Ventilator-associated pneumonia by Staphylococcus aureus. Comparison of methicillin-resistant and methicillin-sensitive episodes.

All episodes of ventilator-associated pneumonia (VAP) caused by Staphylococcus aureus were prospectively analyzed for a 30-mo period. Methicillin-sensitive S. aureus (MSSA) was isolated in 38 episodes and methicillin-resistant S. aureus (MRSA) in 11 others. The two groups were similar regarding sex, severity of underlying diseases, prior surgery, and presence of renal failure, diabetes, cardiopathy, and coma. MRSA-infected persons were more likely to have received steroids before developing infection (relative risk [RR] = 3.45, 95% confidence interval [CI] = 1.38-8.59), to have been ventilated > 6 d (RR = 2.03, 95% CI = 1.36-3.03), to have been older than 25 yr (RR = 1.50, 95% CI = 1.09-2.06), and to have had preceding chronic obstructive pulmonary disease (RR = 2.76, 95% CI = 0.89-8.56) than MSSA-infected patients. MSSA-infected persons were more likely than MRSA-infected patients to have cranioencephalic trauma (RR = 1.94, 95% CI = 1.22-3.09). All patients with MRSA VAP had previously received antibiotics, compared with only 21.1% of those with MSSA infection (p < 0.000001). The incidence of empyema was similar in both groups; nevertheless, the presence of bacteremia and septic shock was more frequent in the MRSA group. Finally, mortality directly related to pneumonia was significantly higher among patients with MRSA episodes (RR = 20.72, 95% CI = 2.78-154.35). This analysis was repeated for monomicrobial episodes, and the difference remained statistically significant. We conclude that MRSA and MSSA strains infect patients with different demographic profiles; previous antibiotic therapy is the most important risk factor for developing MRSA infection.(ABSTRACT TRUNCATED AT 250 WORDS)

[The mechanism of the resistance of methicillin-resistant Staphylococcus aureus to phages from the International Collection]. / K mekhanizmu ustoichivosti metitsillinrezistentnykh Staphylococcus aureus k fagam Mezhdunarodnogo nabora.

The resistance of methicillin-resistant staphylococci to phage 85 is due to the presence of a certain system restriction modification in microbial cells. The loss of the capacity for restricting phage DNA by the cell as the consequence of the loss of the mec determinant is not accompanied by the loss of its capacity for modifying phage DNA.

[Experimental phages for differentiating nontypable methicillin-resistant Staphylococcus aureus]. / Eksperimental'nye fagi dlia differentsirovaniia netipiruemykh metitsillinorezistentnykh Staphylococcus aureus.

The possibility of using phages, isolated from the lysogenic cultures of methicillin-resistant staphylococci and modified in methicillin-resistant cultures of phage 85, for the differentiation of nontypable staphylococcal strains has been studied. The variants of phage 85 cannot be used for the determination of differences between the strains of methicillin-resistant cultures; they are not suited for typing. For this purpose the collection of phages isolated from lysogenic methicillin-resistant cultures should be used.

Methicillin-resistant Staphylococcus aureus bacteremia linked to intravenous drug abusers using a "shooting gallery".

Over a 15-month period, seven intravenous drug abusers had 10 admissions because of bacteremia due to methicillin-resistant Staphylococcus aureus. Seven episodes of probable bacterial endocarditis occurred in four patients; one patient had septic thrombophlebitis and two had soft tissue infections. All seven patients patronized a local "shooting gallery" where paraphernalia were provided and drugs were often administered by a "street doctor." All isolates were phage type 29/77/83A/84/85 and demonstrated resistance only to methicillin, oxacillin, and penicillin. This strain of methicillin-resistant S. aureus has a phage type and antibiogram that is distinct from nosocomial methicillin-resistant S. aureus and was probably acquired by intravenous drug abusers during visits to the "shooting gallery". The "shooting gallery" is an integral part of the drug culture and a likely source for the transmission of antibiotic-resistant organisms.

[Optimal conditions for culturing Staphylococcus aureus strain A-676 to obtain biologically active protein A]. / Izuchenie optimal'nykh uslovii kul'tivirovaniia shtamma Staphylococcus aureus A-676 s tsel'iu polucheniia biologicheski aktivnogo proteina A.

Peptone-yeast and casein-salt culture media have been shown to be equally effective when used for the cultivation of S. aureus strain A-676 with a view to obtaining protein A. The seed dose has been determined and the optimum conditions for growing the producer strain have been established.

In vitro activity of combinations of antibiotics against Staphylococcus aureus resistant to gentamicin and methicillin.

Twenty clinical isolates of Staphylococcus aureus, resistant to both gentamicin and methicillin, were tested in vitro for sensitivity to rifampicin, novobiocin, fusidic acid, vancomycin, teicoplanin and an extended range of aminoglycosides. Rifampicin was the most active compound tested, having an MIC of less than 0.02 mg/l. All the strains were inhibited by 1 mg/l of novobiocin, vancomycin and teicoplanin, and only one strain was resistant to fusidic acid. 50% of the strains were inhibited by less than 1 mg/l of amikacin and netilmicin, but other aminoglycosides were of poor activity. Resistant mutants were selected when strains were grown in the presence of rifampicin, novobiocin or fusidic acid alone, but this did not occur when rifampicin was combined with either novobiocin or vancomycin. Pharmacokinetic and other considerations suggest that a combination of rifampicin and novobiocin deserves further assessment for the treatment of infections caused by this type of organism.

Impact of methicillin-resistant Staphylococcus aureus on the incidence of nosocomial staphylococcal infections.

MRSA strains have become increasingly prevalent in the United States and are now an important cause of nosocomial infections in many large, medical school-affiliated hospitals. In affected institutions, from a few percent to 50% of all hospital-acquired S aureus infections are caused by MRSA strains. It has been suggested that the overall incidence of nosocomial S aureus infections may not increase in hospitals where MRSA strains have become epidemic or endemic and that MRSA strains merely replace methicillin-susceptible strains as a cause of hospital-acquired infections. Several recent studies lend support to this theory. Thompson et al [1] reported that the overall incidence of nosocomial S aureus-associated bacteremias and postoperative wound infections in a university hospital did not increase during a period when MRSA strains caused a significantly greater proportion of such infections. Similarly, Linnemann et al [2] found that the overall incidence of nosocomial S aureus-associated bacteremias did not change during a four-year period when the incidence of MRSA-associated bacteremias increased appreciably. At the University of Mississippi Medical Center, MRSA strains have been recovered from patients with increased frequency since an outbreak of MRSA infections occurred in the burn unit in June 1979 [3]. Continuing surveillance has revealed that the incidence of nosocomial MRSA infections was significantly higher in 1980-1982 than during 1979 (P = 0.002 by Mann-Whitney U test). MRSA strains accounted for 11% of nosocomial S aureus infections in 1979, 38% in 1980, 50% in 1981, 36% in 1982, and 32% in early 1983.(ABSTRACT TRUNCATED AT 250 WORDS)

An outbreak of methicillin-resistant Staphylococcus aureus in a large medical center.

The charts of 100 patients with methicillin-resistant, gentamicin-resistant Staphylococcus aureus (MSRA) were reviewed after an outbreak of MSRA occurred in our hospital. The location of the patients at the time of first positive culture was studied. The NICU was the most common location (24%). The burn unit accounted for nine per cent, and the remaining patients were widely distributed among the surgery services. Patterns of transmission were difficult to determine, and even with strict measures, complete eradication of the organism has not yet been achieved. Vancomycin, a potent and nephrotoxic antibiotic, is the treatment of choice.

Methicillin-resistant Staphylococcus aureus bacteriuria.

Methicillin-resistant Staphylococcus aureus (MRSA) bacteriuria was detected in 11 of 41 patients colonized or infected with MRSA. The patients with bacteriuria generally were older than 40 years of age, five were diabetic, seven had prior indwelling uretheral catheters, two had undergone other urologic manipulations, and only one was clinically symptomatic. Eight patients received variable combinations of antibiotic therapy prior to the diagnosis of MRSA bacteriuria, and seven were still on antibiotic therapy at the time the bacteriuria was detected. Bacteriuria lasted four days to 14 weeks, and was eradicated promptly with cephalosporin therapy in five six patients. Bacteriuria in the untreated patients cleared spontaneously in one month. A single MRSA serotype (83A) predominated. The MRSA isolates were resistant in vitro to most antibiotics except vancomycin. Resistant colonies were observed within cephalothin disc zones of inhibition at 30C (resistance was confirmed by microtube-dilution sensitivity testing). MRSA disc sensitivity testing for cephalothin may be unreliable when performed at 35C.

Synergy of vancomycin plus cefazolin or cephalothin against methicillin-resistance Staphylococcus epidermidis.

The in vitro activity of cephalothin, cefazolin, and vancomycin against 25 isolates of methicillin-resistant Staphylococcus epidermidis was determined by means of a broth dilution technique with two sizes of inoculum. The size of the inoculum had a marked effect on the minimal inhibitory concentrations and the minimal bactericidal concentrations of all three antibiotics. With a small inoculum, 100% of the isolates were inhibited by 3.12 micrograms of vancomycin/ml, 76% by 12.5 micrograms of cephalothin/ml, and 64% by 12.5 micrograms of cefazolin/ml. With a large inoculum 100% of the isolates were inhibited by 200 micrograms of vancomycin/ml, 40% by 12.5 micrograms of cephalothin/ml, and 12% by 12.5 micrograms of cefazolin/ml. As determined by a tube dilution checkerboard technique for both sizes of inoculum, the combination of vancomycin plus cephalothin was synergistic against methicillin-resistant S. epidermidis in 45 of 50 cases, and the combination of vancomycin plus cefazolin was synergistic in 39 or 50 cases. These data from in vitro studies suggest that these antibiotic combinations should be evaluated clinically in patients with severe infections caused by methicillin-resistant S. epidermidis.

[Mechanism of the heterogeneity of a staphylococcal population with respect to methicillin resistance]. / K mekhanizmu geterogennosti stafilokokkovoi populiatsii poustoichivosti k metitsillinu

The study of the staphylococcal population heterogeneity with respect to methicillin resistance by 2 methods revealed different numbers of the resistant cells in the population. Thus, when the microbial suspension was plated on an agarized medium with methicillin (50 gamma/ml), only 0.0007--0.0005 per cent of the resistant cells were found. When the colonies were replicated from a medium without methicillin to a medium containing methicillin (50 gamma/ml), 84.3--97.3 per cent of the resistant microbial cells were found in the population of the same strains. The main mechanism in the heterogeneity of the staphylococcal population with respect to methicillin resistance was impairement of the phenotype manifestation of the antibiotic resistance under definite conditions.