and 9%, respectively. Antibiotic resistance was found mainly in the 5 serotypes included in the pneumococcal conjugate vaccines (6B, 9V, 14, 19F and 23F) and in 2 related serotypes (6A and 19A). In the vaccinated group a clear and significant reduction of the carriage rate of the serotypes included in the vaccine and the related serotype 6A as well as an increase in the carriage rate of the serotypes not included in the vaccine were observed. In parallel a significant decrease in carriage rate of antibiotic-resistant pneumococci was observed. The reduction of carriage of antibiotic-resistant pneumococci was seen in all age windows but was greater in the age window <36 months.

CONCLUSIONS

The carriage rate of antibiotic-resistant S. pneumoniae, including multiply resistant S. pneumoniae, in DCC attendees is high. Pneumococcal conjugate vaccines seem to be an important tool for reducing the carriage rate of antibiotic-resistant pneumonia in DCCs.

Impact of single dose azithromycin on group A streptococci in the upper respiratory tract and skin of Aboriginal children

BACKGROUND

Aboriginal children living in remote Australia experience high rates of bacterial infection such as trachoma, otitis media and streptococcal skin infection, which often progress to associated chronic diseases in later life.

METHODS

In February, 1995, single dose azithromycin was given to 130 Aboriginal children with trachoma and their contacts. The impact of this program on respiratory and skin group A Streptococcus pyogenes carriage and infection was also monitored.

RESULTS

Immediately before treatment 90% of children had skin sores, 38% of sores had pus and 74% of sores with pus had group A Streptococcus (GAS). Overall 57% of children had GAS skin infections. At 2 to 3 weeks and 2 and 6 months after treatment, this proportion was 10, 32 and 51%, respectively. For the upper respiratory tract GAS recovery rates were 8% before treatment and 0, 11 and 15% at the 2- to 3-week, 2-month and 6-month posttreatment visits, respectively. Multiple types occurred concurrently in individuals, particularly after treatment. Identical types were sometimes recovered simultaneously from the upper respiratory tract and skin, suggesting that the high rates of acute rheumatic fever in this population in the absence of high rates of detectable throat GAS carriage could be related to high rates of skin GAS infection.

CONCLUSIONS

There is an urgent need for education, adequate housing, scabies eradication and improved hygiene to reduce skin trauma and subsequent GAS infection in this population. Clinical trials are needed to determine how these measures can best be integrated with the trachoma eradication program to maximize health outcomes.

Early onset pneumococcal sepsis in children hospitalized for noninfectious life-threatening events

During a 13-year period 9 patients admitted to a pediatric intensive care unit for life-threatening noninfectious conditions developed pneumococcal sepsis within 48 h of admission. All patients were Bedouins, a population group characterized by high prevalence of respiratory carriage of Streptococcus pneumoniae. In populations with high carriage rates of S. pneumoniae, critically ill children appear to be at increased risk of pneumococcal sepsis.

In vitro activity of novel fluoroquinolones against Streptococcus pneumoniae isolated from children with acute otitis media

BACKGROUND

In recent years, novel fluoroquinolones with improved activity against gram-positive organisms have been introduced into clinical practice. These drugs may be of potential benefit for the treatment of pneumococcal otitis media, including infections caused by organisms resistant to conventional drugs.

METHODS

In vitro activity of 6 fluoroquinolones against 77 pneumococcal isolates from middle-ear fluid was determined by the E test.

RESULTS

Resistance to penicillin, co-trimoxazole, erythromycin, clindamycin, and tetracycline was present in 59 (76.6%), 47 (61.0%), 19 (24.7%), 11 (14.3%), and 17 (22.1%) isolates, respectively. Fluoroquinolone MIC(50) and MIC(90) (in microg/ml) were as follows: ciprofloxacin: 1.0 and 3.0, levofloxacin: 0.75 and 1.0, sparfloxacin: 0.25 and 0.38, grepafloxacin: 0.25 and 0.38, trovafloxacin: 0.094 and 0.125, and moxifloxacin: 0.19 and 0.25, respectively.

CONCLUSIONS

Novel fluoroquinolones and especially trovafloxacin and moxifloxacin appear to be of potential value for the treatment of acute otitis media caused by pneumococci resistant to traditional antibiotics.

A decade (1989-1998) of pediatric invasive pneumococcal disease in 2 populations residing in 1 geographic location: implications for vaccine choice

During 1 decade (1989-1998), data on invasive pneumococcal disease were collected prospectively to assess the burden of disease among Jewish and Bedouin children in southern Israel and the potential reduction in illness that can be achieved by using conjugate vaccines. Data on 513 children <15 years old with bacteriologically proven invasive pneumococcal disease were obtained. Among Jewish and Bedouin children <5 years old, incidence rates were 45 and 139 cases per 100,000 child-years of observation, respectively. Jewish and Bedouin children differed in clinical manifestations, seasonal patterns of disease, serotype distribution, and antibiotic susceptibility rates. The potential coverage by 7-, 9-, and 11-valent conjugate vaccines is 41%, 67%, and 71%, respectively, for Jewish children and 22%, 63%, and 65%, respectively, for Bedouin children. The 9- and 11-valent pneumococcal conjugate vaccines have the potential to substantially decrease invasive pneumococcal disease in southern Israel.

Antibiotic-resistant pneumococci carried by young children do not appear to disseminate to adult members of a closed community

Although antibiotic-resistant pneumococci have been frequently detected among day care center (DCC) attendees, the transmission of these organisms to other members of the community has not been adequately studied. Nasopharyngeal cultures were obtained from 152 children and 244 adult members of a closed community (a kibbutz) in Israel. Serotyping, antibiogram, and pulsed-field gel electrophoresis were performed to determine the relatedness of isolated pneumococci. Twenty (30%) of the 66 isolates from children showed decreased susceptibility to penicillin and 9 isolates (14%) were resistant to > or =3 drugs. Of the 16 isolates from adults, 5 (31%) were intermediately resistant to trimethoprim-sulfamethoxazole. Resistant strains carried by DCC attendees were not isolated either from their parents or from other adult members of the community. Despite the high degree of interpersonal contact occurring in a closed community, resistant pneumococcal strains carried by DCC attendees do not appear to be easily transmitted to the adult population, which suggests the existence of an immunological barrier.

Persistence of two invasive Streptococcus pneumoniae clones of serotypes 1 and 5 in comparison to that of multiple clones of serotypes 6B and 23F among children in southern Israel

We conducted a study to examine the clonal distribution of invasive serotype 1 and 5 isolates as representatives of serotypes that are rarely carried by healthy individuals compared to that of invasive serotype 6B and 23F isolates as representatives of serotypes often carried by young children for prolonged periods. All invasive serotype 1, 5, 6B, and 23F isolates recovered from blood cultures during January 1995 to May 1999 were analyzed; these included 66 serotype 1, 30 serotype 5, 11 serotype 6B, and 15 serotype 23F isolates. One hundred thirty-three nasopharyngeal (NP) isolates of the indicated four serotypes from healthy children were also studied. The strains were characterized using serotyping, antimicrobial susceptibility testing, and pulsed-field gel electrophoresis profiling. We found that both invasive and NP serotype 1 and 5 isolates were susceptible to penicillin and that each serotype showed only one clonal type. In contrast, serotype 6B and 23F strains showed different phenotypic characteristics as well as multiple clonal types; 10 clones were identified among 6B isolates, and 11 clones were identified among 23F isolates.

Epidemiology of invasive pneumococcal disease in urban New South Wales, 1997-1999

OBJECTIVES

To describe the serotypes, incidence and morbidity of invasive pneumococcal disease in urban New South Wales.

DESIGN

Prospective laboratory surveillance.

SETTING

Microbiology laboratories and hospitals in the Sydney, Hunter and Illawarra Statistical Divisions of NSW, June 1997 to May 1999.

RESULTS

1270 cases were identified in two years. Incidence of disease was highest in those aged < 2 years (96.4 per 100,000; 95% CI, 83.7-107.9) and > or = 85 years (100.1 per 100,000; 95% CI, 81.8-121.3). Incidence of disease increased significantly from the age of 60 years, compared with low rates in those aged 5-59 years. Underlying diseases predisposing to pneumococcal infection increased with age, from 4% (< 2 years) to 60% (> or = 65 years). A seven-valent conjugate vaccine would have covered 84.8% of serotypes in those aged 0-14 years, falling to 69% in those > or = 15 years. Penicillin resistance was significantly higher in the < 5 years group (19.0%) than in older people (14.6%).

CONCLUSIONS

Incidence of invasive pneumococcal disease was higher in this study using active surveillance than in previous Australian studies. An effective sevenvalent conjugate pneumococcal vaccine could prevent more than 80% of cases in children aged < 5 years.

Antimicrobial use and colonization with erythromycin-resistant Streptococcus pneumoniae in Greece during the first 2 years of life

We evaluated nasopharyngeal colonization with erythromycin-resistant Streptococcus pneumoniae during the first 2 years of life in central and southern Greece. Of 2448 children studied from February 1997 to February 1999, 766 (31%) carried 781 pneumococcal isolates. Ninety-five (3.9%) of the children attended day care centers. Eighteen percent of the pneumococci were resistant to erythromycin (minimal inhibitory concentration 1 to >128 microg/mL), with 67.9% of them carrying the erm(B) gene and 29.2% mef(A) gene products. Four strains possessed neither the erm(B) nor the mef(A) gene. Multidrug resistance occurred in 97% and 40% of isolates carrying the erm(B) and mef(A) gene, respectively. An association was found between the erm(B) gene and serotypes 6B and 23F and between the mef(A) gene and serotypes 14 and 19F. A significant relationship existed between carriage of erythromycin-resistant pneumococci and use of macrolides or beta-lactams in the previous 3 months; the association was strongest when macrolide therapy was administered during the last month (odds ratio, 5.92; P=.0001). The findings indicate the necessity of a judicious use of both macrolides and beta-lactams in young children to reduce the colonization with erythromycin-resistant pneumococci and the subsequent spread of such strains to the community.

A comparative clinical study of pneumonia by penicillin-resistant and -sensitive Streptococcus pneumoniae in a community hospital

OBJECTIVE

This study aimed to determine the clinical difference of pneumonia between penicillin-resistant and penicillin-sensitive Streptococcus pneumoniae.

METHODOLOGY

Forty-nine cases in 46 patients of pneumococcal pneumonia were studied from December 1992 to May 1997. There were 24 cases (in 22 patients) of penicillin-resistant pneumococci (PRSP) pneumonia which were compared with 25 cases (in 24 patients) with penicillin-sensitive pneumococci (PSSP).

RESULTS

Both the mean age and the underlying disease states did not differ between the two groups. However, hospital-acquired pneumonia and previous use of antibiotics were observed in eight (33.3%) and 12 (50.0%) patients in PRSP compared with three (12.0%) and two (8.0%) in PSSP, respectively. The clinical efficacy rate and bacteriological eradication rates were 87.5 and 87.5% in PRSP compared with 87.5 and 87.0% in PSSP, respectively. Minimum inhibitory concentration (MIC) of antibiotics against 30 pneumococcal isolates was examined, and 10 strains ranged from 0.10-0.78 microg/mL and five strains were more than 1.56 microg/mL against penicillin G, while the MIC showed higher resistance to other antibiotics except for the carbapenems. Serotyping of the isolates by antiserum revealed differences in the predominant types PRSP (19F) and PSSP (6A,9V) [corrected].

CONCLUSIONS

We must care for not only community-acquired infection but also nosocomial transmission of PRSP pneumonia. Most patients with infections due to PRSP tended to have a milder illness with a good outcome (no patient died). As such it appears that empiric therapy for pneumococcal pneumonia does not require modification from what is recommended at present. However, in patients with infection due to highly resistant strains, and who are not responding to conventional therapy should have their treatment modified according to subsequent susceptibility testing.

Marked differences in pneumococcal carriage and resistance patterns between day care centers located within a small area

Carriage rates of Streptococcus pneumoniae and their antibiotic resistance, capsular types, and genetic patterns were studied among 264 children aged 12-35 months attending 8 day care centers located within a 2.5-mile radius in the same city. Nasopharyngeal cultures were obtained within a 2-month interval from all 264 children. Significant differences in each of the studied characteristics were found between day care centers, and each day care center had a unique pattern of the carried pneumococci. Our findings show that day care centers are independent microenvironments and emphasize their role in the transmission and augmentation of antibiotic-resistant S. pneumoniae in the community.

Amplified-fragment length polymorphism analysis versus macro-restriction fragment analysis for molecular typing of Streptococcus pneumoniae isolates

Forty-eight pneumococci were genotyped by on-line laser fluorescence amplified-fragment length polymorphism (AFLP) and pulsed-field gel electrophoresis (PFGE) analysis of chromosomal restriction fragments. Overall, the data generated by the two methods corresponded well. However, with AFLP, clusters were delineated at a higher similarity level, and isolate differentiation was more pronounced. AFLP and PFGE were equally efficient for assessing intraserotype diversity. We conclude that AFLP is a useful alternative to PFGE.

Dynamics of pneumococcal nasopharyngeal colonization during the first days of antibiotic treatment in pediatric patients

BACKGROUND

Nasopharyngeal (NP) carriage of antibiotic-resistant Streptococcus pneumoniae was shown to be associated with recent antibiotic treatment. To date no studies have evaluated early dynamics of pneumococcal NP carriage during antibiotic treatment.

OBJECTIVES

To observe changes in NP pneumococcal carriage within 3 to 4 days after initiation of antibiotic treatment in acute otitis media (AOM).

METHODS

Patients ages 3 to 36 months with AOM treated with various antibiotics were prospectively followed. Nasopharyngeal culture for S. pneumoniae was obtained before (Day 1) and 72 to 96 h after initiation of treatment (Days 4 to 5). Antibiogram and serotyping were performed in all isolates as was also the MIC of penicillin. The disappearance and persistence of the initial isolates as well as the appearance of isolates with new serotype or with new antibiotic susceptibility patterns were investigated.

RESULTS

A total of 120 patients were studied: 106 received beta-lactam antibiotics and 14 received azithromycin. Among the initial 76 pneumococcal isolates 63, 37 and 13% were resistant to > or =1, > or =2 and > or =3 antibiotic drugs. After 3 to 4 days of treatment with various beta-lactam drugs, 45, 63 and 100% of isolates with MIC values of <0.1 microg/ml, 0.125 to 0.25 microg/ml and 0.38 to 1.0 microg/ml, respectively, persisted in the NP (P = 0.038). There was a difference between the various beta-lactam drugs in their effect on NP colonization: a drug with lower MIC values (cefuroxime-axetil) had a better eradication rate of penicillin-susceptible organisms than a less active one (cefaclor), but neither significantly reduced carriage of penicillin nonsusceptible isolates. Azithromycin eliminated carriage of macrolide-susceptible organisms but increased the carriage of macrolide-resistant ones. In 19 of 120 (16%) patients a new S. pneumoniae isolate was recovered 3 to 4 days after initiation of treatment. Of those 16 (84%) were resistant to the drug the patient was receiving.

CONCLUSION

A rapid selection of nonsusceptible NP pneumococcal isolates during antibiotic treatment for AOM is common. This phenomenon may contribute to the spread of resistant pneumococci.

Antibiotic susceptibility patterns of Streptococcus pneumoniae in china and comparison of MICs by agar dilution and E-test methods

Beta-lactam resistance by Streptococcus pneumoniae is becoming a significant threat to public health worldwide. However, data concerning antibiotic susceptibility patterns in China have not been published. In this study, a total of 79 clinical isolates and 244 nasopharyngeal isolates of S. pneumoniae were recovered between June and November 1997 in Beijing. The agreement between the MICs (+/-1 log2 dilution) of penicillin and ceftriaxone obtained by the agar dilution and E-test methods for the 79 clinical strains was very good (97.5 and 93.7%, respectively). Of these 79 strains, 9 (11.4%) were intermediate and 2 (2.5%) were resistant to penicillin. Of the 244 nasopharyngeal strains, 32 (13.1%) were intermediate and 3 (1. 2%) were resistant to penicillin. The total of 277 penicillin-susceptible clinical and nasopharyngeal isolates of Streptococcus pneumoniae were 100% susceptible to amoxicillin-clavulanic acid, cefuroxime, ceftriaxone, and cefotaxime. In the 35 penicillin-intermediate and -resistant nasopharyngeal strains, elevated MICs of amoxicillin-clavulanic acid, cefuroxime, ceftriaxone, and cefotaxime were seen for Collapse

Key Words Collapse

MESH Headings

• Agar
• Drug Resistance, Microbial
• Humans
• Microbial Sensitivity Tests/methods
• Nasopharynx/microbiology
• Streptococcus pneumoniae/drug effects

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Grants

• Wellcome Trust

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Affiliation(s)

H Wang Department of Clinical Laboratories, Peking Union Medical College Hospital, Chinese Academy of Medical Sciences, Beijing 100730, People's Republic of China
R Huebner
M Chen
K Klugman

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Microbiology of acute otitis media in Costa Rican children

BACKGROUND

Because of the increasing number of resistant middle ear pathogens reported from different centers worldwide, an active surveillance of the microbiology and susceptibility pattern of middle ear pathogens is required for proper antimicrobial recommendations among different regions of the world.

OBJECTIVE

To study the microbiology and susceptibility pattern of middle ear pathogens obtained from Costa Rican children with acute otitis media.

METHODS

Between 1992 and 1997 a diagnostic tympanocentesis was performed in 398 Costa Rican patients with acute otitis media. Middle ear fluid was obtained for culture and minimal inhibitory concentrations were determined by the E-test technique in those isolates obtained between October, 1995, and January, 1997.

RESULTS

The most common pathogens cultured were Streptococcus pneumoniae (30%), Haemophilus influenzae (14%), Staphylococcus aureus (4%) and Streptococcus pyogenes (4%). Moraxella catarrhalis was uncommon. Beta-lactamase production was low (3.7%) among the H. influenzae isolates but frequent among the Staphylococcus aureus (57.1%) and M. catarrhalis (100%) strains. Overall 9 of 46 S. pneumoniae isolates (19.6%) exhibited decreased susceptibility to penicillin of which 8 isolates (17.4%) showed intermediate and one strain (2.2%) high level resistance. Among the penicillin-susceptible S. pneumoniae isolates, susceptibility to the following antimicrobials was: 81%, azithromycin; 89%, clarithromycin; and 100%, ceftriaxone and trimethoprim-sulfamethoxazole (TMP-SMX). Among the penicillin-resistant S. pneumoniae isolates the percentage of susceptible strains was 89% for azithromycin, clarithromycin and ceftriaxone and 67% for TMP-SMX.

CONCLUSIONS

Based on this microbiologic information the agents considered first line drugs in the treatment of acute otitis media in Costa Rica remain amoxicillin or TMP-SMX.

Antimicrobial susceptibilities of Campylobacter jejuni and coli by using E-test in Taiwan

To report the in vitro antibiotic susceptibility of Campylobacter species, we determined the MICs of 6 antibiotics by E-test for 93 human clinical strains and 35 chicken strains. The 6 antimicrobial agents tested were gentamicin, erythromycin, clindamycin, tetracycline, ciprofloxacin, and nalidixic acid. Isolates from humans were significantly more susceptible than chicken strains to erythromycin, clindamycin and ciprofloxacin. Nearly all of the human and chicken strains were susceptible to gentamicin. Among human isolates of C. jejuni, cross-resistance between nalidixic acid and ciprofloxacin was found in 66% of the strains, but none of the nalidixic acid-susceptible strains was resistant to ciprofloxacin. The higher prevalence of ciprofloxacin resistance in this area may be attributable to the large amount use of quinolones in poultry. Because of the high resistance rates of chicken isolates to the commonly used antimicrobial agents, it is necessary to create innovative methods to limit the inappropriate use of antibiotics in poultry in order to prevent the spread of the drug-resistant strains to humans.

Determination of penicillin MICs for Streptococcus pneumoniae by using a two- or three-disk diffusion procedure

The potential for the use of the disk diffusion method to accurately predict penicillin MICs for Streptococcus pneumoniae was investigated with penicillin (6 microg), methicillin (5 microg), and oxacillin (1 microg) disks. A total of 183 S. pneumoniae isolates were tested by three MIC procedures (agar dilution, microdilution, and E-test). Regression analyses of the geometric mean of the three MIC results against (i) the sum of the zone diameters for methicillin, penicillin, and oxacillin disks; (ii) the sum of the zone diameters for methicillin and penicillin disks; and (iii) each of the three individual zone diameters were performed. Calculated MICs were determined from each of these regression analyses and compared to the mean reference MICs. A high level of correlation was obtained with both the two- and the three-disk procedures (r = 0.97), with essential agreement rates (+/-1 doubling dilution) between MICs calculated by the three-disk procedure and the two-disk procedure and the mean reference MICs of 98.4 and 98.9%, respectively. No major or very major errors were obtained with the two- or three-disk procedures. The accuracy of the disks used individually was lower (r = 0.84 to 0.93). However, oxacillin and methicillin disk testing remain excellent for screening strains, with all penicillin-susceptible strains having zones of >21 and >22 mm, respectively. The combination disk procedure, which involves the use of three disks (methicillin, oxacillin, and penicillin) or two disks (methicillin and penicillin) for testing S. pneumoniae, can provide accurate penicillin MICs and qualitative category results that are comparable to results obtained by the E-test, agar, and microdilution MIC methods.

Reduction of pneumococcal nasopharyngeal carriage in early infancy after immunization with tetravalent pneumococcal vaccines conjugated to either tetanus toxoid or diphtheria toxoid

BACKGROUND

Pneumococcal nasopharyngeal colonization is important for transmission of the organisms. We assessed the ability of two tetravalent conjugate vaccines administered in early infancy to prevent carriage of vaccine-related pneumococci.

METHODS

A vaccine containing pneumococcal type 6B, 14, 19F and 23F polysaccharide conjugated to tetanus toxoid (Pnc-T) and a vaccine containing the same four polysaccharides conjugated to diphtheria toxoid (Pnc-D) were compared with placebo, in a double blinded study (25 infants per group). Vaccines (or placebo) were injected at 2, 4 and 6 months of age. At 12 months of age a native (nonconjugate) polysaccharide vaccine was administered as a booster. Serum type-specific anticapsular antibody concentrations were measured and nasopharyngeal cultures were obtained at 2, 4, 6, 7, 12 and 13 months of age.

RESULTS

In general carriage of all pneumococci (vaccine- and non-vaccine-related) was low at age 2 months and increased with age. However, for the vaccine-related serotypes (6A, 6B, 14, 19F and 23F) carriage was not increased with age in Pnc-D or Pnc-T recipients. Of all cultures obtained after the full primary series, 7 of 72 (10%), 3 of 62 (5%) and 19 or 70 (27%) were positive for the vaccine-related pneumococcal serotypes among the Pnc-D, Pnc-T and placebo recipients, respectively (P = 0.001 for Pnc-D vs. placebo; P = 0.014 for Pnc-T vs. placebo). Most of the antibiotic-resistant isolates belonged to the vaccine-related serotypes.

CONCLUSIONS

A significant reduction in the carriage of vaccine-related strains after administration of conjugate vaccines was observed. These preliminary results suggest that transmission of specific pneumococcal serotypes most often associated with disease and antibiotic resistance may at least partially be controlled by immunization.

Comparison of E-test with agar dilution for determining susceptibility of Streptococcus pneumoniae to penicillin

Minimum inhibitory concentrations (MICs) of penicillin for Streptococcus pneumoniae were determined by the E-test and the agar dilution method. Ninety Streptococcus pneumoniae strains were tested, of which 16 were resistant, 33 intermediate, and 41 susceptible by agar dilution. By the E-test, 80 (88.9%) strains agreed with these determinations within one log2 dilution step, and no strains disagreed by more than two dilution steps. Sixty-eight of the 70 strains with discrepant MICs read lower in the E-test, resulting in 15 strains being placed in different susceptibility categories when classified by this test. Exact MICs rather than classification groups should be used to determine appropriate antibiotic therapy, since small differences in MICs determined by different methods can lead to a significant degree of misclassification.

Evaluation of penicillin susceptibility in clinical isolates of Streptococcus pneumoniae oxacillin resistant

Antibiotic resistant pneumococci have been reported from all continents. Because of the importance of pneumococci in the aetiology of life-threatening diseases, the screening for penicillin resistance with oxacillin disc on all clinically significant isolates is suggested. However, discrepancy between the determination of penicillin resistance by oxacillin disc diffusion and the determination of penicillin minimum inhibitory concentration (MIC) has been reported. On this basis we have examined seven strains of Streptococcus pneumoniae isolated from patients recovered for the exacerbation of chronic bronchitis which were oxacillin-resistant. The assay of penicillin MICs showed that three isolates were moderately resistant to this agent, while four isolates resulted sensitive to penicillin as well as to cefotaxime. These results suggest that a further evaluation of penicillin MIC should be performed on those strains of S. pneumoniae resulting oxacillin-resistant.

Comparison of Etest to broth microdilution method for testing Streptococcus pneumoniae susceptibility to levofloxacin and three macrolides

When the Etest was compared to broth microdilution for susceptibility testing of Streptococcus pneumoniae, levofloxacin, erythromycin, and penicillin results correlated for both methods; azithromycin and clarithromycin showed discrepancies of > or = 2 dilutions for 95.8% and 31.5% of the isolates, respectively. Levofloxacin was active against 141 of 142 isolates (< or = 2.0 micrograms/ml), making it a potentially useful new fluoroquinolone.

Detection of penicillin resistance in Streptococcus pneumoniae by diffusion tests

Four different diffusion tests used to detect penicillin resistance in Streptococcus pneumoniae were evaluated for 34 penicillin-susceptible pneumococci (MIC < 0.1 microgram/ml), 35 intermediate pencillin-resistant (MIC 0.1-1.0 microgram/ml) and 23 penicillin-resistant strains (MIC > 2 micrograms/ml). The 1 microgram oxacillin disk from AB Biodisk, the 1 microgram oxacillin Neo-Sensitabs from Rosco, the 5 micrograms penicillin Low Neo-Sensitabs and the penicillin E test were tested on Mueller-Hinton blood agar, PDM Antibiotic Sensitivity Medium II supplemented with blood, and Danish Blood Agar. MICs obtained by the agar dilution method were used as reference. The 1 microgram oxacillin AB Biodisk was able to separate all the penicillin-susceptible pneumococci correctly from those with reduced penicillin susceptibility (MIC > or = 0.1 microgram/ml), whereas use of the 1 microgram oxacillin Neo-Sensitabs resulted in high frequencies (14-29%) of intermediate penicillin-resistant strains interpreted as penicillin susceptible. The 5 micrograms penicillin Low Neo-Sensitabs proved completely useless for detecting penicillin resistance in pneumococci. High rates of agreement (82-93%) were found between the penicillin E test and the reference MIC determination method on all the tested media.

Streptococcus pneumoniae carriage and penicillin/ceftriaxone resistance in hospitalised children in Darwin

BACKGROUND

The prevalence of resistant Streptococcus pneumoniae (SP) is increasing world-wide. Pneumococcal prevalence and susceptibility patterns are not known for children in the Top End of the Northern Territory.

AIMS

To determine the prevalence of nasopharyngeal carriage of pneumococci in children hospitalised in Darwin, and the extent of penicillin and ceftriaxone resistance in these isolates.

METHODS

Nasopharyngeal swabs were collected on admission from 85 children who had not received antimicrobials for their admission illness. Antimicrobial resistance was determined following selective culture for SP isolates. Minimal inhibitory concentrations (MICs) for penicillin and ceftriaxone were determined using the E-test method.

RESULTS

The overall prevalence of nasopharyngeal SP carriage was 44%. Carriage occurred more often in Aboriginal children from rural areas (56%) than in urban children (24%) (OR 3.94, 95% CI 1.35-11.78, p < 0.01). Thirty per cent of isolates were penicillin resistant, 35% were ceftriaxone resistant, and 49% were resistant to at least one of these. One isolate showed high-level resistance to both antimicrobials; all other resistant isolates were of intermediate-level resistance. For the same isolate, MICs for ceftriaxone were more often higher than those for penicillin. Five isolates had intermediate resistance to ceftriaxone whilst remaining sensitive to penicillin.

CONCLUSIONS

The prevalence of pneumococcal resistance to penicillin and ceftriaxone in hospitalised children in Darwin is much higher than previously reported in Australia. This has implications for future antimicrobial management and highlights the need for regular regional surveillance of SP resistance. The development of conjugate pneumococcal vaccines for children under two years is a priority.