Beta-lactam antibiotics and viridans group streptococci.

The aim of this review is to present an update on the susceptibility of viridans group streptococci (VGS) to ß-lactam antimicrobials, with emphasis on the Argentinean scenario. VGS are a heterogeneous group including five groups of species, each one exhibiting peculiar susceptibility patterns to penicillin (PEN). Species of the Streptococcus mitis group are frequently nonsusceptible to PEN. PEN resistance is associated with changes in PEN-binding proteins. In Argentina, one to two thirds of VGS are nonsusceptible to PEN. Third generation cephalosporins and carbapenems are currently more effective in vitro than PEN against VGS. Mortality was associated to nonsusceptibility to PEN in at least two studies involving patients with bacteremia caused by VGS. Treatment of endocarditis due to VGS should be adjusted/to the PEN susceptibility of the isolates. Vancomycin may be an alternative choice for treating endocarditis caused by PEN-resistant isolates (MIC≥4µg/ml).

[Development of a simple medium for the selective isolation of bacteria belonging to the Streptococcus anginosus group]. / Desarrollo de un medio simple para el aislamiento selectivo de bacterias del grupo Streptococcus anginosus.

Bacteria of the Streptococcus anginosus group (SAG) have recently been recognized as contributors of bronchopulmonary disease in cystic fibrosis (CF). Routine detection and quantification are limited by current CF microbiology protocols. The development of the CHROMagar™ StrepB chromogenic medium modified by the addition of plasma, nalidixic acid, colistin and sulfadiazine to make it selective for SAG bacteria is described. This medium could be used as a diagnostic tool to detect SAG in respiratory samples from patients suffering from chronic lung disease.

Resistance to ß-lactams in Streptococcus pneumoniae.

Streptococcus pneumoniae is an important causal agent of pneumonia, meningitis, sepsis, bacteremia, and otitis media. Penicillin resistance rates in S. pneumoniae have remained stable in Argentina in the last years. In the late '90s more isolates with MIC of penicillin ≥2µg/ml were observed; however, their frequency has decreased in recent years. The phenotypic expression of penicillin resistance is due to a modification in penicillin-binding proteins associated with a mosaic structure in the coding genes. The expansion of successful resistant clones varies among the different regions and is influenced by the use of antibiotics, vaccines, particularly conjugated ones, as well as population density. Parenteral treatment with high doses of penicillin G continues to be effective for the treatment of pneumonia and bacteremia, oral aminopenicillins for otitis media and sinusitis and third generation cephalosporins for meningitis.

Resistance to ß-lactams in enterococci.

Enterococci are intrinsically resistant to several antimicrobial classes and show a great ability to acquire new mechanisms of resistance. Resistance to ß-lactam antibiotics is a major concern because these drugs either alone or in combination are commonly used for the treatment of enterococcal infections. Ampicillin resistance, which is rare in Enterococcus faecalis, occurs in most of the hospital-associated Enterococcus faecium isolates. High-level resistance to ampicillin in E. faecium is mainly due to the enhanced production of PBP5 and/or by polymorphisms in the beta subunit of this protein. The dissemination of high-level ampicillin resistance can be the result of both clonal spread of strains with mutated pbp5 genes and horizontal gene transfer.

[Susceptibility of Streptococcus pyogenes isolated from invasive infections to trimethoprim-sulfamethoxazole]. / Sensibilidad a trimetoprima-sulfametoxazol de Streptococcus pyogenes aislados de infecciones invasivas.

It is erroneously believed that group A streptococci (GAS) are universally resistant to trimethoprim-sulfamethoxazole (TMS). This is mainly because media commonly used for in vitro determination of susceptibility to antibiotics contain thymidine, a nucleoside that antagonizes the antibiotic effect of TMS. The objective of this work was to determine EGA sensitivity to TMS in the presence and absence of thymidine. To this aim, 95 GAS isolates obtained from clinical tissues with i nvasive infections were analyzed. Susceptibility tests were performed by diffusion with TMS discs in Mueller Hinton agar supplemented either with 5% sheep blood or with 5% lysed equine blood (MH-LEB). Lysed equine blood contains thymidine phosphorylase, which degrades this nucleoside. Epsilometry (Etest) was used as gold standard. Quality controls with Enterococcus faecalis strain ATCC 29212 were satisfactory with both media. A 100% sensitivity to TMS was found in MH-SEL whereas 6 isolates (6.3%) resulted resistant in MH-SC; only one of them was found to have intermediate susceptibility by Etest (MIC > 1.5/28 υg/ml). The genetic determinants most frequently associated to TMS resistant EGA were not found in this isolate. Probably, if more accurate GAS-specific cut-off points were established for diffusion, the correlation with dilution methods or with the Etest could be improved, even employing MH-SB.

Susceptibility to ß-lactams in ß-hemolytic streptococci.

Group A (GAS), B (GBS), C (GCS) and G (GGS) ß-hemolytic streptococci are important human pathogens. They cause infections of different severity and frequency. Nowadays, after 70 years of use, penicillin is still universally active against GAS, GCS and GGS. However, therapeutic failures have been recorded in 2-28% of pharyngitis cases (median: 12%) attributable to different causes. By contrast, some GBS with reduced susceptibility to penicillin have been described, especially in Japan. In this group of bacteria, it is important to highlight that confirmation by reference methods is mandatory when decreased susceptibility to penicillin is suspected as well as checked for the detection of the mechanisms involved.

Group B streptococcal necrotizing pneumonia in a diabetic adult patient.

The aim of this report is to describe a rare case of necrotizing pneumonia due to group B Streptococcus serotype III in a relatively young male adult (48 years old) suffering from diabetes. The organism was isolated from his pleural fluid and was only resistant to tetracycline. The patient first received ceftazidime (2g/8h i.v.)+clindamycin (300mg/8h) for 18 days and then he was discharged home and orally treated with amoxicillin clavulanic acid (1g/12h) for 23 days with an uneventful evolution. As in the cases of invasive infection by Streptococcus pyogenes, clindamycin could prevent streptococcal toxic shock syndrome.

Molecular characterization of invasive Streptococcus dysgalactiae subsp. equisimilis. Multicenter study: Argentina 2011-2012.

Streptococcus dysgalactiae subsp. equisimilis (SDSE) has virulence factors similar to those of Streptococcus pyogenes. Therefore, it causes pharyngitis and severe infections indistinguishable from those caused by the classic pathogen. The objectives of this study were: to know the prevalence of SDSE invasive infections in Argentina, to study the genetic diversity, to determine the presence of virulence genes, to study antibiotic susceptibility and to detect antibiotic resistance genes. Conventional methods of identification were used. Antibiotic susceptibility was determined by the disk diffusion and the agar dilution methods and the E-test. Twenty eight centers from 16 Argentinean cities participated in the study. Twenty three isolates (16 group G and 7 group C) were obtained between July 1 2011 and June 30 2012. Two adult patients died (8.7%). Most of the isolates were recovered from blood (60.9%). All isolates carried speJ and ssa genes. stG62647, stG653 and stG840 were the most frequent emm types. Nineteen different PFGE patterns were detected. All isolates were susceptible to penicillin and levofloxacin, 6 (26.1%) showed resistance or reduced susceptibility to erythromycin [1 mef(A), 3 erm(TR), 1 mef(A)+erm(TR) and 1 erm(TR)+erm(B)] and 7 (30.4%) were resistant or exhibited reduced susceptibility to tetracycline [2 tet(M), 5 tet(M)+tet(O)]. The prevalence in Argentina was of at least 23 invasive infections by SDSE. A wide genetic diversity was observed. All isolates carried speJ and ssa genes. Similarly to other studies, macrolide resistance (26.1%) was mainly associated to the MLSB phenotype.

[Infections due to unusual bacteria and bacterial oncogenesis]. / Infecciones por bacterias poco comunes y oncogénesis bacteriana.

The recovery of an unusual organism in the clinical microbiology laboratory may be an indicator of an immunological abnormality in the patient. For instance, an important relationship between Clostridium septicum and colon carcinoma as well as between leukemia or lymphoma with species frequently considered contaminants (Bacillus spp., Corynebacterium spp.) or others rarely isolated from different contexts (Capnocytophaga spp.) were described. Some bacteria are almost exclusively isolated from AIDS patients (Rhodococcus equi). Campylobacter spp., Aeromonas spp., group G and mitis group streptococci were more frequently isolated in individuals suffering from any type of cancer than in other patients. Furthermore, some other bacteria can be considered markers of an undetected cancer that can be found mostly in neutropenic patients rather than in immunologically normal individuals. Possible mechanisms of bacterial oncogenesis include a modification of the inflammatory response, antigen-derived lymphoproliferation, and induction of hormones that increase epithelial cell proliferation. Typical examples of the above are: gastric adenocarcinoma induced by Helicobacter pylori, the association between group bovis bacteremia and colon carcinoma and the mucosa-associated lymphoid tissue (MALT) related to Helicobacter species (gastric MALT) and Chlamydophila spp. (ocular MALT). Isolation of any of these pathogens should require a thorough search for possible malignant diseases.

Serotype distribution of pneumococci isolated from pediatric patients with acute otitis media and invasive infections, and potential coverage of pneumococcal conjugated vaccines.

A 16-month prospective, descriptive study was conducted on pneumococcal serotype distribution isolated from children with acute otitis media (AOM) and invasive infections (INV). Eighty-nine children with pneumococcal INV and 324 with a first episode of AOM were included. Bacterial pathogens (N = 326) were isolated from the middle-ear fluid of 250 patients. A total of 30 pneumococcal serotypes were identified. Prevalent serotypes were 14, 19A, 9V, 3, 19F, 6A, 23F, and 18C in AOM and 14, 1, 19A, 5, 12F, 6B, and 18C in INV. Potential coverage with PCV10 vaccine would be 46.5 % and 60.7 % for pneumococci involved in AOM and INV, respectively; it would be 71.7 % and 73 % with PCV13. PCV10, conjugated with a Haemophilus protein, would have an immunologic coverage of 39.9 % for AOM vs. 18.5 % with PCV13. However, differences in the prevention of INV were crucial for the decision to include the 13-valent vaccine in the national calendar for children less than two years old in Argentina.

Macrolide resistance in Streptococcus pneumoniae isolated from Argentinian pediatric patients suffering from acute otitis media.

Macrolide-resistant Streptococcus pneumoniae emerged in Argentina in 1995, representing 26% of invasive infection isolates in children under 5 years old. The objectives of this study were to describe the prevalence of ermB and mefA genes in macrolide-resistant S. pneumoniae isolates from acute otitis media (AOM) and to determine their genetic relatedness. Between May 2009 and August 2010, 126 S. pneumoniae isolates from 324 otherwise healthy children with a first episode of AOM were included. Twenty six of these isolates (20.6%) were resistant to erythromycin. Most frequent serotypes were: 14 (46.2%), 6A (23.1%), 19F (7.7%) and 9V (7.7%). Twenty (76.9%) carried the mefA gene, 5 (19.2%) have the ermB gene, and 1 (3.9%) both ermB + mefA. Ten clonal types were identified, mostly related to Sweden(15A)-25/ST782 (SLV63), CloneB(6A)/ST473 and England(14)-9/ ST9. This is the first study assessing the mechanisms of macrolide resistance in pneumococci isolates from pediatric AOM in Argentina and their genetic relatedness.

Isolation of Serratia rubidaea from a mixed infection after a horse bite.

Horse bite infections are very rarely reported in the medical literature. Here we present a case of a severe facial infection in a 2-year-old boy after a horse bite, from which Serratia rubidaea and Enterobacter cloacae were isolated. Some pieces of grass were found inside the wound and were removed before performing a surgical toilet. The presence of these two gram-negative bacteria associated with a horse bite infection, as well as other organisms such as anaerobes, Pseudomonas, gram-positive cocci, Actinobacillus spp., previously described in other works, should be taken into account when selecting the antibiotics for prophylactic treatment of farm animal bites.

Epidemiology of Invasive Infections Caused by Streptococcus agalactiae in Argentina.

In recent years, an increase in the number of cases of invasive infections due to Streptococcus agalactiae (group B Streptococcus [GBS]) in adults has been reported. During 2014 and 2015, a multicentric, observational, and prospective study, including 40 health centers, was developed to describe the phenotypic and genotypic characteristics of GBS isolates circulating in Argentina and to analyze the clinical and demographic characteristics of patients with invasive infections. We recovered 162 invasive (GBSi) isolates from adult patients (n = 130, 80.2%), neonates (n = 24, 15%), and children below 18 years of age (n = 8, 4.8%), and colonizing (GBSc) isolates were recovered in prenatal GBS screening. GBS infection in adults was associated with underlying diseases, mainly diabetes mellitus. All isolates were penicillin susceptible. Resistance rates to erythromycin (25%) and clindamycin (26%) among the GBSc isolates were significantly higher than those from GBSi strains (17.3% and 16.1%, respectively); by contrast, levofloxacin resistance was significantly higher in GBSi isolates (14.8% vs. 7%). Serotype Ia was the most frequent in neonates and Ib was most frequent in adults. Serotypes Ia and III were prevalent in GBSc isolates. The increase of levofloxacin resistance was associated with the presence of a serotype Ib clone. This work emphasizes the need for GBS infection surveillance studies to implement correct treatments and adequate prevention strategies.

[Capability of national reference laboratories in Latin America to detect emerging resistance mechanisms]. / Capacidad de los laboratorios nacionales de referencia en Latinoamérica para detectar mecanismos de resistencia emergentes.

OBJECTIVE: To evaluate the capability of 17 national reference laboratories participating in the Latin American Quality Control Program in Bacteriology and Antibiotic Resistance (LA-EQAS) to detect emerging resistance mechanisms- namely: resistance of enterobacteria to carbapenems due to the presence of Klebsiella pneumoniae carbapenemase (KPC) and metallo-beta-lactamase (MBL) type IMP, and intermediate resistance of Staphylococcus aureus isolates to vancomycin (vancomycin-intermediate resistant S. aureus-VISA). METHODS: The following three isolates were sent to the 17 participating LA-EQAS laboratories: KPC -producing Klebsiella pneumoniae PAHO-161, IMP-producing Enterobacter cloacae PAHO-166, and S. aureus PAHO-165 with intermediate resistance to vancomycin. Performance of each of the following operations was evaluated: interpretation of sensitivity tests, detection of the resistance mechanism, and assessment of either inhibition halo size (disk diffusion method) or minimum inhibitory concentration (MIC). RESULTS: Concordance in the detection of resistance mechanisms was 76.4%, 73.3%, and 66.7% for the K. pneumoniae PAHO-161, E. cloacae PAHO-166, and S. aureus PAHO-165 strains, respectively. Concordance between the inhibition areas observed by the participating laboratories and the ranges established by the coordinating laboratory was acceptable for all three isolates, at 90.8%, 92.8%, and 88.9%, respectively. CONCLUSIONS: Overall concordance in on the detection of KPC, MBL, and VISA resistance mechanisms was 72.1%. We consider the national reference laboratories in Latin America capable of recognizing these emerging resistance mechanisms and expect that maximum levels of concordance will be reached in the future.

[Tinea capitis: two years experience in a paediatric hospital of Buenos Aires, Argentina]. / Tinea capitis. Experiencia de 2 años en un hospital de pediatría de Buenos Aires, Argentina.

Tinea capitis is an infection caused by dermatophytes of the genera Microsporum and Trichophyton, and constitutes a major health problem in Argentina. The aim of the present study was to find out the incidence of those etiological agents and the therapeutic response in patients attending a High-Complexity Paediatric Hospital within a two-year period. A total of 98 tinea capitis were diagnosed, 13 of which were Celsus kerion. Microsporum canis was isolated in 61.28%. The range of values for minimum inhibitory concentrations were >32, 0.06-4; <0.015-2; <0.015-0.25; 0.13-8; 0.06-128 microg/mL for fluconazole itraconazole, voriconazole, terbinafine, ketoconazole and griseofulvin, respectively.

Argentinian multicenter study on urinary tract infections due to Streptococcus agalactiae in adult patients.

INTRODUCTION: Streptococcus agalactiae (group B streptococcus, GBS) is a recognized urinary pathogen both in males and pregnant or non-pregnant women. Data regarding GBS serotypes recovered from urinary tract infections (UTIs) are scarce. The aim of this study was to describe the clinical and microbiological characteristics of UTIs caused by GBS in adult patients in Argentina. METHODOLOGY: A prospective multicenter study involving 86 centers was conducted in Argentina between July 1st, 2014 and June 30th, 2015. Antimicrobial susceptibility and serotype distribution of GBS isolated from the urinary tract of adult patients were determined. Susceptibility tests were performed by the disk diffusion and/or agar dilution methods. Epidemiological and clinical characteristics of the patients were considered to identify associated comorbilities. RESULTS: Seven hundred and one GBS were sent to the reference laboratory in the above mentioned period, however, only 211 fulfilled our selection criteria (demographic data availability, underlying diseases reported, colony counts greater than 105 CFU/mL, single organism isolated from the urine sample). No penicillin-resistant GBS was found but fluoroquinolone resistance was high (12.8%), especially among GBS isolated from men and non-pregnant women. UTIs due to GBS were associated to underlying diseases in men and non-pregnant women, particularly diabetes mellitus. Most of the isolates showed serotypes Ia and III. CONCLUSIONS: GBS are still susceptible to penicillin but fluoroquinolone resistance is a growing concern, at least in Argentina. There are underlying conditions that could be associated to urinary infections caused by GBS.

Fluoroquinolone-Resistant Streptococcus agalactiae Invasive Isolates Recovered in Argentina.

Background: Streptococcus agalactiae or group B Streptococcus (GBS) is an important pathogen in neonates and nonpregnant individuals. Epidemiological studies of GBS resistance to fluoroquinolones (FQs) in Latin America are scarce. This study aimed to determine the local prevalence of FQ resistance in the frame of a national, prospective multicenter study of invasive GBS infections and to investigate mechanisms of resistance, serotype distribution, and clonal relationships among resistant isolates. Methods: From July 2014 to July 2015, 162 invasive GBS isolates were collected from 86 health care centers in 32 Argentinean cities. All isolates were screened for FQ nonsusceptibility using a five-disc scheme: levofloxacin (LVX), ciprofloxacin, norfloxacin (NOR), ofloxacin, and pefloxacin (PF). LVX minimal inhibitory concentration (MIC) was determined by the agar dilution method. Sequencing of internal regions of gyrA and parC genes was performed. Capsular typing and genetic characterization of nonsusceptible isolates were assessed by latex agglutination, pulsed-field gel electrophoresis (PFGE), and multilocus sequence typing. Results: Twenty-four of one hundred sixty-two GBS isolates exhibited no inhibition zones to all tested FQs with an MIC range of 16-32 mg/L for LVX, and one isolate with MIC = 1 mg/L showed no inhibition zones around NOR and PF discs. In all resistant isolates, point mutations were detected in both genes. Serotype Ib was prevalent (88%). One PFGE type accounted for 84% of the FQ-resistant isolates and belonged to serotype Ib, sequence type 10. Conclusions: The prevalence of FQ resistance was 14.8% likely to be associated with dissemination of an ST10/serotype Ib clone. The unexpected high rate of resistance emphasizes the relevance for continuous surveillance of GBS epidemiology and antibiotic susceptibility.