Trends in the epidemiology and antibiotic resistance of clinical Staphylococcus strains in Italy--a review

This review analyses the current Italian problem of clinical Staphylococcus isolates and trends in their antibiotic resistance. Most information has come from two recent nationwide collaborative studies. Some data have also been derived from particular experiences in individual laboratories. S. aureus was predominant among Staphylococcus isolates from most clinical sources. S. epidermidis predominated in strains isolated from artificial devices, blood, and cerebrospinal fluid. S. saprophyticus was isolated with greater frequency from outpatients than from inpatients, predominantly from urinary specimens. In spite of marked laboratory-to-laboratory and geographical variations, greater staphylococcal resistance to methicillin and most other antibiotics was noted. Overall, among clinical Staphylococcus strains isolated in Italy, more than a third of organisms from inpatients and more than a fifth of those from outpatients currently proved to be resistant to methicillin. The incidence of methicillin resistance was generally lower in Southern Italy than in the rest of the country, occurred at a twofold higher rate in isolates from inpatients than from outpatients, and was generally higher among isolates from intensive care units than from other hospital departments. There was increasing involvement of coagulase-negative staphylococci in human infections which made up about half of all clinical Staphylococcus isolates. Coagulase-negative staphylococci were more frequent than S. aureus in specimens from intensive care and surgical wards, and also were more resistant to many antibiotics including methicillin.

Psittacosis in a highly endemic area in Italy

In one locality in Italy where the incidence of psittacosis has increased rapidly since 1980, a hospital-based study and a seroepidemiological survey were carried out in order to define the clinical and epidemiological features of psittacosis in that area. Registers of the Virology Unit of the University of Ancona, Italy, were reviewed and all hospitalized patients with a serological diagnosis of psittacosis were identified. A total of 76 cases were found and studied. A presumptive bird source was identified in 80% of 62 patients, on whom a detailed investigation had been possible. Poultry represented the most frequent probable source of infection. Clinically, the predominant pattern of illness was a moderately severe lower respiratory tract infection, with chest X-rays showing pulmonary shadowings in 68 patients (89%). In the seroepidemiological study, 51 out of 143 subjects were exposed to birds (35.7%), but only 7 out of 96 urban adult blood donors (7.3%) were positive for chlamydial antibodies using the microimmunofluorescence test.

Plasmid-mediated sulfonamide resistance in Neisseria meningitidis

An 8.5-megadalton plasmid coding for sulfonamide resistance was found in a clinical isolate of Neisseria meningitidis, as demonstrated by plasmid elimination and transformation experiments. The plasmid complemented a mutation which determines the production of a thermosensitive dihydropteroate synthetase in Escherichia coli, thus suggesting that the mechanism of resistance involved a plasmid-encoded dihydropteroate synthetase.

Adherence of gram-negative uropathogens to human uroepithelial cells

The ability of bacteria to adhere to the mucosal surface is generally regarded as an important factor in infection. In particular, most urinary tract pathogens reach the kidney from the bladder. The attachment to the mucosa may promote colonization of the ureters and penetration of the renal pelvis by ascending infection. We have examined 50 patients with urinary tract infection and the uropathogens isolated from their urines were tested for adhesion to epithelial cells from fresh morning urine of healthy women. The results confirm that adherence of the microorganisms to uroepithelial cells is important for the establishment of infections of the upper urinary tract.

In vitro activity of imipenem against enterococci and staphylococci and evidence for high rates of synergism with teicoplanin, fosfomycin, and rifampin

The in vitro activities of imipenem alone and in combination with teicoplanin, fosfomycin, and rifampin were tested against clinical isolates of enterococci and staphylococci. In both groups of organisms, the three combinations demonstrated high rates of synergism in both checkerboard and time-kill studies.

Epidemiologic study of Staphylococcus strains isolated from clinical material in 24 Italian hospitals

A nationwide epidemiologic study of clinical Staphylococcus isolates was performed in Italy by 24 operative units distributed throughout the country. A total of 7,017 Staphylococcus strains were examined according to a standard protocol. Three species of acknowledged importance in human infections (namely S. aureus, S. epidermidis, and S. saprophyticus) were identified singly, whereas the other staphylococci were considered as a whole and designated Staphylococcus spp. S. aureus totalled 55% of total isolates and was reported by most operative units as the predominant species among isolates both from various inpatient departments and from outpatients. S. saprophyticus was twofold more frequent among isolates from out- than from inpatients. Susceptibility to methicillin varied considerably from hospital to hospital, but a general tendency toward an increasing spread of resistance was noted. The overall incidence of methicillin resistance (29%) resulted from a wide range of values generally higher in isolates from inpatients (35%) than from outpatients (21%). Particularly high percentages of resistance (45%) were recorded in isolates from intensive care departments. Susceptibility testing to four additional beta-lactams (cefoxitin, cefuroxime, cefotaxime, and piperacillin) and to four aminoglycosides (gentamicin, tobramycin, amikacin, and netilmicin) indicated that antibiotic resistance was widespread and in all species more frequent among methicillin-resistant than among methicillin-sensitive staphylococci. Netilmicin proved more active than the other antibiotics tested; its greater activity was most evident against methicillin-resistant strains. Coagulase-negative staphylococci were more resistant than S. aureus to methicillin and most of the other antibiotics, suggesting their increasing involvement in human infections.

Susceptibility of some Staphylococcus species to aminoglycosides

The Staphylococcal strains, identified by "The Simplified Lyogroups System" were tested for their susceptibility to methicillin and some aminoglycosides. The results, besides showing a higher ratio of susceptibility against aminoglycosides in methicillin-susceptible (MS) strains, show a different trend within each lyogroup. A total of 1616 wild Staphylococcus strains were isolated in microbiological units in Catania, Messina, Rome and Genoa. The results show a high susceptibility to aminoglycosides, both in MS and methicillin-resistant (MR) groups but with different trends among lyogroups.

Additional differentiating characters of the two subspecies of Staphylococcus hyicus

Forty-five strains of Staphylococcus hyicus subsp. hyicus and 36 strains of S. hyicus subsp. chromogenes were examined for bacteriolytic activity with the same assay system previously used in taxonomic studies on staphylococci. The two subspecies differed from each other chiefly in that for optimal lytic activity S. hyicus subsp. hyicus strains required a higher salt concentration in the test medium than S. hyicus subsp. chromogenes strains. The lack of lytic activity on B15TP1 medium was a major difference between S. hyicus and S. aureus, and the lack of activity on TP2P medium was a major difference between S. hyicus and S. intermedius. Penicillin-binding proteins (PBPs) were studied in 40 S. hyicus strains. The S. hyicus subsp. hyicus strains had only one PBP (mol. wt 79 000) while the S. hyicus subsp. chromogenes strains had three distinct PBPs (mol. wts 84 000, 82 000 and 79 000).

Different staphylococcal species contain various numbers of penicillin-binding proteins ranging from four (Staphylococcus aureus) to only one (Staphylococcus hyicus)

The penicillin-binding proteins of a total of 25 staphylococcal strains belonging to five different species were analyzed. All strains of the same species showed an identical penicillin-binding protein pattern which clearly differed from that of strains of the other species. Staphylococcus aureus, Staphylococcus intermedius, Staphylococcus simulans, and the dolphin strains were found to contain two to four penicillin-binding proteins. Strains of Staphylococcus hyicus exhibited only one penicillin-binding protein.

In vitro activities of rifapentine and rifampin, alone and in combination with six other antibiotics, against methicillin-susceptible and methicillin-resistant staphylococci of different species

The antistaphylococcal activity of rifapentine, a new rifamycin SV derivative, was evaluated in vitro and compared with that of rifampin. A total of 313 staphylococcal strains freshly isolated from clinical material and including representatives of all currently recognized Staphylococcus species of human origin were used. The susceptibility to methicillin of all the test strains was determined preliminarily. Despite minor differences with some species, the MICs of rifapentine were found to be substantially similar to those of rifampin. Methicillin-resistant strains of all species were most resistant to rifapentine and rifampin than were their methicillin-susceptible counterparts. For most strains tested, the MBCs of both rifamycins exceeded by twofold the respective MICs. Both the checkerboard dilution and time-kill methods were used to determine the interactions of rifapentine or rifampin with six different antibiotics: cefamandole, vancomycin, teicoplanin, gentamicin, erythromycin, and fusidic acid. No significant differences between the two rifamycins in the combinations were observed against either methicillin-susceptible or methicillin-resistant strains. Minor differences were noted depending on the second antibiotic tested or the staphylococcal species examined. Antagonism was never observed, and indifference was the prevalent response. Cases of synergism were observed occasionally with the checkerboard method and slightly more often with the time-kill method.

Identification, clinical distribution, and susceptibility to methicillin and 18 additional antibiotics of clinical Staphylococcus isolates: nationwide investigation in Italy

A multicentric study of clinical Staphylococcus isolates was performed by seven operative units working in different areas of Italy. Over a 6-month period, a total of 3,226 staphylococci, isolated from in- and outpatients, were identified and tested for antimicrobial susceptibility by a protocol agreed upon by all units. On the basis of their bacteriolytic-activity patterns and other conventional tests, the isolates were identified by lyogroups , which closely correlate with human Staphylococcus species. Lyogroup I (Staphylococcus aureus) and lyogroup III (Staphylococcus capitis) were the most and the least frequently isolated staphylococci, respectively. Significant differences depending on strain origin from in- or outpatients were only observed with lyogroup IV (i.e., novobiocin- resistant staphylococci), whose isolation from outpatients was three times greater than from inpatients. Lyogroup I was predominant among isolates from most clinical sources. Lyogroup IV predominated in strains isolated from the urinary tract; lyogroup V (Staphylococcus epidermidis) predominated in strains from blood, cerebrospinal fluid, and indwelling artificial devices; and lyogroup VI ( Staphylococcus hominis, Staphylococcus haemolyticus, and Staphylococcus warneri ) predominated in strains from bile and the male genital tract. The incidence of methicillin resistance within the different lyogroups varied from unit to unit, suggesting epidemiological differences among different hospitals and different geographical areas. On the whole, methicillin resistance was more frequent in coagulase-negative staphylococci than in S. aureus and ranged from 19% for lyogroups I and III to 30% for lyogroup II (Staphylococcus simulans). Laboratory testing with 18 additional antibiotics suggested the occurrence of some specific differences in susceptibility among the different lyogroups . The rate of organisms resistant to the various antibiotics was greater among methicillin-resistant than among methicillin -susceptible staphylococci; particularly marked differences occurred with cephalosporins, rifampin, gentamicin, and tobramycin. The results suggested an increasing spread in Italy, during the last few years, of staphylococcal resistance to methicillin and to many other antibiotics. Some questions about the actual reliability of laboratory tests for the determination of staphylococcal susceptibility to methicillin and other beta-lactam antibiotics were raised by parallel test performances in which both unsupplemented and 5% NaCl-supplemented Mueller-Hinton agars were used. The presence of NaCl heightened, on the whole, the number of resistant strains detected; however, a few isolates resistant in the unsupplemented medium and susceptible in the salt-supplemented medium were also encountered. This was true not only for methicillin but also for all other beta-lactam antibiotics tested except cefamandole. With cefamandole, the presence of 5% NaCl reduced the number of resistant strains detected.

In-vitro effects of vancomycin and rifampicin, alone and in combination, against methicillin-sensitive and methicillin-resistant staphylococci

The in-vitro inhibitory and bactericidal activities of vancomycin and rifampicin were tested against several Staphylococcus strains recently isolated from clinical material. All strains were first tested for their susceptibility to methicillin, and typed by lyogroup. With vancomycin, minimum inhibitory concentrations (MICs) fell within a narrow range (0.62-2.5 mg/l), and significant differences were not observed both among different lyogroups and between methicillin-sensitive (M-S) and methicillin-resistant (M-R) strains. Minimum bactericidal concentrations (MBCs) of vancomycin either equalled or exceeded by twofold the MICs. With rifampicin, MICs were found to be distributed over a wide range (0.002 to greater than 5 mg/l), and susceptibility appeared to be less in M-R than in M-S isolates. Although MICs greater than or equal to mg/l were only observed in three of the six lyogroups, data appeared insufficient to substantiate definite interspecies differences in staphylococcal susceptibility to rifampicin. MBCs of rifampicin either equalled or exceeded by two- to eightfold the MICs. In-vitro interactions between vancomycin and rifampicin, were investigated both by checkerboard and time-kill tests. By both methods, indifference was observed with the great majority of isolates. Synergism was a rare event, and antagonism was never observed.

Biochemical and physical properties of the endo-beta-N-acetylglucosaminidases from Staphylococcus aureus, Staphylococcus simulans, and Staphylococcus saprophyticus

Biochemical and physical properties of the pure bacteriolytic enzymes excreted by three different Staphylococcus species (S. aureus, S. simulans, and S. saprophyticus) were investigated. Although the three enzymes have previously been shown to share the same specificity of action (endo-beta-N-acetylglucosaminidase activity), their biochemical features clearly indicated that they were three different enzymes, confirming what had previously been suggested by the different lytic-activity patterns displayed by each species and the different procedures needed to achieve purification of each enzyme. Very different values resulted from molecular weight determination: 80,000 for the S. aureus enzyme, 45,000 for the S. simulans enzyme and 31,000 for the S. saprophyticus enzyme. Other important differences were observed in their kinetics of activity on Micrococcus luteus purified cell walls; their stability; their bacteriolytic spectrum against heat-killed cells of various microorganisms; and their response to physical and chemical factors, such as temperature, pH, ionic strength, divalent cations, chelating agents, thiol compounds, and glucose derivatives.

In vitro activity of teichomycin and vancomycin alone and in combination with rifampin

The antibacterial activity of teichomycin, a glycopeptide antibiotic similar to vancomycin, has been evaluated in vitro and compared with that of vancomycin. Test strains included 130 staphylococci and 132 streptococci, with representatives of the major currently recognized species or groups, and lesser numbers of clostridia, propionibacteria, and group JK bacteria. Teichomycin was found to be more active than vancomycin. Its minimum inhibitory concentration (MIC) was two- to fourfold lower than that of vancomycin with staphylococci and anaerobic bacteria, and two- to eightfold lower with streptococci. No significant differences were observed with group JK bacteria. For most strains tested, minimum bactericidal concentrations (MBCs) of both teichomycin and vancomycin either equalled or exceeded by twofold the respective MICs. Higher MBC-to-MIC ratios were obtained for enterococci and pneumococci with both antibiotics. Both teichomycin and vancomycin showed similar in vitro interactions with rifampin in combination tests. Neither antagonism nor (with very few exceptions) synergism occurred.

Purification and characterization of three separate bacteriolytic enzymes excreted by Staphylococcus aureus, Staphylococcus simulans, and Staphylococcus saprophyticus

As a further development of previous investigations showing that different staphylococcal species display different bacteriolytic activity patterns (lyogroups), the bacteriolytic enzymes excreted by three different Staphylococcus species, Staphylococcus aureus (lyogroup I), S. simulans (lyogroup II), and S. saprophyticus (lyogroup IV); have been purified and characterized. A representative strain from each species was grown in a preselected medium made of fully dialyzable products. Culture supernatants were collected in the appropriate growth phase. Two different affinity adsorbents were used for enzyme purification. One was obtained by coupling lysozyme-digested pure peptidoglycan from Micrococcus luteus to cyanogen bromide-activated Sepharose 4B. The second affinity adsorbent used was chitin. The S. aureus bacteriolytic enzyme bound to the solubilized peptidoglycan but not to chitin, whereas the opposite was true for the S. simulans enzyme. The bacteriolytic enzyme from S. saprophyticus did not bind to either the Sepharose 4B-peptidoglycan resin or to chitin, and its purification was achieved by two ion-exchange chromatography steps combined with gel filtration. All three enzymes were purified to apparent homogeneity. Their subsequent characterization indicated that all acted as endo-beta-N-acetylglucosaminidases. However, the three glucosaminidases differed significantly in their kinetics of activity and bacteriolytic spectrum against heat-killed cells of a variety of microorganisms. Very different values also resulted from molecular weight determinations: 80,000 for the S. aureus enzyme, 45,000 for the S. simulans enzyme, and 31,000 for the S. saprophyticus enzyme. Other important differences were observed in their stability, optimal pH and ionic strength for their activity, and their responses to temperature and divalent cations. These results confirmed the previous proposal that different staphylococcal species excrete different lytic enzymes.

High-level potentiation of lysostaphin anti-staphylococcal activity by lysozyme

The purpose of this study was to determine whether lysostaphin would enhance its anti-staphylococcal efficacy in combination with lysozyme. Minimum inhibitory concentrations (MICs) of lysostaphin and lysozyme were separately determined for 41 strains belonging to 10 different species of human staphylococci. Lysozyme was virtually inactive and showed MICs of 15 mg/ml. On the contrary, all strains were susceptible to lysostaphin and showed MICs ranging from 2.5 to 60 micrograms/ml for the different Staphylococcus species. When the MIC of lysostaphin was determined in media containing submultiples of the MIC of lysozyme, the values obtained were much lower. The reduction of the lysostaphin MIC ranged from 16- to 200-fold in the different species tested. In Staphylococcus aureus, in particular, the combination of lysostaphin with 1.5 mg of lysozyme per ml reduced the MIC of lysostaphin by 25-fold. The activities of two combinations of the two enzymes were evaluated: one combination was expected to be active on S. aureus only, and the other combination was expected to inhibit all Staphylococcus strains. The first combination (0.5 micrograms of lysostaphin plus 0.5 mg of lysozyme per ml) was inhibitory to all of the 84 S. aureus strains tested, whereas 137 of 151 strains of other Staphylococcus species were unaffected. On the contrary, all of the 235 Staphylococcus strains tested were inhibited by the second combination (4 micrograms of lysostaphin plus 5 mg of lysozyme per ml). The possible mechanisms of lysostaphin potentiation by lysozyme are considered, and the potential use of a lysostaphin-lysozyme combination for topical therapy of staphylococcal infections resistant to other antibiotics is discussed.

Production of inhibitors of lytic activity in the Micrococcaceae

Eight Staphylococcus xylosus strains lacking lytic activity (LA) were found to excrete agar-diffusible factors inhibiting the LA of LA-positive strains of the same species. The same eight strains, when tested against LA-positive indicator strains from other species of Micrococcaceae, caused marked LA inhibition only of strains of S, saprophyticus and S. cohnii, both species closely related to S. xylosus. Micrococci and planococci, unlike staphylococci, do not normally show LA, yet Micrococcus lylae and M. sedentarius strains produced inhibitors effective against the LA of almost all the indicator strains, and planococci inhibited the LA of a few indicator strains. Micrococcus luteus strains caused LA inhibition of homologous indicators only, i.e. exceptional M. luteus strains exhibiting LA. Thus, a specific and a non-specific type of LA inhibition can be distinguished, and it is suggested that the apparent lack of LA might, in some instances, be explained by the simultaneous production of a specific inhibitor.

Clinical distribution and antibiotic sensitivities of staphylococcal strains isolated over an eight-month period

A total of 842 staphylococci isolated from clinical material over an eight-month period and regarded as probable pathogens were identified according to lyogroup. Almost half the isolates belonged to lyogroups other than lyogroup I (Staphylococcus aureus), suggesting that coagulase-negative staphylococci are increasingly involved in human infections. All isolates were tested for sensitivity to 12 antibiotics. A greater resistance was observed in non-lyogroup I isolates, which again suggests a pathogenic significance of coagulase-negative staphylococci. Only lyogroup I strains, however, were obtained more frequently from clinical isolates than from healthy human skin. The distribution of the isolates in each lyogroup according to their clinical source is reported.

Stimulation of spreading of trypsinized human fibroblasts by lysozymes from Staphylococcus aureus, hen egg white, and human urine

The effect of lysozyme from three different sources--Staphylococcus aureus, hen egg white, and human urine--on adhesion to substrate and spreading of trypsinized human fibroblasts was studied. Several fibroblast strains were tested under various conditions. It was found that the different cell strains did not show the same capability of spreading and stably attaching to substrates when resuspended in media not containing serum. Some strains did not spread, whereas others spread even in the absence of serum. Cell spreading in these strains did not occur when the cells were pregrown for 5 weeks in media supplemented with 1% fetal bovine serum. Lysozyme from S. aureus allowed stable adhesion to substrate and spreading of all the fibroblast strains unable to elongate in nonsupplemented minimal essential medium. This enzyme accelerated and augmented spreading of the strains capable of elongating in the absence of serum. S. aureus lysozyme also allowed spreading and stable adhesion to substrates of all these strains when they were pregrown for 5 weeks in the presence of 1% fetal bovine serum. Furthermore, hen egg white lysozyme and the lysozyme purified from human urine were both capable of stimulating anchorage to substrate and spreading of trypsinized fibroblasts although their effect was less pronounced than that of the S. aureus lysozyme. Some tentative hypotheses for the mechanism of cell spreading in the presence of lysozyme are made. The possibility that lysozymes, virtually ubiquitous enzymes, may play a specific role in nature in the regulation of cell differentiation and tissue development is finally raised and discussed in light of several previous observations and findings.

Simplified lyogroup system, a new method for routine identification of staphylococci: description and comparison with three other methods

A simplified system for routine identification of the six lyogroups of human staphylococci is described. The method is based on the determination of the lytic activity on five different test media and of the phosphatase activity of each isolate. A total of 689 staphylococci isolated from clinical material over a 6-month period were identified according to this simplified system. The same strains were identified in parallel using three other methods designed for routine identification of staphylococci: the Kloos and Schleifer abbreviated scheme (J Clin. Microbiol. 1:82-88, 1975) the scheme proposed by the Subcommittee on the Taxonomy of Staphylococci and Micrococci (Int. J. Syst. Bacteriol. 26:332-334, 1976), and the API STAPH micromethod. Isolated whose identification was in disagreement were identified on a taxonomic level according to the extensive classification scheme of Schleifer and Kloos. In addition, 42 reference staphylococci of known identity were reidentified using the simplified lyogroup system as well as the three other routine methods. The results of this comparative study was detailed and discussed. A primary advantage of the simplified lyogroup system is that it also provides separation of staphylococci from micrococci, which must be performed separately when the other methods are used. Other significant advantages concerned with reliability, speed, and practicality are shown.

Effects of Staphylococcus aureus lysozyme on human fibroblasts

The purified lysozyme excreted by Staphylococcus aureus strains promotes elongation and spreading on plastic surfaces and stimulates DNA synthesis of human fibroblasts (WI38). This enzyme also raises twofold the saturation density level of cultures of these cells. It is suggested that the primitive and main effect of lysozyme on fibroblasts is the triggering of morphogenesis.

Detection of bacterial phosphatase activity by means of an original and simple test

A new test for the detection of bacterial phosphatase activity has been devised. The test is performed using agar media containing both methyl green (MG) and phenolphthalein diphosphate (PDP); in these media phosphatase-producing strains grow deep-green-stained colonies whereas non-producing strains do not. A total of 739 different strains were tested, including 593 staphylococci, 95 micrococci, 11 streptococci, 10 corynebacteria, 14 enterobacteria, and 16 candidae. All strains found phosphatase-positive according to the conventional phosphatase test displayed deep-green-stained colonies on MG-PDP media, whereas all phosphatase-negative strains showed unstained colonies on the same media. The main advantages of the present phosphatase test as compared with other conventional ones are that it is more simple to perform, it can reveal the phosphatase activity of colonies grown in deep agar, and can be incorporated into commercial multitest kits.

Routine separation of staphylococci from micrococci based on bacteriolytic activity production

A new method is described by which separation of staphylococci from micrococci can be achieved in routine laboratory use. The basis of this method is that bacteriolytic activity is produced by staphylococci but not by micrococci.

Bacteriolytic activity in staphylococci

The bacteriolytic activity of Staphylococcus aureus and Staphylococcus albus strains was tested with various media. Whereas S. aureus strains were found to be active under all conditions, the percentage of active S. albus strains was significantly influenced by the composition of the medium. Ionic strength and concentration of the organic nitrogen source were found to be the main factors affecting the expression of bacteriolytic activity of straphylococci. Virtually all of 318 S. aureus and 603 S. albus strains were active on a medium containing 3% peptone, 0.3% glucose, 0.2% yeast extract, 0.1% disodium phosphate, 2.2% sodium chloride and 0.9% agar. The optimal conditions for the bacteriolytic activity of S. aureus strains were different from those of most S. albus strains. Within S. albus, optimal conditions differed also from strain to strain. It is suggested that further studies on this subject may prove useful for the identification and taxonomy of staphylococci. A possible relationship between the production of extracellular bacteriolytic enzymes and pathogenic properties of staphylococci is also considered.