Identification of coagulase-negative staphylococci other than Staphylococcus epidermidis by automated ribotyping

As routine identification of coagulase-negative staphylococci is problematic, the performance of automated ribotyping was evaluated for identification of coagulase-negative staphylococci other than Staphylococcus epidermidis. In total, 177 isolates were tested, comprising 149 isolates from blood samples, 15 isolates that were not identified by internal transcribed spacer (ITS)-PCR in a previous study, and 13 reference strains. The identification results were compared with those obtained by the API 20 Staph system, with standard phenotypic and molecular methods as reference. Most (n = 166; 93.8%) isolates were identified correctly by automated ribotyping. For 61 isolates, API 20 Staph and ribotyping were in agreement, but for 105 isolates, ribotyping provided correct identification and API 20 Staph did not. Four isolates not identified by automated ribotyping were recognised correctly by API 20 Staph. The remaining seven isolates could not be identified by either of the two methods. Automated ribotyping was able to distinguish Staphylococcus capitis reliably from Staphylococcus caprae. The results demonstrate the value of automated ribotyping for identification of coagulase-negative Staphylococcus (CoNS) isolates from human sources and may help to clarify the clinical relevance of CoNS species. In addition, automated ribotyping was able to detect polymorphisms that may be useful for epidemiological purposes within S. capitis, Staphylococcus hominis, Staphylococcus haemolyticus, Staphylococcus simulans, S. caprae, Staphylococcus warneri, Staphylococcus lugdunensis, Staphylococcus schleiferi, Staphylococcus sciuri, Staphylococcus pasteuri and Staphylococcus xylosus.

Normally functioning murF is essential for the optimal expression of methicillin resistance in Staphylococcus aureus

A carboxy-terminal fragment of murF was used to construct and insert a suicide plasmid into the chromosomal copy of the gene in the highly and homogeneously methicillin-resistant Staphylococcus aureus (MRSA) strain COL by Campbell type integration. The plasmid insertion generated a mutant in which the MIC value for oxacillin was reduced from 400 microg/ml of the parental strain to 0.75 microg/ml in 90% of the cells of the mutant cultures that were heterogeneous: they contained subpopulations of bacteria with a frequency of 10(-3) that were capable of expressing resistance at nearly the parental level. The impact of the murF mutation on antibiotic resistance was selective for beta-lactam antibiotics: there was no change in the susceptibility of the mutant to D-cycloserine, fosfomycin, beta-D-chloro-alanine, moenomycin, bacitracin, or vancomycin. Analysis of the mutant peptidoglycan showed decrease in the percentage of oligomeric components in rough proportion to the accumulation of several abnormal muropeptide components, which were identified as structural variants of the disaccharide tripeptide monomer. An abnormal cell wall precursor identified as UDP MurNac tripeptide was also detected in the cytoplasmic pool of the mutant strain. A normal proportion of oligomers and a greatly reduced representation of the disaccharide tripeptide were demonstrated in the cell wall of the murF mutant's subpopulation that has retained the parental level of resistance. Northern analysis demonstrated a drastic reduction in the transcription rate of mecA in mutant F9 whereas mecA transcription increased in the subpopulation of bacteria that retained high-level resistance.

From ecological reservoir to disease: the nasopharynx, day-care centres and drug-resistant clones of Streptococcus pneumoniae

Several lines of epidemiological and microbiological studies point to the multiple and critical roles of the nasopharynx of children-particularly those of pre-school age and attending day-care centres (DCCs)-in the emergence and spread of drug-resistant Streptococcus pneumoniae (DRP). A systematic yearly surveillance of the nasopharyngeal flora of children attending DCCs has been carried out in Lisbon since 1996. Molecular typing of several hundred DRP isolates showed that the great majority of DRP were represented by a relatively few clonal types that were frequently carried by many children in geographically distant DCCs and over several years of surveillance. The same epidemic DRP clones were also frequent among pneumococci causing both paediatric and adult disease worldwide. Penicillin-resistant pneumococci carry sequences of heterologous origin in their pbp genes and also in the recently identified murM: a gene essential for expression of penicillin resistance and for the unique cell wall structure of penicillin-resistant pneumococci. Virtually all DRP express only a limited number (five or six) of the very large genetic repertoire (up to 90) of serotypes available for this bacterial species and the serotypes of drug-resistant strains happens to be the same as the serotypes of drug-susceptible pneumococci that most frequently colonize pre-school age children. These observations strongly suggest that the nasopharynx of children is an important global ecological reservoir of DRP and may also play a critical role as the favoured anatomical site for the evolution of DRP.

Epidemiological study of staphylococcal colonization and cross-infection in two West African Hospitals

Surveillance in two medium-size (250-300 beds) hospitals located in the most populated islands of Cape Verde was undertaken in July 1997 in order to obtain data concerning nasal carriage of staphylococci. Nasal swabs (172) taken from inpatients and health care workers (HCW) from different internment services yielded 68 Staphylococcus aureus and 105 coagulase-negative staphylococcal (CNS) isolates, demonstrating extensive colonization of both inpatients and HCW by S. aureus (carriage rate 41%) and CNS (carriage rate 65%). The most frequent CNS species were S. epidermidis and S. haemolyticus. Three species--S. aureus, S. epidermidis, and S. sciuri-were recovered from wound swabs. The antibiotic susceptibility profiles of S. aureus and CNS differed sharply: all 68 S. aureus were resistant to penicillin but were fully susceptible to oxacillin as well as the other antimicrobial agents tested-gentamicin; erythromycin, except for three strains; ciprofloxacin; sulfamethoxazole-trimethoprim, except for two strains; vancomycin; and amoxicillin/clavulanate. In contrast, most (91/105) of CNS were resistant to both penicillin and oxacillin, and a variable but substantial proportion of CNS isolates also carried multiresistant traits to gentamicin, erythromycin, sulfamethoxazole-trimethoprim, and amoxicillin/clavulanate. The analysis by PFGE of the methicillin-susceptible S. aureus (MSSA) and the methicillin-resistant S. epidermidis (MRSE) strains provided evidence for extensive cross-infection and cross-colonization from HCW to patients.

Massive reduction in methicillin resistance by transposon inactivation of the normal PBP2 in a methicillin-resistant strain of Staphylococcus aureus

Screening of a large transposon library constructed in the background of a highly and homogeneously methicillin-resistant Staphylococcus aureus (MRSA) strain (methicillin MIC 1,600 micrograms/ml) for Tn551 mutants with reduced resistance, identified mutant RUSA130 with a methicillin MIC of 12 micrograms/ml. Cloning in E. coli followed by sequencing located the Tn551 insert omega 703 near the C-terminal of the PBP2 gene. Penicillin-binding assays with mutant RUSA130 showed the presence of normal amounts of penicillin-binding protein 2A (PBP2A) but the absence of PBP2. These observations suggest that the mecA gene product PBP2A is not the sole catalyst of peptidoglycan synthesis in MRSA growing in the presence of beta-lactam antibiotics, since an intact PBP2 is also essential for the optimal expression of methicillin resistance in MRSA.

Carriage of respiratory tract pathogens and molecular epidemiology of Streptococcus pneumoniae colonization in healthy children attending day care centers in Lisbon, Portugal

In an effort to establish the rate of carriage of antibiotic resistant respiratory pathogens in children attending urban day care centers (DCC) in Portugal, seven DCC in Lisbon were selected for determining the rate of nasopharyngeal colonization of children between the ages of 6 months to 6 years by Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis. Of the 586 children studied between January and March 1996, 47% carried S. pneumoniae, 72% H. influenzae, and 54% M. catarrhalis. Twenty-four percent of the pneumococci had reduced susceptibility to penicillin, and most of these belonged to serogroups 19, 23, 14, and 6. An additional 19% were fully susceptible to penicillin but showed decreased susceptibility to other antimicrobials. These isolates expressed serogroups 6, 11, 14, 18, 19, and 34. The majority (96%) of M. catarrhalis and 20% of H. influenzae were penicillin resistant due to the production of beta-lactamases. Recent antimicrobial use was associated with carriage of penicillin non-susceptible pneumococci and beta-lactamase producing H. influenzae (p < 0.05). Individual DCC differed substantially from one another in their rates of carriage of antibiotic resistant H. influenzae and S. pneumoniae. Characterization of antibiotic resistant S. pneumoniae isolates by molecular fingerprinting techniques showed that each DCC had a unique microbiological profile, suggesting little, if any, exchange of the resistant microbial flora among them. An exception to this was the presence of isolates belonging to two internationally spread epidemic clones: the multiresistant Spanish/USA clone expressing serotype 23F, and the penicillin and sulfamethoxazole-trimethoprim resistant French/Spanish clone (serotype 14) which were detected in four and three DCC, respectively.

Antibiotic resistance as a stress response: complete sequencing of a large number of chromosomal loci in Staphylococcus aureus strain COL that impact on the expression of resistance to methicillin

Tn551 inactivation has identified several determinants--fem or auxiliary genes--that, in addition to the mecA gene, are also critical for the expression of high-level and homogeneous resistance to methicillin. Genetic and/or biochemical analysis has shown that of the nearly dozen aux mutations described so far most are in genes involved in cell wall synthesis (murE, pbp2, glmM, glnR, femA/B, llm, etc.) or in complex regulatory functions (sigmaB), suggesting that optimal expression of resistance may involve the cooperative functioning of a number of genes in cell wall metabolism as well as stress response. The exact mechanism of these functions is not known. In an attempt to explore this unusual aspect of methicillin resistance more fully, a Tn551 transposon library, constructed in the background of the highly and homogeneously methicillin-resistant Staphylococcus aureus strain COL, was screened for all independent insertional mutants in which the level of methicillin resistance of the parental strain (MIC, 1,600 microg/ml) was reduced by at least 15-fold and up to 500-fold. We now describe the sequencing of 21 Tn551-inactivated genes and their vicinities in 23 new auxiliary mutants that have been studied before. Using the inverted polymerase chain reaction (IPCR), we amplified fragments corresponding to the right and left junction of the Tn551 insertions, which were then sequenced by primer walking. The two largest groups of these new auxiliary genes encoded either proteins of unknown functions (6 genes) or showed homology with genes encoding proteins involved with putative sensory/regulatory activities (7 genes: protein kinases, ABC transporters, and a catabolite control protein). Sequencing upstream and downstream allowed the identification of a number of additional open reading frames, some of which may also include functions relevant for the expression of antibiotic resistance.

Mrp--a new auxiliary gene essential for optimal expression of methicillin resistance in Staphylococcus aureus

Screening of a library of Tn551 insertional mutants selected for reduction in the methicillin resistance level of the parental Staphylococcus aureus strain COL resulted in the isolation of mutant RUSA266 in which the minimal inhibitory concentration (MIC) of the parent was reduced from 1,600 to 1.5 micrograms/mL. Cloning and sequencing of the vicinity of the insertion site omega 726 identified an open reading frame (orf1365) encoding a very large polypeptide of more than 1,365 amino acids. A unique feature of the deduced amino acid sequence was the presence of multiple tandem repeats of 75 amino acids in the polypeptide, reminiscent of the structure of high-molecular-weight cell-surface proteins EF* and Emb identified in some streptococcal strains. Mutant RUSA266 with the inactivated gene, which we shall provisionally refer to as mrp (for multiple repeat polypeptide), produced a peptidoglycan with altered muropeptide composition, and both the reduced antibiotic resistance and the altered cell wall composition were co-transduced in back-crosses into the parental strain COL. Additional sequencing upstream of mrp has revealed that this gene was part of a five-gene cluster occupying a 9.2-kb region of the staphylococcal chromosome and was composed of glmM (directly upstream of mrp), two open reading frames orf310 and orf269 coding for two hypothetical proteins, and the gene encoding the staphylococcal arginase (arg). Transcriptional analysis demonstrated that the five genes in the cluster were transcribed together.

An investigation of vancomycin-resistant Enterococcus faecium within the pediatric service of a large urban medical center

BACKGROUND

Between 1990 to 1992 and 1993 to 1995 there was a >5-fold increase (16.7% to 89.8%) in vancomycin-resistant Enterococcus faecium isolates as a percentage of all isolates of vancomycin-resistant enterococci on the pediatric units of The New York Hospital-Cornell Medical Center (NYH-CMC). A molecular epidemiologic investigation was undertaken to determine the extent to which this increase was associated with the spread of a vanA-containing clone of vancomycin-resistant E. faecium that had been previously defined in adults hospitalized at NYH-CMC or with the spread of another vanA clone that had been defined in children hospitalized on the pediatric service at Memorial Sloan-Kettering Cancer Center, which shares a common pediatric intensive care unit and pediatric house staff with NYH-CMC.

METHODS

Molecular genotyping of vancomycin-resistant E. faecium isolates obtained from pediatric patients from 1993 to 1995 was performed by pulsed field gel electrophoresis of chromosomal SmaI digests. Southern hybridization was performed using vanA- and vanB-specific probes. Medical records of patients were reviewed for pertinent clinical and demographic information.

RESULTS

A single vanB clone of vancomycin-resistant E. faecium was responsible for 17 (77.3%) of 22 isolates in the neonatal intensive care unit (NICU) of NYH-CMC. Two other vanB strains of vancomycin-resistant E. faecium and 2 vanA strains were identified among the 5 remaining NICU isolates. Vancomycin-resistant E. faecium isolates from the other pediatric units represented a heterogeneous population of primarily vanA strains, but vanA clonal strains previously identified from patients on adult services at NYH-CMC and from children hospitalized at Memorial Sloan-Kettering Cancer Center were not detected.

CONCLUSION

A newly identified vanB clone was responsible for the increase in vancomycin-resistant E. faecium isolates in the NICU of NYH-CMC. The increase of vancomycin-resistant E. faecium among children hospitalized at NYH-CMC was unrelated to the spread of vancomycin-resistant E. faecium among adults in the same hospital or among children at an affiliated facility cared for by the same house staff and sharing a common pediatric intensive care unit.

Three new temperate phages of Bacillus subtilis

Three temperate bacteriophages of Bacillus subtilis were isolated from soil samples and analysed, together with all the other known temperate phages of this organism, with respect to their host range, immunity, serology and DNA restriction pattern, and by other tests. The results show that the newly isolated phages are new members of the immunity sub-group I of the group III of B. subtilis temperate bacteriophages. We named these new phages IG1, IG3 and IG4.

Resistance of a Bacillus subtilis mutant to a group of temperate bacteriophages

A mutant of Bacillus subtilis 168 was isolated which resists infection by all the group III temperate bacteriophages except SPR, while allowing full infection by phages of the other groups (I, II and IV). The mutation conferring this phenotype, pha-3, shows 52-54% PBS1-mediated cotransduction with the hisAl marker, mapping therefore in the gtaA and gtaB region of the B. subtilis chromosome. Nevertheless, it does not affect the infection by phages sensitive to gta mutations.

Homology between phages SPP1, 41c, 22a, rho 15 and SF6 of Bacillus subtilis

Bacteriophages SPP1, 41c, 22a, rho 15 and SF6 of Bacillus subtilis share a common and specific host receptor site for adsorption. Experiments described here have established the relatedness between these phages. They were indistinguishable on the basis of host-range, plating efficiency, various growth parameters and serological properties. In addition, they shared the ability to carry out generalized transduction. They could be differentiated, however, by the restriction patterns of their DNAs, with the exception of 41c and 22a, which seemed to be identical. Recombination between 41c and SPP1 was demonstrated by transfection with mixed digests of their DNAs.