Penicillin-resistant and multidrug-resistant Streptococcus pneumoniae in a pediatric hospital in Zagreb, Croatia

Nomenclature of major antimicrobial-resistant clones of Streptococcus pneumoniae defined by the pneumococcal molecular epidemiology network

The emergence of disease caused by penicillin-resistant and multidrug-resistant pneumococci has become a global concern, necessitating the identification of the epidemiological spread of such strains. The Pneumococcal Molecular Epidemiology Network was established in 1997 under the auspices of the International Union of Microbiological Societies with the aim of characterizing, standardizing, naming, and classifying antimicrobial agent-resistant pneumococcal clones. Here we describe the nomenclature for 16 pneumococcal clones that have contributed to the increase in antimicrobial resistance worldwide. Guidelines for the recognition of these clones using molecular typing procedures (pulsed-field gel electrophoresis, BOX-PCR, and multilocus sequence typing) are presented, as are the penicillin-binding profiles and macrolide resistance determinants for the 16 clones. This network can serve as a prototype for the collaboration of scientists in identifying clones of important human pathogens and as a model for the development of other networks.

Antimicrobial susceptibility of invasive Streptococcus pneumoniae in Italy by agar dilution method and E test

Few data on antimicrobial susceptibility of invasive Streptococcus pneumoniae isolated in Italy are available. Ninety-two invasive isolates from all over the country collected from January 1997 to April 1998 were tested for sensitivity to penicillin, erythromycin, ceftriaxone, chloramphenicol, tetracycline, and trimethoprim/sulfamethoxazole by the agar dilution method. Five (5.4%) strains were resistant to penicillin (one highly, four intermediately resistant), 8 (8.7%) to chloramphenicol, 27 (29.3%) to erythromycin, 17 (18.5%) to tetracycline (16 highly, one intermediately), and 21 (22.8%) to trimethoprim/sulfamethoxazole (14 highly, 7 intermediately). All strains were susceptible to ceftriaxone, although the penicillin-resistant strain had the highest minimal inhibitory concentration. (MIC) value (0.5 microg/ml); three penicillin-resistant strains were also resistant to erythromycin. Eight strains were multi-drug resistant, being also resistant to at least three antibiotics. The commercially available E test was compared with the standard agar dilution method for the determination of MIC of penicillin, erythromycin, ceftriaxone, chloramphenicol, and trimethoprim/sulfamethoxazole. E test established the same susceptibility categories for 100% of the strains tested for penicillin and ceftriaxone, 99% for chloramphenicol, 97% for erythromycin, and 74% for trimethoprim/sulfamethoxazole. According to our results, E test was simple to perform, easy to interpret, and a valid method for susceptibility testing of S. pneumoniae. Our study shows that in Italy the rate of penicillin resistance in invasive isolates of S. pneumoniae is one of the lowest in Europe (5.4%), while the rate of erythromycin is very high (29.3%) and is reaching the highest rates of other Southern European countries.

Penicillin-resistant Streptococcus pneumoniae in Argentina: frequent occurrence of an internationally spread serotype 14 clone

Six Latin-American countries participated in an epidemiological surveillance study conducted by the Pan American Health Organization in order to determine the relative prevalence of capsular types and antimicrobial resistance patterns of Streptococcus pneumoniae (SPN) causing invasive infections in children <5 years of age. In Argentina, the incidence of penicillin resistance (PR) was 24.4%, and it was significantly associated with serotype 14 (p < 0.001). The chromosomal DNA of 56 of those SPN isolates, 39 PR and 17 susceptible, was digested with SmaI and resolved by PFGE. Eighty-two percent (32/39) of the PR isolates shared characteristics with the widely spread International Spanish/French clone (clone B). All members of clone B except one expressed serotype 14, with the exception of one isolate that expressed serotype 19F and probably resulted from an in vivo capsular transformation event. Only a single isolate shared features with the 23F International Spanish/USA clone (clone A). The 17 penicillin-susceptible (PS) SPN isolates presented an enormous degree of variation in the chromosomal background, expressing 12 serotypes and 13 PFGE patterns. The data suggest that over 80% of the SPN-PR isolates in Argentina were imported, and this confirms the importance of the geographic spread of SPN clones in South America.

Geographic distribution of penicillin resistance of Streptococcus pneumoniae in Brazil: genetic relatedness

From January 1993 through December 1996, 1,252 Streptococcus pneumoniae strains from different geographic regions of Brazil were studied for penicillin (Pen) susceptibility. All pneumococci were isolated from normally sterile fluids from patients, newborns to 88 years old. Pen resistance (R) had a mean rate of 15.1%, with 14.5% of strains showing intermediate level Pen-R and 0.6% showing high-level Pen-R. Similar Pen-R rates were observed in different regions of the country, in the range of 9.5% to 17.1%. A Pen-R increase was noted from 9.6% in 1993 to 20.6% in 1996. Pen-R was mostly associated to serotypes 6B, 14, 19A, and 23F (89%). Chromosomal DNA relatedness of Pen-R strains was determined by pulsed field gel electrophoresis (PFGE). High genetic diversity was identified, being represented by 27 patterns among the 92 strains. Two important features were observed: the predominance of relatively low-level Pen MIC (range 0.1-0.5 mg/L) in 86 of the 92 strains, and the presence of 60.8% as four major PFGE clusters unique to Brazil. Another feature was the geographic spread of these clusters over large distances in the country. The city of São Paulo seems to be a Pen-R focus (18.4%) in Brazil. Only two strains representing the international clone B widely spread in France, Portugal, and Spain, belonging to serotype 14, were found.

Susceptibility and genetic relatedness of invasive Haemophilus influenzae type b in Italy

Haemophilus influenzae type b (Hib) still causes a large portion of meningitis in children less than 5 year old in Italy because vaccination against this agent has not been fully implemented in the country. We have studied 78 Hib strains and 4 nontypable H. influenzae (NTHi) isolated from the cerebrospinal fluid of subjects with meningitis for susceptibility to ampicillin, chloramphenicol, and ceftriaxone. The macrorestriction profiles of chromosomal DNA obtained by pulsed-field gel electrophoresis (PFGE) following digestion with SmaI and ApaI were also determined. All strains except one were equally susceptible to the antibiotics tested. One Hib strain, the only beta-lactamase producer, showed an intermediate susceptibility to ampicillin (MIC = 2 microg/ml), while maintaining full susceptibility to chloramphenicol and ceftriaxone. The analysis of the PFGE patterns showed that most of the Hib isolates, including the beta-lactamase-positive Hib strain, belonged to the same clone or to closely related subclones. For three PCR-confirmed NTHi isolates, we obtained completely different PFGE profiles. In conclusion, resistance to ampicillin still appears to be a rare finding in Hib strains causing meningitis in Italy; moreover, PFGE showed that the population structure of invasive Hib is essentially clonal.

Spread of the serotype 23F multidrug-resistant Streptococcus pneumoniae clone to South Korea

Thirty-eight antibiotic-resistant isolates of Streptococcus pneumoniae recovered in a hospital in Seoul, Korea, between February 1990 and March 1992 were analyzed for serotype, antibiotic susceptibility patterns, and chromosomal relatedness using pulsed-field gel electrophoretic (PFGE) analysis of SmaI chromosomal digests. Most of the isolates were from sputum samples, and a few strains were from otitis media and meningitis. The great majority of isolates (34 of 38, or 89%) were multiresistant, sharing virtually identical, elevated minimal inhibitory concentration (MIC) values (microgram/ml) for penicillin (1-2), chloramphenicol (12-25), tetracycline (25-30), and sulfamethoxazole/trimethoprim (> 100). Twenty of the isolates were also resistant to erythromycin, and all isolates were also considered to be resistant to ceftriaxone and cefotaxime (1-2) according to the new breakpoint definitions. The most frequent serotypes were 23F (17 of 38) and 19F(14 of 38); 2 belonged to serotype 15B and 1 of 24F. Of the remaining 4 isolates (2 serotype 3, 1 type 6B, and 1 type 9V) all were resistant to tetracycline and sulfamethoxazole/trimethoprim and with the exception of 1 of the type 3 strains, were also resistant to chloramphenicol. Eleven of the 14 serotype 19F isolates shared a relatively homogeneous PFGE pattern, which was indistinguishable from the PFGE pattern shown by most (12 of 17) of the 23F isolates. The PFGE pattern of these 19F and 23F isolates was also indistinguishable from the PFGE pattern shown by representative multiresistant capsular type 23F isolates from Croatia, Portugal, and New York City and the findings document the extensive geographic spread of this multidrug-resistant S. pneumoniae clone. The data also suggests in vivo capsular transformation of the multiresistant clone from serotype 23F to serotype 19F.

The apparent importation of penicillin-resistant capsular type 14 Spanish/French clone of Streptococcus pneumoniae into Uruguay in the early 1990s

Since 1987, Streptococcus pneumoniae (SPN) has been monitored in pediatric and adult populations. In 1994, the SIREVA/PAHO surveillance allowed the assessment of a dramatic increase of penicillin resistance, mainly associated to SPN type 14 also resistance to trimethoprim/sulfamethoxazole. To determine the genetic relatedness of the resistant isolates, analysis of SmaI digests of 61 isolates was performed by pulsed field gel electrophoresis (PFGE). Twelve different profiles were identified. The type 14 resistant SPN (n = 47) displayed a common B pattern, with 15 genetically related subtypes (1-6 bands of difference), with B1 the predominant one (51%). One of the subtypes (B12) was indistinguishable from a French isolate (M13P). This strain represented a South European clone, identified in the late 1980s, that also included serogroup 9 isolates. The type 23F isolates (n = 3) were identical with a representative strain of the well-characterized intercontinental type 23F clone. Neither the type 14 penicillin-susceptible (n = 4) nor the resistant SPN of other serotypes (n = 10) belonged to the B pattern. In summary, the results suggest that the dramatic increase of penicillin resistance in Uruguay depends on the introduction and spread of a type 14 clone, apparently imported from the south of Europe. Follow-up of this phenomenon is mandatory from the point of view of epidemiology and is also a priority for biologic research.

Predominance of the multiresistant 23F international clone of Streptococcus pneumoniae among isolates from Mexico

During a surveillance study to determine the relative prevalence of capsular types of Streptococcus pneumoniae and antimicrobial susceptibility of invasive isolates in children <5 years old in Mexico City, 220 isolates were collected. The serotype 23F was the most common found, followed by types 6A + B, 14, 19F, and 19A. Diminished susceptibility to penicillin was detected in 106 isolates (48.2%), and high penicillin resistance was found in 49 strains (22.2%), 31 belonging to type 23F. Resistance was also observed to erythromycin (13.1%), to chloramphenicol (43.1%), and to cefotaxime (10.9%). No strains were resistant to ofloxacin or vancomycin. Forty-four of the highly penicillin resistant isolates (penicillin MIC > or =2.0 microg/ml) were examined with molecular fingerprinting techniques; 29 (65.9%) of these isolates (all except two strains) were serotype 23F and shared subtype variants of PFGE type A characteristic of the internationally spread Spanish/USA clone of S. pneumoniae. These strains were also resistant to trimethoprim/sulfametoxasole (TMP/SMX), chloramphenicol, and tetracycline, and most of them were susceptible to erythromycin. Another 6 of the highly penicillin-resistant strains (serogroups 9 and 14) showed PFGE fingerprints and antimicrobial susceptibility pattern characteristic of a second internationally spread clone (French/Spanish clone) and carried resistance to penicillin and TMP/SMX. The rest of the 9 penicillin-resistant isolates were represented by 7 distinct additional PFGE types. The findings suggest that almost 80% of all highly penicillin resistant strains may have been "imported" into Mexico.

Molecular epidemiologic characterization of penicillin-resistant Streptococcus pneumoniae invasive pediatric isolates recovered in six Latin-American countries: an overview. PAHO/Rockefeller University Workshop. Pan American Health Organization

The Pan American Health Organization (PAHO) has conducted a study of Streptococcus pneumoniae in six Latin-American countries: Argentina, Brazil, Chile, Colombia, Mexico, and Uruguay. Sterile site isolates from children aged < or =5 years showing clinical symptoms of pneumonia (as defined by the clinical criteria of WHO), meningitis, sepsis or bacteremia (without infectious foci), arthritis, and peritonitis were the source of most of the invasive pneumococcal isolates collected between the end of 1993 and 1996 in the six participating countries. Partial characterization of these isolates (antibiotic resistance and serotyping) have already been described (Microbial Drug Resistance 3:(2):131-163, 1997). In the next phase of the study, 326 S. pneumoniae isolates with reduced penicillin susceptibility were transferred to the Laboratory of Microbiology at The Rockefeller University for molecular characterization, and a summary and overview of the findings is described in this article. Some of the most interesting findings were as follows: (1) There was a surprisingly high representation of two internationally spread clones, which made up >80% of the strains with penicillin MIC of 1 microg/ml or higher; most of these isolates were recovered in large cities, supporting the likelihood that the source of these clones is through international travel. (2) The frequency of resistance to trimethoprim/sulfamethoxazole was extremely high (present in 85% of all isolates with decreased penicillin susceptibility). (3) None of these isolates was resistant to ofloxacin, and macrolide resistance was rare (present in 6.4% of the isolates). (4) There was an apparent inverse relationship between level of penicillin resistance and genetic diversity. (5) There were striking differences in the "microbiologic profiles" of the six different Latin-American countries.

Penicillin-resistant Streptococcus pneumoniae in Colombia: presence of international epidemic clones. Colombian pneumococcal study group

The global spread of multidrug-resistant Streptococcus pneumoniae clones is well documented in the literature. A study to determine type distribution and antimicrobial susceptibility of invasive pneumococcal isolates from Colombian children under the age of 5 was conducted from 1994 to 1996. Health centers in Santa Fe de Bogota, Medellin, Cali, and other cities collected 409 Streptococcus pneumoniae isolates. Diminished susceptibility to penicillin (DSP) was 15.6%; from these, 11.5% showed intermediate-level resistance (ILR) and 4.1% showed high-level resistance (HLR). Fifty-nine of the DSP isolates were examined by pulse field gel electrophoresis (PFGE). Capsular isolate types were 23F (54%), 14 (24%), 19F (10%), 6B (7%), 9V (3%), and 34 (2%). PFGE analysis revealed that 8 isolates shared the Spanish/USA international clone's characteristic features: PFGE pattern type A, serotype 23F; 87.5% exhibited HLR for penicillin, and all were resistant to trimethoprim/sulfamethoxazole (TMP-SMX), tetracycline, and chloramphenicol. Another 7 isolates showed the French/Spanish international clone's features: PFGE pattern type B, 2 of them being serotype 9V; and 5 type 14; HLR to penicillin was 71%, and all proved resistant to TMP-SMX. A large cluster of 24 isolates (41% of all isolates examined) shared a common PFGE type C, with 14 subtypes; all but one, serotype 34, were serotype 23F and had ILR to penicillin; 58% were resistant to TMP-SMX and 50% to tetracycline, but none presented erythromycin or chloramphenicol resistance. The remaining 20 isolates could be grouped into 12 different PFGE types; ILR was shown in 75% of isolates, 70% were resistant to TMP-SMX and to tetracycline, 15% were resistant to erythromycin, and none were resistant to chloramphenicol. These data suggest that some Colombian isolates are clonally related to two of the well-known international epidemic S. pneumoniae clones.

Spread of the Spanish multi-resistant serotype 23F clone of Streptococcus pneumoniae to Seoul, Korea

Multi-resistant serotype 23F pneumococcal strains from an outbreak in a day-care centre in South Africa and strains from sporadic cases in Korea were analysed for their relatedness, by means of arbitrarily-primed PCR (AP-PCR), repetitive extragenic palindromic PCR (rep-PCR) and penicillin-binding protein (PBP) gene profiles. The South African strains previously shown to be identical to the 23F Spanish clone had identical AP-PCR and rep-PCR patterns to 13 Korean isolates. PBP gene analysis of strains from this cluster showed identical fingerprints, suggesting clonality. Isolates, identical genotypically to the 23F clone appeared to have acquired the type 19F and 14 capsular serotypes, respectively, a result that suggests horizontal transfer of capsular biosynthetic genes. These same techniques revealed three serotype 9V isolates not closely related to the 23F clone but which harbour PBP genes identical to the 23F clone. The data presented suggests that a clone of S. pneumoniae serotype 23F related to isolates from Spain and South Africa has become disseminated in Korea.

Ubiquitous distribution of the competence related genes comA and comC among isolates of Streptococcus pneumoniae

DNA probes specific for the pneumococcal competence regulatory genes comA and comC were used to test the presence of these genes in 214 pneumococcal isolates selected to represent a wide variety of clonal types and genetic backgrounds (as defined by chromosomal macrorestriction patterns and multilocus enzyme analysis), a variety of serotypes, isolation dates (between 1916 and 1996), geographic origins (on four continents), as well as different clinical origins (including both infection sites and colonization sites). Each isolate gave positive signal with both DNA probes. The comA and comC genes were never on the same SmaI restriction fragment and the comA gene showed a considerable degree of polymorphism from one strain to another. While DNA sequencing of 50 of the isolates have identified three distinct alleles of the comC gene, the number of mutations within the leader peptide were minimal. The results suggest that the mechanism to undergo genetic transformation is widespread within the species of Streptococcus pneumoniae.

Clonally related penicillin-nonsusceptible Streptococcus pneumoniae serotype 14 from cases of meningitis in Salvador, Brazil

Active hospital-based surveillance in the city of Salvador, Brazil, from December 1995 through October 1998, identified 221 patients with confirmed pneumococcal meningitis. Of these 221 patients, 29 (13%) had isolates with intermediate-level resistance to penicillin. Infection with these penicillin-nonsusceptible isolates was significantly associated with age of <2 years (P<.0019), previous antibiotic use (P<.0006), and coresistance to trimethoprim-sulfamethoxazole (P<.0000). Serotype 14 was the most prevalent serotype (55.2%) of penicillin-nonsusceptible isolates. Strain typing by repetitive element BOX polymerase chain reaction (PCR) analysis showed that penicillin-nonsusceptible serotype 14 isolates had closely related BOX PCR patterns, whereas penicillin-susceptible serotype 14 isolates each had distinct, unrelated patterns. Penicillin-nonsusceptible serotype 14 isolates from Salvador and other Brazilian cities had similar BOX PCR patterns. These observations indicate that in Brazil a large proportion of cases of penicillin-nonsusceptible pneumococcal meningitis appear to be caused by a closely related group of serotype 14 strains that may have disseminated to widely separate geographic areas.

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.

Molecular characterization of penicillin-resistant Streptococcus pneumoniae isolates from Bulgaria

As part of an ongoing surveillance program of antibiotic-resistant Streptococcus pneumoniae in Sofia, Bulgaria, 120 penicillin-resistant strains (PRSP) (most of them recovered from children hospitalized with pneumococcal disease) were analyzed by microbiological and molecular methods. Several unique features of this collection are of particular interest. (i) Most isolates (112 of 120) were also resistant to trimethoprim-sulfamethoxazole (SXT) (97 of 120 isolates, or 80%), and over 70% (86 of 120) of the isolates were resistant to at least three antibiotics in addition to penicillin. (ii) Close to 80% of all isolates were represented by large clusters of bacteria, each with a unique serotype, antibiotype, and chromosomal macrorestriction pattern (determined by pulsed-field gel electrophoresis), as well as unique restriction fragmentation length polymorphisms of the penicillin-binding protein genes pbp1a, pbp2x, and pbp2b. (iii) A large proportion (45 of 120, or 38%) of the strains belonged to two internationally spread epidemic clones of S. pneumoniae, the first expressing capsular type 23F and the second expressing serotype 9. (iv) A unique Bulgarian cluster composed of eight serotype 19F isolates was resistant to tetracycline, SXT, cefotaxime, and extremely high levels of penicillin and erythromycin. Nevertheless, this clone did not react with either the erm or the mef DNA probes, and thus the mechanism of macrolide resistance in this group of PRSP remains to be elucidated.

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

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

The ethnic minority traveler

Although the ethnic minority traveler is exposed to the same risks as other travelers, there are special considerations that make them vulnerable to certain diseases. In addition, many ethnic minority travelers are traditionally underserved by the medical community and often travel without the benefit of adequate counseling and immunization. The specific disease entities covered in this article include parasitic diseases (e.g. malaria, trypanosomiasis, intestinal helminths), tuberculosis, and other respiratory diseases, dengue, and sexually transmitted diseases and HIV.