Species identification of coagulase-negative staphylococci from urinary tract isolates.

A new scheme for identification of coagulase-negative staphylococci was applied to 138 consecutive urinary isolates of coagulase-negative staphylococci. The most common species were Staphylococcus epidermidis (53%), S. hominis (12%), and S. haemolyticus (10%). S. saprophyticus comprised only 5%. The disk method for antibiotic susceptibility for all species grouped together disclosed resistance most commonly to penicillin (35%), tetracycline (33%), methicillin (27%), and sulfonamide (24%). This pattern was also seen specifically with S. epidermidis. Further studies are needed to determine the incidence of species-specific antibiotic resistance and species-specific infection by site. This may be of particular interest in those patients with nosocomial infections due to coagulase-negative staphylococci.     

Urinary tract infections due to coagulase-negative staphylococci

A survey of Staphylococcus albus urinary infections is reported from a general hospital. The infection followed urethral instrumentation in 75% of the patients, and was usually caused by organisms already present in the urethra. Novobiocin-resistant strains caused infections in four out-patients with no predisposing lesions or instrumentation of the urinary tract.     

Species identification and antibiotic susceptibilities of coagulase-negative staphylococci isolated from clinical specimens

Identification of potentially significant coagulase-negative staphylococci isolated from clinical specimens was performed along with antibiotic susceptibility determinations, S. epidermidis accounted for 75% of these isolates, with S. haemolyticus and S. hominis being the second and third most frequently encountered species, respectively. Although there were many instances of single blood culture isolations of questionable significance, all three species were also found in multiple blood cultures from individual patients, indicating the ability to cause significant bacteremia. The most common source for most species was blood, except for S. saprophyticus and S. simulans, which were found more frequently in urine. Of urinary tract isolates, however, S. epidermidis was more common than S. saprophyticus. Antibiotic susceptibility profiles demonstrated that S. haemolyticus and S. epidermidis were frequently multiply antibiotic resistant. S. haemolyticus had a higher percentage of isolates that were oxacillin, cephalothin, aminoglycoside, erythromycin, and clindamycin resistant than did S. epidermidis. We found that species identification could be of benefit for both epidemiological as well as patient care purposes, and that this additional information is readily available, using convenient and rapid new methods.     

Species identification and susceptibility to 17 antibiotics of coagulase-negative staphylococci isolated from clinical specimens.

A total of 299 isolates of gram-positive, catalase-positive, coagulase-negative cocci were isolated from a variety of specimens collected from patients at a large university hospital, and 281 (94%) were identified as staphylococci by established methods. Using the scheme of Kloos and Schleifer, we determined the species of the coagulase-negative staphylococci. Staphylococcus epidermidis was the cause of all bacteremias and the most commonly isolated species from bone, joint, and wound infections. Staphylococcus haemolyticus was the second most common isolate from wound infections, and Staphylococcus saprophyticus was the most commonly isolated species from urinary tract infections. Antibiograms to 17 antimicrobial agents were performed by a microdilution technique, and the results revealed that S. epidermidis was resistant to a water spectrum of antimicrobial agents than the other species of staphylococci were.     

Biotyping coagulase-negative staphylococci.

The biochemical profiles obtained with Staph-Ident (Analytab Products, Plainview, N.Y.) panels were combined with the results of adherence and synergistic hemolysis tests to define biotypes among 1,064 clinical isolates representing eight species of coagulase-negative staphylococci. The 672 isolates of Staphylococcus epidermidis were aligned in 69 of 144 potential biotypes in our scheme because of 18 different biochemical profiles and the eight physiologic subtypes. Isolates of most other species were in fewer biotypes because of more uniform adherence and synergistic hemolysis data, as well as fewer biochemical profiles. Since adherence and synergistic hemolysis may prove to be related to virulence and pathogenicity, biotyping with these test results would help evaluate the reliability of adherence and synergistic hemolysis as possible indices of the clinical significance of some of these organisms. When the antimicrobial susceptibility and plasmid profiles obtained on two clusters of S. epidermidis isolates were compared with the biotyping results, one cluster was not further differentiated by plasmid profiles, but was by antimicrobial profiles; the other cluster with only two biotypes was further divided into five distinct types by plasmid profiles but was not separated at all by antimicrobial profiles.     

Identification of coagulase-negative Staphylococci isolated from urinary tract infections

Coagulase-negative Staphylococci isolated from urinary tract infections were identified using the API Staph-Ident System. Organisms were excluded if there was no sign of pyuria or if normal urethral flora was present in significant amounts. While Staphylococcus saprophyticus and Staphylococcus epidermidis accounted for 81% of the isolates from females, 87% of isolates from males were S. epidermidis, Staphylococcus warneri, or Staphylococcus haemolyticus. The females fell into two main age groups, those with infections due to S. saprophyticus (mean age 25 years) and those due to other Staphylococci (mean age 40-49 years). All males were in a single age group (mean age 70-74 years) irrespective of the infecting agent. In males, S. warneri was associated with cellular changes in the bladder. No similar association was apparent with the other organisms. The results suggest that, apart from S. saprophyticus, three species of Staphylococcus (S. epidermidis, S. haemolyticus, S. warneri) account for most urinary tract infections, irrespective of the sex of the patient.     

Isolation of methicillin-resistant coagulase-negative staphylococci from chickens.

Methicillin-resistant coagulase-negative staphylococci were isolated from the nares and skin of 1- to 8-week-old healthy chickens in three flocks from a farm. Isolation of methicillin-resistant coagulase-negative staphylococci was positive for 72 (25.7%) of the 280 chickens tested, with the frequency varying from 2.2 to 100% according to flock. A total of 45 appropriate isolates were selected and subjected to identification. Of the 45 methicillin-resistant coagulase-negative staphylococcal isolates selected, 37 were identified as Staphylococcus sciuri, 5 were identified as Staphylococcus epidermidis, and 3 were identified as Staphylococcus saprophyticus. The distribution of the species was different among the flocks. Comparative analysis of the SmaI-digested chromosomal DNA by pulsed-field gel electrophoresis revealed that the isolates could have originated from a single clone of each of S. sciuri and S. saprophyticus and three clones of S. epidermidis. By two methods based on the PCR technique, the mecA gene was detected in all five representative isolates of each methicillin-resistant coagulase-negative staphylococcal clone. The nucleotide sequence of a PCR fragment obtained from an isolate of S. sciuri was completely identical to the corresponding region of mecA genes reported in human methicillin-resistant Staphylococcus aureus isolates and Staphylococcus epidermidis isolates. The representative methicillin-resistant coagulase-negative staphylococcal isolates were resistant to many beta-lactam antibiotics, and some isolates were also resistant to macrolide and aminoglycoside antibiotics. This is the first evidence of the existence of methicillin-resistant coagulase-negative staphylococci from animals possessing the mecA gene.     

Ribotyping of coagulase-negative staphylococci.

The discriminative capacity of ribotyping was initially assessed without knowledge of results obtained for the same isolates by use of more established typing methods. Forty-eight isolates of coagulase-negative staphylococci (CNS) from peritoneal fluids were studied. They were collected prospectively during 31 consecutive episodes of infection associated with peritoneal dialysis in 17 patients. DNA was digested by the restriction endonucleases EcoRI or HindIII and ribotyped by means of a biotinylated cDNA probe to 16S + 23S staphylococcal ribosomal RNA gene sequences. These methods in combination produced a total of 27 types which compared well with numbers of groups distinguished by other typing methods: limited biotype-antibiotic resistogram (ARB; 28), antibiotic resistogram alone (25), API-Staph (12), phage typing (9) and plasmid analysis (22). Ribotyping was highly reproducible and typed all isolates, including those that were not phage-typable (35) or did not contain plasmids (4). When used in a hierarchical manner with ARB, ribotyping results produced 13 additional types in comparison with the other three methods. When used hierarchically with all other typing systems, a further five types were found among isolates from two patients. However, some of the differences observed as a result of ribotyping could have been due to subtle changes produced by mutation, lysogenisation or gene transposition. Since the method requires additional time, expense and technical expertise, it is likely to be useful only when answers to specific epidemiological problems are required or as an initial screen before using other methods of genetic analysis.     

Characterization of clinically significant strains of coagulase-negative staphylococci

On occasion, a patient may have two or more clinical cultures yielding a coagulase-negative staphylococcus If these multiple isolates have the same phenotype, one might conclude that the same strain was reisolated from the patient, indicating its persistent and pathological presence. We examined the validity of this conclusion when we applied a number of characterizing systems to a collection of 143 isolates of coagulase-negative staphylococci collected during an outbreak of intravascular catheter-associated sepsis. The probability of classifying two random isolates as the same phenotype or species was as follows: P = 0.356 for phage typing, P = 0.348 for Baird-Parker biotyping, P = 0.346 for the API STAPH-IDENT (Analytab Products) system, P = 0.327 for Bentley et al. biotyping, and P = 0.077 for antimicrobial susceptibility patterns. Although antimicrobial susceptibility patterns had the lowest probability, a variability in test results of 7.7% and a tendency for strains to have similar antibiograms effectively raised the probability to P = 0.897. The combination of the API STAPH-IDENT with antibiograms resulted in a probability of P = 0.037 to P = 0.147. When all of the above methods were used together a probability of P = 0.014 was achieved. Five patients had isolates from two or more blood cultures spaced more than 1 day apart that were identical by all of the above criteria, thus confirming prolonged bacteremia. The collection was also examined for the incidence of slime production. Slime production was not associated with any of the above groups, but was associated with symptomatic infections (P less than 0.05) and gentamicin resistance (P less than 0.01). Slime production was strain stable and was of assistance in typing strains of coagulase-negative staphylococci.     

Emergence of teicoplanin-resistant coagulase-negative staphylococci.

Over a period of 5 years we have recovered 32 clinical isolates of coagulase-negative staphylococci (CoNS) exhibiting either decreased levels of susceptibility or true resistance to teicoplanin (MICs, 16 to 128 micrograms/ml); these isolates make up 0.55% of the total CoNS isolated by us. Twenty-nine of the strains were also methicillin resistant, and all were susceptible to vancomycin. Fourteen of the strains were Staphylococcus epidermidis, fourteen were Staphylococcus haemolyticus, and four were Staphylococcus hominis. In one case, a strain of S. haemolyticus was isolated with a vancomycin-resistant, teicoplanin-resistant Enterococcus faecalis strain. All strains were nosocomially acquired and were isolated from 17 different wards. Teicoplanin resistance occurred as a sporadic phenomenon, and none of the isolates were epidemiologically related. The isolates were from 30 patients, 13 of whom presented with true infections (43%). Five (38%) of the 13 patients with true infections had been previously treated with vancomycin. None of the infected patients were previously treated with teicoplanin. The in vivo development of resistance to teicoplanin among CoNS strains limits the therapy of infections by these microorganisms. There is a need for surveillance of nosocomial isolates of CoNS to determine resistance to glycopeptides.     

Bacteriophage typing of coagulase-negative staphylococci.

Cultures comprising the 10 species of coagulase-negative staphylococci proposed by Kloos and Schleifer (J. Clin. Microbiol. 1:82--88, 1975) were typed with bacteriophages isolated from Staphylococcus epidermidis. Although only 10.5% were typable, 50% of those identified as S. epidermidis were typed. Cultures from patients with middle ear infections were also classified by this system and phage typed.     

Clinical significance of coagulase-negative staphylococci.

Although coagulase-negative staphylococci (C-NS) have been implicated in certain human infections, they are generally regarded as contaminants, and their clinical significance is questioned. To assess their role as pathogens, we studied 205 isolates of C-NS from wounds and body fluids (blood, urine, pleural and peritoneal fluids, etc.). Patient's charts were reviewed, and, by using strict criteria, a determination was made regarding the clinical significance of these isolates. The organisms were then identified to determine whether certain species of C-NS were associated with specific infections. S epidermidis sensu stricto accounted for 81% of the C-NS isolated. The frequencies of other species were: S. haemolyticus (6%), S. hominis (5%), S. capitis (4%), S. warneri (3%), and others (1%). Only two isolates were novobiocin resistant; neither was identified as S. saprophyticus. By using our criteria, 22% of the C-NS were considered to be clinically significant, and the majority of these (93%) was S. epidermidis. The most common source of the clinically relevant C-NS isolates was wounds. These data suggest that identification of C-NS species other than S. epidermidis may be of limited value in predicting clinical significance.     

Coagulase-negative staphylococci and micrococci in urinary tract infections.

One hundred catalase-positive, coagulase-negative, Gram-positive cocci isolated in significant numbers from the urine of patients with urinary tract infections, provisionally subdivided by their sensitivity to nonoviocin, were classified according to a slightly model version of Baird-Parker''s schemes (1965 and 1972). It appeared that strains of Micrococcus were nearly all of sub-group 3, and that these were important pathogens of young women presenting with urinary infections in general practice. All such strains were resistant to novobiocin. Strains of staphylococcus were heterogeneous, and were found principally in infections arising in hospital, among older prople. Most staphylococci were sensitive to novobiocin. It is suggested that it is easy and sufficiently accurate to separate staphylococci and micrococci isolated from cases of urinary tract infection on the basis of their sensitivity or resistance to novo-biocin. The distinction is useful because of its therapeutic and epidemiological significance.     

Encapsulation of coagulase-negative staphylococci

It is becoming clear that encapsulation is frequent among coagulase negative staphylococci and is unrelated to the formation of extracellular polysaccharide slime by many strains. Crude slime may contain capsular polysaccharides or proteins, as well as cell wall components, but this is probably the result of cell wall turnover in growing bacteria. As in coagulase-positive staphylococci the capsules confer resistance to phagocytosis and can be regarded as important virulence factors. The observation that within the species S. epidermidis several different capsular types can be distinguished serologically suggests the possibility of using the presence and serotype of capsule for biotyping. There is a great need for detailed structural studies of capsular polysaccharides and for the investigation of the role of proteins in the capsules. Several published analyses fail to account for substantial proportions of the weight of isolated capsular material, indicating the presence of components yet to be recognised. Preliminary studies have revealed interesting biological activities of capsular components in humans and experimental animals and further work is likely to provide important new information about the pathogenesis of opportunistic infections by this group of bacteria.